O. S. Adesina

Bio: O. S. Adesina is an academic researcher from Tshwane University of Technology. The author has contributed to research in topics: Titanium alloy & Indentation hardness. The author has an hindex of 5, co-authored 14 publications receiving 100 citations. Previous affiliations of O. S. Adesina include Landmark University.

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.

Microstructural and tribological behavior of in situ synthesized Ti/Co coatings on Ti-6Al-4V alloy using laser surface cladding technique

Abstract: The enhancement of the tribological properties of titanium (Ti-6Al-4V) has been the subject of wide range research over the years. The constraints associated with Ti-6Al-4V in severe tribological conditions due of its low hardness and poor wear properties can be enhanced by appropriate enhancement of the microstructure via surface modification technique without altering the bulk material. In this work, Cp-Ti and Co powders were deposited at different admixed percentages by laser cladding on Ti-6Al-4V substrates with respect to laser processing parameters. The laser optimized parameters used are laser power 900 W, powder feed rate 1.0 g/min, beam spot size 3 mm, and gas flow rate 1.2 L/min while scan speed were varied at 0.6and 1.2m/min. The microstructural evolution as well as wear morphology of the coatings were studied using scanning electron microscope equipped with energy dispersed spectrometry (SEM/EDS) while the phase identification were observed using X-ray diffractometer (XRD). Microhardness values of the coatings were obtained while wear test was conducted using a reciprocating set up. The coatings exhibited a good metallurgical bonding between the coatings and the substrate. Results revealed that laser clad sample with high scan speed was more effective in improving the hardness and wear resistance of Ti-Co/Ti6Al4Vcompared to low scan speed. The coatings possess an average hardness value of 730 HV0.1, a value that is about two times greater than that of the substrate. The enhanced wear resistance with high laser scan speed has been attributed to the presence of flower-like structures and formation of fractions of CoTi2, CoTi, AlTi2, AlCo5, AlCo2Ti, and Al2Ti inter-metallic phases dispersed within the coating matrix. In addition, analysis of worn surfaces and wear mechanism indicated improved resistance to tribological actions.

Laser Surface Modification — A Focus on the Wear Degradation of Titanium Alloy

Abstract: Over the years, engineering materials are being developed due to the need for better service performance. Wear, a common phenomenon in applications requiring surface interaction, leads to catastrophic failure of materials in the industry. Hence, prevent‐ ing this form of degradation requires the selection of an appropriate surface modifica‐ tion technique. Laser surface modification techniques have been established by researchers to improve mechanical and tribological properties of materials. In this chapter, adequate knowledge about laser surface cladding and its processing parame‐ ters coupled with the oxidation, wear and corrosion performances of laser-modified ti‐ tanium has been reviewed.

Computational analysis of heat transfer within a Ti-6Al-4V alloy substrate during laser cladding process

Abstract: Heat transfer in materials during laser material processing serves as a key indicator to existing phases in the material, which governs the mechanical and chemical properties of the material during service. Without the knowledge of the property and behaviour of a material under service, loss of lives and values may be inevitable. This study presents the numerical modeling of the effect of laser parameters on the nature of phases present on the surface of Ti-6Al-4V alloy via heat transfer phenomenon. COMSOL 5.3a software was used to create a model of Ti-6Al-4V substrate, subjected to laser radiation during laser surface cladding. Boundary conditions were applied to the surfaces of the block samples while temperature distribution was measured with set boundary probes. Isothermal plots revealed that the material heating from the free surface was not sufficient enough to develop a large zone of phase change along the depth of the substrate. This was related to the high cooling rate of laser cladding.

Computational Dynamics of Anti-Corrosion Performance of Laser Alloyed Metallic Materials

Abstract: Laser surface alloying (LSA) is a material processing technique that utilizes the high pow‐ er density available from defocused laser beam to melt both reinforcement powders and a part of the underlying substrate. Because melting occurs solitary at the surface, large temperature gradients exist across the boundary between the underlying solid substrate and the melted surface region, which results in rapid self-quenching and resolidifications. Reinforcement powders are deposited in the molten pool of the substrate to produce cor‐ rosion-resistant coatings. These processes influence the structure and properties of the al‐ loyed region. A 3D mathematical model is developed to obtain insights on the behavior of laser melted pools subjected to various process parameters. It is expected that the melt pool flow, thermal and solidification characteristics will have a profound effect on the mi‐ crostructure of the solidified region.

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.

Laser Material Processing

Abstract: Processing of Laser Materials have a variety of industrial operations in which work piece is modified by laser operation, for example, by melting it or removing material from it. In recent years, laser based technologies became important or even dominant in industrial applications such as welding, cutting or drilling. Manufacturing technology will rely on lasers and laser-based material processing for the development of new material processing methodologies and multi-functional device integration solutions. Further possibilities of processing, innovation, and advancement of laser material treatments are still in progress and very challenging. The very broad field of laser materials processing is still very fast developing. To extend this developing field of material processing, a well-organised database can give a noble guideline and great reference. That can be used as fundamentals for any research or it may help industry to choose right type of laser for specific techniques.

Laser cladding in-situ carbide particle reinforced Fe-based composite coatings with rare earth oxide addition

Abstract: Particulate reinforced metal matrix composite(PR-MMC) has excellent properties such as good wear resistance,corrosion resistance and high temperature properties.Laser cladding is usually used to form PR-MMC on metal surface with various volume fractions of ceramic particles.Recent literatures showed that laser melting of powder mixture containing carbon and carbide-forming elements,was favorable for the formation of in-situ synthesized carbide particles.In this paper,rare earth oxide(RE2O3) was added into t...

Ni-P-TiO2 nanocomposite coatings with uniformly dispersed Ni3Ti intermetallics: Effects of current density and post heat treatment

Abstract: In the present work, the influences of current density and post heat treatment on the morphology, phase structure, microhardness, and corrosion performance of the Ni-P-TiO2 nanocomposite coatings were investigated. Scanning electron microscope (SEM) and X-ray diffraction (XRD) were employed to study the morphological and microstructural features of the coatings, respectively. In addition, corrosion performance of the coatings was evaluated via electrochemical impedance spectroscopy (EIS) and Tafel polarization. Results demonstrated that the Ni3Ti intermetallics forms all over the microstructure of the coatings. The volume fraction and distribution uniformity of such intermetallics is examined as a function of applied current density. In general, the as-plated coatings at current density of 15 A dm−2 exhibit the superior microhardness as well as corrosion resistance originated from their higher Ni3Ti amount. However, the morphology of the particles accompanied by chemical composition of constituent phases did not altered with change in current density. The electrodeposited coatings were heat treated at 400 °C in an argon atmosphere of electrical furnace. XRD patterns of the heat treated coatings show Ni3P and Ni phases. In addition, microhardness of the coatings noticeably increased with application of heat treatment mainly due to the precipitation of hard Ni3P intermetallics.