Fabrication And Tribological Properties Of Ti₃Al_1.2-xSn_xC₂Solid Solution

New materials which have low wear rate, low coefficient of friction or proper and stable friction coefficient with wider temperature range are in great demand because of the development of high technology industry. More than50kinds of MAX phases ceramics, which are thermodynamically stable phase with nano layered structures, have been attracted more and more attention in recent years. During dry sliding friction in air environment, the self-generating oxide film covered the surfaces of MAX phases (such as Ti3AIC2, Ti3SiC2) are responsible for tribological behaviors. This has been confirmed in the previous work. In this study, we postulated that the composition and morphology of the frictional film can be adapted to a wide range of tribological conditions if elements are partially substituted into the A sites of solid solutions. Ti3Al1.2-xSnxC2(x=0～1) solid solutions with good characteristics have been fabricated and the tribological properties, as well as the tribological surface self-adaptivity of the solid solutions have been investigated.In this paper, a nearly pure Ti3Al1.2-xSnxC2(x=0,0.2,0.4) powder are prepared by pressureless sintering a mixture of Ti, Sn and TiC powders at1270℃for10min in Argon atmosphere. And then, a nearly pure and dense Ti3Al1.2-xSnxC2(x=0,0.2,0.4) bulks have been synthesised by two-time hot-pressing sintering the powders at1450℃with30MPa for30min in Argon atmosphere; a nearly pure and dense Ti2SnC material has prepared by hot-pressing sintering a mixture of Ti, Sn and graphite powder at1450℃with30MPa for30min in vacuum atmosphere. The typical micrograph of Ti3Al(Sn)C2solid solution shows that the grains have a plate-like shape and layered structure. In the same preparation conditions, with the increase of Sn content in Ti3Al(Sn)C2solid solution, the grain size decreases, the lattice parameter a increases slowly while the lattice parameter c remains almost unchanged.Significant strengthening effects are observed after incorporation of0.2Sn and0.4Sn to form Ti3Al(Sn)C2solid solution. The micro-vickers hardness increases to3.53GPa and3.51GPa, respectively, these values are about12%higer than that of single Ti3AlC2(～3.1GPa). The flexural strengths are measured to be560MPa and620MPa, these values are increased by51%and67%, respectively, than that of Ti3AlC2(～370MPa). Grain buckling, delamination, kink band formation and crack deflection are responsible for the good mechanical properties and good damage tolerance.Ti3Al1.2-xSnxC2(x=0-1) solid solutions show good tribological properties during dry sliding against a low-carbon steel disk at high sliding speed. Tribological surface self-adaptability of the series of Ti3Al1-2-xSnxC2(x=0-1) materials is also investigated at a sliding speed of10-30m/s under normal loads of20～80N. The results show that the friction coefficient could be adapted to fall within the range of0.13-0.46and the wear rate could be adapted to fall within the range of1.3～7.9×10-6mm3/N·m, but it remains at a relatively low level. With increase in the sliding speed or normal load, the friction coefficient of Ti3Al(Sn)C2solid solution decreases gradually, while the wear rate increases slightly. With the increase of Sn content, the friction coefficient increases. At a sliding speed of30m/s and a normal load in the range of20～80N, the friction coefficient of Ti3AlC2is measured to a range of0.13～0.16. With the accession of the0.2Sn and0.4Sn, the friction coefficient of Ti3Al(Sn)C2solid solution are adapted to fall within the range of0.26～0.30and0.30-0.33, respectively.Adjustable friction coefficient and excellent wear properties of Ti3Al(Sn)C2solid solution are mainly attributed to the formation of a self-adaptable friction oxide film in the process of the friction test. The tribological oxide film is composed of Ti, Sn, Al and Fe oxides composition. Its thickness is0.5～1.5μm. Sn affected the combination of the mixed oxides with the tin oxide. The compositions of phases and crystal states in the tribofilms are different after incorporating different amouts of Sn, leading to the different physical morphology of the tribolofilms. The different characteristics of the frictional film thun directly led to different friction coefficients and wear rates. Under the experimental conditions, the frictional oxide film of Ti3AIC2is amorphous and in a fused state on the friction surface during sliding friction, leading to a very low friction coefficient and wear rate. While the frictional film of Ti3AlSno.2C2solid solution is composed of crystallization phases and amorphous phases, and that of Ti3Al0.8Sn0.4C2solid solution is a combination of crystallization phases and exist in a soft state on the friction surface during sliding friction, leading to the larger friction coefficient. The anti-wear character of the oxide film was retained, resulting in excellent wear resistance.