A computational investigation of the phase and microstructural stability in transition metal carbides and nitrides
September 17-20, 2017
The group IVB and VB transition metal carbides and nitrides represent one of the major classes of ultrahigh temperature ceramics (UHTCs). Here, we investigate the stability of these compound at low temperature for a wide range of stoichiometries using electronic structure density functional theory (DFT). This, combined with intelligent search algorithms, have been able to suggest potential stable phases in these materials. The results of which have highlight a competition between vacancy ordering in the carbon/nitrogen depleted rocksalt matrix with other stacking fault derived structures, such as the nanolamellar zeta phase (M4C3 or M4N3). Using this DFT phase stability information, a model has been constructed that provides direct insight into how phase stability controls microstructure. Through this model, we have found that a barrier-free state can exist for the nucleation of the stacking fault phases, which now can describe the propensity of faulting in specific types of carbides and nitrides. Even more intriguing is the consequence in microstructure formation between the meta-stable and stable versions of the zeta phase in the carbides and nitrides respectively. Through these computational tools and models, we are able to elucidate the underlying physics that gives rise to phase and microstructure stability for this particular class of UHTCs.
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Christopher R. Weinberger, Xiao-Xiang Yu, Hang Yu, and Gregory Thompson, "A computational investigation of the phase and microstructural stability in transition metal carbides and nitrides" in "Ultra-High Temperature Ceramics: Materials for Extreme Environment Applications IV", Jon Binner, The University of Birmingham, Edgbaston, United Kingdom Bill Lee, Imperial College, London, United Kingdom Eds, ECI Symposium Series, (2017). http://dc.engconfintl.org/uhtc_iv/45