Abrasive_wear_behaviour_of_laser_sintered_iron___SiC_composites_Wear.pdf

This article appeared in a journal published by Elsevier. The attachedcopy is furnished to the author for internal non-commercial researchand education use, including for instruction at the authors institution

and sharing with colleagues.

Other uses, including reproduction and distribution, or selling orlicensing copies, or posting to personal, institutional or third party

websites are prohibited.

In most cases authors are permitted to post their version of thearticle (e.g. in Word or Tex form) to their personal website orinstitutional repository. Authors requiring further informationregarding Elseviers archiving and manuscript policies are

encouraged to visit:

http://www.elsevier.com/copyright

Author's personal copy

Wear 267 (2009) 17771783

Contents lists available at ScienceDirect

Wear

journa l homepage: www.e lsev ier .com/ locate /wear

Abrasive wear behaviour of laser sintered ironSiC composites

C.S. Ramesh a,, C.K. Srinivas b, B.H. Channabasappa c

a Mechanical Engineering, PES Institute of Technology, BSK III Stage, Bangalore 560 085, Indiab Central Manufacturing Technology Institute, Tumkur Road, Bangalore 560 022, Indiac PES Institute of Technology, BSK III Stage, Bangalore 560 085, India

a r t i c l e i n f o

Article history:Received 18 September 2008Received in revised form29 December 2008Accepted 31 December 2008Available online 24 January 2009

Keywords:Direct metal laser sinteringAbrasive wearMetal matrix compositeRapid prototyping

a b s t r a c t

Direct metal laser sintering (DMLS) is one of the popular rapid prototyping technologies for produc-ing metal prototypes and tooling of complex geometry in a short time. However, processing of metalmatrix composites (MMCs) by laser sintering is still in infant stage. Thermal cracks and de-bonding ofreinforcements are reported while processing MMCs by laser sintering process. There are reports onuse of metallic-coated ceramic reinforcements to overcome these problems. The present investigation isaimed at using nickel-coated SiC in developing iron composites by DMLS technique and to characterizeits abrasive wear behaviour.

Microstructure, microhardness, and abrasive wear tests have been carried out on both DMLS iron andits composites sintered at a laser scan speed of 100 mm/s. Abrasion wear tests have been carried out usinga pin-on-disc type machine. SiC abrasive papers of grit size 60, 80, and 150 having an average particlesize of 268, 192, and 93m, respectively, have been used. Load was varied between 5 and 25 N in stepsof 5, while the sliding distance and sliding velocity of 540 m and 2.5 m/s, respectively was adopted forall the tests. Optical, scanning electron micrograph and surface roughness observation of worn surfaceshave been undertaken.

An increase in microhardness and a decrease in density of the laser sintered ironSiC compositeswas observed with increase in SiC content. The abrasive wear resistance of composites increases withincreased content of SiC in iron matrix. For a given grit size of SiC abrasive paper, at all the loads studied,ironSiC composites exhibit excellent abrasive wear resistance. Increase in abrasive wear was observedwith the increase in abrasive particle size.

2009 Elsevier B.V. All rights reserved.

1. Introduction

Wear can be dened as the gradual removal of material fromsolid surfaces as a result of mechanical action. Abrasive wearaccounts for 50% of wear encountered in industrial situations [1].Abrasive wear occurs when hard rough surface slides against asoft surface thereby removing material in the form of elongatedchips. It is well accepted that abrasive wear rate of a surface isinversely proportional to its hardness [2]. Metal matrix compos-ites (MMCs) which are currently the most sought after materialshave excellent mechanical properties such as high strength, stiff-ness and hardness when compared with the matrix alloy. Theyhave a potential for increased wear resistance over the unreinforcedalloy. Das et al. have performed abrasive wear test on AlSi alloyand its composite with SiC as reinforcement. It is reported thatthe composite has better wear resistance when compared withAlSi alloy [3]. Gurcan et al. have conducted abrasive wear test

Corresponding author. Tel.: +91 80 26720886.E-mail address: csr [email protected] (C.S. Ramesh).

