Improvement of wear resistance and safety of cobalt-chromium alloys for metal-on-metal type artificial joint

采用一种Co-29mass%Cr-6mass%Mo合金（ASTM F799-95），在准生物环境下，在空气和磷酸盐缓冲盐水（PBS(-)）中分别施加1.0、3.5和5.0MPa的应力，采用平针式往复摩擦试验机对其进行摩擦磨损性能评价，以了解该合金用于金属对金属型人工髋关节的性能。另外，对试验后溶解在PBS中的金属离子（-）进行定量。结果表明，在PBS（-）中的磨损量远小于在空气中的磨损量，且在空气和PBS（-）中磨损量都随着外加应力的增大而增大，而在PBS（-）中的稳态摩擦系数大于在空气中的摩擦系数。PBS（-）中的磨损损伤比空气中的磨损损伤小，但在PBS（-）中观察到的不规则度比空气中的小。通过向合金中注入氮离子，降低合金中镍的含量，提高合金的摩擦磨损性能。对未注入和注入氮离子的Co-Cr-Mo合金的摩擦磨损性能进行了评价。从磨损屑和PBS（-）的润滑行为可以看出，PBS（-）中的磨损损失远小于空气中的磨损损失，并且随着空气和PBS（-）中施加应力的增加而增加，而试验过程中稳态的摩擦系数在PBS（-）中大于空气中的摩擦系数。氮离子注入能有效降低Co-Cr-Mo合金滑动界面处PBS（-）的摩擦系数，减少PBS（-）中的磨损屑。利用x射线光电子能谱分析了离子注入、高压灭菌和汉克斯溶液作为模拟体液浸泡后合金表层成分的变化，以评估材料的稳定性，预测材料的安全性和组织相容性。氮注入后，氮原子以氮化钴的形式存在于基体表面氧化物的正下方，NH_3或NH_4以氮化钴的形式存在于基体表面氧化物中，且随着注入剂量的增加而增加。离子注入后，铬在表面氧化物中富集，而在基体中富集。钴在高压灭菌过程中被优先氧化，并在高压灭菌后在基体中被耗尽。少

Friction-wear properties of a Co-29mass%Cr-6mass%Mo alloy (ASTM F799-95) but reducing the amount of nickel were evaluated with friction-wear test using a pin-on-flat type reciprocating friction tester in air and phosphate buffered saline, PBS(-), as a quasi-biological environment under applied stress of 1.0, 3.5 and 5.0MPa to understand the performance of this alloy for metal-on-metal type artificial hip joints. In addition, metal ions dissolved in PBS(-) after the test was quantified. As a result, wear loss in PBS(-) is much smaller than that in air and increases with the increase of applied stress in both air and PBS(-), while the coefficient of friction in steady state during the test is larger in PBS(-) than in air. Wear damage in PBS(-) is smaller than that in air, however more small scale of irregularity is observed in PBS(-) than that in air.Nitrogen ions were implanted in the alloy with reducing the amount of nickel in order to improve the friction-wear properties. The friction … More -wear properties of unimplanted and nitrogen-ion-implanted Co-Cr-Mo alloys were evaluated. As a result, the wear loss in PBS(-) was much smaller than that in air and increased with the increase of applied stress in both air and PBS(-), while the friction coefficient in a steady state during the test was larger in PBS(-) than in air, according to the lubrication behaviors of wear debris and PBS(-). Nitrogen-ion implantation is effective to decrease the friction coefficient in PBS(-) at the sliding interface between mutual Co-Cr-Mo alloys as well as to decrease the wear debris in PBS(-).Changes in the composition of the surface layer of the alloy with ion implantation, autoclaving, and immersion in Hanks' solution as a simulated body fluid were characterized using X-ray photoelectron spectroscopy to evaluate the stability of the material and predict the safety and tissue compatibility of the material. After N-implantation, nitrogen atoms existed as cobalt nitride in the substrate just under the surface oxide and NH_3 or NH_4 in the surface oxide, and these amounts increased with the increase of the dose. Chromium was concentrated in the surface oxide but depleted in the substrate with ion implantation. Cobalt was preferentially oxidized by autoclaving and depleted in the substrate after autoclaving. Less