Key Engineering Materials Vols. 336-338

Abstract: In this work, the reaction between Ti3AlC2 and Cu in the synthesis process of Cu/Ti3AlC2 composites has been studied. According to the results of XRD, SEM and EDS, Ti3AlC2 reacts easily with Cu to generate TiC and intermetallic compound Cu9Al4 when the holding temperature is higher than 950°C, no matter how much Cu is contained. In addition, when the content of Cu increases, more layered Ti3AlC2 grains react with Cu and form irregular shaped grain containing Cu, Ti, Al and C elements. Therefore, the Cu/Ti3AlC2 composites cannot be synthesized above 950°C by hot-pressed method if no specific treatment is used.

Abstract: Laser cladding technique was used to form Ni3(Si,Ti) intermetallic composite coating reinforced by in-situ formation TiC particles on Ni-based superalloy substrate. The experimental results showed that an excellent bonding between the coating and the substrate was ensured by a strong metallurgical interface. The clad coating was very well and free from cracks and pores. By means of scanning electron microscopy (SEM), energy dispersive spectroscopy (EDS), and X-ray diffraction (XRD), the effect of Ti-C addition to the microstructure and microhardness of the coating was investigated. The microstructure of the coating was mainly composed of Ni(Si), Ni3(Si,Ti) and TiC. The average microhardness of the coating was improved with increasing the Ti-C content. The microhardness was up to 780Hv when Ti-C addition was 20 wt. pct, which was much greater than that of Ni-based superalloy substrate.

Abstract: Ti5Si3-TiC-Ti3SiC2 composites containing different Ti3SiC2 volume fractions from 0 to 50% were in-situ fabricated by spark plasma sintering using Ti and SiC powders through adjusting the molar ratio of Ti to SiC. The morphologies of the fracture surfaces were analyzed by scanning electron microscopy (SEM). The room temperature mechanical properties of composites including hardness, bending strength and fracture toughness were tested.

Abstract: Green compact containing Yellow River sand and several additives was prepared by slip casting and the as-made compact was used to synthesize SiAlON multiphase ceramics by carbothermal reduction nitridation. The processing parameters of slip casting including the type and concentration of dispersant, solid loading, ball milling time, pH value and particle size distribution were optimized by orthogonal experiments. The results indicated that the raw materials could disperse uniformly in the suspension under the use of the mixed dispersant of skip liquid (SL, PT) and sodium carboxymethylcellulose (CMC). The green body with high bulk density of 1.86 g·cm-3 was obtained. After sintered in flowing N2, the compact could transform to SiAlON multiphase ceramics.

Abstract: Steel-bonded cemented carbide GT35 was fabricated from natural ilmenite by in-situ synthesis and vacuum pressureless sintering. The thermodynamics of the synthesis process were analyzed. The results indicated that the stable phases were TiC and iron in the FeTiO3-C system. During the synthesis process, ilmenite was reduced by graphite via a series of titanium oxides to obtain hard phase (TiC) and the steel matrix as the ultimate products. The experimental results shown that GT35 had a reasonable phase composition and fine TiC particles embedded uniformly in the steel matrixes. The composites exhibited excellent mechanical properties: the relative density was higher than 97%, the hardness reached HRC 61.5 and the maximal bending strength was about 1270MPa.

Abstract: Cu/Ti3AlC2 cermets prepared by pressless sintering a mixture of Ti3AlC2 and copper powders were investigated. It was found that the Cu/Ti3AlC2 possesses an unusual microstructure made up of sub-micro-sheet layered Ti3C2 and Cu-Al alloy within one Ti3AlC2 particulate. The fracture strength measured by the three-point-bending manner is increased but the deformation rate is reduced with increase in the volume content of Ti3AlC2 from 30 % to 90 %. The highest fracture strength reached to as higher as 983.9 MPa, corresponding to an extreme strain of 2.64 %. The fracture in mode was changed from brittle to ductile with reduce in the content of Ti3AlC2. The higher fracture strength can be attributed to a stronger interface bond between Ti3AlC2 and Cu-Al phase. A significant network feature formed by the Cu-Al alloy surrounding Ti3AlC2 particulates was observed from the fracture face.

Abstract: Titanium aluminide composite reinforced with submicron Al2O3 has been prepared by a reactive hot press method using TiO2, Al and Ti powder as source materials. The reaction synthesis processing is particularly investigated. Results show that the matrix of the as-prepared material is a mixture of TiAl and a small amount of Ti3Al. Fine Al2O3 particles that act as reinforcing phase are dispersed along the interface of the matrix. The reduction of TiO2 involves many transitional stages, including Ti-Al reaction, TiO2-Ti reducing reaction, reaction between TiO2 and Al, etc.

Abstract: PST/Bi2Ti2O7 composite thin films were prepared by sol-gel method through heavily doping Bi3+ into lead strontium titanate (PST). The film with mono pyrochlore phase of Bi2Ti2O7 was also fabricated by controlling the Ti content in precursors. XRD, SEM and impedance analyzer measured the phase status, morphology and dielectric properties of the thin films, respectively. As a result, in the composite thin films, there was some Pb and Sr dissolved in Bi2Ti2O7, and the amount of dissolving ions decreased with the reduction of their composition in precursors. Bi4Ti3O12 impurity in crystalline Bi2Ti2O7 was due to the instability of Bi, and excess Ti in stoichiometry could make the film maintain to be mono pyrochlore phase. PST/Bi2Ti2O7 composite thin films had lower permittivity and lower dielectric loss than mono PST thin films.

Abstract: Copper-coated alumina powders were prepared by a chemical plating method. The processing parameters such as compositions of plating solution, dispersants and passivants were optimized to obtain high-quality Cu-coated alumina powders. The phase composition, surface morphology and granularity of the coated powders were analyzed. Experimental results showed that the alumina powders coated with copper can be successfully prepared by the chemical plating method at room temperature, and the additions of dispersant and passivant can sufficiently improve the dispersity of powders and can depress the oxidation of copper layers precipitated from the plating solution. The granularity of alumina powders is increased by about 60 nm after being coated with the copper layer.