Improved Wear Performance Research Articles

Physical and Chemical Evolution of PTFE-α-Al2O3 Composites Versus 304 SS Tribofilms During Dry Sliding

Polytetrafluoroethylene (PTFE) is renowned for its remarkably low friction coefficient (µ ~ 0.1) yet exhibits notably high wear rates (K ~ 104) in dry sliding applications. To mitigate this, various metallic and non-metallic fillers have been explored, consistently demonstrating a reduction in wear rates of unfilled PTFE between 10 and 104 times. Among these fillers, α-Al2O3 is one of the most extensively studied materials. 5 wt% of α-Al2O3 filler into PTFE yields a composite material, PTFE- α-Al2O3, characterized by a wear rate a staggering 104 times lower than unfilled PTFE. This reduction in wear has been attributed to the formation of tribofilms on the PTFE composite and metal counterbody material. These tribofilms emerge due to the interaction between broken fluropolymer chains and environmental water and oxygen. This interaction results in the creation of carboxylate salt groups, which subsequently react with metal/metal oxide particles (both from the counterbody and the metal filler) to form tribofilms. Despite numerous studies scrutinizing the chemical composition of the tribofilms pre- and post-test, the chemical development of these films has remained largely unexplored. In this study, the authors utilize attenuated total reflection infrared spectroscopy (ATR-IR), transmission infrared (IR) spectroscopy, optical microscopy, and stylus profilometry to observe tribofilm development. A thorough topographical and chemical description of the tribofilm is provided via these techniques. The ratio of carboxylate salt groups directly corresponds with improved wear performance and these changes are very local to the worn polymer surface. This discovery contributes to a deeper understanding of the tribological behavior of PTFE-α-Al2O3 composites.Graphical

LONG-TERM SURVIVORSHIP OF METAL-ON-METAL HIP RESURFACING ARTHROPLASTY: COMPARATIVE COHORT STUDY AT 15 YEARS

In 1997 the Birmingham Hip Resurfacing was introduced to address the needs of young active patients. Alternative designs were introduced to try and improve wear performance. The aim of this study was a comparative cohort study of two types of metal-on-metal bearing to determine the mechanism of failure at 15 years.The study reviewed 91 Brimingham Hip Resurfacings (BHR) (Smith and Nephew) and 715 DUROM hip resurfacing (Zimmer) procedures in prior to 2009. Failure was defined as revision of either component for any reason. Kaplan-Meyer survivorship analysis performed. Routine follow-up with serum metal ion levels and radiographs.Mean follow-up was 17.9 years (range 15.2 – 25.1). The mean age at operation was 51.6 years (SD 8.6, range 20.7 to 70.2), including 299 women (37.1%). The Birmingham resurfacing demonstrated 92.3% survivorship at 15 years (SE 2.8, 95% CI 3.9 – 7.8) and 90.0% at latest follow-up (SE 3.5, 95% CI 4.9 to 9.4). By comparison, the DUROM survivorship at 15 years was 89.1% at 15 years (SE 1.2, 95% CI 2.0 to 2.5) and 87.4% (SE 1.3, 95% CI 2.5 to 2.3) at latest follow-up. There was no statistically significant difference in survivorship between groups (p= 0.32). Survival in male patients was 92.7% compared to 80.0% in females. The reported failures occurred from Adverse Reaction to Metal Debris (32 patients), periprosthetic femoral neck fracture (6) and aseptic loosening (41), PJI (12) and undiagnosed pain (6). The mean cobalt and chromium levels at last follow-up were 33.4 nmol/L and 36.5 nmol/L respectively.This study demonstrates two differently designed metal-on-metal hip resurfacing provided a durable alternative to total hip replacement, particularly in younger male patients with osteoarthritis. Differences in design did determine the reason for revision with acetabular fixation being one of the principal failure mechanisms for the DUROM compared to elevated ion levels.

