Understanding Friction and Wear Mechanisms of High-Purity Titanium against Steel in Liquid Nitrogen Temperature

Abstract

Although the friction and wear properties of several metallic alloys in unlubricated conditions are widely investigated, such understanding for high-purity metals in cryogenic environment is rather limited. This article reports the tribological properties of high-purity a-titanium (a-Ti), prepared by cold rolling and recrystallization annealing, under liquid nitrogen (LN2) and room temperature (RT) environments against steel (bearing grade: SAE 52100) at varying loads (up to 15 N) and sliding speeds (0.6 to 4.19 m/s). It has been found that the steady-state coefficient of friction (COF) of titanium under LN2 environment (~0.27 to 0.33) is lower than that at RT COF (~0.33 to 0.58) irrespective of sliding speed. For cryogenic sliding conditions, the COF decreased steadily with sliding speed to a mean value of about 0.28 and no appreciable variation in COF is noticed for sliding speed of more than 1.5 m/s. The wear rate under both environment conditions was of the order of 10 -3 mm 3 N -1 m -1 irrespective of variation in operating parameters, but the RT wear rate was found to be higher compared to the LN2 case. Overall, the experimental results demonstrate improved tribological properties of high-purity titanium at LN2 temperature compared to the RT. Flow localization at tribological interfaces because of the large strain rate and subsequent damage accumulation at the titanium test piece are some of the attributes of the wear of Ti at LN2 temperature. In addition, the galling of titanium was also observed to occur under large contact stress and sliding speed conditions.

Dry Sliding Wear Behaviour of Titanium (Grade 5) Alloy by Using Response Surface Methodology

“…They found that by increasing the sliding speed, a transition from oxidative wear to delamination occurs with a corresponding minimum in the wear rate. Basu et al [19] found that friction and wear of high purity titanium decreased when sliding against steel in liquid nitrogen. In general, wear volume of titanium alloy for both dry and cryogenic conditions increases with increase in sliding speed, applied load, or sliding distance and this increase is more pronounced at higher levels of the variables.…”

Tribological properties of titanium-based alloys

“…The above mechanism is supported by the fact that the coefficient of friction of CP Ti becomes lower and more stable when tested at liquid nitrogen temperature than at room temperature (Fig. 3.7) (Basu et al, 2009). The flash temperature at the tribocontact is much higher when tested in air than in liquid nitrogen.…”

“…Comparison of frictional behaviour of a-Ti/steel tribocouple between LN2 and RT environments at a sliding speed of 0.89 ms -1 under 10 N load (Basu et al, 2009). to keep the surfaces completely apart. Consequently, direct contact between titanium asperities and the counterfaces will occur, leading to boundary lubrication.…”

Overview: Cryogenic Wear Properties of Materials

“…12,13 High -purity Ti was thermomechanically processed and recrystallized to produce samples with grain size of 9, 17, and 37 μ m. These titanium samples were slid against a bearing -steel counterbody at 10 -N load and at varying sliding speeds of 0.67, 1.11, and 4.19 m/s in an LN2 environment. The results of sliding wear experiments conducted on high -purity titanium (Ti) against bearing steel in a LN2 (boiling point, 77 K) environment are recently reported.…”