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−N2 reactive atmosphere. The mechanical properties and the 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 suggest that nitrogen is generally dissolved in the α-Ti matrix as interstitial solute atoms. The beneficial N content has a critical limit of ~0.43 wt.%. The ductility of CP-Ti will decrease drastically if its N content exceeds this limit. A constitutive model is developed for predicting the tensile deformation behavior of the in situ strengthened CP-Ti with various solute concentrations and grain sizes. This work demonstrates a promising methodology for the production of high-performance metallic components and extends the fundamental understanding of SLM process under the reactive atmosphere.