Key Engineering Materials Vol. 658

Abstract: Adhesion, hardness and surface morphology are important properties of thin film coated by PVD. Interlayer lying between substrate and coating layer plays an important role on these properties. In this research, type and thickness of interlayer for Cr-Zr-N film are varied to investigate their effect on properties of film. Cr, Zr and mixed Cr+Zr interlayer were selected for this research. Thickness of interlayer was varied by varying coating time from 5 to 45 min. The effect of interlayer on formation of Cr-Zr-N film was analyzed by XRD. Surface morphology was observed by OM, SEM and AFM. Hardness and adhesion were measure by nanoindentation tester and scatch tester. This research found that for surface morphology and hardness, Cr+Zr is the most appropriate interlayer while Zr interlayer provides the best adhesion properties.

Abstract: Diamond grinding wheel is used in high precision grinding process, when work piece has a very high hardness. For a specific grinding interval, the wheel must be properly dressed, in order to remove swarf, sharpen the worn diamond grits, open up new diamond protrusions, and recondition the bond material. Dressing of diamond grinding wheel by alumina dressing tool has been simulated in a pin-on-disk machine in the research. Sharpening of the wheel is indicated by the increase of its roughness value, and surface microstructure with protruding sharp diamond grits. It was found that increasing of sliding distant from 100 to 500 m will increase the roughness of the wheel. The increase of contact load from 10 to 20 N will also increase roughness of the wheel, and the severity of wheel wear, indicated by high values of friction coefficient. A proper dressing of this nickel bonded SD1200 diamond wheel is by sliding against alumina dressing tool for at least 300 m under 10 N load. Sliding velocity has minimal effect to the results. A too large sliding distant and load will cause severe damage to wheel surface, and severe wheel wear, indicated by its large mass loss.

Abstract: Methanesulfonic acid (MSA) is an environmentally benign supporting electrolyte that is an attractive alternative to traditional copper and tin plating baths based on cyanide or fluoborate. This is mainly due to its low toxicity, volatility, and good biodegradability as well as other desirable characteristics for electrodeposition such as high metal salt solubility and conductivity. The role of fluorosurfactant on Cu-Sn electrodeposition from methanesulfonic acid was explored through the use of an electrochemical quartz crystal nanobalance to monitor surfactant adsorption and desorption from the electrode surface. It was found that the surfactant adsorbs on the surface and inhibits copper deposition by blocking the reduction and oxidation reaction for copper.

Abstract: The electro-oxidation of 40 degree of alcohol as a local-commercial of spirituous liquor in Thailand compared with pure ethanol solution on the metal catalyst of PtSn/C was carried out. With using the 5 cm² anode electrode of PtSn/C catalyst, the direct alcohol fuel cell was employed and then fed with 1 M of spirituous liquor at flow rate of 1 ml/min under operating condition of atmospheric pressure. The results from an output electrical power of 40 degree liquor fed into direct alcohol fuel cell (celled 40DFC) indicated that, at the initial time, the spirituous liquor provided the higher power density of 6 mW/cm² compared with ethanol solution (celled DEFC) at the same concentration. For the cell open circuit voltage (OCV) using the spirituous liquor as fuel, it was 0.63 V which slightly lower than ethanol solution one. Nevertheless, 15 minutes left after applying the liquor, the cell performance was dramatic dropped due to the poisoned species of sulfur contained in liquor. The anode catalyst performance loss was also proved by using hydrogen gas for rechecking of the permanent degradation of fuel cell caused by feeding liquor onto the PtSn catalyst surface.

Abstract: Metallic foam is currently one of very active research topics in worldwide research communities, owing to its high potential to be employed in numerous industrial applications. Around 150 institutions are reported to be working in metallic foam research and development. In Thailand, it has been a research focus of universities and research institutes for many years. Most of them involve fabrication, characterization, improvement of metallic foam quality and process, and development of novel metallic foams. The majority of metallic foam research is conducted at Chulalongkorn University. The present article reports a review of metallic foam researches in Thailand.