Ionic Liquids as Extreme Pressure Additives for Bearing Steel Applications

The protection of steel surfaces from wear under extreme pressure conditions is of major importance in several industries as it provides better performance and longer life of machinery. The motivation for this work was to study the lubrication of steel by ionic liquids (ILs), which have recently emerged as greener alternatives to commercial lubricants and additives. Three ILs based on sulfur-containing anions, used as 2-wt% additives in polyethylene glycol base oil (MW 200; PEG 200), were tested in the lubrication of ASTM 52100 bearing steel contacts in extreme pressure conditions (under mixed lubrication with a Hertzian pressure of 1.12 GPa) using a mini traction machine (MTM). Due to the poor resistance to corrosion of bearing steel, a semi-ester of succinic acid derivative corrosion inhibitor (Lanxess RC 4801) was added to the mixtures at a 1 wt% concentration. The ILs 1-hexyl-methylimidazolium trifluoromethanesulfonate ([C6mim][TfO]) and 1-hexyl-4-picolinium trifluoromethanesulfonate ([C6-4-pic][TfO]) revealed promising results in terms of surface protection of bearing steel. In contrast, 4-picolinium hydrogen sulfate ([4-picH][HSO4]) as 2-wt% additive to PEG 200 + 1% RC 4801 did not show any improvement in wear performance compared to neat PEG 200 + 1% RC 4801. PEG 200 + 2% [C6mim][TfO] + 1%RC 4801 allowed for a decrease in wear up to ~ 76% and PEG 200 + 2% [C6-4-pic][TfO] + 1%RC 4801 up to ~ 46% when compared with neat PEG 200 + 1% RC 4801. Optical microscopy images suggest the formation of an adsorbed layer, which was further supported by chemical analysis via x-ray photoelectron spectroscopy (XPS) data for [C6mim][TfO].Graphical abstract

Wear performance of MoS2 doped Al2O3 CPED coatings on TC6 titanium alloy

The innovative work presented in the paper focused on microstructures and wear performance of MoS2 doped Al2O3 coatings on TC6 alloy. Nano- and micron-sized MoS2 particles doped Al2O3 coatings (n and m-MoS2/Al2O3 coating) were fabricated on TC6 alloy via cathodic plasma electrolytic deposition (CPED) technique. The microstructures and compositions of the coatings were characterized, the tribological behaviors were tested, and doping mechanism of MoS2 particles was discussed. The results showed that, doped coatings were composed of α-Al2O3, γ-Al2O3 and MoS2. The doping of MoS2 particles promoted the transformation from γ-Al2O3 to α-Al2O3 during CPED process, and increased the compactness and crystallinity of doped coatings. The friction coefficients of TC6 alloy, Al2O3 coating, n-MoS2/Al2O3 coating and m-MoS2/Al2O3 coating were about 0.7, 0.6, 0.55 and 0.45 in sequence, and the wear rates of n-MoS2/Al2O3 coating and m-MoS2/Al2O3 coating were about 75 % and 58 % of Al2O3 coating. MoS2 particles played the role of lubrication and contributed to improving wear performance of doped coatings, both friction coefficients and wear rates were declined, and micron-sized MoS2 particles presented better wear performance than nano-sized particles.

A practical approach to fabrication of nano-Al2O3 reinforced MMC coatings by cold spray: Characterization of nanomechanical and tribological performance

