Papers by Author: T.I. Khan

Abstract: The electrodeposition of nanostructured composite coatings involves the co-deposition of nanosized oxide particles such as TiO₂, Al₂O₃ and Y₂O₃ into a corrosion resistant metal matrix such as nickel to improve the high temperature oxidation and erosion resistance of nickel coatings. The technique has several advantages over other methods for producing nanostructured composite coatings such as thermal metal spraying. Some of the main advantages are lower cost for equipment setup and lower material cost and the ease with which the process can be controlled. Although electrodeposited nanostructured coatings are being developed for various aerospace and marine applications, they have not yet been considered for protecting surfaces of components and piping that is used in technologies for the oil sands industry such as the In-Situ Combustion (ISC) process. The challenge with in-situ combustion oil production is that the combination of high temperature combustion gases and the presence of moving sand particles create an extremely severe environment in which high oxidation and erosion rates are expected. As a result there is a need to develop function specific coatings that can withstand both high temperatures and erosive environments in the oil sands industry. This paper presents results of high temperature oxidation behaviour of nickel coatings containing two types of nanosized oxide dispersions (TiO₂ and Al₂O₃). High temperature oxidation tests were conducted in dry air for 500°C and 700°C. The oxidized specimens were examined by metallographic surface analysis and surface composition techniques such as Scanning Electron Microscopy (SEM), Wavelength Dispersive X-Ray Spectroscopy (WDS). The effects of nanosized oxide particles on high temperature oxidation behavior of nickel coatings have been studied. The results show an improvement in the high temperature oxidation resistance of nickel coatings dispersed with Al₂O₃ and TiO₂.

Abstract: Tungsten carbide cobalt coating has been extensively used for cutting and mining tools, aerospace, automotive and other wear resistance applications. These coatings not only have superior mechanical properties like high hardness, toughness and compressive strength but have also excellent controllable tribological properties. In this paper a comparison of wear properties and structural phases has been presented to consider for tribological applications. It is found that nanocrystalline duplex coatings have shown much superior properties as compared to the microcrystalline coatings. Evidence of clusters of WC particles was found in microcrystalline coating as compared to homogeneous dense coating structure observed in the nanocrystalline coating. These results are discussed to assess their suitability for super hard wear resistance applications.

Abstract: Nitinol (NiTi) shape memory alloys are widely used in a variety of biomedical applications, such as dental implants, cervical and lumbar vertebral replacements, joint replacements and stents. In this study, commercially pure Ti and Ni foils ~100 um thick were diffusion bonded in vacuum. The experimental conditions were optimized to achieve a near equiatomic composition to produce NiTi SMA thin foil of approx. 5-8 micron thick. The cross-sectional surfaces of joint were subjected to metallographic investigation using optical microscope after grinding, polishing and etching. Scanning electron microscope equipped with EDX system was utilized to characterize the bonded layer and compositional analysis. Differential scanning calorimetry (DSC) technique was employed to determine the shape memory effect. The samples were subjected to X-ray diffraction analysis in order to establish phase structures formed during the diffusion bonding stage. An ultra fast femto-second laser facility was utilized to ensure the production of complex shapes or patterns within micron scale.

Abstract: This study concerns the development of wear resistant coatings of Ni-Al2O3 composite on steel substrates by electrodeposition. Each of the coating experiments was performed in an electrolytic bath, containing a nano-sized dispersion of Al2O3 particles in nickel sulfate and boric acid solution. Composition of the coating mixture was systematically varied with respect to the contents of the dispersed particles, while the amount of the dissolved nickel sulfate, and boric acid and the applied current were kept constant during the experimental measurements. The coated substrates were characterized for their morphology, Vickers hardness, and scratch resistance properties. It was observed that hardness and scratch resistance of the coated substrates increased with an increase in the Al2O3 content in the coating. It was noted that hardness of the composite coating decreased after heat treatment at 400oC in air atmosphere.

Abstract: The oil and gas industry of Alberta, Canada use coiled tubing made from high strength low alloyed steel (HSLA) to extract oil from reservoirs deep beneath the earth’s surface. The repeated use of the coiled tubing in down-hole wells results in fatigue failure of the tube material. In order to repair the coiled tube, a section of tubing is fusion welded using tungsten inert gas welding onto the remaining tube steel. However, the fusion weld often fails within the weld region and therefore, alternative joining methods need to be explored to minimize detrimental changes at the joint region. In this study transient liquid phase (TLP) bonding is used with the aid of metal interlayers based on the Ag-Cu and Ni-P systems. These interlayers form a liquid at the melting point and the gradual diffusion of alloying elements into the joint and the diffusion of elements out of the joint region induces isothermal solidification whilst the joint is held at the bonding temperature. The TLP bonding behaviour of the HSLA steel as a function of bonding parameters was investigated and the quality of the joint region determined using metallurgical techniques (light and scanning electron microscopy, energy dispersive spectroscopy) and mechanical testing.

Abstract: Dissimilar metal combinations are often necessary when manufacturing a component in order to meet particular functional and engineering requirements or protect against environmental degradation. Stainless steels are used in a diverse range of applications due to their excellent corrosion resistance, formability and strength. The 316L stainless steel also shows good crashworthiness due to its high strain rate sensitivity which makes it suitable for the transportation industry. The joining together of the 316L steel and AZ31 magnesium alloy cannot be achieved using conventional fusion welding methods and therefore, diffusion bonding using interlayers was used to overcome the differences in their physical properties. The results show that Cu and Ni interlayers form a eutectic with the magnesium which enhances wettability and bond formation through isothermal solidification. The effect of hold time on the microstructural developments across the joint region was studied at a bonding temperature of 530oC and 510oC for the Cu and Ni interlayers respectively using a bonding pressure of 0.2 MPa. This preliminary investigation shows that by increasing the bonding time from 5 to 60 minutes results in a Cu-Mg and Ni-Mg eutectic phase structure forming along the bond interface. By holding the joint at the bonding temperature for 15 minutes initiates isothermal solidification of the joint and this was confirmed by DSC analysis. However, the movement of the solid/liquid interface on solidification pushes intermetallic phases into the center of the bond during the solidification stage. The intermetallics increase the hardness value of the bond interface and lower final bond strengths.