Materials Science Forum Vols. 773-774

Abstract: Currently, the focus in materials development is on processing of hybrid metal matrix composites (MMCs) in particular aluminum (Al) based owing to their flexibility in achieving tailor made properties. Till date, only processing, characterization of mechanical and adhesive wear behavior of various hybrid MMCs have received much attention. However, solid erosion wear of hybrid MMCs has not yet been reported. This assessment will further enlarge the range of applications of hybrid MMCs in particular for components in operation for military applications especially in desert areas. In the light of the above, the present paper discusses the air jet erosion behavior of developed Al6061-SiC-carbon fibre hybrid composite prepared by combination of powder metallurgy and casting process followed by hot extrusion at temperature of 550°C using extrusion ratio of 1:4. The solid sand erodent particle size used was 312 μm while the operating pressure and velocity was maintained at 1.4 bar and 30 m/sec respectively. The adopted feed rate of the sand particles was 2.0 g/min with standoff distance being 10 mm. The sample size was 25 mm x 25 mm x 10 mm. The effect of silicon carbide (SiC), Carbon fibre (C_f), test duration and angle of impingement of the erodent on the erosion wear loss of the developed hybrid composite will be discussed at length.

Abstract: Plating solution of tin free steel (TFS) presents strong corrosion and special chemical action properties of chrome ions and fluoride ions. Electrochemistry behavior of their ions in the plating process of TFS was investigated by means of cyclic voltammetry (CV). The results show that hydrogen and oxygen evolution peaks can only be found in CV curves of the carbon anode in fluoride solution. CV curves of the carbon anode in chromium trioxide solution consist of five anodic peaks and two cathodic peaks. When fluoride ions are added into chrome ions solution, anodic peak disappears at peak potential of 1.18V. For CV curves of lead alloy anode, anodic peak can be found at peak potential of-0.2V in fluoride solution, and oxidation process is in asymmetry with reductive process in chromium trioxide solution or the mixed solution. As to CV curves of lead oxide anode, the current density of all peaks in chrome ions solution is lower compared with that of carbon anode and lead alloy anode. When fluoride ions are added into chrome ions solution, the current density of the oxidation process obviously decreases, while the absolute value of reductive process increase remarkably

Abstract: Improving accuracy ofthe gear tooth surface has become an important challenge, because the toothsurface accuracy greatly influences vibration of gears. However, for the spiralbevel gear, the tooth surface accuracy is considered to be very difficult toevaluate because the geometrical theory is difficult. Generally, the managementof tooth surface accuracy has conventionally been substituted by the toothsurface contact evaluation with red lead, which is a kind of paint. However,the results of visual examinations are too subjective. We therefore focused onthe infrared ray imagery to investigate the gear tooth meshing. In this research,a high response infrared thermography was used to estimate the tooth contact ofa hypoid gear under running conditions. Specifically, we looked at the increasein temperature on the tooth surface caused by gear meshing. The results clearlyshowed that the temperature was affected by load, sliding speed between toothsurfaces, and the average peripheral speed of tooth surface. We also proposedan equation that predicts tooth surface temperature rise and showed its utility.Thus, the proposed method effectively evaluates the tooth surface accuracy ofhypoid gear.

Abstract: Stellite 6 coatings were produced using laser cladding of two different steel substrates (martensitic and austenitic stainless steels). The chemical composition and microstructure of these coatings were characterized by atomic absorption spectroscopy, optical microscopy and scanning electron microscopy. The microhardness of the coatings was measured and the wear mechanism of the coatings was examined using a pin-on-plate (reciprocating) wear testing machine. The results showed less cracking and pore development for Stellite 6 coatings applied to the martensitic stainless steel (SS) substrate. The wear test results showed that the weight loss for the coating on martensitic SS was significantly lower than for the austenitic SS substrate. It is concluded that the higher hardness of the coating on the martensitic SS, together with the harder and more rigid substrate increase the wear resistance of the Stellite 6 coating.

