Effect of Heat Treatment on Crystal Structure, Microstructure, and Hydrogenation Behavior of BCC 52Ti-12V-36Cr Alloys wi
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NTRODUCTION
TITANIUM-BASED solid solution body-centered cubic (BCC) alloys are considered to be interesting candidates for hydrogen storage, because of their relatively high hydrogen capacity (around 3.5 wt pct) at room temperature under low hydrogen pressure (less than 20 bars).[1–4] However, the reversible capacity of these alloys is usually around 2 wt pct due to the very stable plateau pressure of the monohydride.[2] Heat treatment is one of the efficient ways to change crystal structure, phase distribution, and phase compositions which may influence hydrogenation.[5] The respective effect of additive and heat treatment has been investigated by many researchers. For example, Liu et al. presented an effective improvement in flatness of the plateau after heat treatment due to homogenization of the microstructure of 32Ti-46Cr-22V (at pct).[6] Unless stated otherwise, all compositions are given in at pct. They also showed that the flatness of the plateau improved further for heat-treated 32Ti-46Cr-22V + 4 pct Ce. This amelioration in hydrogen capacity was due to the reduction of oxygen concentration and homogenization of the microstructure. Hang et al. reported the presence of C14-type Laves phase and BCC phase,
AMOL KAMBLE is with the IRH, Universite´ du Que´bec a´ TroisRivie´res, Trois-Rivie´res, QC G9A5H7, Canada, and also with the Department of Energy Science & Engineering, IIT Bombay, Mumbai, Maharashtra 400076, India, and also with the Amity School of Engineering & Technology, Amity University Mumbai, Maharashtra 410206, India. Contact e-mail: [email protected] PRATIBHA SHARMA is with the Department of Energy Science & Engineering, IIT Bombay. JACQUES HUOT is with the IRH, Universite´ du Que´bec a´ Trois-Rivie´res. Contact e-mail: [email protected] Manuscript submitted June 15, 2019.
METALLURGICAL AND MATERIALS TRANSACTIONS A
before and after annealing of 10Ti-77V-6Cr-6Fe-Zr.[7] The BCC phase abundance increased after annealing and the hydrogenation plateau pressure was flattened. The total hydrogen capacity was reduced but the reversible capacity increased. Zhou et al. mentioned the presence of C14-type Laves phase after annealing in a previously single-phase BCC 35V-20Ti-45Cr alloy.[4] The first hydrogenation (activation) performance and kinetic properties were improved greatly after annealing due to the presence of C14-type Laves phase. Young et al. reported that, in 15.6Ti-2.1Zr-40V-11.2Cr-6.9Mn-1.4Co-22.5Ni-0.3Al alloy, beside BCC phase, C14-type Laves phase and TiNi were present in the as-cast alloy while Ti2Ni and r-VNi phases were seen after annealing.[8] They optimized annealing temperature and holding time on the basis of abundance of hydrogen-absorbing BCC phase. They reported that annealing at 1173 K for 12 hours resulted in an alloy with high abundance of BCC phase. Banerjee et al. also mentioned the appearance of the C15-type Laves phase when 50Ti-25Cr-25V alloy with additive ZrFe1.8V0.2 was annealed at 1173 K for 2 days. The coexistence of C15-type Laves phase with BCC 50Ti-25Cr-25V led to quic
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