Abstract: In this work, a new method to fabricate high-purity Ti3AlC2 powder by pressureless
sintering (PLS) was reported 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 the molar ratio of 3 : 1.2 : 2. The effect of sintering temperature on the purity of Ti3AlC2 was investigated at the range of 800°C to 1400°C. The results showed that high-purity Ti3AlC2 powders, in which almost no TiC phase could be found, were stably fabricated by pressureless synthesis at 1400°C for 5 mins in flow
Ar atmosphere. The roles of B2O3 addition were discussed in the paper.
Abstract: The friction behavior of a high-purity bulk titanium aluminum carbide (Ti3AlC2) material dryly sliding against low carbon steel was investigated. Tests were performed using a block-on-disk type high-speed friction tester under sliding speed of 20 m/s and 60 m/s, several normal pressures from 0.1 to 0.8 MPa. The results showed that the friction coefficient is as low as about 0.18 for sliding speed of 20 m/s and only 0.1 for 60 m/s, and that almost not changes with the normal pressure. The reason could be related with the presence of a surface layer on the friction surface. The layer was analyzed to consist of Ti, Al and Fe oxides, which played a lubricate part inducing the friction coefficient decrease on the friction surface.
Abstract: The investigation on joining of SiC to SiC has been conducted for some years. It is essential that the mechanical and thermal properties of the joints should meet the requirements of engineering. In view of the fact that the ternary carbide Ti3SiC2 has shown unique mechanical and thermal properties, it is promising to join SiC to SiC using ternary carbide Ti3SiC2 as filler (welding compound), and this is the subject to deal with in this paper. The joining of SiC to SiC has been successfully realized by hot pressing reaction joining process using Ti3SiC2 powder as filler. The
optimized technological parameters have been obtained by orthogonal experiments, under which the achieved weld strength is higher than that of the welding base material SiC ceramic. Ti3SiC2 is stable up to 1200oC in Ar atmosphere with an external pressure. At the joining temperatures of 1300～ 1600oC the main phases of the interface are Ti3SiC2, TiC and TiSi2. The mechanism of bonding at the interface is interdiffusion and chemical reaction.
Abstract: In this paper, tribological tests for Ti3SiC2 sliding against low carbon steel were made on a block-on-disc type friction tester, with the normal pressures from 0.1 to 0.8 MPa and the sliding speed of 30 to 50 m/s. The surface state was observed and analyzed by SEM and XRD. A definite tribo-glazing layer was found over the worn surface of the Ti3SiC2 block, which seems to be primary reason for Ti3SiC2 to have comparatively lower friction coefficient and wear rate, because the tribo-glazing layer would be fusible under high frictional temperature. The tribo-glazing layer was the results of tribo-chemical oxidation reaction and the cause forming it could be the high frictional temperature and the mechanical catabolism in the surface of Ti3SiC2 during sliding friction. Due to the tribo-oxidation reaction is un-reversible and self-adaptive, the tribo-glazing layer in area and thickness are function of normal pressures and sliding speed.
Abstract: The erosion resistance of α-Al2O3 ceramics in flowing suspensions of solid particles was investigated with a rotary disk erosion wear tester. The effect of different abrasive particle hardness on its erosion resistance was studied and the microcosmic failure mechanism of its surface was analyzed. The results show that the erosion resistance of α-Al2O3 is more and more excellent than that of the metal Cr15Mo3 with the hardness enhancement of the abrasive particles. When SiO2,
Al2O3, SiC is in turn selected as the abrasive, the erosion resistance of α-Al2O3 ceramics is 4.06, 5.20, 5.77 times than that of Cr15Mo3 respectively due to the different hardness of such abrasives. Due to erosion, Cr15Mo3 is worn out most in the whole, the erosion holes are very clear and its failure pattern is in “W” shape. The wear of α-Al2O3 mainly occurs in the binding phase of the crystal boundary for its grain is fine and dense enough. So although the crystal grains are exposed at
last, no breaks and cracks can be found on the erosion surface. Its failure pattern is in “U” shape.
Abstract: Carbon fibre reinforced SiC (Cf /SiC) as a promising high temperature structural material possesses broad prospects for aeronautical and astronautical applications. Joining technique is very important from both technical and economical points of view. Joining of Cf/SiC to itself has been realized by reaction joining process using a preceramic polymer, polysilazane, as joining material (welding compound). The weld strength of joints is strongly affected by joining temperature and number of times of reinforcement, which comprises infiltration and pyrolysis of polysilazane.
Samples were joined at temperatures ranging from 1100oC -1400oC. The maximum weld strength of joints is obtained at 1250oC. The reinforcement can remarkably increase the weld strength of joints. After three times of reinforcement the shearing strength of joints reaches 27.78MPa. Microstructural study and phase analysis reveal that the joining material has transformed into an amorphous ceramic interlayer composed of Si, C and N at 1100~1250oC, which is uniform and densified. The thickness of the interlayer is 2-3µm. The contact at the interfaces is good without
obvious cracks and pores. The amorphous ceramic interlayer transforms into crystal SiC and Si3N4 at 1400oC.
Abstract: In this paper, single-phase Yb α-SiAlON ceramics were prepared by pressureless sintering and the densification, phase transformation as well as microstructure development were studied. It was demonstrated that the phase transformation could be completed at 1700 °C and elevated temperature was beneficial to grain growth. Additionally, effect of the addition of seed crystals prepared by combustion synthesis was discussed. From the experimental results, it was found that the
added seed crystals facilitated the phase transformation and improved the microstructure development, resulting in the formation of elongated grains.
Abstract: A new method, which allowed lamination at room temperature without any additional
adhesive, was described in this paper. A low Tg styrene-acrylic latex binder was used to forming the green tape via a water-based slurry. The green tapes could adhere to each other at room temperature under low or slight pressure. The density and deformation of laminated green parts depended significantly on lamination pressure, but the density of green parts did not increase after the lamination pressure exceeded a specific value of 4MPa. The interface between the tapes had been investigated in the green and sintered state by SEM. The experimental results showed that the microstructure of interface and density of lamination ceramics was a function of fraction of binder, plasticizer, and laminated pressure.
Abstract: α-Si3N4 ceramics were sintered at a low temperature of 1773K by using a
spark-plasma-sintering (SPS) method with different heating rates, and then they were further heat-treated at different temperatures from 1773K to 2273K, to study the effect of the heating rate of SPS on the microstructure and the thermal conductivity of Si3N4 ceramics after the heat-treatment. Results show that the heating rate of SPS has great influence on the phase transformation and the microstructure of the β-Si3N4, but it has little influence on the thermal conductivity of the ceramics. This proves that the thermal conductivity of the ceramics does not
have an obvious relationship with the ratio and the size of the columnar β-Si3N4 grain.
Abstract: The oxidation behavior of Ca-α-Sialon composites prepared by using the powders of
α-Si3N4, AlN, Al2O3 and CaCO3 as the starting materials has been studied, for the composition Ca0.8Si8.8Al3.2O16N14.4 in the temperature range of 1200 to 1400°C for 24 to 96h in an air stream. The bending strength and weight gain of the samples before and after oxidation experiment were measured, and the phases of surfaces of the samples were examined by XRD, the microstructures of sections and surfaces of the samples were observed by SEM. The results show that the weight gain increased and the bending strength decreased as the oxidation time increased, and the oxidation layers contained bar cristobalite and glass phase at 1200°C, bubbles and glass phase at 1300°C, transparent glassy film and the pores at 1400°C, the phases of oxidation layers consisted of cristobalite, CaAl2Si2O8, and glass phase.