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

Global burden and strength of evidence for 88 risk factors in 204 countries and 811 subnational locations, 1990–2021: a systematic analysis for the Global Burden of Disease Study 2021

Background: Understanding the health consequences associated with exposure to risk factors is necessary to inform public health policy and practice. To systematically quantify the contributions of risk factor exposures to specific health outcomes, the Global Burden of Diseases, Injuries, and Risk Factors Study (GBD) 2021 aims to provide comprehensive estimates of exposure levels, relative health risks, and attributable burden of disease for 88 risk factors in 204 countries and territories and 811 subnational locations, from 1990 to 2021. Methods: The GBD 2021 risk factor analysis used data from 54 561 total distinct sources to produce epidemiological estimates for 88 risk factors and their associated health outcomes for a total of 631 risk–outcome pairs. Pairs were included on the basis of data-driven determination of a risk–outcome association. Age-sex-location-year-specific estimates were generated at global, regional, and national levels. Our approach followed the comparative risk assessment framework predicated on a causal web of hierarchically organised, potentially combinative, modifiable risks. Relative risks (RRs) of a given outcome occurring as a function of risk factor exposure were estimated separately for each risk–outcome pair, and summary exposure values (SEVs), representing risk-weighted exposure prevalence, and theoretical minimum risk exposure levels (TMRELs) were estimated for each risk factor. These estimates were used to calculate the population attributable fraction (PAF; ie, the proportional change in health risk that would occur if exposure to a risk factor were reduced to the TMREL). The product of PAFs and disease burden associated with a given outcome, measured in disability-adjusted life-years (DALYs), yielded measures of attributable burden (ie, the proportion of total disease burden attributable to a particular risk factor or combination of risk factors). Adjustments for mediation were applied to account for relationships involving risk factors that act indirectly on outcomes via intermediate risks. Attributable burden estimates were stratified by Socio-demographic Index (SDI) quintile and presented as counts, age-standardised rates, and rankings. To complement estimates of RR and attributable burden, newly developed burden of proof risk function (BPRF) methods were applied to yield supplementary, conservative interpretations of risk–outcome associations based on the consistency of underlying evidence, accounting for unexplained heterogeneity between input data from different studies. Estimates reported represent the mean value across 500 draws from the estimate's distribution, with 95% uncertainty intervals (UIs) calculated as the 2·5th and 97·5th percentile values across the draws. Findings: Among the specific risk factors analysed for this study, particulate matter air pollution was the leading contributor to the global disease burden in 2021, contributing 8·0% (95% UI 6·7–9·4) of total DALYs, followed by high systolic blood pressure (SBP; 7·8% [6·4–9·2]), smoking (5·7% [4·7–6·8]), low birthweight and short gestation (5·6% [4·8–6·3]), and high fasting plasma glucose (FPG; 5·4% [4·8–6·0]). For younger demographics (ie, those aged 0–4 years and 5–14 years), risks such as low birthweight and short gestation and unsafe water, sanitation, and handwashing (WaSH) were among the leading risk factors, while for older age groups, metabolic risks such as high SBP, high body-mass index (BMI), high FPG, and high LDL cholesterol had a greater impact. From 2000 to 2021, there was an observable shift in global health challenges, marked by a decline in the number of all-age DALYs broadly attributable to behavioural risks (decrease of 20·7% [13·9–27·7]) and environmental and occupational risks (decrease of 22·0% [15·5–28·8]), coupled with a 49·4% (42·3–56·9) increase in DALYs attributable to metabolic risks, all reflecting ageing populations and changing lifestyles on a global scale. Age-standardised global DALY rates attributable to high BMI and high FPG rose considerably (15·7% [9·9–21·7] for high BMI and 7·9% [3·3–12·9] for high FPG) over this period, with exposure to these risks increasing annually at rates of 1·8% (1·6–1·9) for high BMI and 1·3% (1·1–1·5) for high FPG. By contrast, the global risk-attributable burden and exposure to many other risk factors declined, notably for risks such as child growth failure and unsafe water source, with age-standardised attributable DALYs decreasing by 71·5% (64·4–78·8) for child growth failure and 66·3% (60·2–72·0) for unsafe water source. We separated risk factors into three groups according to trajectory over time: those with a decreasing attributable burden, due largely to declining risk exposure (eg, diet high in trans-fat and household air pollution) but also to proportionally smaller child and youth populations (eg, child and maternal malnutrition); those for which the burden increased moderately in spite of declining risk exposure, due largely to population ageing (eg, smoking); and those for which the burden increased considerably due to both increasing risk exposure and population ageing (eg, ambient particulate matter air pollution, high BMI, high FPG, and high SBP). Interpretation: Substantial progress has been made in reducing the global disease burden attributable to a range of risk factors, particularly those related to maternal and child health, WaSH, and household air pollution. Maintaining efforts to minimise the impact of these risk factors, especially in low SDI locations, is necessary to sustain progress. Successes in moderating the smoking-related burden by reducing risk exposure highlight the need to advance policies that reduce exposure to other leading risk factors such as ambient particulate matter air pollution and high SBP. Troubling increases in high FPG, high BMI, and other risk factors related to obesity and metabolic syndrome indicate an urgent need to identify and implement interventions. Funding: Bill & Melinda Gates Foundation

Global burden of 288 causes of death and life expectancy decomposition in 204 countries and territories and 811 subnational locations, 1990–2021: a systematic analysis for the Global Burden of Disease Study 2021

