Evaluation of Tribological aspects of Al-Si 12 alloy and their Metal Matrix hybrid Composites produced by Liquid-metal Forging Method

Particulate Aluminium Metal Matrix Composites (Al-MMC) have emerged as advanced engineering materials in view of their improved properties. Ceramic reinforced Al-MMC were more suitable because of being economical and exhibiting isotropic properties. Al-MMCs manufacturing methods are expensive, demand skilled and complex operations and vortex liquid metallurgy results into higher porosity. The liquid-metal forging/squeezed casting of stirred molten slurry can eliminate porosity as molten metal is pressurized during solidification forming near net shapes. During many instances, influence of process parameter (PP)s on mechanical part properties is being studied. In the present study, composites were produced using Al-Si12 alloy as base material, aluminium oxide and silicon carbide particles as reinforcements by varying the PPs. Tribological tests were conducted under dry sliding condition at room temperature showed hard reinforcements in Al alloy reduced the wear rate (WR) and increased the coefficient of friction (f) for all PPs. For PPs, increasing the squeeze pressure and decreasing the pouring and die preheating temperature resulted in a reduction of WR and f with an increase in normal load and sliding velocity. Initially f falls and then raised with an increase in normal load, but only raised with growing sliding velocity compared to Aluminium base material.

Evaluation of Tribological aspects of Al-Si 12 alloy and their Metal Matrix hybrid Composites produced by Liquid-metal Forging Method

Particulate Aluminium Metal Matrix Composites (Al-MMC) have emerged as advanced engineering materials in view of their improved properties. Ceramic reinforced Al-MMC were more suitable because of being economical and exhibiting isotropic properties. Al-MMCs manufacturing methods are expensive, demand skilled and complex operations and vortex liquid metallurgy results into higher porosity. The liquid-metal forging/squeezed casting of stirred molten slurry can eliminate porosity as molten metal is pressurized during solidification forming near net shapes. During many instances, influence of process parameter (PP)s on mechanical part properties is being studied. In the present study, composites were produced using Al-Si12 alloy as base material, aluminium oxide and silicon carbide particles as reinforcements by varying the PPs. Tribological tests were conducted under dry sliding condition at room temperature showed hard reinforcements in Al alloy reduced the wear rate (WR) and increased the coefficient of friction (f) for all PPs. For PPs, increasing the squeeze pressure and decreasing the pouring and die preheating temperature resulted in a reduction of WR and f with an increase in normal load and sliding velocity. Initially f falls and then raised with an increase in normal load, but only raised with growing sliding velocity compared to Aluminium base material.

A Closer Look at Precision Hard Turning of AISI4340: Multi-Objective Optimization for Simultaneous Low Surface Roughness and High Productivity

This article reports an extended investigation into the precision hard turning of AISI 4340 alloy steel when machined by two different types of inserts: wiper nose and conventional round nose. It provides a closer look at previously published work and aims at determining the optimal process parameters for simultaneously minimizing surface roughness and maximizing productivity. In the mathematical models developed by the authors, surface roughness at different cutting speeds, depths of cut and feed rates is treated as the objective function. Three robust multi-objective techniques, (1) multi-objective genetic algorithm (MOGA), (2) multi-objective Pareto search algorithm (MOPSA) and (3) multi-objective emperor penguin colony algorithm (MOEPCA), were used to determine the optimal turning parameters when either the wiper or the conventional insert is used, and the results were experimentally validated. To investigate the practicality of the optimization algorithms, two turning scenarios were used. These were the machining of the combustion chamber of a gun barrel, first with an average roughness (Ra) of 0.4 µm and then with 0.8 µm, under conditions of high productivity. In terms of the simultaneous achievement of both high surface quality and productivity in precision hard turning of AISI 4340 alloy steel, this work illustrates that MOPSA provides the best optimal solution for the wiper insert case, and MOEPCA results are the best for the conventional insert. Furthermore, the results extracted from Pareto front plots show that the wiper insert is capable of successfully meeting both the requirements of Ra values of 0.4 µm and 0.8 µm and high productivity. However, the conventional insert could not meet the 0.4 µm Ra requirement; the recorded global minimum was Ra = 0.454 µm, which reveals the superiority of the wiper compared to the conventional insert

Effect of Synthesized Titanium Dioxide Nanofibers Weight Fraction on the Tribological Characteristics of Magnesium Nanocomposites Used in Biomedical Applications

