Licentiate presentation Carl Andersson

Carl Andersson have successfully presented his licentiate thesis. The thesis with the title "Modelling of grain structure and residual stresses in additive manufactured nickel-based superalloys" was thoroughly scrutinized and discussed with the discussion leader Daniel Berglund from Aerobase AB.

Additive manufacturing (AM) aims to improve resource efficiency during manufacturing. Some of the weldable nickel-based superalloys are frequently used for AM due to their good weldability. In the aerospace industry, nickel-based superalloys are used in high-temperature applications such as in the rear section of jet engines where superior mechanical properties are essential. Both grain structure and residual stresses must be carefully controlled during manufacturing to achieve the desired properties. The grain structure forms during solidification in AM and influences the mechanical properties such as the strength of the manufactured parts. The formation of residual stresses is unavoidable because of the non-uniform heating and cooling in AM. The residual stresses may distort the parts, reduce the fatigue performance, or decrease the load-bearing capacity. The aim of simulation in this work is to link process parameters in AM to the generated grain structure and the residual stresses in the part. This would further enhance the resource efficiency of AM since trial-and-error manufacturing can be reduced. Simulation requires models that are relatively fast and accurate to be useful in the aerospace industry. This work is divided into two papers where models for predicting the grain structure and residual stresses in AM are developed and evaluated. A Cellular Automata Finite Element (CA-FE) framework was developed to predict the grain structure in laser-based powder bed fusion (PBF-LB) manufactured alloy 625 in the first paper. The inherent strain method (ISM) was used to predict the residual stresses in PBF-LB manufactured alloy 718 in the second paper. Both alloys 625 and 718 belong to the group of nickelbased superalloys and the two alloys combine good weldability with excellent strength at high temperatures. The results showed that the CA-FE and the ISM model can capture the general trends of both the experimentally observed grain structure and the residual stress field in a wall component that was manufactured using PBF-LB in alloy 625 and 718, respectively. The CA-FE and ISM models are also relatively fast which makes them suitable for product development in the aerospace industry among other industries.