CuZn39Pb3 leaded brass is one of the most widely used alloys in machining, with a 100% machinability index. However, there has been a lack of research on the effects of coldworking on surface integrity (SI) and operating behaviour of CuZn39Pb3 components. This study addresses this knowledge gap by examining the effects of three optimised combined processes on surface roughness, a key SI characteristic. Specifically, samples were subjected to a turning process followed by diamond burnishing (DB); this combined process was performed under three conditions: conventional flood lubrication (F), dry (D), and dry and cool-assisted (D+C) conditions. Cool-assisted conditions were achieved using a special device with a cold air nozzle operating on the vortex tube principle. The D and D+C conditions represent environmentally sustainable alternatives because they eliminate the use of cutting fluids, thereby reducing their adverse effects on both the environment and human health. The resulting surfaces obtained after each of the three optimised combined processes (F, D, and D+C) exhibited mirror-like finishes with minimum average roughness Ra values of 0.054, 0.079, and 0.082 μm, respectively. In addition, the F- and D+C-processes resulted in surface profiles with negative skewness and kurtosis values greater than three. Since roughness shape parameters are known to influence the operating behaviour of machined components, these processes are suitable for improving wear resistance in boundary lubrication regimes.

The article presents a study of the possibilities for restoring the working surfaces of molds for high-pressure casting of non-ferrous metals by laser surfacing using a filler material. Test specimens with parameters of real forming elements were manufactured. The influence of nitriding on welded layers and basic material was studied in comparison with one without nitriding. The X-ray diffraction method was used to obtain the phase composition of the surface of the samples in areas submitted to nitriding. Scanning electron microscopy (SEM) was used to determine the microstructure of the nitriding layers, welded layers and bulk material. Energy-dispersive X-ray spectrometry (EDX) was applied to investigate the chemical composition in the welded and nitrided zone. Mechanical property means of microhardness measurements were studied. Four zones were identified after nitriding in the weld area. The first zone closest to the surface with a thickness of 0.025 mm is characterized by a higher microhardness, which reaches 700 HV. The second zone, which is part of the diffusion zone, is 0.1 mm thick, and it is characterized by the same size grains with a similar shape and microhardness, which reaches 600 HV. The microhardness measured in the welded zone after nitriding is 50% greater than that without nitriding. The thickness of the diffusion zone in 1.2343 steel reaches about 0.15 mm, and the microhardness is about 900 HV near the edge, but quickly decreases to 400 HV.

CuZn39Pb3 leaded brass is one of the most widely used alloys in machining. Despite its good machinability, there is a lack of information in the literature on the effects of surface cold working on the surface microhardness, microhardness profile, introduced residual stresses, microstructure, and the operating behaviour of machined components. This article reveals the capabilities of conventional diamond burnishing (DB) (implemented under flood-lubrication conditions) to improve the surface integrity and high- and mega-cycle fatigue strength of CuZn39Pb3 cylindrical components such as axles and shafts. The results show that both the smoothing and hardening DB processes achieve mirror-like surfaces, introduce significant residual compressive stresses at depths greater than 0.5 mm, and significantly increase the fatigue strength in the high- and mega-cycle regions compared to the reference condition (turned and polished specimens). However, the surface microhardness is weakly affected by the degree of surface cold working. Given the almost identical microhardness profiles and the equivalent distribution in depth of the introduced residual stresses by the two DB processes, the possible reason for the more pronounced effect of the hardening process on the fatigue strength lies in the thicker affected layer and the reduced negative skewness introduced by this process.

When chromium-nickel austenitic stainless steels must satisfy a requirement for a high degree of strain-hardening, the nickel content is limited to 8 - 9 wt. %. The surface cold working of these steels causes the martensitic transformation γ → α′. Thus, the surface microhardness and residual compressive stresses increase due to the presence of the harder strain-induced a’-martensite phase. This article investigates the influence of the governing factors of diamond burnishing (DB) on the percentage content of the a’-martensite in the surface layer of AISI 304 steel using planned experiment, analysis of variance and regression analysis. A mathematical model of the percentage content of a’- martensite depending on the burnishing force, feed rate and burnishing velocity was created. Of the three governing factors, the most significant is feed rate, and the least important is burnishing force. Thermal effects have a greater impact on martensitic transformation γ → α′ compared to the mechanical effect. The percentage of martensite in the surface and subsurface layers is necessary information for determining the residual stresses by the X-ray method when studying the effect of DB on the surface integrity of austenitic stainless steels.

This article presents an optimised deep rolling process, implemented using a single-toroidal-roller burnishing method, to improve the surface integrity and high-cycle fatigue strength of 42CrMo4 steel axles and shafts. A second-order composition plan, regression analyses, and multi-objective optimisation were employed. The solution was based on a non-dominated sorting genetic algorithm (NSGA-II) and Pareto front search approach. The compromise optimal solution yields an average roughness Ra of 0.190 μm, average surface microhardness of 503 HV, and average surface residual axial stress of –855 MPa. Deep rolling conducted using the selected optimal values (a burnishing force of 1000 N and feed rate of 0.11 mm/rev) of the governing factors achieves stable surface integrity characteristics under multiple repetitions of the process. Rotating bending fatigue tests showed that the positive effect of deep rolling begins to manifest itself after 10⁴ cycles, i.e., in the second half of the high-cycle fatigue field and in the mega-cycle region, where the fatigue strength increases from 390 (after turning and polishing) to 440 MPa (after turning and subsequent deep rolling).