M2 high-speed steel samples were fabricated by laser additive manufacturing and tempered at different times at a temperature of 560°C. The microstructures of deposited samples were characterised by fine equiaxial grains, dendrites and inter-dendritic network-shape eutectic carbides and were composed of supersaturated martensite, retained austenite and M2C-type carbides. The content of retained austenite gradually decreased with increasing tempering times. Meanwhile, the micro-hardness of deposited samples was 688 ± 10 HV, while the first, second and third tempering times were 833 ± 13 Hv, 710 ± 6 Hv and 740 ± 7 Hv, respectively (standard deviations).Wear resistances of all samples showed an adhesive wear mechanism, and M2 HSS without tempering had a lower friction coefficient with an average of 0.52. M2 HSS after tempering twice at 560°C/2 h had a larger wear volume loss than others.
Purpose Laser additive manufacturing (LAM) technology based on powder bed has been used to manufacture complex geometrical components. In this study, IN625 superalloys were fabricated by high-power fiber laser without cracks, bounding errors or porosity. Meanwhile, the objectives of this paper are to systemically investigate the microstructures, micro-hardness and the precipitated Laves phase of deposited-IN625 under different annealing temperatures. Design/methodology/approach The effects of annealing temperatures on the microstructure, micro-hardness and the precipitated Laves phase were studied by optical microscope (OM), scanning electron microscopy (SEM), X-ray diffraction (XRD), energy dispersive spectrometer (EDS), selected area electron diffraction (SAED), backscattered electron (BSE) imaging in the SEM and transmission electron microscopy (TEM), respectively. The thermal stability of the dendritic morphology about IN625 superalloys was investigated through annealing at temperatures range from 1,000°C to 1,200°C. Findings It is found that the microstructure of deposited-IN625 was typical dendrite structure. Besides, some Laves phase precipitated in the interdendritic region results in the segregation of niobium and molybdenum. The thermal stability indicate that the morphology of dendrite can be stable up to 1,000°C. With the annealing temperatures increasing from 1,000 to 1,200°C, the Laves phase partially dissolves into the γ-Ni matrix, and the morphology of the remaining Laves phase is changing from irregular shape to rod-like or block-like shape. Research limitations/implications The heat treatment used on the IN625 superalloys is helpful for knowing the evolution of microstructures and precipitated phases thermal stability and mechanical properties. Practical implications Due to the different kinds of application conditions, the original microstructure of the IN625 superalloys fabricated by LAM may not be ideal. So exploring the influence of annealing treatment on IN625 superalloys can bring theory basis and guidance for actual production. Originality/value This study continues valuing the fabrication of IN625 by LAM. It shows the effect of annealing temperatures on the shape, size and distribution of Laves phase and the microstructures of deposited-IN625 superalloys.
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