Ca-Mg Multiple Deoxidation of Ti-50Al-2Cr-2Nb Intermetallic Compound Powder for Additive Manufacturing

In this study, we investigated Ca-Mg multiple deoxidation of Ti-50Al-2Cr-2Nb intermetallic compound powder for additive manufacturing. The crystal structure, surface morphology, and oxygen reduction rate of Ti-50Al-2Cr-2Nb powder before and after deoxidation according to particle size were observed through XRD, SEM, BET and O/N analyses. In addition, the oxide layer of the surface before and after deoxidation was observed through TEM analysis. In our previous study, Ti-48Al-2Cr-2Nb powder deoxidized by only calcium at 1,100 °C for 2 h showed the oxygen concentration of 320 ppm. Compared to the previous result, it was found that a low oxygen Ti-50Al-2Cr-2Nb intermetallic compound powder less than 155 ppm was obtained by Ca-Mg multiple deoxidation at 900 °C for 2 h. It is considered that the decrease in the deoxidation temperature from 1,100 °C to 900 °C for Ti-50Al-2Cr-2Nb powder was due to only existing γ-TiAl phase with a fast oxygen diffusion coefficient without α2-Ti3Al phase at 900 °C. As a result, it was established that the oxygen reduction rate of the Ti-50Al-2Cr-2Nb powder depended on the specific surface area because the Ti-50Al-2Cr-2Nb powder without β-Ti phase was mainly deoxidized by oxygen reduction on the surface oxide layer more than interstitial oxygen.