Olawale S. Fatoba

Bio: Olawale S. Fatoba is an academic researcher from University of Johannesburg. The author has contributed to research in topics: Microstructure & Titanium alloy. The author has an hindex of 11, co-authored 67 publications receiving 356 citations. Previous affiliations of Olawale S. Fatoba include Vaughn College of Aeronautics and Technology.

Experimental Study of Hardness Property and Microstructure of TiZnNi Laser Deposited on Titanium Alloy

Abstract: The study is aimed at using laser cladding technique to deposit a thick coating of composite TiZnNi on titanium alloy Ti-6Al-4V substrate. The composite powder was mixed with Zinc (Zn), Nickel (Ni) and Titanium (Ti), in which the tubular mixer was used to prepare the mixture. The laser metal deposition technique that was employed in the process was used to control the heat input, which governed the resulting microstructure of the ZnNiTi coating that was produced. This was based on the analysis that was conducted. The results of the hardness obtained from the Vickers micro-indenter revealed that there was an improvement as the hardness measured for the cladded ZnNiTi layer was approximately 1396.90 HV 0. 1 and the hardness of the Ti-6Al-4V substrate was measured to be 320.8 HV 0. 1• This improvement was attributed to the NiTi, Ni3 Ti, hard Ni 4 Ti 3 and intermetallic phases that formed, this was confirmed by the analysis done on the cladded layer by employing EDS and XRD. The grain form and structure as well as the mechanical properties of the cladded layer were significantly affected by the heat input from the laser beam. At higher scanning speed of 1.0 m/min, the coating and substrate being limitedly mixed, resulted in the cladded layer having a significantly higher hardness than the substrate, but some hardness values gradually reduced after the cladded layer towards the interface and heat affected zone. The behaviour of the coating hardness property was improved by 4.4 compared to the hardness of the uncoated titanium substrate. The characteristics of the hardness of the deposited coating was heavily affected by processing parameters, which the grain morphologies and concentration of phase composition formed were predominant in the result of the hardness properties. Industries of biomedical and mechanical components may implement the application of composite ZnNiTi coating since there was an improvement on the hardness characteristics, which is usually of major concern in industrial applications.

Influence of Rapid Solidification and Optimized Process Parameters on the Microstructural Evolution of Additive Manufactured Titanium Alloy Grade 5 Composite

Abstract: The study experimentally investigates the effects that Ytterbium Laser System process parameters, such as laser power, powder feed rate and traverse speed, has on the resultant microstructure of Ti- 6Al-4V grade 5 alloy. The deposition process was conducted employing a 3kW (CW) Ytterbium Laser System (YLS-2000-TR) machine, coaxial to the reinforcement powder. The laser scanning speed and power were varied between the intervals of 1-1.2 m/min and 900-1000 W. All other parameters kept constant where the rate of gas flow, the spot diameter, and the rate of powder flow. The microstructure was characterized by grain size and morphology by using Optical Microscopy (OM) and Scanning Electron Microscopy (SEM). The microstructural and mechanical properties were ascertained and the relationships with the process parameters were achieved. As a result of rapid cooling, the morphological features of α and α’ are distinctive and appear acicular. The structures appear coarsened. The metallurgy of the samples identifies with a morphology of multi-scale; with the coarsened alpha structures being reduced, plate-like, discrete and finer. The alpha grains closer to the fusion zone grew epitaxially, and the ones above these are acicular and lamellar. The results also indicated that slow traverse speeds increase the scale of columnar grains, while other process parameters were kept constant. Columnar microstructures became prevalent due to the dynamic temperature gradients/spikes, and sustainable cooling rates, pertaining to fabricating direct laser deposited Ti-6Al-4V grade 5 alloy. It was ascertained that by increasing the traverse speeds, the cooling rates increased, which resulted in a decrease in the width of the columnar grains.

Corrosion Inhibition of Martensitic Stainless Steel in Chloride Medium by Calcium Gluconate-Solanum Tuberosum Extract as Surfactant

Abstract: Corrosion inhibition of martensitic stainless steel (MSS) in magnesium chloride was investigated in the absence and presence of calcium gluconate as corrosion inhibitor at ambient temperature. The effects of inhibitor concentration were studied using weight loss and polarization method. The results obtained showed that calcium gluconate acts as an inhibitor for martensitic stainless steel in MgCl and decreases the corrosion rate. The inhibition performance was found to increase with the increase in inhibitor concentration. The maximum inhibition efficiency obtained was 99 % at 2g/v inhibitor concentration, the adsorption of calcium gluconate on the surface of Martensitic stainless steel was found to obey Langmuir adsorption isotherm. However, the addition of solanum tuberosum extract in the inhibitor decreases the corrosion rate of martesitic steel significantly in chloride solution.