of AA6061 aluminium and its composite reinforced with SiC. It isreported that composite containing 60% SiC has a wear rate vetimes lower than the 20% SiC composite [4]. Sahin has performedabrasive wear test on Al-2014 and its composite having 10 wt.% SiC.It is reported that there was an improvement in the wear resistanceof composites compared with matrix alloy. Further an increase inapplied load has resulted in increase in wear rate [5]. Deuis et al.in their review paper on abrasive wear of aluminium compositeshave reported that increasing the volume fraction of reinforcingphase has resulted in improved wear resistance of composites. Fur-ther, wear increases with the increase in grit size up to a particularvalue beyond which the wear rate is independent of the abrasivegrit size [6]. Sahin et al. have constructed a abrasive wear modelfor wear behaviour of aluminium-based composite and have foundthat wear rate of the composite increased with increase in appliedload, abrasive size and decreased with sliding distance [7]. Tjonget al. have performed abrasive wear test on TiB2/Al4 wt.% cop-per composites produced by isostatic pressing. It is reported thatabrasive wear resistance of the composite increased with increas-ing TiB2 content [8]. Development of MMCs by rapid prototypingtechnique is still in the infant stage. Few researchers have done

0043-1648/$ see front matter 2009 Elsevier B.V. All rights reserved.doi:10.1016/j.wear.2008.12.026


1778 C.S. Ramesh et al. / Wear 267 (2009) 17771783

Table 1Grit size to particle size conversion.

Grit size of SiC abrasive paper

60 80 150

Average size of abrasiveparticle (m)

268 192 93

experiments on fabrication MMCs by laser sintering. Voucher etal. have performed experiments in producing AlSiC and TiSiCMMCs by laser sintering and is reported to have built few lay-ers [9]. However meagre information is available on the abrasive

wear characterisation metal matrix composites produced by rapidprototyping technology.

The aim of the present study is to investigate the abrasive wearbehaviour of iron and ironSiC (nickel coated) composites producedby DMLS process.

2. Experimental

Iron and SiC in particulate form was used to produce MMCs. Themorphology of iron powder and SiC (green in colour) was evalu-ated using scanning electron microscope and the grain size wasevaluated using particle size counter equipment. SiC was coated

Fig. 1. (ad) Scanning electron micrographs of iron and SiC powders.

Fig. 2. (a and b) Optical micrograph of iron and ironSiC composites sintered at laser speed of 100 mm/s.


C.S. Ramesh et al. / Wear 267 (2009) 17771783 1779

Fig. 3. Variation of density of iron and ironSiC composites with increase in wt.% ofSiC.

with nickel by electroless plating process as described elsewhere[10]. Nickel-coated SiC was mixed with iron powder in a conicalmixer and the mixing time was optimised to achieve a homoge-neous mix. Three different powder mixtures were prepared with 1,2, and 3 wt.% of coated SiC. Microstructure and abrasive wear spec-imens of iron and ironSiC composites were prepared using DMLSmachine. Laser power was maintained at 180W with a beam diame-ter of 0.4 mm. Sintering speed, hatch width, hatch spacing and layerthickness were maintained at 100 mm/s, 5 mm, 0.2 mm and 50m,respectively. Wear specimens were built to a size of diameter 12 mmand to height 28 mm. Microhardness tests were conducted on pol-ished surfaces of the sintered specimens at different locations alongthe sintered surface using a load of 0.25 N for test duration of 9 s.Density of sintered parts was evaluated using Archimedean princi-ple of weighing in air followed by in water. Pin-on-disc equipmentwas used to carry out the abrasive wear test. SiC abrasive papers ofgrit size 60, 80 and 150 were used as abrasive media. Table 1 showsthe average size of abrasive particles (m) for different grit sizes.Abrasive papers cut in a circular form were xed on to the disc of thepin-on-disc wear testing machine using adhesive. Sliding velocitywas maintained at 2.5 m/s while the load was varied from 5 to 25 Nin steps of 5. Tests were conducted for a travel distance of 540 m. Themass loss of the specimens during abrasive wear test was measuredusing electronic digital balance having an accuracy of 107 kg. Fur-ther, the volumetric wear rate was evaluated using the density ofthe sintered specimens. Optical and scanning electron micrographstudies of worn out tracks were carried out. The depth of groovesin wear tracks of the tested specimens were measured using Form

Fig. 5. Microhardness of laser sintered iron and ironSiC composites.

Talysurf series 2, surface roughness tester using a diamond tip ofdiameter 4m. A cut-off length and evaluation length of 0.8 and5 mm, respectively were adopted.

