热处理工艺对SLM打印成形CoCrMoW显微结构和力学性能的影响

Effect of Heat Treatment on Microstructure and Mechanical Properties of Selective-Laser-Melted CoCrMoW

摘要:

CoCrMoW合金是烤瓷牙金属基底和可拆卸活动支架的理想材料。针对SLM成形CoCrMoW合金的热处理工艺，尤其是较长的时效时间导致的生产效率过低，以及热处理后SLM成形件尺寸一致性和翘曲变形程度等问题，对热处理后的合金性能进行了研究。以气雾化CoCrMoW合金粉末（粒度15—53 μm）为原材料，采用SLM方法打印CoCrMoW合金试样，并将其分别在920、960和1 000 ℃下进行热处理并保温1 h，随炉冷却至600 ℃后取出。采用SEM、EDS和拉伸测试等方法，研究热处理工艺对SLM打印态CoCrMoW合金的显微结构及力学性能的影响。结果表明：热处理后合金基体的晶内、晶界均析出了第二相颗粒，在温度920和960 ℃下析出相颗粒分布均匀且密集，而在温度1 000 ℃下晶内部分析出相溶解；随着热处理温度的提高，析出相明显生长得更加粗大。根据EDS成分分析，判断析出相为金属间化合物Co₃(Mo,W)₂Si。不同热处理条件下，试样的力学性能有明显差异，并且与析出相的分布、数量、尺寸密切相关。当在920 ℃下进行热处理时，密集细小的析出相对基体的强化效果最为显著，表现为最高的屈服强度（1 134 MPa）、最低的塑性（延伸率7%），断口为脆性倾向的准解理断裂。随着热处理温度升高，析出相发生了粗化且部分溶解，试样的强度逐渐下降，而塑性逐渐提升。在1 000 ℃下进行热处理时，合金的力学性能恢复至接近打印态水平，屈服强度892 MPa、延伸率14.8%，断口为韧性倾向的准解理断裂，此时合金兼具高强度和高塑韧性。此外，较高的热处理温度可以更有效地释放残余应力，减小翘曲变形，经1 000 ℃热处理后的试样形变量最小（0.13 mm）。热处理条件对SLM成形CoCrMoW合金的性能和形变控制至关重要，可以根据不同应用需求进行选择。

Abstract:

CoCrMoW alloy is an ideal material for metal substructures in porcelain-fused-to-metal crowns and removable partial dentures. This study focuses on the heat treatment process of selective-laser-melted CoCrMoW alloy， particularly addressing issues such as low production efficiency due to prolonged aging time， as well as part dimension consistency and warping after heat treatment.In this study， specimens were printed using 15—53 μm gas-atomized powder as raw material， and were subjected to heat treatment at temperatures of 920， 960， 1 000 ℃ for 1 hour， followed by furnace cooling to 600 ℃ before removal. The effects of heat treatment on the microstructure and mechanical properties were investigated using metallographic microscopy， SEM， EDS， tensile testing. It was found that after heat treatment， the second phase precipitated in both the intra-granular and inter-granular regions of the alloy matrix. After heat treatment at 920 ℃ and 960 ℃， the precipitates were uniformly distributed and dense， while after heat treatment at 1 000 ℃， the precipitates within the grains had partially dissolved. Furthermore， the size of the precipitates noticeably increased with increasing heat treatment temperature. Based on EDS compositional analysis， the precipitates was identified as possibly the intermetallic compound Co₃（Mo，W）₂Si. Under different heat treatment conditions， the mechanical properties of the samples differed significantly， closely related to the distribution， quantity， and size of the precipitates. The dense and fine precipitates at 920 ℃ showed the most significant strengthening effect on the matrix， resulting in the highest yield strength （1 134 MPa）， lowest plasticity （7% elongation）， and quasi-cleavage fracture with brittle tendency. As the precipitates coarsened and partially dissolved， the strength gradually decreased while the plasticity increased. At 1 000 ℃， the mechanical properties were restored to levels close to the as-built state， with a yield strength of 892 MPa， elongation of 14.8%， and quasi-cleavage fracture with ductile tendency， demonstrating both high strength and high plasticity. Additionally， heat treatment at higher temperatures can reduce residual stress and warping deformation more effectively， with the smallest deformation （0.13 mm） observed in specimens treated at 1 000 ℃. The choice of heat treatment conditions depends on the requirements of different applications and is crucial for controlling the performance and deformation of selective-laser-melted CoCrMoW alloy.