EFFECT OF DIFFRENT LOADS ON THE WEAR BEHAVIORS OF 5Cr5Mo2V STEEL AT 700 °C

The effect of different loads on the high-temperature wear behavior of 5Cr5Mo2V steel at 700 °C was investigated. Wear morphologies, oxide compositions and matrix evolution were studied. The results showed that the wear rate increased with an increased test load, and the wear mechanism transformed from abrasive-oxidative wear to adhesive-oxidative wear. The relation between a delaminated oxide layer and cracks in the matrix were investigated. The exfoliation of carbides and displacement difference between the matrix and carbides caused a crack initiation. The wear rate strongly related to carbides, and coarse M6C carbides with poor holding power led to a high wear rate. Besides, a diagram of wear characteristics under different loads was suggested in this work.

Investigation on failure mechanism of electrical connectors under repetitive mechanical insertion and withdrawal operations

Electrical connector is an essential accessory component for electrical and electronic interconnection circuit. In order to investigate the degradation behavior of electrical connector, a series of repetitive mechanical insertion and withdrawal operations of electrical connector have been carried out. The results indicate that there is an increasing trend in insertion/extraction force in the initial stage. Afterwards, it becomes a gradually decreasing trend attributed to the mechanical wear of the contact components. In addition, the oxidative wear of substrate copper alloy material causes the fluctuation phenomenon of contact resistance. The relevant mathematic models for insertion/extraction force and contact resistance calculation are presented to research the dynamic insertion/extraction process. Finally, the degradation behavior and associated physical mechanisms are proposed by analysing the laser confocal photographs and parameter waveforms comparison.

Effect of Micro-Textured Surfaces and Sliding Speed on the Lubrication Mechanism and Friction-Wear Characteristics of CF/PEEK Rubbing against 316L Stainless Steel under Seawater Lubrication

In this work, the lubrication mechanism and friction-wear characteristics of the friction pair between carbon-fiber-reinforced polyether ether ketone (CF/PPEK) and 316L stainless steel with a micro-hemispherical pit textured surface at different sliding speeds under seawater lubrication were studied through numerical simulation and experimental investigation. The study results indicate that the seawater moves following the sliding direction of the upper specimen, forms a vortex ring flow in the hemispherical pit of the bottom specimen, uses the convergent gap to generate a hydrodynamic effect, produces the bearing capacity, and realizes fluid lubrication. The hemispherical pit diminishes the abrasive wear during the friction process by storing the wear debris, and the main wear forms of the hemispherical-pit surface friction pair are oxidative wear and adhesive wear. The friction coefficient of the hemispherical-pit surface friction pair is 0.018–0.027, the specimen contact temperature is 40.2–55.1 °C, and it is always in the hydrodynamic lubrication state in a rotation speed ranging from 1000 r/min to 1750 r/min. As the sliding speed increases, the specimen contact temperature climbs, and the oxidation reaction gradually becomes full. Oxidative wear and adhesive wear alternately play a dominant role in the friction, and the wear rate first decreases and then increases sharply.

Effective Wear Resistance Parameters of Ion-Plasma Tribological Coatings

Comparative studies of wear resistance during dry friction of vacuum ion-plasma coatings of nitride systems TiAlN and CrAlSiN are carried out. The structural parameters, coating thickness, and physical and mechanical properties were chosen as comparison parameters. A fundamental difference in the wear mechanisms of the coatings is demonstrated. In the TiAlN-system coatings develop an oxidative wear mechanism due to their insufficient heat resistance. The CrAlSiN-system coatings have maximum resistance to plastic deformation. And they are wear out according to the fatigue mechanism, which is typical for coatings with a high level of mechanical properties.

Effect of Martensite Volume Fraction on Oxidative and Adhesive Wear

It is generally known that microstructure can considerably affect the tribological behavior of non-lubricated rubbing. However, there is still a lack of awareness about the effect of microstructure on oxidative wear. The present study focused on the effect of martensite volume fraction (MVF) on oxidative wear by using 25CD4 dual-phase steel. Dry friction tests were performed on a ball-on-flat tribometer with a normal load of 15 N and a mean sliding velocity of 0.013 m/s. Friction coefficient and wear rate increase with the increasing MVF. SEM observation and EDXS analyses of the wear scars showed that the oxidation increases with decreasing MVF. For lower MVF, the main wear mechanism is mild oxidative wear. For higher MVF, severe adhesion is predominant as a wear mechanism. The size of the debris decreases with decreasing MVF.

