Phase Continuity, Brittle to Ductile Transition Temperature, and Creep Behavior of a Eutectic Mo–20Si–52.8Ti Alloy

Abstract

Mo–Si–Ti alloys, like eutectic Mo–20Si–52.8Ti (at%), have previously been intensely investigated, owing to their excellent oxidation and creep resistance. To better understand high‐temperature mechanical behavior, a holistic assessment of microstructural features is necessary. Correspondingly, 3D‐focused ion beam tomography is carried out in Mo–20Si–52.8Ti. The results indicate a severely interconnected network of Mo solid solution (MoSS) and intermetallic (Ti,Mo)5Si3. Both phases retain similar network connectivity, lamellar sizes, etc. The brittle to ductile transition temperature (BDTT) is then determined through a series of bending tests and interpreted using the microstructural information. The BDTT is found to be ≈1100–1150 °C, different from Mo–9Si–8B with a continuous MoSS network. The BDTT is an immediate consequence of the continuous network of both MoSS and (Ti,Mo)5Si3. The MoSS network is instrumental in crack trapping and bridging, indicating that the present phase distribution maximized the mechanical performance over (Ti,Mo)5Si3. Having determined the network microstructure and BDTT, tensile creep behavior is evaluated and compared to previously published compressive creep results. The results show consistency in terms of strain rate, stress exponent, and microstructural features indicating a reliably good creep resistance for the network microstructure of Mo–20Si–52.8Ti regardless of loading direction.

Effect of Microstructure on Oxidation and Micro-mechanical Behavior of Arc Consolidated Mo-Ti-Si-(B) Alloys

“…(Mo, Ti) 5 SiB 2 phase exhibited the highest strength (5.9 GPa) followed by (Ti, Mo) 5 Si 3 (4.5 GPa) and then (Mo, Ti) ss (2.8 GPa). Nano-indentation studies have also shown that the highest hardness is exhibited by the (Mo, Ti) 5 SiB 2 phase followed by the (Ti, Mo) 5 Si 3 phase and then the (Mo, Ti) ss which agrees qualitatively with the observed trend of compressive strength ( Ref 28,29).…”

“…The samples were irradiated using 3.5 MeV proton beam of $ 10 nA current. 429, 718 and 2125 keV prompt gamma rays from 10 B(p,ac)7Be, 1 0 B(p,p¢c) 10 B and 11 B(p,p¢c) 11 B, 983 keV of 4 8 Ti(p,p¢c) 48 Ti and 1273 and 1779 keV of 29 Si(p,p¢c)29Si and 28 Si(p,p¢c) 28 Si were detected during irradiation using HPGe detector for quantification of B, Ti and Si in the alloy. PIGE spectrum is shown in Fig.…”