WC-Co硬质合金/CVD金刚石涂层刀具研究现状

Research Progress on Cutting Tools Made from WC-Co Cemented Carbide Substrates and Coated with CVD Diamond

化学气相沉积(Chemical vapor deposition,CVD)金刚石涂层刀具具有高硬度、优异的耐磨性、良好的冲击韧性和化学稳定性,能满足高效率、高精度的加工要求,逐渐成为切削铝和高硅铝合金、碳纤维增强复合材料及石墨等轻质量高强度难加工材料的主流涂层刀具。基于WC-Co硬质合金为基体的CVD金刚石涂层刀具在切削加工过程中容易发生CVD金刚石涂层的剥落,自主研发结合性能优良、长时间加工稳定的WC-Co硬质合金/CVD金刚石涂层刀具仍是该领域国内外发展的必然趋势。目前,研究者为了提高WC-Co硬质合金/CVD金刚石涂层刀具的结合性能,采用化学刻蚀法和机械处理法相结合去除WC-Co硬质合金基体表层中的Co粘结相,发现其能增强涂层与基体的结合强度,但基体表层Co粘结相含量的减少容易导致基体中形成脆化层,降低基体的强度和韧性。为了减少基体的强度和韧性损失,研究者在WC-Co硬质合金基体和金刚石涂层之间制备稳定的含Co中间化合物或沉积中间层,成功阻挡Co粘结相的热扩散。除了上述方法外,研究者还通过调控金刚石涂层工艺参数和结构,将微米晶与纳米晶金刚石层叠相结合,来提高金刚石涂层刀具的摩擦学性能和涂层与基体间结合强度。本文综述了WC-Co硬质合金/CVD金刚石涂层刀具的应用进展,明确了WC-Co硬质合金与CVD金刚石涂层间附着失效是刀具切削加工中最主要的失效形式,详细分析了影响附着失效的主要原因。在此基础上,着重介绍了各种优化工艺对增强涂层刀具性能影响的最新研究进展;指出了WC-Co硬质合金/CVD金刚石涂层刀具的性能受化学刻蚀、机械刻蚀、形成含钴化合物层、沉积中间层等基体前处理以及金刚石涂层工艺参数和结构的影响较大,对于不同牌号或不同厂家生产的同种牌号的WC-Co硬质合金基材,需要进行不同的表面前处理,而针对不同的切削加工材料,需要采用合适的金刚石涂层沉积工艺和结构以提高涂层与基材之间的结合强度,进而提高刀具的性能;最后提出了研制一种普适性强的基体前处理、涂层工艺和结构创新策略,以实现不同应用场景下WC-Co硬质合金/CVD金刚石涂层刀具的高效长寿命切削,可能是未来的研究方向。

Chemical vapour deposition(CVD)diamond-coated tools have high hardness,excellent wear resistance,good impact toughness,and chemical stability.These tools can meet the requirements of high efficiency and precision machining.Therefore,this technology has been used as commercial coating tools for light-weight,high-strength,and difficult-to-process materials,such as high-silicon aluminium alloys,carbon fiber-reinforced composite materials and graphite.However,CVD diamond-coated tools based on WC-Co cemented carbide are prone to peeling off during the cutting process.Therefore,the development of WC-Co cemented carbide/CVD diamond-coated tools with excellent wear resistance and long-term processing stability is inevitable.Recently,it has been reported that a combination of chemical etching and mechanical treatment can be used to remove the Co binder in the substrate,which enhances the adhesion strength of the diamond coating.Thereby,the bonding performance of WC-Co cemented carbide/CVD diamond-coated tools is improved.However,these techniques lead to the formation of a brittle layer and decreased substrate strength and toughness.A Co-containing compound or deposited intermediate layer,which can successfully block the Co binder,is formed between the WC-Co cemented carbide substrate and diamond-coating to prevent a reduction in substrate strength.Moreover,the tribological properties and adhesion strength of diamond-coated tools were also reported to be improved by adjusting the diamond layer s process parameters and structure and combining microcrystalline and nanocrystalline diamond layers.Firstly,this paper reviews the current applications and existing problems related to WC-Co cemented carbide/CVD diamond-coated cutting tools.Subsequently,the main causes of tool adhesion failure are analysed.Based on the initial review of literature,the latest research progress in the performance improvement of coated tools by various optimisation processes is introduced.Furthermore,this paper presents different grades of WC-Co cemented carbide/CVD diamond-coated tools and the same grades sourced from different manufacturers that were greatly affected by the substrate pretreatment method,such as chemical etching,mechanical etching,the formation of a Co-containing compound or deposited intermediate layer,and the adjustment of the process parameters and structure of the diamond layers.In conclusion,it is proposed that obtaining a universal pretreatment and deposition technology for realising high-efficiency and long-life cutting of WC-Co cemented carbide/CVD diamond-coated tools for different application scenarios may be a future research prospect.