Tribological behavior of NiTi alloy processed under different cooling conditions

Abstract

Structural materials are subjected to severe forms of material degradation for a prolonged life period. The most common material degradation is wear, erosion, and corrosion which severely impairs the service life of the components. State-of-art-of materials are of paramount importance to mitigate these forms of degradation phenomenon. NiTi alloy exhibits outstanding properties in terms of superelasticity, high fatigue strength, and exceptional corrosion resistance. In this work, the tribological behavior of NiTi alloy synthesized using arc melter (TIG) under different cooling conditions (ambient and water quenching) was studied via cavitation erosion, sliding wear, slurry erosion-corrosion and electrochemical corrosion. The microstructural study disclosed the formation of dendritic structures for both the samples. Hardness observed for the ambient cooled sample was around 980 HV which is 1.3 times higher than the quenched NiTi alloy. The difference in the hardness was attributed to the presence of pores for the latter. Both the NiTi alloy samples showed significant improvement in the degradation behavior compared to SS316L under pure erosion and erosion-corrosion conditions. Despite the lower hardness obtained for the quenched NiTi alloy, almost similar degradation resistance in terms of cavitation erosion and dry sliding wear was observed for both the alloyed samples. This is explained based on the work hardening ability behavior of the NiTi alloy. Slurry and sliding wear performed under 3.5% NaCl solution portrayed greater results for quenched alloy which is attributed to its higher corrosion and passivation resistance compared to the ambient NiTi alloy and SS316L. In conclusion, the microstructural, mechanical and tribological behavioral study of NiTi alloy indicated its dominance over SS316L in dry as well as wet conditions and hereby, emphasizing its importance as an alternative material for marine applications in hydrodynamic environment.