Fazal Ahmad Khalid

Instant nano-hydroxyapatite: a continuous and rapid hydrothermal synthesis

Nano-particle hydroxyapatite (HA) rods, were rapidly synthesised using a three pump continuous hydrothermal process (using a water feed at up to 400 degrees C and at 24 MPa): the product was obtained as a highly crystalline and phase pure material, without the need for an ageing step or subsequent heat treatment.

Sintering and Morphology of Porous Structure in NiTi Shape Memory Alloys for Biomedical Applications

The combination of attractive properties of porous NiTi shape memory alloys like high recoverable strain due to superelasticity and shape memory effect, good corrosion resistance, improved biocompatibilty, low density and stiffness along with its porous structure similar to that of bone make them best materials for biomedical implants. In current study porous NiTi SMAs have been fabricated successfully by space holder technique via pressureless sintering using NaCl powder as a spacer. Various volume fractions of NaCl powders have been involved to study their effect on the pore characteristics as well as on mechanical properties of foam. Porous NiTi with average porosity in the range of 44.3%-63.5% have been fabricated having average pore size 419µm which were very appropriate for various biomedical implants. Porous NiTi SMAs exhibited superelasticity at room temperature and shape memory effect was also determined. Maximum recoverable strain of 6.79% was demonstrated by the porous NiTi alloy with 44.3% porosity and it was diminishing with increasing porosity. Compression strength and elastic modulus have shown a decreasing trend with increasing porosity content. Elastic modulus of porous NiTi extends from 1.38 to 5.42GPa depending upon the pore volume which was very much comparable to that of various kinds of bones.

Investigating the Effects of Synthesis Parameter on the Yield and Structural Health of In-Situ Grown Carbon Nanotubes

Investigating the Effects of Synthesis Parameter on the Yield and Structural Health of In-Situ Grown Carbon Nanotubes Carbon nanotubes have proved to be very unique and versatile reinforcing agent for the development of nanocomposites in recent times. In this study, CNTs were grown on cobalt based nano particles by Alcoholic Catalytic Chemical Vapor Deposition process for the fabrication and promotion of hard metallic in-situ nanocomposites materials. Alcoholic (ethanol) precursor was preferred as it minimizes defects on CNTs surfaces. Besides in-situ growth of CNTs, other main objective of this study was to optimize a reaction temperature (among several), which offered better yield and quality of grown CNTs. Yield and quality index of CNTs were better at 900oC. Influence of synthesis reaction temperatures on quality of grown CNTs was investigated by Raman Spectroscopic technique. CNTs graphitic hexagonal crystal planes were confirmed by XRD spectra.

Effect of Thermal Treatment on Nano-Crystallites and Phase Transformation of CaZrO3Thermal Barrier Coatings

Thermal barrier coatings (TBCs) are multilayered coatings having the complex structure. In thermal spray coatings characteristic features of deposited molten particle and its microstructure is very important in defining coating properties. In this work stainless steel (AISI 316) was used as substrate material on which bond coat of Ni-20Cr and top coat of CaZrO3 were deposited by air plasma spraying method. Effect of isothermal treatment on the internal microstructure structure of lamella (splat) and phase changes in CaZrO3 coating was studied. The fractured surface of coatings was investigated to observe the splat morphology. It was observed that the nanocrystallites present within the splat grew with increase in temperature. Further, the monoclinic phase was formed as function of temperature and time.

Non-Destructive Evaluation of Plasma Sprayed CaZrO3 Coatings by Eddy Current Technique

Eddy current as a non-destructive technique has been used for evaluation of thermal barrier coatings (TBCs) system. In this study the TBCs system which consists of substrate material of stainless steel 316, Ni-20Cr as a bond coat and top coat of CaZrO3 was produced by air plasma spraying technique. Isothermal treatment of TBCs system was performed and its effect on the microstructures and oxide formation was investigated. The chromium oxide formation as a function of temperature and time was observed. The observed changes in microstructure and formation of chromium oxide were then correlated with variation in eddy current values.

Wear Behaviour of HVOF Sprayed WC-Cobalt Coatings

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.

Aging Response to Microstructure and Properties of Ferromagnetic Shape Memory Alloys

Ni-Mn-Ga magnetic shape memory alloys are employed for applications in actuators and sensing devices. Ni-Mn-Ga single crystalline alloys exhibit ferromagnetic shape memory effect with large reproducible strains in moderate magnetic fields. The cost for producing single crystals is high and there is a requirement to investigate the polycrystalline Ni-Mn-Ga alloys for similar applications. This work presents a study of the effect of composition and heat treatment on the microstructure, in polycrystalline off-stoichiometric compositions of high Ni, Ni-Mn-Ga alloys. Cast polycrystalline alloys were homogenized and analysed using optical microscopy, X-ray diffraction, and thermal analysis. Stability of the martensitic transformation temperature was studied by aging the alloys at different temperatures. Martensitic structure was found in both the alloys (~ 54at% and 58 at%). The alloy with high Ni~58 at% content was found to be having a dual phase structure (martensite and FCC γ). Single phase Ni-Mn-Ga alloy has shown transformation at temperature >400K while the dual phase alloy with Ni ~58at% has transformed at temperature >700K thus making it suitable for high temperature applications. Martensitic stabilization effect was observed in alloy with Ni ~54 at% after aging treatment while it was absent in alloy with ~58at% Ni.