The influence of the laser scan strategy on grain structure and cracking behaviour in SLM powder-bed fabricated nickel superalloy
By L. Carter, Chris Martin, P. J. Withers, Moataz M. Attallah. 2014
731 citations recorded by the source corpus.
Abstract During the development of a processing route for the Selective Laser Melting (SLM) powder-bed fabrication of the nickel superalloy CM247LC it has been observed that the ‘island’ scan-strategy used as standard by the Concept Laser M2 SLM powder-bed system strongly influences the grain structure of the material. Optical and SEM micrographs are presented to show the observed grain structure in the SLM fabricated and Hot Isostatically Pressed (HIPped) material. The repeating pattern shown in the grain structure has been linked to the overlapping of the ‘island’ pattern used as standard in the Concept Laser M2 powder-bed facility. It is suggested that the formation of this bi-modal grain structure can be linked to the heat transfer away from the solidifying melt pool. The concept of a ‘band’ heating effect across each ‘island’ rather than ‘moving point’ heating has been suggested and has been supported by Electron Back Scattered Diffraction (EBSD) evidence. For comparison an EBSD map from a sample formed using a simple ‘back-and-forth’ strategy has also been presented and reveals a dramatically different grain structure and crystallographic orientation. MicroCT evidence, supported by SEM microscopy, shows that in the as-fabricated material the bimodal structure caused by the ‘island’ scan-strategy translates directly into the macroscopic pattern for the regions of extensive weld cracking associated with the SLM fabrication of γ′ hardenable materials. Similar microCT data has shown that HIPping can effectively close the internal cracks to provide a retro-fix solution.
Subfields: Aerospace Engineering, Mechanical Engineering
View Paper: https://www.semanticscholar.org/paper/3abb40d1dedd170771f727f5325b0ccef93611c2
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Citations in the corpus
- Additive manufacturing of Ni-based superalloys: The outstanding issues (2016, neutral): “Welding literature suggests that DDC occurs due to the formation of carbides at grain boundaries (58), with some reports also suggesting grain boundary shearing (59-61).”
- Additive manufacturing of fatigue resistant materials: Challenges and opportunities (2017, background): “In general, as-built AM parts inherently consist of anisotropic microstructure due to an uneven thermal history and directional heat transfer that the parts experience during fabrication [42,43].”
- Anisotropy and heterogeneity of microstructure and mechanical properties in metal additive manufacturing: A critical review (2018, methodology): “The scan strategies that are commonly used in PBF systems include bi-directional, snaking and checker box [64-66].”
- Mesoscale modelling of selective laser melting: Thermal fluid dynamics and microstructural evolution (2017, methodology): “Research on experiments of SLM has been either concentrated on characterising densification, microstructure and property [10] or using X-ray diffraction to better understand cracking bahaviour [11].”
- On the role of melt flow into the surface structure and porosity development during selective laser melting (2015, background): “These studies have been carried out on a number of materials such as Ni-based superalloys [1,2], Ti-based alloys [3–5], Al-based alloys [6,7], steels [8] and composites [9,10].”