Biomedical applications, such as artificial implants, are very significant for the disabled due to their usage in orthopedics. Nevertheless, available materials in such applications have insufficient mechanical and tribological properties. The current study investigated the mechanical and tribological properties of a biomedical metallic material, magnesium (Mg), after incorporating titanium dioxide nanofibers (TiO2) with different loading fractions. The TiO2 nanofibers were synthesized using the electrospinning technique. The ball-milling technique was utilized to ensure the homogenous distribution of TiO2 nanofibers inside the Mg matrix. Then, samples of the mixed powder with different loading fractions of TiO2 nanofibers, 0, 1, 3, 5, and 10 wt.%, were fabricated using a high-frequency induction heat sintering technique. The physicomechanical and tribological properties of the produced Mg/TiO2 nanocomposites were evaluated experimentally. Results showed an enhancement in mechanical properties and wear resistance accompanied by an increase in the weight fraction of TiO2 nanofibers up to 5%. A finite element model was built to assess the load-carrying capacity of the Mg/TiO2 composite to estimate different contact stresses during the frictional process. The finite element results showed an agreement with the experimental results

Investigation of the Mechanical and Tribological Behavior of Epoxy-Based Hybrid Composite

The main target of this study is to evaluate the impact of hybrid reinforcement using Al2O3 nanoparticles and graphite on the epoxy nanocomposites’ mechanical and tribological properties. Various weight fractions of the reinforcement materials, ranging from 0 to 0.5 wt.%, were incorporated into the epoxy. The aim is to enhance the characteristics and durability of the polymers for potential utilization in different mechanical applications. The addition of hybrid additives consisting of Al2O3 nanoparticles and graphite to the epoxy resin had a noticeable effect on the performance of the epoxy nanocomposites. The incorporation of these additives resulted in increased elasticity, strength, toughness, ductility, and hardness as the concentration of reinforcement increased. The enhancement in the stiffness, mechanical strength, toughness and ductility reached 33.9%, 25.97%, 25.3% and 16.7%, respectively. Furthermore, the frictional tests demonstrated a notable decrease in both the coefficient of friction and wear with the rise of the additives’ weight fraction. This improvement in the structural integrity of the epoxy nanocomposites led to enhanced mechanical properties and wear resistance. The SEM was utilized to assess the surfaces of tested samples and provide insights into the wear mechanism

EPIdemiology of Surgery-Associated Acute Kidney Injury (EPIS-AKI) : Study protocol for a multicentre, observational trial

More than 300 million surgical procedures are performed each year. Acute kidney injury (AKI) is a common complication after major surgery and is associated with adverse short-term and long-term outcomes. However, there is a large variation in the incidence of reported AKI rates. The establishment of an accurate epidemiology of surgery-associated AKI is important for healthcare policy, quality initiatives, clinical trials, as well as for improving guidelines. The objective of the Epidemiology of Surgery-associated Acute Kidney Injury (EPIS-AKI) trial is to prospectively evaluate the epidemiology of AKI after major surgery using the latest Kidney Disease: Improving Global Outcomes (KDIGO) consensus definition of AKI. EPIS-AKI is an international prospective, observational, multicentre cohort study including 10 000 patients undergoing major surgery who are subsequently admitted to the ICU or a similar high dependency unit. The primary endpoint is the incidence of AKI within 72 hours after surgery according to the KDIGO criteria. Secondary endpoints include use of renal replacement therapy (RRT), mortality during ICU and hospital stay, length of ICU and hospital stay and major adverse kidney events (combined endpoint consisting of persistent renal dysfunction, RRT and mortality) at day 90. Further, we will evaluate preoperative and intraoperative risk factors affecting the incidence of postoperative AKI. In an add-on analysis, we will assess urinary biomarkers for early detection of AKI. EPIS-AKI has been approved by the leading Ethics Committee of the Medical Council North Rhine-Westphalia, of the Westphalian Wilhelms-University Münster and the corresponding Ethics Committee at each participating site. Results will be disseminated widely and published in peer-reviewed journals, presented at conferences and used to design further AKI-related trials. Trial registration number NCT04165369

Enhancement of hardness and wear strength of pure Cu and Cu–TiO2 composites via a friction stir process while maintaining electrical resistivity

