First-principles approaches to intrinsic strength and deformation of materials: perfect crystals, nano-structures, surfaces and interfaces

Abstract

First-principles studies on the intrinsic mechanical properties of various materials and systems through ab initio tensile and shear testing simulations based on density-functional theory are reviewed. For various materials, ideal tensile and shear strength and features of the deformation of bulk crystals without any defects have been examined, and the relation with the bonding nature has been analyzed. The surfaces or low-dimensional nano-structures reveal peculiar strength and deformation behavior due to local different bonding nature. For grain boundaries and metal/ceramic interfaces, tensile and shear behaviors depend on the interface bonding, which impacts on the research of real engineering materials. Remaining problems and future directions in this research field are discussed.

Intrinsic hardness of crystalline solids

“…Detailed analysis [39] of the mechanics of nanoindentation has shown that after proper consideration of the crystallography of loading and the correction of the nonlinearity of the elastic response at large strains, the measured values can be compared quantitatively to the results of the first-principles calculations. In the calculations, the ideal strength is defined as the maximum stress in the stress-strain curve in the weakest tensile stretch or shear slip direction [40,41]. Since first-principles ideal strength calculations explore the stress-strain energy profile at large structural deformation, changes in the electronic structure under strain are also correctly reproduced.…”

“…This is accomplished by calculation of the tensile stresses along candidate crystallographic directions [40,41]. For a given tensile direction, the relevant lattice vectors are deformed in the direction of the applied strains.…”

“…10 [42]. The ideal strengths of many metals, metal alloys, hard ceramic materials and nanostructures have been studied with ab inito calculations [41]. The method has also been applied to potential superhard materials such as transition metal carbides and nitrides, carbon nitrides, and boron carbides.…”

Ideal strength and structural instability of aluminum at finite temperatures

“…Recent developments in computational physics have enabled firstprinciples calculations of peak stresses (i.e., ideal strengths) in the stress-strain relations of a crystal lattice along specific deformation paths and the structural deformation modes leading to elastic instabilities [1][2][3][4][5][6][7][8][9][10][11] . Meanwhile, dynamic instability of a crystal lattice has been studied via separate calculations of the phonon spectra of the crystal lattice at each step along every deformation pathway.…”

“…Despite numerous past studies 1,3,8,9,12,[16][17][18][19][20][21][22][23][24][25] , there remain questions on the fundamental properties of Al, such as how the temperature would affect the strength under various loading conditions and whether the lattice instability behaviors predicted at T=0 K would change with rising temperature. Previous first-principles calculations (at T=0 K) predict that under the <001>, <011>, <111> uniaxial tension and the {111} <112> shear deformation, dynamic phonon instabilities always precede the elastic instabilities determined by the peak stresses in ideal strength calculations 12 .…”