Scanning Electron Microscopy Fractography Research Articles

Strain-rate sensitivity analysis of microwave processed polypropylene-carbon nanotube composites

The study investigates the strain rate sensitivity of microwave-processed polypropylene nanocomposites containing a 10% volume fraction of multi-walled carbon nanotubes (MWCNTs), synthesized using a domestic microwave applicator (DMA). Through experimental analysis under various loading conditions including tensile, flexural, and multistep relaxation loads, the mechanical strength of these nanocomposites is assessed alongside destructive testing and scanning electron microscopy (SEM) results. Mathematical models are proposed to elucidate the mechanical response under different strain rate loadings. The nanocomposite exhibits elastoplastic behavior, with maximum elongation observed at a strain rate of 3 mm/min. During uniaxial tension tests, the ultimate strength increases significantly from 5.74 MPa at 1.52 mm/min to 13.8 MPa and 15.7 MPa at 1 mm/min and 2 mm/min respectively during multistep relaxation tests. The true stress-true strain curve follows a power law of strain hardening under high strain rate tensile tests. Flexural tests reveal maximum flexural strength and modulus at a strain rate of 1.25 mm/min, with elongation peaking at 1.50 mm/min. Mechanical properties, including modulus and ultimate strength, show an increasing trend with strain rate until a limiting value is reached, beyond which thermal softening occurs. SEM fractography illustrates the random and spatial distribution of CNTs at low strain rates, whereas agglomeration and CNT pull-out are observed at higher strain rates. This comprehensive analysis sheds light on the intricate mechanical behavior of microwave-processed polypropylene nanocomposites, offering insights into their potential applications and optimization strategies.

Insights into the dynamic impact behavior of intercritically annealed automotive-grade Fe–7Mn–4Al −0.18C steel

Recently, medium manganese steels (MMnS) have been developed due to their excellent strength and improved ductility to meet automotive manufacturer demands. However, research on the impact toughness of automobile parts developed from these steels needs considerable attention to meet safety standards. Therefore, the present investigation focuses on the effect of annealing time (30, 60 and 180 min) on the impact behavior of intercritically annealed (750 °C) Fe–7Mn–4Al-0.18C (wt. %) steel. The microstructure of intercritically annealed steel, as revealed by scanning electron microscopy (SEM) and transmission electron microscopy (TEM), consists of blocky and lath-type reverted austenite (RA), fine intercritical ferrite (IF), lath-type martensite (M) and coarse elongated ferrite (EF). The impact toughness of the samples is evaluated at room temperature using a Zwick/Roell HIT450P Charpy impact machine. The sample annealed for 60 min absorbs the highest amount of impact energy among the three annealed samples. This is due to an increased volume fraction of RA, the transformation-induced plasticity (TRIP) effect, and an increase in the fraction of high angle grain boundaries (HAGBs). The microtexture analysis reveals that the presence of γ-fiber {111}//ND texture in ferrite and Rotated Goss texture {011} <011> in austenite contributes to the improved impact toughness in the specimen annealed for 60 min. The SEM fractographs of the sample annealed for 60 min exhibit crack branching and larger dimple size with inhomogeneous dimple distribution indicating higher energy absorption during crack initiation. Martensitic transformation nucleation sites are activated by a high volume fraction of RA in the sample annealed for 60 min, leading to increased impact toughness and the development of secondary cracks. In addition, the impact energy decreases when the sample annealed for 60 min is subjected to an impact test at temperatures lower than room temperature.

Optimized PCL/CNF bio-nanocomposites for medical bio-plotted applications: Rheological, structural, and thermomechanical aspects

The use of bioabsorbable and biodegradable composites in the medical field has experienced significant growth. Cellulose nanofibers (CNF) have been employed to reinforce medical-grade poly[ε-caprolactone], enhancing both its load-bearing capacity and stiffness compared to pure polycaprolactone PCL. The manufacturing process involved a series of steps applied to five different grades of PCL/CNF filaments. Initially, melt extrusion and pelletization were performed on the filament, followed by 3D bioplotting to create the specimens. The influence of CNF reinforcement on poly[ε-caprolactone] was evaluated through a range of tests, including rheological, thermomechanical, and in situ micromechanical assessments. To further characterize the samples, Micro-Computed Tomography and Scanning Electron Microscopy fractography were employed for the microstructural and morphological analyses, respectively. The mechanical properties of poly[ε-caprolactone]/CNF composites with 6 wt % CNF content exhibited a 23.8% increase in tensile strength and a 19.1% increase in flexural strength compared to the pure matrix, while also displaying minimal porosity.

Electrophoretically Deposited Multiscale Graphene Oxide/Carbon Nanotube Construct Mediated Interfacial Engineering in Carbon Fiber Epoxy Composites.

