Wear and friction performance evaluation of nickel based nanocomposite coatings under refrigerant lubrication

Environmental concerns related to global warming has enforced the introduction of newly artificially formulated refrigerants. HFE-7000 is a replacement solution for the existing harmful refrigerants and thermo-fluids having a broad range of application areas including usage in green energy, low carbon technologies, in aerospace and automotive industries. In this study five different types of coatings namely, Ni-ZrO2, Ni-Al2O3, Ni-SiC, Ni-Graphene and Nickel-only have been used to study the wear and friction performance of these coatings in systems based on HFE-7000 refrigerant. Extensive experimentation has been performed on these coated contacts using a modified pressurised lubricity tester by changing the refrigerant temperature and the applied normal load in an attempt to enhance the tribological performance of interacting machine parts employing HFE-7000. EDS analysis performed on all the sample pairs within the contact region revealed the presence of fluorine and oxygen based tribo-films. These oxygenated and fluorinated tribo-films help prevent metal-to-metal contact leading to a drop in friction and wear. All coatings presented an improvement in the micro-hardness and in hardness to elastic modulus ratio compared to uncoated steel. The results of friction and wear of coated samples were compared to uncoated steel as well. The results show an improvement in wear and friction at most of the operating conditions by applying nickel based coatings on a steel substrate in the presence of HFE-7000. Friction and wear performance of nickel based coatings does drop for some of the coatings at particular testing conditions which leads to conclude that a careful selection of the coatings has to be made depending on the operating refrigerant temperature and load. The results of this study provide a guideline and will be extremely useful in selecting the type of coating based on the application area

Wear Performance Analysis of Ni-Al2O3 Nanocomposite Coatings under Nonconventional Lubrication

This article presents the wear study of Ni-Al2O3 nanocomposite coatings in comparison to uncoated steel contacts under reciprocating motion. A ball-on-flat type contact configuration has been used in this study in which a reciprocating flat steel sample has been used in coated and uncoated state against a stationary steel ball under refrigerant lubrication. The next generation of environmentally friendly refrigerant HFE-7000 has been used as lubricant in this study without the influence of any external lubricant. The thermodynamic applications and performance of HFE-7000 is being studied worldwide as it is replacing the previous generation of refrigerants. No work however has been performed to evaluate the wear performance of HFE-7000 using nanocomposite coatings. The wear scar developed on each of the flat and ball samples was studied under a Scanning Electron Microscope (SEM). The micrographs show that a combination of adhesive and abrasive wear occurs when using uncoated steel samples. Micro-delamination is observed in the case of Ni-Al2O3 nanocomposite coatings accompanied by adhesive and abrasive wear. Wear volume of the wear track was calculated using a White Light Interferometer. Energy-Dispersive X-ray Spectroscopic (EDS) Analysis of the samples reveal fluorine and oxygen on the rubbing parts when tested using coated as well as uncoated samples. The formation of these fluorinated and oxygenated tribo-films help reduce wear and their formation is accelerated by increasing the refrigerant temperature. Ni-Al2O3 nanocomposite coatings show good wear performance at low and high loads in comparison to uncoated contacts. At intermediate loads the coated contacts resulted in increased wear especially at low loads. This increase in wear is associated with the delamination of the coating and the slow formation of protective surface films under these testing conditions

Novel experimental setup to assess surfaces in tribo-contact lubricated by the next generation of environmentally friendly thermo-fluids.

Environmental concerns related to global warming and ozone depletion triggered the introduction of the fourth generation of thermo-fluids. Amongst the recently introduced thermo-fluids, one of the most promising fourth generation of thermo-fluids are Hydrofluoroethers (HFEs). Hydrofluoroethers have zero ozone depletion potential and have a lower global warming potential as compared to widely used thermo-fluids. The type of thermo-fluid used in a thermodynamic cycle directly affects the tribological performance of the system. HFEs have been reported to have good thermodynamic properties. The overall tribological performance of Hydrofluoroethers however have to be investigated in detail in-order to fully assess the mechanical behaviour of interacting components utilizing these thermo-fluids. This study is concerned with the experimental test rig design modifications and commissioning to conduct tribological testing with HFEs as lubricants. This article covers the experimental test rig design and setup. Experiments to analyse the frictional force, the coefficient of friction and wear by using Hydrofluororther-7000 (HFE-347mcc3) as lubrication medium have been conducted. Industrial applications were simulated by varying test conditions and the results are presented in this paper

Corrosion performance of nanocomposite coatings in moist SO2 environment.

This paper presents a study of corrosion behavior of electrodeposited Ni, Ni-Al2O3, Ni-ZrO2, and Ni-Graphene (Gr) coatings in moist SO2 environment. Nanocomposite coatings were deposited on steel substrate by pulse electrodeposition technique with an average thickness of 9 ± 1 μm. Coatings were characterized by using nanoindentation and scratch tests to measure their mechanical properties prior to conducting corrosion tests. The corrosion resistance of coatings was evaluated according to G87-02 Method B, employing SO2 cyclic spray in the presence of moisture followed by drying. The results indicated that the addition of nanoparticles is beneficial both for enhancing mechanical properties and improving the corrosion resistance of these coatings. Higher surface corrosion resistance was observed for Ni-Gr coating. Corrosion behavior of coating was also quantified by open circuit potential measurement in 0.5 M H2SO4 environment. The results suggest that the nanocomposite Ni coatings have improved corrosion resistance compared to pure Ni coating. This work will bring significant impacts in terms of industrial applications such as architectural, automotive and marine industries in the presence of S-pollutants because it can cause corrosion either due to acid rain or by the reaction of moisture with dry deposition of Sulfur

A Historical Review on the Tribological Performance of Refrigerants used in Compressors

Refrigerants directly affect the tribological performance of interacting components in a compressor. Since the introduction of artificially formulated refrigerants, the types of refrigerants used in compressors have changed over the years. Apart from evaluating the physical, chemical and thermodynamic properties of refrigerants, the refrigerants have also been studied from a view point of tribology by various researchers worldwide. Changing a refrigerant in a compressor not only has an effect on the thermodynamic cycle but also effects the lubricants viscosity, lubricants pressure-viscosity coefficient, oil film thickness, lubricant/refrigerant miscibility, friction, wear, durability, reliability and overall power consumption. Refrigerants have been studied from a view point of tribology by varying the contact geometries, by using different lubricating oils with and without additives, by altering the environmental pressure/temperature, by changing the phase of the refrigerant, by using different interacting materials and by applying numerous surface treatments. The tribological behavior of refrigerants can be better understood by consolidating the findings in a comprehensive manner. An in-depth review on the tribological behavior of refrigerants is missing from the literature. This article reviews the tribological studies carried out on refrigerants, with focus on refrigerants used in domestic appliances, automobile air-conditioning systems and small scale industrial and commercial applications

A review of friction performance of lubricants with nano additives

: It has been established in literature that nanoparticle’s addition in lubricants at optimum con-centration results in lower coefficient of friction as compared to lubricants with no nanoparticle additive. This review paper shows a comparison of different lubricants based on COF (Coefficient of Friction) with nano additives. The effect of nanoparticle addition on friction coefficient is an-alyzed for both synthetic and biolubricants separately. The limitations associated with the use of nanoparticles are explained. The mechanisms responsible for the friction reduction, when nano-particles are used as additive are also discussed. Various nanoparticles that are most widely used in recent years and have shown good performance with lubricants include CuO (Copper Oxide), MoS2 (Molybdenum disulfide) and TiO2 (Titanium Dioxide). The paper also indicates some research gaps which need to be addressed