Abstract

Diamond-like carbon (DLC) coatings have undergone a significant amount of research over the last several years and shows promise as a coating material in reducing the friction between moving components of machinery and various other applications. This study investigated the reduction of friction coefficients on these surfaces by applying an external electric field under the assumption that thermal plasma would be generated under an inert gas atmosphere and that the number of hydrocarbons generated by thermal decomposition could also be controlled. Results show that the friction coefficient of DLC heated to 200 °C by laser irradiation was indeed controlled by an external electric field. Although the friction coefficient without the bias voltage between the DLC and leaf spring was approximately 0.35, applying a positive bias voltage to DLC of + 10 and + 20 V corresponding to an electric field of 80 and 160 kV m⁻¹ decreased to 0.1. Meanwhile, the negative bias voltage did not show a reduction in the friction coefficient. Raman spectroscopy of the pin surface after the friction test indicated that the hydrocarbons generated by the thermal decomposition of DLC were transferred onto the pin surface by applying a positive bias voltage of + 10 and + 20 V. Meanwhile, we measured the current from DLC heated using a hotplate on the counter surface of the Si wafer insulated with the DLC using a ceramic ring by applying a bias voltage to the DLC. The current from the DLC forward Si wafer was changed by the applied electric field. When a positive voltage is applied to the DLC, the current flows from the DLC to the Si wafer, and when a negative voltage is applied, the current flows from the Si wafer to the DLC. This dependence on the electric field intensity shows the opposite tendency to that of the friction coefficient on the electric field intensity. Therefore, the hydrocarbon ions generated by the thermal decomposition of the DLC are attracted to the pin surface as the counter surface side by the electric field when an appropriate positive bias voltage is applied to the DLC. Subsequently, liquid hydrocarbons are transferred and deposited on the pin surface, and the friction coefficient decreases owing to the lubrication effect of the adhered hydrocarbons. If this voltage becomes too large, thermal electron emissions from the DLC will be suppressed, and the amount of hydrocarbon generation will decrease. In contrast, when a negative voltage is applied to the DLC, the thermal electron emissions are increased by the work function reduction due to the electric field; however, the hydrocarbon ions are attracted to the DLC and redeposited to the DLC. Finally, we estimated that the number of hydrocarbons transferred to the pin surface could be controlled by the external electric field, and these hydrocarbons changed the friction coefficient of the DLC.

Graphic Abstract

中文翻译：

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电场对激光辐照加热类金刚石碳膜摩擦系数的影响

摘要

类金刚石碳 (DLC) 涂层在过去几年中进行了大量研究，并显示出作为减少机械运动部件和各种其他应用之间摩擦的涂层材料的前景。本研究假设在惰性气体气氛下会产生热等离子体，并且通过热分解产生的碳氢化合物的数量也可以控制，通过施加外部电场来降低这些表面的摩擦系数。结果表明，通过激光照射加热到 200℃的 DLC 的摩擦系数确实受外部电场控制。虽然DLC和板簧之间没有偏置电压的摩擦系数约为0.35，⁻¹下降到 0.1。同时，负偏压并未显示摩擦系数降低。摩擦试验后销钉表面的拉曼光谱表明，通过施加 + 10 和 + 20 V 的正偏置电压，DLC 热分解产生的碳氢化合物转移到销钉表面。 同时，我们测量了 DLC 加热的电流通过向 DLC 施加偏置电压，使用陶瓷环在与 DLC 绝缘的 Si 晶片的反面上使用加热板。来自 DLC 正向硅晶片的电流因施加的电场而改变。当对DLC施加正电压时，电流从DLC流向Si晶片，当施加负电压时，电流从Si晶片流向DLC。这种对电场强度的依赖性显示出与摩擦系数对电场强度的依赖性相反的趋势。因此，当对DLC施加适当的正偏压时，由DLC的热分解产生的烃离子被电场吸引到作为反面侧的销表面。随后，液态碳氢化合物转移并沉积在销表面，由于粘附碳氢化合物的润滑作用，摩擦系数降低。如果该电压过大，则来自DLC的热电子发射将受到抑制，碳氢化合物的生成量将减少。相反，当向 DLC 施加负电压时，由于电场引起的功函数降低，热电子发射增加；然而，烃离子被吸引到 DLC 并重新沉积到 DLC。最后，我们估计转移到销表面的碳氢化合物的数量可以通过外部电场控制，这些碳氢化合物改变了 DLC 的摩擦系数。

图形摘要