Laser-cladded Al-Cr-Ti ternary alloy coatings on Ti-4Al-2V alloy: Specific microstructure and enhanced surface performance

Abstract

In this study, two Al-Cr-Ti ternary alloy coatings (denoted as AlCr and AlCrTi0.5) were fabricated on a Ti-4Al-2V alloy substrate by using a pulsed laser cladding method. Specific microstructure characteristics of those coatings were thoroughly revealed by using various characterization methods, with their hardnesses and wear rates measured by a Vickers indenter and a tribological tester. The results reveal that both AlCr and AlCrTi0.5 coatings are comprised of a body-centered cubic phase (β-Ti phase with average grain sizes of 12.6 ± 9.1 μm and 14.6 ± 10.0 μm, respectively), which is related to non-equilibrium solidification and sluggish diffusion of alloying elements during the laser processing. Heat-affected zones of both the laser-cladded specimens are mainly composed of submicron martensitic laths (α′-Ti). Average microhardness values of the AlCr and the AlCrTi0.5 coatings are measured to be 526 ± 37 HV and 510 ± 24 HV, respectively, approximately two times higher than the substrate (270 ± 8 HV). Their wear rates are almost the same, ~2.2 × 10−4 mm3 N−1 m−1, only ~1/3 of that of the substrate. Based on dedicated microstructure analyses, the greatly enhanced performance of the laser-cladded coatings could be attributed to joint strengthening from strong solid solution and lattice distortion, as well as Al/Cr-induced phase structure differences from the substrate.