Papers by Keyword: Hardening Mechanism

Abstract: Selective laser melting (SLM) can produce Ni-based superalloys with a unique hierarchical structure consisting of micrometer-scale crystallographic lamellar microstructure and nanometer-scale cellular structure under optimized process parameters. This work investigated the effects of input energy density on the morphology of the cells and its influence on the tensile properties of Ni-based superalloy prepared by SLM. We found that the cell spacing decreases with decreasing input energy density. Further investigation of the cells clarified that the boundary of cells is a low angle grain boundary with dislocation cell wall and segregation of certain elements such as Nb and Ti. Moreover, it was demonstrated that the boundary of cells performs as a significant barrier to the griding dislocation. Thus, the cell boundary leads to strong strengthening through the Hall-Petch law.

Abstract: This article studies the mechanism of work hardening of austenitic high manganese steel alloyed with chromium and vanadium. The steel was annealed at 650°C before austenitizing at 1100°C, and then was quenched with water. We have observed that after the heat treatment, the size of austenite grain was small (1,950μm² - level 6). The hardness of the steel was 223HB and the toughness was 115J/cm². After impact loading, there was no martensite but twinning and sliding in the microstructure of the steel. The nano austenite was found in the microstructure. The steel was also hardened by small austenite grain and the carbide particles were finely dispersed in the microstructure.

Abstract: The AlMgSi1 alloy is generally used in automotive industry owing to its excellent mechanical properties, which can be further improved by applying severe plastic deformation and heat treatment. The dislocation density in the material increases significantly during severe plastic deformation due to the characteristic intensive shear strain. Therefore the motion of dislocations becomes more and more retarded, consequently the strength improves. In addition, the motion of dislocations can be prevented by aging due to formation of coherent precipitations in the metal matrix in order to realize further increasing in strength. In this paper the combined effect of severe plastic deformation and artificial aging treatment on the evolution of mechanical properties was investigated. The samples were subjected to multiple forging (MF) process at room and enhanced temperature. One part of the deformed samples were heat treated at 150°C for different times. The deformed as well as deformed and heat treated samples were investigated by micro hardness testing and X-ray profile analysis.

Abstract: This article researched the cementation and hardening mechanisms of cement asphalt emulsion and waterborne epoxy mortar by using the XRD, and heat of hydration testing methods. The results of this study show that the mixture of cement with epoxy and cement- asphalt-epoxy are endothermic reaction. There are occurring endothermic reactions between cement with epoxy. The waterborne epoxy resin and basic structure unit of ettringite [Ca3Al(OH)6•12H2O] were reacted and formed Ca-complex at earlier period of hydration.

Abstract: In most of the simulation studies of equal channel angular pressing (ECAP) it has been assumed that materials obey isotropic hardening law. However, in the case of precipitation hardenable alloys, an accurate prediction of the deformation behavior requires incorporation of kinematic hardening model. In this study, the influences of kinematic, isotropic and combined hardening laws on deformation behavior have been investigated. For this purpose, an ECAP die consisting of two 120° channels has been selected, and the effect of hardening law on the strain profile and ram pressure at the final exit channel has been studied. The simulation results showed that the hardening mechanism does not affect the strain profiles extensively; but, when kinematic hardening mechanism was considered the ram pressure decreases significantly due to less hardening of the material during reverse loading in the final exit channel.

Abstract: To develop Cu alloy with tensile strength of 800 MPa and electrical conductivity of 80 %IACS (International Annealed Copper Standard), the variation of mechanical strength and electrical conductivity in Cu-Ag alloy during fabrication processes including casting, solid solution and ageing treatment were investigated. Solid solution hardening leads to a large drop in electrical conductivity of Cu-Ag alloys due to super-saturation of Ag solute in Cu matrix. Ageing hardening gives rise to enhance both of the mechanical strength and the electrical conductivity. Therefore, it can be mentioned that the electrical conductivity of Cu-Ag alloys was affected dominantly by Ag solute in Cu matrix.

Abstract: The temperature, time and cooling rate are key factors in the hardening process using the grinding heat instead of the high frequency induction heat source. Thus, this paper established the mathematical model estimating the grind-hardening temperature, experimentally determined the grinding temperature and the cooling rate of different grinding parameters for 48MnV microalloyed steel using the conventional aluminum grinding wheel on a surface grinder, and investigated the grind-hardening effects and the forming mechanism of grind-hardening layer. The results show that the estimating temperatures are comparatively close to the measuring ones and hence the model could be utilized to optimize the processing parameters, and the satisfactory grind-hardening temperature and cooling rate could be achieved under the optimized processing parameters. The microstructure of the grind-hardening layer, the fine needlelike martensite in the entirely hardened zone, the martensite and ferrite in the transitional region is similar to that acquired through the high frequency induction technique. Especially, the average hardness of the entirely hardened zone is 740HV and the depth of the hardened layer is adjacent to 1.5mm, which indicate that the grind-hardening effects are very excellent. Different from the forming mechanism of the high frequency induction hardened layer, higher grind-hardening temperature is needed to compensate shorter time austenitization, and because of thermo-mechanical loading induced during grinding, from surface to inside, the morphology of martensite changes from fine to thicker, then to finer, other than from thick to finer.