金刚石涂层硬质合金HfC-SiC过渡层制备及结合强度研究

发布时间：2018-09-11 18:25

【摘要】：采用化学气相沉积方法,将金刚石沉积到硬质合金(WC-Co)刀体表面获得的涂层刀具,既可以发挥金刚石高硬度、高耐磨性和高导热性的优势,又可以保持硬质合金韧性好、强度高的特点,在有色金属及其合金、各种颗粒或纤维增强复合材料、高性能陶瓷等材料加工领域有着广阔的应用前景。然而,金刚石涂层与硬质合金基体间结合强度较低,在一定程度上限制了金刚石涂层刀具的应用。导致其结合强度低的原因主要有两方面:一是硬质合金中的Co在金刚石涂层的沉积过程中会抑制金刚石形核,导致界面处石墨和非晶碳形成;二是金刚石与硬质合金材料间存在硬度、热膨胀系数(CTE)等差异,导致涂层热应力问题。本论文利用双辉等离子表面冶金技术(DGPSA)的技术优势,结合碳化铪(HfC)和碳化硅(Si C)具有较高硬度和较低CTE的特点,在硬质合金表面制备与基体冶金结合的SiC/HfC和HfC-SiC/HfC两种新型过渡层,以减小Co的负面催化作用,调配过渡层的热膨胀系数,改善金刚石涂层的结合强度。其中,SiC/HfC为双层组织结构,由HfC内层和SiC外层组成;HfC-Si C/HfC则为双层梯度组织结构,主要由HfC内层和成分梯度分布的HfC-SiC外层组成。论文通过对DGPSA装置进行优化改进,获得两种新型过渡层组织结构,结合物相分析、组织结构表征和性能测试,研究了典型过渡层结构对金刚石涂层结合强度的影响,为提高金刚石涂层/硬质合金间的结合强度提供了参考依据。本文主要研究内容及研究结果如下:(1)探究了dgpsa技术制备sic的可行性,借助comsol软件对dgpsa装置内气体流场进行了数值模拟和优化设计,根据模拟结果对装置进行了改进,并利用改进后的装置对模拟优化的结果进行了验证。实验表明,采用现有的装置即使在四甲基硅烷(tms)流量较高的条件下,也无法实现sic的沉积,装置中的保温罩对反应气体的阻挡是无法实现sic制备的主要原因。而气体由保温罩侧面进入、由测温观察孔和新增出气孔同时流出的方式,可以在样品上方及等离子体区域获得均匀且强度较高的气体流场,是最有可能实现sic合成的进出气方式。验证实验表明,根据模拟结果改进的装置可以在较宽的工艺范围内沉积sic涂层,但所制备的sic涂层受co催化作用的影响,致密性与结合强度较差,不适合直接用作金刚石涂层硬质合金的过渡层。(2)使用改进的dgpsa装置,分别以基体温度和tms流量为变量,在wc-co硬质合金基体上制备了sic/hfc双层过渡层,对所制备过渡层的表面和界面形貌、物相组成、硬度及结合强度等进行了测试分析,探讨了适用的sic/hfc双层过渡层的结构性能和制备条件。实验结果表明,基体温度为800℃,tms流量为2.0sccm时,sic/hfc双层过渡层组织致密,显微硬度较高,且与基体间结合良好。该参数下制备的过渡层可以有效地阻挡co向沉积表面扩散,并能够在其表面沉积致密均匀且具有较高强度的纳米金刚石涂层,涂层结合强度达到hf3级。(3)在研究结果(2)的基础上,通过在dgpsa过程中不断增大tms流量的方式,在硬质合金表面制备出HfC-SiC/HfC双层梯度过渡层,并研究了不同流量增速对过渡层成分、微观组织和性能的影响规律。随后,在结构优化的双层梯度过渡层上沉积了金刚石涂层,对比分析了两种过渡层表面金刚石涂层的结合性能及内在成因。结果表明,HfC-SiC/HfC双层梯度过渡层的组织结构与SiC/HfC双层过渡层类似,但是内外层之间的界面过渡良好,在外层中HfC和SiC呈梯度分布。TMS流量增速为0.20 sccm时,过渡层具有较高的表面粗糙度和结合强度,同时表面显微硬度也较高。与SiC/HfC双层过渡层表面沉积的金刚石涂层相比,在HfC-SiC/HfC双层梯度过渡层表面获得的金刚石涂层,具有更高的结合强度和更低的热应力,表明成分和性能梯度分布的HfC-Si C/HfC双层过渡层是改善金刚石涂层/硬质合金体系结合强度的一种有效的方法和途径。
[Abstract]:The coated cutting tools obtained by depositing diamond on the surface of carbide (WC-Co) cutter body by chemical vapor deposition can not only give full play to the advantages of high hardness, high wear resistance and high thermal conductivity of diamond, but also keep the characteristics of good toughness and high strength of cemented carbide, such as non-ferrous metals and their alloys, various particles or fiber reinforced composites. However, the low bonding strength between diamond coatings and cemented carbide matrix limits the application of diamond coated tools to a certain extent. There are two main reasons for the low bonding strength: one is the deposition process of Co in cemented carbide in diamond coatings. It can inhibit the nucleation of diamond and lead to the formation of graphite and amorphous carbon at the interface. Secondly, there are differences in hardness and thermal expansion coefficient (CTE) between diamond and cemented carbide, which lead to the thermal stress problem of the coating. SiC/HfC and HfC-SiC/HfC transition layers metallurgically bonded to cemented carbide substrate were prepared to reduce the negative catalytic effect of Co, adjust the thermal expansion coefficient of transition layer and improve the bonding strength of diamond coating. C/HfC is a double-layer gradient structure, mainly composed of HfC inner layer and HfC-SiC outer layer with gradient distribution of