SUNConferences, 17th Annual Conference of the Rapid Product Development Association of South Africa

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Optimising post-process heat treatments of SLM produced Ti-6Al-4V to achieve superior mechanical properties
Gerrit Matthys Ter Haar

Last modified: 2016-09-30

Abstract


The Additive Manufacturing (AM) process of Selective Laser Melting (SLM) has seen an exponential growth in sales and development in the past fifteen years. Whereas the capability of SLM was initially limited to rapid prototyping, progress in research and development (R&D) has allowed SLM to be capable of fully functional parts. This technology is still at a primitive stage and technical knowledge of the vast number of variables influencing final part quality is limited. Ongoing research and development of the sensitive printing process and post processes is of utmost importance in order to qualify SLM parts to meet international standards.

Quality concern in Ti-6Al-4V manufactured through SLM has been identified, which include: high residual stresses, part porosity, low ductility and anisotropic mechanical properties. Whereas significant quality improvements have been made through optimising printing parameters, research indicates as-produced part ductility to be a major limiting factor when compared to its wrought counterpart.

This study aims at achieving an in-depth understanding of the underlining links between SLM produced Ti-6Al-4V microstructure and its mechanical properties. Knowledge of microstructural transformation kinetics of Ti-6Al-4V allows for the optimisation of post process heat treatments thereby achieving the required process route to manufacture high quality SLM produced Ti-6Al-4V parts.

Experimental results confirm that a low temperature heat treatment is capable of transforming the as-produced, metastable martensitic microstructure into an ultra-fine equilibrium microstructure exhibiting both a high strength and improved ductility. Furthermore, the isotropy of mechanical properties can be achieved through a high temperature anneal. Mechanical properties identical to that of wrought Ti-6Al-4V can therefore be achieved through an optimised process route.


Keywords


SLM; Ti-6Al-4V; mechanical properties; microstructure; heat treatments; optimisation SLM; Ti-6Al-4V; mechanical properties; microstructure; heat treatments; optimisation