Abstract
There is a growing interest in laser melting processes, e.g., for metal additive manufacturing. Modelling and numerical simulation can help to understand and control microstructure evolution in these processes. However, standard methods of microstructure simulation are generally not suited to model the kinetic effects associated with rapid solidification in laser processing, especially for material systems that contain intermetallic phases. In this paper, we present and employ a tailored phase-field model to demonstrate unique features of microstructure evolution in such systems. Initially, the problem of anomalous partitioning during rapid solidification of intermetallics is revisited using the tailored phase-field model, and the model predictions are assessed against the existing experimental data for the B2 phase in the Ni-Al binary system. The model is subsequently combined with a Potts model of grain growth to simulate laser processing of polycrystalline alloys containing intermetallic phases. Examples of simulations are presented for laser processing of a nickel-rich Ni-Al alloy, to demonstrate the application of the method in studying the effect of processing conditions on various microstructural features, such as distribution of intermetallic phases in the melt pool and the heat-affected zone. The computational framework used in this study is envisaged to provide additional insight into the evolution of microstructure in laser processing of industrially relevant materials, e.g., in laser welding or additive manufacturing of Ni-based superalloys.
Highlights
Laser melting is the basis of various modern processing and fabrication techniques, such as laser surface alloying, laser welding and metal additive manufacturing (AM)
Large thermal gradients, and rapid solidification in these processes often result in the formation of strong texture and metastable microstructures, which can greatly affect the performance of the fabricated parts [1,2,3,4]
Metal AM can be associated with further microstructural complexities, such as precipitation or dissolution of secondary solid phases in the heat-affected zone (HAZ) [8] or compositional banding in the melt pool [9]
Summary
Laser melting is the basis of various modern processing and fabrication techniques, such as laser surface alloying, laser welding and metal additive manufacturing (AM). In contrast to conventional solidification processing of metals, on the other hand, laser treatment provides a unique opportunity to control the local thermal history of the material by manipulating the process parameters, namely the energy input, the scan rate, and the spot size [10,11]. All these parameters can be linked to the local temperature gradient, cooling rate and solidification velocity, be used to control the resulting microstructure. It has been shown how solidification morphology can influence solute segregation and lead to the formation of unwanted phases [15,16,17]
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