Metallographic Research Articles

INVESTIGATION OF STRUCTURAL AND MECHANICAL PROPERTIES OF TUBING STEELS

The study of the structural and mechanical properties of tubing steels used in wells at oil and gas condensate fields is of particular interest due to the resource intensity of these systems and the high cost of their repair and restoration. Tubing is operated under conditions of increased loads under the influence of its own weight, internal pressure and constant contact with highly aggressive media. As a result of simultaneous exposure to corrosive media and operational loads, tubing is the most consumable downhole material. The destruction and, as a result, the breakage of the tubing suspension occurs as a result of mechanical abrasion and cracking of the pipe body, the development of fatigue cracks in the thread, etc. Contact with aggressive agents of the extracted fluid and reservoir waters leads to various types of corrosion damage: ulcerative, pitting, corrosion fatigue, corrosion cracking, meza corrosion, biocorrosion, etc. Corrosion foci are localized on the inner and outer surfaces of pipes. The problem is complicated by the increased content of carbon dioxide (CO2), hydrogen sulfide (H2S), as well as the presence of various bacteria in oil and gas fields.This article is devoted to the study of the mechanical characteristics and microstructure of tubing steels that were in operation under conditions of complicating factors and highly aggressive corrosive environment. Tubing pipes Ø73x5.5 of strength group E. were tested. The following research methods were carried out: visual inspection; determination of the chemical composition of steel; determination of hardness; uniaxial tensile test; optical microscopy.As a result of the tests, quantitative characteristics of the mechanical properties of the steels were obtained. A significant decrease in the hardness, tensile strength and yield strength of steel has been established under prolonged exposure to complicated operating conditions. Metallographic studies have established the contamination of steels with silicates of various shapes, amounting to 3 and 2 points according to GOST 1778. Microstructural studies have been carried out. The fine-grained ferrite-carbide structure of steels has been revealed. This structure corresponds to the heat treatment mode: quenching followed by tempering.

Fabrication of Cu/Al–Al2O3 laminar composites using squeeze casting and roll bonding techniques: Evaluation of microstructure, mechanical properties and wear characteristics

The influence of Al2O3 whiskers addition on the microstructure, tensile, hardness, and wear characteristics of Cu/Al–Al2O3 composites were examined. The squeeze casting was used to fabricate Al–Al2O3 composites with different volume fractions of whiskers. Then, they were bonded to Cu layers. The microstructural and morphological examination were carried out by using SEM, XRD, and EBSD analyses. For the as-cast composites, the agglomeration of whiskers was observed which was then decreased by the following roll bonding process. For the roll bonded composites, the tensile strengths of composites were 210 MPa, 233 MPa, and 250 MPa For Cu/Al-(5 % vol) Al2O3, Cu/Al-(15 % vol) Al2O3, and Cu/Al-(25 % vol) Al2O3, respectively. The wear rate decreased versus volume fraction of whiskers which is correlated with the enhanced hardness of layers in composites. Less material loss and less debris were observed in composites with a higher volume fraction of whiskers.

Joining dissimilar metals by additive manufacturing: A review

The demand for lightweight materials, site-specific properties, and customized features drives the need for joining components made from dissimilar materials. However, dissimilar welding poses challenges such as the formation of large heat affected zones and intermetallic compounds at the interface, leading to easy premature failure and cracking. In recent years, additive manufacturing (AM) of dissimilar metallic materials has gained popularity as a solution to these challenges, as evidenced by numerous review articles discussing various aspects of this field. However, a comprehensive review focusing on microstructural analysis at the joint interface of a wide range of materials combinations produced by AM has been lacking. This review aims to address this gap by providing an in-depth examination of microstructures and mechanical properties at the interface for various metal combinations. Furthermore, it delves into different processing approaches and the challenges associated with manufacturing dissimilar structures. This review serves as a valuable resource for beginners in the field, offering a thorough discussion and comparison of the reported results. The paper presents major conclusions and identifies outstanding issues for future investigations. By providing valuable insights crucial for the widespread implementation of dissimilar AM technologies, this analysis will assist current AM processing for dissimilar structures. It is particularly significant for understanding the microstructure at the joint interface of various miscible and immiscible dissimilar structures manufactured using different additive manufacturing techniques.

