应用X射线衍射测定了过饱和α2单相的Ti—45％Al合金在950℃等温分解过程中，初生片层形成时的γ相转变分数及α2和γ相晶格参数的变化.结果表明，初生片层中α2相是亚稳相，其成分可以由自由能成分曲线的亚稳态α2相与γ相自由能成分曲线公切线的切点确定，该成分的确定对定量计算合金自由能及发生不连续粗化的转变驱动力有十分重要的作用;等温分解过程中原α晶粒内部将产生相变应力，在垂直于初生片层的方向上可以产生约50MPa的压应力,该应力将对合金的组织形态有显著的影响
During isothermal decomposition of the supersaturated α2 phase in Ti-45%Al alloy at 950℃, the volume fractions of the decomposed γ phase and the lattice parameters of both α2 and γ phases have been investigated by X-ray diffraction. The results show that α2 phase in the primary lamellar microstructure (PLMS) is a metastable phase, and its composition should be identified by the tangency point on the common tangent of metastable α2 and γ phase free-energy curves. This composition is very important in calculation of free energy of the alloy and the driving force of discontinuous coarsening (DC). There exists transformation stress inside the original α grains at the direction perpendicular to PLMS which is a compress stress of about 50 MPa and will greatly affect the microstructure of the alloy.
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