Abstract:The microstructure evolution of Ti–43Al–3Si (at-) alloy solidified in alumina crucible was investigated by directional solidification technology. After directional solidification, the microstructure of the alloy is consisted of γ-TiAl, α2-Ti3Al, ξ-Ti5Si3 phases and Al2O3 particles. There are three morphologies of ξ phases formed in the alloy, namely, long rod-like, cluster-like with eutectic morphology, and needle-like shape. The volume fraction of ξ phases decreases with increasing growth rates. Al2O3 particl… Show more
“…The microstructure near the solidification interface of TiAl alloy directionally solidified within alumina crucible is shown in Figure 2 [38]. Appearance of Al 2 O 3 particles is not only affected by thermodynamic factors but also related to the dissolution of SiO 2 binder in alumina crucible [31]. The schematic diagram of the contamination processing of Al 2 O 3 particles from alumina crucible is shown in Figure 3 [31].…”
Section: Oxide Casting Mould Materialsmentioning
confidence: 99%
“… Figure 2 Dendritic morphology on longitudinal section in quenching region of directionally solidified Ti–43Al–3Si alloy (Black phase are Al 2 O 3 particles) [38]. Figure 3 Schematic diagram of reaction between the alumina crucible and the melt of TiAl alloy: (a) before reaction; (b) SiO 2 binder reacted with melt alloy; (c) Al 2 O 3 particle entered into the melt alloy [31]. …”
Section: Oxide Casting Mould Materialsmentioning
confidence: 99%
“…Schematic diagram of reaction between the alumina crucible and the melt of TiAl alloy: (a) before reaction; (b) SiO 2 binder reacted with melt alloy; (c) Al 2 O 3 particle entered into the melt alloy [31]. …”
Section: Oxide Casting Mould Materialsmentioning
confidence: 99%
“…Al 2 O 3 has high thermal stability, good formability and low cost [25][26][27][28][29][30][31][32][33]. At the same time, the thermal expansion coefficient of Al 2 O 3 is similar to that of TiAl alloys, which can reduce the cracking probability during casting process [34].…”
Intermetallic TiAl alloys are new generation high-temperature material. However, extensive application of TiAl alloys is hindered by some disadvantages, especially the high processing cost. Currently, precision casting is an effective method to manufacture TiAl components with complex shape. However, the interfacial reaction between the TiAl alloy melt and mould affects the quality of the castings and hinders extensive applications of casting TiAl components. In this paper, the research status of mould materials for the casting of TiAl alloys is reviewed. Performances of present used mould materials are compared in details. Reaction mechanisms between mould materials and the melts of TiAl alloys are also summarised. Finally, the future development tendency and prospect are pointed out.
“…The microstructure near the solidification interface of TiAl alloy directionally solidified within alumina crucible is shown in Figure 2 [38]. Appearance of Al 2 O 3 particles is not only affected by thermodynamic factors but also related to the dissolution of SiO 2 binder in alumina crucible [31]. The schematic diagram of the contamination processing of Al 2 O 3 particles from alumina crucible is shown in Figure 3 [31].…”
Section: Oxide Casting Mould Materialsmentioning
confidence: 99%
“… Figure 2 Dendritic morphology on longitudinal section in quenching region of directionally solidified Ti–43Al–3Si alloy (Black phase are Al 2 O 3 particles) [38]. Figure 3 Schematic diagram of reaction between the alumina crucible and the melt of TiAl alloy: (a) before reaction; (b) SiO 2 binder reacted with melt alloy; (c) Al 2 O 3 particle entered into the melt alloy [31]. …”
Section: Oxide Casting Mould Materialsmentioning
confidence: 99%
“…Schematic diagram of reaction between the alumina crucible and the melt of TiAl alloy: (a) before reaction; (b) SiO 2 binder reacted with melt alloy; (c) Al 2 O 3 particle entered into the melt alloy [31]. …”
Section: Oxide Casting Mould Materialsmentioning
confidence: 99%
“…Al 2 O 3 has high thermal stability, good formability and low cost [25][26][27][28][29][30][31][32][33]. At the same time, the thermal expansion coefficient of Al 2 O 3 is similar to that of TiAl alloys, which can reduce the cracking probability during casting process [34].…”
Intermetallic TiAl alloys are new generation high-temperature material. However, extensive application of TiAl alloys is hindered by some disadvantages, especially the high processing cost. Currently, precision casting is an effective method to manufacture TiAl components with complex shape. However, the interfacial reaction between the TiAl alloy melt and mould affects the quality of the castings and hinders extensive applications of casting TiAl components. In this paper, the research status of mould materials for the casting of TiAl alloys is reviewed. Performances of present used mould materials are compared in details. Reaction mechanisms between mould materials and the melts of TiAl alloys are also summarised. Finally, the future development tendency and prospect are pointed out.
“…Hence, imparting the inner face of the mould with high chemical stability, mechanical stability, and thermal stability is a key factor for the precision casting of γ-TiAl alloys2728. In the case of TiAl alloys, the materials commonly used for crucibles or moulds are oxide ceramics such as Y 2 O 3 2930, CaO31, Al 2 O 3 3233343536, ZrO 2 3738, CaZrO 3 39, AlN40 or BN41. The reaction between the TiAl alloy melt and crucible can be controlled over a relatively short solidification time using these materials3342.…”
The microstructure evolution and interface characteristics of a directionally solidified Ti-43Al-3Si (at.%) alloy in an alumina (Al2O3) crucible with new Y2O3 skull-aided technology were investigated. The Y2O3-skull that is in contact with the TiAl-melt is relatively stable, which results in a more controlled reaction between the skull and the melt than in the case of an Al2O3 crucible is used. A thin reaction layer was formed between the mould and the melt through mutual diffusion. The layer thickness increased with increasing reaction time. The thickness of this layer was less than 80 μm for reaction times up to 5800 s. Y2O3 particles were not found in the specimen because the mould coating was prepared with fine Y2O3 powder without a binder, which prevented the Y2O3 particles splitting from the coating as a consequence of thermal physical erosion. The oxygen content of the TiAl-alloy increased with increasing reaction time. The total oxygen content of the solidified specimen was less than that of the specimen solidified in the Al2O3 crucibles. This new Y2O3 skull-aided technology is expected to improve the surface quality of TiAl-alloys and reduce the reaction between the crucible/mould and molten TiAl alloys during directional solidification processing with longer contact times.
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