Research of selective laser melting process and properties of Y₂O₃ dispersion strengthened high speed steel

M2 high speed steel (W₆Mo₅Cr₄V₂) is an important engineering material, and with modern industry progressing, increased requirements are put forward for improved performance of high speed steel. To improve its comprehensive properties, M2 high speed steel powder is mixed with nano-sized Y₂O₃ particles through mechanical alloying. This mixture is then used to create Y₂O₃ dispersion strengthened M2 high speed steel by selective laser melting (SLM) electrometallurgy technology. The process parameters for SLM are as follows: laser power of 220 W, scanning speed of 800 mm·s⁻¹, powder layer thickness of 0.03 mm, scanning spacing of 0.1 mm, and a substrate preheating temperature of 200 ℃. The effects of Y₂O₃ particles on the microstructure and mechanical properties of the prepared high speed steel were investigated using various techniques, including optical microscopy, scanning electron microscopy, energy-dispersive X-ray spectroscopy, transmission electron microscopy, and mechanical property tests. Experimental results show that after low-energy ball milling, the M2 high speed steel powder remains mostly spherical with minimal deformation, preventing uneven spreading during the powder laying process. The surface of M2 high speed steel powder is coated with a large number of nanometer-sized Y₂O₃ particles. The relative density of Y₂O₃ dispersion strengthened samples formed by SLM is 98.3%. These samples exhibit a relatively smooth surface without obvious cracks, and the quality of the top surface quality is better than that of the side surfaces. The material’s basic structure and morphology are influenced by the molten pool and channel. Hexagonal honeycomb grains are evident in the molten channel, with fine grains distributed at the edges and slightly larger grains inside. The molten pool consists mainly of equiaxed crystals at the center and columnar dendrites at the boundaries, with grains growing epitaxially along the molten pool boundary. EDS (energy dispersive spectrometer) results show that elements Y and O are evenly distributed within the matrix, with no significant segregation. Subsequently, phase analysis reveals that adding Y₂O₃ particles has little effect on the phase composition of M2 high speed steel, which remains mainly martensite, residual austenite, and carbides. Owing to the small amount of Y₂O₃ added, no diffraction peaks of Y₂O₃ were found in the detection range. TEM results show that Y₂O₃ particles are larger at grain boundaries, reaching up to 90 nm, while smaller nanoparticles are diffusely distributed within the grains. Mechanical testing indicates that Y₂O₃ dispersion strengthened high speed steel samples fabricated by SLM exhibit good mechanical properties, with tensile strength reaching 943 MPa, a 36% increase compared to M2 high speed steel without Y₂O₃ particles. Its fracture surface is flat with a few cleavage steps and columnar crystals, indicating brittle fracture behavior. The addition of Y₂O₃ particles produces a larger number of nucleation sites, refines grain size, and hinders dislocation movement, preventing crack propagation along grain boundaries, thereby enhancing the mechanical properties of M2 high speed steel.