Cold spray is a crucial solid-state deposition technique involving high-speed spraying of different-sized particles onto a base material. In this study, Ni-based powder reinforced with different proportions of nano-Al2O3 particles was sprayed onto Al6061 alloy by cold spray to improve the coating performance. Nanoparticles are very difficult to deposition as they are affected by the aerodynamic forces generated during cold spraying. With a practical approach, nanoparticles were agglomerated with micron-sized feedstock powders, and nanoparticles in the sprayed powder acted as larger particles and successfully defeated the aerodynamic force. The effects of adding nano-particles on the microstructural, nanomechanical, and tribological properties were investigated. Microstructural analyses revealed that MMC coating layers comprised ceramic particles and metal matrix (Ni and Zn). Due to the high spraying speed, the nano-particles were spread in the relatively ductile matrix formed by Ni and Zn. The micro- and nanohardness values were increased with nanoparticle volume by two mechanisms. In the first mechanism, the hard particle volume increased with the addition of nano powders, and in the second mechanism, the plastic deformation of the matrix increased due to the nano-particles. The sample without nanoparticle reinforcement exhibited plastic deformation during the initial stage of the nanoscratch test. The dry sliding wear test results showed that the nano-Al2O3-reinforced spraying powders increased the wear resistance approximately 1.9 times. According to FESEM and EDS examinations of worn surfaces and WC counter-bodies, nano-particles reduced the transferred layers caused by adhesion to the abrasive counter-body. In addition, the nano-particles were provided a more homogeneous hard particle distribution and improved wear performance.

Post-Treatment and Hybrid Techniques for Prolonging the Service Life of Fused Deposition Modeling Printed Automotive Parts: A Wear Strength Perspective

<div>This study aims to explore the wear characteristics of fused deposition modeling (FDM) printed automotive parts and techniques to improve wear performance. The surface roughness of the parts printed from this widely used additive manufacturing technology requires more attention to reduce surface roughness further and subsequently the mechanical strength of the printed geometries. The main aspect of this study is to examine the effect of process parameters and annealing on the surface roughness and the wear rate of FDM printed acrylonitrile butadiene styrene (ABS) parts to diminish the issue mentioned above. American Society for Testing and Materials (ASTM) G99 specified test specimens were fabricated for the investigations. The parameters considered in this study were nozzle temperature, infill density, printing velocity, and top/bottom pattern. The hybrid tool, i.e., GA–ANN (genetic algorithm–artificial neural network) has been opted to train, predict, and optimize the surface roughness and sliding wear of the printed parts. Results disclose that the minimum surface roughness obtained with GA–ANN was 1.05482 μm for infill density of 68%, nozzle temperature of 230°C, printing velocity of 80 mm/sec, and for concentric type of top/bottom pattern. In extension of this study, annealing was performed on the specimens printed on the optimized results obtained from the analysis at three different temperatures of 110°C, 150°C, and 190°C and for a fixed period of time of 60 min as a post-treatment process to further study the impact of annealing on the surface roughness and wear rate. The surface roughness of the samples showed a discernible improvement as a result of annealing, which can further make significant inroads in automotive industries.</div>

Muti-mechanism of the improving wear performance for titanium alloy via laser powder bed fusion

Wear is the key issue hindering the further application of titanium alloy. The aim of this work was to explore the strengthening mechanisms for the wear properties of Ti–15Mo alloys via laser powder bed fusion (LPBF) by the La2O3 addition. The results showed that the grain of LPBF-fabricated Ti–15Mo/La2O3 composites was obviously refined after La2O3 addition by heterogeneous nucleation and inhibited grain growth. The average grain size of Ti–15Mo/(0.2 wt%, 0.4 wt%, 0.6 wt% and 0.8 wt%) La2O3 composites is 11.75 μm, 10.85 μm, 10.39 μm, and 9.99 μm, respectively. The wear rate of Ti–15Mo/(0.2 wt% - 0.8 wt%) La2O3 composites is 1.5916 × 10−4mm3N−1m−1, 1.2885 × 10−4mm3N−1m−1, 0.6821 × 10−4mm3N−1m−1 and 0.6063 × 10−4mm3N−1m−1, respectively. Thanks to the combined effect of fine grain strengthening, grain boundary strengthening, precipitation strengthening, dispersion strengthening and dislocation strengthening, the wear resistance of the obtained sample exceeds that of the LPBF-fabricated Ti–15Mo sample more than five times and that of the LPBF-fabricated CP-Ti sample more than ten times.

