Processing, Microstructures And Properties Of Al₃Ti Intermetallic Alloy

The titanium aluminide alloys are of interest due to their low density, high melting point,high specific strength, high elastic modulus and excellent oxidation resistance, corrosion resistance, etc. Compared with other homologous intermetallic alloys, such as Ti3Al and TiAl alloys,Al3Ti possesses the lowest density,～3.36 g/cm-3, highest Young’s modulus,～216GPa and highest oxidation resistance to high temperature. In recent years, there is a great interest in the new material called Ti/Al3Ti metallic-intermetallic laminate (MIL) composite, which is a very promising high temperature structure material in aerospace applications. To thoroughly understand the overall mechanical behavior of the MIL composites, it is essential to know the deformation and fracture mechanics behavior of each component in the composites. However,the published data of the mechanical behavior of the ductile metal reinforcement of Ti is abundant, the result of the matrix brittle phase of Al3Ti is less, it is therefore hard to find some basic mechanical properties of Al3Ti provided for the numerical simulation.The dense monothetic Al3Ti intermetallic alloy was synthesized successfully using Ti and Al foils through vacuum pressing reactive sintering process based on the preparation technology of the MIL composite. And the process parameters were optimized with a right thickness ratio of the original Ti and Al foils. Scanning electron microscopy (SEM), X-ray diffractometry (XRD),energy dispersive spectrometer (EDS) and thermal analysis were employed to characterize the microstructures, compositions and thermal behaviors of Al3Ti alloy. The results showed that Al3Ti is the only synthesized Ti-Al intermetallic compound.The quasi-static and dynamic compression tests were carried out on Instron machine and Split Hopkinson Pressure Bar (SHPB) experimental system, respectively. The results of compression tests demonstrated that the monothetic Al3Ti alloy has obvious effects of the strain rate sensitivity, and there is no any plastic deformation in the process of failure of Al3Ti alloy, the intergranular failure mode dominates fracture behavior, along with transgranular crack visible. It was found from the comparison between the performance of Al3Ti alloys prepared by different raw foils of TC4 and commercial pure Ti, that the compressive strength of Al3Ti alloy prepared by TC4 is higher than the Al3Ti alloy prepared by commercial pure Ti.The ultral-fine and super-pure powders of Al3Ti were successfully fabricated using the fragments of fractured samples after compression tests via mechanical ball-milling with different time periods. The XRD analysis results show that the size of the Al3Ti powders decreasing with increasing milling time, when the milling time incrased to a given time, the Al3Ti alloy will transform from crystalline to amorphous microstrauture. There is only a very weak peak in the main peak location of Al3Ti after 12 hours of milling.