Microstructure and yield strength of SLM-fabricated CM247LC Ni-Superalloy

Abstract

Specimens of Selectively Laser Melted (SLM) CM247LC powder have been characterised using analytical scanning and transmission electron microscopy. In specimens from the bulk, it has been found that longitudinal sections consist mainly of columnar γ grains, containing virtually identically oriented cells, approximately 700 nm in width and length up to hundreds of microns. These cells are separated from adjacent cells and from adjacent grains by γ'/γ eutectic, by high densities of Hf/Ti/Ta/W-rich precipitates and high densities of dislocations. The eutectic γ' is up to about 50 nm in diameter but up to 10 nm within the cells. The microstructure in the top layer is similar to that taken from the bulk, but single-track samples are heterogeneous along the track length. The microstructures are interpreted in terms of the precipitation sequence, the volume fraction of eutectic and partitioning of the solute elements during solidification and the influence of subsequent laser-tracks. The cooling rate during solidification, calculated from the observed cell diameters is about 10 6 K/s, but the value obtained from the size of γ' within the bulk is about 10 4 K/s. It is suggested that the discrepancy is due to the limited accuracy of this approach. Tensile tests on as-fabricated samples show that the yield strength is comparable with that of cast samples after standard heat treatments. The high strength of the as-fabricated samples is interpreted in terms the high densities of precipitates and dislocations in cell boundaries, the fine cell structure and the γ' within cells.

Additively Manufactured Inconel 718 : Microstructures and Mechanical Properties

“…So far, the Ni-base superalloys applied to SLM are mainly the weldable ones, i.e., IN718 [113,[160][161][162][163][164][165][166][167], IN625 [79,80,168,169], Hastelloy X [170][171][172][173][174], Nimonic 263 [110], which have low additions of both Ti and Al and are less susceptible to strain age cracking. Expansion to the less-weldable Ni-base superalloys has also been attempted, such as IN939 [175], IN100 [176], IN738LC [177][178][179][180][181], CM247LC [114,[182][183][184] and Rene 142 [81]. These researches have shown the great potential for manufacturing complex-geometry critical and functional components for high temperature application via SLM.…”

“…Correlating the dendrite arm spacing with cooling rate is commonly applied to analyse the solidification behaviours in, for instance, cast and welded materials. However, such correlation by extrapolation might give poor accuracy for the SLM cases [184]. Therefore, the future work on the solidification metallurgy might have to be thought outside the box of traditional solidification scope.…”

Mechanism of heat affected zone cracking in Ni-based superalloy DZ125L fabricated by laser 3D printing technique

“…The strains in the substrate are relatively low and homogeneous, but much more inhomogeneous strains are observed in the cladding layers with particularly large strain concentration near the interdendritic regions, because the dislocation movement is greatly retarded by the interdendritic phases, especially nano-sized MC particles. As a consequence, the susceptibility to cracking may get more pronounced due to the difficulty of dislocation movements [43]. The primary HAZ is subjected to a significantly higher strain state, and a clearly decreasing strain gradient from the HAZ/cladding interface to deep inside the substrate is visible.…”

Thermal debinding mass transfer mechanism and dynamics of copper green parts fabricated by an innovative 3D printing method

“…Metal 3D printing technologies such as laser micro sintering (LMS), selective laser melting (SLM) and electron beam melting (EBM) are capable of manufacturing metal components with complex structures and advanced functionalities 1,2 and have been widely applied in aviation, medical and other high-end elds. [3][4][5] However, the extremely fast conditions during the laser or electron beam melt-forming process oen makes it easy to form crack defects, severely affecting the mechanical properties. A recent study reported that the use of a nano zirconiumbased nucleating agent to assemble alloy powder can effectively inhibit micro-cracks and improve the strength of the alloy.…”