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Metal Powder Report �Volume 72, Number 6 �November/December 2017 metal-powder.net

Ideas for future hardmetal research:some suggestions made to the EPMAEuroHM GroupKenneth J.A. Brookes

IntroductionBased on my 70 years’ experience of powder metallurgy, including

66 in the hardmetals industry, EuroPM asked me to suggest a few

topics which might make interesting or even valuable research

projects for EuroHM (the EPMA Hard Materials Group). Some of

these suggestions derive from completed or uncompleted research

projects of my own, though few records remain and hardly any-

thing has previously been published. Others are simply ideas for

possibly helpful research, where fundamental knowledge,

manufacturing methods or quality control might be improved.

As far as I know, none of the technology mentioned here is

encumbered by patents or patent applications.

In just about every instance I personally carried out (almost

always unpublished) research on the subject, often leading to

successful commercial products and in some cases properties

and productivity unavailable even at the present time.

The reader might ask why, if the research was successful, these

products are not available today, nor have the research results been

published except in general terms in the author’s own publica-

tions, or on a confidential basis to consultancy clients. The reasons

are an unusual and possibly unique combination of circumstances,

explained in some detail in Parts 1 and 2 of this paper.

Part 1: BackgroundTechnology from Teco (Tungsten Electric Corporation) USA,Osramwerke and Krupp Widia, Germany, and in-house Teco(Tungsten Electric Company and R.G, McLeod Tools Ltd) UKIn 1951 I joined hardmetal manufacturer Tungsten Electric Co

(Teco) at Kings Cross, London. I was in my early twenties (Fig. 1)

and the appointment was based on some modest experience of

powder metallurgy (including lithium-strontium mixed or me-

chanically alloyed powders to fight metal/mold reaction in sand-

cast aluminum alloys, some early work on PM titanium, and some

highly secret work on uranium for Britain’s Tube Alloys project) at

$ Based on an invited Keynote Presentation to the EuroHM Open Meeting atthe EPMA Congress in Milan, Italy in October 2017.

E-mail address: kenbrookes@intercarb.org.

4080026-0657/ã 2017 Kenneth J

BNFMRA (the British Non-Ferrous Metals Research Association),

about a kilometer away near London’s Euston Station.

Teco (not to be confused with a present-day Spanish company

with similar name) had been founded during the 1930s as a joint

venture between R.G. (Roderick George) McLeod, a wealthy Scot-

tish entrepreneur, Lord Riverdale (formerly Arthur Balfour, with a

well-known steel-manufacturing plant of that name in Sheffield),

and the Tungsten Electric Corporation (USA). At some stage before

I joined, McLeod had bought out the other partners and in the late

1940s was involved in a famous patent case with Krupp Widia,

which went all the way to the House of Lords, the highest court in

the land. Some of Teco UK’s know-how came from Tungsten

Electric Corporation, some from Krupp-Widia (though I’m still

not sure whether it was from a pre-war licence from Krupp-Wida

and/or Osramwerke, part of post-war reparations, or simply de-

rived from the well-known BIOS Reports and other limited-circu-

lation UK government publications), and some vital ingredients

from in-house development. Teco USA was a subsidiary of Callite

Tungsten (founded by Dr C.A. Laise, a pioneer of the tungsten

industry), which later became an important component of

Sylvania.

The Kings Cross factory (Fig. 2) had been completed in 1947,

soon after the 1939–45 war, under a British government ‘Super-

Priority’ scheme. Teco had not only played an important part in

the war effort but was now, through its resellers, a major supplier

to the coal industry, on which the nation’s recovery depended.

The original Teco UK plant had been built in Peckham, South

London, in the 1930s, but was bombed early in the war and spent

the rest of hostilities in a government-requisitioned garage in

Kenton, north London. Its products were often resold under a

variety of other companies’ trade names, and it was a major

supplier to many famous aviation and automotive firms, from

Vauxhall, Ford and Rolls-Royce in the UK to General Motors

Holdens in Australia.

I never met my predecessor at Teco, who had apparently left at

short notice. Like myself, he was the only scientifically qualified

individual on the staff, so I had no-one to teach me the techno-

logical ropes except the knowledgeable factory foreman.

A Brookes. Published by Elsevier Ltd. All rights reserved. http://dx.doi.org/10.1016/j.mprp.2017.08.067

FIGURE 1

Ken Brookes, Works Metallurgist and subsequently Technical Manager ofTungsten Electric Co in the 1950s.

FIGURE 2

Completed in 1947, apparently on a reclaimed wartime bombsite, Teco'snational importance meant that its new London factory near Kings CrossStation was built under Super-Priority legislation to replace therequisitioned garage employed during the Second World War.