Poster 352: Histopathological Etiology of Mucoid Degeneration of the Anterior Cruciate Ligament

Objectives: Mucoid degeneration of the anterior cruciate ligament (ACL) is an uncommon clinical condition with reported prevalence below 0.5%. There is a paucity of histopathological description in the literature, which has limited our understanding of the underlying pathophysiology. Such limited understanding has resulted in treatment options limited to mechanical debridement rather than biologic interventions to prevent development or progression of mucoid degeneration. The purpose of this study is to define the histopathology of mucoid degeneration of the ACL to better guide future biologic and surgical management options. Methods: This is a case control study where a retrospective series of 10 patients were identified to have mucoid degeneration of the ACL from 2002 to 2023. They were evaluated and treated by two senior attending orthopedic sports medicine surgeons. Magnetic resonance images (MRI) were evaluated for multiple anatomic and morphometric measures. Tissue samples were obtained at the time of arthroscopic partial debridement of the ACL for all patients. Intra-operative ACL samples and cadaveric control tissues were prepared for histologic examination of microstructure and composition, and gene expression using multiplex transcriptional profiling. For the gene expression analysis RNA was isolated from archived formalin-fixed and paraffin-embedded (FFPE) sections. Three consecutive 6mm sections were pooled to generate one RNA sample and total RNA was extracted using a High Pure FFPET RNA Isolation Kit per the manufacturer’s protocol and stored at -80°C until further analysis. RNA concentration and integrity was evaluated using an Agilent BioAnalyzer 2100 and a corrected input of 50ng of total RNA was used for NanoString analyses using the NanoString nCounter® Human Fibrosis V2 Panel for multiplex molecular analysis of 770 genes. Analysis was performed using nSolver 4.0 Software and only probes with counts above background were included following the manufacturer instructions. Results: All 10 patients reported pain and limited knee flexion. MRI exhibited a bulbous appearance of the ACL. There was an increased posterior tibial slope (PTS), narrow notch width index, and increased signal intensity of the ACL. Medial meniscus tear and cartilage degeneration were reported with high prevalence. The histological analysis showed significant differences in the architecture of the tissue compared with normal ACL controls, with disorganized collagen matrix and increased glycosaminoglycan content. NanoString analysis demonstrated a total of 155 differentially expressed genes (DEGs) between the mucoid degeneration and control groups after adjustments for multiple comparisons (p<0.05), with the top 20 DEGs summarized in Table 1. Among all the DEGs identified the 5 most upregulated ones include Fibronectin 1 (FN1), COL5A1, COL6A3, COL3A1 and COL1A2. There were also significant differences in the pathway scores for epithelial-to-mesenchymal transition (EMT), Extracellular matrix Degradation and Synthesis, Collagen Biosynthesis, Focal Adhesion Kinase, PDGF Signaling and PI3K-Akt (Fig. 1). The histology findings demonstrate distinct changes in the structure and composition of the ACL, and we hypothesize that repetitive microtrauma of the ACL may lead to cumulative damage that ultimately results in mucoid degeneration. Increased posterior tibial slope and narrow notch width index may contribute to cumulative loading of the ligament and subsequent mucoid degeneration. Identification of biomechanical risk factors may help to identify high risk patients. Associated injury of the medial meniscus and medial compartment cartilage also suggests that mucoid degeneration of the ACL may be part of an early degenerative process in the knee. Conclusions: Mucoid degeneration of the ACL is an uncommon condition that may represent the result of repetitive microtrauma to the ligament. Current interventions address the condition after it has progressed to an irreversible biological state. By defining the cellular and molecular mechanism(s) of the condition, we aim to broaden treatment options to potentially identify biologic interventions. The association of mucoid degeneration and medial compartment osteoarthritis suggests that patients may benefit from earlier interventions. [Figure: see text][Figure: see text]

Preparation and Properties of a Composite Carbon Foam, as Energy Storage and EMI Shield Additive, for Advanced Cement or Gypsum Boards

