热处理对选区激光熔化18Ni300成形组织性能的影响

Effect of Heat Treatment on Microstructure and Properties of 18Ni300 bySelective Laser Melting

采用选区激光熔化技术成形18Ni300马氏体时效钢,并对成形件经固溶时效热处理研究。结果表明,固液界面前沿的温度梯度与凝固速率的比值(G/V_s)决定了沉积态微熔池底部到顶部的胞-柱状枝晶的微观演变;而在微结构区域存在的六角胞、伸长胞及条带组织的相互过渡是通过几何拓扑变换来实现。经热处理后,沉积态胞状、柱状及亚微米组织结构消失,出现细小板条状马氏体,并在马氏体基中形成细小颗粒状沉淀相;而热处理前后性能测试表明,经固溶时效热处理后,维氏显微硬度增加,抗拉强度也显著增加,延伸率降低,断口形貌呈现典型的韧性断裂。

18 Ni300 maraging steel was formed by selective laser melting(SLM)technology, the microstructure and mechanical properties of the deposited and heat treated states were investigated of the samples fabricated by SLM with 18 Ni300 raw powder material. The results showed that the evolution mechanism of cell-columnar dendrites from the bottom to top of the micro-melting pool of the as-built sample is determined by the ratio of the temperature gradient to the solidification rate(G/V_s) at the front of the solid-liquid interface. However, the mutual transition of the hexagonal cell, the elongated cell and the strip structure existing in the microstructure is accomplished by geometric topology transformation. After heat treatment, the cell, columnar and sub-micron structures in the microstructure of the as-built sample disappeared, and precipitates fine lath martensite with fine granular precipitate. The mechanical properties test showed that the Vickers micro-hardness and tensile strength increased significantly after solution aging heat treatment, but the elongation decreased. At the same time,the fracture morphology presented a typical ductile fracture.