| The alumina ceramic coating was prepared by micro-arc oxidation (MAO) technique on LY12CZ Al alloy, its outer porous layer was polished by using grinding papers. The Al2O3 coating acts as load support layer, the CrN coating was deposited on top of the Al2O3 coating by radio frequency magnetron sputtering technique. The phase composition of the Al2O3 and CrN coating were identified by using X-ray diffraction, their thickness were measured by using MiniTest1100 equipment, and their nano-hardness were measured by using nano-indenter. The experiments for the friction and wear properties of Al2O3 and CrN coating were done in dry-, water- and oil-lubricated conditions by using tribo-meters. Three-dimensional and sectional morphologies of the wear scars of the wear scars on Al2O3 and CrN coating were observed as well as their wear volumes were measured by using non-contact surface profilers. The specific wear rates which were regarded as assessing the anti-wear properties of Al2O3 and CrN coating were calculated according as the data of the wear volumes. Lastly, the micro-morphologies of the wear scars were observed by using scanning electron microscope (SEM). The research results show: The alumina ceramic coating on LY12CZ Al alloy is mainly composed ofα-Al2O3 andγ-Al2O3 phase, CrN coating is composed of Cr, CrN and Cr2N phase. The nano-hardness of Al alloy is 1.7GPa, the nano-hardness of Al2O3 coating is 12GPa and the nano-hardness of CrN coating is 34GPa. In air condition, with an increase in normal load and sliding speed, the friction coefficient of Al2O3 coating increases from 0.74 to 0.87, but in water- and oil-lubricated condition, it decreases from 0.72 to 0.57 and from 0.24 to 0.11 respectively. In dry-, water- and oil-lubricated condition, with an increase in normal load and sliding speed, the specific wear rate of Al2O3 coating increases from 2.6×10-5mm3/N.m to 9.69×10-5mm3/N.m, from 2.3×10-5mm3/N.m to 4.47×10-5 mm3/N.m and from 1.04×10-5mm3/N.m to 3.06×10-5mm3/N.m respectively. In air condition, with an increase in normal load and sliding speed, the friction coefficient of CrN coating increases from 0.65 to 0.72, but in water- and oil-lubricated condition, it decreases from 0.58 to 0.36 and from 0.2 to 0.08 respectively. In dry-, water- and oil-lubricated condition, with an increase in normal load and sliding speed, the specific wear rate of CrN coating increases from 1.54×10-5mm3/N.m to 4.87×10-5 mm3/N.m, from 1.09×10-5mm3/N.m to 3.16×10-5mm3/N.m and from 0.51×10-5 mm3/N.m to 2.17×10-5mm3/N.m respectively. Moreover, in the same tribological condition and experimental parameter, the friction coefficient and specific wear rate of Al2O3 coating are higher them of CrN coating. Meanwhile, in the same experimental parameter, the maximum for the friction coefficient and specific wear rate of Al2O3 and CrN coating occur in air condition, the smaller them occur in water- lubricated condition, the minimum for them occur in oil-lubricated condition. |
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