Template effect in TiN/AlN multilayered coatings from first principles

Multilayered TiN/AlN coatings find many technological applications where superhardness is suspected to be affected by AlN structures and template effect. Here, we demonstrate, by first-principles calculations on alternative adsorptions of Al and N atoms on Ti- and N-terminated TiN surfaces, that the preferred stacking sequences (i.e., having the largest adsorption energy) transform from fcc- to hcp- mode in first a few AlN layers. Using several analytic methods, we identify that for the T-terminated surface, the third added N layer is critical to inducing the structural transition of AlN, weakening the interaction between the second added Al and first added N atoms. The findings provide insight to the complicated template effects in TiN/AlN multilayered coatings, which are practically relevant for further improving property of multilayered coatings at the atomic scale

An experimental study of the indentation behaviour of Al foam

The indentation response of a closed-cell Al foam under the flat-end cylindrical indenter was experimentally investigated. The effects of indenter sizes, relative density of Al foam and boundary condition on the mechanical and energy absorption characteristics of indentation were also investigated. Experimental results show that the indentation load-displacement response obtained using the flat-end cylindrical indenter is similar to that observed under uniaxial compression. Crosssectional views of the indented specimens show that the deformation is confined only to the region directly under the indenter with very little lateral spread, and that the indentation deformation of Al foam is non-uniform. The tear energy and energy absorbing efficiency of Al foam is not related with the indenter diameter and relative density of Al foam. By increasing the indenter diameter or decreasing relative density, the indentation hardness is linearly decreased, but the energy absorbing capability linearly increases with an increase in indenter diameter or an increase in relative density. At a certain indentation depth range, the difference between rigid foundation and the indentation response of Al foam under simply supported conditions can be ignored

Embedded ZnO nanorods and gas-sensing properties

Regular hexagonal embedded ZnO nanorods were successfully prepared by a simple hydrothermal method. The addition of urea as a homogeneous precursor was found to play a vital role in the embedding of secondary nanorods. The nanostructures were characterized by XRD, SEM, and EDS. The gas-sensing properties of secondary grown embedded nanorods were reported for formaldehyde, ethanol, methanol, acetone, and ammonia at different concentrations and temperatures. A higher response and greater selectivity toward formaldehyde than other gases was observed. A sharp response with the best recovery time was achieved at an optimum temperature of 200 °C

Design of lightweight Ti3Zr1.5NbVx refractory high-entropy alloys with superior mechanical properties

Refractory high-entropy alloys (RHEAs) have attracted extensive attention due to their excellent mechanical properties. However, most RHEAs have high density and exhibit poor ductility at room temperature, which greatly limits their applications. In this work, a series of lightweight Ti3Zr1.5NbVx (x = 0, 1 and 2, respectively) RHEAs with high strength and good ductility were designed and prepared using vacuum arc melting. The effects of V content on the microstructure, mechanical properties and deformation mechanism of the as-cast Ti3Zr1.5NbVx RHEAs were investigated in details. The results showed that all the Ti3Zr1.5NbVx RHEAs exhibit a single body-centered cubic (BCC) phase and their densities are less than 6 g/cm3. With the increase of V content, the grain size of the Ti3Zr1.5NbVx RHEAs decreases from 436.1 to 81.2 μm, and the hardness increases from 199.7 to 297.5 HV. The Ti3Zr1.5NbV2 RHEA possesses optimal tensile mechanical properties with the yield strength of 974.0 MPa, fracture elongation of 6.3%, and a specific yield strength of 165.7 MPa cm3/g, better than most previously reported RHEAs. More importantly, the Ti3Zr1.5NbV2 RHEA also exhibits excellent elevated-temperature mechanical properties with yield strength of 770.9 MPa at 600 °C and 243.6 MPa at 800 °C. The deformation mechanism of the Ti3Zr1.5NbV2 RHEA is governed by dislocation slip, including planar slip bands, dislocation loops, and high density dislocation walls. The high strength of the Ti3Zr1.5NbV2 RHEA is mainly attributed to the solid solution strengthening effect, in which Zr and V elements play an important role

Finite element investigation into torsion test in the range of large strain and deformation

Torsion tests with thin-walled tubular, solid cylindrical and Lindholm-type tubular specimens were simulated using the finite element code ABAQUS, in the range of large strains and deformations. The results showed that for thin-walled tubular and solid cylindrical specimens the radii of the specimens almost remained straight during torsion; for Lindholm-type tubular specimens the twist angle of the cross-section at the two ends of the gauge section did not stay constant, due to the change of the specimen geometry (i.e. the end effect). A correction which considers the end effect should therefore be introduced when the stress-strain relationship is characterized. Compared with the stress-strain relationship obtained previously from experiment, a distinct difference was noted when conventional formulae were used to convert the torque and twist angle into the shear stress and shear strain. Further, the influence of axial constraint conditions at the two ends of the specimen was examined; the results showed that axial strains and stresses had no significant influence on the definition of the shear stress-shear strain relation, and hence these can be neglected when the stress-strain relationship is characterized

