Wimmer M A, Laurent M P, Mathew M T, Nagelli C, Liao Y, Marks L D, Jacobs J J, Fischer A
Rush University Medical Center, Chicago, IL, USA.
Department of Material Science, Northwestern University, Evanston, IL, USA.
Wear. 2015 May-Jun;332-333:643-649. doi: 10.1016/j.wear.2015.02.013.
Tribochemical reactions in a protein lubricated metal-on-metal (MoM) sliding contact may play a significant role for its wear performance. Such reactions lead to the formation of a carbonaceous 'tribofilm', which can act as a protective layer against corrosion and wear. The purpose of this study was to determine the effect of contact load on wear and the formation and retention of tribofilms. Wear tests were performed in a custom-made ball-on-flat testing apparatus that incorporated an electrochemical cell. A ceramic ball was used to articulate against low-carbon wrought CoCrMo alloy pins in bovine serum. Using a range of contact loads at a single potentiostatic condition (close to free potential), weight loss and changes in surface properties were evaluated. We determined that wear was influenced by the loading condition. As expected, wear increased with load, but the association between applied load and measured weight loss was not linear. In the intermediate load region, in the range of 32-48 N (~58-80 MPa), there was more than an order of magnitude drop in the wear per unit load, and the wear versus load data suggested an inflexion point at 49 N. Regression analyses yielded a cubic model (=0.991; =0.0002), where the cubic term, which represents the inflexion, was highly significant (=0.0021). This model is supported by the observations that the minimum in the friction versus load curve is at 52 N and the highest relative increase in polarization resistance occurred at 49 N. Scanning electron microscopy and Raman spectroscopy indicated the absence of a tribofilm for the low and within the contact area of the high load cases. Synergistic interactions of wear and corrosion seem to play an important role.
蛋白质润滑的金属对金属（MoM）滑动接触中的摩擦化学反应可能对其磨损性能起重要作用。此类反应会导致形成含碳的“摩擦膜”，该摩擦膜可作为防止腐蚀和磨损的保护层。本研究的目的是确定接触载荷对磨损以及摩擦膜形成和保留的影响。磨损试验在一个定制的球-平面测试装置中进行，该装置集成了一个电化学电池。使用陶瓷球在牛血清中与低碳锻造CoCrMo合金销进行铰接。在单一恒电位条件（接近自由电位）下使用一系列接触载荷，评估重量损失和表面性能变化。我们确定磨损受加载条件影响。正如预期的那样，磨损随载荷增加，但施加的载荷与测量的重量损失之间的关系不是线性的。在中等载荷区域，即32 - 48 N（约58 - 80 MPa）范围内，单位载荷下的磨损下降超过一个数量级，磨损与载荷数据表明在49 N处有一个拐点。回归分析得出一个三次模型（(R^2 = 0.991)；(p = 0.0002)），其中代表拐点的三次项非常显著（(p = 0.0021)）。该模型得到以下观察结果的支持：摩擦与载荷曲线的最小值在52 N处，极化电阻的最高相对增加发生在49 N处。扫描电子显微镜和拉曼光谱表明，在低载荷和高载荷情况下的接触区域内均不存在摩擦膜。磨损和腐蚀的协同相互作用似乎起重要作用。
