Microstructure and mechanical properties of direct metal laser–sintered 15-5PH steel with different solution annealing heat treatments

Abstract

15-5PH parts that are fabricated using direct metal laser sintering (DMLS) has shown mechanical properties comparable to conventionally manufactured parts. However, DMLS-fabricated 15-5PH parts have shown high anisotropy in their mechanical properties due to the layering nature of additive manufacturing process. In addition, the fatigue life and strength of DMLS 15-5PH varies significantly between horizontally and vertically fabricated parts and both orientations are inferior to conventionally manufactured parts. Reliability and large variations in performance remain as a barrier from employing 15-5PH parts fabricated using DMLS. Standard heat treatment of 15-5PH is insufficient to eliminate the anisotropy and homogenize the DMLS parts. Modified precipitation hardening heat treatments did not show further improvement in published literature. Therefore, in this paper, we investigate the influence of different solution annealing heat treatments on the microstructure and mechanical properties of 15-5PH steel produced using DMLS. Three different solution annealing heat treatments were investigated: the standard solution heat treatment, the second heat treatment extended the time from 1 to 3 h, the third heat treatment increased the temperature from 1038 to 1200 °C. For each heat treatment, three patches of specimens were fabricated each in one of the three principal orientations X, Y, and Z. In addition, three patches, one of each orientation, were tested in as-built condition. The specimens were tensile tested and their microstructure and fractured surfaces were imaged. It was found that extending the time of the heat treatment improved the homogenization while increasing the temperature of the heat treatment to 1200 °C had detrimental effects, especially on vertically fabricated specimens.