O. S. Fatoba

Electrochemical Studies on the Corrosion Behaviour of Laser Alloyed Zn-Sn Coatings on UNS G10150 Steel in 1M HCl Solution

Surface deterioration by corrosion is one of the complications associated with ageing facilities and components especially under some service environments. This study was designed to investigate the enhancement in the corrosion and hardness properties of UNS G10150 steel laser alloyed with three different premixed compositions of Zn-Sn binary powders using a 4.4 KW continuous wave (CW) Rofin Sinar Nd:YAG laser processing system. The steel alloyed samples were cut to corrosion coupons, immersed in hydrochloric acid (1M HCl) solution at 30 °C using an electrochemical technique and investigated for their corrosion behaviour. The morphologies and microstructures of the developed coatings and uncoated samples were characterized by an Optic Nikon Optical microscope (OPM) and a scanning electron microscope (SEM/EDS). Moreover, a X-ray diffractometer (XRD) was used to identify the phases present. An improvement of 2.5-times the hardness of the steel substrate was achieved in A1(0.8) which may be attributed to the fine microstructure, dislocations and the high degree of saturation of solid solution brought by the high scanning speed. At a scanning speed of 0.8 m/min, sample A1 exhibited the highest polarization resistance Rp (3163000 O.cm2), lowest corrosion current density icorr (7.95X10-8A/cm2), with a lowest corrosion rate Cr (0.000924 mm/year) in 1M HCl solution. The polarization resistance Rp (3163000 O.cm2) is 392,281-times the polarization of the UNS G10150 steel substrate with a 99.9994 % reduction in the corrosion rate.

The Effects of Silicon Carbide Reinforcement on the Properties of Cu/SiCp Composites

Copper, possessing a desirable combination of high electrical and thermal conductivities is widely used in thermal and electronic applications. The prospective requirements for dependable materials in electronic industries are always increasing.. The main pronounced failure that occurs during microelectronic circuits’ application involves thermal fatigue. Heat generated in electronic packages can be dissipated by developing suitable materials as heat sinks. Copper metal matrix composites reinforced with silicon carbide (SiC) proffer possibility of meeting these demands. This research work entails producing copper matrix using silicon carbides (SiC) as reinforcement. Copper silicon carbide composites were produced in 80 % Cu-20 % SiC, 70 % Cu-30 % SiC, 60 % Cu-40 % SiC, 50 % Cu-50 % SiC, 40 % Cu-60 % SiC ratios with an average grain size of 212 μ m, 425 μ m and 710 μ m respectively via liquid metallurgy method. The result revealed that increasing volume fraction and particle sizes of the particulate had significant effect on the thermal and electrical conductivity of the composites.

The Influence of Heat Treatment and Process Parameters Optimization on Hardness and Corrosion Properties of Laser Alloyed X12CrNiMo Steel

Martensitic stainless steels are used in the production of steam turbine blades but their application is limited due to low hardness and poor corrosion resistance. Laser surface alloying and heat treatment of X12CrNiMo Martensitic stainless steel was conducted with the aim of enhancing hardness and corrosion properties. A Rofin Sinar Continuous Wave Nd: YAG solid-state laser was used to alloy the specimens. The electrochemical and hardness properties were studied using potentiodynamic polarization technique and Vickers micro hardness tester. The microstructures of the as-received, post-heated and pre-heated specimens were investigated by a Scanning Electron Microscope (SEM) and Optical Micrograph (OM) respectively. From the experimental results, the post-heated specimens exhibited the highest hardness property as compared to all other specimens. There was also significant improvement in the corrosion resistance of the post heated specimen compared to all other specimens and the substrate as evidenced by higher polarization resistance and lower corrosion rates. From the analysis of grey relational grade model, the significant laser processing parameters were identified. The results showed the influence of laser power and scanning speed on the corrosion rate, hardness and alloyed depth. The predicted results were found to be in good agreement with the experimental results.

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

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.

Electrochemical studies and surface analyses of laser deposited Zn-Al-Sn coatings on AISI 1015 steel

Surface hardening of mild steel with Zn-Sn bath is characterised by the traditional phases, whereas presence of aluminium leads to coatings constituted by phase in the inner layers, and by an outer layer made of three phases and inter-metallic phases which made the materials to be brittle. Enhancement in properties of Zn-Al-Sn coating led to the investigation of Zn-Al-Sn coating on mild steel by laser alloying technique. Composition of 25%Zn-50%Al-25%Sn and 30%Zn-40%Al-20%Sn with laser power of 750 W, scanning speed of 0.6 and 0.8 m/min were used in this research. Standard techniques were used for the characterisation of the laser samples and 0.5 M H2SO4 was used for the electrochemical test. The results showed that all the properties were improved by increasing the Al content from 40 to 50%. The optimum properties were obtained at 25%Zn-50%Al-25%Sn at laser power of 750 W and speed of 0.8 m/min. The optimum composition significantly improved the corrosion resistance of Zn-Al-Sn coatings in 0.5 M H2SO4 solutions and 2.2-times the hardness of the substrate was also achieved. It has been established that laser alloying of mild steel with Zn-Al-Sn coatings is promising for improving the surface hardness values and corrosion resistance.

Laser Engineering Net Shaping Method in the Area of Development of Functionally Graded Materials (FGMs) for Aero Engine Applications - A Review

Modern aero engine components are subjected to extreme conditions were high wear rate, excessive fatigue cycles, and severe thermal attack are inevitable. These aggressive conditions reduce the service life of components. Its generic ef‐ fect is magnified in the light of understanding the fact that aero engine parts are highly sensitive to functional and dimensional precision; therefore, repair and re‐ placement are great factors that promote downtime during operation. Hard ther‐ mal barrier coatings have been used in recent times due to their optimized properties for maximum load bearing proficiency with high temperature capabili‐ ty to meet performance and durability required. Nevertheless, less emphasis is being given to the coating-substrate interaction. Functionally graded structures have better synergy and flexibility in composition than coatings, giving rise to controlled microstructure and improved properties in withstanding acute state of affairs. Such materials can be fabricated using Laser Engineered Net Shaping (LENSTM), a laser-based additive manufacturing technique. LENSTM offers a great deal in rapid prototyping, repair, and fabrication of three-dimensional dense structures with superior properties in comparison with traditionally fabricated structures. The manufacture of aero engine components with functionally graded materials, using LENSTM, can absolutely mitigate the nuisance of buy-to-fly ratio, lost time in repair and maintenance, and maximize controlled dimension and multi-geometric properties, enhanced wear resistance, and high temperature strength. This review presents an extensive contribution in terms of insightful un‐ derstanding of processing parameters and their interactions on fabrication of functionally graded stainless steel, which definitely influence the final product quality.