Nb effects on the structural and mechanical properties of TiAl alloy: Density-functional theory study
- PDF / 1,038,615 Bytes
- 9 Pages / 584.957 x 782.986 pts Page_size
- 112 Downloads / 223 Views
Hong Li and Shaoqing Wang Shenyang National Laboratory for Materials Science, Institute of Metal Research, Chinese Academy of Sciences, Shenyang 110016, China
Hengqiang Ye Shenyang National Laboratory for Materials Science, Institute of Metal Research, Chinese Academy of Sciences, Shenyang 110016, China; and Electron Microscope Laboratory, Peking University, Beijing 100871, China (Received 30 November 2008; accepted 17 January 2009)
Nb can improve the oxidation resistance of TiAl; however, the reported concomitant effects on the mechanical properties are controversial. Therefore, the effect of different Nb additions (020.83 at.% Nb) on the lattice distortion as well as dislocation nucleation and mobility of TiAl were examined by density-functional theory calculations to solve the puzzle. The calculation of the formation energy and c/a ratio showed that Nb slightly decreases the phase stability and enhances the anisotropy. The variation of shearing energy barrier demonstrates an interesting staged strengthening effect of Nb on TiAl. Further analyses of the charge density difference and the partial density of states reveal that the physical origination is the electronic anisotropy, which is correlated with the Nb content and distribution.
I. INTRODUCTION
Research on Ti-Al alloys has been conducted for many years because of their major importance in aerospace and automotive industries. However, development of TiAl alloys for industrial application has been greatly retarded by their brittleness at room temperature. It is known that embrittlement of intermetallics can be attributed to the factors such as low cleavage strength, low mobility of super dislocations, weakness of grain boundaries, insufficient sliding systems, and environmental interaction, etc. However, the primary origin of brittleness is associated with their ordered structure that limits the activity and mobility of dislocations. Many technological efforts had been devoted to improve the mechanical properties of TiAl intermetallics in view of both the microstructure control and chemical modifications over the last two decades. For the microstructure control, many methods of stress-induced phase transitions1–8 were tried to produce the duplex materials, because the two-phase alloys (g-TiAl + a2-Ti3Al) were found to possess improved ductility (toughness) than the single phase.9,10 Meanwhile, the effects of ternary addia)
Address all correspondence to this author. e-mail: [email protected] DOI: 10.1557/JMR.2009.0394 J. Mater. Res., Vol. 24, No. 10, Oct 2009
http://journals.cambridge.org
Downloaded: 17 Mar 2015
tions on the physical and mechanical properties of TiAl alloys were considered from the experiment11–24 and calculation25–29 aspects. Nb is one of the most important issues among the ternary additions because of its good oxidation resistance. Therefore, the related research of Nb effects on mechanical properties of TiAl alloys is greatly deserved. Some research concerning the single Nb addition showed that a significant strengthening effect
Data Loading...
