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AFML-TR-69-117Part V
EXPERIMENTAL PHASE EQUILIBRIA OF SELECTEDBINARY, TERNARY, AND HI-GHER ORDER SYSTEMS
Part V. The Phase Diagram W-.,-C
E. RUDY
AEROJET-GENERAL CORPORATION
TECHNICAL REPORT AFR.-TR-69-117, PART V
DDC
AUGUST 9•C
CI L I.R,,qG.!
This documnet has b=c apprvc f s,-r public,%&=s,and sale; its distrijution is un'mited.
AIR FORCE MATERIALS LABORATOiyAIR FORCE SYS-1.ItMS COMMAND
WRIGHT-PAT I')ON AIR FORCF BASE, OHIO
NOTICE
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AFML-TR-69-117Part V
EXPERIMENTAL PHASE EQUILIBRIA OF SELECTEDBINARY, TERNARY, AND HIGHER ORDER SYSTEMS
Part V. The Phase Diagram W-B-C
E. RUDY
this documei ''. :.,"• tudJ~ed on r~•u•+;
This document has bccn approved for public releaseand salc; its distribution is unlimited.
AFML-TR-69- 117Part V
FOREWCRD
The research described in this report was carried out under USAF
Contract F 33 615-67-C-1513 by the Materials Research Laboratory, Aerojet-General Corporation, Sacramento, California. The contract was initiatedunder Project No. 7350, "Refractory Inorganic Nonmetallic Materials",
Task No. 735001, "Refractory Inorganic Nonmetallic Materials: Nongraphitic",and was administered under the direction of the Air Force Materials Laboratory,Wright-Patterson Air Force Base, Ohio, with Captain P. J. Marchiando(MAMC) as Project Engineer. Dr. E. Rudy (now at the Oregon Graduate Center,
Portland, Oregon) was the Principal investigator.
This report covers work conducted during the period April 1967 throughMay 1969. It was submitted by the author February i970.
Other reports issued, or in preparation, under USAF Contract AF 336!5-67-C-1513, are:
Part I. The Phase Diagrams of the Syrtems Ti-Nb-C, Ti-Ta-C,and Ti-Mo-C.
P'art II. Effect of Re and Al Additions on the Metal-i.,n PhaseEquilibria in the Ti-Mo-C and Ti-Nb-C Systems
Part III. Phase Studies in the V-Ta-C and Nrb-Ta-C Systems
Part IV. Effect of Mo and W Additions on the Subcarbide SolidSolutions in the V-Ta-C and Nb-Ta-C Systems.
The technical report has been reviewed and is approved.
W. G. RAMKEChief, Ceramics and Graphite BranchMetals and Ceramics Division
Air Force Materials Laboratory
ii
AFN1 L-TR-&9-I 17Part V
ABSTRACT
The ternary alloy system W-B-C was investigatedexperimentally by means of X-ray, melting point, DTA, andmetallographic techniques on hot-pressed and heat-treated, aswell as melted specimens, and a phase diagram from 1300'Cthrough the melting range established.
No ternary phases are "uo.aed in the svstem and themutual solubilities between ca bide and boride phases are srnall.The solid-1tate sections (<ZO"j°C) are characterize4 by two-phase equilibria existing between the phase pairs WVB + WC,WzB + WC, WC + WB, WB + C. WZBS+ C, IVZB 5 + B4C, andWB4 + BtC. The two-phase equilibriurm WB 4 WC is replacedby an equilibriLm WzC 4 WB above 250'C.
Fifteen ternary isothermal reactions have been found.Five are - ssociated with pseudobinary eutectic equilibria,six with ternary eutectics, and the remaining four with class 11ternary feur-phase reaction isotherms.
iii
"TABLE OF CONTENTSPAGE
!. INTRODUCTION AND SL."MMMR.Y .............
A. Introduction . . . . . . . . . . . . . . . ..
1. Summary .............. 2
Ii. LITERATURE REVIEW ............ .. ..
MI. EXPERIMENTAL .................... 10
A. Starting Material and Alloy Preparation. .......... 10
B. Determination of Melting Temperatures andDifferential Thermal An.alysi .................... 1Z
C. Metalographic, X-Ray,and Chemical Analysis . . .. 12
IV. RESULTS ................. ...................... .. 13
A. Experimental Studies ............. ........... 13
B. Assembly of the Phase Diagram. ........... 39
V. DISCUSSION .......... ............................ 48
R.rences ........................................... 50
LJST OF iLLUSTRATIONS
FIGURE PAGE
1 isometric View of the Constituticn Diagram W-B-C
2 Reaction Diagram for the W-B-C System 4
3 Liquidus Projections in the W-B-C Systems 5
4 Ccnstitution Diagram Tungsten-Carbon 6
Cor.stitution Diagram Tungi ten-Boron 8
6 Constitution Diagram Boron-Carbon 9
7 Section oý the W-B-C System at 1700°C 10
8 Qualitative (X-Rayl Phase Evaluation of the Alloy SeriesHeat-Treated at 150 0 ' C 14
Qualitative (X-Ray) Phase Evaluation of As-MeltedW-B-C Alloys 15
10 DTA-Thermograms Indicating a Solid-State Reaction Around2150°C in an Alloy W-B-C (57-30-13 At.%). 16
11i Transfkrmation of ibe Orthorhombic High Temperature Modi-fication of WB into the Tetragonal Low Temperature Formin Ternary W-B-C Alloys at -2000° C. 17
12. Melting Temperatures of Alloys Located at the Pseudobinary
Eutectic Section W 2B-WZC I.