Background: Regular, detailed reporting on population health by underlying cause of death is fundamental for public health decision making. Cause-specific estimates of mortality and the subsequent effects on life expectancy worldwide are valuable metrics to gauge progress in reducing mortality rates. These estimates are particularly important following large-scale mortality spikes, such as the COVID-19 pandemic. When systematically analysed, mortality rates and life expectancy allow comparisons of the consequences of causes of death globally and over time, providing a nuanced understanding of the effect of these causes on global populations. Methods: The Global Burden of Diseases, Injuries, and Risk Factors Study (GBD) 2021 cause-of-death analysis estimated mortality and years of life lost (YLLs) from 288 causes of death by age-sex-location-year in 204 countries and territories and 811 subnational locations for each year from 1990 until 2021. The analysis used 56 604 data sources, including data from vital registration and verbal autopsy as well as surveys, censuses, surveillance systems, and cancer registries, among others. As with previous GBD rounds, cause-specific death rates for most causes were estimated using the Cause of Death Ensemble model—a modelling tool developed for GBD to assess the out-of-sample predictive validity of different statistical models and covariate permutations and combine those results to produce cause-specific mortality estimates—with alternative strategies adapted to model causes with insufficient data, substantial changes in reporting over the study period, or unusual epidemiology. YLLs were computed as the product of the number of deaths for each cause-age-sex-location-year and the standard life expectancy at each age. As part of the modelling process, uncertainty intervals (UIs) were generated using the 2·5th and 97·5th percentiles from a 1000-draw distribution for each metric. We decomposed life expectancy by cause of death, location, and year to show cause-specific effects on life expectancy from 1990 to 2021. We also used the coefficient of variation and the fraction of population affected by 90% of deaths to highlight concentrations of mortality. Findings are reported in counts and age-standardised rates. Methodological improvements for cause-of-death estimates in GBD 2021 include the expansion of under-5-years age group to include four new age groups, enhanced methods to account for stochastic variation of sparse data, and the inclusion of COVID-19 and other pandemic-related mortality—which includes excess mortality associated with the pandemic, excluding COVID-19, lower respiratory infections, measles, malaria, and pertussis. For this analysis, 199 new country-years of vital registration cause-of-death data, 5 country-years of surveillance data, 21 country-years of verbal autopsy data, and 94 country-years of other data types were added to those used in previous GBD rounds. Findings: The leading causes of age-standardised deaths globally were the same in 2019 as they were in 1990; in descending order, these were, ischaemic heart disease, stroke, chronic obstructive pulmonary disease, and lower respiratory infections. In 2021, however, COVID-19 replaced stroke as the second-leading age-standardised cause of death, with 94·0 deaths (95% UI 89·2–100·0) per 100 000 population. The COVID-19 pandemic shifted the rankings of the leading five causes, lowering stroke to the third-leading and chronic obstructive pulmonary disease to the fourth-leading position. In 2021, the highest age-standardised death rates from COVID-19 occurred in sub-Saharan Africa (271·0 deaths [250·1–290·7] per 100 000 population) and Latin America and the Caribbean (195·4 deaths [182·1–211·4] per 100 000 population). The lowest age-standardised death rates from COVID-19 were in the high-income super-region (48·1 deaths [47·4–48·8] per 100 000 population) and southeast Asia, east Asia, and Oceania (23·2 deaths [16·3–37·2] per 100 000 population). Globally, life expectancy steadily improved between 1990 and 2019 for 18 of the 22 investigated causes. Decomposition of global and regional life expectancy showed the positive effect that reductions in deaths from enteric infections, lower respiratory infections, stroke, and neonatal deaths, among others have contributed to improved survival over the study period. However, a net reduction of 1·6 years occurred in global life expectancy between 2019 and 2021, primarily due to increased death rates from COVID-19 and other pandemic-related mortality. Life expectancy was highly variable between super-regions over the study period, with southeast Asia, east Asia, and Oceania gaining 8·3 years (6·7–9·9) overall, while having the smallest reduction in life expectancy due to COVID-19 (0·4 years). The largest reduction in life expectancy due to COVID-19 occurred in Latin America and the Caribbean (3·6 years). Additionally, 53 of the 288 causes of death were highly concentrated in locations with less than 50% of the global population as of 2021, and these causes of death became progressively more concentrated since 1990, when only 44 causes showed this pattern. The concentration phenomenon is discussed heuristically with respect to enteric and lower respiratory infections, malaria, HIV/AIDS, neonatal disorders, tuberculosis, and measles. Interpretation: Long-standing gains in life expectancy and reductions in many of the leading causes of death have been disrupted by the COVID-19 pandemic, the adverse effects of which were spread unevenly among populations. Despite the pandemic, there has been continued progress in combatting several notable causes of death, leading to improved global life expectancy over the study period. Each of the seven GBD super-regions showed an overall improvement from 1990 and 2021, obscuring the negative effect in the years of the pandemic. Additionally, our findings regarding regional variation in causes of death driving increases in life expectancy hold clear policy utility. Analyses of shifting mortality trends reveal that several causes, once widespread globally, are now increasingly concentrated geographically. These changes in mortality concentration, alongside further investigation of changing risks, interventions, and relevant policy, present an important opportunity to deepen our understanding of mortality-reduction strategies. Examining patterns in mortality concentration might reveal areas where successful public health interventions have been implemented. Translating these successes to locations where certain causes of death remain entrenched can inform policies that work to improve life expectancy for people everywhere. Funding: Bill & Melinda Gates Foundation