Materials Science Forum Vol. 1054

Abstract: The metallographic analysis method is used to study the original austenite grain change law of Nb-containing high-strength ship steel. Adding Nb to the experimental steel will refine the grains to a certain extent. Different Nb content, the corresponding grain size change trend is different. Under the experimental heating environment of 850°C~1150°C, the grains of the two experimental steels have different degrees of coarsening at different heating temperatures. Compared with the low-C and high-Nb steel (EH36) with the high-C and low-Nb steel (AH36), the former can not only control the austenite grain growth well at lower temperature, but also has a strong inhibitory effect in a higher temperature environment. Based on the experimental data, the austenite grain growth kinetic model of the two experimental steels at the heating temperature of 850°C~1150°C is obtained.

Abstract: In this paper, we emphasize that the thermodynamic basis of displacement concept is finite equilibrium region and quasi-static process. By considering the dynamic process of a particle system undergoing reversible deformation under external force, the spatial and temporal distributions of mesoscopic mass, mesoscopic mass flow, mesoscopic energy, and mesoscopic stress are calculated using corresponding mesoscopic theory (e.g., Hertz contact mechanics). Their macroscopic correspondence is calculated by means of coarse-grained average, and the resulting macroscopic mass and mass flow are substituted into the equation that defines the displacement, and the displacement is calculated by integration.

Abstract: In order to analyze the influence of Al-Ag doping on the electrical properties of eigenstate and oxygen vacancy ZnO resistor valves, first principles were used to analyze the crystal structure of Al-Ag single doping and co-doping eigenstate and oxygen vacancy ZnO. Energy, band structure, density of states and electrical conductivity have been calculated. The results show that after doping with acceptor elements, the lattice parameters of the eigenstate unit cell and the oxygen vacancy unit cell are increased, and their potential can be increased. Gradient; when Ag is doped, its formation energy is the lowest, indicating that Ag doping is easier and higher stability; when oxygen vacancies, the nonlinear characteristic of ZnO resistor valve is better than that of eigenstate, but whether it is single doping or Co-doping does not improve its nonlinear characteristics better; doping will slightly increase its conductivity, and the conductivity of Ag doping is the best.

Abstract: Hot dip galvanizing can effectively prevent the corrosion of steel. With the increasing demand of industry for steel strip, higher requirements are put forward for stable and continuous operation of submerged roller bearings in hot dip galvanizing line. The existing sliding bearings for sink roll of galvanizing line mainly depend on imports, and their service life is about two weeks. Two weeks later, the sliding bearing failed, so it is necessary to stop the line and replace the new bearing, wasting a lot of material cost and time cost. In this paper, zinc liquid corrosion test, high temperature pin-and-disc dry friction test and corrosion wear test were carried out on the materials of sliding bearing pair of submerged roller, mainly alumina ceramic bushing and three kinds of metal sleeves (alloy A, alloy B and 316L stainless steel) under simulated actual working conditions. The status of corrosion and wear in bearing failure was compared and analyzed, and the hydrodynamic lubrication effect formed by zinc liquid under test conditions was considered, and the main failure mechanism was comprehensively analyzed.

Abstract: In this work, CdS nanosheets were synthesized by microwave hydrothermal method. We used a simple synthesis method to prepare Mn₃O₄/CdS composites. The crystal phase, surface chemical component and optical properties of Mn₃O₄/CdS, Mn₃O₄ and CdS were analyzed based on the characterizations such as XRD, FT-IR, DRS and PL. Mn₃O₄/Cd composites showed obvious broadened visible-light adsorption at wavelength over 460 nm. When the mass ratio of Mn₃O₄ and CdS was 1.0%, Mn₃O₄/CdS displayed the best RhB degradation efficiency which was 22.39% higher than the pure CdS. The improved photocatalytic efficiency should be attributed to the lower photo-induced electron–hole pair recombination rate and accelerated transfer rate of photogenerated electrons based on heterojunction structure. The achievements provided new way to exploring novel CdS-based heterojunctions for decomposing organic pollutants.

