Microstructure and mechanical properties of WC reinforced 18Ni300 composites produced by selective laser melting

Abstract

Spherical Tungsten Carbide (WC) powders were chosen as reinforcements to produce 18Ni300 steel matrix composites by selective laser melting (SLM). The microstructures and tensile properties of the composites were observed and analyzed. The results manifest that the addition of spherical WC powders significantly affects the microstructure and properties of 18Ni300. With the addition of WC, the austenite (γ-Fe) phase and WC1-X appear, and the grain morphology and orientation change. Moreover, an obvious interface layer (about 1 μm in thickness) is formed due to partial dissolution of WC particles and diffusion of W and C. With increasing WC fraction, the α-Fe in the matrix decreases, and γ-Fe, W2C and WC1-X increase. The spherical WC powders are broken into many small irregular powders distributed in the matrix. The macro-cracks generate when WC content is more than 25%. The hardness, Young's modulus and tensile strength of the composites first decrease and then increase with an increase of WC contents ranging from 0% to 20%, while the relative density exhibits the opposite change rules. The elongation at break first increases and then gradually decreases with increasing WC contents. The composite specimens generally exhibit brittle fracture characterization, different from the plastic fracture characterization of the 18Ni300 matrix. Many cracks generate around the WC and in the matrix. The cracks, tearing ridges and cleavage steps, pits and small irregular WC powders gradually increase with increasing WC contents.