B 和 Si 掺杂对 CrAlN 涂层结构和切削钛合金寿命的影响

Because CrAlN coating has excellent oxidation resistance components, it is widely used in the field of cutting tool coating. However, the thermal decomposition of CrAlN coating above 900 ℃ leads to a drop in mechanical properties. Therefore, B and Si doping method was adopted in this study to further improve the performance of CrAlN coating. The structure, hardness, cohesion, thermal and machining properties of Cr_0.42Al_0.58N, Cr_0.35Al_0.59B_0.06N and Cr_0.37Al_0.54Si_0.09N deposited by cathodic arc evaporation were investigated by X-ray diffraction (XRD), scanning electron microscopy (SEM), nano-indentation, scratch test and cutting experiment. The Cr_0.42Al_0.58N and Cr_0.37Al_0.54Si_0.09N coatings presented a single phase cubic structure, whereas the Cr_0.35Al_0.59B_0.06N coating was mixed cubic-wurtzite structure. Cr_0.42Al_0.58N coating presented typical columnar crystal morphology along the growth direction. The addition of B and Si inhibited the growth of columnar crystals. The fracture morphology of Cr_0.35Al_0.59B_0.06N coating and Cr_0.37Al_0.54Si_0.09N coating was composed of fine columnar crystals and nanocrystals respectively. The solid solution strengthening and grain refinement caused by B and Si doping increased the hardness of the coating from (29.8±1.5)GPa of Cr_0.42Al_0.58N coating to (36.9±1.4)GPa of Cr_0.35Al_0.59B_0.06N coating and (33.8±1.6)GPa of Cr_0.37Al_0.54Si_0.09N coating. However, B and Si doping reduced the cohesion with substrate from 116.2 N of Cr_0.42Al_0.58N coating to 58.3 N and 58.0 N of Cr_0.35Al_0.59B_0.06N and Cr_0.37Al_0.54Si_0.09N. The grain refinement caused by the addition of B and Si reduced the elastic modulus of the coating. The elastic modulus of Cr_0.42Al_0.58N, Cr_0.35Al_0.59B_0.06N and Cr_0.37Al_0.54Si_0.09N coatings was 523.6, 484.8 and 431.7 GPa respectively. The addition of B and Si improved the plastic deformation resistance of the coating. The ratios of H³/E² of Cr_0.42Al_0.58N, Cr_0.35Al_0.59B_0.06N and Cr_0.37Al_0.54Si_0.09N coatings were 0.097, 0.213 and 0.206 respectively. The addition of B and Si inhibited the fracture of Cr-N bond, thus retarding the thermal decomposition process. The initial fracture temperature of Cr-N bond increased from 1 000 ℃ of Cr_0.42Al_0.58N to 1 200 ℃ of Cr_0.35Al_0.59B_0.06N and 1 100 ℃ of Cr_0.37Al_0.54Si_0.09N. In addition, the formation temperature of w-AlN increased from 1 000 ℃ of Cr_0.42Al_0.58N to 1 100 ℃ of Cr_0.35Al_0.59B_0.06N. The doping of B and Si promoted the formation of dense oxides on the surface of the coating during oxidation, thus significantly improving the high-temperature oxidation resistance of the coating. After oxidation at 1 100 ℃ for 15 h, the oxide layer thickness of Cr_0.42Al_0.58N and Cr_0.35Al_0.59B_0.06N coatings was 2.38 μm and 1.80 μm. Cr_0.37Al_0.54Si_0.09N coating showed the best oxidation resistance, and the thickness of the oxide layer of the coating was only 0.53 μm. A mixed oxide layer consisting of Al₂O₃, Cr₂O₃ and SiO₂ was grown on the surface of the coating containing Si. The oxide layer could avoid the formation of porous structure, thus maintaining a good combination with the residual nitride layer and providing effective protection for the coating. B and Si doping can improve the cutting performance of CrAlN coating on titanium alloy materials. After 45 min of cutting, the wear amount of Cr_0.42Al_0.58N, Cr_0.35Al_0.59B_0.06N and Cr_0.37Al_0.54Si_0.09N coated inserts is 0.5 mm, 0.071 mm and 0.173 mm respectively.