Full-Potential Lmto Calculation of Brittle Fracture in Titanium Carbide
- PDF / 400,400 Bytes
- 6 Pages / 420.48 x 639 pts Page_size
- 24 Downloads / 210 Views
FULL-POTENTIAL LMTO CALCULATION OF BRITTLE FRACTURE IN TITANIUM CARBIDE.
D.L. Price* and B.R. Cooper*Memphis State University, Dept. of Physics, Memphis, Tennessee 38152 -West Virginia University, Dept. of Physics, Morgantown, West Virginia 26506
ABSTRACT
The refractory transition metal-carbides commonly fail under stress by brittle fracture and the properties and nature of the fracture process are consequently of practical interest. We have calculated the fracture properties of titanium carbide under tensile stress using our full-potential LMTO method, a methodology which is closely related to multiple scattering theory (and includes a true interstitial region). The fracture calculation is accomplished by employing a repeated slab (or repeated cleavage separation) geometry. Within this geometry, the fracture process is simulated most simply by uniformly increasing the gap separation from zero to a distance on the order of a few atomic radii. A more sophisticated search for fracture instability involved stretching the ideal crystal and examining the separation energetics of the strained system. Results of these calculations will be reported both for the ideal, stoichiometric titanium carbide crystal and also for systems containing carbon vacancies. We will discuss the role of such defects in modifying the bonding behavior at the cleavage plane and the resulting effect on resistance to fracture.
INTRODUCTION
The factors controlling the degree of brittleness and other fracture properties of solids have long been an active and important area of study in material science. This is especially true with regard to the fracture properties of the transition metal carbides, since these hard, refractory materials are most often used in stressful applications, where the lifetimes of carbide components axe limited primarily by failure due to brittle fracture. Recent theoretical efforts to understand the fracture process have been increasingly concerned with obtaining a first principles description of the atomic scale conditions controlling fracture properties [1,2], although this is a formidable task. A complete theoretical description of a material's fracture properties, such as fracture planes or tensile yield stress, will depend markedly upon many quantities such as the number and type of impurities and defects in the material, the atomic positional relaxation near a fracture gap, and the competition between various modes of failure. In particular, due to the presence of preexisting cracks which can nucleate fracture, the tensile yield stress of materials is typically found to be orders of magnitude smaller than estimates of the yield stress of the ideal (defect free)
Mat. Res. Soc. Symp. Proc. Vol. 253. Ic)1992 Materials Research Society
376
material. A determination of the yield properties of ideal crystals is, nonetheless, a worthwhile endeavor since, among other things, the ideal crystal characteristics enter into many theories of real material behavior. We describe below an extension of earlier work [3] on the f
Data Loading...