This article explores the cutting-edge advancement of gypsum or cement building boards infused with shape-stabilized n-octadecane, an organic phase change material (PCM). The primary focus is on improving energy efficiency and providing electromagnetic interference (EMI) shielding capabilities for contemporary buildings. This research investigates the integration of these materials into construction materials, using red-mud carbon foam (CCF) as a stabilizer for n-octadecane (OD@CCF). Various analyses, including microstructural examination, porosity, and additive dispersion assessment, were conducted using X-ray microtomography and density measurements. Thermal conductivity measurements demonstrated the enhancement of composite boards as the OD@CCF content increased, while mechanical tests indicated an optimal additive content of up to 20%. The thermally regulated capabilities of these advanced panels were evaluated in a custom-designed room model, equipped with a homemade environmental chamber, ensuring a consistent temperature environment during heating and cooling cycles. The incorporation of OD@CCF into cement boards exhibited improved thermal energy storage properties. Moreover, the examined composite boards displayed efficient electromagnetic shielding performance within the frequency range of 3.2–7.0 GHz, achieving EMI values of approximately 18 and 19.5 dB for gypsum and cement boards, respectively, meeting the minimum value necessary for industrial applications.

Experimental selection of rolling contact length to the average thickness (L\\have) ratio for producing fine-grain Incoloy 907 superalloy sheet by hot-rolling

The current study investigates the effects of L\\have values on the microstructure and tensile properties of the superalloy Incoloy 907. These effects are studied using hot-rolling at 84 % and 96 % thickness reductions. Microstructural examination of the received sample revealed a non-uniform coarse grain structure with precipitates of oxide phases rich in niobium and Laves. These precipitates are shredded and randomly distributed in the microstructure with elongated grains after hot-rolling under 84 % reduction. Following the solution-treatment, this sample's simultaneous static recrystallization and precipitation of secondary-phase particles has formed a banded structure of grain-size and secondary-phase particle bands. The particles of the secondary-phases are locally accumulated on the material's surface in the 96 % hot-rolled sample, creating a duplex grain and non-random microstructures with different cross-sectional conditions. The secondary-phase particle bands caused by the previous solution-treatment are retained in the pre-hot-rolled sample under 84 % reduction after aging. Furthermore, XRD analysis results show that the precipitation peak of γ'/γ phase was more visible and intense in this sample. Tensile tests conducted at room temperature and 649 °C indicate that the pre-hot-rolled sample with an 84 % reduction exhibited a 1 % improvement in cold ductility and an 8 % enhancement in hot ductility compared to the sample with a 96 % reduction.

Surface microstructuring of hot-rolled carbon structural steels under complex exposure to laser radiation

The purpose of the work was to study the effect of laser microstructuring modes of the cutting edge on changes in the structure and mechanical properties of the surface layer of parts made of hot-rolled structural carbon steels grades 20, 35, 45. Methods. Structural carbon steels of grades 20, 35, 45 were selected as objects of research. To study the effect of laser modification on changing the structure and mechanical properties of machine parts using laser cutting, special samples were made in the form of square plates (35×35 mm) with a thickness of 2 mm (St20 and St45) and 4 mm (St35). After laser cutting according to the modes, one of the sides of the sample was subjected to mechanical grinding in order to remove a layer with a modified structure of the material obtained during laser cutting. Next, laser microstructuring of the sample surfaces was performed using a continuous fiber laser. Metallographic and durometric studies were carried out to study the effect of laser microstructuring on changes in the structure and properties of the surface layer. Results. The regularities of the structure of the zone of laser action of structural carbon steels after laser microstructuring have been revealed, which consists of two layers: a non-etching (slightly etching) white layer, which is a finely dispersed martensite of a needle structure and immediately following it a zone of thermal influence, which, depending on the carbon content in the steel, has a different structure: ferrite-pearlite, martensitic, troostomartensitic, martensiticpearlitic. It has been established that laser microstructuring of a pre-polished surface in some cases leads to an increase in the values of microhardness and the length of the laser exposure zone, which may be associated with an increase in the absorption capacity of the material of the polished surface and, accordingly, a decrease in its reflectivity. Conclusion. The results obtained can be used in the creation of resource-saving material processing processes.

