Showing papers by "Olawale S. Fatoba published in 2018"

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.

Effects of rapid solidification on the microstructure and surface analyses of laser-deposited Al-Sn coatings on AISI 1015 steel

Abstract: Corrosion and wear phenomenon has been responsible for the gradual deterioration of components in industrial plants. This deterioration of components results in loss of plant efficiency, total shutdown and aggressive damage in a number of industries. Hence, surface modification and coating technique with enhanced surface properties is desirable. The study was designed to investigate the enhancement in the corrosion, hardness and wear properties of Al-Sn binary coatings on AISI 1015 steel by laser alloying technique using ytterbium laser system (YLS). A laser power of 1000 W, scanning speeds of 0.6 and 0.8 m/min, and alloy compositions of Al-75Sn, Al-50Sn and Al-25Sn were used in this study. Decrease in Sn content from 75 to 25% at different laser processing conditions resulted in improved properties. The enhanced properties were obtained at 75Al-25Sn alloy at laser power of 1000 W and speeds of 0.6 and 0.8 m/min. At optimum composition and speed of 0.8 m/min, there was enhancement of 53.63% in microhardness. At scanning speed of 0.6 m/min, 75Al-25Sn alloy exhibited the highest polarization resistance, R p, (1.06 × 108 Ω cm2); lowest corrosion current density, I corr, (3.12 × 10−7 A/cm2); and lowest corrosion rate, C r, (0.00363 mm/year) in 3.65 wt% NaCl solution. In addendum, significant reduction in wear volume loss of 75Al-25Sn alloy at 0.8 m/min was attributed to excellent wear resistance performance due to metastable intermetallic phases. This research has established the enhanced surface properties of laser alloyed Al-Sn binary coatings on AISI steel for engineering applications.

Experimental investigation of laser metal deposited icosahedral Al-Cu-Fe coatings on grade five titanium alloy

Abstract: Laser Additive Manufacturing is relatively new in the manufacturing industry. This paper focuses on the effect of hybrid coatings of Al-Cu-Fe on a grade five titanium alloy (Ti6Al4V) using laser metal deposition (LMD) process at different laser power and scanning speeds. Icosahedral Al-Cu-Fe as quasicrystals are a relatively new class of materials which exhibit unusual atomic structure and useful physical and chemical properties. Ti6Al4V/Al-Cu-Fe composite were analysed using Optical microscopy, Scanning electron microscopy (SEM) with energy dispersive microscopy (EDS), indentation testing, X-Ray Diffraction (XRD), corrosion and wear testing. deposit width and height, heat affected zone (HAZ) height), dilution rate, aspect ratio and powder efficiency of each sample remarkably increased with increasing laser power due to the laser-material interaction. It was observed that there are higher number of aluminium and titanium presented in the formation of the composite. The indentation testing reveals that for both scanning speed of 0.8m/min and 1m/min, the mean hardness value decreases with increasing laser power. It was found that due to dilution effect, a part of Ti entered into molten pool from the substrate. The results indicate that Ti, Al 3 Ti, Ti 3 Al, CuTi 2 can be produced through the in situ metallurgical reactions during the LMD process.

Numerical investigation of laser deposited Al-based coatings on Ti-6Al-4V alloy

Abstract: Titanium Alloy (Ti6Al4V) opened a wide range of useful applications in aerospace industries; these industries make use of different additive manufacturing (AM) techniques to obtain parts of different properties for different uses by this titanium alloy. Ttitanium alloy mainly stands out due to the properties such as high specific strength to weight ratio, and excellent corrosion resistance. Despite these benefits, the formation of defects such as pores and cracks play a vital role in the quality of the deposited coatings. The presence of these unwanted artefacts on laser deposited coatings depends on the melting, cooling and solidification of the melt pool. In this research, a simulation of the heat transfers and fluid dynamics of the melt pool is developed to predict the process parameters and reinforcement proportions on the clad geometry quality. The results were compared to the experimental results for confirmation and validation. Numerical modelling using COMSOL multiphysics 5.2 revealed the thermal behaviour of the coated samples.

Influence of scanning speed on the microstructure of deposited Al-Cu-Fe coatings on a titanium alloy substrate by laser metal deposition process

Abstract: Laser Additive Manufacturing is relatively new in the manufacturing industry. This paper focuses on the influence of scanning speed on Al-Cu-Fe coating powders on a titanium alloy using laser metal deposition (LMD) process. Al-Cu-Fe as quasicrystals are a relatively new class of materials which exhibit unusual atomic structure and useful physical and chemical properties. The intermetallic section where the hybrid coating bonded into grade five titanium alloy substrate were observed. It was found that the geometrical properties of the deposits such as deposit width, deposit height and the Heat Affected Zone (HAZ) of each sample decreases with increasing scanning speed due to the laser-material interaction. It was observed that an increase in scanning speed results in an increase in both dilution and aspect ratio. However, this is not true for the graph of powder efficiency as a function of scanning speed, increasing scanning speed decreases the powder efficiency. The smoother surface observed at low scanning speed that is as a result of proper melting of Ti powder due to the large laser material interaction time. As the scanning speed increases, the laser material interaction time reduces causing more and more unmelted Ti powder to be seen. The mean hardness value decreases with increasing scanning speed. XRD analysis showed that increasing scanning speed will significantly increase the diffraction peak of Ti and Ti 3 Al.

