Effect of Mixed Rare Earth Fluorides on the Mechanical and Tribological Characteristics of Ni-Based Alloy

In this paper, Ni-based alloys with different addition amounts of mixed rare earth fluoride were prepared using a P/M method in an intermediate frequency inductive furnace. The effect of mixed rare earth fluoride (30.9 wt.% LaF₃ and 69.1 wt.% DyF₃ in composition) additions on the mechanical strength of the alloy was investigated and compared with that of a CeF₃ addition. The findings indicated that by adding 3 wt.% mixed rare earth fluorides the improved toughness can be obtained. By adding 3 wt.% and 5 wt.% of mixed rare earth fluorides the compressive strength at 700°C were increased. The friction and wear behavior of the composite sliding against a high temperature self-lubricating composite at room temperature and 600°C in air were investigated on a pin-on-disk tribometer. The composites showed better tribological performances at 600°C than at room temperature.     

Friction and Wear Behaviors of Ni-based Composites Containing Graphite/Ag2MoO4 Lubricants

In order to improve the tribological properties of Ni-based composites, novel adaptive Ni-based composites containing multiple lubricants were prepared via a mechanical alloying and hot-press sintering technique. The phase constituents and microstructure of the composites were characterized and the tribological properties were evaluated from room temperature to 700 °C. The results showed that the Ag₂MoO₄ phase decomposed and new phases of Mo₂C, Ag, and MoO₃ formed in the sintered composites, which can be attributed to the solid state reaction of silver molybdate lubricant during the sintering process. The wear test results indicated that the Ni-based composites containing graphite and silver molybdate lubricants exhibited superior tribological properties at ambient and high temperatures. Subsequently, the Raman results demonstrated that the composition of the tribo-layers on the worn surface of the Ni-based composites was varied with increasing temperature. Combined with the wear test results, it can be proposed that the improvement of tribological properties is due to the synergistic lubricating action of silver molybdate, iron oxide, and nickel oxide. Furthermore, Raman results of the composite containing silver molybdate and silver/molybdenum trioxide lubricants revealed that the silver molybdate lubricant can reproduce easily by the direct reaction between molybdenum trioxide and silver in the agglomerate state.     

Tribological behaviour and wear mechanism of MoS2–Cr coatings sliding against various counterbody

MoS₂–Cr coatings with different Cr contents have been deposited on high speed steel substrates by closed field unbalanced magnetron (CFUBM) sputtering. The tribological properties of the coatings have been tested against different counterbodies under dry conditions using an oscillating friction and wear tester. The coating microstructures, mechanical properties and wear resistance vary according to the Cr metal-content. MoS₂ tribological properties are improved with a Cr metal dopant in the MoS₂ matrix. The optimum Cr content varies with different counterbodies. Showing especially good tribological properties were MoS₂–Cr8% coating sliding against either AISI 1045 steel or AA 6061 aluminum alloy, and MoS₂–Cr5% coating sliding against bronze. Enhanced tribological behavior included low wear depth on coating, low wear width on counterbody, low friction coefficients and long durability.     

The antiwear and extreme pressure action mechanism of CeF3 in grease

Cerium (III) fluoride as an antiwear or extreme pressure additive has been used in grease and bonded solid film lubricant, but its action mechanism has not been clarified. In this paper, the tribological characteristics of lithium grease containing CeF₃, CaF₂, SbF₃, CeO₂ and graphite fluoride ((CF)_n) were evaluated with an SRV tester. The results show that pastes containing CaF₂ and (CF)_n give good antiwear and anti-friction performance, but do not possess extreme pressure properties. Adding CeO₂ to grease offers no benefit to the antiwear and anti-friction performance of the paste. Paste containing SbF₃ has poor lubricating properties. XPS analysis shows that the good antiwear and extreme pressure properties of paste containing CeF₃ can be attributable to the formation of a physically adherent film and a chemical reaction film on the rubbing surface. Thermogravimetry shows that CeF₃ acts as an agent for the slow release of the fluorine element.     

