(1. 上海交通大学 金属基复合材料国家重点实验室，上海 200040；
2. ARC Centre of Excellence for Design in Light Metals, Monash University, Melbourne, 3168, Australia)
摘 要: 在金属直接激光快速成形过程中，冷却速率是决定相应材料熔融后显微组织状态的关键之一。通过合理控制基板厚度可改变加热时间和冷却时间，从而影响冷却速率以改变凝固后的显微组织。分别采用脉冲波和连续波集中研究了基板厚度对沉积过程温度场和显微组织的影响规律。结果发现，随着基板厚度的增加，Ti-6Al-4V合金薄壁试样中心部位柱状晶变短变细，且体积分数降低，金相组织由大量等轴晶粒组成；与激光脉冲波沉积试样相比，采用激光连续波可获得几乎100%细小的等轴晶粒；且厚基板在沉积初始阶段可获得较小的温度峰值，但可获得较大的冷却速率，从而改变合金的显微组织状态。
关键字: 直接激光制造；Ti6Al4V；等轴晶粒；柱状晶；热分析；显微组织
（1. State Key Laboratory of Metal Matrix Composites, Shanghai Jiaotong University, Shanghai 200040, China;
2. ARC Centre of Excellence for Design in Light Metals, Monash University, Melbourne, 3168, Australia）
Abstract:Cooling rate is one of the most important factors in determining the resultant microstructure of the material during the direct laser fabrication process (DLF). A gradual heating or prolonged cooling effects are obtained and it is possible to dictate the cooling rates and affect the solidification microstructure through reasonable controlling the thickness of substrate. Pulse wave and continuous wave laser were used to study the effect of various thickness of substrate on the microstructure of the specimens, respectively. It is found that a few volume fractions of columnar grains located in the center of the samples turn to coarser and shorter, and the sample is composed of a large number of equiaxed grains with the increasing of the substrate thickness. Compared with the pulse laser, nearly 100% fine equiaxed grain could be obtained through using continuous wave laser. Thick substrate can get a smaller peak temperature but higher cooling rate to change the microstructure in the initial stage.
Key words: direct laser fabrication; Ti-6Al-4V; equiaxed grain; columnar grain; thermal analysis; microstructure