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Laboratory facilities were basic and would be considered very

primitive today. They included combustion carbon, Fisher Sub-

Sieve Sizer (Fig. 3), Rockwell and Vickers hardness testing

machines, the latter being modified to enhance accuracy and

reproducibility (Fig. 4), precision balance for density measure-

ments (Fig. 5), a seldom- used transverse rupture test machine

and an excellent optical metallurgical microscope taking glass

plates. Not forgetting a substantial anvil and 2 kg hammer for

dynamic toughness tests. No magnetic tests of any kind, no SEM,

nothing electronic (this was the early 1950s), though I did add a

Wheatstone bridge for special purposes later on. Because surface

flow is scarcely a hazard with sintered hardmetals, we used die-

polishing rather than standard metallographic techniques to pre-

pare test specimens for microexamination. We could go from

fracture to polished surface in less than 10 min. I developed

color-etching techniques for eta-phase and non-WC additional

phases.

Surprisingly, I was lucky in having such limited lab equipment,

since most research and development had to be carried out in the

factory on the latest production plant. As a result, all my inves-

tigations were made at full scale, typically with a 5 kg minimum

powder sample, and by necessity I had to find a valid commercial

use for the experimental material from any research project.

Although to academics this might be thought a severe limitation,

in fact it concentrated the mind wonderfully toward commercial

development. Modern experimenters in the hardmetal industry

appreciate how difficult it is to reproduce production conditions at

tiny lab-scale.

What is more, Teco’s production plant was by no means insig-

nificant, being capable of virtually any process employed in hard-

metal production except the refining of tungsten, cobalt or other

ores (impractical because of the limitations of the Central London

location). Outsourced raw materials were made to our own, often

unique, specifications and included cold-crystallized ammonium

paratungstate needles, cobalt rondells, superfine graphite powder

and oxides of titanium, chromium and tantalum-niobium. The

rondells were dissolved in nitric acid, precipitated as extremely

high-purity oxalate by additions of oxalic acid, then heated to

form the Co3O4 oxide to be milled with W or WC. High-purity

hydrogen was produced in-house from an electrolytic plant that

previously produced gas for London’s wartime protective barrage

balloons. Key plant included furnaces that could routinely exceed

2000�C, and high-efficiency, high-speed Siebtechnik ‘vibratory’

ball-mills, the prototypes for which were obtained as post-war

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FIGURE 3

Fisher Sub-Sieve Sizer gave (and still gives) a rough measure of averagepowder grain size.

FIGURE 4

Higher magnification greatly improved the measuring accuracy of anotherwise standard Vickers hardness testing machine. We changed thestandard object lens on the Vickers machine for the highest power lensobtainable and recalibrated it against an NPL precision graticule.

FIGURE 5

Precision balance for specific gravity measurements.

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reparations from the Krupp-Widia plant in Essen. These mills

produced so much vibrational energy that they had to be mounted

on their own foundations in the factory basement.

Teco even had a row of specialized machines (designed in-

house) for precision cutting of presintered carbide blocks with

ultrathin diamond cutoff blades. Their skilled operators helped the

company to offer one-day delivery for even a single part with a

complex special profile.

Importantly, there were no vacuum furnaces, which can make

life more difficult when trying to hold stoichiometric carbon

values; no attritors, which widen grain-size distribution rather

than narrowing it like the Siebtechnik mills; and no HIP (which

had not been invented) so porous sintered carbide would have

been scrap rather than easily rectified. Luckily this was a rare event.

Having been ‘thrown in at the deep end,’ my job was simply

defined. It was to produce and update a complete range of sintered

carbides that equalled or outperformed those of every other com-

petitive producer. For ten years I was the only scientifically quali-

fied member of staff. As it happened, Teco was already ten to

fifteen years ahead of most national and international competitors

when I joined, though I only realized this years later because of the

extreme secrecy that plagued the industry.

What happened to Teco and its technology?In 1961 McLeod was looking to retire but had no family member

wishing to take on the hardmetal industry. I left in 1961 to marry

and wanted to get into industrial journalism and authorship. Soon

afterwards the company was sold to one of its most important

customers, who converted the London factory to a stockholding

facility and moved hardmetal manufacture to Tenbury Wells in

Worcestershire, significantly employing bought-in raw materials.

As far as I know, most of the technical and research records,

especially the many hundreds of glass-plate photomicrographs,

were lost, destroyed or discarded. Teco was later purchased by

Howle Holdings, incorporated into Elektron PLC, rebranded as

Total Carbide, acquired by Versarien plc and in 2016 moved to its

current manufacturing facility in Westcott Venture Park, Buck-

inghamshire. The Total company claims on its website to be ‘the

leading European manufacturer of sintered Tungsten Carbide wear

parts’ but publishes no production or sales data on its website

and is not listed as a member by EPMA.

Returning to the Teco that I knew in London, almost nothing –

apart from my own publications and some winning results in

government tests – has ever been printed about its plant,

manufacturing processes or hardmetal products. It took a few

years and visits to numerous other manufacturers for me to realize

that most of what remained of the 1950s Teco technology was (and

to an extent still is) in my personal memories.

Data gatheringIn the 1950s, most sintered carbide manufacturers had what could

only be described as an ‘industrial espionage’ department, reading

anything published on the subject, plus analyzing and checking

the properties and performance of any competitive material upon

which hands could be laid. I also acted as such a ‘department’ in

my own time.