composition.In this paper, two new transition layer structures were obtained by optimizing and improving the DGPSA device. The bonding strength of typical transition layer structure to diamond coating was studied by phase analysis, microstructure characterization and performance testing. The main research contents and results are as follows: (1) the feasibility of fabricating SiC by DGPSA technology is explored. the gas flow field in DGPSA device is simulated and optimized by COMSOL software. the device is designed according to the simulation results. The experimental results show that the existing device can not realize the deposition of SiC even under the condition of high TMS flow rate. The main reason for the failure of SiC preparation is that the thermal shield blocks the reaction gas. It is possible to obtain uniform and high intensity gas flow field above the sample and in the plasma region by means of surface entry and simultaneous outflow of temperature observation holes and new outflow holes. However, the prepared SiC coating is not suitable for direct use as the transition layer of diamond-coated cemented carbide because of its poor compactness and bonding strength due to the influence of CO catalysis. (2) SiC / HFC double-layer transition layer was prepared on WC-Co cemented carbide substrate by using an improved DGPSA device with matrix temperature and TMS flow rate as variables, respectively. The surface and interface morphology, phase composition, hardness and bonding strength of the SiC / HFC double-layer transition layer were tested and analyzed, and the suitable structure, properties and preparation conditions of the SiC / HFC double-layer transition layer were discussed. Good. the transition layer prepared under these parameters can effectively prevent the diffusion of CO to the deposited surface, and can deposit dense and uniform nano-diamond coatings with high strength. the bonding strength of the coatings reaches hf_3 level. (3) on the basis of the research results (2), by increasing the TMS flow rate in the DGPSA process, in the way of hard bonding. HfC-SiC/HfC double-layer gradient transition layers were prepared on the diamond surface, and the effects of different flow rates on the composition, microstructure and properties of the transition layers were studied. The results show that the microstructure of HfC-SiC/HfC double-layer gradient transition layer is similar to that of SiC/HfC double-layer transition layer, but the interface transition between the inner and outer layers is good, and the HfC and SiC are gradient distributed in the outer layer. Compared with the diamond coating deposited on the HfC-SiC/HfC double-layer gradient transition layer, the diamond coating deposited on the HfC-SiC/HfC double-layer gradient transition layer has higher bond strength and lower thermal stress, which indicates that the HfC-Si C/HfC double-layer transition layer with gradient distribution of composition and property is an effective way to improve the bond strength of the diamond coating/cemented carbide system. Ways and means.
【学位授予单位】：太原理工大学
【学位级别】：博士
【学位授予年份】：2017
【分类号】：TG174.4

【相似文献】