Abstract: When three welding conditions, including welding configuration, welding speed and laser power, are sequentially altered, supersaturation of liquid aluminum is crystallography-dependently determined to limit growth kinetics of dendrite tip with decease of thermo-metallurgical factors for solidification cracking to salvage the weld properties during emerging laser welding repair of multicomponent nickel-based single-crystal superalloy. After comparing growth crystallography between right side and left side of weld, the distribution of supersaturation of liquid aluminum is axis- symmetrically developed by favorite (001)/[100] dendrite growth kinetics, while the distribution is nonaxisymmetrically developed by detrimental (001)/[110] dendrite growth kinetics. High heat input is inappropriately procured by either high laser power or slow welding speed to insidiously boost supersaturation of liquid aluminum, worsen alloying partition and solute copiousness, heterogeneously exacerbate morphology and size of dendrite growth, whereby stray grain formation is strongly produced. In order to ameliorate dendrite growth, low heat input is usefully rendered by either low laser power or high welding speed to attenuate supersaturation of liquid aluminum, narrow solidification temperature range and obviate dendrite tip undercooling alongside columnar interface in order to augment crack-resistant dendrite of epitaxial growth. The overall supersaturation of liquid aluminum is crystallography-dependent. During across whole melt-pool solidification interface, supersaturation of nonsymmetric (001)/[110] welding configuration is not as small as symmetric (001)/[100] welding configuration under well-controlled heat input, thereby fosters the kinetic factors for stray grain development to obstruct columnar dendrite and consequently weaken unidirectional morphology. It is crystallographically favorable for relief of supersaturation with axis- symmetrical dendrite growth. The mechanism of crack-vulnerable dendrite growth elimination through circumspect improvement of supersaturation-controlled growth kinetics is constructively proposed for feasible crackless rejuvenation of laser welding or laser cladding. The theoretical predictions are scrupulously supported by corroborative metallograph observation.

Abstract: The dependency of morphology development and dendrite growth on welding conditions (laser power, welding speed and welding configuration) is numerically analyzed to decrease nucleation and growth of stray grain formation during laser processing aerospace component surface of ternary Ni-Cr-Al single-crystal superalloy. Proper (001)/[100] welding configuration crystallographically initiates three axisymmetrical distributions of microstructure development, i.e. stray grain formation, morphology development and dendrite trunk spacing, alongside the advancing solid/liquid interface of molten pool, whereby metallurgical properties are increased. Unpromising (001)/[110] welding configuration tends to crystallographically possesses unaxisymmetrical microstructure development to favor substantial crack-vulnerable dendrite size and morphology. Epitaxial [001] columnar dendrite growth region is favored for single-crystal dendrite growth, while vulnerable [100] equiaxed dendrite growth region is more susceptible to solidification cracking. The lower heat input is used, the smaller stray grain formation, negligible columnar/equiaxed transition (CET) and finer dendrite trunk spacing are consistently promoted by narrower constitutional undercooling ahead of solid/liquid interface to improve crack-resistant microstructure development and weld integrity. When comparing between [100] dendrite growth region on the right side and [010] dendrite growth region on the left side, (001)/[110] welding configuration spontaneously engenders severer stray grain formation, insidious columnar/equiaxed transition and coarser dendrite trunk spacing on the right side to deteriorate microstructure development with restriction of the same heat input on both sides of weld pool. The mechanism of asymmetrical solidification cracking as result of crystallography-induced microstructure degradation is therefore proposed. The theoretical predictions of asymmetrical solidification cracking susceptibility are comparable with experiments.

Abstract: The heat dissipation of electronic components is of great importance to the development of microelectronics industry. Polymer matrix composites have become a research hotspot due to their advantages in molding, insulation and cost. In this paper, the mechanism and influencing factors of thermal conductivity of polymer matrix composites are introduced, the research status of thermal network formation is reviewed, and the development trend of thermal conductivity composites is forecasted.

Abstract: In order to study the influence of the pitch of the spiral toolpath on the forming quality in the single-point incremental forming, three kinds of spiral toolpath with pitch of 0.2 mm, 0.5 mm and 1 mm were generated by using the UG software, and the thickness distribution, contour dimensional accuracy and equivalent stress of the formed parts based on the spiral toolpath with the three kinds of pitch were compared and analyzed through numerical simulation by using the ANSYS/LS-DYNA software. The research result show that the smaller the pitch of the spiral toolpath, the better the forming quality of the formed part.

Abstract: This paper examines the forming of sheet materials by incremental forming. Proposed and researched methods of deformation and the tool path based on which choice is the most appropriate circuits and paths for receiving the hemispherical parts. Abaqus software package is used to develop a method to model incremental forming. All simulation results are analyzed and considered during making conclusion about this forming process.