PSI - Issue 5

Hirotaka Tanabe et al. / Procedia Structural Integrity 5 (2017) 1005–1010 H Tanabe et al. / Structural Integrity Procedia 00 (2017) 000 – 000

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combination of ceramic coating and laser heat treatment, “laser quenching after coating”, was developed. In this method, a steel substrate is first coated with a ceramic thin film by PVD or CVD method, and then the substrate is quenched by laser irradiation to the ceramic coated surface. By applying this method, it was possible to improve the adhesive strength and substrate hardness of ceramic coated steels effectively without compromising the film hardness and the toughness. Moreover, by the advantages of laser quenching, high dimensional accuracy can be achieved and “energy saving and environment - friendly” process can be expected. From these strong points, it was considered that the raceway of ball bearing could be one of the good applications of this method. The objective of this study is to obtain the basic data about the effects of “laser quenching after coating” on the rolling contact fatigue strength of ceramic coated steels. In this study, the thrust type rolling contact fatigue tests were carried out for ceramic coated steel processed by laser quenching after coating under various laser power conditions, and the relationships between laser power and delamination initiation life was discussed. The material used for the substrate was carbon tool steel JIS SK105. The substrate dimensions were 55 mm  55 mm  5 mm. The surface was finished by polishing, and the surface roughness R a was about 0.05 μm. In our previous studies [1-4], it was found that CrAlN was one of the suitable coating material for laser quenching after coating process because of its high hardness (20GPa), high oxidization temperature (1373K) and high heat absorption (85%). Therefore, in this study, CrAlN was chosen as coating material. CrAlN coating was deposited onto the substrates by arc ion plating (AIP) method. The thickness was 2.5 μm. The deposition temperature was approximately 673 K. In this study, a thrust type rolling contact fatigue testing machine (Kashima Bearings Corporation, Japan) was used. Figure 1 shows the Schematic illustration of rolling contact fatigue testing machine. In this test, the parts of the thrust ball bearing JIS 51305: a retainer, a ball-holder and 11 balls (JIS-SUJ2 steel, diameter 9.525mm) were used. The pitch circle diameter (P.C.D) of the balls was 38.6mm. The rotation speed was 1800rpm. The test load applied by dead weight was 550N. The test was carried out in the oil bath filled with turbine oil (MIL-PRF-23699, Showa Shell Sekiyu KK, Japan). In order to check the initiation of the delamination, the fatigue tests were sometimes interrupted. A digital microscope (VH8000, KEYENCE, Japan) was used for the observation of the specimen surface. 2.2. Rolling contact fatigue test 2. Experimental method 2.1. Specimens

Fig. 1. Schematic illustration of rolling contact fatigue testing machine.