Tribological characteristics of nickel based composite coatings
TL;DR: In this paper, a theoretical model was used to predict the wear rates of the composite coatings and the predicted wear rates were in reasonable agreement with the experimental values, however, they did not consider the effect of load and sliding speed on both the coefficient of friction and wear rates.
Abstract: Nickel composite coatings have been prepared on mild steel substrates by sediment electro-co-deposition (SECD) technique. Silicon nitride, fly ash and calcium fluoride are used as the reinforcements. Metallographic studies, microhardness, friction and wear tests under various loads and sliding speeds have been carried out on these coatings. Optical and scanning electron microscopy (SEM) studies on the worn surfaces were conducted. A theoretical model was used to predict the wear rates of the composite coatings. All the composite coatings exhibited a lower coefficient of friction and better wear resistance when compared with nickel coatings at all loads and sliding velocities studied. However, nickel–calcium fluoride composite coatings possessed the lowest coefficient of friction and wear rates. Significant effect of load and sliding speed on both the coefficient of friction and wear rates of nickel, nickel–silicon nitride and nickel–fly ash coatings has been observed. SEM studies of the worn surfaces reveal delamination process at higher loads. The predicted wear rates are in reasonable agreement with the experimental values.
TL;DR: In this article, NiCo/SiC nanocomposite coatings with various contents of SiC nano-particulates were prepared by electrodeposition in a Ni-Co plating bath containing SiC nanoparticulates to be co-deposited.
Abstract: Ni–Co/SiC nanocomposite coatings with various contents of SiC nano-particulates were prepared by electrodeposition in a Ni–Co plating bath containing SiC nano-particulates to be co-deposited. The influences of the nanoparticulates concentration, current density, stirring rate and temperature of the plating bath on the composition of the coatings were investigated. The shape and size of the SiC nano-particulates were observed and determined using a transmission electron microscope. The polarization behavior of the composite plating bath was examined on a PAR-273A potentiostat/galvanostat device. The wear behavior of the Ni–Co/SiC nanocomposite coatings was evaluated on a ball-on-disk UMT-2MT test rig. The worn surface morphologies of the Ni–Co/SiC nanocomposite coatings were observed using a scanning electron microscope. The corrosion behavior of the nanocomposite coatings was evaluated by charting the Tafel curves of the solution of 0.5 mol L −1 NaCl at room temperature. It was found that the cathodic polarization potential of the composite electrolyte increased with increasing SiC concentration in the plating bath. The microhardness and wear and corrosion resistance of the nanocomposite coatings also increased with increasing content of the nano-SiC in the plating bath, and the morphologies of the nanocomposite coatings varied with varying SiC concentration in the plating bath as well. Moreover, the co-deposited SiC nano-particulates were uniformly distributed in the Ni–Co matrix and contributed to greatly increase the microhardness and wear resistance of the Ni–Co alloy coating.
TL;DR: In this article, the nano-coated Ni and Ni-TiO 2 nanocomposite coatings with various contents of TiO 2 nanoparticles were prepared by electrodeposition in a Ni plating bath containing TiO2 nanoparticles to be codeposited.
Abstract: Ni–TiO 2 nanocomposite coatings with various contents of TiO 2 nanoparticles were prepared by electrodeposition in a Ni plating bath containing TiO 2 nanoparticles to be codeposited. The influences of the TiO 2 nanoparticle concentration in the plating bath, the current density and the stirring rate on the composition of nanocomposite coatings were investigated. The composition of coatings was studied by using energy dispersive X-ray system (EDX). The wear behavior of the pure Ni and Ni–TiO 2 nanocomposite coatings were evaluated by a pin-on-disc tribometer. The corrosion performance of coatings in 0.5 M NaCl, 1 M NaOH and 1 M HNO 3 as corrosive solutions was investigated by potentiodynamic polarization and electrochemical impedance spectroscopy methods (EIS). The microhardness and wear resistance of the nanocomposite coatings increase with increasing of TiO 2 nanoparticle content in the coating. With increasing of TiO 2 nanoparticle content in the coating, the polarization resistance increases, the corrosion current decreases and the corrosion potential shifts to more positive values.
TL;DR: In this article, a new class of copper based composite material by dispersing both hard and soft reinforcement in appropriate proportions to ensure optimum tribological characteristics was developed by liquid metallurgy route and the results show that the hybrid composites possess higher hardness, higher tensile strength, better wear resistance and lower coefficient of friction when compared to pure copper.
