Hong Xiang Zhai

Frictional Layer and Its Antifriction Effect in High-Purity Ti3SiC2 and TiC-Contained Ti3SiC2

Characteristics of the frictional layer in high-purity Ti3SiC2 and TiC-contained Ti3SiC2, sliding against low carbon steel, were investigated. The friction and wear tests were made using a block-on-disk type friction tester with sliding speed of 20 m/s and several normal pressures from 0.1 MPa to 0.8 MPa. It was found that all friction surfaces, whether high-purity Ti3SiC2 or TiC-contained Ti3SiC2, were covered by a layer consisting of the oxides of Ti, Si and Fe. The layer was sticky, superimposed layer-by-layer, and the compact was increased with the normal pressure increasing. Because its antifriction effect, the friction coefficient decreases from the maximum 0.35 to 0.27 with increase in the normal pressure from 0.2 MPa to 0.8 MPa for the high-purity Ti3SiC2, and decreases from the maximum 0.55 to 0.37 for the same change of the normal pressure for the TiC-contained Ti3SiC2. The contained TiC grains had effects on the stickiness, liquidness, as well as the morphology of the layer, and induced the friction coefficient to increase in the entire level.

Unusual Microstructures and Strength Characteristics of Cu/Ti3AlC2 Cermets

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.

Ti3AlC2 — A Soft Ceramic Exhibiting Low Friction Coefficient

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.

Interformational Exfoliation of Ti3Al2 Induced by Cu

An interformational exfoliation behavior of the layered Ti3AlC2 induced by copper was firstly investigated via a “Cu-Ti3AlC2-Cu” sandwich sample infiltration-sintered at 1100oC to 1200oC. It was found that the molten Cu accelerates Ti3AlC2 to decompose, induces the interformational exfoliation to generate, and consequently forming a sub-micro-layered structure making up of TiC0.67 layers and Cu-Al alloy layers within a Ti3AlC2 grain. This interformational exfoliation behavior can be attributed to a topotactic mechanism due to the outward diffusion of Al the entering of Cu.

Self-Lubricant Effect of Tri-Oxidizing Layer in Surface of Bulk Ti3SiC2 Materials

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.

Sliding Friction Behavior of Bulk Ti3SiC2 under Difference Normal Pressures

The friction behavior of Ti3SiC2 sliding against low carbon steel was studied. Tests were carried out on a block-on-disk type friction tester, with the normal pressures from 0.2 MPa to 0.8 MPa and the sliding speed of 20 m/s. The results showed that, irrespective of the normal pressure, the friction coefficient exhibits a transition period in the initial stage of a sliding friction process, in which the friction coefficient increases from an initial value and tends to a saturation value, and then enters into a relatively steady stage. The results also showed that, the friction coefficient of the steady stage decreases gradually from 0.35 to 0.26 with increase in normal pressure from 0.2 MPa to 0.8 MPa. The friction surfaces were observed by using SEM. It was found that all the surfaces were covered by a layer consisting of the frictional products with antifriction effect, and that the denseness and the thickness of the layer were increased with increase in normal pressure applied.

Tribo-Chemical Reaction in Bulk Ti3SiC2 under Sliding Friction

The Ti3SiC2 samples with a second phase TiC, prepared by hot-pressing progress route, were rubbed against low carbon steel disk with a sliding speed of 20 m/s under normal pressure 0.8 Mpa in atmosphere on a block-on-disk type friction tester. The morphology was observed by scanning electron microscope (SEM) and meanwhile the composition was checked by energy dispersion spectroscopy (EDS). X-ray diffraction (XRD) patterns show some impurity phases containing Ti, Si and Fe oxides in the samples. The possible tribo-chemical reaction mechanism on surface layer of Ti3SiC2 was suggested.

Preparation of Composites from Al and Ti3AlC2 and its Tribo-Chemistry Reactions against Low Carbon Steel

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.

Effects of Sintering Process on the Properties of Ti3SiC2/Cu Composite

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.

High Performance of Sub-Micro-Layered Ti3C2/(Cu-Al) Cermets Prepared by In-Situ Hot-Extruding Method

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.