K.A.H. Al Mahmud

An updated overview of diamond-like carbon coating in tribology

During the last two decades, the industry (including scientists) has focused on diamond-like carbon (DLC) coating because of its wide range of application in various fields. This material has numerous applications in mechanical, electrical, tribological, biomedical, and optical fields. Severe friction and wear in some machine parts consumes high amount of energy, which makes the process energy inefficient. Thus, DLC coating can be an effective means to lower the friction and wear rate. Some important process variables that affect the tribological characteristics of DLC coating are adhesion promoter intermediate layer, substrate surface roughness, hydrogen incorporation or hydrogen non involvement, and coating deposition parameters (e.g., bias voltage, etching, current, precursor gas, time, and substrate temperature). Working condition of DLC-coated parts also affects the tribological characteristics, such as temperature, sliding speed and load, relative humidity, counter surface, and lubrication media (DLC additive interaction). Different types of lubricated oils and additives are used in engine parts to minimize friction and wear. DLC can be coated to the respective engine parts; however, DLC does not behave accordingly after coating because of lubricant oil and additive interaction with DLC. Some additive interacts positively and some behave negatively because of the tribochemical reactions between DLC coating and additives. Numerous conflicting views have been presented by several researchers regarding this coating additive interaction, resulting in unclear determination of true mechanism of such interaction. However, lubricant additive has been established to be more inert to DLC coating compared with uncoated metal surface because the additive is fabricated in such a way that it can react with metal surfaces. In this article, the tribological characteristics of different types of DLC coating in dry and lubricated conditions will be presented, and their behavior will be discussed in relation to working condition and processing parameters.

The Effect of Temperature on Tribological Properties of Chemically Modified Bio-Based Lubricant

Vegetable oil has several characteristics that provide advantages for use as lubricant. This includes a high viscosity index, high flash point, high biodegradability, and friction and wear reduction properties. However, vegetable oil has some disadvantages such as low oxidation stability and low thermal stability. The transesterification process of palm oil using trimethylolpropane (TMP) alcohol has been proven to reduce the oxidation stability of vegetable oil. However, little research has been carried out on the effect of TMP ester as a lubricant in term of friction and wear. Therefore, this study investigated the effect of temperature on the tribological properties of TMP ester using a four-ball machine. The load and speed of the sample were set at 40 kg and 1,200 rpm, respectively. Temperature was varied between 50 and 100°C. It was found that TMP ester improved the friction properties by around 15–20%. At low temperature, TMP esters have a higher coefficient of friction (COF) compared to paraffin oil. However, as the temperature increased higher than 80°C, paraffin oil had a highere COF value. This is because at high temperature, the lubricant filmed formed by fatty acids tends to be less stable and breaks down more easily.

Tribological Study of a Tetrahedral Diamond-Like Carbon Coating under Vegetable Oil–Based Lubricated Condition

Maintaining a clean environment is the major concern of industries that produce fuel and lubricants for automotive applications. Thus, vegetable-based oils are being explored for the preparation of biobased lubricants because of their biodegradability and nontoxicity. Despite their low thermal stability, vegetable oils show better tribological characteristics than mineral oils. Nonetheless, the thermal stability of vegetable oils could be improved by transesterification. In this study, three vegetable-based oils (sunflower, palm, and coconut) were used to investigate the tribological properties of ta-C diamond-like carbon (DLC) coating under DLC–steel contact condition. A BICERI ball-on-a plate tribotesting machine was used to conduct experiments. During the experiment, test contacts of tribopairs lubricated with sunflower oil exhibited better tribological characteristics than those using coconut oil as a lubricant.

Tribological Characteristics of Diamond like Carbon Coating in the Presence of Environment Friendly Vegetable Based Oils

Nowadays environmental awareness issue draws the attention of the scientists; lubricant industry also focuses on environment friendly lubricating oils. Therefore, vegetable oils draw the attention of scientists because of environmental friendly as well as good lubricating characteristics. However, good lubricating vegetable oils often shows inferior property because of low thermal stability, hence, to enhance the performance of vegetable oils self-lubricating diamond like carbon coating is considered, which helps in lowering the friction force which in turn lower friction induced heating, as a result stability of vegetable oils increases. In this current research, three vegetable based oils (sunflower, palm, coconut) are considered as lubricating oil. Tribological tests are conducted by ball on plate tribo-testing machine, tetrahedral type diamond like carbon coated plates and uncoated balls are used in the tribo-pair. Among the testing conditions sunflower oil shows good friction and wear characteristics and coconut oil shows inferior friction and wear characteristics.

