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

本文研究了Ti-Al-M三元体系中β （bcc或B2）、α (hcp)和γ (L1_0)相在高温下的相平衡，其中M是纯钛的β稳定元素。在1473 K以上存在β (B2) + α + γ三相共存区，并随着温度的升高向高铝高M方向发展。添加M对相平衡的改变与纯钛的α <互变异构体> β同素异形体转变温度有关，并且可以用M与Ti的晶格稳定比LAMBDA进行热力学解释。例如，三元Ti-Al-M体系中β对α的λ定义如下：λ ^< β * α >_i=DELTA G^< β * α >_/DELTA G^< β * α >_。δ G^< β * α >_表示纯M的bcc （β）结构和hcp （α）结构的吉布斯自由能差，δ G^< β * α >_表示纯钛的δ G^< β * α >_表示纯钛的吉布斯自由能差。对于每个元素，LAMBDA^<beta*alpha bbb_i的值几乎等于10，并且至少比LAMBDA^<alpha*gamma bbb_i的值大一个数量级。λ ^< β * α >_i对各元素具有较大的正值的原因是δ G^< β * α >_的值比δ G^< β * α >_的值要小得多，因为所研究的温度距离纯Ti的β * α同素异向转变温度T^< β / α >_ （1155 K）仅300 K。当温度升高，与T^< β / α >_的温差变大时，δ G^< β * α >_的值基本保持不变，而δ G^< β * α >_的值增大，导致δ G^< β * α >_i的值变小。这是随着温度的升高，三相共存区向高铝、高M浓度方向发展的原因。在二元体系中低于α <互变异构体> α _2同温T^b_ （T^b_: 1452K）的温度下，α _2- ti_3al相也与其他三个相一起作为稳定相出现。我们发现，当第三元素M稳定α - 2相时，高温下的β + α + γ三相共存区通过过渡周反应（β + α <互变异构体> α - 2+ γ）转变为低温下的β + α - 2+ γ三相共存区。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