Fabrication of low-cost metal polishing machine for preparation of microstructure samples of lightweight alloy and composite material

A metallographic specimen should be performed to determine the microstructure of a material. One of the processes of preparation of metallographic specimen is polishing process. The designing and manufacturing a polishing machine will be very helpful in the process of polishing the metallographic specimen. This apparatus includes a motor, aluminum circular disc, switch and speed controller, and base plate. The polishing machine is constructed from these individual parts. This paper is proposed to design and fabrication a metal polishing machine for laboratory scale. In this paper, several stages of the process are performed, such as designing the model, preparing tools and materials used, making components, assembling and testing the polishing machine. The results obtained are polishing machine that works well and can be used for the metallographic test for students and researchers. It can be concluded that this polishing machine can produce the level of specimen preparation for a metallographic test.

Influence of post-weld explosive treatment on low cycle fatigue of AA7075-T651 friction stir welded joint

In this investigation the friction stir welded joint of 5 mm thick AA7075-T651 alloy has been subjected to the post-weld explosive treatment. To assess the influence of the proposed treatment on the joint properties, a comprehensive analysis was conducted, including microstructural examination, microhardness testing, static tensile tests, low-cycle fatigue testing, and fracture surface observations. The strain amplitudes of 0.35 %, 0.4 %, 0.5 %, and 0.6 % with asymmetry coefficient R = 0.1, were used for the examined samples. It was concluded that the explosively treated FSW joints are characterized by a lower amplitude of plastic deformation, a reduced number of cycles to failure and show a tendency for cyclic softening. The differences in the fatigue crack propagation primarily concern the initiation area of the crack near the hardened surface. Explosive treatment did not influence the location of material decohesion, which occurs in the low-hardness zone.

Influence of hBN on the abradable performance of AlSi-based coatings: Bridging the gap between tribological assessment and abradability testing

Abradable coatings have been proven to significantly improve the performance of turbomachinery by serving as a protective barrier between rotating blades and stationary casing. However, there is still a pressing need to develop more efficient abradable materials that can withstand the growing energy requirements and prolong the service life of gas turbines, which continues to pose a significant challenge to the aerospace industry. In the present study, two thermally sprayed aluminum‑silicon-based (AlSi) coatings were investigated, the first containing 40 wt% polyester (referred to as AlSi-Poly), and the second containing 6 wt% hexagonal boron nitride (hBN) and 20 wt% polyester (referred to as AlSi-hBN-Poly) as filler material. The microstructure, HR15Y hardness, and surface roughness were systematically examined in the fabricated coatings. Tribological studies were conducted using ball-on-flat and ball-on-disk testing conditions against titanium counterballs. In addition, a cost-effective abradable test rig has been developed to assess the abradability performance of both coatings under closer simulated aircraft turbine conditions. The microstructural examination of the coatings revealed that the filler materials were uniformly distributed throughout the coating, with the hBN particles embedded within the matrix. The average hardness of the AlSi-hBN-Poly coating was higher than that of the AlSi-Poly coating, which is consistent with the area fraction of filler materials present in each coating. The tribological assessment of the coatings revealed similar frictional coefficients, no apparent wear on the counterballs and higher wear depth and width for AlSi-hBN-Poly coating. This was attributed to significant third-body abrasion and higher transfer during testing in the case of the AlSi-hBN-Poly coating. Similarly, the abradability evaluation showed no blade wear against both coatings and slightly different transfer film formation. However, the AlSi-Poly coating presented a smoother rubbing wear track than the AlSi-hBN-Poly, which showed deeper rubbing grooves. These findings provide valuable insights into the tribological behaviour of these coatings and can aid in the development of more effective wear-resistant coatings.

