First principles study of stability, mechanical, and electronic properties of chromium silicides

Through the first principles calculations, the chemical stability, mechanical, and electronic properties of chromium silicides are predicted. Estimating enthalpies and binding energies, density state density and electron density distribution are combined to analyse the thermodynamic stability and physical properties of chrome-silicon binary compounds. The chromium silicide includes Cr3 Si, Cr5 Si3, CrSi, and CrSi2. The chemical stability and the information about electronic structure, mechanical properties, Debye temperature, and anisotropy properties are obtained by density functional theory and Debye quasi-harmonic approximation. Meanwhile, the calculation of elastic modulus shows that Cr3 Si has the highest body modulus value（251 GPa） and CrSi2 possesses the highest shear modulus（169.5 GPa） and Young＇s modulus（394.9 GPa）. In addition, the Debye temperature and the speed of sound of these Cr–Si compounds are also calculated.Since the calculated bulk modulus is different from Young＇s modulus anisotropy index, and also different from Young＇s modulus of a three-dimensional surface shape, the different mechanical anisotropies of all the compounds are obtained.

Effects of Ta content on microstructure and oxidation behavior of AlCoCrFeNiYTa_(x)high entropy alloy

The oxidation behavior of the Al CoCrFeNiYTa_(x)high entropy alloy(HEA)doped with different Ta contents at 1100℃is investigated.In this study,different reasons for the spallation of the oxide scales of HEAs without/with excessive Ta addition after 1000 h of oxidation are discussed,and the most suitable Ta doping content for this HEA is explored,in which the HEA exhibits both an exceptionally low oxidation rate,and the formation of oxide scales composed of intact a-Al_(2)O_(3).Meanwhile,it is found that the addition of Ta can effectively inhibit the phase transition of β phase,which makes the surface of the oxide scale smoother.By combining our experimental results with Wagner–Hauffe theory,the influence of Ta drag effect on oxide scale growth is explained,which provides some theoretical guidance for the subsequent design of AlCoCrFeNi HEAs,and can lead to the development of thermal barrier coatings at higher service temperature.

Properties of Fe-Mn-Al alloys with different Mn contents using density functional theory

The chemical stability,electronic structures,mechanical properties and Debye temperature of Fe-MnAl alloys were investigated using first-principles calculations.The formation enthalpy and cohesive energy are negative for Fe-Mn-Al alloys,showing that they are thermodynamically stable.FeAl has the lowest formation enthalpy,indicating that FeAl is the most stable alloy in the Fe-Mn-Al system.The partial density of states,total density of states and electron density distribution maps were used to analyze the physical properties of the Fe-MnAl alloys.A combination of mainly covalent and metallic bonds exists in these Fe-Mn-Al alloys,resulting in good electronic conductivity,high melting points,and high hardness.These alloys display disparate anisotropy due to the calculated different shapes of the 3D curved surface of the Young's modulus and anisotropic index.FeAl has the highest bulk modulus,shear modulus and Yong's modulus of 187.1,119.8 and 296.2 GPa,respectively.Further,the Debye temperatures and sound velocity of these Fe-Mn-Al compounds were explored.

Surface layer structure change and tribological property of Cu/FeS composite under electric field

The microstructural evolvement and friction performance of Cu/FeS self-lubricating composites within electric field were studied by molecular dynamics simulation.The atoms distribution and movement of the Cu/FeS composite under different electric field strengths were considered.The results show that some Fe atoms and S atoms break away from the original structure and move along the electric field,but the movement of Fe atoms and S atoms is not synchronized in stronger electric field strength.Thus,the whole material system becomes chaotic and its temperature rises.The unevenly electric field force appears in the material for the nonuniform FeS distribution,so the internal stress of the composite is generated.For the internal solid lubricating phases move along the direction of the electric field to the surface of the composite,the adhesive wear and the friction coefficient reduce.The movement of the phases leaves over some voids in the composite,which induces arc wear easily.