材料期刊网

Phase transformations and mechanical properties of both Ti-29Nb-13Ta-4 center dot 6Zr and Ti-39Nb-13Ta-4 center dot 6Zr (wt-%) alloys were investigated. The microstructure of the 29Nb alloy is sensitive to solution and aging treatment. Ice water quenching from the solution treatment temperature resulted in (beta+alpha '') microstructure but air or furnace cooling led to a mixture of (beta+omega). The formation of the orthorhombic alpha '' martensite thus suppresses omega formation in the ice water quenched 29Nb alloy. Cooling rate from the solution treatment temperature also has a significant effect on the formation of alpha and omega phases during subsequent isothermal aging below the omega start temperature: slow cooling enhances omega but depresses alpha formation. This cooling rate dependence of aged microstructure was attributed to alpha '' martensite acting as precursor of the alpha phase, thus providing a low energy path to the precipitation of alpha at the expense of omega. Phase transformation in the 39Nb alloy is more sluggish than that in the 29Nb alloy, owing to the presence of the higher content of beta stabiliser Nb. For the 29Nb alloy, Young's modulus and mechanical properties are sensitive to the fraction of phases, and change significantly during aging, in contrast with the 39Nb alloy.