Jinghui Li

Microstructure and Tribological Properties of AlCoCrFeNiTi0.5 High-Entropy Alloy in Hydrogen Peroxide Solution

Microstructure and tribological properties of an AlCoCrFeNiTi0.5 high-entropy alloy in high-concentration hydrogen peroxide solution were investigated in this work. The results show that the sigma phase precipitates and the content of bcc2 decrease during the annealing process. Meanwhile, the complex construction of the interdendrite region changes into simple isolated-island shape, and much more spherical precipitates are formed. Those changes of microstructure during the annealing process lead to the increase of hardness of this alloy. In the testing conditions, the AlCoCrFeNiTi0.5 alloy shows smoother worn surfaces and steadier coefficient of friction curves than does the 1Cr18Ni9Ti stainless steel, and SiC ceramic preserves better wear resistance than ZrO2 ceramic. After annealing, the wear resistance of the AlCoCrFeNiTi0.5 alloy increases coupled with SiC counterface but decreases with ZrO2 counterface.

Microstructure Evolution and Mechanical Properties of a Ti-Based Bulk Metallic Glass Composite

Abstract The tensile deformation behavior of Ti50Zr20Nb12Cu5Be13 bulk metallic glass composite at ambient temperature was investigated by uniaxial tensile tests. All stress-strain curves of Ti50Zr20Nb12Cu5Be13 demonstrated work hardening and work softening during deformation. Many shear bands were generated during deformation. In parallel, the dendrite of Ti50Zr20Nb12Cu5Be13 underwent severe plastic deformation. Shear bands turned into microcracks during tensile deformation. By observing the fracture surface, the fractograph showed only a ductile dimple fracture pattern. Therefore, the excellent plasticity of the Ti50Zr20Nb12Cu5Be13 bulk metallic glass composite was due to the formation of plastic dimple fracture and many shear bands during tensile deformation.

Microhardness Distribution and Microstructural Evolution in Pure Aluminum Subjected to Severe Plastic Deformation: Elliptical Cross-Sectioned Spiral Equal-Channel Extrusion (ECSEE)

Abstract Elliptical cross-sectioned spiral equal-channel extrusion (ECSEE), one of the severe plastic deformation techniques, is of great efficiency in producing bulk ultrafine or nanostructured materials. In this paper, the simulation and experimental researches on ECSEE of high-purity aluminum were conducted to investigate the equivalent strain distribution and microhardness distribution on three orthogonal planes, as well as microstructural evolution. Simulation result shows a significant strain gradient on three planes. Microhardness tests comprise the similar results to strain distribution. According to transmission electron microscopy (TEM) results, microstructural evolution ranged from coarse structures to ultrafine structures by undergoing the shear bands, subgrains, high-angle misorientation grain boundaries and equiaxed structures. There are also some distinctions with reference to grain refinement level, grain boundary styles and dislocation distribution on different positions. The TEM investigations are in good agreement with microhardness tests.

Microstructure and Microtexture Evolution of Pure Titanium during Single Direction Torsion and Alternating Cyclic Torsion

Systematic experimental studies of microstructure and crystallographic texture of pure titanium during the Single Direction Torsion (SDT) and Alternating Cyclic Torsion (ACT) are carried out at room temperature. The microstructure evolution indicates that the grain size can be refined during SDT, while the grain morphology can be controlled during ACT. Also, lots of {10-12} and few {11-22} twins are observed and their area percentages increase with increasing torsion angles during SDT. The microtexture evolution states that the deformation texture first approaches to the B fiber (0, 90, 0 to 60 deg), and then stays away from B fiber (0, 90, 0 to 60 deg) with increasing plastic strain during SDT. The change of deformation texture is mainly attributed to the appearance of {10-12} twin. However, the deformation texture is always close to B fiber (0, 90, 0 to 60 deg) during ACT. Finally, the effects of different dislocation movements caused by SDT and ACT are discussed. Quantities of subgrains with high density dislocation are observed during SDT while the {10-12} and {11-22} twins intersect with each other, and high density dislocations distribute the twin during ACT.

Micro-structural Evolution in Metals Subjected to Simple Shear by a Particular Severe Plastic Deformation Method

Simple shear (SS) has been considered an optimal deformation method of severe plastic deformation (SPD). To achieve SS, a particular SPD method known as mutative channel torsion extrusion (MCTE) was designed based on the geometric equivalence of SS, and the cavity parameters of a die were calculated according to strain equivalence. To investigate the characteristics of micro-structural evolution subjected to MCTE, simulated and experimental investigations were conducted. The simulated results indicate that equivalent strain distribution on the cross section is relatively uniform, and the metallographic observations confirm the simulated phenomenon. Transmission electron microscopy investigations show that the process of grain refinement undergoes the formation of shear bands, dislocation cells, dislocation forests, large-angle grain boundaries, and recrystallization nuclei. Two types of mechanisms are proposed in view of the different effects of SS on grain refinement. Eventually, MCTE is ensured as an effective method for grain refinement.

