激光沉积预混合的近α钛合金和Ti2AlNb合金粉末中成分偏析与层错诱导亚晶结构形成

Formation of Sub-grain Structure Induced by Composition Segregation and Stacking Faults in Laser-Deposited Premixed Near-α Titanium Alloy and Ti2AlNb Alloy Powders

摘要:

通过激光沉积在近α钛合金基板上制备了不同比例的预混合近α钛合金和Ti₂AlNb合金粉末，并对2种粉末的微观组织演变和结构特征进行了分析和讨论。结果表明，Ti₂AlNb含量在40%（质量分数，下同）以上的激光沉积预混合钛合金粉末的等轴B2晶粒内形成了许多河流状亚晶粒结构，而Ti₂AlNb含量在40%以下的粗柱状β晶粒内则呈现针状结构。值得注意的是，降低激光功率和扫描速度可以促进亚晶粒结构的形成。基于实验结果的分析可以推断出，这种亚晶粒结构的形成不仅与亚晶界成分微偏析导致的O相析出有关，还与激光沉积过程中内应力诱导的堆垛层错密不可分。

Abstract:

Near-α titanium alloy and Ti₂AlNb alloy powders premixed with different proportions were prepared on the near-α titanium alloy substrate by laser deposition technique, and the microstructure characteristics were analyzed and discussed. Results show that numerous river-like sub-grain structures are formed inside the equiaxed B2 grains of the laser-deposited premixed titanium alloy powders with the proportion of Ti₂AlNb above 40wt%, whereas the needle-like structure within coarse columnar β grains exist with the proportion of Ti₂AlNb below 40wt%. It is noteworthy that the decrease in laser power and scanning speed can accelerate the formation of sub-grain structures. Based on the analysis of experimental results, it can be inferred that the formation of sub-grain structure not only is related to the precipitation of O phase due to composition micro-segregation at sub-grain boundaries, but also is inseparable from the stacking faults caused by the internal stress during the laser deposition.