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Characterization of functionally graded commercially pure titanium (CPTI) and titanium carbide (TiC) powders

  • Authors: Akinlabi, Esther Titilayo , Akinlabi, Stephen A.
  • Date: 2015-07-01
  • Subjects: Functional graded materials , Laser metal deposition , Titanium , Titanium carbide
  • Type: Article
  • Identifier: uj:5136 , ISBN 9789881404701 , http://hdl.handle.net/10210/14102
  • Description: Functionally Graded Materials (FGM) are advanced materials fabricated using additive manufacturing techniques. It belongs to a class of advanced material characterization in which the properties of the material composition is varied. The resulting property of the composite is always different from the properties of the individual material employed in the formation of the composite. They are known to also exhibit good mechanical and chemical properties and as such, are used for different industrial applications. One of the techniques employed in the fabrication of FGMs is called Laser Metal Deposition (LMD) technique. It uses laser beam to melt powder material on a substrate forming a melt pool that solidifies upon cooling. This paper reports on the material characterization of functionally graded Titanium and Titanium Carbide (TiC) powders deposited on Titanium substrate by laser metal deposition approach. The formed deposits were fabricated by varying the processing parameters such as laser power, scanning speed and the powder flow rate. From the result obtained, the microstructures showed that the laser power has much influence on the grain growth of the material. In addition, with the SEM analysis of the microstructure since the percentages of the titanium and titanium carbide were varied, it was observed that the sharp boundaries of the Titanium Carbide were reduced greatly and this resulting effect can be attributed to the thermal effect of the laser. The microstructures further revealed that as the percentage of TiC decreases, it becomes more difficult to see the TiC as a different material in the composite, emphasizing this as one of the best characteristics of functionally graded materials, which is the elimination of sharp interfaces and layers. Furthermore, it was observed that the laser power has great influence on the evolving hardness of the material compared to the TiC content.
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Laser forming of titanium and its alloys – an overview

On development of ultrahard hafnium and titanium carbide materials

  • Authors: Maseko, Emily Tholakele
  • Date: 2012-09-10
  • Subjects: Hafnium , Titanium
  • Type: Thesis
  • Identifier: uj:9812 , http://hdl.handle.net/10210/7215
  • Description: M.Tech. , A mixture of HfC and TiC powders and a (Hf,Ti)C powder have been hot pressed with 4wt% Ni. In the absence of Ni the hot pressed temperature was 2000 °C and in the presence of Ni 1650 °C. The pressure of 30 MPa was applied in both cases. The starting powders were substoichiometric, as deduced from XRD spectra analyses, and the (Hf,Ti)C powders consisted of a range of compositions, as indicated by the width of the XRD peaks. In the absence of Ni the powders sintered without the formation of a liquid phase. In the case of HfC and TiC mixture, high- energy dry milled HfC + TiC +C black powder sintering occurred with simultaneous formation of (Hf,Ti)C solid solution. On account of mutual solid solubility of two carbides vacancy interdiffusion controlled the solution as well as the sintering process, assisted by the high concentration of vacancies in the starting powders. In the case of (Hf,Ti)C powder diffusion was also the controlling process because t he solid solution was not h omogeneous a nd the system t ended to homogenization, as shown by t he narrowing of t he XRD peaks after sintering. Since the diffusion of HfC into TiC did not occur at the same rate as the diffusion of TiC into HfC (as expected, on account of the different melting points of the two materials) diffusional porosity was observed in some of the (Hf, Ti) C grains. Grain growth was substantial but uniform. In the presence of Ni, sintering occurred with the formation of a liquid phase. The volume fraction of the liquid phase formed was sufficient to yield a low porosity. Grain growth was less than in the case of material sintered without Ni, probably just on account of lower sintering temperature. In the case of high- energy dry milled the reduction in particle size was observed.
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Microstructural and mechanical evaluation of laser-assisted cold sprayed bio-ceramic coatings : potential use for biomedical applications

  • Authors: Tlotleng, Monnamme , Akinlabi, Esther Titilayo , Shukla, Mukul , Pityana, Sisa
  • Date: 2014
  • Subjects: Titanium , Laser power , Cold spray , Laser-assisted cold spray , Hydroxyapatite
  • Type: Article
  • Identifier: uj:5135 , ISSN 1544-1016 , http://hdl.handle.net/10210/14101
  • Description: Bio-composite coatings of 20 wt.%, HAP and 80 wt.%, HAP were synthesized on Ti-6Al-4V substrates using LACS technique. The coatings were produced with a laser power of 2.5 kW, powder-laser spot trailing by 5 s. The coatings were analyzed for the microstructures, microhardness, composition, and bio-corrosion using SEM-EDS, XRD, hardness tester, and Metrohm PGSTAT101 machine. SEM images indicated least pores and crack-free coating with dark-spots of Ti-HAP for the 20 wt.%, HAP as opposed to the 80 wt.%, HAP coating which was solid, porous and finely cracked and had semi-melted Ti-HAP particles. The EDS mappings showed high content of HAP for the 80 wt.%, HAP coating. The diffraction patterns were similar, even though the Ti-HAP peak was broader in the 80 wt.%, HAP coating and the HAP intensities were lower for this coating except for the (004) peak. The hardness values taken at the interface inferred that the 80 wt.%, HAP coating was least bonded. It was possible to conclude that when this phase material increased the hardness dropped considerably. The bio-corrosion tests indicated that the presence of HAP in coating leads to a kinetically active coating as opposed to pure titanium coating.
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Biphenolate and cyclopentadienyl-derived complexes of zirconium and titanium as catalysts for the polymerisation of alpha olefins

  • Authors: Van Zyl, Aletta
  • Date: 2012-09-04
  • Subjects: Oligomers , Polymerization , Zirconium , Alkenes , Titanium
  • Type: Thesis
  • Identifier: uj:3459 , http://hdl.handle.net/10210/6852
  • Description: M.Sc. , An annual production of approximately 46 million metric tons of polyolefins worldwide, emphasizes the industrial importance of this product and the polymerisation process. Olefins are the basic building block of the petrochemical industry and are therefore readily available and cheap. Reactivity of olefins decreases from ethylene to propylene to 1-octene and makes the study of polymerisation catalysts more complex, seeing that the activity of a catalyst differs from monomer to monomer. In this study zirconocene complexes with bridged cyclopentadienyl ligands have been prepared and investigated as , possible catalysts for the polymerisation of higher aolefins. Fulvenes have been reductively coupled and used as ligands for zirconium complexes. Steric bulk of the substituents on the ligand have been increased and changes in the polymeric products have been studied. The tacticty, endgroups and chain lengths of the polyolefins have been investigated. There is currently a considerable interest in the development of 'non-metallocene' catalysts as alternatives for the polymerisation and oligomerisation of a-olefins. Chelating diamide complexes of Group 4 metals have been the focus of much attention and these compounds have shown moderate to high reactivity. However, only a few examples of the corresponding chelating alkoxides are known. In this study, alkoxide complexes of zirconium and titanium have been prepared with Schiff bases as ligands. These complexes have been evaluated as polymerisation catalysts and the products have been studied. The titanium complexes were more active than the zirconium analogues. The narrow molecular weight distribution of the polyolefins gave evidence that these catalysts are single-sited catalysts.
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