TiC_(0.91)N_(0.09)和TiC_(0.77)N_(0.23)涂层高温抗氧化性能的研究

High-temperature Oxidation Resistance Behavior of TiC_(0.91)N_(0.09)and TiC_(0.77)N_(0.23)Coating

目的研究2种不同碳含量的TiCN涂层的抗氧化性能,为改善TiCN涂层抗氧化性能提供理论依据。方法在WC-Co硬质合金上化学气相沉积TiC_(0.91)N_(0.09)和TiC_(0.77)N_(0.23)涂层,采用热重法和静态氧化在900℃进行氧化试验。采用X射线衍射仪、拉曼光谱仪和场发射扫描电镜分析氧化前后涂层的物相组成和微观形貌。比较TiC_(0.91)N_(0.09)和TiC_(0.77)N_(0.23)涂层的抗氧化性能,分析涂层氧化动力学和氧化机理。结果TiC_(0.91)N_(0.09)涂层的氧化质量增量和氧化膜厚度都大于TiC_(0.77)N_(0.23)涂层。TiCN涂层900℃下的热重曲线分线性、抛物线2个阶段。TiC_(0.91)N_(0.09)和TiC_(0.77)N_(0.23)涂层分别于0.225、0.81 h进入抛物线阶段,拟合方程分别为ΔM_(2)=37.23-137.84 t+131.20 t~2和ΔM_(2)=93.89-199.74 t+112.60 t~2。相比于TiC_(0.77)N_(0.23)涂层,TiC_(0.91)N_(0.09)涂层进入扩散控制的抛物线阶段更早,抛物线阶段的氧化速率更快,氧化质量增量更大。TiC_(0.91)N_(0.09)涂层在氧化反应过程中的产气量更大,形成的金红石型TiO_(2)氧化膜更疏松,孔隙、发状裂隙、裂纹等缺陷更多,更易形成连续的扩散通道,O、Ti、W、Co等元素在TiC_(0.91)N_(0.09)涂层氧化膜内的扩散更快,生成更多的基体氧化产物WO_(3)和Co WO_(4),基体氧化物WO_(x)的挥发又会导致涂层氧化更严重。结论TiC_(0.77)N_(0.23)涂层的抗氧化性能优于TiC_(0.91)N_(0.09)涂层。抑制元素在氧化膜中的扩散可有效提高TiCN涂层的抗氧化性能。热重法能获得更丰富的氧化动力学信息,是涂层抗氧化性能和机理研究有效的试验方法。

TiCN is widely used as coating of cutting tools since it combines the advantages of TiN and TiC.Carbon content has an important effect on the properties of TiCN coatings in terms of hardness,toughness,wear resistance and oxidation resistance,etc.The work aims to investigate the oxidation resistance behavior of TiCN coatings with different carbon content,and provide a theoretical support for improving the oxidation resistance of TiCN coatings.In this work,TiC_(0.91)N_(0.09)coatings and TiC_(0.77)N_(0.23)coatings were chosen to investigate the oxidation resistance behavior of TiCN coatings.In addition to static oxidation,thermogravimetry was adopted since it can provide a complete and continuous weight gain curve through real-time measurement,and obtain more information to analyze the whole oxidation process comprehensively.TiC_(0.91)N_(0.09)coatings and TiC_(0.77)N_(0.23)coatings were deposited by chemical vapor deposition on cemented carbide substrate(WC-Co).Thermogravimetry and static oxidation experiments were carried out at 900℃.The phases and morphologies of unoxidized and oxidized TiC_(0.91)N_(0.09)coatings and TiC_(0.77)N_(0.23)coatings were analyzed by X-ray diffractometer(XRD),Raman spectrometer and field emission scanning electron microscopy(FSEM).The oxidation resistance of TiC_(0.91)N_(0.09)coatings and TiC_(0.77)N_(0.23)coatings was compared.In order to better analyze the oxidation kinetics and oxidation mechanism,a thermogravimetric analyzer(THEMYS,Setaram Inc.,France)was used,which was equipped with a real-time microbalance with an accuracy of 0.002μg.After static oxidation at 900℃for 2 h,the oxidation weight gain and the oxidation layer thickness of TiC_(0.91)N_(0.09)coatings were 2.66 and 1.39 times of TiC_(0.77)N_(0.23)coatings,respectively.The porosity of the oxidation layer of TiC_(0.91)N_(0.09)coatings and TiC_(0.77)N_(0.23)coatings was 14.9%and 6.1%,respectively.After thermogravimetric oxidation at 900℃for 2 h,the weight gain of TiC_(0.91)N_(0.09)coatings was 10.45 times of TiC_(0.77)N_(0.23)coatings.According to the above results,compared with TiC_(0.77)N_(0.23)coatings,the TiC_(0.91)N_(0.09)coatings gained more oxidation weight,and the oxidation layer of TiC_(0.91)N_(0.09)coatings was thicker and looser.The thermogravimetric oxidation results further showed that the weight gain curve of TiCN coatings at900℃was divided into reaction-controlled linear stage and diffusion-controlled parabolic stage.It took TiC_(0.91)N_(0.09)coatings and TiC_(0.77)N_(0.23)coatings 0.225 h and 0.81 h to enter the parabolic stage respectively.The fitting oxidation kinetic equations of TiC_(0.91)N_(0.09)coatings and TiC~2_(0.77)N_(0.23)coatings in the parabolic stage wereΔM_(2)=37.23-137.84 t+131.20 t andΔM_(2)=93.89-199.74 t+112.60 t~2,respectively.TiC_(0.91)N_(0.09)coatings entered the diffusion-controlled parabolic stage earlier,were oxidized more quickly in the parabolic stage and gained more oxidation weight.More gas were generated during the oxidation reaction of TiC_(0.91)N_(0.09)coatings with more carbon content,the formed rutile TiO_(2)oxide layer was looser,there were more defects such as pores,fissures and cracks.Therefore,it was easier to provide continuous diffusion channels for TiC_(0.91)N_(0.09)coatings than TiC_(0.77)N_(0.23)coatings.The diffusion of O,Ti,W and Co in the oxidized TiC_(0.91)N_(0.09)coatings was faster,and more oxidation products of substrate such as WO_3 and CoWO_(4)were generated.The volatilization of WO_x also resulted in more pores and cracks in the oxidation layer,leading to more serious oxidation.In conclusion,TiC_(0.77)N_(0.23)coatings have better oxidation resistance than TiC_(0.91)N_(0.09)coatings.The oxidation resistance of TiCN coatings can be improved effectively by inhibiting the diffusion of elements in the oxidation layer.In addition,thermogravimetry is a good method to investigate the oxidation resistance behavior and mechanism of coatings because it can provide more informations about oxidation kinetics.