Materials Science Forum Vols. 828-829

Abstract: In the present study, combinations of a Phosphonato silane DEPETES with MTEOS silane, in various ratios were applied on Mg6ZnCa alloy. The coating morphology was characterized using scanning electron microscopy (SEM) and hydrogen evolution and pH variation of the samples were studied. The results showed that the sol-gel coatings reduced the hydrogen evolution rate of the magnesium alloy in m-simulated body fluid (m-SBF) solution. Moreover, biological response like cell attachment on the coated sample was found to be enhanced considerably compared to the bare alloy

Abstract: Biodegradable implant material for medical applications has to fulfill specific therapeutic tasks. For our investigations, synthetic polymers, polyurethanes (PUR) and polyetherimide (PEI), were used. Both systems have been used to coat an Al-free Mg alloy. Characterization of materials was performed by IR, spark spectral analysis, microscopy and EIS. Electrochemical investigations of the different treated samples in aqueous NaCl and Hank's Balanced Salt Solution indicate specific response of the polymer/substrate system to corrosion attack.

Abstract: PVD hard coating is a well-known surface treatment technology for steels to improve wear resistance and, to some extent, corrosion resistance. In principle, hard coating can be carried out for Al alloys, but due to the natural oxide layer and the insufficient load-bearing capacity of the soft base material, the application of this technology for wear protection of components is not regarded as being particularly promising. The research activities described in this paper focused on electron beam (EB) surface alloying with a Co-based additive, and the influence of two different hardness levels (270HV0.1 and 390HV0.1) on the improvement of the local load-bearing capacity of Al alloys with thin PVD hard coatings. A further focus of this research was on the material-specific aspects of the coating deposition. Compared to steels, the hard coated surface of Al alloys is rougher and the measured adhesion of the coating is significantly lower. For this purpose, different technological PVD parameters (e.g. Ti interlayer, deposition temperature, and time) were adapted to optimize the coating properties – especially adhesion. The paper deals with comparative studies of single (PVD hard coating of Al base material) and duplex treatment (EB alloying of Al base material and subsequent PVD hard coating) by means of improvement of the coating and compound hardness, friction and wear behavior (pin-on-disc test), as well as the corrosion resistance (potentiodynamic measurements in 0.05M H₂SO₄). While the level of improvement in wear resistance as a result of the duplex treatments strongly depended on the adhesion of the thin coatings, the corrosion behavior was strongly influenced by the PVD deposition process and coating thickness.

Abstract: A wire brushing and annealing process is developed and utilized to modify the surface layer microstructure of AZ31 magnesium sheet material and assess its effect on uniaxial tensile ductility and bendability. Wire brushing process utilizing fine brass wires is optimized to minimize deterioration in original surface quality by varying spindle rotational speed and depth of cut per wire brushing pass. Wire brushed material is then subjected to annealing to recrystallize the severely deformed surface layer. Rotational speed of 2800 RPM, feed rate of 1 mm/s, and a very small depth of cut coupled with annealing at 200 °C for 60 minutes results in a refined grain layer of grain size 5.5 μm and depth 30 μm on the surface. A texture study of wire brushed and annealed surface by X-ray diffraction reveals a randomized texture on the surface. Refined grain size and randomized texture result in about 38% enhancement in uniaxial tensile elongation in AZ31 compared to non-wire brushed annealed material. The role of surface microstructure and texture in improving sheet tensile ductility and bendability is discussed.

Abstract: The design of tribocorrosion resistant composite on Ti6Al4V alloy by laser surface cladding of admixed metal-ceramic powder was successfully achieved using a 2 kW CW ytterbium laser system (YLS). The effects of TiNiZrO₂ addition on the tribocorrosion properties of the synthesized composite coatings were investigated in 1 M H₂SO₄ solution using open circuit potential and potentiodynamic polarization techniques. The experimental results showed that TiNiZrO₂ refined the microstructure to flower-like structure. A strong metallurgical bond was obtained between the coatings and the Ti6Al4V alloy substrate with inter-columnar widmansttaten α΄ grains at the interface. There was a significant increase in surface microindentation hardness values of the clad layers. Also, the presence of zirconia shifted the tribocorrosion potential to more noble values and significantly enhanced the tribocorrosion resistance of the composites.