13, W-B-C (67-24-9 At.%), Melted and Rapidly Cooled 19
14. W-B-C (68-18-14 At.%}, Melted and Rapidly Cooled 19
15. W -B-C 67-12-21 At.T}, Rapidly Cooled from LiquidusTemperatures z0
16. W-B-C (80-10-10 At.%), Melted and Rapidly Cooled 20
17. W-B-C (75-15-10 At.%), Melted and Rapidly Cooled 2i
18. W-B-C (731-12-15 At.%), Melted a: Iapidly Cooled" 21
19. Melting in Alloys at the Pseudobinazey Eutectic SectionWB-WZC 2z
vi
LIST OF ILLUSTRATIONS (Cont'd)
FIGUIRE PAGE
20 W-B-C (64-11-Z5 At.%/), Rapidly Cooled from Liquiduz
Temperatures 23
21 W-B-C (58-30-12 At.%), Rapidly Cooled from LiquidusTemperatures 23
Z-> W-B-C (60-20-20 At.%), As-Melted 24
23 Sample Shown in Figure 28 Reequilibrated for 3 hours at18000 C and Rapidly Cooled 24
24 W-B-C (64-23-13 At.%), Rapidly Cooled from LiquidusT-.nperatures 25
25 W-B-C (54-30-16 At.%), Rapidly Cooled from LiquidusTemperatures 26
26 W-B-C (55-25-20 At.%), Melted and Rapidly Cooled Z6
27 W-B-C (59-16-25 At.%), Melted and Rapidly Cooled 27
28 W-B-C (57-14-Z9 At.%), Rapidly Cooled from Liquidus
Temperatures 28
29 W-B-C (55-10-35 At.%), Rapidly Cooled from Liquidua
Temperatures 29
30 Experimental Melting Temperatu.-:s of Samples Located
Along the Pseudobinary Section WB-C 30
31 W-B-C (43-42-15 At.%), Melted and Rapidly Cooled 31
32 W-B-C (50-40-10 At.%),Melted and Rapidly Cooled 3Z
33 W-B-C (45-35-20 At.%), Rapidly Cooled from Liquidus
Temperatures 33
34 Melting Temperatures of Alloys Located Along the Pseudo-binary Section WzBs-C. 34
35 W--B-C (31-64-5 At.%), Rapidly Cooled from Liquidus
Temperatures. 33
vii
LIST OF ILLUSTRATIONS (Cont'd)
FIGURE PAGE
36 W-B-C (30-63-7 At.%), Rapidly Cooled from LiquidusTemperatures 35
37 W-B-C (26-54-Z0 At.%), Melted and Rapidly Cooled 36
38 W-B-C (39-56-5 At.-,6), Melted and Rapidly Cooled 36
39 Melting Temperatures of Alloys Located at the PseudeainarySection WzB 5-B 4 C. 37
40 W-B-C (34-55-11 At.%,, Melted and Rapidly Cooled 38
41 W-B-C (25-70-5 At.%), Melted and Rapidly Cooled 38
42 W-B-C (18-68-14 At,!,'), Melted and Rapidly Cooled 39
43 Isothermal Section of the W-B-C System at 15000C 40
44 Isothermal Section of the W-B-C System at 2000°C 41
45 Isothermal Section of the W-B-C System at 21500C 4Z
45 Isothermal Section of the W-B-C Systerr at 2320 0 C 43
47 Isothermal Section of the W-B-C System at 23500C 44
48 Isothermal Section of the W-B-C System at 25000C 45
49 Isothermal Section of the W-B-C System at 27000 C 46
50 Isothermal Section of the W-B-C System at 2800°C 47
viii
I. INTRODTJCTION AND SUMMARY
A. INTRODUCTION
Next- to the refractory carbides, the borides of the refractory
transition metals are among the highest melting materials known. While
they compare in hardness and mechanical properties with the carbides, the
borides generally have much better oxidation resistance at elevated tempera-
tures. In spite of these interesting properties, however, efforts undertaken
to utilize the borides in parts for high temperature service are hampered by
their extreme brittleness and their reactivity with other alloys; the latter
property especially has so far prevented the successful development of
suitable metal binder alloys to reduce the mechani'al and thermal shock
sensitivity of the compounds.
To gain a better understanding of the behavior of
refractory, boride and carbide phases in the presence of other high melting
zompounds, including other borides and carbides, as well as silicides, nitrides,
and metal phases, a systematic study of ternary alloy systems was initiated(1)
a few years ago. These investigations have led, especially in the case of
the carbides, to a comprehensive interpretation and classification of the high
temperature reaction behavior of these compounds.
The current effort was undertaken to study Che high tempera-
ture phase equilibrium charact.eristics of a Me-B-C system involving a group
VI refractory transition metal, after borocarbide systems involving group IV metals
(Ti,Zr,Hf) have been treated under the preceding program. (1) Points of
specific interest included phase equilibria involving boron carbide; the mutual
solubilities of carbide and boride phases, and the eventual formation of new
ternary phases.
I
B. SUMMARY
The ternary alloy system W-B-C was investigated experi.-
mentally by means of X.ray, melting point, metallographic, and differential-
thermoanalytical techniques, using hot-pressed, and sintered, as well a&
melted specimens, and a phase diagram was established. An isometric view
of the system is shown in Figure 1.
Fifteen ternary isothermal reactions occur in the experi-
mentally investigated temperature range from 15000C through melting (Figure 2).
Five isothermal reactions are associated with the formation of pseudobinary
eutectic equilibria between the phase pairs W2B + WzC (2370°C, 41 mole%
W 2C), WB+ WC (Z330°C, 33 mole% W 2 C), WB + C (2360'C, 13 At.% C),
WzBs+ C (2275-C, 7 At.% C), and WB 5 + B4 C (2ZZ 0 °C, 24 moo!e% B4 C). Six
reaction isotherms are associated with ternary eutectics,
L Z W+ WzC + WzB at 23550 C
L ZWC + WzB + WB at 23050 C.
L W 2C + WC + WB at Z300°G
L : WB + W2B 5 + C at Z2400 C
L W W 2 3s+ C + B4C at 2l8 0 °C
L WB.; + B + B4C at 195V C,
and four with class II (two-over-two) four-phase equilibria:
L + a-WC1..x _ W2C + WC at 25700C
L+ C-:WC+ WB at 23500C
W 2C + WB : WzB - WC at Z150 0 C
L + W2B5 WB•.€ + B4 C at 2000'C
3425*--,
2 3 5 0 " 2
24530
Lsotr~~~~~~etri233.. Viw oIh osiui~ iga - G
-A,3.
