Stepwise Laser Cladding of TiNbZr and TiTaZr Medium-Entropy Alloys on Pure Ti Substrate

This work aimed to fabricate two varieties of near-equiatomic TiNbZr and TiTaZr medium-entropy alloy (MEA) claddings on pure Ti as protective layers by stepwise laser cladding. Their stratified component distribution, microstructural characteristics, and phase constitutions were analyzed, with their hardness and wear resistance were compared with that of pristine Ti. It was found that a single body-centered-cubic solid-solution phase in both MEA claddings were realized on the hexagonal closed-packed pure Ti substrates. The subgrain structures in the TiNbZr cladding were cellular grains, while the ones in the TiTaZr cladding were much denser dendrite arms, which led to increased residual stress. The results showed that the hardness of the TiNbZr and TiTaZr claddings were 450 ± 30 HV0.2 and 513 ± 27 HV0.2, respectively, 2.6 times and 3 times that of the pure Ti (170 ± 11 HV0.2). Also, the consequent wear rates decreased from 2.08 × 10−4 mm3·N−1·m−1 (pure Ti) to 0.49 × 10−4 mm3·N−1·m−1 (TiNbZr) and 0.32 × 10−4 mm3·N−1·m−1 (TiTaZr). Such high hardness and enhanced wear resistance are attributed to the solid-solution strengthening of the body-centered-cubic phase and the residual stress in the claddings. The realization of hard MEA layers by stepwise laser cladding offers a flexible and effective way for protecting pure Ti.