Mechanical Properties of Harmonic Structured Composite with Pure Titanium and Ti-48 at%Al Alloy by MM/SPS Process

Ti-Al alloy demonstrates high strength in high-temperature environments. Thus, the Ti-Al alloys are expected in an application as high temperature materials. However, the Ti-Al alloys demonstrate low strength and limited ductility at room temperature. Harmonic-structured materials with a network fine grain structure and a dispersed coarse grain structure show high strength and sufficient ductility at room temperature. In addition, a composite of different materials is also effective in improving both strength and ductility. Therefore, the harmonic-structured composite with pure titanium (Ti) and Ti-48at%Al alloy (Ti-48Al) were fabricated by the combination of the mechanical milling (MM) and the spark plasma sintering (SPS) process. The harmonic-structured composite has a fine grained network Ti-Al alloy and a dispersed coarse grain Ti region. The XRD result reveals that the harmonic-structured composite composes of Ti, TiAl and Ti3Al phases. The harmonic-structured composite demonstrates high strength and sufficient ductility compared with the conventional compact consisting of only Ti-48Al. Advanced ductility of the harmonic-structured composite is attributed to an obstruction of the crack propagation by the dispersed coarse grain region. After heat treatment of the Ti/Ti-48Al harmonic-structured composite, its hardness decreased to much lesser than that of the pure Ti compact.