调制周期对CrAlN/ZrN纳米多层膜韧性的影响

目的研究调制周期对纳米多层膜性能的影响。方法采用磁控溅射方法制备了CrAlN与ZrN的固定厚度比为2.6,不同调制周期(Λ为6,8,10,20 nm)的CrAlN/ZrN纳米多层膜。利用场发射扫描电镜(FESEM)表征薄膜的形貌、结构。用Dektak150型台阶仪测薄膜表面粗糙度。用Agilent Technologies G200纳米压痕仪检测涂层的硬度和弹性模量。用划痕仪测薄膜/基材的结合力,同时,引入抗裂纹扩展系数(CPR)表征纳米多层膜的韧性。结果 CrAlN/ZrN纳米多层膜断面皆为穿晶柱状结构,调制周期为20 nm时,多层膜层与层之间的界面清晰;多层膜表面呈致密的花椰菜状,厚度均约为2μm。调制周期为8 nm时,硬度为20.4 GPa,进一步增大调制周期,硬度下降。调制周期为8 nm的多层膜临界载荷L_(c2)为18 N,CPR值为73.2,L_(c2)与CPR值均高于其他调制周期的多层膜。在临界载荷L_(c2)处,裂纹扩展导致薄膜发生了严重的片状剥落,露出了亮白的热轧钢基底,薄膜失去了保护作用。结论实验表明,在多层膜厚度、调制比不变的条件下,改变调制周期能够改变多层膜的韧性。随着调制周期的增大,韧性呈先上升、后下降的趋势。调制周期为8 nm时,纳米多层膜的硬度最高,韧性最好,综合性能良好。

Effect of Modulation Period on Toughness of CrAlN/ ZrN Nano-multilayer Films

Objective To study the effect of modulation period on the properties of nano-multilayers. Methods CrAlN/ ZrN nano-multilayers were deposited with different modulation periods in a magnetron sputtering system, fixing the layer thickness ratio CrAlN : ZrN as 2. 6. To characterize the morphology and structure of the films, the field emission scanning electron microscopy (FESEM) was used. The Dektak 150 surface profiler was used to measure the coatings' roughness. Agilent Technologies G200 nanoindentation was used to test the coatings' hardness and elastic modulus. Automatic scratch tester was used to measure film critical loads. The toughness of the films was characterized by CPR (crack propagation resistances). Results CrAlN / ZrN nano-multi-layers' sections were transgranular columnar structure. When the modulation period was 20 nm, the distinction between layer and layer was clear. The surface of nano-multilayers was dense like the cauliflower. The thickness of nano-multilayers was about 2 microns. When the modulation period was 8 nm, the hardness was 20. 4 GPa. After further increasing the modulation period, the hardness decreased. The critical load Lc2 was 18 N, CPR number was 73. 2, when the modulation period was 8 nm. The nano-mul-tilayer's critical load Lc2 and CPR number were higher than other nano-multilayers. At the critical load Lc2 , the coatings were peeled off as the result of crack propagation. And the bright white hot rolled steel substrate was exposed and the nano-multilayers lost the protective effect to substrates. Conclusion Changing the modulation period will affect the nano-multilayer coating's toughness under the condition, keeping the multilayer coat's thickness and modulation ratio invariable. With the increase of modulation period, toughness properties is improved then descended. The film has the highest hardness and toughness and gets the best comprehensive performance when the modulation period is 8 nm.