w-c W, W-8- C W-B 23-C
L- L-,- tl --+ IL* L+7 ÷ L ÷- L+c l L +
-- 27 -- 1•- ii 2 6Oi
I_ 2 0 A7 0 ~ y ~ , 2 7. .- . IL +S ----I.. ,t. II , • ~ ' • ,
' 3700 I-.- .337 ,
;75 Lp~ 2570- 23500 23
Lb.y2 ILC^ I 20ý70-' i1 4""__I!____ Y 3* ""11 L- • • _I___'-x. IIi , • , , ? , 0• I
, Etl, ,2355-
25307 0 . .- o, -
:2500\ 22200.25
f Y20*1218010 eaed z oWS (riT +L T.R • ++y+ cy+(- ,I I y3W! C 2 1 T
I KI
', : ';i -•F • °°- 7 • =- : O'K ;i a-W,-',° . ,, . 1 I95 F - ++-L--- -- 8 -Z•eI? ,5,C,
* II ; S X = i ;1511O) I 19500- - .1 "•=2B L =Met* 150600
/ 3+ Y+ _ +Y+ C )- +8+ý ,+V'x .16+4 t+_2+ =77+B, eir+x 0+_c r,+6 _t ,+C a+ I _+i +L
Figure 2. Reaction Diagram for the W-B-C System
A projection of the melting troughs and liquidus isotherms in the system
is depicted in Figure 3. Additional isothermal reactions resulting from the
high temperature transformation of the binary WB and the sublattice order-
disorder transitions in WZC were not studied in detail a•nd thus were not
included in the phase diagram assemblies.
The lower temperature (<Z100°C) solid state-sections in the
system are characterized by very limited mutual solubilities between boride
and carbide phases and the existence of two-phase equilibria between the pairs
4
20100 ,e
1970%,e 1950, E
2070, Ap \2030'D
S/:
Z•40°2, 50-., \C'j23800,e 0
2365,max *A/ *,C
2275 0.t ;°.• xo 2340*,e 2601
/ 1224o*o ./ • n,,
IIN.."•....6 '"
".00o007,5e
35 W 2?i0=,e" 2776•',mox 27?m-.2776',D -- ATOMIC % CARBON
Figure 3. Eiquidus Projections in the W-E3-C System
W 2 B+ WZC, WzB+ WC, WC+ WB, WB+ C, W 2 B 5 + C, WzB5 +B 4 G, and
WB.•. 4 + B4 C. Above Z1500 CG, the equilibrium W'2B + WC. is replaced by an
eauilibrium between WB and W2 zC.
II. LITERATURE REVIEW
The most recent version of the phase diagram of the W-C system,
Cp 240 4)* (5
compiled from previous work{2"'4 as well as .our investigations( 6, is shown
in Figure 4. The system contains three intermediate phases of which two,
W2 C and a-W~xix(Bl1), melt congruently, while the third, WC, decomposes
. ......
3800- Homrogeneous ordering in W2CDisplacive transformationI
- .Change of subattice order
3600 /
,-3423± 260 z ~35500'3400 L4Cgos
2720±1'3N(Uatin)
3200; 47012
cr 3000 L- +05±2
27776+100
a- 2800 1\\27±O
2600 22<2I r I-
32.6 WC+C2'400 2S±0
2200- ~ w
201 ATOC 20A30 4 50 60__W~4~ - ATII vCRO
Figure 4. Constitution Diagram Tungst.en -Carbon
in a peritectic reaction at 27760C. The subcarbide, W3,C, exists in several
5'tates of sublattice order (Table 1) and shows a complex transition behavior
(Figure 4). The cubic carbide a-WCi..x is stable at high temperatures only
and decomposes in a rapid eutectoid reaction at 25300 C into the disordered
modification of W2G and. tungsten monocarbide.
Although the structure of the tungsten bor-ide phases have been estab-(11,13)
lished for quite some time ,the phase diagram of the tungsten-boron
6
Table 1. Structure and Lattice Parameters of Phases in theTungsten-Carbon and Tung stein -Boron System
Phase Structure Lattice Parameters,
W 2 C hex., L'3-type(>248 0 *C)(7) a=2.985 at 29.5At./Cc=4.716
(5)hex., C6-type (8) a= 3. 000 at 32.8 At. C(
c=4.730
Orthorh.f -FezN-type a=4.738(2100 to 2480-C) b=6.009 at 32.6 At.% C (7)
c= 5. i93
hex., e-FeZN-type a5 184c=4.721
a-WCGIx fcc., Bl-type a=4.215 (?,3)a=4.2Z0 at - 38 At.% C (5)
WC hex., Bh-type a=2.906Z (10)(D1t-P 6 m 2 ) a=2.3368
WzB Tetr., C16-type a=5.564; c-4.740 (11)a=5.570 to 5.572 (12)
c= 4. 144 to 4. 746
WB Tetrag., Bg-type a=3.115; c=16.93 (11)Low Temp. a= 3. 093 to 3.120 (12)Modif. c=16.99
WB O-thorh., CrB-t-pe a=3.19; b=8.40; c=3.07 (13)High Temp. a=3.142; b=8.506; c=3.065 (12)Modif.
WzBs hew., D8 h-t-ye a=Z.982; c=13.87 (11)a= I.Q980; c=13.88 (12)
WB (n-4) hex., P6.rmmC a=5.200; c=6.340 (14)a=3.004; c=3. 174 (hex.subcell)(15)
7
system was established only recently by E. Rudy et al. (Figure 5)(12"* The
system contains four phases. W 2B, WB, W?B 5 , and WB,. 4 (Table 1), of which
the first three melt congruently, whereas the boron-richest phase was indi-
catea to melt under decomposition. The monoboride exists in a tetragonal
modification below approxina tely 2100* C, and an orthorhornbic high tempera -
ture polymorph, which is stable between -Z100°C and the melting point.
3600 --- T
Z3423_+2603400
32G00
3000 1S~2670t; 60
628oo ~33.5S27+05 I 2665t+160
3 70-48
-. a - 2- 5 8 0 2± 12001 260 4C •±i 020
u.: --W - TOc. % B8_+1
88±
63±1 -- 21001,
2200 2337±70
•,23 1I_7 ° - 7--"2 1 ' ± 0 - 2 1 7 0 ± 7 0 0' - 9
0 20 c 60 2020±30
W8
S.. ;-R; • ii i ii20.00 I II.• i i 4 III W8m
(16)The boron carbon systernm6 (Figure 6) contains onr• intermediate
phase, %.C, which has an extended range of homogeneity. The s'ructur- of
B4 C is rhornbohedral, with a R=5.19A0, = 66° 18'1(0).
