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纳米Al2O3对等离子喷涂ZrC-ZrSi2复合涂层结构与性能的影响∗

  • 邵宇轩1,2

    机 构：

    1. 河北工业大学材料科学与工程学院 天津 300401

    2. 河北省新型功能材料重点实验室 天津 300401

    ×
  • ， 王磊1

    机 构：

    1. 河北工业大学材料科学与工程学院 天津 300401

    ×
  • ， 杨勇1,2

    机 构：

    1. 河北工业大学材料科学与工程学院 天津 300401

    2. 河北省新型功能材料重点实验室 天津 300401

    ×
  • ， 赵策策1

    机 构：

    1. 河北工业大学材料科学与工程学院 天津 300401

    ×
  • ， 王彦伟1

    机 构：

    1. 河北工业大学材料科学与工程学院 天津 300401

    ×
  • ， 马玉夺1

    机 构：

    1. 河北工业大学材料科学与工程学院 天津 300401

    ×
  • ， 崔宇航1

    机 构：

    1. 河北工业大学材料科学与工程学院 天津 300401

    ×

1. 河北工业大学材料科学与工程学院 天津 300401；
2. 河北省新型功能材料重点实验室 天津 300401；

Effects of Nano-Al 2O3 on the Microstructure and Properties of ZrC-ZrSi 2 Composite Coating Prepared by Plasma Spraying

  • SHAO Yuxuan1,2

    Affiliation：

    1. School of Material Science and Engineering, Hebei University of Technology, Tianjin 300401 , China

    2. Key Lab.for New Type of Functional Materials in Hebei Province, Tianjin 300401 , China

    ×
  • ， WANG Lei1

    Affiliation：

    1. School of Material Science and Engineering, Hebei University of Technology, Tianjin 300401 , China

    ×
  • ， YANG Yong1,2

    Affiliation：

    1. School of Material Science and Engineering, Hebei University of Technology, Tianjin 300401 , China

    2. Key Lab.for New Type of Functional Materials in Hebei Province, Tianjin 300401 , China

    ×
  • ， ZHAO Cece1

    Affiliation：

    1. School of Material Science and Engineering, Hebei University of Technology, Tianjin 300401 , China

    ×
  • ， WANG Yanwei1

    Affiliation：

    1. School of Material Science and Engineering, Hebei University of Technology, Tianjin 300401 , China

    ×
  • ， MA Yuduo1

    Affiliation：

    1. School of Material Science and Engineering, Hebei University of Technology, Tianjin 300401 , China

    ×
  • ， CUI Yuhang1

    Affiliation：

    1. School of Material Science and Engineering, Hebei University of Technology, Tianjin 300401 , China

    ×

1. School of Material Science and Engineering, Hebei University of Technology, Tianjin 300401 , China；
2. Key Lab.for New Type of Functional Materials in Hebei Province, Tianjin 300401 , China；

作者简介:

杨勇(通信作者),男,1980年出生,博士,教授,博士研究生导师。主要研究方向为表面工程、热喷涂。E-mail:yangyonghebut@163.com

中图分类号:TQ174

DOI:10.11933/j.issn.1007-9289.20210421002

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目录contents

    摘要

    大气等离子喷涂 ZrC-ZrSi 2 陶瓷涂层的孔隙率高,提高等离子喷涂 ZrC-ZrSi 2 陶瓷涂层的致密度成为亟待解决的问题。 在 TC4 钛合金表面采用大气等离子喷涂 ZrC-ZrSi 2 复合粉和 ZrC-ZrSi 2 -Al 2O3 复合粉分别制备两种复合涂层。 研究纳米 Al 2O3 对等离子喷涂 ZrC-ZrSi 2 复合涂层组织结构与性能的影响。 结果表明,添加了 Al 2O3 的 ZrC-ZrSi 2 复合涂层的组织结构更为致密,相较于 ZrC-ZrSi 2 复合涂层具有更优异的力学性能。 熔点相对较低的 Al 2O3 能够在喷涂焰流中先熔化,熔融态的 Al 2O3 能够填充在 ZrC-ZrSi 2 复合涂层的孔洞处,提高复合涂层的致密度,改善涂层的力学性能。 研究成果可为提高大气等离子喷涂制备含高熔点组分复合涂层的致密度提供指导。

