Jie Jin, Shao Tianmin
State Key Laboratory of Tribology, Tsinghua University, Beijing 100084, China.
Materials (Basel). 2017 Oct 19;10(10):1204. doi: 10.3390/ma10101204.
M50 bearing steels were alternately implanted with Ti⁺ and N⁺ ions using solid and gas ion sources of implantation system, respectively. N-implantation was carried out at an energy of about 80 keV and a fluence of 2 × 10 ions/cm², and Ti-implantation at an energy of about 40-90 keV and a fluence of 2 × 10 ions/cm². The microstructures of modification layers were analyzed by grazing-incidence X-ray diffraction, auger electron spectroscopy, X-ray photoelectron spectroscopy, and transmission electron microscopy. The results showed that the gradient structure was formed under the M50 bearing steel subsurface, along the ion implantation influence zone composed of amorphous, nanocrystalline, and gradient-refinement phases. A layer of precipitation compounds like TiN is formed. In addition, nano-indentation hardness and tribological properties of the gradient structure subsurface were examined using a nano-indenter and a friction and wear tester. The nano-indentation hardness of N + Ti-co-implanted sample is above 12 GPa, ~1.3 times than that of pristine samples. The friction coefficient is smaller than 0.2, which is 22.2% of that of pristine samples. The synergism between precipitation-phase strengthening and gradient microstructure is the main mechanism for improving the mechanical properties of M50 materials.
分别使用注入系统的固体和气体离子源对M50轴承钢交替注入Ti⁺和N⁺离子。N注入能量约为80 keV，注量为2×10离子/cm²，Ti注入能量约为40 - 90 keV，注量为2×10离子/cm²。采用掠入射X射线衍射、俄歇电子能谱、X射线光电子能谱和透射电子显微镜对改性层的微观结构进行了分析。结果表明，在M50轴承钢亚表层沿着由非晶相、纳米晶相和梯度细化相组成的离子注入影响区形成了梯度结构。形成了一层如TiN的析出化合物。此外，使用纳米压痕仪和摩擦磨损试验机对梯度结构亚表层的纳米压痕硬度和摩擦学性能进行了检测。N + Ti共注入样品的纳米压痕硬度高于12 GPa，约为原始样品的1.3倍。摩擦系数小于0.2，为原始样品的22.2%。析出相强化与梯度微观结构之间的协同作用是改善M50材料力学性能的主要机制。
