Multi-scale modelling of solidification and microstructure evolution in laser-deposition of T15 high speed steel

Abstract

Laser powder deposition (LPD) process is used in additive manufacturing for powder deposition of metal alloys, it involves parts building and re-manufacturing. However, this process is subjected to high cooling rates and rapid solidification hence the prediction of solidifying microstructure becomes challenging. In order to model the solidification process of the LPD of single track T15 steel, a phase field model (PFM) was proposed coupled with a nucleation, phase transition and heat transfer models. This model was employed to simulate the different microstructure phases and solute distribution. Further, a level set volume of fluid (LS-VOF) model was used to calculate the cooling rate and thermal gradient of the melt pool where these variables are subsequently used as a comparison with the PFM. PF results showed two main phases of microstructure identified as cellular and equiaxed which evolved as solidification took place. The results were compared to thermal analysis and experimental results. Experimental analysis showed cellular microstructure dominated at the substrate-track interface and equiaxed microstructure in the remainder of the track. The grains size distribution obtained from PFM at different location in the track was compared to Scanning electron microscopy (SEM) imaging. The paper showed that the proposed PFM is a promising tool for microstructure prediction in LPD process.