On the tribo-cryogenic characteristics of titanium alloys

Friction and wear behaviours of Ti-6Al-4V (Ti64) and Ti-5Al-4V-0.6Mo-0.4Fe (Ti54) alloys sliding against a tungsten carbide wheel under dry and cryogenic sliding conditions were investigated at different sliding speeds, loads, and distances. Mathematical models utilizing response surface methodology were developed as a function of sliding conditions for predicting the friction and wear characteristics of both titanium alloys. The controlling variables were determined by utilizing design of experiments. The developed models are able to predict the measured friction coefficient and wear volume with reasonable degree of accuracy for both titanium alloys within the ranges of studied parameters. Results showed no substantial difference between tribo-characteristics of both titanium alloys. Under cryogenic sliding condition, tribo-characteristics were lower than those obtained under dry sliding, except at higher load, cryogenic sliding surprisingly gave higher friction coefficient. Analyses of worn surfaces and wear debris by using scanning electron microscopy and energy-dispersive spectroscopy revealed that the role of cryogenic conditions at the sliding interface was partially attributed to changing material properties and possible hydrodynamic effect. Under dry sliding, the main wear modes were adhesion and delamination, while under cryogenic sliding, in addition to delamination, abrasion wear mode dominated.