Abstract: Electrochemical discharge machining (ECDM) is an ideal process for machining of nonconductive materials in micro-domain. The material removal takes place due to combined action of localised sparks and electrolysis in an electrolytic chamber. The electrolyte is most important process parameter for ECDM as it governs spark action as well as electrolysis. This article presents a comparison of three preferred electrolytes used in ECDM viz. NaCl, KOH and NaOH on drilling of glass workpiece material. The quality characteristics measured are material removal rate (MRR) and hole overcut. Results reveal that NaOH provides 9.7 and 3.8 times higher MRR than NaCl and KOH respectively. MRR and hole overcut are found significantly affected by spark characteristics.

Abstract: The aim of this research was to study semi-solid state joining of SSM A356 aluminum alloys which welded at its semi-solid state temperature by using oxygen – acetylene heat source. Then a stirrer was used to stir the weld seam. The joining parameters were rotation speed 1,110 with welding speed 120 mm/min and rotation speed 1,320 rpm with welding speed 160 mm/min. The joining temperatures were 575-590 and 590-610 oC. Joining was performed under nitrogen shielding gas and under argon shielding gas. Physical appearance, macrostructure, microstructure and mechanical properties were analyzed. The results indicated that the weld’s microstructure consisted of globular structure. In addition, porosities were found at the top of weld. However, minimum porosities were obtained from joints under argon shielding gas. The highest tensile strength was achieved from rotation speed at 1,110 rpm with welding speed at 120 mm/min under argon shielding gas with the value of 173 MPa. The joint efficiency was 86 % compared to the base metal.

Abstract: The repair welding of aluminum alloy 5083 was studied using Gas Metal Arc welding (GMAW) process. The effect of heat cycles from welding was investigated in some details. Butt joints of 6 mm and 3 mm thick were welded with 5356 filler metal. Then weld was removed by grinding and repeatedly welded again for 2 times. After each repair weld, the weld was assessed by macrostructure, microstructure and mechanical tests. The results revealed porosities of all weld samples. The repair welds indicated lower tensile strength compared with the new welds. In addition, all tensile strengths were much lower than the base metal. All samples were fractured at the weld metal.

Abstract: The objective of this research is to study the mechanism of the decomposition of zinc ferrite to obtain crude zinc oxide (ZnO) and iron oxide by using carbon (activated carbon) powder as the reducing agent. Zinc ferrite could be mostly found in electric arc furnace dust (EAFD). Carbon with a purity of 99.99 percent by weight was ground to be fine powder with an average size of 75 microns. Then the mixer between zinc ferrite with carbon powder and EAFD with carbon at the ratio of 1:1, 1:2 and 1:3 by mole was carried out. The samples were treated in the range of temperatures at 600, 700 and 800 °C in TGA. The treated samples were analyzed by XRD in order to identify the phase transformation of zinc ferrite. It was found that the quantity of zinc ferrite, both either pure zinc ferrite and the zinc ferrite in EAFD were decreased after treating by carbon when using treating time at 120 minutes with the temperatures of 600, 700 and 800 °C, and ratio of zinc ferrite with carbon powder at 1:3 by mole. Moreover about 70% of zinc ferrite was decomposed to be zinc oxide (ZnO) and iron oxides.

Abstract: Chromate conversion coating is an important surface finishing process for electroplated zinc coatings that are widely employed in automotive applications. In addition to providing enhanced corrosion protection, the conversion coating offers a shade of colors to the coated products, both for aesthetic and functional benefits. Due to the stringent requirements on environmental issues, the industry is replacing the conventional hexavalent chromate with a more environmentally friendly trivalent chromate for the production of coatings. This effectively poses the requirement of the fundamental understanding on how the keys processing parameters of trivalent chromate conversion coating may relate to coloring of the coating products. In this work, for the first time, a systematic study is carried out to correlate the electroplating parameters, including the current density and electrolyte’s additives, on the formation of the trivalent chromate conversion coating, and hence the color appearance of the top-coats. Focusing on the black conversion coating, the color and optical properties are analyzed using a colorimeter and an optical spectrometer. The results notably show that, while the additives highly influence the observable shade of blackness, current density affects the optical properties in the visual spectrums. The microstructural and chemical characterization techniques, namely FE-SEM, OM, and XRD, are used to shed some light on the underlying mechanism that controls the color appearance. The understanding developed in this study will impact the design and fabrication of the electrogalvanizing products of desired color and esteemed functional performance.