Influence of Homogenization and Quench-Aging Heat Treatments on Dry Wear Behavior of Al-40Zn-3Cu Alloy

The influence of homogenization and quench-aging treatments on the dry sliding friction and wear behavior of Al-40Zn-3Cu bearing alloy was experimentally studied. These treatments removed dendritic structure of the alloy and caused the formation of zinc-rich precipitates distributed homogenously in the matrix of the alloy. It was observed that quench-aging treatment carried out at temperatures of 100 °C and 150 °C significantly improved both hardness and strength of the alloy as compared to homogenization treatment. However, aging at 200 °C lowered these values of the alloy but increased its elongation. Dry sliding wear test results displayed that homogenization and quench-aging treatments increased the wear performance of the alloy. However, it is found that the quench-aging treatment created more powerful effect for improving wear performance of the alloy than homogenization. Quench-aging treatment at 100 °C for 300 min resulted in a decrease in the lowest specific wear rate of the alloy by causing the highest increases in its hardness (from 119 HB to 178 HB), yield strength (from 288 MPa to 383 MPa) and tensile strength (from 319 MPa to 407 MPa) due to the age hardening mechanism. It was observed that the worn surfaces of the alloy samples were composed of adhered and smeared material and delaminated areas. This observation suggested that adhesion and delamination were the operative wear mechanisms of the alloy. The results were explained and discussed in terms of microstructural features, mechanical properties, and wear mechanisms of Al-40Zn-3Cu alloy.

Improving wear performance, physical, and mechanical properties of iron sand/epoxy composite modified with carbon powder

This study was conducted to investigate the usage of iron sand as composite reinforcement. The addition of carbon powder with variations of 15 wt%, 20 wt%, and 30 wt% is expected to enhance the interfacial bond between iron sand and epoxy matrix to be better. Physical and mechanical properties of the composite were investigated using a wear resistance test Pin on Disc method, shore-D hardness, bending test, X-ray diffraction (XRD), Fourier Transform Infrared (FTIR) and Scanning Electron Microscope (SEM). The results showed an increase in wear resistance and mechanical properties of composite due to the addition of carbon powder. This was confirmed by the fact that the HCP composite with 30 wt% carbon powder showed a good increase in wear resistance but a reduction in flexural properties and hardness values. Meanwhile, the LCP composite with 20 wt% carbon powder was recommended in terms of good flexural properties. The increased mechanical properties of composite were supported by composite crystallinity index value recorded to be 59.45 % from the XRD test. SEM analysis showed better dispersion and interfacial bonding for carbon powder and iron sand in the composite matrix. These results are expected to contribute to the new development of composite brake pad.

Dry sliding wear characteristics of in-situ hybrid (Al3Ni + Al2O3)–Al composites

Dry sliding wear characteristics of in-situ hybrid (Al3Ni + Al2O3)/Al composites synthesised by solid-state combustion of Al– xNiO ( x = 8 wt%, 10 wt%, 12 wt% and 15 wt%) system were investigated. The results indicate that the in-situ hybrid Al3Ni + Al2O3 particles can markedly improve wear performance of composites. The increase of wear resistance with an increase in NiO content at room temperature can be attributed to high hardness offered by high volume fraction of hard Al3Ni and Al2O3 particles. While, at 200 °C, the increase in wear resistance of composites with higher NiO contents can be attributed to the high thermal stability of composites. With the increase of NiO content from 8% to 15%, the wear mode of composites also is discussed at room temperature and 200 °C.

A comprehensive structural and electrochemical study on the performance of Mn-phosphate layers

Several manganese phosphating routes, including the influence of immersion time (15 min. and 30 min.), addition of accelerators (Ni(NO3)2, 2 g/l), modification in the activation stage (increased concentration in the activator), and ultrasonic stirring, were used to obtain films with a variety of characteristics. This research uses the following common analytical methods for the phosphate characterisation: scanning electron microscopy (SEM) and electrochemical techniques (potentiodynamic polarisation and electrochemical impedance spectroscopy (EIS). Thus, modifications in the coating mass, covering efficiency, surface appearance, and chemical composition/structure could be determined. This study showed that accelerators induced the formation of thicker layers (up to 125 % bigger), whereas ultrasonic stirring assisted with reducing the crystal sizes and developing denser films (up to 50 % reduction in the icorr values). The dry frictional tests showed that the wear behaviour depended on the phosphate thickness, crystal density, and film tortuosity. A fine-grained structure or a thick film contributed to an improved wear performance (near 80 % reduction in the coefficient of friction), but grains that are too fine along with an intricate structure worsened the behaviour under frictional forces.

