Understanding the Structural Integrity and Post-processing of L-PBF As-Built Ti-6Al-4V Parts: A Literature Review

Despite the exponential increase in research and industrial application of laser powder bed fusion (L-PBF), Ti-6Al-4V parts produced still fail to meet the structural integrity of most functional requirements in the as-built conditions. The major drawbacks are high surface roughness, high residual stresses, martensitic microstructure, high porosity and anisotropic material properties. The drawbacks are a result of the inherent nature of a typical L-PBF process characterised by rapid heating and cooling and line-by-line and layer-by-layer processes. To provide more insight and confidence in the L-PBF technology, the causes of these drawbacks must be carefully investigated. This involves the integration of three factors: technology, skills and industry requirements. Currently, such understanding is not widely available. The focus is usually separated (on materials and processes or standardisation and qualification capabilities) instead of being integrated. This paper is a two-fold literature review of firstly, the L-PBF output parameters (resultant part characteristics), which are critical to the structural integrity of Ti-6Al-4V produced by L-PBF and secondly, the potential problem-solving strategies for the martensitic microstructure, porosity, residual stresses and surface roughness. The methodology used involved a triangulation of the literature followed by an inclusion-exclusion criterion of the relevant literature. The outcome of this work was a contribution towards a better understanding of the technology to boost the industry confidence in additive manufacturing.