Influence of Scanning Speed on the Microstructure and Performance of a TiAl Coating Formed by Selective Laser Melting on a Titanium Alloy Surface

Abstract In order to improve the surface performance of aviation titanium alloy and enhance the safety level and reliability of the overall structure during the service phase, selective laser melting (SLM) technology was used to prepare TiAl coatings on the surface of TC4 titanium alloy. The influence of laser scanning speed on the coating performance was systematically investigated. The microstructure, element distribution, phase composition, and microhardness of the coatings at different scanning speeds were characterized by scanning electron microscopy (SEM), X-ray diffraction (XRD), and energy-dispersive X-ray spectroscopy (EDS). The results show that when the scanning speed is 1000 or 1100 mm/s, multiple penetrating longitudinal and transverse cracks are formed at the interface between the coating and the substrate; at 1200 mm/s, the coating and substrate interface is flat and crack-free, with a stable Ti/Al mass percentage of 1:12.9, and the Sc element is fully dissolved to form an Al3Sc strengthening phase, with Ti–Al phases mainly composed of Ti3Al and Ti2Al, showing uniform element distribution, stable phase composition, and a high-quality structure with a maximum hardness of 565.8 HV0.2. When the scanning speed is increased to 1300 mm/s, the number of cracks is reduced compared with 1000 and 1100 mm/s, mostly short longitudinal cracks, with the appearance of delamination on the outer surface of the coating and poor flatness. The control law of scanning speed on the process, structure, and performance of TiAl coatings formed by SLM is clarified, providing a theoretical basis and practical guidance for the preparation of high-performance TiAl coatings using SLM technology.