Tribological Behavior of PTFE Composites Filled with PEEK and Nano-Al2O3

In this study, the tribological properties of polytetrafluoroethylene (PTFE) composites filled with polyetheretherketone (PEEK) and nano-Al₂O₃ particles were studied using a block-on-ring wear tester. The tribological performance of the composites was affected by the experimental parameters (sliding speed, normal load, and environmental temperature) and the composites achieved a high-speed sliding friction state. The results showed that the PEEK and nano-Al₂O₃ particles significantly improved the wear resistance of the PTFE composites. In addition, the nano-Al₂O₃ particles increased the hardness of the composites and enhanced the mechanical properties to enable applications in a wider range of industrial fields. The effects of the sliding speed and normal load on the tribological properties were more significant than that of the environmental temperature. In addition, the entire wear process was divided into three stages (the initial wear stage, severe wear transition stage, and ultralow stable wear stage), according to the evolution of the tribological characteristics (wear rate, morphology of the worn surface and transfer film, and wear debris morphology).     

Sliding Wear of Ni–17.5Si–29.3Cr Alloy under Water Lubrication

The tribological properties of Ni–17.5Si–29.3Cr alloy against Si₃N₄ under water lubrication conditions were studied on a ball-on-disc reciprocating 1tribotester. The effects of load and sliding speed on tribological properties of the alloy were investigated. The worn surfaces of the alloy were examined with SEM, TEM and an X-ray photoelectron spectroscope (XPS). It was found that the tribological properties of the alloy were closely dependent on the sliding conditions. Wear rate with the load of the alloy increased slightly at low and moderate load and increased dramatically at high load. Wear rate with the sliding speed of the alloy increased slightly at low and moderate sliding speed and increased dramatically at high sliding speed, which showed the same trend as that with the load. The friction coefficient increased with the load (especially at high load), and decreased with sliding speed at low sliding speed and increased significantly at high sliding speed. Wear mechanism of the alloy was mainly microploughing and delamination at low and moderate load and transformed to microfracture and delamination at high load.     

Tribological Properties of Al<Subscript>2</Subscript>O<Subscript>3</Subscript>/CuCrZr Composites

Al₂O₃ particles reinforced Cu–Cr–Zr alloy matrix composite was fabricated through a powder metallurgy plus hot extrusion process by using the water atomization Cu–Cr–Zr powder as raw material. The effect of aging treatment on the tribological behavior of the composite was investigated. Experimental results show that tiny coherent precipitated phases were formed in the matrix after proper aging treatment and therefore good combination properties could be obtained. The wear rates of the Al₂O₃/CuCrZr composite and its matrix alloy were obviously influenced by the aging treatment, wherein the best wear resistance was reached at the aging temperature corresponding to the highest Vickers hardness. The major reason was that the depth of plastic deformation in the subsurface region was dramatically decreased due to the improvement of mechanical properties of the matrix, and therefore adhesion induced surface materials loss could be markedly alleviated. By comparing with the SiC20 vol%/Cu composite, it is indicated that the Al₂O₃/CuCrZr composite exhibited much better wear resistance as well as higher electrical conductivity.     

Tribological properties of Ni-17.5Si-29.3Cr alloy at room and elevated temperatures

The tribological properties of Ni-17.5Si-29.3Cr alloy against Si₃N₄ were studied on a ball-on-disc tribotester between room temperature and 1000 °C. The effects of temperature on the tribological properties of the alloy were investigated. The worn surfaces of the alloy were examined using scanning electron microscopy (SEM) and X-ray photoelectron spectroscopy (XPS). The results indicated that the tribological behavior of the alloy expressed some differences with increase in testing temperature. At low and moderate temperatures (below 800 °C), the alloy showed excellent wear and oxidation resistances, and the wear rate of the alloy remained in the magnitude of 10^?5 mm³/Nm; but at elevated temperature (800–1000 °C), the wear and oxidation resistances decreased, and the wear rate of the alloy increased up to 10^?4 mm³/Nm. The friction coefficient decreased from 0.58 to 0.46 with the rising of testing temperature from 20 to 600 °C, and then remained nearly constant. The wear mechanism of the alloy was mainly fracture and delamination at low and moderate temperatures, and transformed to adhesive and oxidation at elevated temperatures.     