This came to the notice of the Ministry of Aviation and the

Distillers’ Company’s CeDeCut subsidiary in its second incarna-

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tion. As a result I collaborated (in the late 1950s) in a UK Govern-

ment project to evaluate all hardmetals available in the UK for

machining ‘difficult-to-deform’ metallic materials. To help them, I

compiled a comprehensive chart showing the recommended

applications of all sintered carbides then on sale in the UK.

Interestingly (to me), in the resultant 1961 W.S. Hollis Report

the only grade recommended for cutting Nimonic nickel-base

superalloys was one I’d personally developed, Teco CL, with

nominal composition 90.5WC/0.5Cr3C2/9Co, and the report’s

primary recommendation for machining stainless steel was my

tough, heat-resistant WC/TiC/(TaNb)C/Co monophase grade Teco

EEV with rounded carbide crystals.

With Roderick McLeod’s permission and encouragement, I

started publishing my grade charts, now expanded to the world’s

cemented carbides rather than just those sold in the UK, initially in

Britain but eventually in German, Italian and US technical maga-

zines. By the 1970s I’d acquired so many catalogues, reference

manuals and the like, and visited so many hardmetal producers,

that I felt that it was time to publish a reference book with even

more data. That was my first World Directory & Handbook of

Hardmetals, which caused shockwaves in the industry.

Part 2: Target audienceJust who am I trying to reach with my suggestions? Primarily it

must be the teaching staff, undergraduates and other students in

those parts of our modern universities that study the science and

technology of hard materials, secondly the EPMA itself, which

promotes and organizes cooperative research in this area, and then

the manufacturing industry itself. I have the greatest admiration

for many of our hardmetal producers but, having visited or advised

many of these around the world, I am inhibited by commercial

secrecy even in mentioning the current standards of their abilities,

equipment and products, except where these details are in the

public domain.

Remember that commercial producers have a collective interest

in NOT improving the service lives of their many products, since

the longer their operational lives, the less product they expect to

sell. Amazingly, the 94WC/6Co composition chosen by Osram-

werke Berlin in about 1923 for drawing tungsten wire for lamp-

bulbs, then licensed to Krupp Stahl as a possible material for

cutting tools, is still the first choice of many academic researchers

or their sponsors for their investigations, as though there had been

no progress in nearly a century. Compare that situation with

research into electronics, aviation, space travel, communications,

entertainment or almost any other technical subject. Basically,

much, if not most, of basic hardmetal research is trapped in a

ninety-year-old timewarp, from which EuroHM perhaps has the

opportunity and ability to drag it into the 21st century.

Take note also of the fact that we have no international, and few

worthwhile national, standards for hardmetals. Instead we have

the slightly ridiculous pseudo-standards of ISO 513, which basi-

cally standardizes nomenclature of ill-defined applications, then

adds extra codes to indicate, for example, an undefined but

performance-enhancing coating. It is many years since the US

government, metaphorically speaking, locked all the American

steel manufacturers in a room and refused to let them out until

they had a agreed a detailed standard for steels. The cemented

carbide industry has always resisted any similar suggestion, and to

this day it is virtually impossible to purchase hardmetals to a

generally accepted standard for which acceptance testing can be

carried out.

Virtually none of my suggestions is costly or beyond the abilities

of today’s excellent professors and students. Neither are any

revolutionary in intention. But collectively they could enable

the quality of research to be greatly improved, to the benefit of

productivity and more meaningful future research.

Part 3: Research suggestionsProject 1: Carburizing furnace atmospheresInvestigate gas reactions in carburizing furnaceatmospheres and optimize operational parametersWhen describing the carburizing of tungsten to form tungsten

carbide, we often see the equation W + C = WC. But that’s much

too simplistic. That equation would imply a solely solid-state

reaction, which we know would be very slow except in agglom-

erates at points of contact. However, we also need to take into

account that the W would initially have a thin layer of W oxide

(possibly WO2 or WO3) on its many surfaces. So even in nominal

vacuo we need to look at possible reactions involving gases.

The simplest gas environments for carburizing start as high-

temperature reaction products of W oxides and particles of carbon

black in a vacuum furnace, or in a flow of dry, high-purity hydro-

gen, probably in some kind of pusher furnace. The reaction

products could include CO or CO2, which subsequently react with

the underlying W to form WC.

In nominal vacuo it is difficult to control carbon content to the

critical stoichiometric value because the reacted oxygen from the

W oxide takes carbon with it, and the amount of carbon lost in this

way cannot always be predicted. If non-stoichiometric, the final

product is likely to contain W2C or C as well as WC, leading to

unwanted free carbon or embrittling eta-phase in the sintered

material.

