Hardfacing deposits of ER NiCr-B alloy were fabricated in single and double layer configurations on 12 mm thick AISI 316L(N) stainless steel substrate using the cold metal transfer process (CMT) with an 80% Ar + 20% CO 2 shielding gas mixture. Microstructural analysis revealed that the precipitate (carbide and boride) fractions increased from 13.12% in the first layer to 17.84% in the second layer, yielding corresponding hardness values of ∼482 VHN and ∼602 VHN. Tribological performance of the hardface deposits was evaluated under a 2 N load across ambient, 25 °C-vacuum, and 550 °C-vacuum conditions. For the first layer deposit, friction coefficients of 0.62, 0.72, and 0.38 were observed in three different test conditions, with corresponding wear rates of 6.17 × 10 −16 , 9.4 × 10 −16 and 4.72 × 10 −16 m 3 /N·m. The second layer deposit exhibited lower friction coefficients (0.58, 0.59, and 0.48) and reduced wear rates (2.44 × 10 −16 , 2.95 × 10 −16 , and 2.07 × 10 −16 m 3 /N·m). Detailed investigation was performed using electron microscopy, Raman spectroscopy, and profilometry of the wear tracks . Wear mechanism in ambient condition was predominantly abrasive, whereas at 550 °C-vacuum condition adhesive wear was significant. At 25 °C-vacuum condition, wear was governed by both abrasive and adhesive mechanisms, characterized by highest wear rate. The results indicate that the addition of CO 2 in the argon shielding gas promotes crack-free, low-dilution deposits with enhanced hardness and favorable wear resistance, emphasizing the effectiveness of CMT process for producing durable NiCr-B hardface deposits on stainless steel substrates.
This study investigates the dry sliding tribological behavior of as-received Armox 500T steel using a pin-on-disc tribometer across three rotational speeds (350, 400, and 450 RPM) and four applied loads (20, 30, 90, and 120 N). Microstructural characterization confirmed a fine lath martensitic structure with retained austenite, yielding an average Vickers microhardness of 528.64 HV. Volume loss, specific wear rate, coefficient of friction, and surface roughness were evaluated as tribological responses. Rotational speed drove a mild-to-severe wear regime transition and dominated specific wear rate (similar to 88% ANOVA contribution), while applied load exclusively governed coefficient of friction (COF) (similar to 99.8%). An inverse relationship between surface roughness and specific wear rate at higher speeds was attributed to thermally induced surface flattening and mechanically mixed layer formation. The Time & times; Applied Load interaction was the largest contributor to volume loss, confirming the time-dependent nature of material removal. These findings provide practical guidance for avoiding critical speed-load combinations in sliding applications.
This study investigates the tribological performance of 65 Mn steel plow surfaces modified by combined ultrasonic shot peening and snake-inspired microtexturing under water lubrication. Ultrasonic shot peening was first applied to enhance surface hardness, followed by laser texturing to fabricate microstructures with different texture densities (18%, 27%, and 36%). Surface characteristics, including hardness, roughness, and morphology, were systematically characterized. Reciprocating friction and wear tests were conducted, and the lubrication mechanism was analyzed using numerical simulations in Ansys Fluent. Results show that shot peening significantly improves wear resistance despite increasing surface roughness, while microtexturing alone provides limited improvement. The combined treatment exhibits the best tribological performance at 27% texture density, reducing friction coefficient and wear rate by 25.58% and 69.14%, respectively. This improvement is attributed to enhanced hydrodynamic lubrication and load-carrying capacity induced by the microtextures, providing guidance for biomimetic wear-resistant surface design of agricultural tools under water lubrication.
This study systematically examines the wear performance and machining efficiency of vacuum-brazed diamond-coated milling tools under optimized processing conditions. Two widely used metamorphic-origin marbles, Mu & gbreve;la White (MW) and U & scedil;ak White (UW), were selected as workpieces. The experimental methodology involved milling operations on a CNC machining center, where spindle speed (6000-12000 rpm), feed rate (1500-3000 mm/min), and a constant depth of cut (1 mm) were selected as the key input process parameters. Machining performance was evaluated through surface roughness (Ra), cutting force (Fr), specific energy consumption (SE), and material removal rate (MRR), while wear mechanisms were characterized using Scanning Electron Microscopy (SEM) and digital microscopy on machined areas of 1 to 7 m2. Optimization analysis determined the ideal processing conditions to be 6000 rpm and 2281 mm/min for MW, and 12000 rpm and 3000 mm/min for UW, which were subsequently confirmed by validation experiments. Comparative findings indicated that the lower mechanical strength of MW marble resulted in greater material removal but increased tool wear (54%) compared to UW (47%). These results highlight the decisive influence of microstructural characteristics and operating parameters on tool wear, thereby contributing to the industry by offering guidelines for extending tool lifecycle and enhancing energy efficiency.
Ambient exposure to water vapour and oxygen undermines the long-term lubricity of magnetron-sputtered molybdenum disulphide (MoS2) coatings, yet the individual and synergistic contributions of the two species remain poorly quantified. Here we decouple their effects by ageing 1 & micro;m PVD-MoS2 films for 500 h in six precisely controlled gas/humidity atmospheres (dry, 25% RH and 50% RH; N-2 or air) followed by micro-tribological testing in dry N-2. Complementary "unaged" samples were slid directly in identical environments to probe instantaneous reactivity. Coefficient-of-friction data, Raman spectroscopy, SEM-EDS mapping and cross-sectional TEM reveal three key findings: (i) humidity alone raises steady-state friction by up to 2.5-fold, whereas dry oxygen has little effect; (ii) concurrent H2O and O-2 during storage triggers sub-surface penetration of O-species, formation of MoO2/MoO3 within wear scars and inhibition of basal-plane realignment, yielding a persistent friction penalty (& micro; approximate to 0.12) independent of run-in; (iii) ageing in dry or humid N-2 preserves lamellar re-orientation and maintains low friction (& micro; approximate to 0.05) after only 50 cycles. A mechanistic model is proposed in which adsorbed water lowers the activation barrier for oxygen insertion at defect and edge sites, corroborated by a 2-3 cm(-1) blue shift of the E-2(g)1 Raman band. By isolating the water-assisted oxidation pathway at ambient temperature, this study provides the first quantitative guideline for MoS2 component storage: moisture-free inert gas environments effectively arrest chemical degradation, whereas even moderate humidity in air accelerates tribo-oxidative damage. The insights inform design tools for precision-mechanical assemblies where pre-deployment shelf life is critical.