Effect of the Synergetic Action on Tribological Characteristics of Ni-Based Composites Containing Multiple-Lubricants

Ni-based self-lubricating composites with multiple-lubricants addition were prepared by a powder metallurgy technique, and the effect of multiple-lubricants on tribological properties was investigated from room temperature to 700?°C. The synergetic effects of graphite, MoS₂, and metallic silver lubricants on the tribological characteristics of composites were analyzed. XRD analysis showed that new Cr _x S _y and Mo₂C phase were formed in the composites containing graphite, MoS₂ and metallic Ag lubricants during the sintering process. The average friction coefficients (0.69?C0.22) and wear rates (11.90?C0.09?×?10^?5?mm³?N^?1?m^?1) were obtained when rubbing against Inconel 718 alloy from room temperature to 700?°C due to synergetic lubricating action of multiple-lubricants. A smooth lubricating was gradually generated on the worn surface, and the improving of tribological properties was attributed to the formation of lubricious glaze film on the worn surface and their partially transferred to the counterface. The graphite played the main role of lubrication at room temperature, while molybdate phase and graphite were responsible for low friction coefficients and wear rates at mid/high temperatures. The synergetic lubricating effect of molybdate (produced in the rubbing process at high temperatures) iron oxide (transfer from disk material to the pin) and remaining graphite multiple-lubricants play an important lubricating role during friction tests at a wide temperature range.     

Tribological properties of molybdenum disulfide nanosheets by monolayer restacking process as additive in liquid paraffin

Molybdenum disulfide nanosheets were prepared by monolayer restacking process. Results of transmission electron microscopy (TEM), high-resolution transmission electron microscopy (HRTEM), and scanning electron microscopy (SEM) showed that the obtained MoS₂ nanosheets had a thickness about 30-70 nm. The tribological properties of the so-prepared MoS₂ nanosheets were investigated on a MQ-800 four-ball tribometer. The results showed the base oil with MoS₂ nanosheets had better friction reduction, wear resistance and extreme pressure than those with commercial micro-MoS₂. The good tribological properties of MoS₂ nanosheets were mainly ascribed to the surface effect and the dimension effect of nanoparticles. Moreover, the formation of MoO₃ and FeSO₄ complex film on the rubbed surface also played an important role in friction reduction and wear resistance.     

Sliding wear characteristics of plasma-sprayed Al2O3 and Cr2O3 coatings against copper alloy under severe conditions

Al₂O₃ and Cr₂O₃ coatings were deposited by atmospheric plasma spraying and their tribological properties dry sliding against copper alloy were evaluated using a block-on-ring configuration at room temperature. It was found that the wear resistance of Al₂O₃ coating was superior to that of the Cr₂O₃ coating under the conditions used in the present study. This mainly attributed to its better thermal conductivity of Al₂O₃ coating, which was considered to effectively facilitate the dissipation of tribological heat and alleviate the reduction of hardness due to the accumulated tribological heat. As for the Al₂O₃ coating, the wear mechanism was plastic deformation along with some micro-abrasion and fatigue-induced brittle fracture, while the failure of Cr₂O₃ coating was predominantly the crack propagation-induced detachment of transferred films and splats spallation.     