Enhanced Wear Behavior of a Stainless Steel Coating Deposited on a Medium-Carbon Low-Alloy Steel Using Ultrasonic Impact Treatment

This study aims to explore the effects of ultrasonic impact parameters on the surface modification of a stainless steel coating deposited on a medium-carbon low-alloy steel using argon arc surfacing welding. Ultrasonic impact treatment (UIT), at three different vibration strike numbers (40,000 times/(mm2), 57,600 times/(mm2), and 75,000 times/(mm2)) marked UIT–1, UIT–2, and UIT–3, respectively, was carried out to modify the surface structure and properties of the stainless steel coating. The surface morphological and structural features, phase compositions, grain size, topography, micro-mechanical properties, as well as the wear resistance of the coating before and after UIT with different impact parameters were experimentally investigated. The results of optical microscopy (OM), scanning electron microscopy (SEM), electron backscatter diffraction (EBSD), and X-ray diffraction (XRD) analyses revealed that the grain refinement accompanied by the formation of the strain-induced α′–martensite occurred on the UIT-treated coating surface. With the increase in the vibration strike number, the surface grain size and roughness decreased, while the α′–martensite content increased. Micro-hardness after UIT was increased by about 19% (UIT–1), 39% (UIT–2), and 57% (UIT–3), and the corresponding wear rate obtained was decreased by 39%, 72%, and 85%, respectively. Significant improvements in wear resistance were achieved using UIT. However, an excessive vibration strike number on the per unit area (/mm2) might result in unwanted micro-cracks and delamination on the treated surface, deteriorating the performance of the coating. These findings validate that UIT parameters (such as the vibration strike number on per unit area) are of great importance to bringing about improvements in wear performance, and UIT is found to have a high potential in modifying the surface characteristics and optimizing the mechanical performances of the deposited coating for a wide range of potential applications.

Tribological and morphological properties of bentonite nano‐clay/CaCO3 reinforced high‐density polyethylene nanocomposites

AbstractElastomeric polymers such as high‐density polyethylene, have a variety of desirable features, that have supplanted traditional materials. However, high‐density polyethylene (HDPE) shows inadequate wear resistance, which limits its use for industrial applications, particularly in low‐load‐bearing applications such as flexible energy harvesting devices and sensors. The current work is engrossed in investigating the influence of hybrid reinforcements CaCO3 particles and bentonite nano clay as secondary reinforcements in high‐density polyethylene (HDPE)‐based composites on the wear and friction properties. The reinforcements were melt compounded with HDPE using a Brabender mixer and sampled using an injection molding machine. The wear test (ASTM G‐99‐04) was performed by a pin‐on‐disk tribo‐tester. In comparison to a base matrix, the synthesized hybrid composite achieved the maximum improvement in wear rate of 93%. The results revealed that there is a significant improvement in wear resistance. Morphological analysis revealed that due to the encapsulation and compatibilization effect of bentonite nano clay the hybrid composite exhibited improved wear performance. The results signify the synergistic effect of filler particles resulted in sufficient bonding for stress transfer due to the encapsulation of CaCO3 by nano clay. The wear mechanism observed optically was abrasion, fatigue, and adhesion wear that changed with the change in the weight percent of nanoparticles. Finally, the prepared composite with enhanced tribological properties such as low wear rate, low friction coefficient, and enhanced morphology can be used in low load‐bearing wear applications such as turbo nanogenerators and piezo nanogenerators.Highlights Bentonite nano clay and CaCO3 dispersed homogeneously in HDPE matrix. Wear resistance of HDPE increases by reinforcing particles (nano‐clay and CaCO3). Micro‐cutting, deformations, and particle husks were the possible wear mechanism. Encapsulation effects the hybrid composite to exhibit improved wear performance.

