Optimization of microstructural manipulation and ductility in laser powder bed fusion Ti-6Al-4V through hydrogen heat treatments

In laser powder bed fusion additive manufacturing of Ti-6Al-4V the resulting microstructure in the as-printed state is martensitic in nature due to the rapid cooling rates and thermal cycling which results in high strength, low ductility tensile properties. Post additive manufacturing heat treatments can be used to decompose these martensitic microstructures and improve the ductility, but due to the continuous network of retained & beta; phase the manipulation of these microstructures is limited. In this work, a post-processing heat treat utilizing a hydrogen atmosphere is explored as a method to manipulate the microstructure and to improve tensile ductility of extra low interstitial Ti-6Al-4V produced by laser powder bed fusion. This heat treatment, known as thermo hydrogen refinement of microstructure (THRM), utilizes hydrogen as a temporary alloying element to induce grain refinement and provide a pathway to produce wrought-like microstructures. Additionally, the effects of maximum temperature during THRM heat treatment on tensile properties are investigated. Low maximum temperatures coupled with an inert globularization heat treatment are found to produce tensile properties comparable with hot isostatic pressing reaching ultimate strengths of 1 GPa and 19% elongation at failure.