Nano-scratch and fretting wear study of DLC coatings for biomedical application

The generation of wear particles is now considered one of the most important failures in total arthroplasty. It is especially needed to study damage process of the particles at slight movement and lower load for long-term service of implanted materials. The wear and abrasion behavior of particles on Ti–6Al–4V coated with diamond-like carbon (DLC) were appropriately simulated in the present paper by fretting wear and nano-scratch test. The coatings with a thickness of 2.5 μm were deposited with an r.f.-plasma enhanced chemical vapor deposition method. The analytic techniques employed to assess DLC coatings characterization include SEM, AFM, Raman and IR spectroscopy. Assessment of hardness, elastic modulus, abrasion and adhesion of the coatings were performed using a Nano Indenter XP system with attachments of continuous stiffness measurements (CSM) and lateral force measurements (LFM). Tribological properties of the coatings were evaluated by a fretting wear test. It was concluded that the DLC coatings had a smooth surface morphology with a rms of 6.8 nm and possessed good adhesion to the substrate, they recovered fully elastic at lower load (60 mN) and were ploughed and delaminated only partially at higher load (400 mN). Nevertheless, there was wear debris concurrently generated during the nano-scratch and fretting test, which was more evident at high loads for a definite coatings, indicating an essential necessity of the work to improve the wear resistant of the coatings to avoid the generation of wear debris. The friction coefficient of DLC coatings against corundum obtained by fretting test decreased with the increase of relative humidity, it was below 0.1 in an aqueous condition, this may be beneficial to their biomedical applications in body fluids.     

氮表面改性非晶碳基涂层的摩擦及腐蚀行为

目的 在本征无氢非晶碳涂层表面进行掺N表面改性处理,研究其摩擦性能与海水腐蚀行为的演变规律,为海洋防护非晶碳涂层应用提供新思路。方法 采用直流磁控溅射固体石墨靶制备非晶碳涂层,并在顶层进行N掺杂表面改性。改变Ar/N2气流量比来控制顶层掺N量,调控沉积时间,控制涂层厚度一致。SEM用于观测涂层厚度与截面形貌,XPS和Raman光谱仪分别用于表征涂层N掺杂量和碳键结构。涂层力学性能和动态摩擦因数则通过连续刚度模式纳米压痕仪和球盘式摩擦实验机测试得到。采用含有三电极体系的Gamry电化学工作站测量涂层的动电位极化曲线、电化学交流阻抗谱等电化学性能。结果 对无氢非晶碳涂层进行表面改性,随顶层改性N含量的增加,sp2—C易与N结合,导致sp2相含量降低。随着N含量的增加,涂层的力学性能逐渐提升,当N质量分数为21%时,硬度与弹性模量达到最大值,分别为11.71GPa和284.28GPa;但当N质量分数最小（12%）时,涂层的断裂韧性与抗弹塑性变形能力最优。由于顶层引入掺N层后,sp2润滑相减少,涂层摩擦因数显著上升,且随N含量的增大逐渐增大。在顶层引入N掺杂量较少的改性层有利于提高非晶碳的耐蚀...