State of the Art of Laser Hardening and Cladding

In this paper an overview is given about laser surface modification processes, which are developed especially with the aim of hardness improvement for an enhanced fatigue and wear behaviour. The processes can be divided into such with and without filler material and in solid-state and melting processes. Actual work on shock hardening, transformation hardening, remelting, alloying and cladding is reviewed, where the main focus was on scientific work from the 21st century

Investigation of the Scanning Microarc Oxidation Process

Scanning microarc oxidation (SMAO) is a coating process which is based on conventional microarc oxidation (MAO). The key difference is that deposition in SMAO is achieved by using a stainless steel nozzle to spray an electrolyte stream on the substrate surface as opposed to immersing the workpiece in an electrolyzer. In the present study, SMAO discharge characteristics, coating morphology, and properties are analyzed and compared to results obtained from MAO under similar conditions. Results show that MAO and SMAO have comparable spark and microarc lifetimes and sizes, though significant differences in incubation time and discharge distribution were evident. Results also showed that the voltage and current density for MAO and SMAO demonstrate similar behavior but have markedly different transient and steady-state values. Results obtained from coating A356 aluminum sheet show that oxide thickness and growth rate in SMAO are strongly dependent on interelectrode spacing and travel speed. Analysis of the SMAO coating morphology and structure showed that a denser and slightly harder layer was deposited in comparison to MAO and is attributed to reduced porosity and increased formation of α-Al2O3. Preliminary results indicate that SMAO represents a viable process for coating of aluminum surfaces

Methods of measuring residual stresses in components

Residual stresses occur in many manufactured structures and components. Large number of investigations have been carried out to study this phenomenon and its effect on the mechanical characteristics of these components. Over the years, different methods have been developed to measure residual stress for different types of components in order to obtain reliable assessment. The various specific methods have evolved over several decades and their practical applications have greatly benefited from the development of complementary technologies, notably in material cutting, full-field deformation measurement techniques, numerical methods and computing power. These complementary technologies have stimulated advances not only in measurement accuracy and reliability, but also in range of application; much greater detail in residual stresses measurement is now available. This paper aims to classify the different residual stresses measurement methods and to provide an overview of some of the recent advances in this area to help researchers on selecting their techniques among destructive, semi destructive and non destructive techniques depends on their application and the availabilities of those techniques. For each method scope, physical limitation, advantages and disadvantages are summarized. In the end this paper indicates some promising directions for future developments

Computational analysis on micro-shunt of minimally invasive glaucoma-surgery (MIGS) in severe glaucoma

Incurable blindness, known as glaucoma, is one of the leading eye diseases ever recorded worldwide. Novel treatment of micro-device implanted in the eye to drained the undesired amount of aqueous humour (AH) has been introduced. Minimally�Invasive Glaucoma-Surgery (MIGS) is a device for controlling the disease. Thus, this study was conducted to evaluate the MIGS micro shunt device’s performances based on the range of intraocular pressure, IOP produced. Four (4) different MIGS devices, namely Cypass, Ex-Press, InnFocus, and Xen Gel micro shunts, were compared according to clinical reports and research article. Computational fluid dynamics (CFD) analysis on the AH hydrodynamics considering glaucomatous condition was done on all four MIGS models. A commercially available CFD ANSYS Fluent version 19.2 was employed for simulation work; the velocity vector analysis and pressure distribution were discussed. An experiment on the fabricated one-part novel simplified laboratory-scale prototype-model was conducted to validate the CFD simulation results. 3D printer technology (Wang et al., 2019) and casting process (Darlis et al., 2017) were used in model fabrication. Water-glycerine solution as the working fluid used in experiment (Darlis et al., 2017). The experimental model produces no leaking problem. In a simulation study, the AH flow behaviour inside the human eye anterior chamber (AC) with the MIGS devices model was discussed. Among those four (4) MIGS) models, InnFocus model, produced an ideal IOP level for glaucoma treatment (1882.2970 Pa to 2658.6641 Pa) and the lowest possibility to cause Pigmentation Dispersion Syndrome (PDS) through wall shear stress (WSS) analysis (maximum WSS of 0.00066 Pa). It also creates medium flow behaviour without any fluctuation and high velocity as compared to the other. The simulation study also shows that the Ex-Press model produces the highest velocity fluctuation and irregularity in its flow behaviour. It also creates the highest level of WSS up to 5.2 Pa on the posterior iris. This finding helps to minimize the percentage of visual impairment caused by glaucoma surgical procedure in Malaysian glaucoma patients and contribute to a global eye health action plan 2020-2025 by World Health Organization (WHO)

Nanoparticle-enabled phase control for arc welding of unweldable aluminum alloy 7075.