3. Results and discussions

3.1. Morphology of iron and SiC particles

The morphology of iron and SiC shown in Fig. 1 reveals that theiron particles are spherical in shape whereas SiC particles are irreg-ular and sharp edged. The average grain size of the iron powderwas 50m and that of SiC was 20m. Fig. 1(c) shows the scanningmicrograph of nickel-coated silicon carbide. Uniform coating ofnickel on SiC is observed in Fig. 1(c). Energy dispersive spectroscopystudies of the coated SiC particles shown in Fig. 1(d) conrms thepresence of nickel.

3.2. Microstructural studies

Optical micrographs of laser sintered iron and ironSiC com-posites taken along the sintered surface are shown in Fig. 2. Unmeltpowder or porous structures are observed in sintered iron as shownin Fig. 2(a). However, a uniform distribution of SiC particles isobserved in iron composites as shown in Fig. 2(b). The porousstructure in sintered iron can be attributed to the balling effect asexplained in Section 3.3. Addition of reinforcements reduces theballing effect in sintered composites leading to reduced porosity.

Fig. 4. (a and b) Macrophotographs of iron parts sintered at laser speed of 50 and 100 mm/s.



Fig. 6. (ad) Optical micrographs of wear tracks of iron and its composites tested at a load of 25 N, sliding distance 540 m and grit size 80.

Fig. 7. (ad) Scanning electron micrograph of wear tracks of iron and its composites tested at a load of 25 N, sliding distance 540 m and grit size 80.



Fig. 8. (ad) Surface roughness of wear tracks of iron and its composites tested at a load of 25 N, sliding distance 540 m and grit size 80.

3.3. Density

Fig. 3 shows the variation in density of laser sintered iron andironSiC composites sintered at 50 and 100 mm/s. It is observed that

Fig. 9. Energy dispersive spectroscopy of SiC particle embedded in ironSiC com-posites.

there is a decrease in density of ironSiC composites with increasein SiC reinforcement. As the density of SiC is less than that of iron, anincrease in its weight percentage in iron matrix reduces the densityof composite. Nickel phosphide coating on SiC having low-eutectictemperature has assisted in good binding of iron and SiC particlesthereby reducing the balling effect leading to improved density ofcomposites compared to iron. The lowest density obtained in ironcan be attributed to the fact that balling effect is predominant ata laser speed of 100 mm/s. Laser energy available for sintering isdirectly proportional to laser power and inversely proportional tothe laser scan speed [11]. At lower laser speed, higher energy isavailable for full melting thereby dense parts are produced.

Fig. 10. Effect of abrasive grit size on the wear behaviour of iron and ironSiC com-posites (sintered at 100 mm/s laser speed) tested at 25 N load.



Fig. 11. (ac) Volumetric wear rate of iron and ironSiC composites (sintered at 100 mm/s laser speed) tested under different loads and grit size.

Fig. 4(a) and (b) shows the macrophotos of iron specimens sin-tered at 50 and 100 mm/s. It is observed that the integrity of meltedpowder is more on parts sintered at 50 mm/s when compared withthose sintered at 100 mm/s. Similar observations are reported byRombouts while sintering alloyed steel powders [12]. However,thermal cracks are predominant at reduced laser speeds.

3.4. Microhardness

Variation of hardness of iron and ironSiC composites withincreased SiC content is shown Fig. 5. Sintered iron has an hardnessof 240 VHN where as a maximum hardness of 400 VHN is achievedfor composite with 3 wt.% of SiC. An increase in hardness of thecomposite is observed with increase in SiC content. Improvementof hardness can be attributed to high hardness of silicon carbide.Further, the thermal mismatch between iron and silicon carbidescan lead to generation of high density of dislocation at the inter-face of iron and SiC which in turn retards the plastic deformation.Similar results are achieved by other researchers while producingaluminium alloy composite by inltration process [13].