Abstract: Copper based composites having hard reinforcements like alumina, silicon carbide and cerium oxide possess higher strength, better wear resistance and higher coefficient of friction when compared to copper. However, they pose machining issues such as higher tool wear and rough surface finish. Conversely, copper composites with soft dispersoids such as graphite and molybdenum disulphide exhibit lower coefficient of friction and better machinability characteristics. Hence an attempt is made to develop a new class of copper based composite material by dispersing both hard and soft reinforcement in appropriate proportions to ensure optimum tribological characteristics. The present investigation deals with the development of copper–SiC–Gr hybrid composites by liquid metallurgy route. Metallographic study, microhardness, tensile strength, friction and wear tests have been conducted. The results show that the hybrid composites possess higher hardness, higher tensile strength, better wear resistance and lower coefficient of friction when compared to pure copper.
TL;DR: In this paper, the authors investigated the wear performance of Alloy-Based Metal Matrix Composites (MMCs) by liquid metallurgy route and found that increased contents of TiO2 resulted in higher hardness and lower wear coefficient of composites under identical test conditions.
Abstract: In recent years, aluminum alloy based metal matrix composites (MMC) are gaining wide spread acceptance in several interesting applications such as piston, connecting rod, microwave filters, vibrator component, contactors, impellers and space structures. These composites possess excellent wear resistance in addition to other superior mechanical properties such as strength, modulus and hardness when compared with conventional alloys. Of all the aluminum alloys, 6061 is quite popular choice as a matrix material to prepare MMCs owing to its better formability characteristics and option of modification of the strength of composites by adopting optimal heat treatment. From the literature, it is quite evident that the focus has been centered on processing of MMCs and characterization of mechanical properties of MMCs. Tribological characteristics of several MMC systems involving glass, flyash, SiC, Al2O3 as discontinuous dispersoids have been reported. However, meagre data are available as regards the theoretical prediction of wear rate of MMCs. Prediction of wear rate gains impetus in present industrial scenario to assess the life of sliding components in advance to avoid huge economic losses that incur due to wear. In the light of the above, the present investigation deals with preparation of Al6061–TiO2 composites by liquid metallurgy route. The extent of incorporation of TiO2 in the composite was varied from 2 to 10 wt%. Microstructure studies, hardness and wear test were conducted on the cast Al6061–TiO2 composites. Pin on disc machine was used to assess the wear resistance of the prepared composites. Load was varied from 10 to 40 N while the sliding distance was from 90 to 540 m. Wear coefficients were evaluated by using Archard's and Yang's theoretical models. Increased contents of TiO2 resulted in higher hardness and lower wear coefficient of the composites under identical test conditions. The wear coefficient of all the Al6061–TiO2 composites studied decreased at higher loads and larger sliding distances. The predicted values of the wear coefficient are in close agreement with the experimental ones.
TL;DR: In this article, the mechanism of electrodeposition and effect of operational parameters and deposit microstructure, together with the mechanical, electrochemical and tribological characteristics of Ni Co alloys and included particle, composite deposits.
Abstract: Ni Co alloy electrodeposits have been widely employed in industry due to their good corrosion and wear resistance, high mechanical strength, moderate thermal conductivity and outstanding electrocatalytic and magnetic properties. This review aims to provide an insight into the mechanism of electrodeposition and effect of operational parameters and deposit microstructure, together with the mechanical, electrochemical and tribological characteristics of Ni Co alloys and included particle, composite deposits. Potential applications of the coatings have also been considered in applications as diverse as additive manufacturing, micro-tools, micro-sensors, electronic imaging and electrochemical energy conversion.
TL;DR: In this article, solid lubricants, which can be used above 300°C in air, are discussed; coatings and self-lubricating composite bearing materials are also covered.
Abstract: Solid lubricants, which can be used above 300°C in air, are discussed; coatings and self-lubricating composite bearing materials are also covered. The lubricants considered are representative dichalcogenides, graphite, graphite fluoride, polyimides, soft oxides, oxidatively stable fluorides and hard coat materials. A few general design considerations relevant to solid lubrication are mentioned
TL;DR: Friction and wear of Si3N4 sliding on itself were measured at room temperature in different gaseous and liquid environments as discussed by the authors, showing that wear occurs by two fracture mechanisms: within 1 μm of the surface, asperity contact produces very large local stresses and cracking on a very fine scale; 3-5 μm deeper the fracture follows weaknesses of the material and is intergranular fracture with some transgranular cleavage.
Abstract: Friction and wear of Si3N4 sliding on itself were measured at room temperature in different gaseous and liquid environments. At low sliding speed the friction coefficient ƒ is 0.85 in dry argon and nitrogen and 0.8 in laboratory air and oxygen. In dry gases, wear occurs by two fracture mechanisms: within 1 μm of the surface, asperity contact produces very large local stresses and cracking on a very fine scale; 3–5 μm deeper the fracture follows weaknesses of the material and is intergranular fracture with some transgranular cleavage. No evidence of plastic deformation was obtained. In water- and humidity-saturated gases wear is predominantly by a tribochemical reaction which produces an amorphous protective layer in humid gas and dissolution in liquid water. In intermediate humidity, wear is a combination of fracture and tribochemistry; the latter increases adhesion between wear particles to form a layer of compacted wear particles on the wear track. The fact that humidity decreases wear in Si3N4 and increases it in A12O3 is explained by the differences in chemical reactivity and susceptibility to stress corrosion cracking between the two materials.