2 6 0 0 r . . . I I ... "-- -- -- 1"-T
L L 2450±250 L+C}
2400 L+P4 C 2380±200
28±1.5J
c•- 22CO /L LC
0 - _2O0°; 84
< 2000rr ,,.20800
a.8_ 1 84C+C
uW 1800
B+B 4 C
1600-
1* f1400oL-- , , , ,
0 20 40 60
B -ATOMIC % CARBON--
Figure 6. CZonstitution Diagram Borcn-Carbon.
(Compiled from R.T. Doloff (18) R.P. Elliottand Own Investigations)
An isothermal section of the W-B-C system at 1700'C was established(15)
by E. Rudy et al. (Figure 7). Qualitative inveFI-igations of .he behavior
of borides in the presence of carbon have been carried out by Glaser(Z0) and
Brewer and Haraldsen(2 1 )
9
B
(n 1'2)- B4CW2B5 -• - i
W 8
W2 a
W W2C WC C
Figure 7. Section of the W-B-C System at 1700'C.
(After E. Rudy et al., 1963).
III. EXPERIMENTAL
A. STARTING MATERIAL ;.ND ALLOY PREPARATION
The elemental powders, as well as master alloys of WzB5
and WC, served as the starting materials for the preparation of the -experi-
mental alloys.
The tungsten powder (Wah Chang Corp., Albany, Oregon)
contained the following impurities (in pp.-n): Mo-50, 0-720, Fe-40; Ni-20;
N-430, and the sum of other metallic contaminants-<60. The average grain
size of the tungsten powder was 6.8 rnicrons, and a lattice parameter of
3. 1665A was determined from a Debye-Scherrer exposure with Cu-Ku
radiation.
10
The analysis of the spectcographic grade graphite powder
(National Carbon Corp.) was as follows (in ppm): Al-0.3; Cu-0.1; Fe-.0.2;
Mg - 0.1; and Si-0. Z.
Boron powder of ý?'4.55% overall purity was purchased from
United Mineral and Chemical Corporation, New York. Major impurities
were iron (0.25%), and carbon (0.1%).
Tungsten monocarbide was prepared by reacting the cold-
compacted mixtures of the elemental powders in a graphite-element furnace
for 4 hours at 2100'C under hydrogen. After cooling under vacuum, the reac-
tion lumps were comminuted to a grain size less than 60 microns in carbide-
lined ball mills. Cobalt traces picked up during milling were removed by
acid-leaching in a mixture of hydrochloric and sulfuric acid, the resulting
slurry centrifuged, washed with ether, and then vacuum dried. Chemical
analysis indicated a total carbon conteat of 50.7 * 0.3 At. %, and an oxygen
contamination level of less than 150 ppm. The lattice parameters measured
were a = 2.906A, and c = Z.837A.
W 2B 5 was prepared by direct combination of the elements at
high temperatures. The well-blended mixture of tungsten and boron powder
was cold compacted, the compacts stacked into tantalum cans, and the
assembly loaded into the heat-ng zone of a graphite element high temperature
furnace. The reaction was initiated at about 1200°C and brought to comple-
tion by a two hour vacuitm treatment at 17500 C. The reaction lumps were
then crushed, acid leached, and further processed in the same manner as
described for the tungsten monocarbide. Chemical analysis determined a boron
content of 70.7 ± 0. 5 At. %, and a carbon content of 0.1Z Wt. %. The follow-
ing impurities were determined spectrographically: Fe-500, Si-100, Mg-100,
A!-500, Ca-100, Cu-100, Ni-100, Mn-100, Cr-100, Mo-l00, Ti-,00. The
11
lattice parameters measured from an exposure with Cu-K radiation,were
a= 2.982A, and c= i3.88A.
Specimens for the experimental investigations were prepa-.ed
by short duratior. hot pressing of the ingredient mixtures in graphite dies
at temperatures between 1800 and 22( 0"C. Specimens for melting point and
DTA-studies were used in the as-pressed conditions and were equilibrated
in the melting point or DTA-furna ; prior to the runs. The heat treat-
ment s.nedules for the alloys prepared for the determination of the isothermal
sections of the system were 140 hrs at 1500°C, and 6 hrs at 20C0"C. To
establibh the t emperature change of certain equilibria in the solidus region
ard also to obtain rapid cooling rates, selecred alloys were equilibrated in
the melting point furnace and tiAn-quenched. Mostly for metallographic purposes,
a piece of each alloy was also arc melted under helium in a non-consumable
electrode arc furnace.
B. DETERMINATION OF MELTING TEMPERATURES AND
DIFFERENTIAL THERMAL ANALYSIS
Melting temperatures of the alloys were determined with the
Pirani-technique, using a high purity helium atmosphere of 1 atm pressure.
The design of the apparatus used in this laboratory and temperature calibra-
(22, 23)tion procedures have been described in detail in earlier publications
2.•eDTA-uns(23)The DTA-runs ( were also made under helium, using graphite
as container material and tantalum monocarbide as comparison standard.
C. METALLOGRAPHIC, X- RAY, AND CHEMICAL ANALYSIS
For the microscopic inspections of the alloy structures, the
samples were mounted in F mixture of diallylphtalate and lucite-coated
copper powder. After coarse grinding on silicon carbide papers (grit sizes
12
between 1?0 and 600), the samples were polished on nylon cloth, using a
suspension of 0.3 micron alumina in a 5% chromic acid solution. After polish-
ing, the samples were electroetched in a 2% aqueous solution of sodium
hydroxide.
Boron in the alloys was determined by dissolution of the
powdered samples in a melt of pre-dried sodium carbonate at 1000°C. The
resulting melt was dissolved in water, the excess carbonate removed
by barium hydroxide, and the boric acid determined by differential titration
oi the boro-mannitol complex with N/10 NaOH between pH-values of 5.3 and
8. 5. The consistence of the data obtained by this method varied between
about + 0. 1 and :- 1 At.% B absolute.
Carbon :-as det.rrnined by the standard combustion technique,
using a commercial Leco carbon analyzer. Oxygena, nitrogen, and hydrogen
were analyzed by the gas -fusion technique, while low level metallic impurities
were de:ermined semiquantitatively by spectrog-aphic methods.
X-ray powder aiffraction patterns using Cu..K, radiation were
prepared from all alloys fabricated in the course of the system investigation.
IV. RESULTS
A. EXPERIMENTAL STUDIES
Due to the very limited mutual solubilities, the experimental
investigation and the interpretation of the results was straight-forward and
s imple.