Tribological Properties of Muscovite/La2O3 Composite Powders as Lubricant Additives

Muscovite/La₂O₃ composite powders were prepared by ball-milling solid-state chemical reaction at room temperature. The phase composition and micromorphology of the composite powders were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), and energy dispersive X-ray spectroscopy (EDX). The tribological properties of different samples were tested and compared using four-ball wear testing on an MMW-1A multifunctional friction and wear testing machine. The SEM micrography and energy spectrum of the composite powders illustrated that La₂O₃ particles were coated on the surface of muscovite particles. The results of the friction tests indicated that lubrication oil with muscovite/La₂O₃ composite powders presents better friction reducing and antiwear properties than that of the base oil, and the friction coefficients and diameters of wear scars decreased by 47.6 and 11.2% using 500SN base oil with 0.6g/L of muscovite/La₂O₃ composite powders as additives, respectively. The composite powders with 5 wt% La₂O₃ present the best comprehensive tribological properties. The micromorphology and chemical composition of the worn surface were analyzed by SEM and EDX, which confirm that the composite powders directly participate in the complicated physicochemical process of reactions on the worn surfaces, therefore improving the tribological properties of the base oil.     

Existence of Good Bonding between Coated B4C Reinforcement and Al Matrix via Semisolid Techniques: Enhancement of Wear Resistance and Mechanical Properties

An Al 6061 alloy matrix reinforced with the coated B₄C particles was used for the present study. The cohesion of the reinforcing ceramic particles is poor at temperatures near the melting point of aluminum and leads to inferior mechanical and tribological properties of developed aluminum matrix composites with nonuniform distribution of the reinforcement. The main reason for coating the particles is to improve the bond between the reinforcement and molten alloy and thus to eliminate interfacial reactions. The great enhancement in strength values of the composites in this study can be ascribed to the effective load-bearing capacity of disintegrated B₄C particles that are adherently bonded to the matrix alloy. Homogeneity and reduction in the particle size of B₄C during the extrusion process is evidenced in the microstructural studies.     

镍基合金喷熔层摩擦学行为与机制的研究

采用热喷熔工艺制备了两种镍基合金喷熔层,并选用高锰钢、不锈钢作为对比材料,研究了镍基合金喷熔层的摩擦磨损性能。研究结果表明：镍基合金喷熔层具有良好的耐磨损性能和较低的摩擦系数。镍含量对喷熔层的摩擦学性能有显著影响,高镍含量的镍基合金,其耐磨性能明显优于低镍含量的镍基合金。在低速轻载条件下,镍基合金喷熔层的磨损机理为微观犁削;高速重载时,表现为粘着磨损和磨料磨损,其中高镍含量的喷熔层表面形成了致密的转移膜,有效地降低了磨损率。     

Microstructural and Tribological Properties of A356 Al–Si Alloy Reinforced with Al<Subscript>2</Subscript>O<Subscript>3</Subscript> Particles

In the present study, the effect of the Al₂O₃ particles (average size of 12 μm, 3 and 10 wt.%) reinforcement on the microstructure and tribological properties of Al–Si alloy (A356) was investigated. Composites were produced by applying compocasting process. Tribological properties of unreinforced alloy and composites were studied, using pin-on-disc tribometer, under dry sliding conditions at different specific loads and sliding speed of 1 m/s. Microhardness measurements, optical microscope and scanning electron microscope were used for microstructural characterization and investigation of worn surfaces and wear debris. During compocasting of A356 alloy, a transformation from a typical dendritic primary α phase to a non-dendritic rosette-like structure occurred. Composites exhibited better wear resistance compared with unreinforced alloy. Presence of 3 wt.% Al₂O₃ particles in the composite material affected the wear resistance only at specific loads up to 1 MPa. The wear rate of composite with 10 wt.% Al₂O₃ particles was nearly two order of the magnitude lower than the wear rate of the matrix alloy. Dominant wear mechanism for all materials was adhesion, with others mechanisms: oxidation, abrasion and delamination as minor ones.     

