Selective laser melting under the reactive atmosphere: A convenient and efficient approach to fabricate ultrahigh strength commercially pure titanium without sacrificing ductility

This study presents a novel approach for the fabrication of commercially pure titanium (CP-Ti) components. The approach conferred superb strength to CP-Ti without sacrificing its ductility. A yield strength of 807 MPa combined with 19.15% elongation was realized through selective laser melting (SLM) by using a high-power laser and incorporating solute atoms from the Ar - N-2 reactive atmosphere. Mechanical properties and microstructures of the as-printed CP-Ti were systematically investigated. Transmission electron microscopy, electron backscatter diffraction, and atom probe tomography were employed to reveal the mechanism underlying the in situ reaction between CP-Ti and the reactive atmosphere. Results suggested that nitrogen generally dissolved in the alpha'-Ti matrix as interstitial solute atoms. The beneficial N content has a critical limit of similar to 0.43 wt%. The ductility of CP-Ti will decrease drastically if its N content exceeds this limit. A constitutive model was developed for describing the tensile deformation behavior of the in-situ strengthened CP-Ti over various solute contents and grain sizes. This work demonstrates a promising methodology for the fabrication of high-performance metallic components and extends the fundamental understanding of SLM process under the reactive atmosphere.