Microstructures and High-Temperature Friction–Wear Performance of Laser-Remelted WC-12Co Coatings by HVOF

A WC-12Co coating prepared by high-velocity oxygen fuel (HVOF) was remelted with a CO₂ laser, and the surface–interface morphologies, plane energy spectrum, and phases of the coating were analyzed by means of field emission scanning electron microscopy (FESEM), energy-dispersive spectrometry (EDS), and X-ray diffraction (XRD), respectively. The friction and wear behaviors of the WC-12Co coating were investigated at high temperature with a wear test, and the morphologies and the changes in chemical elements on the wear scar after the wear test were analyzed with SEM and EDS, respectively. In addition, the influence of high temperature on the coefficient of friction (COF) and wear performance is discussed. The results show that the substrate is closely bonded with the substrate after laser remelting (LR), which includes mechanical bonding accompanied by metallurgical bonding. The average coefficient of friction (COF) at 600, 700, and 800°C is 0.6832, 0.3957, and 0.1922, respectively. The wear mechanisms of WC-12Co coating at 600 and 700°C are adhesive wear, abrasive wear, and oxidative wear, respectively, and the wear mechanism of the coating at 800°C is serious oxidative wear.     

The Friction and Wear Properties of Ti–Al–Nb Intermetallics by Plasma Surface Alloying

Both plasma chromizing and carburization following plasma chromizing (duplex treatment) for Ti–Al–Nb alloy were performed, respectively, and the microstructure, dynamic ultra-microhardness, and elastic modulus of the alloying layer were determined. Using silicon nitride (Si₃N₄) balls as the counterface materials, dry sliding friction tests on the substrate, the chromized layer, and the duplex-treated layer were completed by ball-on-disk tribometer at room temperature. The results indicated that the duplex-treated layer was mainly composed of Cr₂₃C₆, Cr₂Nb, pure chromium, and carbon phases, while the chromized layer consisted of Al₈Cr₅ and Cr₂Nb phases. The ultra-microhardness of the duplex-treated layer was higher than that of the chromized layer, whereas the elastic modulus of the duplex-treated layer was lower than that of the chromized layer. The friction coefficient of the duplex-treated layer was about three times lower than that of the chromized layer, while the wear rate was one order of magnitude lower than that of the chromized layer.     

The Microstructure and Wear Characteristics of Cu–Fe Matrix Friction Material with Addition of SiC

The Cu–Fe matrix continuous braking friction materials using SiC as abrasive were fabricated by powder metallurgy technique, and the effect of content and size of SiC were investigated. The tribological properties of friction materials sliding against AISI 1045 steel ring were carried out on a block-on-ring tester at different loads and sliding speeds. The strengthening effect of nano-SiC (55 nm) was superior to that of micro-SiC (70 μm) of the tribological properties for friction materials. The friction coefficients of friction materials increased with increasing nano-SiC content. However, the wear rates decreased with increasing nano-SiC content and then increased when the content of nano-SiC particle exceeded 10 wt%. The specimen contained 10% nano-SiC had the best tribological properties at different testing conditions.     

Role of Third Bodies in Friction and Wear of Cold-Sprayed Ti and Ti–TiC Composite Coatings

Titanium (Ti) and Ti-based alloy wear performance is often poor unless coating or lubricants are used. An alternative is to use hard phase reinforcement. Cold spray is a relatively new method to deposit composite coatings, where here we report the deposition of a Ti–TiC coating and its sliding wear behavior. Mixtures of mechanically blended Ti–TiC with various TiC content were injected into a de Laval nozzle and sprayed onto substrates. Two composite coatings and a pure Ti coating are reported here, where the as-sprayed compositions of the composites were 13.8 and 33.4 vol% TiC. Reciprocating dry sliding wear was performed using a custom-built in situ tribometer. All tests were conducted with a sliding speed of 3 mm/s and at a normal load of 0.5 N. Using a transparent sapphire hemisphere of 6.25 mm as counterface, dynamic behavior of third bodies was directly observed. It was found that adhesive transfer of Ti was the primary wear mechanism for the Ti coating, with oxidative and abrasive wear also occurring for longer sliding cycles. The superior wear resistance of the composite coatings compared to Ti was related to dual function of TiC particles, where they reinforced the Ti matrix and facilitated the formation of a stable and protective tribofilms. The tribofilms contained carbonaceous material that provided easier shear and lower friction. The formation of these tribofilms was highly dependent on the TiC particles, which contained excess carbon compared to the equilibrium composition. Higher TiC content was more effective in quickly developing and sustaining the tribofilms.     

