Regulation of microstructures and properties of molybdenum‑silicon‑boron alloy subjected to selective laser melting

Abstract

Molybdenum–silicon–boron (Mo–Si–B) alloy, which is considered a promising material for manufacturing aero-engines, is mainly processed by methods including arc smelting and powder metallurgy. Selective laser melting (SLM), as the most commonly used processing method in additive manufacturing at present, provides another option for processing Mo–Si–B alloy. To study defects appearing during SLM of Mo–Si–B alloy, the effects of SLM parameters on the relative density were investigated based on orthogonal tests. It is found that the layer thickness has the largest influence on the relative density, followed by the laser power and hatch spacing, while the scanning speed exerts the smallest influence. By regulating SLM parameters, compact Mo–Si–B samples with a relative density larger than 99% can be obtained. Furthermore, a large number of intergranular cracks are found in Mo–Si–B alloy subjected to SLM, which can be regulated by preheating the substrate. When preheating the substrate at 400 °C, cracks on a horizontal section almost disappear and the reduction of cracks improves the compressive properties of the samples to some extent. The compressive strength of the samples without substrate preheating is 1065 MPa and it reaches 1610 MPa when preheating the substrate at 400 °C. The microhardness of the samples is about 360 HV, where the microhardness of a longitudinal section is higher than that of the horizontal section. Grains on each section have unique characteristics. For the longitudinal section, grains are columnar crystals along the building direction and the average grain size is about 8.69 μm. In terms of the horizontal section, grains are irregular and the average grain size is 3.12 μm. There are 〈001〉 textures in the main phases α-Mo of each section, and the existence of textures may lead to anisotropic properties of the samples.