Obtaining Heterogeneous Microstructure and Enhanced Mechanical Properties in ECAP-Processed AZ61 Alloys via Single-Pass Rolling with Increased Rolling Reduction

Material design and preparation based on constructing heterogeneous microstructures can break the conventional performance limitations of fine-grained magnesium alloys. In this study, AZ61 alloys processed via multi-pass equal channel angular pressing (ECAP) were subjected to single-pass rolling (SPR) with increased rolling reductions. The effect of rolling reduction on the formation of heterogeneous microstructure and the mechanical properties of the alloy was investigated. Microstructural examinations revealed that a heterogeneous microstructure was formed in the alloy at varied rolling reductions, but the desired heterostructure with higher fine grain contents could only be achieved at increased rolling reduction. This was mainly due to the fact that the alloy underwent partial dynamic recrystallization (PDRX) under SPR, and PDRX more easily occurred with higher rolling reduction. The tensile test results showed that with increased rolling reduction, the strength of the alloy first increased and then decreased slightly, with the ductility steadily increasing. Improved mechanical properties were achieved in the alloy rolled at increased rolling reductions owing to the heterogeneous microstructure with a greater content of fine grains.

The Effect of Cryogenic Treatment on Wear Resistance and Hardness of Tool Steel AISI “D2”

The purpose of this paper intended to study different heat treatments in conjunction with a special Cryogenic treatment process and its effect on the wear behavior, and hardness of AISI D2 tool steel. An experimental demonstration of this study was first carried out by a set of specimens left for one week in air after conventional treatment to make stabilization and the other set conditioned at 60°C for one hour before shallow and deep cryogenic treatment. This investigation has shown that an improvement of hardness and wear resistance in deep cryogenic (DCT) process compared to shallow cryogenic treatment (SCT) for different soaking time which was approved by micro-structural examination especially in the stabilized specimens. This finding is in agreement with other results found in the research using similar tool steel and other specific cryogenic processes.

Quantitative evaluation of spheroidisation in 15CrMo steel based on deep learning

ABSTRACT 15CrMo steel has good mechanical properties and is widely used in high-temperature pressure components. After long term service, it is easy to cause material spheroidisation. The metallographic and mechanical property tests are used to evaluate the spheroidisation of specimens. Ultrasonic backscattering signal is sensitive to microstructure and contains more microstructure information, which can be used for the evaluation of spheroidisation. However, the ultrasonic backscattering signal is nonlinear, and feature extraction is difficult. In this study, ultrasonic testing is used to scan different spheroidisation specimens, and the ultrasonic backscattering signal is extracted as the input to the deep learning model, which is used to extract features from the backscattering signal. The models are evaluated using classification and regression evaluation metrics. The results show that the proposed CNN-LSTM model has good identification performance for the classification of spheroidisation and the prediction of mechanical properties. The classification accuracy, recall, precision, and F1-score are all 1. Additionally, the maximum predicted RMSE and MAE values are only 2.33 MPa and 1.70 MPa, and the minimum R 2 is only 0.97. The worst prediction is the tensile strength, with an average value of 442.2 MPa and a maximum value of 481.1 MPa.

Ultrasonic monitoring of plastic deformation

Accident impact assessment, safety analysis, and risk reduction are among the core research topics in the field of shipping. Analysis of emergency situations shows that all of them in most cases are characterized by a combination of some causes, one of which is the occurrence of inadmissible stress-strain state in ship elements. Determining the nature of fracture is one of the ship’s reliability improving measures. The presence of plastic deformation is a sign of the limiting condition when monitoring the structure. This leads to a visible change in the geometry of the structural components, but not to a violation of continuity, which, according to the rules of the Register, is controlled during the technical inspection of the ship. Having only regulated standard controls at its disposal, it is not possible to identify plastic deformation. The article discusses the issues of plastic deformations’ control in 10ХСНД shipbuilding steel by a method that is based on the analysis of the ultrasonic wave propagation characteristics in a controlled product. The complex of mechanical tensile tests and metallographic studies is described. The uniaxial stress-strain state of the material was created by tensile testing of a flat proportional sample. Changes in the metal structure were investigated when the required level of deformation was reached. The analysis of ultrasonic data with pulsed ultrasonic sensing and the level of second harmonic generation with continuous monochromatic ultrasonic emission is presented. Experimental data demonstrate the ability of the ultrasonic method to detect the pre-existing defects in metal under static loading, and allow for a more accurate assessment of the stress and strain state of ship's components, which can fundamentally change the picture of destruction. The use of ultrasonic plastic deformation monitoring in the framework of ship maintenance will help reduce accidents in the fleet.