Tribological Performance of Ti–Si-Based in Situ Composites

In this study, a series of Ti–Si-based in situ composites was manufactured by means of a common argon arc melting technique and tribologically evaluated using a sliding ball-on-disc tester under simulated body fluid lubrication. The composite microstructure, mechanical properties, and surface roughness were characterized using light and scanning electron microscopy (SEM), vertical scanning interferometry (VSI), X-ray diffraction (XRD) analysis, and hardness measurements. The evolution of coefficients of friction (COFs) and the appearance of contacting surfaces showed that two the principal wear mechanisms were mixed elastohydrodynamic lubrication (EHL), typically followed by abrasive wear. The mixed EHL was due to the combined effect of serum solution lubrication and surface irregularities, which were produced during the routine surface preparation of samples. The mixed EHL provided the absence of wear and low and stable COFs, which did not depend on the phase composition, microstructure, or hardness of Ti–Si-based alloys. However, in most cases, the change in contact geometry led to the transition from mixed EHL to conventional boundary lubrication, accompanied by increased and unstable friction, adhesive material transfer of metal to the ceramic counterbodies, and abrasive wear. In this respect, the low wear resistance and high adhesion affinity of the titanium matrix of Ti–Si-based alloys should be improved.     

The Relative Wear Performance of Neutral and Basic Zinc Dithiophosphates in Engines©

Over the years, many bench tests have been used to guide synthetic organic chemists in their quest for new molecules to prevent valve train wear. Which bench tests to choose has always been an important issue, especially when the goal is to prevent valve train wear in an internal combustion engine, a very complicated system. Essential antiwear additives in modern engine oils are zinc dithiophosphates (ZnDTPs) and, although these materials have been used extensively, the fundamental mechanisms of their chemistries are not that well understood.

In this paper, several nontraditional bench tests have been evaluated, some involving surfaces but no rubbing, and others lacking rubbing surfaces entirely. Despite these apparent deficiencies, these nontraditional chemistry-based tests all could be interpreted to predict a wear advantage for the neutral ZnDTP species relative to the basic ZnDTP species.

This paper reports on engine tests of a neutral commercial-like ZnDTP and a basic commercial-like ZnDTP, with the result supporting the interpretation of the nontraditional bench tests: the neutral ZnDTP is better than the basic ZnDTP in engines with respect to valve train wear performance, with high statistical significance. Fundamental understanding of the chemistry of neutral and basic ZdTP has been shown to yield a practical result.     

Advanced Tribometer for In Situ Studies of Friction, Wear, and Contact Condition—Advanced Tribometer for Friction and Wear Studies

An advanced ball-on-disk tribometer was developed for in situ studies of friction, wear, and contact condition during sliding. Kinetic friction force, contact resistance (R _c), acoustic emission (AE), ball position perpendicular () to the plane of the disk (ball and disk wear), and disk surface reflectance (disk wear) were all measured simultaneously during sliding experiments. Metal (440C steel) balls were slid against ceramic (n-doped polysilicon) wafers at light load (10g) and short test duration (2.5min). Significant changes in measured parameters were observed as sliding progressed. These changes are discussed, and when considered together provide new insights into friction and wear mechanisms not readily obtainable from more standard tribometers. The effects of disk run-out (effective surface waviness) on and R _c were also investigated. Friction and R _c were periodic with a period equal to the period of disk rotation. The behavior was complex, but generally going up a hill increased and decreased R _c, with the opposite behavior going down a hill. We established a critical link between low-frequency friction oscillations (LFFO) and the nature of the contact between sliding surfaces (R _c measurement). The geometric ratchet mechanism was ruled out as a cause of LFFO, as the surface slope was too small to explain the large friction oscillations. Coating the balls and wafers with lower friction materials resulted in negligible LFFO, which makes it unlikely that LFFO were simply a result of an oscillating normal force created by dynamic effects. LFFO likely have their origins in the complex nature of the contact between rubbing surfaces.     

