Abstract
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 × 1017 ions/cm2, and Ti-implantation at an energy of about 40–90 keV and a fluence of 2 × 1017 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.
Highlights
The bearings of aero engines operate in alternating high-speed and high-contact stress environments, in which damage could arise from contact fatigue, wear, and corrosion [1]
New surface modification technologies have been developed for application to bearings in order to improve the performance of main shaft bearings in aero engines operating under harsh environments [3,4,5,6]
The hardness and tribological performance of M50 bearing steels can be improved by ion
Summary
The bearings of aero engines operate in alternating high-speed and high-contact stress environments, in which damage could arise from contact fatigue, wear, and corrosion [1]. Surface modification can efficiently improve the surface mechanical properties of bearing materials, in terms of reducing the friction coefficient and improving wear resistance. Ion implantation is one of the most suitable technologies for surface modification of bearing components, improving their wear-resistance [7], surface hardness [7,8], and contact fatigue [8] due to its unique advantage of maintaining the size of the workpiece and working accuracy during ion implantation [9]. The range of energy used for ion implantation ranges from 20 keV to 100 keV [10,11,12,13], and the mechanism of enhancing wear resistance of metal materials by ion implantation is believed to be associated with the increase of surface hardness and decrease of friction coefficient. Research on the microscopic mechanism of wear resistance in the implanted layer is still lacking, Materials 2017, 10, 1204; doi:10.3390/ma10101204 www.mdpi.com/journal/materials
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