Optimization of the mechanical properties of Ti-6Al-4V alloy produced by three dimensional additive manufacturing using termochemical processes

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2017
Bilgin, Güney Mert
Selective laser melting (SLM) is an additive manufacturing (AM) technology used for aerospace and biomedical Ti-6Al-4V alloys to produce parts with complex geometry at one step with reduced production time, scrap and cost. However, parts produced by SLM are lack of ductility due to microstructures similar to those cast products and residual stresses generated during laser processing. In this study, Ti6Al-4V alloys produced by SLM were treated by thermo-hydrogen process (THP) to increase ductility and to refine the microstructure without changing the parts‟ final geometry as opposed to thermo-mechanical processes. It has been observed that conventional 4-step THP decrease alloy‟s mechanical properties despite refined microstructure because of grain boundary α-phase formation during β-solutionizing and eutectoid decomposition steps. Additionally, excessive growth of β-grains occurred during β-solutionizing was another drawback of the 4-step process. On the other hand, modified 2-step THP, which was conducted below α/β transition temperature, was found to increase the alloy‟s ductility without degrading its strength. Although similar microstructures were developed in samples treated by 2- and 4-step THP, grain growth and grain boundary α- phase formation was not encountered in samples treated by 2-step THP. Even though hydrogen absorption of the alloy has not been changed considerably, initial microstructure of the alloy was found to be effective on final properties. THP transformed α'-martensite to fine α and β phases by significant increase in ductility, while it did not alter the type of phases and ductility too much in samples containing lamellar α+β microstructure; however, a discontinuous morphology was obtained. 

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Citation Formats
G. M. Bilgin, “Optimization of the mechanical properties of Ti-6Al-4V alloy produced by three dimensional additive manufacturing using termochemical processes,” M.S. - Master of Science, Middle East Technical University, 2017.