Papers by Author: Zhen Ying Huang

Abstract: In this paper, a new type of Ti₃SiC₂/Cu composites with the volume fractions of 30% Ti₃SiC₂ particle was prepared by hot pressing and vacuum sintering respectively. The effects of sintering temperature and holding time on the density, resistance and Vickers hardness of Cu-30vol%Ti₃SiC₂ composite were investigated. The results show that the mechanical properties of the composites prepared by hot pressing are better than that prepared by vacuum sintering. The relative densities of Cu-30vol% Ti₃SiC₂ composites are rather high in suitable sintering conditions. It achieved 100% for the composites prepared by hot pressing at 930°C for 2h, and 98.4% for the composites prepared by vacuum sintering at 1250°C for 1h. At the same time, the maximum Vickers hardness reached 1735MPa at 900°C by hot pressing. The resistance and Vickers hardness of the composites decreased with an increase in sintering temperature, whereas the density increased. Scanning electron microscope (SEM) and energy-dispersive spectroscopy (EDS) were used to observe the microstructure of the composites. The relationship between microstructure and mechanical properties was discussed.

Abstract: A high purity of Ti₂AlC powder has been synthesized by pressureless sintering a mixture of Ti-Al-TiC-Sn (Sn as an additive) powders. Four recipes with different mole ratios of Ti-Al-TiC-Sn were examined at sintering temperature from 1400°C to 1480°C. A high purity of Ti₂AlC powder can be obtained by sintering all these four recipes at temperature 1450°C for 10 min in an Ar atmosphere. The synthesis of Ti₂AlC on this large mole ratio scale of starting materials is associated with the evaporation of Al at high temperature and the structure stability of Ti₂AlC. From the X-ray diffraction analysis, a reaction path for the Ti₂AlC formation is proposed. Scanning electron microscopy was also used to characterize the samples.

Abstract: A series of new sub-micro-layered Ti3C2/(Cu-Al) cermets were prepared by in-situ hot-extruding a mixture of Ti3AlC2 and Cu powders, and some properties of these materials were tested. These cermets have quite high fracture strength and electric conductivity, due to the strong combination between Ti3C2 and (Cu-Al), and a special network microstructure formed by the (Cu-Al) phase surrounding the sub-micro-sheet layered Ti3C2 phase. The in-situ hot-extruding after pressless sintering can effectively eliminate pores contained in (Cu-Al) phase, and accelerate the diffusing of Cu towards the interlayer between Ti3C2 layers, so the fracture strength and electric conductivity are increased. With increasing the content of the ceramic phase, the strength of the cermets can be further increased while the ductility is reduced.

Abstract: A cold-extruding and temper means was developed in order to densify the Ti3AlC2 toughened Cu matrix composites with a lower content of Ti3AlC2 ceramic. The Ti3AlC2/Cu samples, with 10%, 15% and 20% of Ti3AlC2 in volume ratio, ware prepared by pressless sintering a mixture of copper and Ti3AlC2 powders, after which were formed by the cold isostatic compaction. The sintered samples ware extruded at room temperature, and then tempered at 950oC. Such treatment was performed twice for obtaining a more remarkable densifying effect. Changes in microstructures were observed by SEM after every extrusion and temper. The results show that particle size of Ti3AlC2 was reduced more than 50% after secondary extrusion and temper, and the particles distribution became more uniform in compared with the untreated samples. As a result of the microstructural change, the densities of the Ti3AlC2/Cu samples were increased about 5 %, and defects such as pores and microcracks were almost entirely slaked.

Abstract: Highly pure and dense bulk Ti2AlC was prepared by hot-pressing a mixture of the “312” phase Ti3AlC2 powders, and the element Ti and Al powders. Different ratios of the starting materials and different sintering temperature were attempted in order to obtain a highly pure and dense bulk Ti2AlC sample. Phase analysis and microstructures observing were performed by using by XRD, SEM as well as an X-ray fluorescence spectrometer. The results show that a nearly full dense bulk Ti2AlC sample can be prepared at 1300°C and 30MPa for 30 minutes in argon atmosphere. A dominant mechanism to form the “211” phase Ti2AlC can be attributed to the directly connecting between Al and Ti6C octahedron, which is as an intermediate phase in the Al-rich liquid mediator during the hot pressing.

