Heterogeneous microstructure and mechanical properties of Monel alloy parts repaired by laser directed energy deposition

Abstract

Additive manufacturing (AM) offers the advantages of direct near-net-shape production, reduced material waste, and shortened production lead time, showing great potential to revolutionise the manufacturing industry. The flexible movements of the deposition head and the build platform allow directed energy deposition (DED) to conduct the repair process of damaged high-value metallic parts. However, the resulting heterogeneous microstructure and its effect on the mechanical properties of the repaired parts have not been widely realised. In this work, the repair of Monel alloy parts, known for their excellent mechanical properties and high corrosion resistance, was conducted by the laser-DED process with low and high laser power settings, respectively. Different from the fine, equiaxed grains in the original part, the as-deposited Monel alloy consists of large columnar grains. The mechanical performance across the interface between the original and newly deposited material was tested and analysed along horizontal and vertical loading directions. The yield strength and elongation of repaired Monel alloy parts were 409.1 MPa and 35.2% along the horizontal loading direction, which both significantly surpass the corresponding values along the vertical loading direction. This study lays the groundwork for designing a laser-DED process to achieve high performance for repaired metallic parts.