PSI - Issue 59

Olha Maksymiv et al. / Procedia Structural Integrity 59 (2024) 378–384 Olha Maksymiv et al. / Structural Integrity Procedia 00 (2019) 000 – 000

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The content of hydrogen, oxygen and carbon in the surface metal layer was evaluated after contact fatigue studies by secondary ion emission analysis described by Oura et al. (2013) using CAMECA SMI 300 apparatus. It enables evaluating element concentration on the surface areas of 100…200 µm 2 . The microhardness was measured using PMT-3 equipment at a load of 100 g. The residual stresses were evaluated using a mechanical method based on the measurements of bending strain that appeared at the layer-by-layer electrochemical etching of the metal developed by Berezhnitskaya et al. (2003). The contact durability was investigated using MKB-K equipment with the specimen rotating frequency of 250 Hz under working loads on a specimen of 4000 MPa relative to the working conditions of drilling bits and rolling bearings. Industrial oil and tap water were used as test environments. The equipment with a double-disk scheme of the contact loading is shown in Fig. 1. The rotation of the specimen and working load was brought into action by loading disk 1 with 150 mm in diameter which was activated by a direct current motor through its frictional contact with the specimen, simultaneously increasing specimen rotational frequency proportionally to the ratio of their diameters (150/10). The machine was automatically turned off simultaneously with the appearance of a pitting.

Fig. 1. The test scheme ( a ): 1 – loading disk, 2 – medium supply, 3 – specimen, V 1 and V 2 – disk and specimen rotational speed.

3. Results discussion Martensite - austenite structure with a grain size of martensite of 27.2, 23 and 20.6 nm has been generated in the surface layer of steel due to MPT in air, an aqueous solution of emulsol and industrial oil, respectively. The microhardness (Fig. 2) differs not significantly but the depth of the strengthened layer is the smallest after MPT in

Fig. 2 . The microhardness distribution in the depth of the steel’s surface layer with NCS after MPT in different T F: 1 – industrial oil, 2 – air, 3 – 10 % aqueous solution of emulsol.