Friction and Wear Characteristics of Hydrogenated and Hydrogen-Free DLC Coatings when Lubricated with Biodegradable Vegetable Oil

Large amount of unsaturated and polar component of oils enhance the lubrication of ferrous materials. DLC coatings can effectively lower the coefficient of friction (CoF) and wear rate of engine components, consequently improving the fuel efficiency and durability of these components. Therefore, the interaction between nonferrous coatings (e.g., DLC) and vegetal oil must be investigated. A ball-on-plate tribotester was used to run the experiments using stainless steel plates coated with amorphous hydrogenated (a-C:H) DLC and hydrogen-free tetrahedral (ta-C) DLC sliding against 440C stainless steel ball. Raman analysis was performed to investigate the structural change of the coatings. At high temperatures, the CoF decreases in both coatings but the wear rate increases in the a-C:H and decreases in the ta-C DLC-coated plates. CoF and wear rate (coated layer and counter surface) are mostly influenced by coating graphitization. The degree of graphitization increases with increasing temperature. Graphitization occurs in the tribological contact because of friction-induced heating under contact and high contact stress conditions.

Tribological Characteristics of Amorphous Hydrogenated DLC in the Presence of Commercial Lubricating Oil

Currently diamond like carbon (DLC) coatings application for automotive components is becoming a favorable strategy to cope with new challenges faced by automotive industries. DLC coating is very effective to lower the coefficient of friction and wear rate, which in turn could improve fuel efficiency and durability of the engine components. Commercially available fully formulated lubricating oils are specially produced to enhance the lubrication of ferrous materials. Therefore, nonferrous coating (DLC) interaction with commercial lubricating oil needs to be investigated. In this current investigation, coefficient of friction and wear rate were investigated by ball on plate tribo testing machine at different temperatures in the presence of SAE 40 lubricating oil. At high test temperature coefficient of friction decreases, however wear rate increases for the a-C:H coated plate, however, steel/steel contact shows opposite trend of coefficient of friction and wear rate change.

Comparative Study of Properties and Engine Performance Using Blend of Palm and Coconut Biodiesel

Now-a-days the demand of alternative fuel is continuously increasing all over the world due to the rapid depletion of fossil fuel and increased global demand. Biodiesel is renewable and sustainable energy source derived from vegetable oils and animal fats which can be the best substitute of fossil fuel. This paper investigates the property of different biodiesel such as palm, coconut and their blends with conventional diesel also analyzed the engine performance like engine break power, speed, break specific fuel consumption (BSFC), torque in diesel engine. In this paper 20% palm biodiesel with diesel (P20), 20% coconut biodiesel with diesel (C20), 30% palm biodiesel with diesel (P30), 30% coconut biodiesel with diesel (C30) and combination of 15% palm biodiesel and 15% of coconut biodiesel with diesel (C15P15) were used for study. Biodiesel was produced by using transesterification process. The density and kinematic viscosity for C15P15 fuel is slightly higher and flash point is slightly lower than diesel fuel as well as others two biodiesel blends whereas pure palm oil biodiesel shows the higher flash point and acid value. Engine performance test was carried out at 75 kg load condition with variable speeds of 1400 rpm to 2000 rpm at an interval of 200 rpm. Engine brake power produced by mixed biodiesel (C15P15) is slightly lower than the fossil diesel but slightly higher than biodiesel (only palm or coconut). Engine torque produce by the mixed biodiesel is almost the same with the fossil diesel but higher than the others biodiesel blends. Engine brake specific fuel consumption of mixed biodiesel is slightly higher than fossil diesel but lower than others existing biodiesel. It can be reported that the fuel C15P15 showed better performance and can be used as fuel alternative to diesel fuel to reduce the greenhouse gas emission and dependency on crude oil.

Tribological Characteristics of Tetrahedral (ta-C) DLC Coating in the Presence of Commercial Lubricating Oil

Currently, the application of diamond-like carbon (DLC) coatings for automotive components is becoming a favorable strategy to cope with the new challenges faced by the automotive industry. DLC coatings can effectively lower the coefficient of friction (CoF) and wear rate of engine components, consequently improving the fuel efficiency and durability of these components. Commercially available fully formulated lubricating oils enhance the lubrication of ferrous materials. Therefore, the interaction between nonferrous coatings (e.g., DLC) and commercial lubricating oil must be investigated. A ball-on-plate tribotester was used to run the experiments using stainless steel plates coated with tetrahedral DLC (ta-C) sliding against a 440C stainless steel ball. Wear track was investigated by scanning electron microscopy and atomic force microscopy. Energy dispersive spectroscopy was used to analyze the tribofilms inside the wear track. Raman analysis was performed to investigate the structural change of the coatings. At high temperatures, the CoF decreases but the wear rate increases in the ta-C DLC-coated plates. CoF and wear rate (coated layer and counter surface) are mostly influenced by coating graphitization.