Effect of annealing treatments on microstructure, tensile and wear properties of cold-rolled FeCoCrNiMn high entropy alloy

The equiatomic FeCoCrNiMn is a highly studied high-entropy alloy (HEA) known for its exceptional properties. In this study, FeCoCrNiMn HEAs with varying grain sizes were prepared by heavy cold rolling and subsequent annealing at 900 °C for different durations. Ultrafine-grained sample with an average grain size of about 0.75 μm was obtained after annealing for 2 min, which displayed an enhanced strength-ductility combination with a yield strength of around 620 MPa, an ultimate strength of around 778 and a tensile elongation of over 30 %. Grain boundary strengthening contributed significantly to the mechanical strength of the resulting alloy. The grain size of the alloy increased with annealing times, aligning well with the linear Hall-Petch relationship, and the processed HEA demonstrated the expected strength-ductility trade-off. The ultrafine-grained sample exhibited improved wear performance with reduced wear rate and improved worn surface characteristics compared to the coarser-grained samples. The wear mechanism of the FeCoCrNiMn alloy primarily involved abrasive wear and oxidative wear.

Synthesis and Wear Behaviour Analysis of SiC- and Rice Husk Ash-Based Aluminium Metal Matrix Composites

Research efforts seek to develop aluminium alloy composites to enhance the poor tribological performance of aluminium alloy base matrix. In this research, a hybrid metal matrix composite (HMMC) was developed by reinforcing an aluminium alloy (AA8011) with SiC and rice husk ash (RHA) using a stir casting technique. RHA was prepared by the cracking of rice husk, which is abundantly available in the Indian subcontinent. The samples were cast by keeping the amount of RHA constant at 2.5 wt.% and varying the amount of SiC from 0.0 wt.% to 8 wt.%. The samples were machined to manufacture pins for wear tests (at ambient temperature, 100 °C, and 200 °C) and hardness measurement. The microstructures of the cast samples were analysed using an X-ray diffractometer (XRD) and a scanning electron microscope (SEM), along with energy-dispersive X-ray spectroscopy (EDS). It was observed that the composites with greater reinforcement of SiC exhibited improved hardness and wear resistance, but the coefficient of friction increased with the addition of RHA and SiC, and the wear performance deteriorated with an increase in the operating temperature. The contribution of RHA alone to the improvement in wear performance was marginal compared to the pure alloy. It was also confirmed that the reinforced composites could be a better option for automotive applications to replace aluminium alloys.

Sliding wear behaviour of austempered ductile iron, boron steel and AISI 1045 steel of similar hardness: effect of microstructure, yield strength, and strain hardening

ABSTRACT A study on dry sliding wear investigated four alloys: fully austenitized ADI (F-ADI), intercritically austenitized austempered ductile iron (I-ADI), hardened and tempered Boron steel (B-Steel), and hardened and tempered AISI 1045 steel (EN-Steel). Despite their similar hardness levels, these alloys differ in composition and microstructure. Testing was conducted using a Ball-On-Disc setup (ASTM G99-05) with a chrome steel ball, maintaining a constant sliding speed of 0.6 m/s and applying loads between 20 and 80 N. This study aimed to understand the influence of yield strength (σy ), strain hardening coefficient (n), and microstructure on sliding wear under uniform hardness conditions. The findings indicated a strong connection between sliding wear resistance, strain hardening coefficient, toughness, and yield strength. Wear mechanisms varied slightly among materials; F-ADI and I-ADI exhibited deformed layers with increased hardness and oxide formation, while B-Steel and EN-Steel showed micro-cutting and micro-ploughing. F-ADI's high-carbon austenite film and I-ADI's proeutectoid ferrite contributed to improved wear performance. The hardness of the deformation layer on FADI and I-ADI's worn surfaces highlighted the benefits of strain hardening in dry sliding wear.

