Al stabilized TiC twinning platelets
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Xiaohui Wang High-Performance Ceramic Division, Shenyang National Laboratory for Materials Science, Institute of Metal Research, Chinese Academy of Sciences, Shenyang 110016, China
Zhaojin Li High-Performance Ceramic Division, Shenyang National Laboratory for Materials Science, Institute of Metal Research, Chinese Academy of Sciences, Shenyang 110016, China; and University of Chinese Academy of Sciences, Beijing 100049, China
Yanchun Zhoua) Science and Technology of Advanced Functional Composite Laboratory, ARIMPT, Beijing 100076, China (Received 11 February 2014; accepted 25 March 2014)
Titanium carbide (TiC) twins are believed to be extremely unstable because of their high twin boundary energy. Here, we report that TiC twins are always presented in platelets with dimensions of 2–3 lm in length and less than 300 nm in width. In-depth microstructural characterizations by high-resolution transmission electron microscopy demonstrate that Al atoms at the twin boundary play a decisive role in stabilizing TiC twins. With different amounts of Al, perfect and defective TiC twins are formed. For perfect twins, three types of twin boundaries can be formed depending on the amount of remaining Al at the twin boundary. With inadequate Al, the TiC twins become defective with certain degrees of deviation from the perfect twin orientation. Based on a detailed analysis of the microstructure of the twin boundaries, a mechanism for the formation and stabilization of TiC twins is proposed.
I. INTRODUCTION
Titanium carbide (TiC) is of technological importance and has vast industrial applications because of its low density, high hardness, and high strength. To improve the mechanical performance of TiC and TiC-containing composites, the grain size and morphology of TiC have been tailored to modulate the mechanical properties.1–5 As a new way to improve the mechanical properties of metals and ceramics,6–8 nanotwins have been introduced into TiC (as well as other carbides) containing composites.9–13 The stacking-fault energy (SFE) of TiC is in the range between 130 and 300 mJ/m2.14,15 Therefore, TiC twins are extremely unstable from an energetic point of view, and there have been few reports of deformation or growth twins in bulk TiC samples. Nonetheless, research on the stacking faults (SFs) and microtwins of TiC has been reported in the literature. Venables et al.16 found that the SFs of TiC are associated with impurity atoms. Kooi et al.14 proposed that Si can induce SFs in TiC a)
Address all correspondence to this author. e-mail: [email protected] DOI: 10.1557/jmr.2014.80 J. Mater. Res., Vol. 29, No. 9, May 14, 2014
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grains. Yu et al.11 further confirmed that Al atoms can reduce the SFE of TiC. Through the de-intercalation of Al atoms in Ti3AlC2, Zhang et al.17 synthesized TiCx–Cu composites with TiC nanotwins. However, to the best of our knowledge, the successful synthesis of TiC twins with large size has not been reported. This is partially due to the lack of knowledge o
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