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This study aimed to determine the effect of surface roughness and counter body material on the wear behavior of AISI 4140 steel based on the elastoplastic flattening model. Most studies in tribology based on the elastoplastic regime focus on modeling the contact between a sphere and a flat surface. However, these models’ main challenge is determining the real contact area. This study claims that the real contact area can be detected with high accuracy through interface software used in optical microscopy. The sample surfaces were roughened and then supposed to dry sliding wear tests using the AISI 52100 and Al2O3 abrasive counter bodies under varying loads and test durations. It was concluded from the calculations that the sample’s surface roughness value significantly affects the contact pair’s plasticity index and, thus, the sample’s wear behavior against the counter body material. Higher plasticity index values indicating the abrasive effect were obtained with the Al2O3 ball, which has a higher hardness and elasticity modulus than the AISI 52100 steel ball. The surface damage of the sample with a high roughness value was less than the other samples. The COF values obtained with the steel ball were detected as lower than that of the alumina ball. Also, it was seen that the surface roughness parameter and plasticity index values calculated were compatible with the wear characteristics of the test samples. As a result, determining the real contact area between the contacting surfaces and its usability in calculating the elastoplastic flattening model parameters were experimentally tested and verified.

Iron-based superalloys are alloys produced for use in corrosive environments as an alternative to high-cost nickel-based superalloys. However, their average strength and hardness, attributed to their austenitic structures, limit their use in tribological applications. In an attempt to counter these drawbacks, boriding was applied to an iron-based A286 superalloy having an initial surface hardness of 320 HV. Boriding kinetics, some mechanical properties, and tribo-wear (ambient air and 3.5 NaCl environment) behaviors of the formed boride layers were investigated. Multicomponent boride layers (consist of FeB, Fe2B, CrB, NiB, Ni4B3) were formed on the surface of the alloy, with hardness and thickness values of 1498-1961 HV and 20-130 mu m, respectively, depending on the boriding temperature and the treatment time. The integral diffusion model was adopted to deal with the kinetics of monoboride and hemiboride layers formed on the surface. The boron activation energies of FeB, Fe2B, and DZ layer were estimated as equal to 175.86, 198.7, and 205.73 kJ mol- 1, respectively. As a result of increased surface hardness, all of the borided samples displayed reduced friction coefficients and higher wear resistance compared to the untreated alloy, in both ambient air and 3.5% NaCl. However, the increase in wear resistance was not proportional to the increase in hardness; while the best wear resistance was obtained in samples borided at 850-950 degrees C for 6 h, the lowest wear resistance was obtained in samples borided for 4-6 h at 1050 degrees C. This situation was caused by the Kirkendall effect and residual stresses in the structure of alloying elements with different diffusion rates due to the high-temperature effect of the boriding process.

Boronizing processes were carried out at 900 ◦C, 950 ◦C and 1000 ◦C for 2, 4 and 6 h to improve the wear performance of Monel 400 alloy. According to microstructure analyses and nanoindentation tests, Ni2B, FeNiB and FeB phases were detected as dominant phases in the boronized layer. Apart from this, it was observed that the amount of Cu deposits in the boronized layers increased depending on the increasing boronizing temperature. After the boronizing process, the boride layer thickness and hardness values were found to be in the range of 32–272 μm and 12.76–17.83 GPa, respectively. From the results of dry sliding wear test, the wear volume loss values of the boronized Monel 400 alloy decreased by approximately 25 times compared to the untreated samples. The lowest volume loss value among all test samples was observed in the boronized sample at 950 ◦C for 4 h. In addition to the hardness value, it was determined that the morphology and mechanical properties of the boronized layer were also effective on the wear results. Plastic deformation, delamination and oxidation type wear mechanisms were observed as the dominant wear mechanisms in the room and high temperature tests of boronized samples.