If hydrogen is employed as carburizing atmosphere, it acts as

catalyst for the WC reaction, converting the carbon black to a

gaseous hydrocarbon and then reacting with the W to form WC

and regenerate H2 or hydrocarbon. Hydrogen is much more effi-

cient than carbon black in removing adsorbed W oxides, making it

easier to hold stoichiometric values for carbon content. Probably

at higher temperatures, hydrogen/carbon reactions predominate,

forming hydrocarbons like methane and propane as carbon car-

riers for WC formation.

But there is much that we don’t know in this simplified descrip-

tion. For a start, we know that purity and low water content in the

hydrogen are critical in minimizing grain growth. A dewpoint of

�40� is traditionally sought, though whether this was chosen in

the 1930s, so many years ago, because it would be unnecessary to

specify C or F is a moot point. But hydrogen flow rate is as critical as

dewpoint in maintaining fine, reproducible grain size.

My impression is that every WC powder manufacturer has

empirically developed a set of parameters to suit their equipment

and product line, but these are not backed by solid research. What

we’d like to know includes, for example:

1. Exactly what reactions take place, when and how

2. Optimal temperatures at different process stages

3. Variation in product quality with changes in furnace

atmospheric humidity

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4. Changes in chemical composition of furnace atmosphere,

monitored on continuous basis during reactions.

5. Effects of ‘atmospheric doping’ by adding measured additional

amounts of hydrocarbons, such as methane, propane, octane,

during the process

6. Comparison of economics, output quality and other param-

eters for continuous and semi-continuous (e.g. boats in

pusher-type tube furnace) operation.

But all these considerations apply specifically to high-purity

WC. Different considerations apply when GGIs or GGI precursors

are present. For this we need to look at both Cr and V and their

compounds. One objective is to ensure that all Cr and/or V are in

solid solution or otherwise intimately associated with the WC. Any

Cr or V carbide visible as discrete particles in the final microstruc-

ture of the cemented carbide act as microstress-raiser, cannot be

contributing to GGI and should be avoided by modifying the

flowsheet (see Project 2A). But in addition we know very little

in detail of their reactions with and within the furnace atmo-

sphere, including catalysis and diffusion. Though complicating

the investigation, this (+GGI) research would arguably be more

important than the manufacture of simple WC, since the Cr-

containing and/or VC-containing variants have become near-

ubiquitous in modern micrograin and nanograin sintered car-

bides.

Project 2A: GGI optimizationInvestigate and optimize preferred methods ofincorporating Cr-base grain-growth inhibitor in WC/CoFirstly, why Cr? Why not V or Ta?

Before Teco’s work, nobody seems to have looked at chromium

carbide as a commercial grain-growth-inhibiting additive. This

may have been because vanadium carbide seemed more efficient

as GGI, though unfortunately it also caused embrittlement. It is

possible that Krupp-Widia recognized this VC effect in their H2

grade by further additions of Co and TaC to increase its strength,

though it still had the lowest TRS values of all Widia standard

grades, with the exception of the even more brittle high-TiC grade

F2.

TaC by itself has only slight GGI properties and is also expen-

sive. Nevertheless, a surprising number of manufacturers persuad-

ed themselves that they could obtain the GGI qualities of Widia H2

without the brittleness simply be leaving out the VC. In my

consultancy work It proved quite difficult to convert many of

these companies to low-cost, highly efficient Cr carbide, especially

when so many were adding Cr in a way that nullified much of its

advantages. In my opinion this was (and is) because so often the Cr

carbide constituent was (and is) expressed as Cr3C2, when in

practice it might best be present as a WCr carbide solid solution.

There is almost nothing on this in any published literature except

my own.

Based on our extensive research and commercial experience, it

seems that the best way to incorporate chromium GGI in WC/Co is

the following or similar (see also Projects 1 and 2B):

1. Mix chromium oxide (probably Cr2O3) with W powder and

carbon black by milling, preferably in a Siebtechnik-type

‘vibratory’ mill.

2. Carburize conventionally in flowing dry (�40 dewpoint)

hydrogen.

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Alternatives might include employing W oxides or WC as

starting materials with the Cr oxide; using different Cr oxides;

or using nominal vacuo as an alternative to flowing H2. What is

least likely to be a good alternative starting material is Cr3C2,

which is expensive, comparatively coarse, difficult to grind to

smaller grain sizes and slow to diffuse into WC. However, per-

haps it should be included in the research for comparison

purposes.

Remember that every visible particle of chromium carbide in

the microstructure is not only doing nothing toward GGI, but is

also a microstress-raiser, helping to give Cr carbide an undeserved

reputation for lowering fracture toughness.

Incidentally, our standard commercial range of WC/Co-base

hardmetals with Cr-base GGI ranged from 3% to 13% Co binder.

