Synthesis,Microstructure And Properties Of Near-Network Ti₅Si₃/TiAl Composites

Titanium Aluminum is considered as one of the most promising high temperature material, as it has excellent specific stiffness, specific strength, specific elastic modulus. Introducing second phase into TiAl will enhance its strength, toughness and anti-oxidation to enlarge its application. Traditionally, second phase should be homogeneous in composite, which is impossible to get the ideal effect. This research intend to get better property by using near-network TisSi3to strengthen TiAl.Two kinds of composite with different second phase volume fraction are synthesized by pressure infiltration and hot pressed sintering. Microstructures are studied by OM, SEM and TEM, properties like density, hardness, compression and tensile test at high temperature are studied.Ti-Al complex, in which Ti is equally distributed in Al-Si alloy, is prepared by pressure infiltration. By studying the effect of infiltration temperature on Ti-Al complex’s microstructure, we find that there is a optimum temperature. If temperature is too low, the alloy liquid can’t fill in the void between Ti particles, on the other way, high temperature will enhance the infiltration pressure, make the Ti-Al complex heterogeneous and pored.600℃is optimum for Al-12Si alloy, while630℃is optimum for A1-6Si. Reaction route in pressure infiltration is Ti/Al-Si->Ti/Ti(Al,Si)3/Al-Siâ†'Ti/Ti7Al5Si12/Al-Siâ†'Ti/Ti(Al,Si)3/Al-Si.After hot pressed sintering, Ti-Al complex turns into near-network Ti5Si3/TiAl composite. Composite prepared by1200℃720MPa/2h one-step sintering has shortages like heterogeneity and porous.800℃720MPa/1h+1200℃/45MPa/2h two-step sintering makes composite compact, but failed in component. The optimum is630℃/2h+1250℃/70MPa/2h two-step sintering.The microstructure of near-network TisSi3/TiAl composite is that massive TisSi3particles make up near net-work and’shell’in each net-work, while small TisSi3particles distribute heterogeneously in the material, which is the result of Si being pushed. Silicon’s effect on the microstructure is also studied, reducing the Si, net-work and’shell’becomes rare. The near-network TisSi3/TiAl composite, whose matrix is dual phase, has good deformation ability. The surface of sample after compression test is smooth and crackless. After heat treatment, composite’s microstructure is DP, which performs high strength and good plasticity in tensile test, σ=594.4MPa at700℃, δ=40.88%at850℃.