The X-ray evaluation of the alloy series equilibrated at i 500°C
(Figure 8) substantially confirmed our previous findings concerning the gross
13
/ ,-..j• ::x
S""D T~o pieoses7-0+y a" t , -o G. Three ohoses
A ' ý -%- o MuiL:phase,not in/B ( - x 1 " eauil•brim
/ "-.#-, /, s ._ \ .
J VI'
o' WB,,,,(9 °_ "•,•
£ 'th ,-
'e Vixy A m- x•" % CABO C•a
Figure 8. Qualitative (X-.kay)l Phase Evaluation oi" the AlloySeries Heat-Treated at 1500' C.
features of the system below 2-000'C (15). Two-phase equilik-ria are formed
between the phase pairs WzB + W2C, W.:B + WC, WB + WC, WB -: C, WzBn + C,
Wz13s5+ B4C, and WB,4 + B4C. The lattice param~eters of the pha•ses in the
ternary alloys coincided ,irithin the error limits with those of the pure binary
phases. The tc-rnary hormogeneity ranges ot ',oride and carbide are therefore
small, a result, which was independently corroborated by rn~e~allographic
studies.
14
The phase equilibria at solidus teriperatures (Figure 9) are
very similar to those at lower temperatures. The only significant change
involves a owitch of the two-phase equilibrium WzB + WC to another equi-
libriurn. between WC and WB . DTA-studies of alloys lccated within the con-centration range WNzB + Wz C + WC + WB indicated a temperature of 2150°C
for the nonvariant equilibrium
WzB+ WC T>- 21500 C WzC+ WB
B
C6)/' ~'\(D Two phases
~ ( -% 71+X 0 Three phases// j" •-" \ I0 Back reaction L+C--.t/!/ • • / \•WC +WU not campiete
/ -0
IR , - - 8- %-4 0
/, .•• , I \\)
W, 8! 00V
Q0
+ 0
INV
W2-1a• ogIWCCB w Y)-) - ATOMIC % CARBON -- C(S)
Figure 9. Qualitative (X-Ray) Phase Evaluation of As-Melted
W-B-C Alloys.
155
This result -"as independently confirmed by X-ray analysis of alloys equi-
librated at, and quenched from, temperattures above and below the four-phase
plane. DTA-studies also ascertained that the transformation temperatures
of WB are practically unaffected by the presence of carbon (Figures 10 and 11).
Heiting ri * i sec.
Heating rate:60 C per sec.
M Cooling rate: 4CC per sec.
w I
-0 21400
x /23000
21500
I f~V! * I * I , * I * I
2400 2200 2000 1800 1600
STEMPERATURE, °C -
Figure 10. DTA-Thermograms indicat-ing a Solid-
State Reaction Around Zl 50ý C in anAlloy W-B-C (57-30-13 At.-%).
After the gross features of the high temperature phase equi-
libria had been delineated by these preliminary studies, the subsequent
effort concentrated on locating the nonvariant equilibria in the system by a
combination of melting point, DTA, and metallographic techniques.
i6
"" I I I l' '-I-
W W-B -C(46-44 -10 At. %)
01
w
-r- W-B-C0 0 (35-55-!0 At. %)x
20700
I t ,,C.C,22400
2400 2200 200C 1800 1600
4 TEMPERATURE,°C -
Figure 11. Transformation of the Orthorhombic HighTemperature Modification of WB into theTetragonal Low Temperature Fo'rm in Ternary
W -B-C Alloys at -2100°C.
17
Melting point measurements and microscopic inspection of
the as-melted alloys established the existence of a pseudobinary eutectic
equilibrium between WzB and WzC (Figures 12, 13, and 14). Because of the
formation of eutectic equilibria between W and WzC, and W and WzB in the
respective binaries and the absence of ternary compounds, only a ternary
eutectic equilibrium is possible between the three phases W + W2C + WzB.
Melting point as weli as solidus points obtained by difierential thermal analysis
yielded a mean temperature of 23550 C for this ternary eutectic, and a eutectic
composition of W-B-C (71-17-12 At. %) was derived by microscopic inspection
of the alloys. Typical microstructures of melted alloys loLated in the vicinity
of the terrary eutectic are shown in Figures 16, 17,and 18.
2 8 0 0 1 1 1 1 -I -'I 2 7 -6 0
* Incipient melting noted0 Specimen collapsed heterogeneously /
2700k 2670. * Melted isothermally /- Incipient melting by DTA /
0
(2600 /I- /
D/
S2500 , / .30±0 /i ~41-±3 %
2400 0 0/ I ,
23010 2 130 40 60 80 100
W2 B - MOLE % W2 C ----) W2 C
Figure 12. Melting Temperatures of Alloys Located atthe Pseudobinary Eutectic Section WzB-WGC.
18
r 1w--- -- - - --
-~
44
Figure 13. W-B-C (67-24-9 At.%), Melted and Rapidly X440
Cooled.
Primary W2D Crystals in a Matrix o.' W2 3+ WZC Eutectic.
Figure 14. W-B-C (68 -18 -14 At.%), Mlelted and Rapidly X680Cooled.
WC -; W2B Pseudohinary Eutectic.
19
Figure 15. W-B-C (67-1Z-21 At.%), Rapidly Cooled X680
from Liquidits Temperatures.
Primrazy WZC in a Matrix of WzB + WZC Eutectic.
IA
Figure 16. W-B-C (80-10-10 At.%), Melted and X?20
Rapidly Cooled.
Primary Tungsten (Rounded, Light Grains) in aMatrix of Ternary W + W2C + W 2B Eutectic.
20
II
Figure 17. W-B-C (75-15-10 At.,%), Melted and X440
Rapidb/" Cooled.
Primary Tungsten, Smaller Amoln-ts of SecondaryWB, and Ternary W + WB + W•_C Eutectic.
. 1
Figure 18. W -B C(73 -12-1=-' At.,'',), Melted and X680Ra pidlv Cooled.
Primary W + VA.zC. Formed During SolidificationAlong the Eutectic Trough ( 1 + WMt, in a Matrixof W + W+C + WEB cEutectic,
21
The phase WB and WzC also form a pseudobinary eutectic
pair (Figures 18, 20, ?.1). The phase mixture W2 C i WB, which is stable
only above 2150CC, is gradually converted to a mixture of WC + W2B
(Figures 22 and 23) upon reannealing of as-melted and quenched samples
at temperatures below 210 0 °C.
