Advanced Materials Research Vols. 306-307

Abstract: To study the transmutation of organization and texture on direct annealing process of hot-rolled plate. Different annealing experiments were done in the lab. The annealed samples are from steel grade of SPHC. To check the organization of the annealed samples by optical microscopy, to measure grain size by Micro-image Analysis & process software. To measure the mechanical properties by the room temperature tensile test. To check AlN by TEM and EDX.To measure texture by texture measuring instrument, and the data was collected on a computer, using two-step calculation of ODF, measured with constant 45° section of graph. When annealing temperature of the samples reaches 875 °C or more, a relatively low strength , high n value, and high r value is received, but if the holding time is longer, grain coarsening occurs at the time,so the annealing temperature is not more than 925°C.When annealing temperature reaches 875 °C, AlN increased slightly, and the texture is not obvious.

Abstract: Based on microstructure evolution of Mg-20Al-0.8Zn magnesium alloys realized by semisolid isothermal heat-treatment (SSIT), we obtained the non-dendrite or spherical grains microstructure under the suitable technological parameters that isothermal temperature is 495 °C and holding time is 120 min. With the help of special experimental equipment, the semisolid die-casting process has been studied and the specimens have been analyzed. The effects of different parameters as injection speed and pressure on tensile strength, elongation rate, hardness, etc have been investigated. The results indicate that tensile strength was improved along with increasing injection speed and pressure. However, excessive speed will involve gas, which formed defects and reduced the mechanical properties. When the injection pressure is 40MPa and injection speed is 4m/s, the tensile strength and elongation rate can reach maximal 220MPa and 5.63% respectively. Its fracture mechanism was intercrystalline cracking.

Abstract: Electrodes can absorb moisture easily so that the diffusible hydrogen is quite high in the weld bead. Fe₃O₄ powder is used to promote the reaction of myristic acid and the electrode surface, and reduce the diffusible hydrogen, because of its excellent microwave absorption property. Electrodes are immersed to the light petroleum solution which contains myristic and Fe₃O₄ particles, then they are put into the microwave oven and become water-resistant . The results of FT-IR and SEM microscope indicate that Fe₃O₄ powder absorb microwave and melt myristic acid to form the water-resistant film. The best ratio of myristic acid in the petroleum ether is 18% and the diffusible hydrogen of the deposited metal of microwave treated electrode decreased to 83% of the untreated electrode.

Abstract: Al-Cu alloy castings are obtained in the vertical centrifugal field. The effects of solution treatment on the microstructures and mechanical properties of Al-Cu alloy casting were studied by OM, micro hardness tester and room temperature tension and compression test. The results show that, the strength, micro hardness and elongation percentage of Al-Cu alloy casting increase firstly and then decrease as the solution temperature increases, and the mechanical properties reach the maximum values as the solution temperature increases to 530°C. As solution time increasing, the mechanical properties of Al-Cu alloy casting increase firstly and then decrease. When the solution time is up to 6 hours, the mechanical properties reach maximum value.

Abstract: The structure made of alloying and coating layers of TiN was achieved on the surface of 20CrNiMo steel by the needle-shape cathode glow discharging. It is aimed to reduce the friction coefficient of the 20CrNiMo and to improve the property of the wear-resistance. The morphology of TiN modified layer at cross section was observed by the scanning electron microscope (SEM). The friction and wear behavior of the TiN layer under dry sliding against GCr15 steel was evaluated on a MFT-4000 high speed to-and-fro wear test rig. The results showed that it was feasible to prepare TiN modified layer of 40μm thickness by the needle-shape cathode glow plasma discharging. It has been found that the TiN modified layer has excellent friction and wear-resistant behaviors. The friction coefficient of the 20CrNiMo substrate was about 0.324 under dry sliding, while the TiN modified layer experienced much abated friction coefficient to 0.169 under the same testing condition.

Abstract: Laser surface cladding of Ti-6Al-4V alloy by Ti+C+Al powders (Titanium and carbon powders with an atomic ratio of 1:1 were mixed with 20-40wt.% aluminum powders) was investigated. TiC particles were in situ formed mainly during the solidification. Effect of Al content on the porosity and microstructure of the cladding layer was studied. The resultant microstructure in the modified surface layer was characterized and the micro-hardness on the cladding layers was measured, as well as the wear rates. The results show that the coating had good metallurgical bonding with substrate when the Al mass fraction in Al-Ti-C system is 30 %. The micro-hardness of coating is 802HV0.5 which is 2~3 times as that of the Ti-6Al-4V alloy approximately.

Abstract: Addition of Ru in Ni-base single crystal superalloys had been used to improve the elevated temperature strength and other multiple properties. Significant decreases in stacking fault energy of the γ phase and the volume fraction of γ′ phase are observed with the addition of Ru. As well as serving as an effective solid-solution strengthening element in high refractory content Ni-base single crystal superalloys, Ru additions are able to effectively strengthen both the γ and γ′ phases and suppress the formation of TCP phases. Due to the changes in the partitioning behavior of elements and the slight decrease in the supersaturation of refractory elements in γ phase associated with Ru additions, high temperature creep resistance and the microstructural stability of the alloy are improved remarkable. The influence of Ru on the microstructure of Ni-base single crystal superalloys is reviewed.

Abstract: To consider the material properties of functional gradient plate structure change along the thickness, in this paper, the wavelet method is used to solve plate differential equations with initial or boundary conditions. An operational matrix of integration based on the wavelet is established and the procedure for applying the matrix to solve the differential equations is formulated, and gets the temperature, stresses and displacement of the plate when the material properties of gradient plate take arbitrary function. The results show that the proposed way is quite reasonable while comparing to the exact solution.

Abstract: Strain-hardening cement-based composites (SHCC) resist increased tensile stress after first crack formation, over a significant range of tensile strain. This increased strength and strain capacity is achieved by effective crack bridging by fibres, across multiple cracks of widths in the micro-range. Whether the crack width limitation translates into increased durability through retardation of ingress of moisture, gas and other deleterious matter, is scrutinised in this paper. The potential of the comparatively new composite material becomes obvious, yet it is clearly outlined that further research is necessary before we fully understand the basic mechanisms underlying durability of SHCC.

Abstract: Series of AZ91 alloy samples are prepared by adding different levels of Mg-Zn-Y quasicrystal master alloy under normal casting condition. The microstructure and mechanical properties of these samples are investigated by using of XRD, SEM, EDS and tensile test. It is shown that morphology of β- Mg₁₇Al₁₂ phase changes from continuous nets to discontinuous nets or even to particles. As results of these changes, the mechanical properties of AZ91 alloys are significantly improved until the addition level passes 6%.