    Abstract

    There is still a pressing need for improving the densification of ZrC-ZrSi 2 ceramic composite coating prepared by atmospheric plasma spraying. Two kinds of composite coatings were prepared on TC4 (Ti6Al4V) substrate by plasma spraying ZrC-ZrSi 2 and ZrCZrSi 2 -Al 2O3 composite powders. Effects of nano-Al 2O3 on the microstructure and properties of ZrC-ZrSi 2 composite coating prepared by plasma spraying were investigated. Al 2O3 -contained composite coating possessed denser microstructure compared to ZrC-ZrSi 2 composite coating. Correspondingly, enhanced mechanical properties were observed in ZrC-ZrSi 2 -Al 2O3 composite coating. Al 2O3 with relatively low melting point which could firstly melt in the plasma jet is postulated to fill the pores formed during the spraying process. Therefore, Al 2O3 is considered as the promising candidate for improving the microstructure and properties of ZrC-ZrSi 2 composite coating. A guidance is provided for improving the densification of the composite coating containing high-melting point component prepared by plasma spraying.

  • 0 前言

  • 热喷涂技术作为表面工程技术的重要组成部分,可以对材料的耐磨损和耐高温等表面性能进行强化或再生[1],广泛应用于诸如各种金属及合金、陶瓷等大多数固态工程材料的表面涂层的制备[2], 所制备出的涂层应用面广,在提高工程效率、降低成本等方面作用显著[3-4]。针对高端装备制造领域, 热喷涂技术已经成为使基体材料具备超常服役性能不可或缺的技术[5]。而碳化物、氮化物和硼化物类陶瓷材料由于其优异的物理和化学性能成为航空航天领域广泛应用的材料[6-8]。 ZrC具有较高的熔点 (3 580℃)和较高的硬度( 27GPa) [9]。 ZrC优异的力学性能使其可以作为磨料,用于各种硬金属、刚玉或玻璃的加工;还可用于制造耐磨、耐腐蚀的坩埚和刀具[10-12]。同时在复合材料的制备领域, 一方面高熔点的ZrC可以作为增强相与难熔金属相结合得到性能优异的金属陶瓷,另一方面以ZrC为基的复合陶瓷材料作为在高温条件下服役的航天器部件的保护涂层可以有效减缓基体材料的氧化[13]。 ZrSi2 的密度较低, 蠕变强度高, 在高于1 300℃ 的高温服役环境中可以生成硅氧化物膜以保护基体材料不被氧化[14],ZrC与ZrSi2 成分组合的陶瓷涂层可以在硬质涂层和耐火材料方面有更为广泛的应用。

  • 近些年,越来越多的研究者[15-16] 开始使用等离子喷涂的方法制备ZrC基复合涂层。诸多工作同样证实了ZrC基复合陶瓷应用于防护涂层材料的可行性和高利用价值。 WEN等[17] 采用大气等离子喷涂 (APS)技术制备了以W为内层,ZrC为外层的双层涂层,所制备的涂层与基材结合良好。 XU等[18] 采用大气等离子喷涂技术在镁合金基体上制备了ZrB2-ZrC/Ni复合陶瓷涂层,使得基体的耐磨性显著提高。但以上工作所制备的陶瓷涂层致密度不高, 结构疏松。通常在等离子喷涂过程中孔隙的形成有以下两个原因:首先,尽管复合粉中各原料粉混合得较为均匀,但在喷涂焰流中仍有一部分粉末未能完全熔化,未熔融的颗粒在基体上发生简单的机械叠加,进而形成堆积孔洞。另一方面,陶瓷熔滴在沉积过程中会在基体表面产生飞溅,而巨大的过冷度使得每一个熔滴的凝固过程都是极其快速并且相互独立的[19],前一个熔滴产生的指状溅射物会造成遮蔽效应,这将影响后续熔滴的沉积从而形成封闭孔洞。

  • Al2O3 具有化学性能稳定及耐辐射性能好等优点,是制备陶瓷涂层中普遍使用的一种氧化物原料。本工作在采取大气等离子喷涂技术的基础上,通过在以高熔点的ZrC为主相的陶瓷涂层体系中添加熔点较低的Al2O3 组分(2 040℃),以期提高ZrC-ZrSi2 复合涂层的致密度,并进而改善其力学性能。

  • 1 试验准备

  • 1.1 复合粉及涂层的制备与处理

  • 试验中所选用的原料粉为Al2O3 ( α-Al2O3,纯度:99.99%,40nm)、ZrC(纯度:99.99%,2 μm) 和ZrSi2(纯度:99.99%,5 μm)。 ZrC-ZrSi2 复合粉中的主要成分(质量分数)为58.36%ZrC、41.64%ZrSi2; ZrC-ZrSi2-Al2O3 复合粉中的主要成分(质量分数)为36.98%ZrC、26.4%ZrSi2 和36.62%Al2O3。使用高速离心式喷雾干燥机制备复合粉。首先通过1.5h的离心搅拌得到原料粉、去离子水、多聚磷酸钠(分散剂)、羟甲基纤维素钠(粘合剂)混合均匀的浆料, 利用蠕动泵将浆料匀速抽入到雾化器中,在雾化器中通过高速离心将浆料分散成较小的雾滴,雾滴在加热区域快速蒸发,与此同时粘结剂迅速固化,进而得到干燥的复合粉体。