2800 I I 1 1 27?76
A Incipient melting noted0 Specimen collapsed heterogeneously
2700 26 Melted isothermally /- Incidient melting by DTA
,\ /
' 260C - /w"
Ld//0
'• 9500w /
24ý 2330±2000~__/
23003
0 20 40 60 80 100WB 6MOLE %W 2 Cw W2 c
Figure 19. Melting in Alloys at the Pseudobinary EutecticSectibn WB-WzC.
22
Figure Z0. W-B-C (64-11-25 At.%), Rapidly Cooled X680from Liquidus Temperatures.
Primary WVC in a Matrix of W2C +- WB Eutectic.
-wwW OmP% AX-:
* ~ -.- W.-
,~§ ~.\\ * *
Figure 21. WV-B-C (58-.30-12At.%), Rapidly Cooled X400from- LiquIdus Temperatures.
Primary %;B (Showing Intragranular Transformationand Pr-ecipitation Structure) in a WB + W2C Pseudo-binary Eutectic Mlatrix.
23
Figure 22. W-B-C (60-20-20 At.Yo), As-Melted X520
Primary WZG in a WzC + WB Pseudobinary EutecticMatrix. X-Ray: WZC + WB
Figure 23. Sample Shown in Figure 28 Reequilibrated X5 20for 3 hours at 1800C and Rapidly Cooled.
X-Rayt WC + W2B
24
A ternary eutectic between the phases WZC., WzB, and WB is
located at 2305'C2 and a composition W-B-C (62-24-14 At.%o) jFigurea Z4
and 25).
"N'.
I I. _T
Figure 24. W-B-G (64-23-13 At.O,,), Rapidly Cooled X400from Liquidus Temrperatures.
Small Amounts of Primrary W2B, Secondary WzBand W2C formed by Cocrystallization Along theBoundary Line WzB + W2G, and Ternary EutecticWzB + WzC + WB.
A further ternary eutectic, at 2300'C and a composition W-B-C (55-2b-1l,
.At.%) consists of the phases WzC + WC + WB (Figures 26 and 27).
It is interesting to note, that the ternary range of existence
of the cubic monocdarbide a-WC1 .., is restricted to a very small concentra-.
tion (< 3 At.% B) r .ar th-; W-C binary, i.e. throughiout its temperature range
of eXistence. the a-WCI..x phase does not form' equilibria with any of the boride
phaszs.
25
Figure Z5. W-B-C (54-30-16 At.%), Rapidly Cooled X400
from Liquidus Temperatures.
Elongated Crysta.ls of Primary WB (Transformed)
in a Ter.-ary WB + WaG + WC Eutecti-z Matrix.
Figure 26. W-B-C (55-25-20 At.76), Melted and Rapidly X400Cooled.
Trace of Primary WzC in a Ternary WV2 C + WC WBEutez~ic Structure.
26
Irv
Figure 27. W-B-C f5q-16-Z5 At.%/), Melted and Rapidly X400Cooled.
Primary WzG and WzC +I WC + WB Ternary Eutectic.
The investigation of the other sections of the system in the
solidus range need not be described in detail, since the techniques were
analogous to those described above, and the results, shown in data plots
andt a few iielected micrographs in Figures 28 through 42, ate selfexplanatory.
27
Figure 28. W-B-C (57-14-29 At.%), Rapidly Cooled XZ50from Liquidus Temperatures.
Pric-nary WC. Bivariantly Crystallized WZC + WCEutectic-Like Structure, and Ternary WzC + WC
+ WB Eutectic.
Note absence of free carbon, indicating that thesample is located between the boundary linesW 2C + WC and WC + C.
28
Figure 29. W-B-C (55-10-35 At.%), Rapidly Cooled X325from Liquidus Temperatures.
Primary Graphite Surrounded by Walls of SecondaryWC, Tj aces of WB, and Ternary Eutecfic WzC+ WC+ WE.
29
3 4 0 0 j " --- '
A Incipient melting noted 00 Specimen collapsed /
3200- heterogeneously /* Melted iso.hermally /mIncp ient melting
by0DmTA /S3O0o0 /
0w / 0w /
,2800 /X 26650 /
( 1 002 0wJ 2600
240k ~0 23601150 £2400 l f A A A
0 10 20 30 40 50 60
WB - ATOMIC % CARBON-'
Figure 30. Experimental Melting Temperatures ofSamples Located Along the PseudobinarySection WB-C.
30
4,,1
Figure 3 1. WV-B -C (43 -42-15 At.%) Melted and X475Rapidly Cooled.
Primary Graphite and Pseudobinary WB + Crutectic.
31
p
I
Figure 32. W-B-G (50-40-10 At.%),Melted and Rapidly X400Cooled.
Primary WB %Transformed) and Eutectic-TypeSolidification Structure Formed Along the BoundaryLine WC + WB and at the Ternary Eutectic WzC+ WC + WZB Temperature.
Ncte absence of free carbon, indicating that thecomposition of the first produc t of crystallizationlies below the WB + C boundary line.
32
Figure 33. W-B-C (45-35-20 At.%), Rapidly Cooled X525from Liquidus Temperatures.
Primary Graphite in a Eutectic-Like SolidificationStructure Formed Along the Boundary Lines WB
+ C, WB + W\, and at the Ternary Eutectic PointWB+ WZC+ WC.
33
3000- / 0/
// A Incipient melting noted
o 2800 / 0 Specimen collapsed./ heterogeneously
u[/ * Melted isothermallyM - Incipient melting by DTAH2600 /< 0CrU. /a-u 2400 23650 0
A A
2200 7t1,5%
0 10 20 30 40 50 60
W2 B5 - ATOMIC % CARBON
Figure 34. Melting Temperatures of Alloys LocatedAlong the Pseudobinary Section %V2B.C.
34
Figure 35. W-B-C (31 -64 -5 At. q%), Rapidly Cooled X250
from Liquidus Temperatures.
Primary WaB 5 in a P seudobina ry W, B 5 C Eute cticMatrix.
~dw
Figure 36. W-B-G (30-63-7 A,",) Rapidly Cooled X6Z5
from L.iquidus Temperatures,
X.B-IC Pseudlobinary Eutczti',.