Project 2B: Cr-rich coating as GGI bonusAnalyze composition, measure thickness and checkchemical, structural and physical (including anti-cratering)properties of self-developed coatings on optimized WC/Cowith Cr-base GGIIn the 1950s, one of the world’s most important manufacturers of

milling cutters employed Teco grade C (micrograin WC/6Co with

0.5Cr carbide added as oxide before carburizing) as standard for

steel milling. This was due to the tenacious, self-developing and

self-healing continuous coating of unknown composition. Other

than the oxycarbide layer on WC/TiC/Co cemented carbides. It

might indeed have been the first successful coating ever devised for

hardmetals. The feedback from customers around the world

showed no instance where this grade gave lower performance

than the then-conventional WC/TiC/Co grades. In the 1961 Hollis

report, the 9Co variant with higher toughness was rated as the best

available for machining Nimonic alloys, but the chemically resis-

tant coating made both alloys especially suitable for machining

titanium.

The composition and manufacturing method of the 6Co variant

had been developed during the late 1930s or 1940s and was

intended only for efficient grain-growth inhibition. The coating

was a bonus. However, we were very aware of the coating’s

presence, as in those days most milling cutters were made by

carbide-to-steel brazing and these tips were in as-sintered condi-

tion effectively unbrazeable. Thus one of my modest research

successes was to devise a reliable, reproducible and inexpensive

method for brazing.

However, not having the right laboratory equipment, we never

did discover the exact composition of the coating nor its precise

properties. Indeed, we did not even discover if it had a precise

composition or a range within which we had accidentally hit on a

set of effective parameters. But we supposed it might well be a

tungsten-chromium oxycarbide, perhaps an analogue of the tita-

nium oxycarbide that gave Ti-rich hardmetals their resistance to

cratering. According to the cutter manufacturers and their custo-

mers around the world, Teco carbide tips of this grade had similar

crater resistance to WC/TiC-based grades but were much tougher

and more abrasion-resistant.

For research planning, I’d suggest employing alternative meth-

ods for adding the chromium content at, say 0.4, 0.5 and 0.6 Cr3C2

equivalent and both 6 and 9% Co, then checking microstructures

at high and low magnification for average grain size, grain size

FIGURE 6

Seen at the 2017 Paris Air Show, this robotized orbital drilling device wasdesigned for the EU's RODEO project but might be modified as aninexpensive lab-scale Siebtechnik-type powder mill.

FIGURE 7

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distribution, porosity, free Cr3C2, eta-phase, etc., before grinding

(different surface qualities might be tried) and exposing the

ground surface to air to encourage coating formation. Assuming

the coating can be detected, thickness should be measured after

various times to check stability, as well as compositional varia-

tions, microstructures and physical properties. Finally would come

machining tests and the ability of the coating to act as a suitable

interface or substrate for PVD and CVD if desired.

Project 3: Rotary-vibration millingCompare action, efficiency, costs and HM powder productproperties from attriting with those from high-energy`rotary-vibration' millingWhy is a Siebtechnik-type rotary-vibration mill apparently so

efficient? Does it really work like Dr Dawihl thought? Is it eco-

nomically viable for today’s production environment? Can we

update to small-scale lab and ultralarge electromagnetic designs?

There are basically two kinds of comminution milling – impact

and abrasion (or rubbing). The original type of rotary mill, devel-

oped in the early days of hardmetal milling, is a prime example of

impact milling, but very inefficient, With any attempt to increase

speed and output, gyroscopic forces come into play and the mix of

powder, balls and milling liquid sticks to the wall of the container

and the milling action ceases.

Attriting, much simpler and cost-effective, has become the

industry norm. However, all kinds of impact milling produce

the typical ‘bell-shaped’ grain-size distribution which, though

generally masked by agglomeration of fines, widens as milling

time is prolonged. Regular liquid-phase sintering exaggerates the

size differential and lowers the properties of the sintered object.

By contrast, the so-called vibratory milling developed by Siebt-

echnik in Germany during the 1939–45 War, relies not on impact

but on abrasion, a little like flour milling. The mill does not itself

rotate, but its axis rotates instead, with no theoretical limit on

rotation speed or the amount of power that can be applied (apart

from the effect on building structure). As a result, each ball in the

ball/powder/milling-liquid mix rotates on its own axis, which is

constantly changing. As the balls rotate, powder plus milling liquid

passes between them. The finest particles pass through the ball-to-

ball gaps unchanged, whilst the coarser particles are ground down

to smaller sizes. As a result, with extended milling time particle size

distribution tends to narrow, rather than widen.

However, as was explained in Bela Beke’s ‘Principles of Comminu-

tion’ published in Budapest in 1964 and no doubt on every hard-

metal researcher’s bookshelf, there is more happening than might

appear. Whichever method of milling is used, for any combination

of mill design, milling liquid, powder input, balls or other grinding

media, the initial result of the milling operation is to reduce the

average grain size. Then, after a time, this effect seems to stop and

no further reduction in average grain size appears to take place. But

what is happening is that two effects – comminution and agglom-

eration – take place simultaneously. Each of the effects has its own

curve on a graph and where they intersect is the so-called ‘equilib-

rium’ grain size for that set of parameters.

