Characteristics of porous SS316L: Influences of the Sn additive on the interfacial phenomena during the pressureless sintering

Abstract

The interfacial phenomena through the pressureless sintering of porous stainless steel 316L containing Sn additive, and their influence on the sintering behavior, final microstructure and the obtained mechanical properties of the materials were investigated. The powder mixtures contained 0 to 6 wt% Sn were uniaxial cold pressed up to 400 MPa and then, sintered under the nitrogen atmosphere at various temperatures (1250 °C and 1300 °C) for 120 min.The relative densities of the samples were observed to follow an overall decreasing trend. The highest relative density was achieved in sample containing 2 wt% Sn and sintered at 1300 °C. The final phase arrangement mainly included austenite (γ-Fe) in samples sintered at 1250 °C, whereas the Cr-containing ferrite (α-Fe) was the dominant phase in most of the 1300 °C-sintered samples. The sintering behavior of the samples was then analyzed based on the microstructural investigations and phase arrangements, as well as the thermodynamic calculations of the interfacial reactions.It was confirmed that the formation of chromium oxide at the interfaces controls the sintering behavior of the materials. Hence, the higher sintering temperatures were found to promote the formation of the interfacial chromium oxide, thicken the oxide layer and then, postpone neck formation through the atomic diffusion. The presence of Sn, however, was observed to result in improved atomic diffusion through liquid phase sintering. However, the drawn-out of nickel through the liquid tin and the formation of Sn-based interfacial phases were found to negatively affect the neck formation. Through these competitive phenomena, the best combination of mechanical properties was achieved in the samples contained 2 wt% Sn. The fractural investigations, phase analysis, and the semi-quantitative EDS elemental analysis were finally carried out to discuss the obtained mechanical properties as well as compressive strength of the samples.