Research On Microstructure Of Titanium Alloy Prepared By EB-PVD And Aluminization

The microstructure of Ti-based alloy sheet prepared by Electron Beam Physical Vapour Deposition (EB-PVD) and Aluminizated by Pack were studied by X-ray Diffraction (XRD), Optics Microscope (OM), Scanning Electron Microscope (SEM), and so on.It can be seen from the result that the phase structure of the Ti-based alloy sheet of original state was AlTi₃-based solid solution. The diffraction peaks were widen and asymmetrical. The structure of the original state of the Ti-based alloy was compact, uniform and no precipitation. The grains were refined. And the microstruture of the alloy was nonequilibrium state.The phases of the alloy sheet were AITi₃ and Al₃Ti when the aluminization was fulfilled at 600℃and 620℃. The interface between different phases was smooth, and the structure was still compact. However the phase of the alloy sheet was Al₃Ti when the aluminization was fulfilled at 700℃, the Al element concentrated in some micro-area and the structure was also compact, constituent and homogeneous.The structure like laminations was discovered from the surface layer to the inter layer of the alloy sheet when the homogenization was prepared at a low temperature (750℃) under the condition of vacuum. The thickness of every layer was different and no more than 10μm commonly. The contents of Ti element and Al element in different layers were different, the interfaces between different layers were clear and smooth. The smooth interface began to become blurry and closed to the center gradually with the time extended. The structures of several layers were discovered from the surface to the center of the alloy sheet when the homogenization was fulfilled at a high temperature (850℃). The interface of different layers was not smooth, and the thickness of the layers exceeded 10μm commonly. The unsmoothness of the interface aggravated and the desquamation appeared near the interface with the time extended. We think it was the difference of the coefficient of thermal expansion of the different phases at a high temperature that led to the desquamation. The process of aluminum's transportion from powder to the surface of the Ti-based alloy was studied and an equation that evaluates the kinetic parameters of Ti-based alloy was established according to the principles of thermo-dynamics and diffusion. The predicted results were in agreement with experimental data.