But how much do we really know about milling and comminu-

tion, a critical factor in hardmetal production, especially with

regard to genuinely nanosized WC grains? Most of the research

on attritors is empirical, and Beke’s work implies that investiga-

tions based on lab-size equipment do not necessarily scale up. And

what about Siebtechnik-type milling? Kieffer and Schwarzkopf did

not seem to understand it and clearly had no personal experience.

In their massive book on hardmetal production they included

photos of large and small Siebtechnik mills but with no descrip-

tion, explanation or operational data. These mills are also men-

tioned in the more recent Schedler ‘Hartmetall’ volume. Teco used

these mills (some as reparations from Krupp-Widia, others as

copies) for microfine powder compacts. Stellram had some of

these mills, but they disappeared at or about the time that the

company was purchased by a US conglomerate. Krupp-Widia may

have accumulated a fund of data but little seems to be in the public

domain. Interestingly, within the past year, one company has

exhibited a lab-sized device (Fig. 6) that could possibly be modified

as a tiny rotating-axis milling machine, and another has installed

at Harwell, UK, an electromagnetically powered massive vibrating

table (Fig. 7) for testing spacecraft in vacuo, that looks capable

of modification by appropriate linkages. Between what might

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become a family of milling devices, plus variations in ball materi-

als, shapes and sizes, input raw materials of varying compositions

and grain sizes, plus often-neglected milling liquids and organic

binders, a research project might produce a wealth of data for

comparison with parallel work on attritors.

Project 4: Test advantages of milling oxidesAdding and milling oxides rather than metals or carbidesWhy does the industry mill coarse, expensive Cr3C2 as a GGI

additive and metallic Co for binder when we have known for

more than sixty years that milling oxides is faster, more efficient

and cheaper in raw materials?

Why do HM makers pay more for powders containing GGI than

for WC/Co powders without addition, when the GGI and Co

oxide powders (such as Cr2O3 and Co3O4) are cheaper in raw

material costs and easier to process? Why, as another example, are

Co metal powder suppliers proud of attaining 0.5 micrometers in

2017 when in 1945 Walter Dawihl of Osramwerke boasted of 1-

nm Co binder grain size processed via Co3O4?

Examples:Co3O4, NOT CoCr2O3, NOT Cr3C2V2O3, NOT VCTa2O5, NOTTaCNb2O5, NOT Nb

Do we need research for this, or is it glaringly obvious? But if so,

why is it so seldom employed in academic research on GGIs, cobalt

binders and the like?

Project 5A: Produce new test to supplement Palmqvist test withone of more practical value to industryConsider new standard for measurement of toughnesswith diamond pyramid indentation by recording WORSTcrack length in each set of four rather than total or averageIn the real world, users of hardmetals, especially cutting tools or

inserts, are more interested in minimum rather thsn average life. If

they know that tools with an average life of 1000 components may

sometimes fail after 10 components, they will choose to change

the tool after 9 components or less rather than 999. Whilst the tool

manufacturer may offer to replace free of charge an insert that fails

unusually early, few will refund the value of a component dam-

aged by the failing cutting tool, when the partially finished

component may have perhaps 2000 times the value of a cutting

insert. That’s why the MINIMUM life is so important.

Neglecting the important fact that in many applications hard-

metals generally fail by dynamic rather than static stress and

Palmqvist is a static stress test, the Palmqvist method seeks to

obtain an average value and gives equal weight to each individual

test. Thus if one test shows a very long crack at one corner of the

indentation, its importance is minimized by adding in the shorter-

than-average crack lengths at the other corners.

It is suggested that a more critical and useful test might involve

taking just the longest individual crack in a series and discarding

all the others. It might be said that such a test indicates a single

stress raiser such as a pore, cobalt lake or impurity, and is not

indicative of better quality elsewhere in the sample. On the

contrary, a hardmetal tool or component made from such material

is likely to fail at just such a location in actual service.

A new test such as this likely to place sintered hardmetals in a

very different order that that shown in the standard Palmqvist test.

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Project 5B: Dynamic toughness measurement standardDevelop new standard for measurement of toughnessunder dynamic loading to supplement K1c measurementof toughness with static loadsThe hardmetal industry relies on static K1c measurements, based

on cracks around hardness indentations, to indicate ‘toughness’

(resistance to failure by crack elongation and thus fracture during

service) when insufficiently tough sintered carbides generally fail

from dynamic stresses? We need a standardized dynamic test, like

the highly subjective hammer/anvil test employed at Teco in the

1950s and elsewhere in later years. If so, should it be modified

Charpy, as sometimes employed by Sandvik and Kennametal, for

instance, or what? Project should evaluate possibilities and make

recommendations. Note that EuroHM already has a project for

evaluation of fatigue properties employing billions of dynamically

loaded (though non-impact) cycles.

