Characterising laser metal deposited titanium and molybdenum on titanium alloy for surface engineering applications
- Authors: Ntumba, Eric Muipatay
- Date: 2016
- Subjects: Laser-induced breakdown spectroscopy , Pulsed laser deposition , Lasers - Industrial applications , Titanium powder , Metal coating , Molybdenum
- Language: English
- Type: Masters (Thesis)
- Identifier: http://hdl.handle.net/10210/212802 , uj:21029
- Description: Abstract: In this work, sample study was done on the characterisation of Ti-10%Mo powder metal produced via LMD. Different process parameters were employed for the LMD process. The laser power was varied between 1kW and 2.2kW while keeping all other parameters constant. The scanning speed of 0.5m/sec, powder flow rate of pure titanium 1.8g/min and the powder flow rate of molybdenum 2g/min. were used for the coatings. The process parameters were carefully selected to represent low, medium and high settings. The characterisations carried out include optical microscopy and Scanning Electron Microscopy combined with Energy Dispersive Spectroscopy (SEM/EDS) techniques to investigate the particle distribution, microstructural evolution and chemical analysis of the welded samples. Vickers microhardness was used to determine the hardness distribution of the coating Ti6Al4V/Ti-Mo, the dry sliding wear tests were carried out on the deposited Ti6Al4V/Ti-Mo samples to determine the sliding wear of samples and corrosion tests was used to obtain information on the corrosion behavior of Ti6Al4V/Ti-Mo in 3.5% NaCl solution. The characterised laser metal deposited Ti6Al4V and Ti-Mo, revealed that the varied laser power played a main part in the microstructural evolution. It was found that the formation of the Widmanstӓtten structures improved the hardness of Ti6Al4V/Ti-Mo. The highest hardness value was found at the top zone of the clad owing to the presence of the reinforcement particles of Ti-Mo, the highest hardness value for all the samples was found at an average of 496HV. The sample produced at a laser power of 2kW and scanning speed of 0.5m/sec was found to show the lowest percentage of wear volume and the sample produced at laser power of 1.4kW and scanning speed of 0.5m/sec had the lowest percentage of the coefficient of friction; and this outcome can be attributed to the martensitic structure formed during cooling. The results obtained showed that the poor wear behaviour of the titanium alloy has been improved with the addition of Ti-Mo into their lattices. The experimental results indicated that the corrosion rate of the developed composites decreased significantly with the addition of the Ti-Mo powder. The results obtained from the polarization behavior show a decrease in the polarization resistance. While the open-circuit potential (OCP) for the alloy was found to reduce with time due to oxide film thickening on the metal surface... , M.Ing. (Mechanical Engineering Science)
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Laser power interaction effect on the evolving properties of laser metal-deposited titanium
- Authors: Nyoni, Ezekiel
- Date: 2015
- Subjects: Titanium powder , Pulsed laser deposition , Metal coating , Biomedical materials
- Language: English
- Type: Masters (Thesis)
- Identifier: http://hdl.handle.net/10210/58432 , uj:16450
- Description: Abstract: Titanium and its alloys are regarded as super alloys because of their ability to maintain high strength and light weight properties at elevated temperatures. Titanium has posed problems during its machining; as it always reacts with the machining tool at high temperatures, making it one of the most expensive metals to machine. It has been the interest of researchers to be able to use additive manufacturing methods in the fabrication of titanium; and the rise in the use of the Laser Metal Deposition process in the manufacturing of titanium has led to research studies in additive manufacturing. However, complex interrelationships exists between the processing parameters which lay a demand to optimise the parameters. There has also been a rise in the demand for the bone implants recently in the biomedical industry. The main implants on demand are the dental, knee and hip implants. However, the biocompatibility of the existing materials has been an issue for some time; as most of these materials become reactive in the body for long-term implantation. This has led to the development of titanium as a material for bioimplants. This research study presents a platform for analysing the laser power interaction effects on the evolving properties of commercially pure titanium during laser metal deposition tailored for biomedical applications. A set of preliminary studies was first conducted to establish the processing parameter window. A total of seven samples were fabricated by depositing titanium powder onto a Ti-6Al-4V base metal by varying the laser power from 400 to 1600 watts, whilst keeping all the other parameters constant. This was done to check how the laser power relates to the material properties of titanium; as the laser power is recognised as one of the most influential parameters on the evolving properties of laser deposited materials. The microhardness, microstructure, wear resistance and bio-compatibility tests were conducted for the material characterisation of this study. The optimized processing parameters obtained for this research study were: the spot size of 4 mm, powder flow rate of 2 rpm, gas flow rate of 2 l/min, and the scanning speed set at 0.002m/s. The microstructural evaluation revealed that the rate of dilution increased with an increase in the laser power. The increase in the dilution ratio tended to have negative effects on the wear resistance capabilities of the deposited materials. As the dilution increased, the wear resistance of the deposits decreased. This is attributed to the fact that the bond strength of the deposits decreases with an increase in the laser power. Also, the microstructural evaluation showed that finer martensitic... , M.Ing. (Mechanical Engineering)
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