Laser powder bed fusion of molybdenum: Density, structure and mechanical properties at room and elevated temperatures

Abstract

Molybdenum is a material of great industrial interest due to its specific properties, particularly at elevated temperatures. Additive manufacturing technologies have recently been proposed as an alternative to conventional powder metallurgy processes because of their flexibility in producing complex geometries. In this study, interrelations between the laser powder bed fusion process parameters and structural and mechanical properties of printed molybdenum specimens are investigated with a bid to propose an optimal set of process parameters. To support this approach, a plan of experiments was built using a simplified numerical simulation of the temperature field surrounding the melt pool. This approach led to the production of crack-free specimens with a printed density of 97%, an ultimate strength of 510 MPa, a yield strength of 340 MPa, and a maximum strain of 11% (all in compression at room temperature) using an optimized set of printing parameters P = 179 W, v = 133 mm/s, h = 60 μm and t = 30 μm. Compression testing in the 20-1000 °C temperature range revealed that the mechanical properties of printed molybdenum (ultimate strengths of 260 and 150 MPa at 800 and 1000 °C, respectively) are comparable to their conventional powder metallurgy manufactured counterparts. Printing of a series of geometric artifacts, such as walls (down to 0.1 mm in thickness), gaps (down to 0.3 mm in width) and lattice structures (50 and 60% porosity gyroids), has proven the potential of laser powder bed fusion to produce complex molybdenum parts for applications over a wide temperature range.