TL;DR: In this article, the effects of microstructure (namely, particulate volume fraction and particulate size) and the counterface materials on the dry-sliding wear resistance of the aluminum matrix composites 2014A1-SiC and 6061Al-Al2O3 were studied.
Abstract: The effects of microstructure (namely, particulate volume fraction and particulate size) and the counterface materials on the dry-sliding wear resistance of the aluminum matrix composites 2014A1-SiC and 6061Al-Al2O3 were studied. Experiments were performed within a load range of 0.9 to 350 N at a constant sliding velocity of 0.2 ms-1. Two types of counterface materials, SAE 52100 bearing steel and mullite, were used. At low loads, where particles act as loadbearing constituents, the wear resistance of the 2014A1 reinforced with 15.8 µm diameter SiC was superior to that of the alloy with the same volume fraction of SiC but with 2.4 µm diameter. The wear rates of the composites worn against a steel slider were lower compared with those worn against a mullite slider because of the formation of iron-rich layers that act asin situ solid lubricants in the former case. With increasing the applied load, SiC and A12O3 particles fractured and the wear rates of the composites increased to levels comparable to those of unreinforced matrix alloys. The transition to this regime was delayed to higher loads in the composites with a higher volume percentage of particles. Concurrent with particle fracture, large strains and strain gradients were generated within the aluminum layers adjacent to contact surfaces. This led to the subsurface crack growth and delamination. Because the particles and interfaces provided preferential sites for subsurface crack initiation and growth and because of the propensity of the broken particles to act as third-body abrasive elements at the contact surfaces, no improvement of the wear resistance was observed in the composites in this regime relative to unreinforced aluminum alloys. A second transition, to severe wear, occurred at higher loads when the contact surface temperature exceeded a critical value. The transition loads (and temperatures) were higher in the composites. The alloys with higher volume fraction of reinforcement provided better resistance to severe wear. Wearing the materials against a mullite counterface, which has a smaller thermal conductivity than a counterface made of steel, led to the occurrence of severe wear at lower loads.
TL;DR: In this paper, the life of such tools or machine elements as well as their performance are considerably increased, provided that the adhesive strength and the intrinsic cohesion of the coating are sufficient.
Abstract: Chemically vapour-deposited and physically vapour-deposited coatings of hard and wear-resistant materials such as TiC, TiN, Ti(C, N), Cr7C3, Al2O3, SiO2 and TiO2 as well as other carbides, nitrides, borides, oxides and combinations thereof are increasingly used in industrial applications to protect metal, ceramic and in certain cases polymer parts against mechanical and chemical attack, sometimes with a decorative purpose also. Some relevant examples of coated products are cemented carbide throwaway cutting tips (TiC, TiN, Ti(C, N), Al2O3 etc.), high speed steel drills and milling cutters (TiN), hobs, deep drawing tools, ball-bearing elements, gears, machine elements, electrical contacts, body implants, surgical instruments and tools, cutlery, fuel pins and armatures especially for helium- and sodium-cooled nuclear reactors, low Z sputter-resistant protective coatings on parts (limiters, antennae etc.) and walls of the torus in fusion reactors (tokamak) and gold- or silver- or black-coloured watch cases and jewelry pieces. The life of such coated tools or machine elements as well as their performance are considerably increased, provided that the adhesive strength of the coating to the base material and the intrinsic cohesion of the coating are sufficient. Bad adhesion leads to flaking (adhesive failure) while poor cohesion causes chipping (cohesive failure).
TL;DR: In this article, the dry wear characteristics of the Al-(2.7% −5.7%) graphite particle composite were found to deteriorate with the addition of graphite, load and sliding distance.
Abstract: Under lubricated conditions, Al-graphite particle composite is a good antiseizure bearing and antifriction material possessing properties which inhibit excessive temperature rise in bearings. The present study characterizes the dry wear properties of the composite. The dry wear characteristics of the Al-(2.7%–5.7% graphite particle) (50–200μm) composite were found to deteriorate with the addition of graphite, load and sliding distance. Both micro structural and microhardness studies of the worn subsurfaces and analysis of wear debris show that the reductions in strength and ductility of the composite due to graphite addition are the most likely causes of deterioration in the wear properties of the composite.