Project 6: Rounded crystals make tougher hardmetalsComparison of properties between WC-based hardmetalswith rounded and with sharply angular particle shapesThe industry ‘knows’ that maximum toughness in HM is attained

by WC/Co with no GGI additives, either with coarse carbide grain

size or high Co binder content or both. At the other extreme, fine

or superfine carbide with low binder content promotes hardness

and wear resistance but reduces toughness. But that’s not the

whole story. WC crystals in such alloys are not ideal; they often

have sharp corners or edges, concentrating stresses and reducing

toughness. One solution is to employ an alloyed WC-base mono-

phase solid-solution carbide, with no sharp corners on individual

grains but improved high-temperature and anti-corrosion proper-

ties as well as maintained hardness.

Starting with some hints in a paper by Richard Kieffer of

Metallwerk Plansee published in Planseeberichte (a predecessor

of Metal Powder Report), I developed a family of WC/TiC/(Ta,

Nb)C/Co carbides which, when double-carburized at 1700 and

1900�C, contained more than 80% WC (for hardness and wear

resistance) but only a single solid-solution carbide phase. Other

key features included a maximum of 4 wt% (Ta,Nb)C carbide for

enhanced heat resistance, rounded crystals to replace the sharp

stress-raising corners of WC, and significantly lower specific gravi-

ty from the TiC content which proportionately decreased the

material cost of any specific shape and size.

The research project would attempt to reproduce these results,

to extend them with modern analytical and test equipment, and to

put the basic idea on a sound footing.

Note that the 1961 Hollis report on machining difficult-to-

machine alloys found that Teco EEV, the first of such alloys,

was the best cutting-tool material then available for high-speed

machining of highly alloyed stainless steels.

Project 7: Brazing the unbrazeableInvestigating simple techniques to extend the roster ofhardmetals and similar materials that can be brazed togive high-strength bonded jointsIn the 1950s, one of the major selling points for the newly

introduced ‘throwaway’ inserts was the fact that the titanium

carbide content of steelcutting carbide tips prevented, or made

very difficult, their use in what was then conventional brazed

FIGURE 8

Use of low-cost amorphous carbon to replace expensive graphite tubes inhigh-temperature furnaces operating in the graphitizing range.

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tooling. This was because of the surface layer of titanium oxycar-

bide which formed rapidly when the TiC-rich surface was exposed

to air, even at room temperature. Clamped tips, which could be

reground, were ‘clunky’ when compared with the brazed carbide,

and both production and use of throwaway tips, which quickly

developed into indexable multicorner designs, rose rapidly. Now-

adays, with all kinds of PVD and CVD coatings, they dominate the

hardmetal industry.

Nonetheless, there are still limited uses and a potential market,

for brazed joints involving alloy hardmetals with braze-resistant

surfaces. These appear to include high-grade WC/Co-base hard-

metals incorporating Cr carbide GGI and therefore a tenacious

surface layer of Cr oxycarbide or perhaps Cr–W oxycarbide, which

resists brazing. At Teco we produced the last-named for milling

cutters in tens or even hundreds of thousands. The answer we

found in each instance was to remove the surface layer by abrading

with silicon carbide (‘green grit’ – lesser abrasives will not work), at

first by grinding and then by tumbling for mass production, then

IMMEDIATELY to copper-plate by barrel plating, to preserve the

unoxidized surface. This gave a very strong braze, even on auto-

mated machinery, and might be copied, for example on modern

machinery for making woodworking saws or coal-cutters.

There are nowadays many videos on the Internet teaching how

to braze ‘brazeable’ carbide with copper and assorted brazing

alloys. In most cases it is specified that the carbide must be

wettable by brazing alloy, with or without flux. On the contrary,

the method mentioned above was designed specifically for

‘unbrazeable’ or unwettable carbide, has been proved efficient

and reliable in mass production, but even after many years appears

to be undocumented. Maybe someone would like to repeat the

original research and publish a paper, with corresponding video,

about it.

Project 8: Replace expensive graphite with amorphous carbon inhigh-temperature furnacesEmploying carbon tubes that graphitize in situ as aninexpensive substitute for expensive graphite high-temperature furnace tubesAt Teco we had a line of high-temperature graphite-tube carburiz-

ing furnaces, typically operating at temperatures up to 2000�C but,

if needed for research or otherwise, capable of significantly higher

temperatures. Unfortunately for us, the graphite manufacturers

continually ‘improved’ their material’s quality, as a result of which

the electrical resistance of the tubes decreased, the current re-

quired to reach a desired temperature increased and our large

transformers began to overheat. There seemed to be no alternative

to very expensive purchases of new transformers, until I realized

that we were operating in the graphitizing temperature range and

could instead buy so-called amorphous carbon, like the giant

carbon electrodes intended for electric furnaces, at a fraction of

the former cost (Fig. 8). So I set up a production line to machine

tubes from cheap carbon electrodes, the only additional purchase

being a Wheatstone bridge to measure for quality control the very

low resistances.

I know of no comparable conversion of this kind, though it may

exist (I haven’t carried out a patent or literature search), but if not

it would make an interesting project to put the technique and

selected property values on record.