Sliding wear behaviour of conventional and cryotreated PM Cr-V (Vanadis 6) ledeburitic tool steel

Cryogenic treatment is a widely accepted method for extending the tool life of tool steels. This study focuses on investigating the tribological properties of PM Cr-V cold work tool steel subjected to conventional and cryogenic treatments. The aim of the study is to compare the reciprocal sliding wear performance of Cr-V cold work tool steel under different treatment conditions. The Cr-V tool steel specimens were cryotreated at temperatures of −75 °C, −140 °C, or −196 °C, followed by double tempering at 170 °C or 530 °C for 2 h. Cryotreated specimens exhibited a 10% increase in hardness compared to conventionally treated specimens after tempering at 170 °C. However, specimens cryotreated and tempered at 530 °C showed a 7% drop in hardness. Reciprocating sliding wear tests were conducted at room temperature using an Al2O3 ball as the counter-body to simulate abrasive wear. The results indicate that the friction coefficient is primarily influenced by the applied load and sliding velocity rather than the material treatment. Cryogenic treatment at 170 °C improved the wear performance by approximately 24% compared to conventionally treated specimens, while cryotreated specimens tempered at 530 °C did not exhibit any improvement in wear performance compared to conventionally treated specimens.

Synthesis and Properties of Polyurea Greases Based on Silicone Fluids and Poly-α-olefin Oils

The paper describes an investigation of lubricants synthesized by thickening a dispersion medium consisting of silicone oil (PES-5) and poly-α-olefin oil (PAOM-12) with diureas of different compositions. The study revealed the effects of the compositions both of the dispersion medium and urea thickener, as well as their ratio in the lubricating formulation, on the major physicochemical properties of resultant greases. Increasing the content of the hydrocarbon component of the grease was shown to improve the physicochemical properties. Finally, the optimum grease composition was identified: introducing a polyurea thickener that contained diphenylmethane-4,4'-diisocyanate resulted in the synthesis of greases that had adequate operating characteristics and an improved wear performance.

Optimization of wear-, fracture- and corrosion performance of Vanadis 6 steel through cryogenic treatment and tempering

Vanadis 6 cold work tool steel was vacuum austenitized, room temperature quenched, differently cryogenically treated (-75, -140 and -196 °C for different durations) and double tempered, at temperatures of either 170 or 530 °C. Galling resistance was assessed by pin-on-disc testing of differently treated specimens against CuSn bronze, at wide ranges of sliding velocities and loads. The obtained results show that cryogenic treatments combined with low temperature tempering improves anti-galling performance of the steel. The best tribological properties were obtained when high-temperature tempering was combined with cryogenic treatment at -196 °C, due to the maximum extent of microstructural alteration generated by this kind of treatment. The improvement in wear performance is accompanied with slight but undisputable increase in corrosion resistance of the steel, at almost no affected toughness as compared with the state after conventional heat treatment. In conclusion, the obtained results imply an opportunity to simultaneously improve wear performance, corrosion resistance and toughness of the examined steel, by choosing a proper combination of cryogenic treatment and tempering.

Synthesis and Properties of Polyurea Greases Based on Silicone Fluids and Poly-α-olefin Oils

The paper describes an investigation of lubricants synthesized by thickening a dispersion medium consisting of silicone oil (PES-5) and poly-α-olefin oil (PAOM-12) with diureas of different compositions. The study revealed the effects of the compositions both of the dispersion medium and urea thickener, as well as their ratio in the lubricating formulation, on the major physicochemical properties of resultant greases. Increasing the content of the hydrocarbon component of the grease was shown to improve the physicochemical properties. Finally, the optimum grease composition was identified: introducing a polyurea thickener that contained diphenylmethane-4,4'-diisocyanate resulted in the synthesis of greases that had adequate operating characteristics and an improved wear performance.