Experimental investigation on the properties and microstructure of hot isostatic pressed TA15 titanium alloy with hot-dip aluminum coating

To enhance the surface properties of titanium alloys and meet the design requirements for high efficiency and stability, this study employs hot isostatic pressing (HIP) technology to post-process the hot-dip aluminum coating on titanium alloy surfaces. The research investigates the impact of HIP on the microstructure and performance of the hot-dip aluminum coating. Initially, a hot-dip aluminum coating was prepared on the TA15 titanium alloy surface, and the causes of defects were analyzed. Subsequently, the coating underwent post-processing, involving remelting and repair under high temperature and pressure conditions. Microhardness tests were conducted on the interface area near the coating under various processing conditions, and the morphology, microstructure, and elemental distribution of the coating were analyzed. The mechanism by which HIP eliminates defects in the hot-dip aluminum coating and enhances its performance was also explored. Experimental results indicate that samples without post-processing exhibit a microstructure characterized by through-going cracks, a loose transition layer with poor density and porosity, as well as numerous shrinkage pores and cavities. After HIP treatment at 600 °C, the outer coating and transition layer become more porous, with increased defect formation, primarily in the form of pores and cracks. Some portions of the transition layer and original bonding layer transform into a thicker bonding layer. Following HIP treatment at 800 °C, cracks and pores are significantly reduced, the atomic ratio of Ti to Al in the bonding layer approaches 1.17, forming a more stable intermetallic compound, along with the emergence of a new phase, AlV₃. Defects such as pores and cavities are repaired, leading to improved surface hardness across all regions of the coating. Consequently, the microstructure and performance of the titanium alloy surface hot-dip aluminum coating are effectively enhanced.