摘要
N2流量对CrAlYN涂层的结构和性能影响较大,因此,本文系统研究了N2流量对CrAlYN涂层结构、力学及热稳定性的影响。结果表明,当N2流量从23 mL/min增大到38 mL/min时,涂层中氮原子含量从26.45 at.%增加到52.20 at.%。当N2流量为33 mL/min时,涂层中氮含量为49.00 at.%,元素组成符合化学计量比,涂层具有最高的硬度和抗塑性变形能力。XRD和TEM等分析表明,低N2流量下制备的涂层具有纳米晶结构,硬度较低。高N2流量下制备的涂层呈现柱状晶结构,氮原子的注入效应使涂层张应力增大,硬度降低。在33 mL/min的N2流量下制备的涂层晶粒较小,结构致密,硬度达到24.6 GPa,1 000 ℃退火后涂层氧化轻微,硬度为18.4 GPa,高于其他N2流量下制备的涂层,表明该CrAlYN涂层具有最好的综合性能。
采用物理气相沉积(PVD)技术制备的CrAlN陶瓷涂层具有优异的力学性能、热稳定性能、耐磨和耐腐蚀性,有望应用于航空航天发动机和切削刀具表
向涂层中掺杂微量稀土元素Y可使涂层的抗氧化性提高到1 000 ℃,甚至更
采用PVD技术制备涂层时,制备参数如N2分压可显著影响涂层的微观结构、力学性能和热稳定性。卢帅
本文采用PVD真空系统在镍基高温合金基材上沉积CrAlYN涂层,重点围绕N2流量对CrAlYN涂层结构、力学及热稳定性的影响展开研究。通过调控沉积过程中的N2流量制备不同化学组成、结构和性能的涂层,以实现CrAlYN涂层最佳性能的可控制备。为此类涂层的制备及在相关运动部件表面的热防护提供参考依据。
采用PVD真空沉积系统(SP0806SI,北京实力源公司),在Ar和N2的混合气氛中,通过溅射纯Cr靶(99.98%)和AlY合金靶(99.5%,Y的质量分数为10%),在P(111)单晶硅和高温合金钢(牌号为GH4169,Φ25 mm, 8 mm)基材上沉积厚度约为2.5 μm 的CrAlYN涂层。沉积涂层前,对高温合金基材进行抛光、清洗和干燥处理,置于事先清理干净的真空室工件转架上。当真空室气压低于4×1
采用PHI-5702型多功能X射线光电子能谱仪(XPS, Physical Electronics, USA)测定涂层的化学成分和元素含量。对样品进行XPS测试前,利用仪器自带的A
不同N2流量下CrAlYN涂层的化学组成如
N2 流量/ (mL/min) | 化学组成/at.% | |||
---|---|---|---|---|
Cr | Al | Y | N | |
23 | 50.67 | 21.55 | 1.33 | 26.45 |
28 | 36.80 | 23.10 | 1.20 | 38.50 |
33 | 22.94 | 27.02 | 1.04 | 49.00 |
38 | 25.84 | 20.85 | 1.11 | 52.20 |
图1 涂层中N含量和(Cr+Al+Y)/N随N2流量的变化
Fig.1 The variation of nitrogen content and (Cr+Al+Y)/N in the coating with the N2 flow rate
图2 不同N2流量下制备的涂层的断面组织结构
Fig.2 Cross-sectional FESEM images of the coatings prepared with different N2 flow rates
注: (a) 23 mL/mi
图 3 不同N2流量下制备的涂层的XRD谱图
Fig.3 XRD patterns of the coatings prepared with different N2 flow rates
由于在23 mL/min的N2流量下制备的CrAlYN涂层具有特殊的组织结构。因此,利用透射电子显微镜对其微观结构进行详细分析,结果如
图 4 N2流量为23 mL/min时制备涂层的TEM和SAED图
Fig.4 TEM image and SAED pattern of the coating prepared at a N2 flow rate of 23 mL/min
图5 不同N2流量下制备的涂层的内应力
Fig.5 Residual stress of the coatings prepared with different N2 flow rates
图 6 不同N2流量下制备的涂层的硬度和
Fig.6 H and
图 7 不同N2流量下制备的涂层在1000℃退火处理前后的XRD谱图
Fig.7 XRD patterns of the coatings prepared with different N2 flow rates before and after annealing treatment at 1 000 ℃
注: (a) 23 mL/min (b) 28 mL/min (c) 33 mL/min (d) 38 mL/min
图 8 不同N2流量下制备的涂层在1 000 ℃退火处理前后的硬度和弹性模量
Fig.8 Hardness and elastic modules of coatings prepared with different N2 flow rates before and after annealing treatment at 1 000 ℃
需要说明的是,涂层在退火后表面会生成一层氧化物,而采用纳米压痕仪进行硬度测试时,该氧化物层会对涂层的实际硬度造成影响。因此,按照测试原始涂层纳米硬度的方法是不合理的。所以,本论文采取连续压入法测试退火后涂层的硬度。
(a) 加载-卸载曲线
(b) 硬度-压入深度曲线
图9 1 000 ℃退火后涂层硬度测试曲线
Fig.9 Hardness test curves of coatings after annealing at 1 000 ℃
本文采用PVD真空沉积系统在镍基高温合金基材上制备了CrAlYN涂层,并分析了N2流量对涂层的组织结构、力学性能和热稳定性的影响,具体结论如下:
(1) 通过调节涂层沉积过程中的N2流量,制备了四种氮含量不同的CrAlYN涂层。测试结果表明,随着N2流量的提高,涂层中氮含量从26.45 at.%增加到52.20 at.%。XRD和TEM分析发现,在低N2流量下制备的涂层具有纳米晶结构,在高N2流量下制备的涂层呈现柱状晶结构;
(2) 当N2流量为33 mL/min时,涂层中氮含量为49.00 at.%,涂层具有最高的硬度和抗塑性变形能力。当N2流量小于33 mL/min时,涂层中氮含量较低,所以涂层硬度较小。而N2流量太大时,部分氮原子的注入效应使涂层张应力增大,硬度降低;
(3) 当N2流量为33 mL/min时,涂层中氮含量与金属含量的总和相当,即涂层符合化学计量比,因此涂层结构较稳定;另外,较小的晶粒使涂层结构更加致密。退火后该涂层氧化轻微,仍然保持最高的硬度和抗塑性变形能力,所以综合考虑,在33 mL/min的N2流量下制备的CrAlYN涂层具有较好的综合性能。
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