PSI - Issue 81

Viktor Kovalov et al. / Procedia Structural Integrity 81 (2026) 346–352

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operational cutting tests. For reliability assessment, the mean tool life, coefficient of variation, and gamma-percent tool life were determined. For each experimental series, multiple inserts were tested to evaluate both the mean tool life and its scatter. The coefficient of variation was used as a quantitative measure of tool reliability and stability. Comparative analysis between untreated and PMFT treated inserts was performed to assess the effectiveness of pulsed magnetic field treatment 3. Results and Discussion 3.1. Pulsed Magnetic Field Treatment (PMFT) Technique The pulsed magnetic field treatment (PMFT) applied in this study is a specialised technology for modifying the structure of cemented carbides with the aim of improving their structural strength, reducing defectiveness, and increasing resistance to crack initiation under variable loads typical of heavy-duty turning. The method is based on the short-term action of high-intensity magnetic pulses, which induce local microstructural rearrangements by influencing dislocation configurations, residual stress states, and bonding characteristics at WC – WC and WC – Co grain interfaces. The PMFT setup was operated in a mode providing magnetic induction in the range of 2.5 – 3.0 T, with pulse durations of 10 – 50 μs and a repetition frequency of 1 – 5 Hz. This parameter range was experimentally determined as optimal for WC – Co cemented carbides, as it ensures sufficient magneto-mechanical impact without causing thermal degradation of carbide grains or overheating of the cobalt binder. The cutting inserts were positioned inside the working chamber to ensure uniform exposure to the magnetic field and to avoid induction gradients that might lead to non-uniform modification. The treatment was performed at room temperature without additional heating. Each batch of inserts received 50 – 100 pulses, depending on the carbide grade, since cobalt content and grain size distribution strongly influence material responsiveness to magnetic field action. The microstructural effects of PMFT arise from several synergistic mechanisms: relaxation of residual stresses in the cobalt binder; redistribution and rearrangement of dislocations and small defects; increased energetic uniformity at grain boundaries; and modification of the substructure of the cobalt phase, leading to increased fracture toughness and reduced scatter of mechanical properties. After PMFT, comprehensive material characterisation was performed, including fractographic analysis and statistical evaluation of mechanical and operational characteristics. Particular attention was paid to changes in crack behaviour after treatment, including deceleration of crack growth, extension of the stable-growth stage, and reduction in the frequency of catastrophic failures. 3.2. Laboratory Fractography and Crack Morphology Laboratory fracture analysis using optical microscopy and scanning electron microscopy (SEM) revealed significant changes in crack initiation and propagation behaviour after PMFT. Typical fracture focus regions and initial crack growth zones before and after treatment are shown in Fig. 1.

Fig. 1. Fracture focus and initial crack growth zone before and after PMFT

For untreated samples, fracture initiation was frequently associated with technological defects such as pores, binder pools, and carbide agglomerates, which acted as strong stress concentrators. In these cases, rapid quasi-brittle crack growth was observed, leading to premature failure.