The Observation of Frost Growth on the Micro-Texturing in SEM and Surface Design

In general, frost generation on cooled surfaces have a harmful influence on prevention of heat exchange as well as falling frosts can cause contamination of some medical or daily products. The countermeasure of frost growth on the surfaces achieve by heating those surface by electronic heaters even if it is refrigerator. To enhance eco-friendly electronic devices which have heat exchanger, the surface design to prevent or detach frost from itself is highly required. In the current study, micro-texturing and wettability of the surface were hypothesized to have significant influence on growth process of frost. Several surfaces were prepared such as a lotus leaf which is famous material for natural texturing, and line and space type texturing which was manufactured on the silicon wafers. In the environmental scanning electron microscope equipped peltier device behind of sample can generate frost on the specimen surface, hence, in-situ SEM observation of micro frost was conducted. In the case of hydrophilic surface, frost quickly grew on everywhere with low contact angle to the surface, and then the observation area was covered by frost. On the other hand, if we conducted same procedure to obtain frost on hydrophobic surface, the contact angle toward the surface was higher than hydrophilic one and growth speed of frost was lower than hydrophilic surface. From the observation, the frost on hydrophobic surface grew without enhancing their contact area between frost and the lotus surface. In the case of frost grew on hydrophobic surface, the frost did not grow with widen the contact area between lotus leaf. To determine the accommodate micro-texture design, different width and depth of texturing was applied to observe, then the appropriate gap was determined between 2 to 8 μm. The gap could minimize a contact area between frost and cooled surface which could decrease adhesion force

The effect of maximum normal impact load, absorbed energy and contact impulse on the impact craters volume/depth of DLC coating under repetitive impacts

Recently, the requirements for measuring dynamic responses have become severe and varied in many industrial and research applications such as material testing, model analysis and crash testing1). Surface degradation often occurs due to this dynamic response. This phenomenon also appears in the DLC coatings material. In this present work, a self-developed horizontal impact tester can provides this type of response, which gives an effect to the impact craters volume/depth of DLC coating

Raman Spectroscopy Study of Impacted DLC Coatings

Raman scattering is an excellent tool to characterize the structure of carbon atoms in diamond-like carbon (DLC). The study of DLC coatings in the sliding conditions has been conducted for a decade using Raman spectroscopy analysis. However, there is still insufficient information about how the structure of DLC coatings changes during repetitive impact. In this paper changes in the structure under 90o repetitive impact at a large number of cycles are presented

The effects of oil additives and mating materials to the friction, wear and seizure characteristics of a-C: H coating

In this study, friction and wear behaviour of amorphous hydrogenated carbon (a-C:H) DLC coating slide against SUJ2, TiC and TiN mating material disks in Base and ZnDTP+MoDTC oils boundary lubrication is comparatively investigated to determine the most favourable DLC/mating material/lubricant and interrelated tribofilm formation mechanism on each mating mating materials. Tribological tests were executed by utilizing roller on disk friction tester, nano-indentation hardness test, 3D optical surface profiler, and EDS-SEM were used to characterize the tribofilm formed on both worn roller and disk surfaces. The results showed that the wear volume of a-C:H/TiC tribo-pair in ZnDTP+MoDTC marked a tremendous wear volume reduction compared to than that of in Base oil. EDS investigation on tribofilm element investigation revealed that SUJ2 and TiN mating material disk attracted high concentration of Molybdenum at% on its surface that later caused high wear volume on both roller and disk sliding surfaces. TiC mating material disk however, formed a low at% yet helpful tribofilm consisting of a fraction of Zn phosphate from ZnDTP attached on both roller and disk which assisted the reduction of wear volume

Deformation and wear map of DLC coating under cyclic impacts

Generally, the construction of transition maps follow two different approaches ; empirical and physical modelling. However, only empirical approach is used in this study. In this century, there is no development of deformation-wear transition map of the DC coating under cyclic impact loading. Therefore, the aim of this study is to propose a new deformation-wear transition map of DLC coating based on variations of maximum normal impact loads and impact cycles for future design purposes

Design of low-friction PVD coating systems with enhanced running-in performance - carbon overcoats on TaC/aC coatings

The widespread use of low friction PVD coatings on machine elements is limited by the high costs associated with fulfilling the demands on the surface quality of both the supporting substrate and the counter surface. In this work, an attempt is made at lowering these demands, by adding a sacrificial carbon overcoat to a TaC/aC low friction coating. Both coatings were deposited by planar magnetron DC sputtering, as separate steps in a single PVD-process. Coatings were deposited on substrates of two different surface roughnesses, in order to test the ability of this coating system to function on rougher substrates. Reciprocating ball on disc tests was performed, using balls with two different surface roughnesses. The worn surfaces were investigated using 3-D profilometry and SEM. The ability of the different overcoats to initially reduce the roughness of both the coated surface and the counter surface and to produce stable, low-friction conditions was examined for the different initial roughnesses. The implications for design of efficient run-in coatings for various systems are discussed