3.5. Abrasive wear

3.5.1. Effect of reinforcementIt is observed from Fig. 10 that the amount of reinforcement

in the matrix alloy has signicant inuence on the abrasive wearbehaviour for a given load and sliding distance. Increased content ofreinforcement in the matrix alloy enhances the abrasive wear resis-tance of all composites studied. This can be attributed to the fact

that the reinforcement being hard can combat the abrasion, thereby resulting in lower material removal. With increase in reinforce-ment there is an enhancement in the hardness of the compositesas shown in Fig. 5. Higher hardness of the composite leads to bet-ter abrasion resistance. Hutchings have reported that incorporationof hard reinforcements in the soft matrix alloy has beneted inreduced abrasive wear rates [14]. Optical and scanning electronmicrographs of the worn surfaces are shown in Figs. 6 and 7. Thesurface roughness of the worn out tracks shown in Fig. 8, clearlyindicate less extent of grooving in ironSiC composites comparedwith that of iron. The maximum peak-to-valley height (Rt) valuesare 26.6219 and 11.6063m for iron and iron3% SiC composites,respectively. Further, it is evident from Fig. 7(d), that there exists agood bonding between SiC and iron matrix leading to lesser extentof three body abrasion phenomena. Good bonding between SiC andiron matrix leads to lower abrasive wear loss of composites. Energydispersive spectroscopy of SiC particle embedded in iron matrixcomposites is shown in Fig. 9.

3.5.2. Effect of abrasive grit sizeThe effect of grit size of the abrasive on the wear of iron and

its composites is shown in the Fig. 10. It is observed that the vol-umetric wear rate increases with increase in abrasive particle sizefor all the materials studied. This can be attributed to the fact thatthe coarse SiC abrasive particles, which tend to dig in and ploughout the material results in huge material removal. This condition ofabrasive is stated as high-stress abrasion, where in the severity ofthe contact increases and the tendency to fracture of the abrasiveparticles and also the reinforcement increases [15]. Smaller the grit



size of abrasive paper, bigger will be the size of abrasive particlesand vice versa. Therefore, for a given size of abrasive paper, abra-sive particles are less densely populated in smaller grit size papercompared with larger grit size paper. Further, the contact load perabrasive particle will be higher in smaller grit size paper comparedto those particles present in larger grit size paper. Higher contactloads tends to increase the plastic deformation of the abrading sur-face (iron and ironSiC composites) and produces larger groovesin the abrading surface resulting in more abrasive wear loss. How-ever, for a given grit size and load, the penetration depth decreaseswith increase in content of SiC particles in the iron matrix. In caseof ne abrasive particles, little or no fracture of the reinforcementoccurs leading to higher abrasive resistance and is stated as low-stress abrasion [16,17]. Also it can be explained that the ne gradeof abrasives paper having a closer type of structure results in moreof scratching rather than ploughing out resulting in lower materialremoval. The abrasive wear loss due to medium grade emery papercan be considered as medium stress abrasion.

Further, the relative penetration depth which is the ratio of thepenetration of the abrasive grit to the particle mean free path (dis-tance between two reinforcing particles) has a bearing on the wearrate. The wear resistance increases with decrease in the penetrationratio below unity [18]. From the optical micrograph of the ironSiCcomposites shown in Fig. 2(b), the average distance between tworeinforcing particles can be taken as 30m and the groove depth ofthe wear tracks shown in Fig. 8 are 19.3629, 12.8379 and 11.6063mfor 1, 2 and 3 wt.% SiC reinforced iron composites. The relative pen-etration depth ratio is less than unity and decreases with increasein SiC content, resulting in lowering of material removal.

3.5.3. Effect of loadFig. 11 shows the effect of load and grit size on the volumetric

wear rate of iron and its composites. It is observed from the gurethat there is an increase in wear rate of iron and ironSiC compos-ites with increase in load for a given grit size. However the wearrate of iron is substantially more compared to that of its compos-ites at all loads and grit sizes. There is a steady increase in wear upto a load of 20 N and a steep increase in wear is observed at 25 Nfor all the materials studied. The increase in volumetric wear ratewith increased load of all the materials studied can be attributed tothe larger extent of plastic deformation at higher loads. Baker hasreported that the wear loss of MMCs increased with applied loadsince the extent of fracture of the reinforcement also increases asthe load increases [19]. It is also stated that not only the reinforce-ment are strongly bonded to the matrix, but also the fragments ofsilica abrasive particles which fragment at higher loads get embed-ded in to the ductile matrix. This phenomenon results in enhancedconcentration of hard particles in the surface and therefore therelative wear resistance increases. However, in the present investi-gation, the embedment of abrasive particles in to the iron matrixwas not observed.