  • 等离子喷涂所选用的基体材料为TC4钛合金 (Ti6Al4V,尺寸为10mm×10mm×12mm),并对基体进行喷砂处理。粘结涂层和陶瓷涂层使用等离子喷涂系统(GP-80型,中国,九江喷涂设备有限公司) 喷涂Ni-10wt%Al合金粉末和喷雾干燥法得到的复合粉制备而成,喷涂过程中一次气体(Ar)和二次气体(H2)流速分别为80L/min和20L/min,送粉速率为0.15g/s,喷涂功率为35kW,喷涂距离约为100mm。粘结层的喷涂厚度为50~100 μm,陶瓷层的喷涂厚度约为250 μm。在复合涂层制备完成后, 将涂层的表面研磨并抛光,并观察其断口组织形貌。

  • 1.2 复合粉及涂层的结构与性能表征

  • 利用X射线衍射分析 ( XRD, Rigaku DMAX-2500,Cu Kα Radiation,Japan)研究了复合粉体以及复合涂层的物相组成,X射线衍射分析所采取的2θ 角范围为20°~80°,步长为4°;复合粉的整体形貌和复合涂层的表面压痕、划痕、断口及截面形貌通过扫描电子显微镜( SEM,Hitachi S-4800equipped with EDS,Japan)来获取;同时运用每种涂层在扫描电子显微镜下以500倍的放大倍数所获取的20张图像, 借助图像分析工具,得到了两种复合涂层的孔隙率。采用显微维氏硬度计 ( Vickers Hardness Tester,Shimadzu HMV-2T,Japan) 对涂层的硬度进行测定 (工作参数:载荷为0.98N,加载时间为15s,试验次数为20次),涂层的表面压痕同样是通过以上显微维氏硬度计施加载荷所得(工作参数:载荷为4.9N,加载时间为15s,试验次数为20次)。在已抛光的涂层表面上利用涂层附着力自动划痕仪(WS-2005型,中国,兰州中科凯华科技开发有限公司)测试涂层的抗划痕性能。划痕测试仪的划针采用洛氏金刚石压头(尖端半径:0.2mm,锥角大小:120°)

  • 2 结果与讨论

  • 2.1 复合粉的组织结构分析

  • 图1 为ZrC-ZrSi2 复合粉和ZrC-ZrSi2-Al2O3 复合粉XRD图谱。从图中可以看出,ZrC-ZrSi2 复合粉由立方相的ZrC和正交相的ZrSi2 组成, ZrC-ZrSi2-Al2O3 复合粉由立方相的ZrC、正交相的ZrSi2 和 α-Al2O3 组成,结果表明运用喷雾干燥法所制备出的复合粉中不含有其他杂质。

  • 图1 复合粉的XRD图谱

  • Fig.1 XRD patterns of the composite powders

  • 对复合粉作进一步的分析和表征,图2为ZrC-ZrSi2 复合粉和ZrC-ZrSi2-Al2O3 复合粉的SEM图像。从图中可以看出,两种复合粉均为球形或近球形颗粒,粉末粒径在30~60 μm之间。表1为图2中A区域和B区域的能谱分析结果,从图中可以得知ZrC-ZrSi2 复合粉和ZrC-ZrSi2-Al2O3 复合粉分别由Zr、C、Si和Zr、C、Si、Al、O元素组成,不存在杂质元素的掺杂。纳米Al2O3 的加入填补了喷雾造粒时微米级ZrC和ZrSi2 颗粒团聚过程中产生的缝隙,使得ZrC-ZrSi2-Al2O3 复合粉相较于ZrC-ZrSi2 复合粉球化程度更好,表面更为光滑。作为用于热喷涂过程的复合粉,ZrC-ZrSi2-Al2O3 复合粉具有更好的流动性[20]。

