Microstructure and Mechanical Properties of Multi-Material 316L/1.2709 Obtained by Selective Laser Melting

Abstract

The microstructure and mechanical properties of a 316L/1.2709 multi-material obtained by selective laser melting (SLM) are studied. The SLM mode providing minimum porosity of steel 1.2709 is determined. It is established that joining of the materials with an overlap of 0.2 mm minimizes defects in the transition zone. Metallography, x-ray diffraction analysis, and scanning electron microscopy are used to show gradient variation of the chemical composition in the transition zone 400 – 500 μm wide without formation of new phases. Heat treatment (annealing at 950°C for 2 h + aging at 500°C for 6 h) increases the hardness of the zone of steel 1.2709 to 520 HV. In the case of transverse orientation of the transition zone, the properties of the multi-material are close to those of steel 316L (σ_r = 612 MPa, δ = 29.6%); in the case of its longitudinal orientation, the elongation (δ = 3.7%) is close to that of steel 1.2709 at a tensile strength of 961 MPa. The impact toughness of the multi-material (75 J/cm² ) exceeds that of steel 1.2709 (25 J/cm² ) demonstrating a synergistic effect (elevation of the strength and of the impact toughness). The results confirm the perspectives of SLM for creation of articles with combined properties.