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The control of solidification microstructure is critical to successful laser processing of single-crystal (SX) nickel-base superalloys and a practical tool for the microstructural control is processing–microstructure maps. However, the maps presented in literature do not consider the effects of powder feeding during laser additive manufacturing (LAM) of SX superalloys. This paper therefore presents a simple and feasible strategy to deal with the effects of powder feeding and to extend the combined numerical model used to calculate processing–microstructure maps. A characteristic ratio of epitaxial SX growth was defined to quantitatively compare the final solidification microstructure. Resulting processing–microstructure maps can estimate the influence of most processing variables, especially powder feeding rate, on the extent of epitaxial SX growth and the position of columnar-to-equiaxed transition. Using the processing parameters selected according to these processing–microstructure maps, a multi-layer SX deposit with fine dendrites was successfully fabricated by LAM. This successful SX LAM indicates that these new processing–microstructure maps involving powder feeding are reliable and useful because they can determine proper processing windows for LAM of SX superalloys and further advance the understanding of the processing–microstructure relationship in powder-feeding LAM process. [ABSTRACT FROM AUTHOR]

Primary dendritic arm spacing (PDAS) is an important microstructure feature in the nickel-base single-crystal (SX) superalloys by laser rapid directional solidification (LRDS). A combined numerical model was developed in this paper to investigate the influence of laser processing parameters on the PDAS. This model consists of (1) the theoretical PDAS models which relate PDAS to the solidification conditions and (2) the heat-flux calculations of laser processing which provide the solidification conditions as a function of the processing parameters. It is therefore able to immediately relate the PDAS to the processing parameters and obtain corresponding processing–microstructure maps. To verify the predicted accuracy, the PDAS values calculated by different theoretical models were compared with those produced under different processing conditions. Results show that the PDAS firstly decreases and then increases at a lower laser power whereas it decreases with increasing scanning velocity at a higher laser power, leading to nose-shape contour lines. The predicted accuracy depends on appropriate selections of material thermo-physical properties. These processing–microstructure maps can accurately capture the trends of the PDAS variation with the processing parameters and contribute to the control and optimization of dendritic microstructure while determining relevant processing windows for controlled SX laser processing. [ABSTRACT FROM AUTHOR]