Friction-Induced Hardening Behaviors and Tribological Properties of 60NiTi Alloy Lubricated by Lithium Grease Containing Nano-BN and MoS2

Abstract

Hardened 60NiTi alloy, which possesses a unique set of desirable properties, has been considered as an attractive candidate for the bearing materials used in space mechanisms. However, the typical hardening process (quenching from high temperatures with a high cooling rate) may result in quench cracking, especially in casting parts. With this in mind, the feasibility of friction-induced surface hardening of 60NiTi under the lubrication of lithium-based greases containing nanoparticles was explored in our research. In addition, the tribological properties of 60NiTi alloy lubricated with lithium-based greases containing different proportions of nanoparticles were investigated. Scanning electron microscopy (SEM), X-ray diffraction (XRD), and energy-dispersive spectroscopy (EDS) were used to characterize the surface of worn 60NiTi. An obvious friction-induced hardening effect on the 60NiTi alloy disc surface was identified, which was due to the formation of a hard metastable Ti₃Ni₄ phase and B2TiNi phase during the friction process. The lubrication effects of all of the modified grease were superior to those of the base grease, and the antiwear properties were closely related to the types of single nano-additives and the proportion of composite nano-additives.     

Tribological behavior of plasma electrolytic oxidation coatings on the surface of Mg–8Li–1Al alloy

Plasma electrolytic oxidation coatings were fabricated on the surface of Mg–8Li–1Al. The tribological behavior of the coated and uncoated Mg–Li alloy was investigated under dry friction conditions against a Si₃N₄ ball as counter-face material. The results indicated that the tribological behavior is greatly affected by the microstructure and phase compositions of the coatings. The PEO coatings significantly improved the properties of friction and wear of Mg–Li alloy.     

Tribological properties of Fe7Mo6-based alloy under two ionic liquid lubrications

The tribological properties of Fe₇Mo₆-based alloy, Mo, Fe and ASTM class no. 45 cast iron disk specimens were investigated against ASTM 52100 steel balls under the lubrication of two different kinds of hydrophobic ionic liquid: N-methyl-N-propylpiperidinium bis(trifluoromethanesulfonyl)imide (PP13-TFSI) and N-N-N-trimethyl-N-propylammonium bis(trifluoromethanesulfonyl)imide (TMPA-TFSI). When lubricated with PP13-TFSI or TMPA-TFSI, the Fe₇Mo₆-based alloy disk specimens exhibited lower friction coefficients and lower wear rates than the Mo, Fe and ASTM class no. 45 cast iron disk specimens. The low friction coefficients and low wear rates of the Fe₇Mo₆-based alloy were considered to be caused by the formation of low friction materials such as MoO₃ and FeSO₄ on the worn surface.     

Research on the physicochemical and tribological properties of nano-TiO2 in the aqueous rolling liquid

Aqueous rolling liquids with different concentrations of TiO₂ nano-particles are prepared. The dispersing mechanism of nano-TiO₂ in the rolling liquid is studied by FTIR and TEM. Wettability and viscosity of these rolling liquids is evaluated based on Dataphysics OCA50 contact angle measuring device and SYD-265C viscometer, respectively. New viscosity empirical formula that suitable for nano-TiO₂ aqueous rolling liquid is proposed. The tribological property is also investigated by the MM-WIA universal tribological tester. The results indicate that with the increase in the nano-particle’s addition, the contact angle gradually decreases, whereas the viscosity rises, which would contribute to ameliorating the frictional behaviour of aqueous suspensions. The aqueous suspension with 0.7 wt% TiO₂ possesses excellent friction reduction and anti-wear properties.     

Tribological behavior of NiAl matrix composites with addition of oxides at high temperatures

NiAl, NiAl–Cr–Mo alloy and NiAl matrix composites with addition of oxides (ZnO/CuO) were fabricated by powder metallurgy route. It was found that some new phases (such as NiZn₃, Cu_0.81Ni_0.19 and Al₂O₃) are formed during the fabrication process due to a high-temperature solid state reaction. Tribological behavior was studied from room temperature to 1000 °C on an HT-1000 ball-on-disk high temperature tribometer. The results indicated that NiAl had high friction coefficient and wear rate at elevated temperatures, while incorporation of Cr(Mo) not only enhanced mechanical properties evidently but also improved high temperature tribological properties. Among the sintered materials, NiAl matrix composite with addition of ZnO showed the lowest wear rate at 1000 °C, while CuO addition into NiAl matrix composite exhibited the self-lubricating performance and the best tribological properties at 800 °C.