TC18钛合金加热及固溶过程组织动态演变研究

Research on the Dynamic Microstructure Evolution of TC18 Titanium Alloy during Heating and Solid Solution Process

摘要: 某大尺寸国产TC18钛合金锻件在典型两阶段退火后存在锻件各部位组织不均匀、综合性能不达标等问题，给企业造成了巨大的经济和信誉损失。因此，弄清合金在加热及固溶过程组织动态演变规律，对制定合理工艺并改善合金组织和性能具有重要意义。本文采用高温共聚焦显微镜对TC18钛合金在加热及840℃高温固溶阶段显微组织的动态演变过程进行了原位分析。实验结果表明，TC18钛合金在连续加热过程中，晶界α相在加热到650℃时开始出现破碎，当加热到800℃时，晶界α相溶解基本完成；初生α相从650℃开始，首先以短程扩散的形式发生小规模的α→β相变；在720℃~750℃之间，初生α相的尺寸会有长大趋势；当温度超过750℃后，初生α相又开始逐渐转变成β相。在840℃保温时，当保温时间在30 min~60 min范围内时，显微组织基本不发生变化，组织稳定性很好。因此可以通过优化加热工艺将锻件各部位的保温时间均控制在此范围内，以消除因尺寸效应引起的锻件各部位在热处理后的组织及性能差异。

Abstract: A large-size domestic TC18 titanium alloy forging after typical two-stage annealing has problems such as uneven structure of each part of the forging and substandard comprehensive performance, which has caused huge economic and reputation losses to the enterprise. Therefore, understanding the alloy’s dynamic evolution during heating and solid solution is of great significance for formulating a reasonable process and improving the structure and properties of the alloy. In this paper, a high-temperature confocal microscope was used to analyze the dynamic evolution process of the microstructure of TC18 titanium alloy during the heating and solid solution process. The experimental results show that during the continuous heating process, the grain boundary α phase begins to break when heated to 650˚C. When heated to 800˚C, the dissolution of the grain boundary α phase is basically completed. The primary α-phase begins to undergo a phase transition at 650˚C, firstly, the α→β phase transition occurs in the form of short-range diffusion, and then the size of the primary α-phase will have a significant growth trend between 720˚C~750˚C; but when the temperature exceeds At 750˚C, the primary α phase begins to transform into β phase gradually. The microstructure stability of the TC18 alloy is excellent when the temperature is kept at 840˚C for 30 min to 60 min. Therefore, each part of the forging’s heat preservation time can be controlled within this range by optimizing the heating process to eliminate the difference in the structure and performance of each part of the forging after heat treatment caused by the size effect.