Showing items 1 - 13 of 13

Your selections:

Analysis of the selective laser sintering of steel for rapid prototyping parts manufacturing

  • Authors: Smith, Pieter Ernst Scholtz
  • Date: 2015-09-08
  • Subjects: Sintering , Steel, Stainless , Prototypes, Engineering
  • Type: Thesis
  • Identifier: uj:14053 , http://hdl.handle.net/10210/14469
  • Description: M.Ing. , The principle of the laser sintering process as applied to stainless steel powder for rapid prototyping is discussed. This work attempts to present and explain the process-modelling concept with respect to potential analytical and empirical relationships between the input and output parameters. It considers aspects related to process behavior, material characteristics, laser parameters and product accuracy. A comprehensive experimental set- up with empirical results is presented.
  • Full Text:

Development of binderless ultra-tough titanium carbonitride (TiCN) using spark plasma sintering technique

  • Authors: Akinribide, Ojo Jeremiah
  • Date: 2019
  • Subjects: Titanium , Sintering , Nanoparticles
  • Language: English
  • Type: Doctoral (Thesis)
  • Identifier: http://hdl.handle.net/10210/443738 , uj:38757
  • Description: Abstract: Binderless ultra–tough titanium carbonitride (TiCN) was successfully consolidated by spark plasma sintering. The impact of blending and milling parameters on the formation of titanium carbonitride from milled titanium nitride, graphite and multiwalled carbon nanotube (MWCNTs) admixture were investigated. The effect of wet milling and dry milling on the phases and morphology of the developed composites were also studied. The morphology, microstructure and the chemical composition of as – received powders, admilled powders and the sintered compact were characterized by using energy dispersive Xray spectroscopy (EDS), X-ray diffractometer, and scanning electron microscopy respectively. The varying compositions of the ad-milled powders were sintered at 100 oC/min (heating rate), 10 mins (holding time), 50 MPa sintering pressure and 2000 oC (sintering temperature). Vickers hardness test, fracture toughness and modulus of elasticity were carried out on the sintered sample to evaluate the mechanical properties. The sintered TiN-based composites were completely formed without cracks, however with very fewer pores, an indication of a good metallurgical bonding quality achieved at the composite grain boundary interface. The structure of the grains has completely transformed to bimodal grains within the composites at 1 wt.% graphite in TiN for 40 h of milling, and subsequent composites developed was based on the result obtained at 1 wt.% graphite in TiN for 24 and 40 h of milling at different compositions. Much increment was observed in microindentation hardness and fracture toughness values of the sintered compact as the percentage graphite increased. The results show that grain size of the sintered sample decreases as the percentage composition of graphite/MWCNTs particles and milling time increases. Based on the results of the analysis, it was concluded that the incorporation of graphite/MWCNTs enhances the microstructures which ultimately are crucial to the mechanical behaviour of the sintered compacts. , D.Phil. (Metallurgical Engineering)
  • Full Text:

Effect of build direction on the microhardness and dry sliding wear behaviour of laser additive manufactured Ti-6Al-4V

Effect of built orientation on direct metal laser sintering of Ti-6Al-4V

Effect of starting powder particle size and heating rate on spark plasma sintering of Fe- Ni alloys