  • 图2 复合粉的SEM图像

  • Fig.2 SEM images of the composite powders

  • 表1 图2两种复合粉各区域的EDS结果

  • Table1 EDS results of different regions shown in Fig.2

  • 2.2 复合涂层的组织结构分析

  • 图3 为大气等离子喷涂ZrC-ZrSi2 复合涂层和ZrC-ZrSi2-Al2O3 复合涂层的XRD图谱。从图3a中可以看出, ZrC-ZrSi2 复合涂层的主相为ZrC和ZrSi2,同时包括SiO2 和m-ZrO2。从图3b中可以看出,ZrC-ZrSi2-Al2O3 复合涂层的主相为ZrC、ZrSi2, 和 α-Al2O3。对比图1和图4中的XRD图谱可知, ZrC-ZrSi2-Al2O3 复合粉在等离子喷涂过程中基本没有发生氧化,具有较好的稳定性。

  • 图4 为两种复合涂层横截面的SEM图像。从图4a中可以看出,ZrC-ZrSi2 复合涂层内部孔隙数目较多且所占体积较大,存在较为明显的未熔融颗粒堆积的现象(如图4a中B区域),同时存在由于层间热应力诱发形成的裂纹。 ZrC-ZrSi2-Al2O3 复合涂层内部孔隙数目相对较少,在其致密区域进一步观察发现有柱状晶产生(如图4b中D区域),这说明复合粉的熔化状态较好。同时,沉积过程中熔融态的Al2O3(如图4bD区域放大图中较为光亮的部分)在一定程度上填充了沉积过程中产生的孔洞和裂纹,提高了复合涂层的致密度。

  • 图3 复合涂层的XRD图谱

  • Fig.3 XRD patterns of the composite coatings

  • 图4 复合涂层的横截面SEM图像

  • Fig.4 Cross-sectional SEM images of the composite coatings

  • 为进一步对造成两种涂层表观致密度差异的原因进行探讨,对涂层内部的物相组成和孔隙率进行了分析。表2为图4中相关区域的能谱分析结果和主要物相组成。陶瓷涂层的孔隙率是反映涂层质量的重要指标,并且作为一种结构表征结果与涂层的许多其他性能有着密切联系[21]。通过图像分析法得到的大气等离子喷涂制备的ZrC-ZrSi2 复合涂层和ZrC-ZrSi2-Al2O3 复合涂层的孔隙率分别为13.8%和10.5%,这同样印证了以上组织结构分析的结果。

  • 表2 图4各区域的元素含量(质量分数)和主要含有的物相种类

  • Table2 Element content (wt.%) and major compositions of different regions shown in Fig.4

  • 2.3 复合涂层的力学性能

  • 涂层显微硬度是指涂层抵抗外界压入体所引起的变形的能力。首先,致密度较高的涂层一般同样具有较高的显微硬度;其次从结构因素来讲, 涂层中硬质相的含量及其分布均匀性在一定程度上会对涂层硬度水平产生影响。 ZrC-ZrSi2 复合涂层和ZrC-ZrSi2-Al2O3 复合涂层的显微硬度分别为897± 65HV0.1 和1 211 ± 78HV0.1。相较于ZrC-ZrSi2 复合涂层,ZrC-ZrSi2-Al2O3 复合涂层的显微硬度的提高可以主要归结为其较高的致密度。同时可以认为在喷涂焰流中熔融态的Al2O3 所提供的液相环境使得硬质相颗粒在沉积过程中具有更好的分散性,硬质相的均匀分布提高了复合涂层的显微硬度。

  • 陶瓷涂层的韧性可以从压痕韧性和断裂韧性两方面来综合分析。两种复合涂层表面压痕的SEM图像如图5所示。可以看出ZrC-ZrSi2-Al2O3 复合涂层的压痕尺寸更小,这同样印证了上节中添加纳米Al2O3 组分的复合涂层显微硬度更高的结论。从图5a中可以看到ZrC-ZrSi2 复合涂层的压痕边缘存在多条裂纹和明显的裂纹扩展,这说明该种复合涂层的韧性较差[22-23]。图5b中所展示的ZrC-ZrSi2-Al2O3 复合涂层的压痕形貌轮廓清晰,压痕方正且边缘平整,没有明显的塌陷或裂纹,只是顶点处有轻微的裂纹扩展,显示出了较好的压痕韧性。

  • 图5 复合涂层的表面压痕SEM图像

  • Fig.5 SEM images of surface indentation of the composite coatings

  • 两种复合涂层的断裂面形貌SEM图像如图6所示。由于陶瓷涂层是脆性材料,一般在断裂时会发生穿晶断裂或沿晶断裂[24-25]。直观上来看,ZrC-ZrSi2-Al2O3 复合涂层的断口组织更为致密,孔隙和裂纹较少,这代表着该种涂层在发生断裂时内部各物相仍能保持良好的黏结状态。而ZrC-ZrSi2 复合涂层的断口组织较为疏松,存在较多由未熔融的颗粒堆积和尺寸较大的孔洞。