Abstract: Several Ti3C2-Cu(Al) cermets were prepared by pressureless sintering or by in-situ hot-extruding a mixture of Ti3AlC2 and Cu powders, their microstructure and properties were investigated. The Al of Ti3AlC2 was dissolved and diffused into liquid Cu, forming Ti3C2-Cu(Al) cermet. Due to strong combination between Ti3C2 and Cu(Al), and special network microstructure formed by Cu(Al) phase surrounding sub-micro-sheet layered Ti3C2 phase, the cermets have quite high fracture strength and electric conductivity. Properties of cermets fabricated by in-situ hot-extruding were further increased.

Abstract: Joining of Cu/Ti3AlC2 cermet by an argon-arc welding technique without filler was firstly investigated. The results show that the Cu/Ti3AlC2 cermet can be joined firmly. The joining strength at room temperature was measured to be 851 MPa after optimization of the welding parameters with 2.6 A/mm2 for arc current density, 5 s for arc time, 10.8 kPa for applied pressure and 12 V for arc voltage. The microstructure in welded zone shows that fine TiCx particles uniformly dispersed in a network structure of Cu-Al alloys. This feature endows the Cu/Ti3AlC2 cermet with the high joining strength.

Abstract: The Cu/Ti3AlC2 composites were fabricated by pressureless sintering a mixture of Ti3AlC2 and copper powders. Their microstructures and properties were investigated. It was found that the molten Cu accelerating the decomposition of Ti3AlC2, inducing the interfacial exfoliation to generate, and forming a sub-micro-layered structure making up of TiCx layers and Cu-Al alloy layers within a Ti3AlC2 grain. The flexural strength of the composites is reduced with the increase of the volume content of Ti3AlC2 from 50 % to 90 %. The highest flexural strength reaches to as high as 915 MPa. The fracture mode was changed from ductile to brittle with increase in the content of Ti3AlC2. The higher flexural strength can be attributed to a stronger interface bond between TiCx and Cu-Al phase. The electrical resistivity and Vickers hardness of the composites were also measured.

Abstract: Al/Ti3AlC2 composites containing 50vol% Al were prepared with high purity of polycrystalline Ti3AlC2 and aluminum powders by pressureless-sintering route at temperatures of 700°C~ 800°C The tribological properties of the composites were investigated by sliding the composites block dryly against low carbon steel disk under high sliding speed. Before and after friction test, the morphology and phase analysis were observed by scanning electron microscope (SEM) and X-ray diffraction (XRD), separately. A definite tribo-glazing layer was found over the worn surface of the composite block, which was the results of tribo-chemical oxidation reaction and the cause forming it could be the high frictional temperature and the mechanical catabolism between the surface of Al/Ti3AlC2 and low carbon steel during sliding friction. The effect of Ti3AlC2 on tribological properties of Al/Ti3AlC2 composite and the possible tribo-chemical reaction mechanism on surface layer of Al/Ti3AlC2 were suggested.

Abstract: The current-carrying wear characteristics of Ti3AlC2 sliding against low-carbon steel were investigated. Tests were carried out using a block-on-disk type friction tester, with sliding speeds of 20~60 m/s, normal pressures range in 0.4~ 0.8 MPa, and the current intensity of 0 A, 50 A and 100 A. The Ti3AlC2 showed good current-carrying wear properties. At the sliding speed of 20 m/s, the wear rate of the Ti3AlC2 (× 10-6 mm3/Nm) was varied in the range of (2.05 ~ 2.41), (2.64 ~ 2.39) and (6.26 ~ 3.62), under the current of 0 A, 50 A and 100 A, respectively. Both the surfaces of Ti3AlC2 and the steel were covered by a frictional film, which was consisted of iron titanate (Fe2.25Ti0.75O4) and aluminum iron oxide (AlFeO3). The wear rate of Ti3AlC2 with current was composed of two parts: the interaction of micro-arc ablation and mechanical friction, and the coupled action of thermal and mechanical effect. Which one will be the main mechanism depends on the material parameters of Ti3AlC2 and the mechanical parameters such as the normal pressure or the sliding speed.