TA15钛合金焊接热影响区组织演变的数值模拟

Numerical simulation of β to α phase transformation in HAZ during welding of TA15 alloy

关键词:  焊接热影响区  连续冷却相变  TA15钛合金  元胞自动机

Key words:  heat affected zone  continuous cooling phase transformation  TA15  cellular automaton

摘要:

基于相变热力学和动力学经典理论,构建了TA15焊接热影响区β-α相变组织演变元胞自动机模型,并将其应用于不同焊接热影响区位置不同冷却速度的TA15组织演变模拟.该模型考虑了冷却速度对相变过冷度和固溶体溶解度、相变形核率以及相界面迁移率的影响,充分体现了焊接快速冷却过程的相变组织演变规律,计算结果表明,在临界冷却速度范围内,冷却速度越快,扩散型相变组织产物越细小,新相长大速度越快,但最终相变分数降低.综合考虑工艺、组织与力学性能的关系,通过模拟获得最佳焊接工艺应为中等热输入.

Abstract:

Cellular automaton model based on thermodynamic and evolution kinetic analysis was employed to simulate β to α phase transformation upon welding cooling in the heat affected zone (HAZ) of TA15 alloy. In this model,the effect of cooling rate on the phase transformation undercooling,solution solubility, nucleation rate as well as anisotropic interface moving mobility is considered,which is essential for the welding rapid cooling process. Both the nucleation and growth process were quantitatively characterized. The results show that the α/β interface moving velocity and final microstructure morphology depend both on the intrinsic mobility and aluminum atoms diffusion. α phase plates grow fastest at certain temperature among phase transformation temperature range but finer at lower temperature. Finer α phase plates result from shorter solute diffusion distance rather than larger nucleation rate. As the cooling rate increases, α phase plates grow faster due to larger undercooling but the final transformation percent decreases due to shorter transformation time. Considering the relationship between process,microstructure and mechanical properties,the simulation results indicates that medium heat input is the best welding parameter.