Effect of W and B on the Thermo- Physical Properties of Ti-42Al-5Mn Alloys

The thermal conductivity and expansion properties of materials are important factors affecting their application. The effects of W, B addition on the thermo- physical properties such as thermal diffusion rate, thermal conductivity and thermal expansion of Ti-42Al-5Mn alloy (at%, the same below) with low cost and good hotworkability were systematically studied. The results show that with the increase of W content to 1.0at%, the thermal diffusivity of the alloy decreases slightly. On the contrary, after the B content increases to 0.3at%, that of the alloy increases slightly. The promotion of beta(o) phase in microstructure by W addition is the main reason for decreasing the thermal conductivity of the alloy. It is observed that these phases in beta-solidifying gamma-TiAl alloys are followed by gamma, alpha(2), and beta(o) in deceasing order of thermal conductivity. On the other hand, B improving the thermal conductivity of the alloy might be related to the B-containing precipitates in the alloy. W addition (0.5at%-1.0at%) has little effect on the average linear expansion coefficient of Ti-42Al-5Mn alloy. In the range of 100-300., with W content increasing to 1.0at%, the average linear expansion coefficient of the alloy decreases slightly. On the contrary, the influence decreases gradually at higher temperature. The thermal expansion coefficient of TiAl alloy is equivalent to that of cast iron, and lower than that of steel, nickel base superalloy and other materials. It would have certain application value in components requiring very low thermal expansion coefficient such as piston.