Improving the wear resistance of lightweight refractory Al0.5Ti2NbZrM(M = V/Cr/W) HEA coatings on Ti6Al4V through alloying-controlled microstructure

To improve the wear resistance of Ti6Al4V, lightweight refractory high-entropy alloy coatings were deposited on Ti6Al4V using laser-directed energy deposition. This work focuses on the Al0.5Ti2NbZrM(M = V/Cr/W) coatings, aiming to illuminate the role of V, Cr, and W alloying induced microstructural evolution in governing the wear mechanisms at different temperatures. The results show that V alloying resulted in a single-phase BCC, whereas Cr alloying led to a minor ZrCr2 phase and W addition induced multiple BCC precipitates. Strengthening from dislocations, precipitation, and grain refinement in the Cr and W addition coatings improved hardness and deformation resistance. As the microstructure evolves, the wear mechanism transitions from combined abrasive-oxidative to abrasive wear with fatigue spalling at 25 °C, while it evolves from mixed oxidation and abrasive to primarily oxidative wear at 600 °C. Notably, the wear rate of the W-alloyed coating achieved a wear rate as low as 3.68 × 10-5 mm3/Nm at 600 °C. The enhanced wear resistance at elevated temperature is mainly ascribed to multiphase BCC microstructure induced by W alloying that enhances load-bearing capacity and to the development of a dense glaze layer (ZrO2). Moreover, subsurface reinforcement by dispersed W-rich phases stabilizes the glaze layer and suppresses delamination and adhesive spallation.