Papers by Keyword: Hot-Pressing

Abstract: An Al-5vol%Ti3SiC2 nanocomposite has been prepared by ball milling technique. Steel ball, agate ball and zirconia ball were selected during the ball milling process and then the microstructure evolution of the powder mixture was investigated. The homogenous fine mixed powder can be obtained with zirconia ball, whereas the conglomeration will be formed in the case of steel ball and agate ball. The bulk Al/Ti3SiC2 nanocomposite was fabricated by hot pressing technique. The effects of the particle size and agglomerate state of Ti3SiC2, as well as the microstructure of Al/Ti3SiC2 nanocomposite were studied by SEM and TEM. It was found that the nanosized Ti3SiC2 particle could be obtained during the ball milling process and distributed in aluminium homogenously.

Abstract: It is generally known that Ag-CdO electric contact material excels others in characteristics. Thus, the contact material has been widely used, regardless of current strength. However, in a view point of environment, the advanced electric contact material without environmental load element such as cadmium has to be developed. Extensive studies have been carried out on Ag-SnO2 electric contact material as a substitute of Ag-CdO contact materials. In the manufacturing process of Ag-SnO2 electric contact material, it can be mentioned that typical internal oxidation process is not suitable to produce Ag-SnO2 electric contact material because the Sn located around surface may interrupt oxidation of Sn in the middle of material. Therefore, in the present study, powder metallurgy including compaction and sintering is introduced to solve the incomplete oxidation problems in manufacturing process of Ag-SnO2 electrical contact material. The formation of the blends was manufactured by wet blending of powders of Ag and SnO2. The quantity of SnO2 powder was 15wt.%, with intent to optimize the powdering process for the minute powder of which diameter is less than 5μ m. Particle size and grain distribution of Ag powder and SnO2 powder by powder metallurgy were measured by image analyzer. In order to estimate the properties of specimen tested with a variation of mixed time, the micro-hardness measurement was carried out. The Ag-SnO2-based contact material, which was produced through this study, was actually set in an electric switchgear of which working voltage is 462V and current is between 25 and 40A, for the purpose of testing its performance. As the result, it excelled the existing Ag-CdO-based contact materials in terminal-temperature ascent and main contact resistance.

Abstract: Microstructure and mechanical properties of 20% Al-Cu-Cr/Al composites synthesized by hot-pressing technique after annealing, quenching and aging was studied by means of X-ray diffractometer (XRD), scanning electron microscopy (SEM) and transmission electron microscopy (TEM) and uniaxial compressive test. Microstructure of Al-Cu-Cr particles in the composites after hot-pressing is mainly consist of icosahedral quasicrystals and which transformed into decagonal quasicrystals after annealing. Microstructure of matrix in the composites after hot-pressing, annealing, quenching and aging is pure Al, Al + Al2Cu, supersaturated solid solution Al and Al + Al-Cu transition phases respectively. Hardness, fracture strength and the Young’s modulus of the composites are improved by age-hardening.

Abstract: Continuous carbon fiber-reinforced silicon carbide (Cf/SiC) composite was fabricated by hot-pressing, via liquid phase sintering. Sintering conditions strongly affect the densification process, and therefore dominate the mechanical properties and fracture behavior. The composites under the lower sintering temperature behaves less densified matrix and it demonstrates a relatively weak fiber/matrix bonding allowing the longer fibers pull-out. Increasing sintering temperature could accelerate the densified matrix and make fiber/matrix bonding stronger. In this case, the shorter fibers pull-out was predominant fracture behavior and it could improve mechanical properties.

Abstract: Sodium superionic conductor, NASICON ceramic (Na1+xZr2SixP3-xO12, x=2), was hot-press sintered under different temperatures and the electrical properties of the obtained different samples were investigated. Results show that the relative density of the ceramics can be improved by hot-press process efficiently and the crystal size of the samples are closely related to sintering temperature. With the increase of sintering temperature, both the density and the crystal size of samples increase obviously, resulting in the increase of ionic conductivity of samples as the sintering temperature. When the sintering temperature reaches 1150oC, the ionic conductivity of sample is as high is 3.6×10-3S/cm, which is obviously higher than that of sample sintered at 1000oC (2.13×10-3S/cm). As the frequency increase, the real parts and the imaginary parts of complex dielectric constants for all the samples decrease in 8.2 GHz~12.4GHz frequency band. The ceramics obtained at the higher temperature possess the higher dielectric constant.

Abstract: A new method to synthesize high-purity Ti3AlC2 bulk material by hot-pressing was presented through adding a little amount of B2O3 as a low-temperature aid. The elemental Ti, Al, and active carbon powders were used as raw materials with a molar ratio of 3:1.2:2.The effect of sintering temperature on the purity of Ti3AlC2 was investigated at the range of 1200°C to 1500°C. XRD and SEM were used to characterize the product synthesized. High-purity Ti3AlC2 bulk materials, in which almost no TiC phase could be found, were synthesized by hot-pressing at 1400°C and 1500°C for 1h in flow Ar atmosphere. The roles of B2O3 addition were considered as weakening the thermal explosive reaction in the mixture of elemental Ti, Al, and active carbon and increasing the purity of Ti3AlC2 in addition.

Abstract: Ti3SiC2 bulk materials by hot-pressing sintering were presented through adding a little amount of B2O3 as a low-temperature additive in different raw-material systems. In one system, elemental titanium, silicon and active carbon were used as reactants with a molar ratio of 3: 1: 2. In another one, titanium carbide, titanium and silicon reacted together with a molar ratio of 2:1:1. At different temperatures, samples were synthesized by hot-pressing with a heating rate of 30°C min-1 before 1200°C and then 10°C min-1 to peak temperatures, holding for 2h. The effect of sintering temperature on the purity of Ti3SiC2 was investigated at the range of 1200°C to 1500°C. The products mainly contained Ti3SiC2 with TiC as the second phase. In some cases, Ti5Si3 appeared as well. When sintered at 1300°C, above 98vol% Ti3SiC2 was obtained in the elemental system. The roles of B2O3 additive were considered as weakening the thermal explosion reaction in the elemental mixture and affecting the diffusion procedure at low temperature in both systems.

Abstract: Al2O3/Ni composite ceramics toughened by metallic particles was fabricated by the vacuum reduction of Al2O3 and nickel nitrate (Ni(NO3)2•6H2O) mixed powders at 800-1000° for 2-4h and hot pressed at 1400° ~ 1500°C for 1-2h. Three-point bending strength and facture toughness of the composite were studied. With the increase of Ni content, its flexural strength and facture toughness increases significantly. Microstuctural investigations of the composite revealed that fine nickel particles dispersed homogeneously at the matrix grain boundaries, forming the intergranular nanocomposite.