Materials Science Forum Vols. 620-622

Abstract: Pure titanium TA2 and 1Cr18Ni9Ti stainless steel were vacuum diffusion bonded using Nb + Ni foils as interlayers, where Nb foil was adjacent to TA2 and Ni foil adjacent to 1Cr18Ni9Ti. The samples were heated to a temperature of 800°C at a pressure of 10 MPa and kept for 60 min, and then to a temperature of 900°C at a pressure of 1 MPa and kept for 30 min. The mechanical properties of the joint were characterized by the tensile strength test. The average tensile strength of the joints was about 398 MPa. The fracture characteristics of the joint were investigated using scanning electron microscope. The fracture of tensile test samples occurred in the Ni3Nb intermetallic compound formed in the interlayers.

Abstract: Machinable SiC/graphite composites were fabricated by Plasma Activated Sintering (PAS), which characterized by high heating rate, short time sintering and high efficiency process. The staring powder mixture included SiC, graphite power and a few sintering aids. They were sintered by PAS under 30 MPa Pressure in vacuum at 1500°C and 1550°C, respectively. The density, bending strength and hardness were measured. The phase and the microstructure of the composites were also investigated. The results indicated that the relative density of SiC/C(graphite) composite sintered at 1550°C was more than 99.5%, the bending strength was 336.6MPa, but surface Vickers hardness was 5.8GPa far lower than SiC ceramics. The machinability of SiC/Graphite sintered by PAS in 1500°C was good because the continuous weak microstructure played a crucial role in the machining process, including a lot of weak interface between the grains of SiC and graphite partials and nearly 20vol% pores in the composite ceramics.

Abstract: γ-TiAl components due to their unique properties are on the verge of industrial application for increasing operation temperature and improving energy efficiency, especially in aerospace and automobile areas. This paper describes the recent developments of hot precision processing in ingot metallurgy technology including investment casting, canned forging and sheet rolling of TiAl alloys. Alloys development and the melting technology were discussed. Investment casting of TiAl alloys has been successfully developed to manufacture net-shape components. Research aimed at producing TiAl sheets through canned forging and rolling is introduced.

Abstract: The low temperature transformation of ZrO2-3 mol% Y2O3 coatings were investigated at 40 ~100oC using Raman spectroscopy. The results show that the low temperature transformation of ZrO2-3 mol% Y2O3 coatings is considerably effected by water temperature and mainly occurred on the coating surface. However, the transformation can be retarded by addition of Al2O3. The reasons lie in that the addition of Al2O3 can result in improvement of deposition efficiency and Young’s modulus of ZrO2-3 mol% Y2O3 coatings containing Al2O3.

Abstract: HRB500 has been recognized an excellent material for structure. In this paper, Fire Dynamics Simulator (FDS) computer emulator method was adopted to analyze the bending performance and reinforcing ratio of HRB500 and conventional steel bar at the surface temperatures 600°C-900°C and center temperatures of 100°C-300°C underwent fire. The results showed that the HRB500 reinforced bar possessed superior seismic performance after the fire and this is helpful to the future application and design of steel for engineering.

Abstract: C/C-SiC brake materials were prepared by improved chemical liquid vaporized infiltration (CLVI) combined with liquid silicon infiltration (LSI) process, which needed less than thirty hours. The microstructure and frictional properties of the material were investigated. The density and porosity of the C/C-SiC brake material were 2.05 g/cm3 and 4.8%, respectively. The average dynamic friction coefficient of the materials was about 0.36, and the friction coefficient was stable. The average linear wear rate was less than 4.7 µm cycle-1 for rotating and stationary disk. The matrix composition and microstructure resulted in the high frictional performances.

Abstract: Dense multiwall carbon nanotubes (MWNTs) reinforced barium aluminosilicate (BAS)–silicon nitride (Si3N4) composites were fabricated by hot-pressing sintering. The effect of MWNTs on the microstructure, compositional investigations, as well as mechanical characterization of the composites was investigated. The results show that MWNTs were preserved in the composites after sintering and present good adherence to matrix grains. The incorporation of 3% 1-2μm MWNTs effectively improved the fracture toughness of the BAS/Si3N4 composites from 8.02 to 8.6 MPa•m1/2.

Abstract: Two different kinds of mullite precursors with composition 3Al2O3•2SiO2 (3:2) were prepared by conventional drying ethanol solution and spray-drying aqueous solution of aluminum nitrate nanohydrate and tetraethoxysilane, respectively. The results of scanning electron microscope (SEM) indicate that one powder consists of irregular particles with size of 1-10μm, the other powder is made of inhomogeneously sized hollow spherical particles with mean size of 0.5-5μm. The TG-DTA curves indicate the hollow spherical particles are unfavorable to eliminate the decomposed products. After the precursors were sintered by Spark Plasma Sintering at 1450°C for 10min, the microstructures of the former are made of fine equiaxed grains with sizes of around 0.5μm, the latter consist of elongated grains distributed in the matrix of fine grains with imhomogenous size of 0.5~10μm due to the liquid phase forming. The different microstructures lead to the former sintered body is transparent, while, the sample from spray-drying is opaque.

Abstract: Reinforcement was performed to epoxy resin by CaCO3 whisker, and the effect of flexural property of CaCO3 whisker reinforced composite materials was studied. The microstructures of the composite materials were observed by SEM. The results showed that the flexural strength of the composites increased with increasing CaCO3 whisker content, and the flexural strength reached to the maximum value when CaCO3 whisker content was about 15wt.%, and the maximum value was about 11% higher than that of pure epoxy resin. But, the strength would drop sharply with the excessive CaCO3 whisker.

Abstract: “Getting to market first” is extremely intensive pressure on the companies in this competitive business environment. The speed at which products are developed and released to market is tightly linked to profitability and market share. Hence, many companies are still in a desperate need of real Rapid Tooling (RT) technologies which can really help expedite their prototype tooling and pre -production tooling for injection molding. This paper describes how HT (Hybrid Tooling) process has been being successfully established and effectively applied with Metal filled SLS technologies.