Showing papers by "Ahmad Ali Amadeh published in 2015"

Investigations on the wear mechanisms of electroless Ni–B coating during dry sliding and endurance life of the worn surfaces

Abstract: The purpose of the work was to elucidate wear behavior and its mechanisms on electroless Ni–B coatings and to evaluate their endurance life during dry sliding at different normal loads (5 to 60 N) and sliding distances (100 to 700 m). An alkaline bath having borohydride was used to apply electroless Ni–B coatings with a mean thickness of 50–60 μm on the mild carbon steel substrates. Wear experiments were performed in a ball-on-disk configuration pressing alumina balls towards rotating disk specimens. Structure, morphology, hardness and boron content of the coatings were determined using X-ray diffraction analysis (XRD), Scanning Electron Microscope (SEM), Vickers microhardness tester and Inductively Coupled Plasma (ICP) spectrometer, respectively. The worn surfaces and wear debris were studied with SEM, Energy-Dispersive X-ray Spectroscopy (EDS) and X-ray map analysis. The results showed that the coatings were amorphous and contained 6.5 wt.% boron. The coatings exhibited better wear resistance compared to the substrate at the sliding distance of 300 m at all normal loads. Applying Ni–B coating on the mild carbon steel produced major improvement in the wear resistant of the substrate at constant load of 40 N. At sliding distance of 100 m, the dominant wear mechanism was combination of adhesive and abrasive at all applied loads. As the sliding distance increased, variety of wear mechanisms was seen during the sliding process at different applied loads. At normal loads of 40 and 60 N at the sliding distance of 500 m, the dominant wear mechanism was fatigue. The endurance lifetime of Ni–B coating was prolonged when the load was decreased. Ni–B coatings completely failed at sliding distance of 700 m at all normal loads.

Effect of electrodeposition conditions on properties of Ni-Al composite coatings

Abstract: Ni–Al composite coatings were prepared on 6061 Al alloy by pulse electrodeposition from a modified Watts bath containing suspended Al particles. The effect of surfactant and Al concentrations as well as electrodeposition parameters on composition, crystallographic texture, microhardness, adhesion strength and wear resistance of the coatings was investigated. The results indicated that addition of surfactant up to 0·25 g L−1 increased the amount of codeposited Al particles in nickel matrix. The incorporation of Al particles changed the preferred crystallographic orientation of the coating from (200) to (111). By increasing the current density and duty cycle, the amount of Al particles embedded in Ni matrix decreased and, therefore, the adhesion strength of the coating was improved whereas its microhardness reduced. Meanwhile, codeposition of Al particles increased the wear rate of composite coating with respect to pure nickel one. In other words Ni–Al coating is not suitable for wear resistant appl...

Microstructure and Mechanical Properties of Al2024/Ti-6Al-4V Transient Liquid Phase Bonded Joint

Abstract: Transient liquid phase bonding mechanism of two dissimilar alloys Al2024 and Ti-6Al-4V using Sn-Ag-Cu-Ni interlayer with different thicknesses (40, 80, 120 µm) was studied at 510 °C under 10−4 mBar. The results showed that with an increase in bonding time, the interlayer elements diffused into the parent metals and formed various intermetallic compounds in the joint zone. While diffusion mechanism led to isothermal solidification and process completion at 60 min bonding time, remaining interlayer was observed in the bond made with 120-μm-thick interlayer. With an increase in bonding time growth, the hardness of the joints at the interface rose to 139 VHN. Although the shear strength was proportional to the bonding time, the interlayer thickness showed a critical value at which the maximum shear strength was attained.