Abstract
The enhancement of the wear resistance has long been important for bearing steels, hampered in part by the lack of suitable surface strengthening techniques. In this study, ultrasonic shot peening (USP) is employed to enhance the wear resistance of the M50 bearing steel by generating an ultrastrong surface layer with gradient nanograins. The effects of USP treatment on the surface integrity, microstructures, and wear behavior of M50 steel are investigated. The microstructural observation shows that the gradient nanograined surface layer is over 200 μm thick. The lath martensite is refined to nano-martensitic subgrains with few low angle boundaries in the USP-treated M50 steel. Additionally, the microhardness of the nanostructured M50 steel is increased from 795 HV to 987 HV with a penetrating depth of around 800 μm. Wear tests show that the wear rate of the USP-treated M50 steel is reduced by 50.4% under sliding conditions compared to that of the untreated samples. The significantly enhanced wear resistance of the USP-treated M50 is attributed to the ultrastrong gradient nanograined surface layer. The wear mechanism of the USP-treated M50 steel changes from oxidative wear and severe plowing wear to mild plowing wear. Additionally, the thickness of the plastic deformation layer generated during the friction process is reduced. This work provides the materials scientists and engineers with an efficient surface treatment method to enhance the wear resistance of high-strength steels.
Highlights
The bearings applied on aeroengine shafts are required to serve under vibration stresses, high rotational speeds, and aggressive lubrication, etc. [1]
Residual compressive stresses are introduced in the surface layer of the material after shot peening, which enhances the wear resistance, stress corrosion resistance, and fatigue resistance of the bearings [9]
The evolutionary behavior of microstructure and dry sliding wear mechanism of the surface layer of M50 steel after ultrasonic shot peening (USP) treatment are discussed in detail
Summary
The bearings applied on aeroengine shafts are required to serve under vibration stresses, high rotational speeds, and aggressive lubrication, etc. [1]. Surface nitriding and alloying techniques have been widely employed to improve the wear properties of metal alloys [4–6] These techniques are costly and usually performed at high temperatures, which may compromise the service life of metallic materials. If the subsequent superfinishing process is performed, the limited strengthening layer will be removed These disadvantages render SP a poor strengthening method for the bearing materials since they must have a tough core and a hard surface to retard the initiation of cracks against fatigue and wear failures [13,14]. High residual compressive stress [24] and surface hardness [25] after USP treatment improve the fatigue resistance [26] and corrosion resistance [27]. The effects of USP on the changes of surface roughness, microstructure, hardness, residual stress, and wear resistance of M50 steel have been investigated. The evolutionary behavior of microstructure and dry sliding wear mechanism of the surface layer of M50 steel after USP treatment are discussed in detail
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