Antifriction and Wear Characteristics of Electrolessly-Deposited Ni–P with PTFE Composites

This aim of this study was to investigate the tribological properties of a self-lubricating Ni–P–polyfluorotetraethylene (PTFE) composite coating prepared by the electroless plating method. The effects of PTFE contents in the coating, load and rotation speed on the tribological behaviors were evaluated using a ring-on-disk wear machine. The results show that there was a distinct decrease in the average value of the friction coefficient from 0.33 to 0.12 at 70 N with an increase in PTFE content from 4.2 to 15.2 wt%. The coating of Ni–P–4.2 wt% PTFE had good antifriction and wear properties at a load of 30–70 N, and that of Ni–P–10.6 wt% PTFE had passable wear resistance and better antifriction at <50 N. Antifriction and wear mechanisms of Ni–P–PTFE are discussed in detail based on the results from micrograph and element analyses of the worn surface, subsurface stratum and wear debris analysis by scanning electronic microscopy (SEM), and energy-dispersive X-ray analysis (EDAX), respectively. The lubricating film (LF) generated during wear played a key role in the antifriction effect, which in turn was dependent on the integrity and thickness of the film determined by the PTFE concentration and wear conditions. The formation, fracture, and delamination course of the LF during wear were also analyzed and characterized.     

Friction and Wear Phenomena of Vegetable Oil–Based Lubricants with Additives at Severe Sliding Wear Conditions

The tribological responses of palm oil and soybean oil, combined with two commercial antiwear additives (zinc dialkyl dithiophosphate and boron compound), were investigated at a lubricant temperature of 100°C and under severe contact conditions in a reciprocating sliding contact. The friction coefficient of palm oil with zinc dialkyl dithiophosphate was closest to the commercial mineral engine oil, with a 2% difference. The soybean oil with zinc dialkyl dithiophosphate produced a 57% improvement in wear resistance compared to its pure oil state. The existence of boron nitride in vegetable oils was only responsive in reduction of wear rather than friction. The response of commercial antiwear additives with vegetable oils showed a potential for the future improvement in the performance of vegetable oils.     

Dry Reciprocating Sliding Friction and Wear Response of WC–Ni Cemented Carbides

A number of WC–Ni based cemented carbide grades with distinctive binder contents were tested with the goal to evaluate their dry reciprocating sliding friction and wear behaviour against WC–6 wt.%Co cemented carbide using a Plint TE77 tribometer and distinctive normal contact loads. The generated wear tracks were analysed by scanning electron microscopy and quantified volumetrically using surface scanning topography. The experimental results revealed one WC–Ni grade with superior wear performance.     

Investigating Corrosion Performance and Corrosive Wear Behavior of Sol–gel/MAO-Coated Mg Alloy

In this study, a hydroxyapatite composite coating was prepared by a sol–gel technique on the micro-arc oxidation (MAO)-coated AZ31 Mg alloy to seal the micro-pores. The composite coating achieved a larger hardness value and two times thickness more than pure MAO coating. The corrosion and wear resistance of the sol–gel/MAO coating in simulated body fluid were investigated compared to MAO coating. It was found that the composite coating presented a positive corrosion potential and a lower corrosion current density than MAO coating. The sol–gel/MAO composite coating could provide more effective barrier against corrosive ions than single MAO coating for AZ31 alloy. In the wear tests, a ball-on-disk tribometer was used to study the effect of loads on the wear properties of the coatings at 37 °C. The wear resistance of sol–gel/MAO composite coatings was apparently superior to MAO coating. The wear mechanisms of abrasion and adhesion in composite coatings are investigated. Finally, two physical models for the corrosion and sliding wear mechanisms of sol–gel/MAO composite coatings are proposed, respectively.     

Friction,Wear, and Evaporation Rates of Various Materials in Vacuum to 10−7 mm Hg

Evaporation data on soft metals, lubricating inorganic compounds, and various reference materials are reported for temperatures from 75 to 1000 F in vacuum as low as 10^?7 mm Hg. Observations on modes of vacuum degradation (e.g., evaporation or dissociation) and methods of experimentation are related. Friction and wear data are presented for several unlubricated metals (e.g., type 440-C steel) and metals coated with inorganic (e.g., MoS₂, CaF₂) as well as with soft metal films in vacuum at ambient pressures between 10^?6 and 10^?7 mm Hg.     

