Effects of cryogenic treatment on the mechanical and dry-sliding tribological behaviour of an Fe ₇₅Ni ₂₅alloy

An Fe ₇₅Ni ₂₅alloy was subjected to shallow cryogenic treatment (SCT) at -80° C and deep cryogenic treatment (DCT) at -196° C to induce martensitic transformation to different degrees. The effects of cryogenic treatment on phase composition, microstructure, mechanical properties, and wear resistance of Fe ₇₅Ni ₂₅ alloys were investigated. The results showed that after SCT and DCT processes, the volume fraction of retained austenite approximately reduced from 42 per cent to about 30 per cent and 17 per cent, respectively, and the hardness increased from 174 to 276 and 336 HV accordingly. In the dry-sliding test, the cryogenic-treated samples exhibited better wear resistance compared with the conventional heat (annealing) treated samples, but the friction coefficient of the alloys was independent of cryogenic treatment. The improved hardness and wear resistance were likely to be attributed to the increase of martensite volume fraction.