Process-induced microstructural characteristics of laser consolidated IN-738 superalloy

Abstract

Laser consolidation (LC) is a laser cladding based material additive process that could fabricate a “net-shape” functional metallic part through a “layer-upon-layer” deposition directly from a CAD model. The LC process can produce nickel-base IN-738 superalloy with metallurgical soundness. Nevertheless, due to process-induced rapid directional solidification, the LC IN-738 alloy demonstrates certain unique microstructural characteristics, such as, the presence of non-uniform coarse columnar grains (a majority of the grains is in the range of about 56–158 μm in diameter; but their lengths could vary from several hundred μm to the height of the wall being built up) in combination with exceptionally fine directionally solidified dendrites inside (the secondary dendritic arm spacing is about 1.7 μm). Moreover, the “as-consolidated” LC IN-738 alloy, in nature, is a supersaturated γ solid solution, and any precipitation of γ′ particles from the γ matrix is effectively suppressed. Post heat treatment, thus, is essential to achieve the required operational microstructure. On the other hand, the nature and role of conventional “solution plus aging” treatment to the LC IN-738 alloy seem to be different as compared to “as-cast” or wrought IN-738 alloy. In this paper, process-induced microstructural characteristics of the LC IN-738 alloy and its development brought by post heat treatment were fully investigated. The implication on high-temperature mechanical performance of the LC alloy was discussed as well.