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Mesoscale modeling of short crack initiation in metallic selective laser melting microstructures

  • : Tom Andersson1, Anssi Laukkanen2, Tatu Pinomaa3, Antero Jokinen2, Antti Vaajoki2, Tarja Laitinen3
  • : 1VTT Materials and Manufacturing, 2VTT, 3vtt
  • : PDF Download
  • : 2015

Abstract

A core issue of selective laser melted metallic materials is their utilization in key components with high requirements for performance. For example, in the aerospace sector the use of additive manufacturing in elevated temperature parts of rotating components imposes essentially the requirement for the parts to be defect free. However, in practise such material microstructures have proven to be difficult to reach, and issues with process consistency in complex part designs make such efforts ever more laborsome.

In order to address this issue, we present a material defect structure based modeling methodology for evaluating the significance of individual microstructure scale defects to the operational time required for initiation of short microstructural scale fatigue cracks. The approach is based on using imaging extracted information of actual microstructures of a precipitation strengthened high-performance steel to quantify the significance of individual and clusters of defects to the number of fatigue cycles to initiate a propagating fatigue crack.

The results present a systematic approach to performing a fatigue crack initiation analysis of additive manufacturing materials and parts. The influence of individual defect types on fatigue crack initiation is presented using a strain life approach. Coupled effect of residual stresses and defect structures is discussed. The most deleterious defect types are found to be planar joining faults between layers, and a number of defect types with limited significance to part performance are presented, providing guidelines for part certification, quality control, part design and development of metal additive manufacturing processes.

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