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The final surface modification processes enhance the fatigue strength, wear resistance, and corrosion resistance of the workpiece by improving the surface quality, enhancing the microhardness, generating compressive residual stresses on the surface, and creating favorable changes in the microstructure. In this regard, using processes with different mechanisms is regarded as an optimal method to increase the efficiency of the final surface modification processes. This research seeks to experimentally investigate the hybrid laser-ultrasonic assisted ball burnishing (LUAB) process and its effect on the surface integrity and fatigue strength of 4340 alloy steel. The effect of the process on the sample's microstructure was evaluated by the images obtained from the optical microscope and SEM. Further, the parameters of mean surface roughness and microhardness, as well as the results of the uniaxial tensile test and fatigue test of the workpiece were evaluated. In the case of using appropriate parameters in the process, the results indicated a 93.38% reduction in mean surface roughness and an increase of surface microhardness by 3.4 times compared to the initial sample. Additionally, the investigation of microstructure revealed the accessibility of homogeneous and refinement martensitic structures without surface melting. The results of uniaxial tensile and fatigue tests indicated a 6.29% increase in tensile strength and a 20.71% increase in the endurance limit of the treated sample (LUAB) compared to the initial sample. Finally, the results also showed a change in the fracture mode in the uniaxial tensile test and a reduction in the final fracture area in the fatigue test. [ABSTRACT FROM AUTHOR]

Despite the growing demands for personalized items, the capacity of conventional production techniques is restricted to respond to such needs. Instead of conventional manufacturing processes, the intended structure can be directly constructed in a layer-by-layer manner, also known as additive manufacturing (AM). Among AM methods, selective laser melting (SLM) has gained a great deal of attention due to its low cost and availability. However, the poor surface quality in this method is still a problem as it may influence critical mechanical properties of the components like their fatigue life. Therefore, adequate postprocesses are required for additively manufactured metals. In the present study, shot peening (SP) and burnishing were applied as postprocesses to the 316 L stainless steel manufactured by SLM, and then, surface roughness, porosity, microhardness, and fatigue performance were experimentally investigated. Based on the results, the mean surface roughness (Ra) of the as-SLMed sample was 10.907 µm which decreased to 8.543 and 1.324 µm, after SP and the burnishing processes, respectively. Interestingly, the burnishing process was more effective in eliminating near-surface pores and improving microhardness of the samples compared to SP. In addition, the fatigue life of the as-SLMed sample (135,000 cycles) slightly improved after SP (353,000 cycles), while burnishing drastically enhanced the fatigue life of the samples (3,030,000 cycles). [ABSTRACT FROM AUTHOR]

Purpose: First, the effect of magnetic field intensity and nano-ferrofluid concentrations on surface roughness was evaluated in magnetic minimum quantity lubrication (MMQL). Then, the effect of lubricant flow rate and nozzle position on surface roughness was investigated in MQL, MMQL, electrostatic MQL (EMQL) and electromagnetic MQL (EMMQL). Design/methodology/approach: This study examined the performance of MQL under magnetic and electric fields in turning AISI 304 stainless steel in terms of surface roughness and compared the results with those obtained from wet cutting and MQL turning operations. To prepare the nano-ferrofluid used in different states of MQL, Fe3O4 nanoparticles were added to the base fluid. Findings: The results showed that the surface roughness under the EMMQL technique decreased by 36% and 49.4% on average compared with wet and MQL techniques, respectively. The lubrication technique affected the surface roughness by 90.2%, whereas it was 8.3% for the lubricant flow rate. EMQL and EMMQL techniques had no significant difference in their effects on surface roughness. In the innovative MMQL technique, the nano-ferrofluid concentration of 6% and magnetic field intensity of 93 G resulted in lower surface roughness of the workpiece relative to other counterparts. Originality/value: Examining previously published studies showed that using nano-ferrofluids under a magnetic field for cooling purposes in machining processes have less considered by researchers. This study applies an innovative method of lubrication under the concurrent effect of magnetic and electric fields, called EMMQL, to improve the efficiency of MQL in machining hard-to-cut materials. For comprehensively inspecting the newly presented method, the effects of several parameters, including the nano-ferrofluid concentration, magnetic field intensity, lubricant flow rate and position of lubricant spray nozzle, on the surface roughness of workpiece in turning of AISI 304 stainless steel are investigated. [ABSTRACT FROM AUTHOR]