激光直接沉积CoCrFeNiMn高熵合金:气孔-组织结构-拉伸性能之间的关系

Direct laser deposited CoCrFeNiMn high-entropy alloys:relationship between pores-microstructure-tensile properties

采用激光直接沉积技术成功制备等原子CoCrFeNiMn高熵合金。研究沿试样沉积高度方向上的气孔的大小、数量和组织结构及室温(293 K)和低温(77,200 K)下试样的拉伸性能。结果表明:CoCrFeNiMn合金表现出定向结晶规律,在合金底部区域晶界处形成伴有长形气孔的树枝状柱状晶,随着区域靠近试样顶部,晶粒形态转变为等轴晶粒。而在试样顶部区域,气孔形状呈圆形且数量大大降低。比较在77,200 K和293 K温度下的合金的相应拉伸性能可知:试样顶部区域选取的77 K拉伸试样具有更好的性能,但在中部区域的293 K拉伸试样和在底部区域中的200 K拉伸试样的伸长率相似,这是由于试样不同的气孔率和组织结构的差异所致。

The equiatomic CoCrFeNiMn high entropy alloys(HEAs)has been successfully manufactured using direct laser deposition(DLD)technique.The size and number of porosities,the microstructures along the height of samples and the tensile properties of DLDed HEAs prepared under room(293 K)and cryogenic temperatures(77 K and 200 K)were investigated.The results show that DLDed HEAs exhibit directional solidification,forming dendritic columnar grains with long pores at the grain boundary in bottom regions and transiting to equiaxed grains close to top regions.And in the top regions,the pores are round and the numbers are greatly reduced.Compared with tensile properties of DLDed HEAs,the 77 K tensile samples cut from the top region have better performance,but the elongation of 293 K tensile samples in the middle region and 200 K tensile samples in the bottom region are similar,owing to the difference of porosity and microstructure in the two regions.