Element mixing and solidification behavior during multi-track overlapping laser deposition of Cr-based alloys

Abstract

Multi-track overlapping laser deposition has been applied more widely than single track laser deposition in engineering practices. However, it is difficult to predict the solidification behavior and element mixing of multi-track overlapping laser deposition layers under existing conditions. Hence, in this paper, we not only derive the formula for calculating the arbitrary arc length of the overlapping cross-section, but also establish a three-dimensional multi-track overlapping laser deposition element mixing and solidification behavior prediction model. By the proposed model, the solidification behaviors of multi-track overlapping deposition layer and element concentrations of iron (Fe), nickel (Ni) and chromium (Cr) are predicted. The element redistribution and remelting solidification characteristics of the overlapping zone are further investigated. The results reveal that the element of Cr in the overlapping zone is 2 wt % higher than the first track non-overlapping zone. With the increase of deposition track, the concentrations of elements in the deposition layer tend to be uniform. The Peclet_m number, convection time and mixing velocity of the melt pool in the track joint decrease significantly, but these values are still 1.5, 3.5 and 1.5 times higher than at the beginning (35 ms) of first track, respectively. Meanwhile, the change in crystal size and morphology of deposition layer is predicted according to cooling rate ($Gs\bullet Rs$) and morphological parameters (G/R). The crystal size gradually increases from the top to the bottom of the deposition layer, and the morphology changes from equiaxed dendritic, columnar, and cellular crystals to planar crystals. In addition, the element distribution at the edge of multi-track overlapping laser deposition is uneven than in other regions.