Project 9: Multi-dimensional hardmetal phase diagramsWe lack knowledge of virtually all potential hardmetalmaterial compositions, with the solitary exception of WC/Co and limited-scope variantsEven when making small additions of other carbides to the basic

WC/Co combination, the industry is swiftly out of its depth. With

most hardmetal producers purchasing intermediates or ready-to-

press powders from a small group of suppliers, our current knowl-

edge base is in fewer and fewer hands. Suppliers do not offer

improved or more advanced materials because, they say, ‘there is

no demand.’ Users (hardmetal manufacturers) do not demand more

advanced materials because, they say, ‘more advanced materials are

not offered by suppliers.’ And few suppliers nowadays appear to have

the knowledge or ability to make, still less to research and invent,

their own. In consequence, the vast majority of hardmetal sin-

terers are – as in the 1930s – locked into simple WC/Co powders,

with or without grain-growth inhibitors, of a wide range of nomi-

nal grain sizes but very diverse grain size distributions, and cobalt

contents (not always well distributed) from 3% to 30%. It is as if

steel stockists only supplied plain carbon steel, with variable

carbon contents and heat treatments, but no tool steels, stainless

steels or any other kind of alloy steel.

Moreover, much of the industry has been persuaded that be-

cause ‘the coating does all the cutting,’ that ‘the bulk composition of

an insert is of little importance.’ EuroHM members know this isn’t

so, but no longer have sufficient knowledge or facilities to do much

about it.

What is needed is more knowledge. We could start by investi-

gating, in wjatever depth is possible, the four-component hard-

metal system WC/TiC/(Ta,Nb)C/Co. Let’s keep life relatively simple

by assuming near-stoichiometric carbon contents, so that we can

avoid eta-phase analogues. Also, because we’re aiming at potential-

ly commercial products, let’s also limit the amount of relatively

expensive (Ta,Nb)C to a maximum of, say, 5%. The reason for

including mixed Ta and Nb is that they are usually found together,

cost quite a lot to separate and are similar in their metallurgical

effects in spite of the difference in atomic weights and densities. My

own research used 75Ta2O3/25Nb2O3 as raw material, but there is

probably nothing critical about it (Ta materials impart greater heat

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resistance and otherwise improved properties but, for the same

weight, we get twice the volume of Nb and therefore possibly easier

conversion to solid solution). Since there is now (at the time of

writing) a single but apparently reliable supplier of pure Nb-base (i.

e. no Ta) raw materials, 100% Nb materials with no Ta should be

included as an option and perhaps allowed in a higher proportion.

It is assumed that modern materials theoreticians and computers

could make a substantial contribution to this investigation, suggest-

ing avenues to explore in detail and others to be discarded. Howev-

er, from a commercial aspect, I would be looking for solid solutions

of all components, in order to reduce microstress-raisers without

losing much hardness. But more important would be to obtain

information where none exists at present. Presumably the computer

could hold four- or five-dimensional data (including temperature)

in a multilevel database and could print out or put on screen two- or

three-dimensional phase diagrams as required or desired. I envision

some computer wiz putting on-screen a four-dimensional holo-

grammatic diagram through which one could wander,

For experimental research purposes, it would be essential to

have high-temperature furnace equipment. At Teco I used our

standard double-carburizing procedure for alloy carbides, the first

phase at 1700�C to convert all the oxides to carbides and the

second at 1900�C to promote solid solution and stabilize the

product. If we went straight to 1900�C the reaction and gas

generation were too violent, but at 1700�C it would have been

incomplete. Deciding between stable and metastable results would

be just one of the solvable problems of this interesting project.

As with other potential research projects, the first step, of

course, would be a small committee of experts to decide whether

such research would be useful and, if so, where, how and by whom

it should be carried out.

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ConclusionsThese few ideas, based on my own limited experience of some 60

years ago, when little of today’s apparatus and equipment were

available, will – I trust – indicate how little progress has been made

in our knowledge of hardmetals and their manufacture during

more than half a century. Not much has changed in the basics

apart from a few advances in things like granulation, insert coat-

ing, automation, and major cost-cutting exercises, such as attritor

milling and (especially) a switch from in-house processing to

bought-in intermediate powders. Knowledge of how to make

quality hardmetal raw materials is in fewer and fewer hands, with

little commercial interest in improvements that would increase

product life but reduce powder sales.

Apart from their performance enhancing coatings, the best

sintered carbides available today, and the corresponding

manufacturing techniques, are no better, and often substantially

worse, than the best available in 1960. Compare that with

advances in electronics, medicine, communications, food proces-

sing, animal husbandry, satellite engineering or virtually any

other science subject.

More significantly, current teaching on this subject could al-

most as easily have been given 50 or 60 years ago, giving the

erroneous impression that there is little left to learn about hard-

metals. In research, we are perhaps learning more and more about

less and less, not least because our very expensive academic

research facilities cannot reproduce major parts of the hardmetal

manufacturing operation. Of course there are exceptions, but

regrettably all too few. May I hope, therefore, that this brief

document will inspire the present or even a new generation of

researchers, who no longer think ‘we know EVERYTHING about

hardmetals.’