Additive manufacturing of high-strength commercially pure titanium through lanthanum oxide addition

Preventing the formation of columnar grains and refining the microstructure in an effective way have been great challenges in additive manufacturing of titanium and its alloys. In this paper, the effect of La2O3 addition on the microstructure and mechanical properties of commercially pure titanium (CP-Ti) fabricated through selective laser melting (SLM) was comprehensively studied. Experimental results revealed that the microstructure of CP-Ti were composed of massive phase and fine parallel laths, whereas a homogenous microstructure with acicular colonies was obtained in CP-Ti + La2O3. Due to the increase of nucleation sites in SLM-fabricated CP-Ti + La2O3, the massive phase transformation was suppressed, and the average grain size was refined to 1.47 mu m. The spherical La2O3 particles with the size of less than 50 nm were uniformly distributed within the alpha matrix, containing high-density dislocations and twins. After grain refinement, the yield strength and ultimate tensile strength were enhanced up to 858 MPa and 940 MPa, respectively, with the elongation of 8.6%. The enhancement of mechanical properties was mainly attributed to the combined effects of grain refinement strengthening, dislocation strengthening and La2O3 dispersion strengthening.