Applied Mechanics and Materials Vol. 835

Abstract: The electrochemical properties of niobium monoxide, NbO, were investigated as a negative electrode material for lithium-ion batteries. Lithium ions were inserted into and extracted from NbO material at potentials < 1.0 V versus Li/Li⁺, involving formation of a solid electrolyte interface (SEI) on the NbO surface in the first cycle. Its reversible capacity is ~67 mAh g^–1 with the capacity retention of ~109% after 50 cycles. The magnitude of charge transfer resistance was greatly decreased by ball-milling the pristine NbO, whereas the ball-milling had no effect on the SEI resistance.

Abstract: Stainless steel (SS) is one of the most commonly used metallic food contact materials. It may be classified based on its microstructure whether ferritic, austenitic, martensitic, duplex or precipitation hardened. Austenitic SS, among mentioned grades, has the largest contribution to market due to its numerous industrial and domestic applications. In this study, the corrosion behavior of AISI 202 SS – a cheaper grade of stainless steel, in three different solution temperatures of citric acid was investigated using different electrochemical techniques such as open-circuit potential (OCP) measurements, potentiodynamic polarization and electrochemical impedance spectroscopy (EIS). The results were compared to that obtained from conventional AISI 304 SS. OCP, polarization and impedance measurements agreed that AISI 202 SS has comparable resistance to that of AISI 304 SS in citric acid at ambient temperature and at 50 °C. At 70 °C, results of OCP measurements suggest that AISI 304 SS exhibited greater performance as indicated by more positive OCP values in the designated solution. EIS results indicate that the two alloys have identical corrosion resistance even at 70 °C as indicated by their comparable polarization resistance (R_p). The corrosion mechanism in both alloys is charge-transfer controlled as indicated by depressed semi-circular appearance of the generated Nyquist plots. The values of corrosion current densities (i_corr) extracted from polarization curves indicate that the initial corrosion rates were higher in AISI 304 than AISI 202 SS suggesting that formation of more protective film may have occurred on the former alloy.

Abstract: The disturbances of vapor bubble to a laser beam in the underwater laser machinig process importantly limits the material removal rate and cut quality obtained. This issue is more essential for the laser micromachining process that a precise and small trench cut is highly needed. In this study, the ultrasound was used to energize and break up the bubble while the laser beam was performing a cut in water. Silicon was used as a work sample in this study as its significant usage in many micro-components. An ultrasonic transducer was located nearby the workpiece in an attempt to vibrate surrounding water. The results revealed that an increase in ultrasonic power increased the width and depth of cut channel. In addition, the workpiece surface obtained after the ablation was clean as similar to that performed by the ultrasonic cleaning. This combination of laser machining and ultrasonic cleaning processes can be another effective approach to cut thermal sensitive materials and also small components whose thermal damage and deposition of cut debris can be harmful to their functionality after laser ablation.

Abstract: Thermal damage of workpiece material induced by laser machining process can be reduced by using the underwater technique. This method requies the whole workpiece to be submerged in water while a laser beam strikes the work surface for ablation. Though water can cool the workpiece during the ablation, the dynamic features of water can adversely interfere the laser beam. The vapor bubbles created in water can scatter the laser beam and in turn attenuate the laser intensity at the work surface so as the ablation performance. In this paper, the bubble formation caused by laser machining of silicon in water was investigated and analyzed. The shadowgraph technique associated with the high speed camera was used to capture and measure the vapor bubble in water. The bubble size was found to increase with the laser pulse energy. After a number of laser pulses irradiated on the workpiece surface, the bubble was broken up into small ones which can significantly disturb the laser beam so as the ablation performance.

Abstract: One of the reasons causing vibration for gear hob toothing is the shock at the tool’s entry, which is generated by the great length of the cutting edge entering the metal at the same time. This paper proposes a fragmentation of the cutting edge so that its length is much smaller. Moreover, the cutting scheme is also changed, so that the entire tooth line of the piece is made with four consecutive teeth of the tool. Therefore, the impact force input generating shock and vibration is significantly reduced.