Effects of Multi-Axial Compression on the Mechanical and Fretting Wear Properties of Ti-45Nb Alloys

Biocompatible β-type Ti-45Nb alloy with a low elastic modulus is promising in alleviating the stress shielding effect of Ti-based hard-tissue replacement implants. In this work, the ultra-fine-grained (UFG) microstructures with different grain sizes were prepared by multi-axial compression (MAC) processing of Ti-45Nb alloys, and the mechanical properties and the fretting wear properties of Ti-45Nb alloys in different grain sizes were investigated. The results show that the yield strength and ultimate tensile strength of the sample processed by 27 passes MAC increase by 76% and 91%, respectively, with an elongation of more than 9%. After MAC processing, the friction coefficient and volume wear rate gradually decrease. In addition, before MAC processing, the Ti-45Nb sample shows a wear mechanism of severe adhesive wear, oxidative wear and fatigue delamination; while after MAC processing, the wear mechanism switches to abrasive wear and slight adhesive wear with slight oxidative wear, indicating that grain refinement helps to improve the anti-fretting properties of Ti-45Nb alloys.

Microstructures and Wear Resistance of CoCrFeNi2V0.5Tix High-Entropy Alloy Coatings Prepared by Laser Cladding

CoCrFeNi2V0.5Tix high entropy alloy coatings were synthesized by laser cladding on Ti-6Al-4V (annotated as TC4) substrate. The microstructures, hardness, and wear properties of the coatings were studied in detail. The results showed that these coatings were all composed of body-centered cubic (BCC) solid solution, (Co,Ni)Ti2 phase, and Ti-rich phase. With the increase of Ti content (x in the range of 0–1.0), the hardness of these coatings (about 960 HV) was basically unchanged and stabilized, whereas, when x was increased to 1.25, the correspondent hardness was decreased significantly to about 830 HV. Compared with original substrate, the wear resistance of high-entropy alloy (HEA) coatings was greatly improved. In particular, CoCrFeNi2V0.5Ti0.75 (donated as Ti0.75) exhibited the lowest wear rate, width, and depth of tracks of wear, indicating the best wear resistance. Moreover, the wear mechanisms of Ti0.75 coating were mainly adhesive wear and oxidative wear.

Effect of Magnetic Field Coupled Deep Cryogenic Treatment on Wear Resistance of AISI 4140 Steel

In this study, a new magnetic field coupled deep cryogenic treatment (MDCT) is developed and its effect on wear resistance of AISI 4140 steel is investigated. Compared with wear resistance of untreatment (UT), wear resistance of MDCT increases by 29%. Wear resistance is inversely proportional to the friction coefficient. The treatment promotes the phase transformation and dislocation movement to generate more martensite in multidirectional distribution and optimized carbide. It enhances material property and repairs surface defect. Moreover, the wear mechanism of MDCT is only abrasive wear in the form of microscopic cutting, while other process groups are oxidative wear and abrasive wear in the form of microscopic cutting and microscopic fracture.

INNOVATIVE METHOD FOR PREPARATION OF Fe–Al–Cr INTERMETALLIC FUNCTIONALLY GRADED MATERIAL ON 1045 STEEL WITH UNIQUE TRIBOLOGICAL PROPERTIES

By combining the plasma ion implantation (PII) technology and double glow plasma surface metallurgy (DGPSM), a Fe–Al–Cr intermetallic functionally graded material was deposited on 1045 steel. The obtained Fe–Al–Cr intermetallic functionally graded material was around 11[Formula: see text][Formula: see text]m in thickness and was composed of a Cr-enriched layer (Cr-enriched Fe–Cr compounds), a Fe–Al–Cr-enriched layer (Fe2AlCr and Al8Cr5 compounds), and a Fe-enriched layer (Fe-enriched Fe–Cr solid solution). The interfacial contact between the Fe–Al–Cr intermetallic functionally graded material and the steel substrate is excellent due to the metallurgical bonding. The wear rate of the Fe–Al–Cr intermetallic functionally graded material was only around 25% of that of the 1045 steel substrate. Due to the different compound distributions in the Cr-enriched layer, Fe–Al–Cr-enriched layer, and Fe-enriched layer, the friction coefficients were different and their tribological behaviors were abrasive wear, oxidative wear and adhesive wear, respectively.