4. Conclusion

IronSiC composites are successfully produced by laser sinter-ing process. An increase in microhardness and a decrease in density

of laser sintered ironSiC composites were observed with increasein SiC content. Microhardness of 240 and 400 VHN are achieved foriron and iron3 wt.% SiC composites, respectively. The wear rate foriron was 300% more when compared with iron3 wt.% SiC com-posites, tested at a load of 25 N with abrasive paper of grit size60. Volumetric wear rate of ironSiC composites decreases withincrease of SiC content. For a given grit size of SiC abrasive paper, atall the loads studied, ironSiC composites exhibits excellent abra-sive wear resistance. Increase in abrasive wear was observed withthe increase in abrasive particle size.

Acknowledgements

The authors wish to thank Shri B.R. Satyan, Director, CentralManufacturing Technology Institute, Bangalore, and Principal of PESInstitute of Technology, Bangalore for their support in carrying outthis research work.

References

[1] T.S. Eyre, Wear characteristics of metals, Tribology International 10 (1976)203212.

[2] E. Rabinowicz, Friction and Wear of Materials, John Wiley and Sons Inc., NewYork, 1964, p. 173.

[3] S. Das, D.P. Mondal, S. Sawla, N. Ramakrishnan, Synergic effect of reinforcementand heat treatment on two body abrasive wear of an AlSi alloy under varyingloads and abrasive sizes, Wear 264 (2008) 4759.

[4] A.B. Gurcan, T.N. Baker, Wear behaviour of AA6061 aluminium alloy and itscomposites, Wear 188 (1995) 185191.

[5] Y. Sahin, Tribological behaviour of metal matrix and its composite, Materialsand Design 28 (2007) 13481352.

[6] R.L. Deuis, C. Subramanian, J.M. Yellup, Abrasive wear of aluminiumcompositesa review, Wear 201 (1996) 132144.

[7] Y. Sahin, K. Ozdin, A model for the abrasive wear behaviour of aluminium basedcomposites, Materials and Design 29 (2008) 728733.

[8] S.C. Tjong, K.C. Lau, Properties and abrasive wear of TiB2/Al4% Cu compos-ites produced by hot isostatic pressing, Composites Science and Technology 59(1999) 20052013.

[9] S. Vaucher, D. Paraschivescu, C. Andre, O. Beffort, Selective laser sinteringof aluminiumSiC metal matrix composites, Materials Week 2002, 30.09.-02.10.2002, ICM-Munich (ISBN 3-88355-314-X).

[10] C.S. Ramesh, C.K. Srinivas, S.S. Avadani, B.H. Channabasappa, Electroless nickelplating on SiC particles for MMC applications, in: Proceedings of InternationalSymposium on Advanced Materials and Processing, Bagalkot, India, October2007, pp. 150154.

[11] H.J. Niu, T.H. Chang, Selective laser sintering of gas atomized M2 high speedsteel powder, Journal of Material Science 35 (2000) 3138.

[12] M. Rombouts, J.P. Kruth, L. Froyen, P. Mercelis, Fundamentals of selective lasermelting of alloyed steel powders, CIRP 55 (1) (2006) 187192.

[13] Y. Sahin, M. Acilar, Production and properties of SiCp-reinforced aluminiumalloy composites, Composites, Part A 34 (2003) 709718.

[14] I.M. Hutchings, Tribological properties of metal matrix composites, MaterialsScience and Technology 10 (1994) 513517.

[15] I.M. Hutching, A.G. Wang, Wear of aluminiumalumina metal matrix compos-ites by abrasion and erosion, in: D. Holland (Ed.), Conf. Series v111, Institute ofPhysics, London, 1990, pp. 91100.

[16] E. Candan, H. Ahlatei, H. Cimenoglu, Abrasive wear behaviour of AlSiC com-posites produced by pressure inltration technique, Wear 241 (2000) 3340.

[17] O.P. Modi, R.P. Yadav, B.K. Prasad, A.K. Jha, D.P. Mondal, Low stress abrasion ofcast zinc-aluminium alloyalumina particle composites under abrasive media,in: Proceedings of the Third International Conference on Advances in Compos-ites, ADCOMP-2000, Bangalore, 2000, pp. 560569.

[18] A. Wang, H.J. Rack, Abrasive wear of SiC particulate- and whisker-reinforced7091 aluminum matrix composites, Wear 146 (1991) 337.

[19] C. Baker, in: Proceedings of the BNF, 7th International Conference on The mate-rial revolution through the 90s: powders, metal matrix composites, magnetics,Wantage (1989), BNF metals paper 9.

Documents

Abrasive_wear_behaviour_of_laser_sintered_iron___SiC_composites_Wear.pdf