Abstract: Die casting aluminum alloy A380 were recoveredfrom high pressure die cast machining chipsunder a series of designed experiments using Taguchi Method, where flux types (FT), chips/flux ratio (CFR), holding times (Ht) and temperatures (HT) were selected as four factors. For each factor, three levels were chosen to create Taguchi orthogonal array. The recovery rate (R_r) was selected as a response to evaluate the effectiveness of the recovery process. An analysis of the mean of noise-to-signal (S/N) ratios indicates that the recovery rate is affected considerably by the levels in the Taguchi orthogonal array. The optimum combination leads to the highest recovery rate of 92.03% by using Al-clean 101 as the refining flux, 10:5 as the chips/flux ratio, 60 minutes and 760°Cas the holding time and holding temperature.

Abstract: The objective of this study is to investigate the effects of activating fluxes on the weld bead geometry, hot cracking susceptibility and mechanical property of A356 and 6061 aluminum alloy dissimilar welds in the gas metal arc (GMA) welding process. In this activated GMA welding process, there were nine single-component fluxes used in the initial experiment to evaluate the penetration capability of butt-joint GMA welds. The grey relational analysis (GRA) was employed to obtain the better weld bead geometry of welds that were considered with multiple quality characteristics. Based on higher grey relational grade (GRG), four single-component fluxes were selected to create mixed-component flux in the next stage. The experimental results showed that the GMA welds coated with activating flux were provided with better geometry of dissimilar welds. The experimental procedure of activated GMA welding process not only produced a significant increase in tensile strength of welds, but also improved the hot cracking susceptibility of aluminum alloy welds.

Abstract: The effects of root opening process parameters on the phisical and mechanical properties of mild steel specimens of grade LR Gr A having dimensions 200 mm× 100 mm× 12 mm, welded by gas metal arc welding were investigated. The variation of root opening that used were 3 mm, 5 mm and 7 mm. The physical properties examined with regard with microstructure, macrosructure, and corrosion using optical microscope and stereozoom. The measured of mechanical properties with regard to strength, hardness and toughness using, tensile test, Vickers hardness Test, and Charpy impact test. The test results show the base metal had a hardness of approximately 110 VHN and a maximum hardness of approximately 190 VHN that corellates with microstructure of weld metals. Microstructure of base metal and HAZ are ferite and perlite, while microstructure of weld zone are acicular ferrite and grain boundary ferrite. The corrosion rate of weld metals with various root opening categorized as materials having excellent corrosion resistance value. Welding joints with opening roots 3 mm and 5 mm can be used for construction. All welded specimens exhibited fracture at base metals

Abstract: The Present study was undertaken to investigate the porosity defects induced by semi-solid isothermal heat treatment in cast hypereutectic Al-18% Si alloy for different holding time. All specimens were heated up to 585 °C then hold for 10, 20, 30 and 40 min. in an electrically heated resistance furnace with heating rate of 10 °C.min^-1. After the semi-solid heat treatment, the samples were taken out immediately for water quenching. Bulk density, total porosity and pore sizes at center and edge of each treated sample were investigated. It was found that the porosity in final treated samples increases by increasing the holding time. The pore size increases and the density decreases steeply with increasing the semi-solid isothermal holding time. Above 20 min., holding time the pore size at the edge shows higher value compared with that measured at the center of sample. It might be recommended that shorter holding time during semi-solid isothermal heat treatment should be selected in order to obtain minimum porosity percentage and higher density Al-18% Si alloy castings.

Abstract: Si modification behavior by twin probability approach with X-ray diffractometry (XRD) technique and microstructural evolution of the A356 alloys with Al₂Ca and Mg exceeded up to 1.5 mass% during the solution heat treatment were investigated. Al₂Ca added alloys showed the modified Si particles in the microstructure and higher twin density than those of Al₂Ca-free alloy. During the solution heat treatment, the Si particles of Al₂Ca-free alloy became coarser with the time at 540 °C, while there was no coarsening in the Al₂Ca added alloys throughout all the conditions.