Effect of Heat Treatment Cooling Method on the Organization and Properties of 316L Negative Re-entrant Hexagonal Honeycomb Porous Bone Scaffolds by Selective Laser Melting

In a previous study, it was found that annealing heat treatment significantly eliminated the residual stress in 316L porous scaffolds with negative re-entrant hexagonal honeycomb (NRHH) prepared by selective laser melting (SLM), but at the same time reduced the mechanical properties and corrosion resistance. To improve the performance of scaffolds while eliminating residual stress, this paper focuses on the heat treatment cooling mode and explores the effects of heat treatment cooling mode on microstructure evolution and phase transformation, residual stress, mechanical properties, and corrosion resistance to seek a suitable heat treatment process. For this purpose, the SLM-prepared porous scaffolds were held at 800 and 950 degrees C for 2 h, respectively, and then three different cooling methods, water-cooling, air-cooling, and furnace-cooling, were used. The results of the microstructural analysis confirm that the cooling mode of heat treatment significantly affects the microstructural evolution and phase transformation. The slow cooling process is more favorable for the release of residual stresses. The release of residual stresses and grain coarsening after heat treatment led to a decrease in the microhardness of the scaffolds. However, the ferrite phase content increased after water-cooling heat treatment at 800 degrees C, and the microhardness values of the scaffolds increased by 0.89% and 5.15% in the two planes, respectively. The modulus of elasticity of the scaffold increases with the cooling rate, and the maximum stress value decreases with the cooling rate. The corrosion resistance deteriorates with the slowing down of the cooling rate of heat treatment and the increase in temperature, and it is more favorable to resist corrosion after 800 degrees C water-cooling heat treatment.