Recent research and development status of laser cladding: A review

Abstract: In industries such as aerospace, petrochemistry and automobile, many parts of different machines are under environment which shows high temperature and high pressure, and have their proneness to wear and corrosion. Therefore, the wear resistibility and stability under high temperature need to be further improved. Nowadays, Laser cladding (LC) is widely used in machine parts repairing and functional coating due to its advantages such as lower dilution rate, small heat-affected zone and good metallurgical bonding between coating and substrate. In this paper, LC is introduced in detail from aspects of process simulation, monitoring and parameter optimization. At the same time, the paper gives a comprehensive review over LC material system as high entropy alloys (HEAs), amorphous alloy and single crystal alloy have been gradually showing their advantages over traditional metal materials in LC. In addition, the applications of LC in functional coatings and in maintenance of machine parts are also outlined. Also, the existing problems and the development trend of LC is discussed then.

Corrosion of metallic materials fabricated by selective laser melting

Abstract: Additive manufacturing is an emerging technology that challenges traditional manufacturing methods. However, the corrosion behaviour of additively manufactured parts must be considered if additive techniques are to find widespread application. In this paper, we review relationships between the unique microstructures and the corresponding corrosion behaviour of several metallic alloys fabricated by selective laser melting, one of the most popular powder-bed additive technologies for metals and alloys. Common issues related to corrosion in selective laser melted parts, such as pores, molten pool boundaries, surface roughness and anisotropy, are discussed. Widely printed alloys, including Ti-based, Al-based and Fe-based alloys, are selected to illustrate these relationships, and the corrosion properties of alloys produced by selective laser melting are summarised and compared to their conventionally processed counterparts.

Pulsed Nd:YAG laser cladding of stellite 6 on stainless steel

Abstract: A systematic research into the cladding of stellite 6 on stainless steel by pulsed Nd:YAG laser has been carried out. The effects of pulse energy, pulse frequency, powder mass flow rate and spot overlap on the clad layer height, dilution and heat-affected zone (HAZ) have been examined. It was found that both the clad height and penetration into the substrate increase with the pulse energy, spot overlap and pulse frequency, but the effects of these parameters on dilution are complex. The dilution reaches the lowest value (4%) at the incident energy of 18 and 25 J/ pulse, spot overlap of 89% and pulse frequency of 40 Hz. The powder mass flow rate of 22 g/min (for energy of 25 J/pulse and spot overlap of 83%) produces thick clad layer with low dilution but results in the formation of defects. The hardness of the clad layer decreases linearly with increasing dilution. No cracks have been found in single-track clad layers at a spot overlap of 89%, however, cracks occurred at lower spot overlap. These cracks were eliminated by the multi-track cladding when the track increment is less than 1/3 of the width of track, which is believed to be due to the remelting or heat treatment of the previous clad track by the subsequent track. The track bands in multi-track clad show coarser structure, higher element segregation and lower hardness.

Evaluation of microstructure, microhardness, and electrochemical properties of laser-deposited Ti-Co coatings on Ti-6Al-4V Alloy

Abstract: The marine, aerospace, and power machinery industries show progression in the application of titanium alloy components due to their good properties. However, the alloy exhibits poor thermal stability, low hardness, and poor tribological properties; as a result, the use of Ti6Al4V in various industries is restricted. Consequently, a search for surface improvement of Ti6Al4V alloy arose with the intention of enhancing its endurance. The use of laser metal deposition method by integrating chemical barrier coatings is considered as advantageous; therefore, an investigation aimed at surface improvement of Ti6Al4V by incorporation of Ti-Co coatings developed. To fabricate the coatings, a 3-kW continuous wave ytterbium laser system (YLS) was used, and to control the movement of the cladding process, a KUKA robot was attached to the system. The microstructure, corrosion, and mechanical properties of the titanium alloy-cladded surfaces were studied at different laser process parameters. To analyze the microstructure of the cross section, optical and scanning electron microscopy were employed. A laser power of 750 W and scanning rate of 1.2 m/min were found to be the optimum process conditions for a 60Ti-40Co alloy. When comparing the mechanical properties of the alloy and bare substrate, the alloy exhibited a significant increase in terms of the hardness. It was found to have 719 HV as compared to 301 HV which is that of the substrate, this indicates to an increase of 58.14% in the hardness. Lower laser scanning rates result in a larger fraction of hard-intermetallic phases which in turn lead to coatings with enhanced hardness levels. Furthermore, the yield strength and tensile strength of the coatings increased to maxima of 2.30 and1.66 GPa, respectively in comparison to the substrate, due to the addition of Co. Additionally, the corrosion rates of all the coated specimens were reduced as a result of the oxide films formed on the laser-coated Ti6Al4V alloy samples.