W.4,
Figure 3-7. W-B-G (26-54-20 At.%/), Melted and Rapidly X350Cooled.
Primary Graphite in a Partially Divorced, PseudobinaryWzBs+ C Eutectic Matrix.
Figure 38. W-B--C (39-56-5 At.%), Melted and Rapidly X3 75.Cooled.
Prlmary WB (Transformed), Secondary WB + C, andTernary Eutectic WB + W 2 B 5 + C.
36
2500 . " I -24500A Incipient meffing noted 2
0 Specimen collapsed heterogeneouslyS2400 4,5 0 Melled isothermally
0. 2360- incipient melting by DTA
< 2300 Nw N
0A N 2220t 200
24t3 %0/
,. "I , , ,,-
0 20 "20 60 80 100W15 / 2 --- MOLE % B4 C--' B4 C
Figure 39. Melting Temnpermturesg of Alloys Locatedat the Pse doblnar" Sectio), W%35-B 4C.
37
-Al
Figure 40. W -B -C (35-55- II At.%) Melted and Rapidly X475Cooled.
Primary Graphite, Cocrystallized WB + C, and TernaryEutectic \VB W \,B• C, .
~/
Figure 40. W-B-C (25-70-5 At.%), Meltea and Rapidly X275
Cooled.
Primary WGBa a \IA.ix of Pseudobinary TeraBrEtB.iC Eute -ti.
*3''8
I- XI
Figure 42. W-B-C (18-08-'4 At.,'), Mvelted and Rapidly X 2170Cooled.
Some P'rimary Graprhi~te in an Alloy Located Closeto the Ternary Eutectic W2B 5 -t B4 C + C. Also Notethat the Ternary Eutlectic Contains Only Small AmountsOf Graphite.
B. ASSEIM13LY OF TIHE PHASE D.IAGRAMN,
The experimnental results gathered in the course of the invlesti-
gation have been combined to yield the phase- diagram of the system shown
in Figure 1. The diagram is supplemented by a flow diagrami of isothermal
binary and T. ernary reactions (Figure 2) and a projection of the liquidus
surface, shown in Figure 3. For the ccnveniecnce of use, and also to outline
more clearly the temperatu. dependence of the phase equilibria in the system,
a numiber of isothermal sections have been prepared and are shown in Figures
43 through 50.
39
IA
B4C(h)
WBE(n~r4) 15000C
0\0
Q
w~ B
+\
W1.a) WPC(.8 WC,y) -- ATOM;C % CARBON- C)
]Figutre 43. Isotherma•l Section of the W-B-C System
at 1500° C.
40
B ()L +K -L+X+ KL +8
L +877' -ei / B4C(X)
VV2 Fs'! "9, n) ÷J/ /
0\0 LI
S/B
/, / \ W\ r1)3)
W(a) W2C(13) WC(y)- ATOMIC % CARBON C
Figure 44. Isothermal Section of the W--..C System at20000 C.
Note 4-phase Plane (Class II Reaction)
L+ B4C T5 20000o WB, 4 + B4C
41
IL
LV÷
- \x
S/ ,"A\.• +s \
.7a +YPS ',\' ATOMI % CAR"ON
Fiur 45 Ist\ r a Seto of the "--CSs
,• ____ .'- • ..:..• --_ .-. . . . , , ..- :...
at 21 500 C.
N•ote 4-phase Plane (Class II Reaction'
'VB + W( :; T:5 g!SO WC,+ WzB
472
8
/i
L+X 84 C(X) 2320*C
L
~ L!-\\\\ -,\
W'-- L+a \s \
rN. " -.
/\W2B(C)
L+1
W(M, WalC(I3 WC(Y) - ATOMIC % CARBON - C(8)
Figure 46. Isothermal Section of the W-B-C Systemat 23 20 C,.
43
/ \/
SB 4 C!X 23500C
oe 'x ; \- "~1~ L
, -,
/ . "• •. \_ L ++8 0 \ "OW2 - B .)4~W~)' - . \% \ ,
LLS
/ V+-E \- L+/?+"
W2C'-3) WC;-f) -ATOMIC % CARBON - C(8)
Figure 47. Isothermal Section of the W-B-C Systemat 2350° C.
Note 4-phase Plane (Class 11 Reaction)
L +C T -tZ35 0 WB -WC
44
I1't ' •!
B
o 25000 C
\ \\
//\ ,
W2 B(g) "L++ -. L+8
/-L+u+E [c+ j
LL+/
i +a+i3 I z\/ L+ +
W(a) W2 C(P) WC(y) - ATOMIC % CARBON - C8)
Figure 48. Isothermal Section- of the W-B-C Systemat 25000 C.
45
B
• B •\ 1700"C
/\
00
00
;1'
I-..
L
L+++ --,.L+a , \ L +/ '- -~ \
W(:) W2C(.) a-WC•.( 1L) 'WC(y') ATOMIC % CARBON - C(S)
Figure 49. Isothermal Section of the W-B-C Systemat 27000C.
46
/ \
/ '.
/ .
/ 28000 C/
//\/ /' L
07 0
0\0
\\ \,\
A0.
W (a) -- ATOMIC % CARBON (C1
F'igure 50. Isothermal Section of the W-B-C System
at 2800° C.
47
V. DISCU SSION
The observed phase equilibria in the W-B-C system reflect the low
stability of the carbides in relation to the borides, since the monoboride and
W 2B 5 form etable equilibria with graphite. By comparison, in the boron-
carbon systems of the group IV and group V metals(15 '2 4 ), only the diborides
form stable equilibria w~th graphite, be."ides being in equilibrium with the
monocarbides.
The small mutual solubilities between carbides and borides, which
is characteristic of all systems involving the refractory transition metals, is
indicative of large stability differences between the respective crystal struc-
tures. As an example, the free energies of transformation of the stable modi-
ficatioi. of W2 B into the lattice type of W2C and that of WzC into the WzB type,
must be larger than 15 kcai/mole so as to account for the observed metal
exchanges; the transformation energies for WB and WC are of the same oider
of magnitude.
Concerning the technical application of W-B-C alloys, several phase
diagram features and observations made during the phase diagram study con-
cerning alloy properties are of interest.
