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

Nanoindentation Analysis of Evolved Bearing Steel under Rolling Contact Fatigue (RCF)

The bearing material operated under RCF is subjected to the triaxial stress state where work hardening followed by softening has been reported under the contact track. Such nonconformities (hardening/softening along with microstructural alterations) create complexities to model the cyclic hardening of bearing material under RCF. Current study presents a semi-empirical approach to evaluate the evolved subsurface response of bearing material with the help of a three-faced pyramidal Berkovich nanoindenter employing expanding cavity model for strain hardening materials. The expanding cavity model converts the localized measured hardness change to flow stresses which have been evolved during strain-hardening and microstructural phase changes of the bearing material. Moreover, to evaluate the representative stress-strain curve of the altered microstructure, a 5um spherical indenter was employed in a cyclic loading manner. The use of the spherical indenter with the integration of Field and Swain numerical model enables to extract the representative flow curve of the material at highly localized areas which cannot be possible even with miniature uniaxial tension/compression test

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

Evaluation of Dark Etching Regions for Standard Bearing Steel under Accelerated Rolling Contact Fatigue

Subsurface microstructural alterations are formed in the later stages of rolling contact fatigue (RCF) under high contact pressure. The subsurface changes observed as a dark contrast under optical microscopy are classified as Dark Etching Regions (DERs). Despite the fact that DERs have been presented for several decades, the understanding of its development and growth is yet to comprehend. Current research employed a modified high-speed microprocessor rotary tribometer to conduct systematic RCF study under accelerated testing conditions with variable temperatures and contact pressures. Comprehensive RCF data has been acquired, analysed and is reported for the very first time with ball-on-ball point contact loading conditions. The subsurface microscopic investigations have shown the ongoing progression and development of DER extent and are reported to be associated with the accumulation of plasticity during RCF. The comparison of the DER with the responsible stress components have revealed that DER formation is more closely related to the von Mises stresses when superposed with residual stresses. The experimentally observed area fraction of dark etching zones has been evaluated in terms of DER% and compared with the dislocation assisted carbon diffusion model for DER formation. The overprediction of the numerical model in comparison with the presented results in current research manifests its limitations which can be improved with the incorporation of cyclic plasticity governed by evolved von Mises stresses. The evaluated DER results are further presented as a 3D DER% maps incorporating the combined effects of contact stress, temperature and rolling cycles simultaneously which provides a comprehensive understanding of RCF from a microstructural point of view and thus can be used as guidelines for DER formation models

Stimulated effect of organic and inorganically originated transitory nitrogen sources on the nutrient concentration, uptake and production of hybrid maize

Soil productivity one of the essential factors which enhanced either through adding the chemical fertilizer or by incorporation of organic sources of nutrients to the soil. Regardless by the used of imbalanced fertilizer without the application of organic manure and without seeking knowledge of crops and fertility classification of soil causes to much hazards such as deterioration of soil structure, soil and water pollution etc. Two years field experiment was carried out to check the impact of transitory nitrogen sources on the nutrient concentration, uptake and production of hybrid maize at the Agronomic Research Area, University of Agriculture Faisalabad, Pakistan, during the year 2008-2009. Treatments included two hybrids: H1 (Pioneer-30Y87) and H2 (Pioneer-31R88) with six nitrogen sources each, which included at the rate of S0: control (0) kg N ha-1, S1: chemical source (urea) 250 kg N ha-1, S2: poultry manure (PM) 9.6 t ha-1, S3: farm yard manure (FYM) 17.8 t ha-1, S4: pressmud of sugarcane (PMS) 8.5 t ha-1 and S5: compost (C) 10.0 t ha-1. Finding concluded that changing effect of nitrogen sources on both maize hybrid was found to be non significant during 2008-2009 while grain yield was significant during both years. Maximum nutrient concentration, uptake and yield were observed with nitrogen source S1: chemical source (urea) 250 kg N ha-1 during 2008-2009 as compared to other nitrogen sources and minimum was found in control (0) kg N ha-1, respectively. Interaction among hybrid and nitrogen sources was found to be non significant

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

A 3D Finite Element Model of Rolling Contact Fatigue for Evolved Material Response and Residual Stress Estimation

Rolling Bearing elements develop structural changes during rolling contact fatigue (RCF) along with the non-proportional stress histories, evolved residual stresses and extensive work hardening. Considerable work has been reported in the past few decades to model bearing material hardening response under RCF, however, they are mainly based on torsion testing or uniaxial compression testing data. An effort has been made here to model the RCF loading on a standard AISI 52100 bearing steel with the help of a 3D Finite Element Model (FEM) which employs a semi-empirical approach to mimic the material hardening response evolved during cyclic loadings. Standard bearing balls were tested in a rotary tribometer where pure rolling cycles were simulated in a 4-ball configuration. The localised material properties were derived from post-experimental subsurface analysis with the help of nano-indentation in conjunction with the expanding cavity model. These constitutive properties were used as input cyclic hardening parameters for FEM. Simulation results have revealed that the simplistic power-law hardening model based on monotonic compression test underpredicts the residual generation whereas the semi-empirical approach employed in current study corroborated well with the experimental findings from current research work as well as literature cited. The presence of high compressive residual stresses, evolved over millions of RCF cycles, showed a significant reduction of maximum Mises stress, predicting significant improvement in fatigue life. Moreover, the predicted evolved flow stresses are comparable with the progression of subsurface structural changes and be extended to develop numerical models for microstructural alterations

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

Health and wellbeing of indigenous older adults living in the tea gardens of Bangladesh

Background There are currently 1.5 million indigenous people in Bangladesh, constituting 1.8% of the total population and representing one of the country’s most deprived communities. This study explores the health status and quality of life along with their determinants among indigenous older people in Bangladesh in order to fill the knowledge and evidence gap on this topic. Methods A mixed-methods approach was deployed in October 2019 in the Sylhet division of Bangladesh which involved a cross-sectional survey among 400 indigenous older adults (200 males, 200 females) from 8 tea gardens using a pre-tested semi-structured questionnaire. Ten in-depth interviews were also conducted with providers of the tea garden health facilities. Descriptive analysis, multiple logistic and multi-nominal linear regression were performed to explore associated factors around health and quality of life. Results Of the total respondents, the majority (79.5%) had chronic diseases, with visual difficulty being predominant (74%) among the conditions. Almost all (94%) of the respondents experienced delays in receiving treatment and poverty was identified by most (85%) as the primary cause of those delays. Extreme age, being male, living alone and low family income were significantly associated with suffering from chronic conditions. Furthermore, having a chronic condition and extreme age were found to be significantly associated with a low quality of life. Health service providers identified lack of logistical support in the health facilities, the economic crisis and lack of awareness as the major causes of poor health status and poor health seeking behaviour of the indigenous older adults. Conclusion Indigenous older men in extreme old age are more vulnerable to adverse health conditions and poor quality of life. Health literacy and health seeking behaviour is poor among indigenous older adults generally and there is a huge gap in the health services and social supports available to them