Al成分梯度变化对Cr-Al-Si-N纳米多层涂层结构与性能的影响及机理分析

The addition of Al into the Cr-Al-Si-N coating could increase the hardness by solid solution strengthening mechanism and improve high temperature oxidation resistance because Al2O3 is more stable than Cr2O3. However, large stress emerges by the substitution of Al for Cr in the coating, which might reduce the adherence between the coating and substrate. To further increase the oxidation resistance of the coating and avoid lowering the adherence, a novel nano-multilayer Cr-Al-Si-N coating will be prepared by the combination of high power impulse magnetron sputtering and pulse DC magnetron sputtering. The Al content increases from 0 at.% near the substrate to 50-70 at.% at the near surface. The microstructure, mechanical properties, thermal stability, tribological behavior and cutting performance of coated tools will be studied systematic revealing how the modulation period, Al content at the surface and gradient variation of Al content in the nano-multilayer structure affects those properties of the coatings. The result of this research will further improve hardness, toughness, wear resistance, heat resistance and high-speed cutting performance of the Cr-Al-Si-N coating. It can also be used to guide the design and preparation of other nano-multilayer coatings.

Cr-Al-Si-N涂层中Al元素一方面可以通过固溶强化机制提高涂层的硬度；另一方面其在高温下可以生成比Cr2O3更稳定的Al2O3相，提高涂层的耐热性能。但Al替换CrN中Cr的位置会在涂层内产生较大的内应力，影响涂层与基体的结合力。为进一步提高Cr-Al-Si-N涂层的耐高温性能同时不降低涂层与基体的粘附力，本项目拟采用高功率脉冲和直流脉冲磁控溅射复合技术制备Al成分呈梯度变化（Al含量从里到表由0增加至50-70 at.%)的Cr-Al-Si-N纳米多层涂层，系统研究涂层的组织结构、力学性能、耐热性能、摩擦学行为和切削性能，揭示调制周期、表层Al含量和Al成分呈梯度变化的纳米多层结构对涂层各种性能的影响及规律。本研究成果将进一步提升Cr-Al-Si-N涂层的硬度、韧性、耐磨性能、耐热性能和切削性能，同时对其他纳米多层结构涂层的设计与制备具有指导意义。

针对钛合金、高温合金等难加工材料的切削刀具寿命和切削效率低的问题，采用高功率脉冲和脉冲直流共溅射技术制备了几种不同表面Al含量的Al成分梯度变化的CrAlSiN涂层。研究了工艺参数和成分对涂层组织结构、力学性能等的影响及规律。结果表明：不同负偏压下(0~-120V)制备的Al成分梯度变化的CrAlSiN涂层为fcc-(Cr,Al)N相。随着负偏压增加，(111)晶面衍射峰逐渐减弱，(200)晶面衍射峰逐渐增强。当偏压为-30V时，涂层硬度和弹性模量达到最大分别为22.3GPa和232.7GPa。摩擦系数随偏压增加先增加后减小。偏压为-30V时涂层性能最优。.在N2/Ar比为1/1，2/1，3/1，4/1条件下制备的Al成分梯度变化的CrAlSiN涂层主要相均为fcc-(Al,Cr)N相。随着N2/Ar比增加，涂层硬度由26.1GPa下降至23.4GPa，随后增加至25.4GPa。摩擦系数由0.50上升为0.53，磨损率由6.8×10-16m3/(N×m)迅速降低至1.9 ×10-16m3/(N×m)。N2/Ar比为4/1时性能最优。.改变Al靶功率制备了三种不同表面Al含量的Al成分梯度变化的CrAlSiN涂层，涂层主要相均为fcc-(Cr,Al)N相，Si以非晶相的形式存在于涂层中。随着涂层表面Al含量增加，固溶效应增强，衍射峰逐渐向大角度偏移。硬度由30GPa先增加至35.3GPa，随后降低至32.1 GPa。摩擦系数和磨损率也呈先增大后减小趋势，这与涂层H/E*和H3/E*2值相关。.在850 ℃退火后，三种Al成分梯度变化的CrAlSiN涂层依然能保持fcc-(Cr,Al)N相结构。但退火温度升高到1300 ℃时，涂层发生CrN→Cr2N→Cr相转变，(Cr,Al)N衍射峰减弱，fcc-AlN转变为更稳定的hcp-AlN。另外，XRD探测到Cr2O3相。涂层表面Al含量越高，生成氧化膜越薄越致密，因为Al2O3比Cr2O3相更稳定具有更小的PBR值。.切削性能测试表明：CrAlSiN涂层刀具比未涂层刀具使用寿命提高约2.6倍，而Al成分梯度变化的CrAlSiN涂层刀具比CrAlSiN涂层寿命又提高约2.7倍。刀具失效主要形式为磨料磨损和冷焊磨损。Al成分梯度变化的CrAlSiN涂层刀具比CrAlSiN涂层刀具具有更好的抗磨料磨损和抗冷焊磨损能力。