The Application of Additive Manufacturing to Nickel-Base Superalloys for Turbocharger Applications

Metal additive manufacturing (AM) is a disruptive technology which has the potential to deliver numerous benefits over conventional manufacturing including design freedom, increased innovation and shorter lead times. However, adoption of the technology by the automotive industry is currently restricted by the cost, limited availability of suitable engineering alloys and the lack of robust process control. These issues are all relevant in the present discussion on the application of laser powder bed fusion (LPBF) to the nickel-base superalloy IN713C. This alloy, along with other precipitation strengthened nickel-base superalloys, is considered to be “un-weldable” due to its susceptibility to cracking; an issue which makes it similarly challenging to process via LPBF. This thesis addresses both the business case for LPBF in terms of turbocharger componentry, and the behaviour of IN713C under LPBF in terms of understanding the defect response. Statistical design of experiments (DOE), advanced material characterisation and analysis techniques, analytical melt pool modelling, thought experiments and the application of literature models have all been employed, facilitating the development of a process map for LPBF of IN713C. The process map illustrates the thresholds for the onset of defect formation and can be used to direct future work on the design of processing strategies for complex components. Use of the process map alongside statistical response surface methodology enabled the identification of process settings for which porosity in test cube specimens was minimised. The application of literature models for solidification cracking provided insight into the relationships between process settings, solidification conditions and crack susceptibility