  • Authors: Shongwe,M.B. , Ramakokovhu, M.M. , Diouf, S. , Durowoju, M.O. , Obadele, B.A. , Sule, R. , Olubambi, P.A , Sadiku, E.R.
  • Date: 2016
  • Subjects: Densification , Sintering , Microstructure
  • Language: English
  • Type: Article
  • Identifier: http://hdl.handle.net/10210/123446 , uj:20792 , Citation: Shongwe,M.B. et al. 2016. Effect of starting powder particle size and heating rate on spark plasma sintering of Fe- Ni alloys.
  • Description: Abstract: The effect of starting powder particle size and heating rate on spark plasma sintering of Fe-Ni alloys was investigated, with the particle powder size varying from 3 to 70 μm and heating rate from 50 to 150 °C/min. The effect of the starting powder particle size was more obvious when comparing 3-FeNi and 70-FeNi at all heating rates, with the former having better density and hardness than the latter. Sintered densities close to theoretical (≥ 99%) were achieved for a heating rate of 50°C/min for the different starting particle size powders, and decreased with increasing heating rate. The average grain size of alloys sintered at 150°C/min was ~34% smaller than those sintered at 50°C/min. The porosity content of the sintered samples increased with increasing heating for the same particle size. The shrinkage rate depends on both heating rate and particle size. At a particle size of 3 μm and a heating rate of 50oC/min, three peaks were observed indicative of the phenomena responsible for good densification. As the heating rate increases, only two peaks and one peak are observed at heating rates of 100 and 150oC/min, respectively. This suggests that, unlike high heating rates, the longer processing time at low heating rate allows the three phenomena to take place. The hardness measurement revealed a steady decrease with increasing heating rate. At a heating rate of 150°C/min the particles were well packed but no typical dimple structure of a ductile material was observed. However, for samples sintered at 50 and 100°C/min a typical dimple fracture morphology was observed.
  • Full Text:

Effect of thermal treatment on mechanically milled cobalt powder

Localisation of silica sand for additive manufacturing applications

  • Authors: Dady, Oyombo
  • Date: 2020
  • Subjects: Additive manufacturing , Three-dimensional printing , Sintering
  • Language: English
  • Type: Masters (Thesis)
  • Identifier: http://hdl.handle.net/10210/479547 , uj:43381
  • Description: Abstract: Three-dimensional printing (3DP) in the metal industry is used for the rapid production of sand parts, inter alia, moulds and cores. Due to its accessibility and affordability, the sand used most in the metal fabrication industry is silica. Voxeljet sand, an imported sand developed and provided by Voxeljet for use with the Voxeljet 3DP, is more expensive than local sand, making the cost of 3DP prohibitively high and preventing widespread adoption of 3DP for the manufacture of sand parts. If suitable, sourcing the sand locally could offer a cost saving that would assist the local foundry industry... , M.Tech. (Engineering Metallurgy)
  • Full Text:

Sinterability studies of high carbon steel powders containing nickel, molybdenum, cobalt and manganese

  • Authors: Ramabulana, Khodani
  • Date: 2020
  • Subjects: Powders , Powder metallurgy , Sintering
  • Language: English
  • Type: Masters (Thesis)
  • Identifier: http://hdl.handle.net/10210/479636 , uj:43391
  • Description: Abstract: The automobile industry is a major consumer of powder metallurgy (PM) components. Occasionally, as in the current case of this investigation, new alloy compositions are specified for production of PM components and research is required to optimize production. This work was aimed at better understanding the influence of alloying additions on the sintering behaviour of the Fe-based powder mix containing high carbon content (up to 0.9 wt.%), and the alloying elements cobalt, molybdenum and nickel. Both the blended elemental and pre-alloyed powder mixtures were investigated whilst attempting to optimize the sintering conditions to achieve a higher density. Dilatometer, DSC with TGA were used to investigate the influence of alloying elements on the sintering behaviour of the Fe powder. Metallographic examination using optical microscopy along with scanning electron microscopy (SEM) combined with energy dispersive X-ray spectroscopy (EDS) has been performed in an attempt to relate the results obtained from dilatometer to the microstructure of the alloys. Response surface methodology (RSM) with central composite design (CCD) was also applied to study the influence of sintering parameters (sintering temperature, time and hydrogen content) with the aim of maximising the sintered density of the materials... , M.Tech. (Engineering Metallurgy)
  • Full Text:

Sintering of nanostructured titanium carbonitride from carbonitrothermic reduced ilmenite

