Wire + arc additive manufacture of new and multiple materials

Wire + Arc Additive Manufacture (WAAM) features high deposition rates, short lead times and low equipment investment. WAAM is especially suitable for producing large-scale parts made from highly demanding and expensive materials and provides design freedom for multi-material structures. Although WAAM has been successfully applied to titanium alloys, its feasibility to deposit various other single material and multiple materials are yet to be studied, and the resulting WAAM material properties are largely unknown. Maraging steel and Inconel 718 are highly advanced alloys widely used for critical components in aerospace, and Inconel 625 cladded steel pipes are extensively applied in Oil & Gas industry, all of which require an alternative manufacturing process to forging and casting. The present work aims at utilizing WAAM to deposit maraging steel, Inconel 718, and Inconel 625/low alloy steel multimaterial structures complying with the industrial standard. The objective for the single material is to develop the strength comparable to wrought alloy, while dilution control is the concern for the multi-material deposition. Material characterization was carried out to understand the WAAM microstructure resulting from the inherent thermal history and explain the strength inferiority to the wrought material from a crystallographic scale. Industry standard heat treatment and interpass cold rolling were applied to improve the strength of WAAM material to the wrought level based on the understanding of the strengthening mechanisms of a particular material. Besides, environmental factors affecting the deposition feasibility was studied, and strategies controlling the dilution level for multi-material deposition was developed. The research contributes to the WAAM material database of maraging steel and Inconel 718 and proves the capability of building multi-material structures using WAAM. A research pattern for applying WAAM to various new materials and applications is established, and a scientific understanding of the relationship between the WAAM process and material properties was gained.