Combined effect of nanocompositing and addition of interlayer on friction stir welding of aluminum/magnesium joint: a study

ABSTRACT Aluminum and magnesium were welded by friction stir welding while Zinc was used as interlayer and Titanium carbide nanoparticles were applied as reinforcement. The microstructure examination and phase constitution of interfacial zones showed that the base materials reaction successfully proceeded. The changes in heat input and stir action had a very significant effect on microstructural development, the distribution of nanoparticles, wettability at the interface, and intermetallic compound formation (Al3Mg2 and Al12Mg17). Aluminum solid solution, MgZn2, Magnesium/Aluminum/Zinc Intermetallic Compounds and Magnesium were the much important Compounds in the nugget zone. The best joint with the highest tensile strength and elongation percentage of 182 MPa and 1.5%, respectively, was made at transverse speed of 45 mm/min and rotation speed of 750 rpm with presence of Titanium carbide particles and Zinc interlayer material. Meanwhile, the hardness of 185 Hv with relative ductile fracture was detected for the optimized weld sample.

Investigation of the Effect on the Mechanical Properties of Gun Body Produced from Three Different Alloy Steel by Hot Forging Method at Three Different Temperatures

Forging production method is a preferred production method compared to other production methods in terms of high mechanical properties of the product. In the forging production method, production can be made using materials of different qualities. In addition, one of the areas of interest in the forging sector in recent years is the studies on the malleability of alloy steels. The use of alloy steels can show superior properties especially in terms of strength and machinability. In this study, gun bodies were produced from three different alloy steels (41Cr4, 42CrMo4 and AISI420) at different forging temperatures (800°C, 950°C and 1250°C). Hardness, microstructure, notch impact, tensile test and SEM examinations were carried out by taking samples from the gun body and their effects on mechanical properties were investigated. The data obtained as a result of the experiments were verified by microstructure and SEM examinations.

Nitrogen diffusion along the layer boundaries after nitriding of multilayer materials

Diffusion processes play a key role in formation of the structures of new materials and technological processes of strengthening heat treatments, since diffusion is the reason for redistribution of substances in solids. An urgent task is to develop technologically advanced and effective methods for strengthening materials in order to improve their performance properties. There is an increasing need to improve chemical heat treatment methods, which directly affects the wear resistance of working surfaces, and, consequently, the product service life. Near-surface volumes experience increased loads, so the formation of high-strength layers becomes an important task. Quite a few methods of surface hardening are known, among which carburization, nitriding, nitrocarburization and others are widely used. The most interesting is nitriding, since it increases hardness, strength, fatigue limit, and heat resistance. However, despite the proper advantages, nitriding has a number of disadvantages, including the holding duration and small thickness of diffusion layers. The solution is related to intensification of the technological process by increasing the nitriding temperature, activating the nitriding media or directly the parts surface. All these solutions are aimed at accelerating diffusion processes, both in grain volume and along grain boundaries, the velocity along which is many times higher than the velocity of volumetric diffusion. It may be effective to use a new type of structural metal materials with a multilayer structure of hundreds of layers, with thicknesses in the micron and submicron ranges separated by large angular boundaries. The results of metallographic studies showed the effect of the steel layers interchange in the multilayer metal material on diffusion depth after chemical heat treatment. The authors proposed an accelerate diffusion model of diffusible element along the layer boundaries.