  • Authors: Mojisola, Tajudeen
  • Date: 2019
  • Subjects: Sintering , Nanostructured materials , Titanium , Nitrides , Ilmenite
  • Language: English
  • Type: Doctoral (Thesis)
  • Identifier: http://hdl.handle.net/10210/418221 , uj:35451
  • Description: Abstract: In recent years, there has been concerted effort towards the synthesis of cermet materials from low grade titanium ore. This is because the reserve of high grade titanium containing ore, i.e. natural rutile, is fast depleting and rutile becoming more expensive across the globe. Today, titanium containing hard ceramic powders, e.g. TiC, TiN and their solid solution TiCN powders have become important reinforcement materials due to their suitable properties. Titanium carbonitride, which is a boundary solid solution of titanium carbide and titanium nitride combines the excellent properties of both TiC and TiN in one structure of TiCN. In order to make this special material readily available, various methods have been adopted to synthesize titanium carbonitride powder. Although, the synthesis of titanium carbonitride by carbothermic reduction of titanium dioxide (rutile) with carbon under nitrogen atmosphere has been the most widely used for the commercial production of titanium carbonitride. However, this process requires the extraction and purification of titanium dioxide from its ore e.g. ilmenite, which itself is a costly process, or the use of natural rutile, which is fast depleting and becoming more expensive across the globe. Ilmenite (FeTiO3), which is a mineral source of titanium dioxide, is abundantly found in many parts of the world, most especially in South Africa. South Africa, is a leading producer of ilmenite in the world, accounting for about 37% of 6.2 million metric tons of the global production. Hence sourcing and processing of TiCN powder directly from South African ilmenite will be an added advantage. It is on this premises that the urgency for the processing of South African ilmenite to its final products, e.g. titanium containing hard ceramic products, such as TiC, TiN and/or TiCN powders or composite, and titanium metal, is being hung. Hence, this study develops a mechano-chemical processing route for the synthesis of titanium containing hard ceramic powders from ilmenite concentrate, which could be used for the production of cutting tools made of TiC and TiCN composite materials. The study also determines the possibility of sintering bulk TiCN based cermets with different metal matrices. For the synthesis of titanium carbide and titanium nitride/carbonitride powders, mixtures of ilmenite concentrate and graphite were milled in a planetary ball mill (PM 100) for different time intervals of 0, 30, 60 and 120 min, and carbo(nitro)thermally reduced under argon and nitrogen gas in a high temperature laboratory furnace (Thermal Tech., USA), respectively. These carbo(nitro)thermic reductions of mixtures of ilmenite concentrate and graphite result in the formation of Fe –TiC and Fe – TiCN powder composites in which globules of TiC and TiCN particles are embedded in the iron matrix,.. , Ph.D. (Engineering Metallurgy)
  • Full Text:

Spark plasma sintering of duplex stainless steel reinforced with titanium nitride nanoparticles

  • Authors: Oke, Samuel Ranti
  • Date: 2019
  • Subjects: Titanium-aluminum-vanadium alloys , Nanoparticles , Sintering
  • Language: English
  • Type: Doctoral (Thesis)
  • Identifier: http://hdl.handle.net/10210/393783 , uj:32594
  • Description: Abstract : In this study, duplex stainless steel (DSS) micro-powders and titanium nitride (TiN) nanopowders were blended in a tubular mixer. The motivation for choosing to incorporate TiN into duplex stainless steel is develop DSS with improved wear and mechanical properties. The Characterization of the mixed powders was performed using X-ray Diffraction, Transmission Electron Microscopy and Scanning Electron Microscopy. The mixed powders were consolidated using automated spark plasma sintering machine (model HHPD-25, FCT GmbH Germany). Characterization of sintered TiN nanoparticle reinforced DSS was performed using X-ray Diffraction (XRD) and Scanning Electron Microscopy equipped with Energy-dispersive X-ray spectroscopy (EDS), Electron backscattered diffractions (EBSD) and Transmission kikuchi diffraction (TKD). Densities and hardness of the developed composite were investigated. The mechanical properties and tribological properties of the DSS strengthened with varied amounts of TiN nanoparticles were evaluated using nanoindentation system and tribometers respectively. This study produced seven (7) papers, each of the paper respectively investigated (1) the past works that have been conducted on mechanical alloying and SPS of stainless steels and composites (2) the optimization of SPS process parameters in terms of in terms of sintering temperature, holding time and heating rate for the development of a nanostructured duplex stainless steel reinforced with titanium nitride (TiN), (3) the effect of sintering parameters (sintering temperature and holding time) on the microstructure, corrosion and wear behaviour of the nano-strutured stainless steel composite (4) the effects of TiN nanoparticles addition on displacement and shrinkage rate, microstructure, density, hardness and fracture surface of the duplex stainless steels composite (5) phase transformations and grain boundary interactions associated with the dispersion of TiN nanoparticles into DSS (6) the influence of TiN nanoparticle addition on mechanical properties such as elastic, plastic, strain-to-break (H/Er) and plastic deformation (H3 /Er2 ) parameters of the stainless steel composites (7) the effects of TiN reinforcement on wear properties of coefficient of friction, wear loss, wear and specific wear rates under dry sliding conditions and varying loads and worn surface. The following results were obtained. During optimization of SPS parameters, the XRD result showed the evolution of iron nitride phase while the EDS analysis revealed the presence of nano ranged nitride particles segregated at the grain boundaries of the duplex matrix. A decrease in hardness and densification was observed when sintering temperature and heating rate were 1200... , Ph.D. (Metallurgy)
  • Full Text:

