Taguchi methods and gray relational analysis are used to determine optimal processing conditions for the selective laser melting (SLM) of 18Ni-300 maraging steel. The following SLM process parameters are selected for optimization: laser power (P), scanning speed (v), and hatch spacing (h). Statistical analysis indicates that SLM parameter configuration no. 5 (275 W, 700 mm s À1 , 0.08 mm) as most suitable for the simultaneous improvement of tensile strength, elongation (or ductility), hardness, and impact toughness. The order of influence of SLM parameters is identified as follows: P % v > h. Samples with improved mechanical properties can be produced using configurations with higher linear energy density (E L ). This is because the increased laser energy input facilitates complete melting of metal powder, as well as better interlayer bonding between melt pools. Higher E L can be achieved by either increasing P or decreasing v. Digital image correlation analysis indicates that tensile test samples with higher porosity exhibit lower ductility due to its inability to accommodate plastic strain accumulation for prolonged durations. Fractography analysis indicates that during tensile loading, cracks will nucleate around the pore perimeter and propagate via microvoid coalescence. Fracture will occur at regions with higher porosity due to it having multiple crack initiation sites.
Over the last decade, developments in metal additive manufacturing (AM) have opened up new possibilities in various industries. Current metal AM technologies are now capable of processing a larger selection of metals, including steel mold materials such as H13 and P20. In the injection molding industry, mold makers have implemented metal AM technologies to 3D print steel molds. The main challenge currently faced by mold makers is to 3D print steel molds with mechanical properties that are comparable with conventionally made ones. Research on the microstructure evolution in 3D printed steel molds provide the necessary information for tailoring the moldÕs microstructure and improving its mechanical properties. This review presents a unique perspective on the microstructure evolution in 3D printed steel molds. The microstructure evolution is discussed according to two major processing stages. Stage 1 describes the formation of the moldÕs microstructure in as-built condition after it has solidified from its molten state. Subsequently, Stage 2 describes the changes in the moldÕs microstructure post-heat treatment. This review also summarizes the various experimental techniques and numerical models used to study the microstructure evolution in 3D printed components. Advances in experimental microstructure characterization techniques enable researchers to investigate microstructure evolution in situ during metal AM processes. Coupled thermalmicrostructure numerical models serve as an alternative approach for predicting grain growth in 3D printed components. The review concludes by summarizing future prospects in mold making and metal AM research in general.
The influence of SLM process parameters (i.e. laser power, scanning speed, and hatch spacing) on the microstructure and mechanical properties of 3D printed 18Ni-300 maraging steel was investigated. In experiments on 3D printed scan tracks, better fusion of powder material was achieved in parameter configurations with higher linear energy density (i.e. LED ≥ 375.00 J m-1). A higher LED indicates that more laser energy is transferred to the powder material, resulting in complete melting of the powder and the creation of a microstructure with less defects. In experiments on fully built samples, higher relative density was achieved when the hatch spacing was increased or the scanning speed was decreased. Fully built samples produced using parameter configuration B-2 (300 W, 700 mm s-1, 0.10 mm) have higher relative density and ultimate tensile strength as compared to the other parameter configurations.
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