Additive manufacturing of a low modulus biomedical Ti–Nb–Ta–Zr alloy by directed energy deposition

While β titanium alloys have garnered extensive attention as a new generation of biomedical materials designed to mitigate stress shielding due to their low modulus, the realm of additive manufacturing for these alloys is still in its nascent stages. This study focuses on the additive manufacturing of Ti–35Nb–5Ta–7Zr alloy powder via directed energy deposition (DED). The primary objectives were assessing the feasibility of employing DED for this alloy powder and identifying processing parameters to achieve nearly dense components. Systematic exploration of the effect of various processing parameters was performed, and the resultant impact on the densification of the produced specimens was studied. Comprehensive analysis of the microstructure, mechanical properties, electrochemical behavior, and cell studies of fully dense sample coupons were performed. These fully dense samples were found to exclusively comprise the β phase of titanium, resulting in a reduced modulus of elasticity (approximately 44–47 GPa) resulting in high yield strength to elastic modulus ratio. Microstructural examinations revealed the presence of both columnar and equiaxed dendrites, with grains transitioning from columnar to equiaxed (known as CET). Electrochemical testing of the coupons indicated exceptional corrosion resistance in the additively manufactured TNZT alloy. Pre-osteoblasts cultured on the alloys showed good attachment, viability, and growth to confirm cytocompatibility. These findings unveiled the attainment of high strength, favorable ductility, a low elastic modulus, excellent corrosion resistance, and cytocompatibility in dense samples created via DED of Ti–35Nb–5Ta–7Zr. These outcomes hold immense significance for the production of patient-specific medical implants manufactured from β-Ti alloys.

Mechanical and microstructural characterisation on the effect of increasing tool rotational speed of friction stir welded AZ31-B magnesium alloy

ABSTRACT This article intends to deliver the mechanical and microstructural characterisation of the impact of increasing the tool rotational speed on friction stir-welded similar AZ31-B magnesium alloy. The variable tool rotational speeds of 1000, 1200, 1400, and 1600 rpm with a fixed tool traverse speed of 30 mm/min were chosen based on the trail welding method. The macrostructural examination reveals that the lower tool rotational speed of 1000 rpm produced micro tunnel defects due to insufficient heat input, which causes less material intermixing. The microstructural examination shows finer grain size values when increasing the tool's rotational speed for 1000 rpm (12.5μm), 1200 rpm (9μm), 1400 rpm (7μm), and 1600 rpm (7.6μm). The tool rotational speed of 1400 rpm produced a defect-free welded joint with a higher tensile strength value of 215 MPa and a higher hardness value of 74 HV. Fractography analysis reveals all four welded samples were ductile fractured at an angle of 450. The higher welded joint efficiency of 78% was attained at the 1400 rpm welded parameters and the lower efficiency of 48% was achieved at the tool rotational speed of 1000 rpm.

Synergistic Effect of B4C and Multi-Walled CNT on Enhancing the Tribological Performance of Aluminum A383 Hybrid Composites

The requirement for high-performance and energy-saving materials motivated the researchers to develop novel composite materials. This investigation focuses on utilizing aluminum alloy (A383) as the matrix material to produce hybrid metal matrix composites (HMMCs) incorporating boron carbide (B4C) and multi-walled carbon nanotube (MWCNT) through a cost-effective stir casting technique. The synthesis of HMMCs involved varying the weight fractions of B4C (2%, 4%, and 6%) and MWCNT (0.5%, 1%, and 1.5%). The metallographic study was carried out by field emission scanning electron microscopy (FESEM) mapped with EDS analysis. The results indicated a uniform dispersion and robust interfacial interaction between aluminum and the reinforced particles, significantly enhancing the mechanical properties. Micro-hardness and wear characteristics of the fabricated HMMCs were investigated using Vickers microhardness testing and the pin-on-disc tribometer setup. The disc is made of hardened chromium alloy EN 31 steel of hardness 62 HRC. The applied load was varied as 10N, 20N, 30N with a constant sliding speed of 1.5 m/s for different sliding distances. The micro-hardness value of composites reinforced with 1.5 wt% MWCNT and 6 wt% B4C improved by 61% compared to the base alloy. Additionally, the wear resistance of the composite material improved with increasing reinforcement content. Incorporating 1.5% CNT and 6% B4C as reinforcements results in the composite experiencing about a 40% reduction in wear loss compared to the unreinforced aluminum alloy matrix. Furthermore, the volumetric wear loss of the HMMCs was critically analyzed with respect to different applied loads and sliding distances. This research underscores the positive impact of varying the reinforcement content on the mechanical and wear properties of aluminum alloy-based hybrid metal matrix composites.