Abstract
The phase transformation behavior of Ti-42Al-5Mn (at.%) alloy from different phase regions with various cooling rates was investigated based on electron probe micro analyzer-backscattered electrons (EPMA-BSE). It is shown that β→α2′ takes place when this alloy is cooled at a high rate, such as water quenching (WQ), oil cooling (OC), from β single phase. With the decreasing cooling rate to air cooling (AC), β→α2′ is restrained and β→γ is promoted by forming γ platelets. The room-temperature microstructure is βo + α2 when alloy cooled (WQ and OC) from (β + α) dual-phase. However, under AC, β→γ occurs and γ platelets form. It should be noted that α2→γ happens when this alloy cooled from 1180 °C (>Teut) by OC and AC, forming an incomplete lamellae (α2/γ) structure in the α2 phase. However, when the alloy cooled from 1100 °C (<Teut), α2/γ→βo,sec occurs and complete lamellae generates in α2 phase.
Highlights
Ti and Ti alloys are quite attractive for aerospace, medical, and industrial applications [1,2,3,4], of which gamma-titanium aluminide (γ-TiAl) has been considered as one of the topmost candidates for high-temperature structural material due to its low density and high specific modulus and strength [5,6,7,8,9]
As for the conventional gammalloys (CG) alloys, typically four types of microstructures can be obtained by heat treatment around the gamma dissolution temperature (Tγsolv ), namely fully lamellar (FL), nearly lamellar (NL), duplex (DP) and near gamma (NG) [13,14]
Each sample was put into a separate sealing tube filled with argon atmosphere to avoid oxidation, and the sealing tube was placed in the muffle furnace
Summary
Ti and Ti alloys are quite attractive for aerospace, medical, and industrial applications [1,2,3,4], of which gamma-titanium aluminide (γ-TiAl) has been considered as one of the topmost candidates for high-temperature structural material due to its low density and high specific modulus and strength [5,6,7,8,9]. Naka [10], called beta solidified gammalloys (BSG) by Kim in 2018 [11], arousing increasing attention due to their excellent workability and the appropriate solidification process without any peritectic segregation [12]. These BSG alloys usually have one or more β stabilizing elements, such as. In the case of BSG alloys, since they contain a sufficient amount of β-stabilizing elements, the solidification pathway appears to be more complicated, and the typical structures of CG alloys are no longer applicable. Clemens et al [15,16] defined three types of structures for Ti-43.5Al-4Nb-1Mo-0.1B (TNM)
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