Abstract: This paper presents the bio-mechanical compatibility assessment of Titanium-Nickel (TiNi) alloy fabricated using cold spray (CS) process. This research creates opportunity for meeting the increased demand for biomedical implants in orthopedic surgeries brought by sport and traffic related bone injuries. Due to their exceptional properties, TiNi alloys are promising alternative biomedical materials to the traditional Ti6Al4V alloys. Studies show that the conventional methods for producing TiNi alloys have several challenges. As a contribution towards resolving this problem, this paper studied the bio-mechanical properties of Ti and TiNi structures fabricated using CS process. The results of this study show that the porosity, incipient Young’s modulus, and tensile strength of TiNi and Ti coatings are close to the required values for the biomedical implants. Consequently, this research demonstrates that porous TiNi and Ti structures fabricated by CS are possible candidates for biomedical implants and that CS could be a new process for fabricating near-net shape bio-mechanical compatible materials.

Abstract: This paper presents a novel process for fabricating micro-porous Aluminium (Al) alloy structures with possible application in antimicrobial filtration of drinking water which is contaminated with pathogenic micro-organisms responsible for water-borne diseases. This process is an integration of cold spray (CS) with the alloy-de-alloy phenomenon. In this process, the Al, Aluminium oxide () and Copper (Cu) powders with antimicrobial capabilities were mixed and deposited directly onto to a substrate using CS. To create porosity in the Al-Alumina-Cu coating, pores were innovatively engineered by alloying the Al--Cu with pore forming agents followed by preferential de-alloyed of these agents. The resulting structures have promising microstructural composition and porosity which make them favourable for antimicrobial filtration of contaminated drinking water. Consequently, this research demonstrates that via CS, a novel process was developed for fabricating porous Al-Alumina-Cu alloy metal foam for application in decontamination of drinking water.

Abstract: In this manuscript the development of the process parameters to friction stir weld 5.15mm thick AA5182-H111 at a feed rate of 1500mm/min is discussed. Compared to a weld made at 200mm/min the weld-pitch had to be reduced from 2.0rev/mm to 0.3rev/mm and down force increased from 27kN to 59kN to create a weld with tensile-and yield strength exceeding that of the parent material, whilst elongation was only marginally reduced. The low weld pitch coupled with the high feed rate resulted in a reduction in the weld temperature and an increase in the process reaction forces. A lower down force was sufficient to consolidate the stir zone and result in ultimate tensile strength yield strength exceeding that of the parent material. However, elongation was reduced since the low weld pitch also reduced the effectiveness of the flutes on the pin to break up and disperse the oxide layer, rendering a pseudo bond along the ‘Lazy S’. This pseudo bond was eliminated through an increase in the down force.

Abstract: Today’s contact lens professionals must familiarise themselves with the various contact lens manufacturing methodologies that are capable of producing high accuracy optical products for their patients. Contact lens manufacturing dates back to the 19^th century with the development of glass contact lenses and later evolved to various types of optical polymeric materials. The recent advances in the manufacturing of contact lenses can be attributed to the development of advanced polymeric materials and high precision processing technologies. Two basic techniques are identified for contact lens manufacturing. They are moulding method and ultra-high precision machining. Ultra-high precision machining is employed for direct shaping of contact lenses or for making mould inserts that will be used further in lens injection. Mould inserts can be made from high hardness steel, nickel plated steel, aluminium or other nonferrous alloys. Advanced light metal optical aluminium alloys provide a high integrity mould with fine microstructures for optical lens production. This review paper provides a chronological view of the evolution of contact lens manufacturing and identifies the importance of a recently developed aluminium alloy in the production of mould inserts for high quality contact lenses.

Abstract: Machining activities generate aerosols that can be harmful, degrade the environment or slow down theproduction. The main objective of this study was to evaluate the effects of machining conditions (cutting parameters and workpieces materials) on metallic particle emission during milling to help determining the machining conditions leading to ecological and occupational safe machining practices. The workpieces materials tested were aluminium alloys (6061-T0, T4 and T6 and A319) and aluminiummetal matrix composites (MMC) containing hard particles (SiC) for wear resistance and nickel-coated graphite particles for improved friction and machinability. It is found that the reinforcement within the aluminium MMCs reduces the fine particle emission as compared to unreinforced aluminium alloys. In general, the quantity of the particle emitted depends on the machining parameters settings. Among the aluminium alloys, the particle emission appeared to be dependent on material’s ductility.