Research On Aluminizing Kinetics And Microstructure Of Foil-packed Aluminized Ti-Al-V Alloy Sheet

Titanium alloy has advantages such as light weight, low density, high specific strength and so on. It's widely used in aerospace, aviation and many other industries. However, the oxidation and oxygen embrittlement of titanium alloy are major factors which influenced the thermal stability at high temperature. Aluminized is one of the most effective methods to improve the performance of titanium alloy at high temperature. The microstructure of the foil-pack aluminized Ti-Al-V alloys sheet fabricated by electron beam physical vapor deposition (EB-PVD) technology and treated at different temperatures were studied in this thesis. The cross-section morphology and elements distribution of the aluminized coatings were characterized by optical microscopy(OM)and scan electron microscopy(SEM) equipped with energy disperse spectroscopy(EDS). X-ray diffraction(XRD)was used to characterize the phase composition of aluminized coatings and diffusion layers composition of the alloy sheet.The results showed that, the main phase of as-deposited alloy fabricated by EB-PVD wasα-Ti solid solution. The grains of Ti-Al-V alloys sheet was compact, homogenous and fine, without any cracks and macroscopic defects. When the alloy sheet was aluminized at 700℃, 800℃, 900℃for short time, the main phase of the aluminized coating was Al₃Ti. The interface between the coating and substrate was smooth and clear without transition layer. As the aluminized time increased, a little interdiffusion occurred between the coating and the substrate, the diffusion layer was clear but not smooth. Wherein the main phase of the aluminized coating was still Al₃Ti, besides there was a small amount of Al2Ti and TiAl phase. Theoretical proving showed that, the thickness of the aluminized coatings increased as the temperature, and aluminized activation energy was 40kJ/mol. The nano-hardness of coatings was about 9GPa, elastic modulus was about 200GPa, moreover, the hardness and modulus did not change within the depth of 50⁵00nm.After heat treatment at 1000℃and 1100℃, interdiffusion occurred between the coating and substrate, transition layer appeared and the interface between layers was clear. After heat treatment for 4h at 1000℃, the thickness of transition layer reduced, the contrast between layers decreased, and the interfaces gradually became uneven. After heat treatment for 4h at 1100℃, the Ti enrichment of diffusion zone between coating and substrate happened. The main phase is Al₃Ti after heat treatment for 0.5h at 1000℃, and Al₃Ti layer became thinner and finally disappeared as the increase of heat treat time. The main phase of coating was Al2Ti and TiAl after heat treatment at 1100℃.