  • 图6 复合涂层的断裂面的SEM图像

  • Fig.6 SEM images of the fracture surface of the composite coatings

  • 为进一步分析两种涂层的断裂机制,对断口组织中的不同区域进行进一步的观察和分析。图7展示了两种复合涂层局部的断口组织结构。可以看出,ZrC-ZrSi2 复合涂层的断口组织中存在未熔融颗粒的堆积以及组织结构的断裂(如图7a中A区域),另外在断口内部存在有细长的裂纹,这说明涂层的层间结合较差,不能够有效地阻止裂纹的萌生和扩展。并且断口形貌较为平滑,断裂形成的组织较为细小(如图7a中B区域),展示出了典型的脆性断裂的特征和较差的涂层内聚力。图7b展示了ZrC-ZrSi2-Al2O3复合涂层的局部组织结构。整体来讲涂层断口组织较为致密,没有明显的断裂和尺寸较大的扩展裂纹。通过对涂层断口组织的进一步观察,可以发现部分区域的断口组织起伏较大(如图7b中C区域),断裂路径较为曲折(如图7b中D、E区域),这说明涂层在断裂过程中需要消耗更多的能量。同时,对断口形貌进行微观组织观察发现,在涂层较为致密的断口组织中存在均匀分布的纳米尺寸的粒子(如图7b中F区域),这可以使得裂纹扩展路径更加曲折,增加裂纹扩展能,在一定程度上也增加了ZrC-ZrSi2-Al2O3复合涂层的断裂韧性。以上压痕形貌和断口组织的分析说明ZrC-ZrSi2-Al2O3 复合涂层具有更加优异的韧性。

  • 两种复合涂层表面划痕的SEM图像如图8所示。从图8a中可以看到,ZrC-ZrSi2 复合涂层表面存在大量与滑动方向垂直的裂纹,部分裂纹还出现了裂纹扩展[26-27],沿裂纹扩展的方向上(如图8a中A区域)以及划痕边缘(如图8a中B区域)均有剥落坑的产生,较多剥落坑和横向表面裂纹的产生体现出涂层的内聚力不够高,在外加载荷的作用下很容易发生开裂和剥落,这同样代表着涂层具有较差的划痕韧性。而从图8b中可以看到,在ZrC-ZrSi2-Al2O3 复合涂层划痕表面上裂纹数目较少,划痕的整体尺寸也较小,受到外加载荷的作用后的组织(如区域C)也同样十分致密。在涂层沉积过程中,熔融的纳米Al2O3 会将ZrC和ZrSi2 颗粒包裹起来,在一定程度上增加了涂层中各个物相间的粘结强度。而ZrC-ZrSi2-Al2O3 复合涂层较高的显微硬度和韧性对涂层的抗划痕性能的提升同样有重要的作用。

  • 图7 复合涂层的断裂面局部的SEM图像

  • Fig.7 SEM images of the magnified fracture surface of the composite coating

  • 图8 复合涂层的划痕形貌SEM图像

  • Fig.8 SEM images of the scratch morphology of the composite coatings

  • 3 结论

  • 采用喷雾干燥法成功制备ZrC-ZrSi2 和ZrC-ZrSi2-Al2O3 两种体系复合粉,并使用大气等离子喷涂技术制备了复合涂层,表征并测试了两种涂层的微观结构和力学性能,结论如下:

  • (1) 相较于ZrC-ZrSi2 复合涂层,添加Al2O3 组分的ZrC-ZrSi2-Al2O3 复合涂层的组织更加致密且均匀,并且显微硬度更高,韧性更优,抗划痕性能更好。

  • (2) 熔点较低的Al2O3 组分能够在等离子焰流中先熔化,一方面在喷涂焰流中液相的Al2O3 可以包裹住ZrC和ZrSi2 颗粒,提高了涂层中各物相之间的粘结强度;另一方面熔融态的Al2O3 能够填充在涂层沉积过程中产生的孔洞和裂纹处,降低复合涂层的孔隙率,相应地提高涂层的力学性能。 Al2O3 组分的引入为使用大气等离子喷涂制备高熔点陶瓷基复合涂层的致密化提供了新的思路。

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  • 基本信息

    中图分类号: TQ174
    DOI: 10.11933/j.issn.1007-9289.20210421002

    基金信息

    国家自然科学基金资助项目(52072110)；
    Supported by National Natural Science Foundation of China (52072110).；

    引用信息

    稿件历史

    收稿日期: 2021-04-21

  • 参考文献

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