Abstract
The effect of Ta and W additions on microstructure and mechanical properties of tilt-cast Ti-45Al-5Nb-2C (at.%) alloy was investigated. Three alloys with nominal composition Ti-45Al-5Nb-2C-2X (in at.%), where X is Ta or W, were prepared by vacuum induction melting in graphite crucibles followed by tilt casting into graphite moulds. The microstructure of the tilt-cast alloys consists of the α2(Ti3Al) + γ(TiAl) lamellar grains, single γ phase, (Ti,Nb,X)2AlC particles with a small amount of (Ti,Nb,X)C, and β/B2 phase identified only in W containing alloy. The EDS analysis shows that Ta segregates into the carbide particles and reduces dissolution of Nb in both (Ti,Nb,Ta)C and (Ti,Nb,Ta)2AlC phases. The alloying with W reduces Nb content in both carbide phases and leads to stabilisation of β/B2 phase in the lamellar α2 + γ regions. The alloying with Ta and W does not affect the volume fraction of the carbide particles but influences their size and morphology. While the alloying with Ta and W has no significant effect on Vickers hardness and the indentation elastic modulus of the studied alloys, the addition of Ta affects the nanohardness and elastic modulus of the (Ti,Nb,Ta)2AlC phase. The addition of W significantly increases the Vickers microhardness of the lamellar α2 + γ regions.
Highlights
Lightweight alloys based on a TiAl-Nb system are of great interest for applications in aerospace, power engineering, and automotive industry due to their high melting point, low density, high specific strength, and good creep and oxidation resistance [1,2,3,4,5]
The present results indicate that vacuum induction melting (VIM) in graphite crucibles followed by casting into graphite moulds can be applied for processing of TiAl-based alloys containing minor additions of strong carbide forming elements such as Nb, Ta, and W
The following conclusions are reached: 1. The VIM in graphite crucibles followed by tilt casting into graphite moulds leads to the reproducible chemical compositions of the tilt-cast alloys designated as Nb, NbTa, and NbW that correspond well to the nominal ones
Summary
Lightweight alloys based on a TiAl-Nb system are of great interest for applications in aerospace, power engineering, and automotive industry due to their high melting point, low density, high specific strength, and good creep and oxidation resistance [1,2,3,4,5]. The effects of Nb on the microstructure, creep properties, oxidation resistance, and deformation mechanisms of TiAl-based alloys have been well studied [7,8,9,10,11]. As the slower diffuser than Nb in TiAl-based alloys, is considered to be the most effective solute atom to promote the formation of massive γm(TiAl) phase in air-cooling conditions that have a great opportunity to improve the properties of TiAl-Ta alloys [12,13]. Zhang et al [14,15] have reported that the addition of 0.5–1 at.% Ta promotes the formation of ultrafine γ(TiAl) grains through the formation of massive γm phase during quenching from α (Ti-based solid solution with a hexagonal crystal structure) phase field and leads to an improvement of mechanical properties. Lapin et al [18,19] have reported that Ta retards the transformation of α2 lamellae to γ phase and τ(Ti3Al2Ta) precipitates and stabilises the lamellar α2 + γ + τ type of microstructure of TiAl-Ta alloy during long-term ageing at 750 ◦C up to 10,000 h or creep exposure at 700 ◦C up to 30,000 h
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callDisclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