Chemical solution approach to SrTiO3 synthesis using a new precursor

We have synthesized SrTiO3 (STO) using a newly developed precursor route by chemical solution approach. The new STO precursor solution was prepared in ambient atmosphere. Various characteristic methods, including thermal analyses, infrared spectroscopy, and transmission electron microscopic analyses techniques, were applied to study the thermal decomposition and crystallization behavior of STO precursor gel. The acquirement of single-phase STO powders at the different annealing atmospheres demonstrates that STO with perovskite structure is prone to tolerate the oxygen vacancies defect. Epitaxially grown STO film on textured Ni–W substrate by a seeded nucleation method shows a high c-axis orientation and a good out-of-plane texture. Scanning electron microscopy and atomic force microscopy investigations of STO film reveal the continuous, crack-free, and smooth surface morphology. The results suggest that STO film fabricated by the newly developed precursor route may be suitable to be used as buffer layer for subsequent growth of YBCO in coated conductors.

Influence of Deformation Stress Triaxiality on Microstructure and Microhardness of Pure Copper Processed by Simultaneous Torsion and Tension

Simultaneous torsion and tension deformation (STTD) modes were applied on commercial pure copper to investigate the influence of stress triaxiality on microstructure evolution and hardness distribution at room temperature. STTD was divided into pure torsion (PT, a special STTD) and general STTD according to tension loading. Microstructure evolution was observed by optical microscopy, electron backscattering diffraction and transmission electron microscopy. The microhardness distribution was measured on the cross section, and the fracture morphology was observed by scanning electron microscopy. Microstructure observations show that ultrafine grains are separated by high-angle grain boundaries. Microhardness measurements exhibit hardness increased more significantly and uniformly in the specimen processed by general STTD mode than PT mode. Additionally, the fracture morphology indicates the fracture mechanism is different between STTD and PT.

Analysis of Deformation Damage and Fracture of 7050 Aluminum Alloy During Double Shear Based on Experiment and Simulation

Based on the finite element simulation and experimental analysis, this paper mainly studies the deformation damage and fracture of 7050-H112 aluminum alloy during double shear based on the elastic strain energy density. The analyses of deformation damage and fracture for ends-free and ends-constrained specimens in complex stress and strain states have been carried out. The different stress and strain states which are characterized by stress triaxiality and strain Lode parameter have important effects on damage and fracture according to the simulation and experimental results. The final fracture is mainly caused by tensile stress both for specimens with ends free and ends constraint. Meanwhile, the shear planes are mainly in a state of shear strain when fracture occurs according to the analysis of stress triaxiality and strain Lode parameter. Three characteristic areas (radiation area, fiber area and shear lips) are observed from fracture morphology and account for different proportions on fracture surface for ends-free and ends-constrained specimens. The simulated results on the damage evolution and fracture from finite element method (FEM) are in good agreement with the experimental ones. Besides, there are competitive relations between ductile fracture and brittle fracture during the process of fracture in this paper.

Computation of macro-fiber composite integrated thin-walled smart structures

Due to high flexibility, reliability, and strong actuation forces, piezo fiber based composite smart material, macro-fiber composite (MFC), is increasingly applied in various fields for vibration suppression, shape control, and health monitoring. The complexity arrangement of MFC materials makes them difficult in numerical simulations. This paper develops a linear electro-mechanically coupled finite element (FE) model for composite laminated thin-walled smart structures bonded with MFC patches considering arbitrary piezo fiber orientation. Two types of MFCs are considered, namely, MFC-d31 in which the d 31 effect dominates the actuation forces, and MFC-d33 which mainly uses the d 33 effect. The proposed FE model is validated by static analysis of an MFC bonded smart plate.

Micromechanical behavior of single-crystal superalloy with different crystal orientations by microindentation

In order to investigate the anisotropic micromechanical properties of single-crystal nickel-based superalloy DD99 of four crystallographic orientations, (001), (215), (405), and (605), microindentation test (MIT) was conducted with different loads and loading velocities by a sharp Berkovich indenter. Some material parameters reflecting the micro mechanical behavior of DD99, such as microhardness H, Youngs modulus E, yield stress σy, strain hardening component n, and tensile strength σb, can be obtained from load-displacement relations. H and E of four different crystal planes evidently decrease with the increase of h. The reduction of H is due to dislocation hardening while E is related to interplanar spacing and crystal variable. σy of (215) is the largest among four crystal planes, followed by (605), and (001) has the lowest value. n of (215) is the lowest, followed by (605), and that of (001) is the largest. Subsequently, a simplified elastic-plastic material model was employed for 3D microindentation simulation of DD99 with various crystal orientations. The simulation results agreed well with experimental, which confirmed the accuracy of the simplified material model.