Effects of Fe addition on the microstructure and corrosion properties of quasicrystalline Al-Cu-Fe coatings

Abstract: The performance of material surface under wear and corrosion environments cannot be fulfilled by the conventional surface modifications and coatings. Therefore, different industrial sectors need an alternative technique for enhanced surface properties. Titanium and its alloys possess poor tribological properties which limit their use in certain industries. This paper focuses on the effect of hybrid coatings Al-Cu-Fe on a grade five titanium alloy using laser metal deposition (LMD) process. Icosahedral Al-Cu-Fe as quasicrystals are a relatively new class of materials which exhibit unusual atomic structure and useful physical and chemical properties. A 3kW continuous wave ytterbium laser system (YLS) attached to a KUKA robot which controls the movement of the cladding process was utilized for the fabrication of the coatings. The titanium cladded surfaces were investigated for its microstructure and corrosion properties at different laser processing conditions. The samples were cut to corrosion coupons and immersed into 3.5% NaCl solution at 28oC using Linear Polarization (LP) techniques. The cross-sectional view of the samples was analysed. It was found that the geometrical properties of the deposits such as width, height and the Heat Affected Zone (HAZ) of each sample remarkably increased with increasing laser power due to the laser-material interaction. It was observed that there are higher number of aluminium and titanium presented in the formation of the composite. The cladded layer showed a uniform crack free surface due to optimized laser process parameters which led to the refinement of the coatings. Sample Al-Cu-5Fe showed increase of 1538.3-times the polarization resistance of the substrate (Ti-6Al-4V alloy). Large amount of aluminium and less amount of iron favour the chemical performance of composite thereby increasing the polarization resistance.

The Effects of Sn Addition on the Microstructure and Surface Properties of Laser Deposited Al-Si-Sn Coatings on ASTM A29 Steel

Abstract: Aluminium and its alloys have been successful metal materials used for many applications like commodity roles, automotive and vital structural components in aircrafts. A substantial portion of Al-Fe-Si alloy is also used for manufacturing the packaging foils and sheets for common heat exchanger applications. The present research was aimed at studying the morphology and surface analyses of laser deposited Al-Sn-Si coatings on ASTM A29 steel. These Fe-intermetallic compounds influence the material properties during rapid cooling by laser alloying technique and play a crucial role for the material quality. Thus, it is of considerable technological interest to control the morphology and distribution of these phases in order to eliminate the negative effects on microstructure. A 3 kW continuous wave ytterbium laser system (YLS) attached to a KUKA robot which controls the movement of the alloying process was utilized for the fabrication of the coatings at optimum laser parameters. The fabricated coatings were investigated for its hardness and wear resistance performance. The field emission scanning electron microscope equipped with energy dispersive spectroscopy (SEM/EDS) was used to study the morphology of the fabricated coatings and X-ray diffractometer (XRD) for the identification of the phases present in the coatings. The coatings were free of cracks and pores with homogeneous and refined microstructures. The enhanced hardness and wear resistance performance were attributed to metastable intermetallic compounds formed.

Investigating Resulting Residual Stresses during Mechanical Forming Process

Abstract: Most manufacturing processes such as machining, welding, heat treatment, laser forming, laser cladding and, laser metal deposition, etc. are subjected to a form of heat or energy to change the geometrical shape thus changing the inherent engineering and structural properties of the material. These changes often cause the development of locked up stresses referred to as residual stresses as a result of these activities. This study reports on the residual stresses developed due to the mechanical forming process to maintain a suitable structural integrity for the formed components. The result of the analysis through the X-ray diffraction confirmed that residual stresses were induced in the manufactured parts and further revealed that residual stresses were compressive in nature as found in the parent material but with values less than the parent material.

Evaluation of Friction Stir Welds by X-ray Digital Radiographic Non-Destructive Approach

Abstract: This paper focuses on the microstructure evolution and the relationship to the microhardness profiling of the friction stir welded butt joint on similar AA6061-T6 Aluminium alloys The only parameters used and varied for this study were rotational speed and feed rate The geometry of the tool was kept constant and the material used was tool steel, W302 Friction stir welds were evaluated by both visual inspection and the X-ray digital radiography method Evaluation allowed for assessment of the weld integrity by examining for the presence and absence of weld defects The results indicated that the welds do not have any root defects The X-rays showed complete penetration as evidenced by the evaluation of microstructural joint interface

Effect of Bottoming on Material Property during Sheet Forming Process through Finite Element Method

Abstract: Metal forming is one of the conventional manufacturing processes of immense relevance till date even though modern manufacturing processes have evolved over the years. It is a known fact that material tends to return or spring back to its original form during forming or bending. The phenomena have been well managed through its application in various manufacturing processes by compensating for the spring back through overbending and bottoming. Overbending is bending the material beyond the desired shape to allow the material to spring back to the expected shape. Bottoming, on the other hand, is a process of undergoing plastic deformation at the point of bending. This study reports on the finite element analysis of the effect of bottoming on the material property during the sheet forming process with the aim of optimising the process. The result of the analysis revealed that the generated plastic strains are in the order between 1.750e00-1 at the peak of the bending and 3.604e00-2, which was at the early stage of the bending.