Lightweight materials are of paramount importance to reduce energy consumption and emissions in today's society. For materials to qualify for widespread use in lightweight structural assembly, they must be weldable or joinable, which has been a long-standing issue for high strength aluminum alloys, such as 7075 (AA7075) due to their hot crack susceptibility during fusion welding. Here, we show that AA7075 can be safely arc welded without hot cracks by introducing nanoparticle-enabled phase control during welding. Joints welded with an AA7075 filler rod containing TiC nanoparticles not only exhibit fine globular grains and a modified secondary phase, both which intrinsically eliminate the materials hot crack susceptibility, but moreover show exceptional tensile strength in both as-welded and post-weld heat-treated conditions. This rather simple twist to the filler material of a fusion weld could be generally applied to a wide range of hot crack susceptible materials

Effect of electro discharge machining (EDM) on the AISI316L SS white layer microstructure and corrosion resistance

The localised corrosion resistance of austenitic stainless steels is strongly influenced by the quality of finished surface. EDM machining induces substantial changes by the high thermal gradients generated by electric sparks. Experimental techniques such as roughness measurement, scanning electron microscopy (SEM), energy dispersive microanalysis (EDX) and X-ray diffraction technique, reveal microgeometrical, microstructural, chemical and mechanical changes. These changes lead to white and heat-affected layers with a depth less than 100 μm. The white layer is a melted material characterised by dendritic structure and constituted by austenite, chromium carbide and ε-carbide. The heat-affected layer is characterised by very large grain size comparatively to the bulk material. Electrochemical test coupled with metallographic examinations using SEM reveals a weakening of the resistance to pitting and intergranular corrosion comparatively to diamond polished surface. This weakening is correlated to differences in structure and chemical composition of white layer. Susceptibility to stress corrosion cracking has been attributed to the field of tensile residual stresses resulting from thermal effects. The removal of the white layer material by polishing or wire brushing restores the corrosion resistance of the AISI316L SS

MACHINABILITY OF ALUMINIUM METAL MATRIX COMPOSITE REINFORCED WITH ALUMINA USING ELECTRO-DISCHARGE MACHINING

Aluminium metal matrix composites (AMMCs) are making inroads in various engineering applications (aviation, marine, automotive parts as diesel engine pistons, cylinder, and brake components) requiring higher strength and stiffness than those offered by conventional aluminium alloys. Traditional machining of AMMCs however is difficult due to hard reinforcement in the AMMC material which tends to wrap around the cutting tool-bit leading to tool breakage. Electro-discharge machining (EDM) has been successfully applied on standard aluminium alloys such as Al 6061 but yet to be tested on 30% Al2O3 reinforced AMMC. In this study, a specific machining performance on 30% Al2O3 reinforced AMMC is assessed in comparison with Al 6061. The characteristics analyzed are surface roughness (Ra), material removal rate (MRR), tool wear ratio (TWR), overcut (OC) and surface morphology. Process parameters used, are peak current, ON-time (pulse duration) and OFF-time (pause duration), were varied in this research to determine the machinability of AMMC reinforced by 30% Al2O3 by using EDM. The research methodology adopted was using design of experiment (DOE) and results from the experiment were analyzed and interpreted. The response surface methodology (RSM) was used to predict the machining performance and empirical mathematical models for Ra, MRR and TWR using Design Expert software. Results showed that peak current, ON-time and OFF-time have influenced on the EDM performance. Machinability of electro-discharge machining of 30% Al2O3 reinforced AMMC composite using electrolytic copper electrode has been proven feasible at certain parameters setting. Nevertheless, EDM machining performance of Al 6061 is better than that of AMMC. For machining at a specific material removal rate, minimal surface roughness, and low overcut can be obtained at low peak current or short ONtime and longer OFF-time however tool wear ratio remains high. Appropriate setting of EDM parameters that results in optimum machining performance have been identified in this research