Hasan Mahmud | University of Malaya, Malaysia (original) (raw)

Papers by Hasan Mahmud

Surface and Coatings Technology, 2014

During the last two decades, the industry (including scientists) has focused on diamond-like carb... more 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.

n Present work, the properties of Al2O3 powder was studied through incorporation of MgO Nano powd... more n Present work, the properties of Al2O3 powder was studied through incorporation of MgO Nano powder along with ZnO Nano powder
and followed by sintering at various temperatures. Previously ZnO and MgO were introduced with Al2O3 separately to improve physical
and mechanical properties like densification, micro hardness, fracture toughness etc. In current project, 0.25wt% and 0.50wt% MgO
was added with ȕ- Al2O3 matrix along with constant 0.1wt% ZnO and sintered those samples at 14500 oC, 15000 oC, 15500 oC
respectively. Properties like densification, micro hardness, and wear rate of all these sintered products were measured and discussed
where the best composition found was 0.1% ZnO-0.25%MgO-99.65% Al2O3 sintered at 15000oC. Change in properties was observed
due to faster densification rate and pinning effect provided by the doping particles.

Nowadays, maintaining a clean environment is the major concern of industries that produce fuel an... more Nowadays, maintaining a clean environment is the major concern of industries that produce fuel and lubricant for automotive applications. Thus, vegetable-based oils are being
explored for the preparation of bio-based 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 trans-esterification. In this study, three vegetable-based oils (sunflower, palm, and coconut) were used to investigate tribological properties of ta-C DLC coating under DLC/steel contact condition. BICERI ball on a plate tribo-testing machine was used to conduct
experiments. During the experiment, test contacts of tribo-pairs lubricated with sunflower oil exhibited better tribological characteristics than those using coconut oil as lubricant.

Currently, the application of diamond-like carbon (DLC) coatings for automotive components is bec... more 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 amorphous hydrogenated DLC (a-C:H) and 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 and X-ray photoelectron spectroscopy were 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 a-C:H and ta-C DLC-coated plates. CoF and wear rate (coated layer and counter surface) are mostly influenced by coating graphitization. Tribochemical films, such as polyphosphate glass, are formed in ta-C and act as protective layers. Therefore, the wear rate of ta-C DLC is lower than that of a-C:H DLC.

Surface and Coatings Technology, 2014