Mechanical properties and dry-sliding tribological behavior of partially twinned Fe ₇₀Ni ₃₀ alloy

The mechanical properties and wear behavior of an Fe ₇₀Ni ₃₀ alloy with twinned martensite structure obtained by deep cryogenic treatment at -196°c (DCT) were evaluated in comparison with that of coarse-grained (CG) Fe ₇₀Ni ₃₀ alloy (single austenite phase). The results showed that after the introduction of martensite with nano-scale twins, the Vickers hardness of Fe ₇₀Ni ₃₀ increased from 145 to 248Hv. The friction coefficient of both samples was almost the same, and it decreased with increasing applied load and increased with increasing sliding speed. The XPS results indicated that oxide protecting film was formed on the worn surface, which may dominate the friction coefficient. The wear rate for both samples increased with increasing applied load and decreased slightly with increasing sliding speed. The wear resistance of DCT-Fe ₇₀Ni ₃₀ alloy was obviously enhanced. The wear mechanisms were investigated by SEM accordingly.