Spark plasma sintering of multiwall carbon nanotubes reinforced titanium-aluminium-vanadium based nanocomposites

  • Authors: Okoro, Avwerosuoghene Moses
  • Date: 2019
  • Subjects: Titanium-aluminum-vanadium alloys , Nanoparticles , Carbon nanotubes , Sintering
  • Language: English
  • Type: Doctoral (Thesis)
  • Identifier: http://hdl.handle.net/10210/413026 , uj:34780
  • Description: Abstract: Innovations in materials development has engendered the improvement of the properties of titanium alloys for diverse engineering applications. In this study, titanium alloy (Ti6Al4V) and multiwall carbon nanotubes (MWCNT) were mixed using shift-speed ball milling (SSBM) technique to achieve the uniform dispersion of MWCNT in the Ti6Al4V matrix. The starting and admixed powders were characterized using scanning electron microscopy equipped Energy dispersive X-Ray spectroscopy (SEM-EDS), X-ray diffraction (XRD), Raman spectroscopy and Transmission electron microscopy (TEM). Detailed TEM characterization was carried out to reveal the structural evolutions of the MWCNT during the dispersion process using selected area diffraction and fast Fourier transform pattern. The admixed powders were then consolidated using the spark plasma sintering machine (model HHPD-25, FCT GmbH Germany). Furthermore, various characterization technique such as XRD, SEM-EDS, optical microscopy (OM) was employed to understand the phase evolutions, morphology, microstructural changes and fractography of the fabricated nanocomposites. The mechanical properties of the fabricated materials were further investigated using the Vickers microhardness tester (FALCON 500 series) and the nanoindentation technique (ultra nanoindenter) UNHT. The study resulted in five (5) research articles, each article investigated the following respectively; (1) the previous works that have been conducted in SPS of titanium-based nanocomposites reinforced with MWCNT, (2) the dispersibility, structural evolutions and interfacial bonding of MWCNT in Ti6Al4V powders using the SSBM technique, (3) the evaluation of the influence of varying sintering temperature on the sintering and densification behaviours and microhardness of the fabricated alloy and nanocomposites, (4) the effects of MWCNT addition on the change in microstructures and mechanical properties of the fabricated nanocomposites, and (5) the influence of MWCNT on the nanomechanical properties of the fabricated nanocomposites. During the dispersion process, the Raman and XRD pattern of the admixed powders showed that mechanical stresses were induced on the walls of the nanotubes which does not result in defects on the MWCNT. Optimal dispersion of MWCNT was achieved on the nanocomposite grades comprising of 0.5 and 1.0 wt.% nanotubes. Additionally, the dispersibility decreased with the increase in concentration of the MWCNT in the Ti6Al4V matrix. Meanwhile, the nanocomposite grades with higher fraction of MWCNT experienced higher deformation of the nanotubes during the dispersion process. The optimal dispersion of MWCNT in Ti6Al4V matrix with minimal... , D.Ing. (Metallurgy)
  • Full Text:

Spark plasma sintering of nanoceramics dispersion strengthened titanium aluminium vanadium alloy

The effects of particle size distribution and sintering conditions on bending strength of sintered Ni-30þ alloys

  • 1
  • Disclaimer
  • Privacy
  • Copyright
  • Contact