Friction and Wear Behavior of AlMgB14–TiB2 Composite at Elevated Temperature

In this article, field-activated and pressure-assisted synthesis was employed to synthesize an ultra-hard, super-abrasive AlMgB₁₄–TiB₂ composite ceramic. The friction and wear performance of the AlMgB₁₄–TiB₂ composite were evaluated in ambient air at temperatures up to 800 °C by using a reciprocating ball-on-disk high-temperature tribometer. X-ray diffraction experiments were performed to study the crystal structure of worn surfaces of AlMgB₁₄–TiB₂ specimens at various temperatures. Scanning electron microscopy and energy dispersive analysis were used to examine the worn surface features and chemical composition of the AlMgB₁₄–TiB₂ composite, respectively. Results showed that the friction coefficient of the AlMgB₁₄–TiB₂ composite ranged from 0.45 to 0.55 below 300 °C, while the data obtained at 500 and 600 °C were about 0.65. The damage mechanism is transformed from mild abrasive damage at room temperature to adhesive wear at elevated temperature. In the case of 800 °C, the AlMgB₁₄–TiB₂ composite exhibited the lowest friction coefficient as the formation of a lubricious oxide film on the wear track.     

Wear Performance Forecasting of Chopped Fiber–Reinforced Polymer Composites: A New Approach Using Dimensional Analysis

Solid particle erosion of polymer matrix composites is a complex process in which wear occurs from the target surface by impingement of rigid sand particles in an air medium. The rate of material removal (RMR), also referred to as the erosion rate, mainly depends on target material parameters and the erosion conditions such as impact angle, impact velocity, and erodent size. A new semi-empirical model for prediction of the erosion rate of polymer matrix composites has been developed using a dimensional analysis technique based on Buckingham's π theorem. The predictive model analytically rests upon parameters related to chopped glass fiber composites, erodent (target material properties), and operating variables that mainly affect the erosion process of chopped glass fiber–vinyl ester resin composites. The forecasting ability of the predictive model has been assessed and verified by experimental investigations for chopped glass fiber–reinforced vinyl ester resin (VGF) composites. Validation of the theoretical erosion rates obtained from the predictive model showed that they were in good agreement with the experimentally determined erosion rates, where the average error range was estimated to be ～10 to ～20%.     

Effect of Tribo-Oxidation on Friction and Wear Behaviour of HVOF Sprayed WC–10Co–4Cr Coating

Tribology Letters - In current investigation, tribological properties of TiAl matrix composite reinforced with 15&nbsp;vol%Ti2AlN and TiAl alloy prepared through in situ reactive method of...     

Effect of Shaft Microcavity Patterns for Flow and Friction Control on Radial Lip Seal Performance–A Feasibility Study

It has been shown that deterministic microfeatures on the shaft of a radial lip seal impact seal behavior. This work seeks to determine whether it is feasible to control lubricant pumping direction and enhance pump rate with microcavities. The effect of nickel film triangular cavity orientation on seal performance, in particular the flow direction, the pumping rate, and the friction torque, is investigated experimentally. Cavity shape, area fraction, and depth are held constant while cavity orientation is varied. The oil drop test results are compared to those for conventional seals; i.e., plain stainless steel shafts and shafts with an electroplated nickel surface but no micro-cavities. It was found that shafts with surface texture designs can control the pumping direction and increase the sealing capability via enhanced pump rates by up to eight times that of stainless steel shafts. Preferential orientations pumped oil toward the wider end, or base, of the triangular cavities while patterns in neutral, or nonpreferential, orientations were found to reverse pump. The presence of microcavities reduced the friction torque by as much as 51% when pumping and in all cases reduced the operating temperatures. In some cases, the microcavities also reduced the friction torque 8–13% when the seal was operating in a starved condition.     

The Mathematical Simulation and Study of the Electrical Resistance of the Friction Zone of the Hip Joint Endoprosthesis with a Metal–Metal Friction Pair

The paper has described a model of the static load on the hip joint that takes into account the anthropological parameters and a mathematical model of the change in the resistance of the endoprosthesis under the influence of an external load at different rotation angles of the cup component. The theoretical studies have revealed the character of the changes and assessed the possible ranges of variations in the diagnostic parameter that are required to develop diagnostic equipment and methods for testing and interpreting diagnostic information during the tribotesting of individual types of implants.     

Surface Modification of Machine Parts Made of Iron–Carbon Alloys Operating under Conditions of Friction and Wear

The article has described a promising oxyalloying technique for the surface modification of machine parts made of iron–carbon alloys that operate under conditions of friction and wear. The new method has been implemented via the surface impregnation of steel and cast-iron parts with superheated steam of aqueous solutions of salts containing chemically active alloying elements. A multilayer coating formed on the surfaces of parts as a result of this treatment increases their performance characteristics, which has been confirmed by the integrated research.