Assessment of wear and tribological behavior of spark plasma sintered Ti.

Benga, Gabriel Constantin ; Gingu, Oana ; Ciupitu, Ion 等

1. INTRODUCTION

The interest in the tribological behavior of titanium alloys was fuelled up due to its wide applications in aerospace, medicine and chemical industry. Titanium known for high corrosion resistance and a very good specific strength proved also to be a feasible option for osseous surgery, implants due to its biocompatibility. However, Long &Rack pointed out the tendency of titanium to gall and seize in applications where relative sliding between different surfaces was conducted (Long & Rack, 2001; Lee et al., 2008). Extensive research work has been done (Kustas & Misra, 1992; Waterhouse & Iwabuchi, 1985; Molinari et al. 1997) especially focused on titanium's fretting behavior, galling and sliding wear behavior. Few additional studies have been performed in order to analyze the influence of elaboration technology of the titanium versus the tribological behavior and wear rate. Wear and corrosion resistance of biometallic materials are two very important properties that can make the difference in terms of implant surgery (Parks & Lakes, 1992). A comparison between stainless steel and Ti-6Al-4V alloys has been carried out (Choubey et al, 2004) and the results revealed that titanium alloys have a lower wear resistance than stainless steels. In this case it was considered that the main wear mechanism was the plastic deformation corroborated with mass transfer. Spark plasma sintering (SPS) has been developed for the fabrication of ceramics and metallic materials but recently is used also for the fabrication of Ti. This specific technique allows rapid due to the direct heating of the powder and dies using pulsed current electrification. The SPS technique has a specific feature that consists in heating the sample both from outside and inside and significantly increases mass transfer (Ahmad & Sueyoshi, 2009).

Therefore, the research work presented in this paper was mainly focused on the influence of the spark plasma sintering process parameters on the tribological behavior and wear rate of the titanium in dry sliding tests against 100Cr6 hardened steel balls.

2. MATERIALS AND EXPERIMENTAL PROCEDURE

The titanium samples were processed from titanium powder with 1OO[micro]m particles via spark plasma sintering technology at (1000-1100) [degrees]C with a dwell time of 10 and 20 min for each temperature. The four samples were pressed with a 7kN load and the heating rate employed was 10 [degrees]C /min.

The tribological behavior and the wear rate assessment has been performed on a TRB 01-0254 tribometer (CSM Instruments SA) with a linear reciprocating module, equipped with a data acquisition software, InstrumX, version 2.5A.

[FIGURE 1 OMITTED]

The coefficient of friction and the friction force were determined using ball-on-disc dry sliding tests. The balls were made of DIN 100Cr6 hardened steel, 60-64 HRc, Ra=3.2[micro]m and a 6 mm diameter. The titanium samples acted as static counterpiece discs. The friction parameters used were: normal load 2 N, sliding linear velocity = 1 cm/s, room temperature 23 [degrees]C, testing time =788 s which means approximately 5 m length for the distance elapsed. The wear rate was measured using a profilometer Surtronic 25, from Taylor Hobson Precision equipped with Talyprofile Silver software for data acquisition.

3. RESULTS AND DISCUSSIONS

The coefficient of friction COF for all the titanium samples as well as the friction force was determined and the results are presented in tabel 1. The variation of the coefficient of friction with the SPS parameters is presented in figure 1

A- sample obtained by SPS at T=1000 [degrees]C, and t=20 min

B- sample obtained by SPS at T=1000 [degrees]C, and t=10 min

C- sample obtained by SPS at T=1100 [degrees]C, and t=20 min

D- sample obtained by SPS at T=1100 [degrees]C, and t=10 min

From table 1 and figure 2 it can be appreciated that the temperature as well as the dwell time during the SPS technology does not have a significant influence on the COF and the friction force. In figure 3 is presented the profile of the wear track in cross-section determined as an area.

[FIGURE 2 OMITTED]

[FIGURE 3 OMITTED]

The same measurements have been performed for all four samples A, B, C and D.

In figure 3 is presented the profile of the wear track in crosssection determined as an area. The wear rate for all Ti samples is showed in figure 4.

[FIGURE 4 OMITTED]

According to figure 4 it is obvious that lowest wear rate has been attained when the D sample was tested, which can lead us to the conclusion that the most appropriate SPS parameters were T=1100 [degrees]C and dwell time t=10 min.

Figure 5 presents the microstructure of the wear track with for sample D with 50x magnifying. When comparing sample D with the lowest wear rate and sample B with the second lowest wear rate it can be concluded that that the temperature was the main factor that affected the wear rate because the dwell time was maintained constant.

[FIGURE 5 OMITTED]

The wear pattern shows the small regular wear grooves on the ball track but also some particles of ball material (dark spots) that seemed to adhere to the surface. The surface is rather flat comparing to other samples and this is confirmed by the low wear rate presented in figure 4.

4. CONCLUSIONS

1. The SPS parameters (temperature and dwell time) do not affect significantly the coefficient of friction and the friction force. The B sample presented the lowest coefficient of friction during the tribological tests..

2. The lowest wear rate was obtained for the D sample i.e. for SPS at T=1100 [degrees]C and a dwell time of 10 min which seemed to be most appropriate parameters for sintering if wear rate is concerned.

5. REFERENCES

Ahmad, N & Sueyoshi, H. (2009). Properties of Si3N4-TiN composites fabricated by spark plasma sintering by using a mixture of Si3N4 and Ti powders, Ceramics International, 36 (2010), pp. 491-496.

Choubey, A.; Basu, B & Balasubramaniam, R. (2004). Tribological behavior of Ti-based alloys in simulated body fluid solution at fretting contacts, Materials Science and Engineering A, 379 (2004), pp. 234-239

Kustas, F.M. & Misra, M.S. (1992). Friction and titanium alloys, in: ASM Handbook, Friction, lubrication and wear technology, 18, ASM International, PJ Blan (Ed), 1992, pp 778-784

Lee, C.; Sanders, A.; Tikekar, N.& Chandran, K.S. R. (2008). Tribology of titanium boride-coated titanium balls against alumina ceramic: wear, friction and micromechansims, Wear 265, (2008), 375-386

Long M. & Rack, H.J.(2001). Friction and surface behavior of selected titanium alloys during reciprocating sliding motion, Wear, 249, (2001), 157-167

Molinari, A.; Straffelini, T.B. & Bucci, T. (1997). Dry sliding wear mechanism of the Ti6Al4V alloy, Wear 208 (1997), pp. 105-112

Parks, J.B. & Lakes, R.S. (1992). Metallic implant materials Biomaterials-- An Introduction, Plenum Press, New York, pp. 185-222

Waterhouse, R.B. & Iwabuchi, A. (1985). The effect of ion implantation on the fretting wear of four titanium alloys at temperature up to 6000C, Proceedings of the International Conference on Wear Materials, ASME, New York, 1985, pp 471-484

Table 1. COF and friction force Ft for different SPS Ti samples

 A B C D

COF [mu] 0.515 0.493 0.524 0.566
Friction 0.94 0.92 0.95 0.84
force Ft [N]

A--sample obtained by SPS at T=1000[degrees]C, and t=20 min

B--sample obtained by SPS at T=1000[degrees]C, and t=10 min

C--sample obtained by SPS at T=1100[degrees]C, and t=20 min