A constitutive model for the metals subjected to thermomechanical loading with fast heating during heating-assisted forming

Based on the concept of local thermal inconsistency, a constitutive model was developed for the description of the behaviors of metallic materials subjected to thermomechanical loading with fast heating, with reference to heating-assisted forming applications. The model considers effect of plastic deformation, of temperature as well as heating-rate and of recrystallization, on the mechanical property, hardening and damage of the materials. It can account for the reduction of the rupture strength of metallic materials subjected to high heating-rates or heating-rate histories, and the reduction of failure temperature of pre-stressed metallic materials heated at high heating-rates. The constitutive behavior of brass H62 subjected to uniaxial thermomechanical loading with fast heating is described and compared with experimental results. The satisfactory agreement between the computed and the experimental results shows the validity of the proposed model

An experimental study of the indentation behaviour of Al foam

The indentation response of a closed-cell Al foam under the flat-end cylindrical indenter was experimentally investigated. The effects of indenter sizes, relative density of Al foam and boundary condition on the mechanical and energy absorption characteristics of indentation were also investigated. Experimental results show that the indentation load-displacement response obtained using the flat-end cylindrical indenter is similar to that observed under uniaxial compression. Crosssectional views of the indented specimens show that the deformation is confined only to the region directly under the indenter with very little lateral spread, and that the indentation deformation of Al foam is non-uniform. The tear energy and energy absorbing efficiency of Al foam is not related with the indenter diameter and relative density of Al foam. By increasing the indenter diameter or decreasing relative density, the indentation hardness is linearly decreased, but the energy absorbing capability linearly increases with an increase in indenter diameter or an increase in relative density. At a certain indentation depth range, the difference between rigid foundation and the indentation response of Al foam under simply supported conditions can be ignored

春回和內時本構模型二次收益分析

Using thermodynamic consistency elastoplastic large deformation material constitutive model established by a simple mechanism, the model meets basic thermodynamics of irreversible constraints, and taking into account the residual energy stored in the micro stress field, with the corresponding algorithm, prepared a user subroutine UMAT, and embedded into commercial software ABAQUS, the resilience and the secondary yield analyzes of cylindrical workpieces elastic tool upsetting and upsetting when closed mold. comparison of simulation and experiment measured load - displacement relationship can be seen in the plastic deformation of upsetting the first stage of lateral deformation of the workpiece in the axial loading process has been due to the elastic deformation of the mold radial constraint caused by the rapid increase in load; second stage axial pressure reducing mold springback so that the radial deformation of the workpiece can be restored, but with the increase of plastic strain occurs strengthen the work; the third phase of mold constraint lifted, increasing the radial dimension of the work with the constitutive model. calculation closed mold upsetting, showing the calculation results and the experimental results are consistent

Low-density NiAlFeCrMoV eutectic high-entropy alloys with excellent mechanical and wear properties

Eutectic high-entropy alloys (EHEAs) have become a new research frontier and hot topic in the metallic materials community in recent years because of their excellent mechanical properties and great potential in practical engineering applications. In this work, a series of novel low-density (NiAl)100-x(FeCrMoV)x (x = 35, 40 and 45) EHEAs were designed and successfully prepared with arc-melting method. Their phase constitution, microstructure, mechanical and wear properties, as well as the deformation mechanisms were systematically investigated. It was shown that all the EHEAs are composed of BCC and B2 phases and their densities are less than 7 g/cm3. Typical hypoeutectic, eutectic and hypereutectic microstructures could be achieved as x = 35, 40 and 45, respectively. Significantly, as x = 45 the EHEA with hypereutectic microstructure possesses the best mechanical and wear properties at room temperature, of which the true and ultimate compressive yield stresses reach 1695.4 MPa and 2500.2 MPa, and the fracture strain and wear rate can reach 28.5% and 7.267 × 10−6 mm3N−1m−1, respectively, better than most HEAs reported previously. The excellent mechanical and wear properties can mainly be attributed to the small lattice mismatch between the BCC and B2 phases and the high hardness of the alloy. This work is significant because it could provide guidance for the design of high-performance alloys for practical engineering applications

Cylindrical Magnetorheological Fluid Variable Transmission Controlled by Shape-Memory Alloy

Centrifugal fan is an important component of a ventilation system in a nuclear power plant. In this paper, we proposed a magnetorheological speed-adjustment system controlled by shape-memory alloy for centrifugal fan. A theoretical analysis of the effect of the applied magnetic field on the viscoplastic flow between two cylinders in the speed-adjustment system is presented. The expressions for the velocity in viscoplastic flow and the torque transmitted by MR fluids are derived. A sliding mode SMA switch is proposed to modify the magnetic field acting on working gap under thermal effect. The results indicate that with the increases of applied magnetic field, the torque transmitted by MR fluid goes up rapidly