## 3 Results and Discussion
Similarly, for the 150 V mode, the thermocouple measured 343.6 \({}^{\circ}\)C, which, when adjusted for inertia, yields 374.3 \({}^{\circ}\)C. This value corresponds to a deviation of about 6.2% when compared to the numerical value of 398.9 \({}^{\circ}\)C.  
To further verify the numerical reliability of the thermal model, a mesh convergence test was conducted at the 200 V processing mode. The simulation was repeated using two progressively refined grids with approximately 6000 and 40,000 nodes. The calculated maximum surface temperatures for these cases were 878.9 \({}^{\circ}\)C and 878.903 \({}^{\circ}\)C, respectively. Compared to the base mesh with 254 nodes (875.45 \({}^{\circ}\)C), the deviation between the coarsest and finest mesh solutions was only 3.45 \({}^{\circ}\)C, corresponding to a relative error of approximately 0.39%. These results demonstrate that the thermal field distribution stabilizes with increasing mesh resolution, and the base mesh provides sufficiently accurate results for engineering-level simulations while ensuring acceptable computational efficiency. The data reveal a strong correlation between measured and calculated values for the 150 V and 200 V modes. However, a notable discrepancy arises at 250 V, where the numerical calculation estimates a temperature of 1127.1 \({}^{\circ}\)C, while the thermocouple records approximately 870 \({}^{\circ}\)C. This variance is primarily attributed to a technical issue involving compromised thermal contact between the thermocouple and the sample. The LOK-59 solder, used to affix the thermocouple at a 2 mm depth, has a melting point of around 900 \({}^{\circ}\)C. As temperatures surpass this threshold, partial melting of the solder can occur, impeding effective heat transfer between the sample and the thermocouple's sensing element, thereby causing an underestimation of actual temperature values. Furthermore, radiative heat exchange between the sample's heated surface and the surrounding environment becomes more significant above 1000 \({}^{\circ}\)C. This can induce heat redistribution and deviations from the idealized conditions assumed in the model. These factors clarify the divergence between computed and empirical data at 250 V, underscoring the necessity for meticulous interpretation of thermometry results in high-temperature electrolytic plasma hardening scenarios. For future studies involving elevated-temperature EPH regimes, it is recommended to employ thermocouples with higher thermal stability and reduced response time, such as tungsten-fhenium or miniature fast-response sensors. Additionally, the use of high-melting-point solders (e.g., VPR-1 or VPR-11, with melting points exceeding 1000 \({}^{\circ}\)C) is advisable to ensure reliable thermal contact throughout the entire heating cycle. These modifications would enhance the accuracy of temperature measurements and support more robust validation of thermal models under extreme processing conditions. To assess the thermal action efficiency across various EPT modes, the average heating rates at a 2 mm depth from the sample surface were calculated over the entire heating period. Experimentally, these rates were found to be 35.4 \({}^{\circ}\)C/s at 150 V, 62.5 \({}^{\circ}\)C/s at 200 V, and 92.9 \({}^{\circ}\)C/s at 250 V. Numerical estimations produced similar values of 37.9 \({}^{\circ}\)C/s, 67.9 \({}^{\circ}\)C/s, and 112.4 \({}^{\circ}\)C/s, respectively. These findings indicate a strong correlation between experimental results and calculations, accounting for errors introduced by the measuring system's inertia. Notably, the local heating rates near the surface during the initial processing seconds significantly surpass these averages, potentially reaching hundreds of degrees per second, particularly at 250 V. This underscores the thermal effect's intensity and elucidates the rapid attainment of critical temperatures in the material's surface layers.