Papers by Keyword: Microstructure

Abstract: Near α titanium alloys have found wide application as compressor blades, fins in aero engines [1]. In order to achieve better fuel economy, there is a major focus to increase the operating temperature of these components. Addition of small amount of silicon has been found to significantly improve creep resistance [2-7]. Highly stable grain boundary precipitates could reduce the grain boundary sliding and uniform precipitation could restrict the dislocation creep at high temperature. Applications of Si added titanium alloys are limited up to 600oC. Ge being analogous to Si shows better solid solubility, particularly at room temperature [8]. Consequently, it can lead to solid solution strengthening. It has also been reported that germanides have better thermal stability compared to silicides [8]. However, there is no investigation available on the effect of Ge on the microstructural evolution in near α titanium alloys. Therefore, the present study aims at understanding the effect of Si and Ge addition on the evolution of microstructure in near α titanium alloys.

Abstract: The combined effects of the Co addition and Ultrasonic Vibration (USV) on microstructure and properties of Al–20Si–2Cu–1Ni–0.6Mg alloy were studied in this paper. The volume fraction of Co-bearing intermetallic compounds was increased with the increasing of Co content when various levels of Co (from 0% to 1.5%) added respectively into the alloys whether they formed in traditional casting or with USV treatment. The Co-bearing compounds presented as Chinese script or granular when Co was equal or less than 0.7% and turned into dendritic or fish-bone shape when Co was more than 0.7%. USV treatment applied around liquidus temperature of the melt could lead to a refinement of Co-containing compounds by promoting nucleus formation, hindering preferential growth on certain direction, and enlarging solute diffusion coefficient. The addition of equal or less than 0.7% Co, as well as application of USV is very effective in promotion of tensile strength of the hypereutectic Al–Si alloys.

Abstract: As-cast Mg-2Zn-1Mn-xCa (x=0.5 and 1.5 wt.%) alloys are extruded a 553K with an extrusion ratio of 11.3:1 as biomedical materials. The microstructures of the extruded Mg-2Zn-1Mn-xCa alloys are investigated. Microstructures show that the dynamic recrystallization (DRX) occurs after the extruded process. The grain size of the extruded Mg-2Zn-1Mn-1.5Ca alloy is significantly refined compared to that of Mg-2Zn-1Mn-0.5Ca alloy. The tensile strength increases and the elongation decreases with an increase of Ca content. The improvement of tensile strength can be attibuted to the pesence of Mg₂Ca phase. However, Mg₂Ca phase is bristle, which results in the elongation reducing.

Abstract: The microstructures of fine recycled concrete aggregate (FRCA) after modifications in cement mortar were studied. The result indicated that the modification of RFA could strengthen the enhancement effect on microstructure when modified by 20wt% silica fume (SF) grout, 10wt% Polyvinyl alcohol (PVA) solution. After modification by SF grout and PVA solution, the thickness of interfacial transition zone (ITZ) of RFA cement mortar was decreased by 50% compared with the unmodified samples. The ITZ between RFA and cement paste was studied and the surface microstructure and sectional morphology of RFA was observed by scanning electron microscopy (SEM). Analyzing the modification mechanism and Building the superficial micro-structure model of RFA in cement mortar was carried out.

Abstract: In this study, Ni60/Ni-WC composite coatings were first prepared by plasma spraying. Then, the coatings were remelted successively with a CO₂ laser. The influences of laser power on the microstructural characterization and microhardness of the coatings were investigated. The results show that the defects of as-sprayed coating like lamellar stacking microstructure and pores were eliminated by laser remelting, and the remelted coating possessed a denser microstructure. With the increase of the laser power, the burning loss and dissolve of the WC particles is increased, while the dilution rate of the coating becomes large. The laser-remelted samples had higher hardness than the as-sprayed one. Laser power has a great impact on the coating and an optimized process parameter is helpful to achieve appropriate melting of WC particles, which leads to retain a high proportion of hard phase in the coating, good combination between the WC particles and Ni-base matrix alloy, and high microhardness.

Abstract: In this study, Al₂O₃–13 wt% TiO₂ ceramic powders was perset on the substrate of a GH416 Ni-base superalloy by the squash presetting method and cladding coatings were fabricated by a fiber laser. Influences of substrate preheating on the microstructure and interface characterization of laser-clad ceramic coatings were investigated. The results show that the crack formation of the clad ceramic coating can be prevented by substrate preheating. In addition, substrate preheating is helpful to form a good metallurgical bonding between the coating and substrate. Clad ceramic coatings with dense structures, crack-free, low dilutions and good metallurgical bonding to substrate were obtained under the optimum processing parameters. The cross-section of the clad coating indicated three different microstructural regions, namely, fine equiaxed crystals at the upper region, columnar crystals in the middle region, and very fine equiaxed crystals at the bottom region.

Abstract: To produce 130MPa reactive powder concrete with iron tailing sands as aggregation in an economic hot curing system, the effects of curing temperature, curing time and curing conditions on the reactive powder concrete was studied, the reasons of the strength of reactive powder concrete in different curing systems has the difference from the submicroscopic structure point of view was analyzed. The results show that use 90°C hot water to cure reactive powder concrete for 48h can lead it’s 28 day compressive strength reaches 140MPa, the flexural strength reaches 28MPa.

Abstract: In this work, the influence of Ca addition on the power loss of MnZn ferrites was investigated. Mn–Zn ferrites were prepared by conventional oxide ceramic process from calcined powders of different particle sizes in equilibrium sintering atmosphere. It has been found that the optimal amount of Ca addition varies for the Mn–Zn ferrites synthesized by using powders of different particle size.

Abstract: Microwave dielectric properties and microstructures of (Ca_0.8Sr_0.2)ZrO₃ ceramics prepared by the conventional solid-state route have been studied. The values of the dielectric constant (ε_r) were 22-26. The Q×f values of 10400–11500 GHz were obtained when the sintering temperatures were in the range of 1400–1490°C. The temperature coefficient of the resonant frequency τ_f was not sensitive to the sintering temperature. The ε_r value of 26, the Q×f value of 11500 GHz, and the τ_f value of-9 ppm/°C were obtained for (Ca_0.8Sr_0.2)ZrO₃ ceramics sintering at 1490°C. The ceramic, (Ca_0.8Sr_0.2)ZrO₃ is proposed as a suitable candidate material for application in highly selective microwave ceramic passive components.

Abstract: The electrical and physical properties of ZnO-CeO₂ thin films on n-type Si (100) substrates have been examined by sol-gel method. In addition, the structures were heat treated at different temperatures from 600 to 700^oC using the RTA (Rapid Thermal Annealing) process and investigated the influence of RTA effect on their properties. The diffraction pattern showed that the deposited films exhibited a polycrystalline microstructure. All films exhibited ZnO-CeO₂ peaks orientation perpendicular to the substrate surface and the grain size with the dependent on annealing temperature. The dependence of the physical and electrical characteristics on various annealing temperatures was investigated.