Carbide

About: Carbide is a research topic. Over the lifetime, 36331 publications have been published within this topic receiving 503586 citations.

Statistical model for carbide induced brittle fracture in steel

Abstract: Factors affecting the cleavage fracture stress and the fracture toughness K 1C in steel have been examined. A statistical method based on carbide induced cleavage fracture is proposed, by which it is possible to estimate the fracture toughness and study the effect of different variables. The predictions made are in excellent agreement with experimental results for a variety of microstructures.

Vacancy Hardening and Softening in Transition Metal Carbides and Nitrides

Abstract: The effects of vacancies on mechanical properties of the transition metal carbides and nitrides are studied using the ab initio pseudopotential approach. Calculated shear elastic stiffness and electronic structures show that the vacancy produces entirely different effects on the mechanical strength of groups IVb nitrides and Vb carbides. It is found that the occupation of shear-unstable metallic dd bonding states changes essentially in an opposite way for the carbides and nitrides in the presence of vacancies, resulting in different responses to shear stress. Our study provides an atomistic understanding of the anomaly in hardness for these substoichiometric materials.

Interaction potential for silicon carbide: A molecular dynamics study of elastic constants and vibrational density of states for crystalline and amorphous silicon carbide

Abstract: An effective interatomic interaction potential for SiC is proposed. The potential consists of two-body and three-body covalent interactions. The two-body potential includes steric repulsions due to atomic sizes, Coulomb interactions resulting from charge transfer between atoms, charge-induced dipole-interactions due to the electronic polarizability of ions, and induced dipole-dipole (van der Waals) interactions. The covalent characters of the Si–C–Si and C–Si–C bonds are described by the three-body potential. The proposed three-body interaction potential is a modification of the Stillinger-Weber form proposed to describe Si. Using the molecular dynamics method, the interaction potential is used to study structural, elastic, and dynamical properties of crystalline (3C), amorphous, and liquid states of SiC for several densities and temperatures. The structural energy for cubic (3C) structure has the lowest energy, followed by the wurtzite (2H) and rock-salt (RS) structures. The pressure for the structural transformation from 3C-to-RS from the common tangent is found to be 90 GPa. For 3C-SiC, our computed elastic constants (C11, C12, and C44), melting temperature, vibrational density-of-states, and specific heat agree well with the experiments. Predictions are made for the elastic constant as a function of density for the crystalline and amorphous phase. Structural correlations, such as pair distribution function and neutron and x-ray static structure factors are calculated for the amorphous and liquid state.

Effects of solution treatment and continuous cooling on σ-phase precipitation in a 2205 duplex stainless steel

Abstract: A commercial 2205 duplex stainless steel with three different solution treatments (at 1020, 1080 and 1200°C for 3 min) followed by continuous cooling at four respective cooling rates (1, 0.5, 0.25 and 0.1°C s −1 ) has been investigated by means of optical metallography, transmission electron microscopy, electron probe microanalysis, X-ray diffraction and differential thermal analysis. It is found that the lower solution treatment temperature with the lower cooling rate significantly enhanced the σ phase transformation. The σ precipitate could be detected when the specimens were solution-treated at 1020 and 1080°C and cooled at the rate of 0.25°C s −1 ; substantial amounts of σ phase formed when the specimens were cooled at 0.1°C s −1 . The precipitation of σ phase was considerably retarded as the solution temperature increased from 1080 to 1200°C. The precipitation behaviors of σ phase and M 23 C 6 carbide were characterized by transmission electron microscopy. The results indicated that the Cr- and Mo-rich σ phase preferentially nucleated at the pre-formed M 23 C 6 carbide particles, which were located at δ / γ interface or within δ ferrite grain. The selected area diffraction patterns displayed the complicated crystallography of σ phase, and revealed the orientation relationships between the interfacial σ precipitate and adjacent matrix phases.