Papers by Author: M.S.J. Hashmi

Abstract: Miniaturisation of electronic chips which have increasing functionality within the same package size has induced significant increases in requirements for extraction of heat from the integrated circuit (IC). Packaging materials therefore have to be capable to conduct heat efficiently and at the same time have low coefficient of thermal expansion (CTE) to minimize the thermal stress and warping. In the present study, copper silicon carbide was selected with an aim to solve thermal management problem presented by current IC systems. Powder metallurgy routes were chosen to fabricate the MMC based on this materials system. Copper and silicon carbide powders were mixed together in a planetary ball mill, and the green articles were then compacted and sintered to produce the final product of CuSiC. The sintering parameters were investigated for their effects towards the thermal conductivity of the composite. Sintering parameters investigated included temperature, heating duration and the gaseous environment. Upon sintering, the CuSiC particle bond to one another giving a higher strength and a possibility in attaining desirable density. Thus to achieve good thermal conductivity, the recommended sintering parameter suggests that the CuSiC composite should be sintered at 950°C for 7 hours in nitrogen gas.

Abstract: The only grouting material used for anchoring cemented arthroplasties to contiguous bones is PMMA (Polymethyl methacrylate) bone cement. In this study the flow of bone cement through porous cancellous bone is modelled to determine the degree of penetration in total hip replacement using FIDAP simulation software. Power law viscosity model is used with constant consistency index and power law index less than 1 for pseudoplastic behaviour of Simplex P® and Zimmer bone cement. The effect of bone cement amount has been investigated under four different prosthesis insertion velocity 5, 10, 15 and 20 mm/s. The result shows that the depth of penetration increases with decreasing bone cement amount. In the case of Zimmer bone cement more penetration through cancellous bone was observed than Simplex P® bone cement.

Abstract: PMMA (Polymethyl methacrylate) bone cement is currently the only material used for anchoring cemented arthroplasties to contiguous bones. The aim of this work is to model the flow of bone cement through porous cancellous bone to study the degree of penetration in total hip replacement using FIDAP simulation software. Two different viscosity models have been used (a) power law with constant consistency index and power law index less than 1 for pseudoplastic behaviour of Simplex P® and Zimmer bone cement; (b) FORTRAN subroutine for time dependent rheopectic behaviour of CMW3 and Zimmer bone cement. For each type of bone cement the effect of prosthesis insertion velocity have been investigated under four different values 5, 10, 15 and 20 mm/s. It has been observed that the depth of penetration increases with increasing prosthesis insertion velocity. On the other hand, the maximum pressure in bone cement decreases with increasing prosthesis insertion velocity. It has been observed that there is more penetration through cancellous bone for pseudoplastic behaviour than rheopectic behaviour of bone cement.

Abstract: nanostructured coating materials become demanding, since it improves the mechanical properties, such as hardness, through grain refinement. One of the methods of producing nanostructured coatings is to use an arc spray coating process using nanostructured wires. Although the arc spraying process is well developed, the influence of nanoparticles on the fracture toughness of the coating surface has not been examined in details. Consequently, in the present study, arc spraying of nanostructured wires on carbon steel surface is carried out. The influence of coating thickness on the microstructure and fracture toughness of the coating is investigated. It is found that the self-annealing due to large coating thicknesses has a noticeable effect on the microstructure and fracture toughness.

Abstract: In the present study, two layer HVOF coatings of carbon steel is carried out. The microstructural changes in the coating layers and fracture toughness of the coated surface are examined. The micro indentation method is incorporated for the fracture toughness measurements, while optical and scanning electron microscopy are used for the microstructural analysis. It is found that the fracture toughness of the coating surface produced by the tungsten carbide blended powders is less than that of the coating produced by corrosion resistance powders. Key words: HVOF, Diamalloy 2002, Diamalloy 4010, Fracture toughness.

Abstract: In the present study laser nitriding of titanium alloy surface is carried out and fracture toughness of the resulting surface is measured using the micro-indentation method. The fracture toughness is then related to the microstructure of the laser treated surface. It is found that laser gas assisted nitriding lowers the fracture toughness of the surface due to the micro-stress formed at the surface region during the high cooling rates.

Abstract: Laser gas assisted nitriding and TiN coating of Ti-6Al-4V alloy is carried out. The microstructures developed in the laser irradiated region are examined using Scanning Electron Microscope (SEM), Energy Dispersive Spectroscopy (EDS), and X-ray Diffraction (XRD). The laser nitrided surfaces are coated with TiN using the PVD facility to enhance the tribological properties. The heating model incorporating the lump parameter analysis is used to predict the melt layer thickness during the laser treatment process. It is found that laser nitrided surfaces posses δ-TiN+ε-TiN phases and TiN coating of laser nitrided surfaces improves the microhardness at the surface.

Abstract: HVOF coating finds application in industry to protect the surface from the harsh environments such as high temperature, corrosion, and abrasion. In the present study, HVOF coating consisting of Inconel 625 powders blended with WC particles and sprayed on to 304 steel is carried out. The mechanical properties, such as elastic modules and fracture toughness, of the resulting coating are determined using the indentation tests. The influence of the mass fraction of WC on the fracture toughness and elastic modulus of the coating are also examined. It is found that addition of WC particles in Inconel 625 powder enhances the fracture toughness of the resulting surface. This is attributed to increased elastic modules and hardness.

Abstract: The mechanical performance of DLC coatings on 316L stainless steel deposited by a saddle field fast atom beam source has been evaluated using the four point bend (FPB) test. Two different deposition parameters, pressure and current were varied when depositing the films. Load-displacement measurements were carried out during the bend test to determine the load corresponding to crack initiation. This load designated as the cohesive strength of the coating which is also called the cracking resistance of coating and provides a measure of the strength of the coating. The cohesive strength of the coating was calculated based on elementary beam theory. Scanning Electron Microscopy (SEM) was used to determine the location of the crack. Finite element analysis was used to predict the stress distribution across the coating thickness. The experimental work on FPB tests has been used to support the numerical (finite element) model for the determination and prediction of film cohesive strength. It was observed that at lower deposition current, the cohesive strength increases with increased deposition pressure whereas, for higher deposition current, these values do not increase with increasing deposition pressure. The model takes into account the film’s Young’s modulus, thickness and deposition pressure and current, and has shown that it is capable of predicting film cohesive strength when combined with a theoretical formulation for brittle fracture. It has been observed that the maximum stress develops at the outer surface of the film and propagates through the film-substrate interface. This result has only been validated for films with higher Young’s modulus compared to that of the substrate material.

Abstract: HVOF two layer coatings consisting of Diamalloy 2002 (top layer) and 4010 (bottom layer) onto carbon steel sheets are carried. The microstructure and chemical composition of the resulting coatings are examined using the Scanning Electron Microcopy (SEM) and Energy Dispersive Spectroscopy (EDS). The indentation tests are carried out to evaluate the microhardness and surface elastic modules of the resulting coatings. It is found that the coating produced for Diamalloy 2002 results in higher hardness and elastic modules than that corresponding to Diamalloy 4010.