Corrosion and mechanical performance of wrought and additively manufactured Ti-6Al-4V under supercritical carbon dioxide Venus atmospheric conditions

Future long-duration Venusian surface landers will require structural alloys that can withstand the harsh surface conditions; 467 °C temperature and 92.7 bar atmospheric pressure consisting of supercritical CO2. To investigate structural alloy suitability, corrosion and tensile coupons of wrought Ti-6Al-4V (Ti64), laser powder bed fusion printed Ti-6Al-4V (AM Ti64), and wrought 304SS were exposed to a 10-day simulated Venus surface atmospheric condition using the NASA Glenn Extreme Environments Rig (GEER). Corrosion coupons were characterized by gravimetric analysis, X-ray diffraction, transmission electron microscopy, and X-ray photoelectron spectroscopy. Tensile coupons were mechanically interrogated at 460 °C prior to and after GEER exposure. Both Ti-6Al-4V variants formed a thin TiO2 outer scale, a region rich in carbon at the scale-metal interface, and a relatively thick α-case (oxygen-stabilized α-Ti) region. Cu-contamination from fabrication obfuscated SS304 corrosion coupon analysis but not mechanical interrogation. At 460 °C, AM Ti64 was stronger but less ductile than wrought Ti64, and both Ti64 variants were stronger but less ductile than 304SS. No appreciable degradation in mechanical properties (yield strength, ultimate tensile strength, ductility, modulus) was observed for Ti64, AM Ti64, or 304SS after the 10-day Venus exposure, but statistically significant differences in UTS of AM Ti64 (slight decrease after exposure) and wrought Ti64 (slight increase after exposure) were observed and are attributed to microstructural annealing changes rather than corrosion-induced.