The study aims to enhance the hardness and wear of copper and Cu–TiO2-based composites while maintaining high electrical conductivity through friction stir processing (FSP). It assesses the impact of TiO2 volume fractions and groove widths (GWs) on the wear, hardness, resistivity, and microstructure of FSPed Cu and FSPed Cu–TiO2 surface composite. The samples obtained from the stir zone showed an increase in microhardness of the Cu–TiO2 surface composite due to particle refinement, uniform distribution, and efficient sticking of TiO2 with Cu. Furthermore, the wear rate increased with decreasing TiO2 volume fractions in the composite. The worn surface microstructural analysis indicated a transition from harsh to gentle wear with increasing TiO2 volume fractions and GWs. The average grain size reduced significantly in reinforced stir zones compared to pure Cu, and particle size decreased further with increasing groove size. Hardness increased by 25 and 50% compared to unprocessed Cu, but only a negligible increase in electrical resistivity (2.3% Ωm) after FSP

Effect of a Rapid Tooling Technique in a 3D Printed Part for Developing an EDM Electrode

The role of rapid tooling (RT) in additive manufacturing (AM) seems essential in improving and spreading out the vista of manufacturing proficiency. In this article, attempts were made to discover the feasibility and the accomplishments of the RT electrode in the field of electro-discharge machining (EDM). Fused deposition modeling (FDM) is one of the AM processes adopted to fabricate the EDM electrode prototype by coating with copper. The copper is deposited on FDM-built ABS plastic component for about 1 mm through thick electroplating. The copper-coated FDM (CCF) and solid copper (SC) electrodes are used to conduct experiments on a die-sinking EDM machine using tool alloy steel as a workpiece. The CCF polymer electrode can be efficiently used in EDM operations as the build time of any complex shape was substantially reduced. However, the material removal rate (MRR) is far less than that of the SC electrode. It is recommended that the CCF electrode is used for semifinishing and finishing operations in which MRR happens to be less. However, CCF can get spoiled as high temperatures are generated on the machining tool, and the plastic core hardly sustains such high temperatures

Effect of part build orientations and sliding wear factors on tribological characteristics of FDM processed parts

Fused Deposition Modeling (FDM) components are commonly used for either prototypes or end products, mostly made of polymers. Polymers offer low frictional resistance to wear, so most of the engineering polymers find their increased usage in day-to-day industrial as well as domestic needs. The influence of many process controlling elements on the mechanical part properties is already being studied extensively, which demands the study of tribological characteristics like friction and wear rate under varying normal load (NL), sliding velocities (V) and part building orientations (PBO). The results showed a significant impact of the PBO and NL at various V on the tribological properties under various significant suitable sliding circumstances. Cracks were formed in the cylindrical tribometer specimens of Acrylonitrile butadiene styrene (ABS) fabricated at low PBO when operated at high NL, and V. Vertical PBO to the FDM building platform in the layers form where a number of inter-layers can bear maximum NL at higher values of V resulted in uniform wear and low frictions. Friction was noticed very low at minimum NL when PBO was 0° (horizontal) and 90° (vertical), but increased at high NL between PBO of 15° to 60°. The FDM parts improved compared to those from conventional manufacturing processes

High-Temperature Corrosion of APS- and HVOF-Coated Nickel-Based Super Alloy under Air Oxidation and Melted Salt Domains

Various thermal spraying approaches, such as air/atmospheric plasma spraying (APS) and high-velocity oxy-fuel (HVOF) spraying, are widely employed by plants owing to their flexibility, low costs and the high surface quality of the manufactured product. This study focuses on the corrosion behavior of a Ni superalloy coated with powder Cr3C2-25NiCr through APS and HVOF at 950 °C under air oxidation and Na2SO4 + 0.6V2O5 molten salt environments (MSE). The results show that HVOF-deposited Ni superalloys have higher hardness and bond strength than the respective APS coating. The thermo-gravimetric probe reveals that the Ni superalloys exposed to an oxidizing air environment has a minor mass gain compared to those under the MSE domain for both non-coated and coated samples, in line with the parabola curvature rate oxidizing law. The Ni superalloys show good corrosion resistance but poor oxidation resistance in APS-deposited Ni superalloys under the MSE. HVOF-coated Ni superalloys in both environments exhibit better corrosion resistance and lower mass gain than APS-coated superalloys. The excellent coating characteristics of HVOF-coated Ni superalloys lead to their better high-temperature corrosion performance than APS