B4C + WZBs eutectic alloys show excellent castabiliiy and have sur-
prisingly good mechanical impact resistance. Oxidation tests carried out
at 10000C showed good resistance to air attack, probably as a result of a
highly viscous and tightly adhering film of boric acid at the surface of the
specimens. Other alloys which could be of ,nterest are the pseudobinary
eutectics of the WB and WZJB 5 phases with grapihite; the presence of the finely
divided graphite in the eutectic provides a quasi-homogeneous structure with
cinsiderably lower bulk modulus, and thus better" thermal shock sensitivity, than
the pure binary phases. The applicability of other ternary W-B-C alloys,
48
notably the ,seudobinary anJ ternary eutectics involving the WaC, W2B, WB.
and WC phases, appears unlikely a!2 a result of their extreme brittleness.
49
REFERENCES
I. U.S. Air Force Contract AF 33(6i5)-1249 (1964 to 1968), and U. S.Air Force Contract AF 33(615) -67-C-1513 (1967-197f). Report SeriesAFML-TR-65-Z and AFML-69-117, Air Force Materials Laboratory,Wright-Patterson Air Force Base, Ohio.
2. R. T. Doloff and R. V. Sara: WADD TR 60-143, Part Ii, Wright AirDevelopment Division, Wright-Pattr.rson Air Force Base Ohio (1961).
3. R. V. Sara: J.Amer. Ceram.Soc., 48 (1965), 251.
4. E. K. Storms: The Refractory Carbides (Academic Press 1967).
5. E. Rudy, St. Windisch. and J. R. Hoffman. U.S. Air Force Tech.Rept. AFML-TR-65-2, Part 1, Vol. VI (Jan 1q66); AFML-TR-6"-2,Part V (june 1969), Air Force Materials Laboratory, Wright-PattersonAir Force Base, Ohio.
6. E. Rudy and J. R. Hoffman: Planseeber. Pulvermet. 15 (1967), 174.
7. L,. Rudy and St. Windisch: S.Amner.Cerarnic Soc., 50 (1967), 272.
8. L.N. Butorina and Z.G. Pinsker: Kristallografiya, 5 (i960), 585.
9. K. Yven, H. Nowotny, and F. Benesovsky: Monatsh. Chem., 99(1968), 726.
10. W.B. Pearson: Handbook of Lattice Spacings and Structure of Metalsand Alloys (Pergamon, 1958).
11. R. Kiessling: Acta. Chem. Scand. 1 (1947), 893.
12. E. Rudy and St. Windisch: U.S. Air Force Tech. Rept. AFML-TR-65-2,Part.I, Vol. III, Air Force Materials Laberatory, Wright-Patterson AirForce lFase, Ohio (July 1965).
13, B. Post and F. W. Glaser: J. Chem. Phys. 20 (1952), 1050.
14. P.A. Romans and M.P. King: Acta Cryst. 20 (1966), 313.
15. E. Rudy, F. Bene.ovsky, and L. Toth: Z. M.etallkde, 54 (1063), 345.
50
References (Cont'd)
6. Compare the co ilation of earlier data in R.P. Elliott: Consti:utiorn" Bi~ary4 Alo~s, First Supplement (McGraw-Hill, 1965).
17. H.K. Clark and J.L. Hoard: J.Amer.Chem.Soc., 65 (1943), 2115.
18. R.T. Doloff: U.S. Air Force Tech. Rept. WADD 60-143, Part I,Wright Air Development Division, Wright-Patterson Air Force Base,Ohio, (1960).
19. R. P. Elliott: U. S. AEC Contract AT (11-i)-I78, Final ReportARF-2200-12 (1961).
20. F. W. Glaser: J. Metals, 4 (195Z), 391.
21. L. Brewer and H. •araldsen: J. Electrochern.Soc., 102 (1953), 399.
z2. E. Rudy and G. Progulski: Planseeber.Pulvermet., 15 (1967), 13.U.S. Air Force Tech. Report, AFML-TR-65-2, Part. II, Vol. II, AirForce Materials Labo-ratory, Wright-lPatterson Air Force Base, Ohio,(April 1966).
51
Unclassified
DOCUMENT CONTROL DATA - R & D*.~* A. - ~ t.~ ..t .bnc .4 -'de'n be~tf~c W -u. -ncie ..n the oter&Z f.pofl 5. rinniflerd;
Z*..ACO'OA1 Sr.CUrnYAIT eCA,
Materials Research Laboratory UnclaesifiedAerojet-General Corporation M GROUPI Sacramento, California N.A.
Exzperimen~tal Phast_ Equililbria of Selected Bi~nary, Ternary, and Higher Order
Systems.
Part V.T h iagram %V.•-C4 or.C .. I- A-l t~ . ,.S (n .1 etpc*f -d O~CNS, ee dates)
Arril 1967 -May 1969
Rudy, E.
F 33 615-67-C-1543
Task No. 735001 7•r. .T. REPO 40o1) (,,, other crufse that may be a.saned
h AFML-TR-69-117_. Part V
Tbis document has been approved for public release and sale; its distribution
is unlimited.
,- 0
t• ' *•C . 'rQI. 0TC tO2 5PKO(•$RING MSLfTAPY ACTIVITY
Air Force Materials Laboratory (M.AMCGWeight -Patterson AFB, Ohio 45433
"The ternary alloy system W-B-C was investigated experimentally by means of
X-ray, melting point, DTA, and metallographic techniques on hot pressed and
hea- treated, as well as melted specimens, and a phase diagram from 1500'C
through the melting range established.
No ternary phases are formed in the system and the mutual solubilities between
carbide and boride phases are small. The solid state sections (<?000"C) are
characterized by two-phase equilibria existing between the phase pairs WzB+ WC,
WzB + WC, WC + WB, WB + C, WzB5- C, W 2 3 5 + 134C, and WB• + BIC. The two-
phase equilibrium W2 B + WC is replaced by an equilibrium WzC + WB above
2150oC.
Fifteen ttrnary isothermal reactions have been found. Five are associated with
pseudobinary euteccic eqdilibria, six with ternary eutec!ics, and the remaining
four with class H ternary four.,hase reaction isotherms.
//
DD 1.F 2ý$1 4 7 3 UnclassifiedSecu'ily Cla.:ssifict
., Un c•••* .I~~~~~Lk ... sLt-K• 0-••;.i • .. ... .
S.-...54 ~ A ~ - ' -,: • . ... .
Refractory Ca. rbides
Phase Eqailbria[ - --
I I
Pnclashsified
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