Abstract: Plasma sprayed hydroxyapatite coatings were deposited onto mild steel substrates. A Taguchi L₉ design of experiment protocol was used to optimise the coating process parameters. The effect of three factors: (i) power and secondary gas flow rate (X1), (ii) powder feed rate and carrier gas flow rate (X2), and (iii) stand-off distance (X3) on the coating responses was studied. The responses of the plasma sprayed hydroxyapatite coatings were evaluated in terms of porosity, deposition efficiency, microhardness, crystallinity, and surface roughness. A regression analysis established relationships between process parameters and responses. Higher power, lower powder feed rate and the middle stand-off distance of 11 cm lead to optimum attributes of low porosity, high deposition efficiency, high microhardness, high crystallinity, and high surface roughness.

Abstract: Hydroxyapatite (HA) and titanium composite coatings, which demonstrate good biocompatibility and load bearing capacity, are important in the topical area of prosthetics. In this study, hydroxyapatite and titanium composite coatings were deposited on austenitic stainless steel (316L) substrates using the Direct Material Deposition (DMD) technique. The microstructures were characterized using optical microscopy, scanning electron microscopy (SEM) and energy dispersive X-ray spectroscopy (EDS). Surface topography and roughness were assessed by SEM and profilometry, while Raman microscopy was employed to determine the nature of HA in the feedstock. The results indicate that average roughness increases with traverse speed and depends significantly on the power level. The crack orientation was found to be sensitive to traverse speed, while the number of cracks was related to the power level. Porosity decreased as the power level increased.

Abstract: An ultra- thin Ti film with a thickness of less than 30 nm was deposited on the surface of a silicon wafer by the filtered arc deposition system. A novel technique was adopted to create a height step between the coated area and non-coated area (silicon wafer) during deposition. The surface morphology and thickness of the film was detected by atomic force microscopy (AFM). The AFM results showed that the deposited film formed a smooth structure on the silicon wafer and the height step between the coating and silicon wafer was clear enough to give the thickness of the deposited film. The composition of the deposited film was detected by a combined use of Ellipsometry and AFM. Natural oxidisation of Ti (TiO2) was found on the top of the Ti film after deposition, and the thickness of TiO2 was determined by ellipsometry to be about 0.6 nm.

Abstract: In this work, the numerical equation has been established to simulate the vibratory compaction system based on the hysteresis loop of Davidenkov and with the gap ignored between the piston and the materials, and the dynamical characteristics and influence of parameters on the vibration compaction effect were analyzed with different stiffness, damping, amplitude and mass. Two types of experiments were carried out to study the dynamical characteristics and validate the numerical analysis and simulation. The first type of experiments was done with the different exciting vibration amplitude. The second type of experiments was done with the different water saturation instead of the stiffness and damping. The numerical and experimental results show that the equivalent natural frequency and vibration amplitude of the system increased with the stiffness, exciting amplitude increased and damping decreased. The experimental results agree well with results from a theoretical model in general. The research results will be used in intelligent granular compaction in the future.

Abstract: The efficiency of vibrating machines will be greatly improved with the proper working parameters. A new type of hydraulic vibration pile driver extractor is presented in this paper. The machine-pile-soil dynamic model of the hydraulic vibration pile driver extractor based on frictional forces and vibration coupling is established with frictional forces of the pile-soil contact surface and the resistance force of the pile-end. Furthermore, the nonlinear dynamical characteristics of the dynamic model are studied and the influences of different system working parameters on frictional forces of pile-soil interface, working efficiency and capability are discussed by numerical simulation. The different working parameters are exciting force, frequency and stiffness. The results show that the suitable parameters of the vibrating machine can change the soil characteristics and decrease the frictional forces of the pile-soil interface. The work can provide useful guidance for the research on the vibration friction, selection in the suitable parameters of interface surface in engineering and design in the development of such machines.

Abstract: The micro gear molds for powder injection molding were fabricated by electroforming process of Ni-Fe alloys. The residual stress at interface between electrodeposit and substrate was important for micro electroforming. Addition of 6 g/L saccharin lowered residual stress from 466.3 MPa up to 32.8 MPa and increase of Fe content resulted in increase of residual stress. Electrodeposition by pulse current decreased residual stress in deposit although Fe content was increased. These results reveal clearly that decrease of residual stress due to pulse current is larger than increase of residual stress due to higher Fe content. The micro electroformed gear molds with 550 μm and 2,525 μm in outer diameter and 400 μm in height were fabricated by micro electroforming and 316L feedstock was injection-molded into micro molds. As a result, it is suggested strongly that micro electroforming is very useful process to manufacture micro mold with high dimensional accuracy for micro PIM.