Determination of Phase Equilibria by Experiment of Calonlation in F-Al-X Ternary System

研究了Ti-Al-M三元系中β（bcc或B2）、α（hcp）和γ（L1_0）相的高温相平衡。在1473 K以上存在β（B2）+ α + γ三相共存区，并随温度升高向高Al、高M浓度方向移动。通过添加M的相平衡的变化与<tautomer>纯钛的α β同素异形转变温度相关，并且可以用M与Ti的晶格稳定性比LAMBDA来解释。例如，在三元Ti-Al-M系统中，β对α的LAMBDA定义如下：LAMBDA^&lt;beta*alpha&gt;_i= Δ β G^&lt;beta*alpha&gt;_/Δ β G^&lt;beta*alpha&gt;_。Δ Σ G^&lt;beta*alpha&gt;_是指纯M的bcc（beta）结构和hcp（alpha）结构之间的吉布斯自由能的差异，而Δ Σ G^&lt;beta*alpha&gt;_是指纯M的bcc（beta）结构和hcp（alpha）结构之间的吉布斯自由能的差异。 ...更多信息 纯钛每个元素的LAMBDA^&lt;beta*alpha&gt;_i值几乎等于10，并且至少比LAMBDA^&lt;alpha*gamma&gt;_i值大一个数量级。LAMBDA^&lt;beta*alpha&gt;_i对于每种元素具有大正值的原因是Δ β G^&lt;beta*alpha&gt;_的值比Δ β G^&lt;beta*alpha&gt;_的值小得多，因为所关注的温度距离纯Ti的β *alpha同素异形转变温度T^&lt;beta/alpha&gt;_（1155 K）仅300 K。当温度升高并且与T^&lt;beta/alpha&gt;_的温度差变大时，DELTA_G^&lt;beta*alpha&gt;_的值几乎保持不变，而DELTA_G^&lt;beta*alpha&gt;_的值增加，导致LAMBDA^&lt;beta*alpha&gt;_i的值变小。当温度低于<tautomer>二元系中α_2-Ti_3aL相的同成分温度T^B_（T^B_= 1452 K）时，α_2-Ti_3aL相也与其它三相一起成为稳定相。我们发现，当第三元素M稳定α_2相和α相时，高温下的β + α + γ三相共存区通过过渡包析反应（β + α α_2 + γ）转变为低温下的β + α_2 + γ三相共存区<tautomer>。少

Phase equilibria among the beta (bcc or B2), alpha (hcp) and gamma (L1_0) phases in Ti-Al-M ternary systems at elevated temperatures have been studied, where the M is beta stabilizing element for pure titanium. The beta (B2) +alpha+gamma three-phase coexisting region exists at temperatures above 1473 K,and it moves towrds a direction of high aluminum and high M concentrations with increasing temperature. The change in the phase equilibria by the addition M is associated with the alpha<tautomer>beta allotropic transformation temperature of pure titanium and can be thermodynamically interpreted in terms of the lattice stability ratios LAMBDA of M to Ti. The LAMBDA for beta against alpha in ternary Ti-Al-M systems, for example, is defined as follows : LAMBDA^<beta*alpha>_i=DELTAﾟG^<beta*alpha>_/DELTAﾟG^<beta*alpha>_. The DELTAﾟG^<beta*alpha>_ refers to the difference in Gibbs free energy between bcc (beta) structure and hcp (alpha) structure for pure M, and DELTAﾟG^<beta*alpha>_ that for … More pure titanium. The values of LAMBDA^<beta*alpha>_i for each element is nearly equal to 10 and at least one oeder of magnitude larger than those of LAMBDA^<alpha*gamma>_i. The reason the LAMBDA^<beta*alpha>_i has a large positive value for each element is that the value of DELTAﾟG^<beta*alpha>_ is fairly smaller than that of DELTAﾟG^<beta*alpha>_, since the temperature to be interest is only 300 K away from the beta*alpha allotropic transformation temperature T^<beta/alpha>_ (1155 K) of pure Ti. When the temperature raises and the difference in temperature from the T^<beta/alpha>_ becomes large, the value of DELTAﾟG^<beta*alpha>_ almost remains unchanged whereas that of DELTAﾟG^<beta*alpha>_ increases, leading to a smaller value of LAMBDA^<beta*alpha>_i. This is responsible for the three-phase coexisting region moving toward the direction of high aluminum and high M concentration as temperature increases.At the temperature below the alpha<tautomer>alpha_2 congruent temperature T^b_ in the binary system (T^b_ : 1452K), alpha_2-Ti_3aL phase appears as a stable phase as well, together with the other three phases. We identified that the beta+alpha+gamma three-phase coexisting region at higher temperatures changes to beta+alpha_2+gamma three-phase coexisting region at lower temperatures through a transition peritectoid reaction (beta+alpha<tautomer>alpha_2+gamma) when the thrid element M stablizes the alpha_2 phase against alpha phase. Less