碳对高温钛合金组织稳定性的影响

Effect of carbon on microstructural stability of high-temperature titanium alloy

结合实验研究,分析了碳合金化对高温钛合金显微组织、高α+β相区、时效过程中α2和硅化物析出的影响机制及其碳化物的稳定性。α+β相区再结晶,碳化物主要在β转变组织中析出以及碳化物的百分数取决于初生α(αp)体积分数;β相区热处理,碳化物的析出阻碍β晶粒的长大。碳的加入延缓αp体积分数随温度的变化速度,扩大高温钛合金的高α+β相区;同时降低αp相Al的浓度,增加β转变组织中Al和Mo的浓度,导致αp相内α2颗粒直径逐渐减小,颗粒间距增大。β相与碳化物之间的包析反应是碳化物溶解的主要动力。

Microstructural changes with carbon additions, precipitation of ordered a： and silicide during aging treatment, and carbide stability are revealed. During recrystallization in the α ＋ β phase field, carbide particles preferentially form from the β grains of bimodal microstructure and its volume fraction is determined by that of primary α （αp）. During annealing in β phase field the refinement of β grain sizes is due to the carbide grain-boundary pinning effect. Carbon addition retards the change of αp volume fraction with temperature, and decreases the Al concentration of the αp and increases the partitioning of Al and Mo to the transformed β for bimodal microstructure. This makes the α2 particle size smaller and interparticle distance between the α2 precipitates in αp larger after long-term exposure. The peritectoid transformation between β phase and carbide is the main driving force for the dissolution of carbide.