Small Scale testing of Nickel-based Superalloys produced by ALM

Nickel-based superalloys exhibit an impressive range of mechanical properties, from high temperature strength and toughness to excellent oxidation and corrosion resistance. It is for these reasons that they are heavily incorporated in a wide range of industrial sectors, particularly the aerospace industry where they are extensively utilised within the combustor and turbine section of a holistic gas turbine engine, where temperatures often reach arduous conditions. Although nickel-based superalloys are typically manufactured using traditional cast and wrought methodologies, the aerospace industry is becoming increasingly interested in the use of alternative manufacturing methods in an attempt to further drive gas turbine development through weight reduction and increased Turbine Entry Temperatures (TET). As such, interest regarding the use of near-net shape manufacturing technologies such as Additive Layer Manufacturing (ALM) has risen in parallel, but concerns have arisen given the metallurgical complexity of the process and the prevalence of phenomena such as anisotropic behaviour, residual stressing and structural integrity. This thesis has investigated the influence of key process parameters and variables on the mechanical and microstructural behaviour of the two-contrasting nickel-based superalloys, CM247LC and IN718. A novel miniaturised mechanical testing method, Small Punch (SP), in combination with in-depth material characterisation techniques was implemented on a series of Laser Powder Bed Fusion (LPBF) variants of differing build orientation and parameter selections. In addition to this, a robust analytical methodology was employed on a series of LPBF variants in order to ascertain process parameters’ influence on melt pool profile and both alloys relative propensity for defect formation. The findings of this work will help further the understanding of parameter selection and support a key development strategy being implemented by Rolls-Royce plc. regarding the safe incorporation of additive components into service