Fiber-reinforced polymer composites as a structural material have garnered tremendous interest over the past few decades. In particular, carbon fiber-reinforced epoxy (CFRE) laminates have seen extensive use in the aircraft and aerospace industry. The role of the interface between the matrix and fiber is critical and dictates the overall structural properties of the CFRE laminate. Herein, we attempt to use a commercially viable, green, and facile approach, electrophoretic deposition (EPD), to deposit covalently coupled multiscale graphene oxide (GO)/carbon nanotube (CNT) nanoconstructs onto carbon fiber (CF) fabric. The rationale behind using these hybrid conjugates is to exploit the positive synergistic effect of combining two-dimensional (2D) GO and one-dimensional (1D) CNT nanoparticles, which provide strengthening through different mechanisms resulting in a stronger matrix/fiber interface. The modified laminate with just 0.1 wt % GO/CNT content exhibited an improvement in flexural strength (FS) by 24% and interlaminar shear strength (ILSS) by 30% compared to the neat CFRE. Scanning electron microscope (SEM) micrographs confirmed uniform and homogeneous GO and GO/CNT deposition on CF. Raman, Fourier-transform infrared spectroscopy (FTIR), and X-ray photoelectron spectroscopy (XPS) analyses validate the successful functionalization of CNT and covalent coupling of GO and CNT. Atomic force microscope (AFM) and contact angle analyses indicate improved interaction between the CF and matrix. The deposition of the GO/CNT nanoconstruct on the CF improved the performance of CFREs owing to enhanced wettability, surface free energy, and surface roughness, leading to increased mechanical interlocking between the epoxy and CF at the interface. Dynamic mechanical analysis showed decreased segmental motion of epoxy chains due to improved interfacial adhesion following modification. Interesting observations were made in SEM fractography, which showed considerably different failure mechanisms in the modified CFREs. Electromagnetic interference (EMI) shielding effectiveness of -45 dB was achieved in the case of the GO/CNT-CFRE system. Electrothermal heating and de-icing performance of the modified system were also explored in this study. This versatile approach can open up new avenues for CFRE modification leading to considerably improved performance.

Cost-effective bi-functional resin reinforced with a nano-inclusion blend for vat photopolymerization additive manufacturing: The effect of multiple antibacterial nanoparticle agents

Herein, a blend of nanoparticle (NP) inclusions has been arranged at various loadings into a photosensitive resin, while bi-functional three-dimensional (3D) printed specimens were fabricated through a vat photopolymerization process, to elucidate physicochemical mechanisms and synergistic effects, over the filler loading. Energy-dispersive X-ray spectroscopy (EDS), Raman, and thermogravimetric analysis (TGA) revealed the chemical/spectroscopic and thermal properties of the fabricated specimens. Scanning Electron Microscopy (SEM) and Atomic Force Microscopy (AFM) depicted the surface morphology, while SEM fractography demonstrated the morphology of tensile test specimens’ fractured surfaces. Mechanical tests exhibited a strong reinforcement mechanism. The highest reinforcement of 20.8% in the tensile strength is reported for the 2 wt.% nanocomposite. All the prepared recipes exhibited a boosted antibacterial performance, as was documented via a screening agar well diffusion method. The research herein leads towards a novel generation of low-cost bi-functional materials for 3D printing bioactive applications, where mechanical reinforcement and antibacterial performance are required in the operational environment.

Synthesis of microcrystalline cellulose from abaca nonfluorescent flower pistil and its twill weaved fiber‐polyester composites: Viscoelastic, fatigue, and mechanical properties

AbstractThe development of microcrystalline cellulose from banana flower pistil and its twill weaved woven abaca polyester composites were studied in this research. The aim of this research was to explore the viscoelastic, fatigue, and mechanical behavior of surface‐treated twill weaved abaca fiber and unsaturated polyester incorporating banana flower pistil cellulose particles for various composite combinations. Hand layup process was used to construct the bio‐composite laminates, which were then tested in accordance with american society for testing and materials (ASTM) standards. The maximum tensile strength and modulus, flexural strength and modulus, Izod impact strength, as well asinter laminar shear strength (ILSS) values by addition of 3.0 vol% of cellulose were about 124 MPa, 4.48 GPa, 163 MPa, 5.36 GPa, 5.33 J/m2, and 27 MPa respectively, whereas composite having 5.0 vol% of cellulose gave better hardness of 82 shore‐D. Incorporation of cellulose by 3.0 vol% with 50 vol% of abaca fiber increases fatigue life counts up to 35,480, 29,039, 24,802, and 18,247 for 25%, 50%, 70%, and 90% of ultimate tensile strength (UTS) respectively. On comparing all other composite combinations, the composite containing 3.0 vol% of cellulose shows the highest storage modulus of up to 5.6 GPa and the lowest loss factor of 0.38. The scanning electron microscopy (SEM) fractography shows the improved adhesion between fiber and matrix due to the silane treatment on cellulose and abaca fiber. These novel functional materials could be employed in a large range of applications, including industrial, automobile, electronic and household equipment.

Imidazoline behavior as corrosion inhibitor in the electrochemical characterization of SCC behavior of an API X70 steel exposed to brine solution

Abstract The effect of concentration of an organic imidazoline as inhibitor on internal stress corrosion cracking (SCC) behavior of an API X70 pipeline steel exposed to a brine solution was studied. The SCC process using simultaneously the slow strain rate stress test (SSRT) and electrochemical measurements was performed. Fracture surface analysis and secondary cracking were observed through a scanning electron microscopy (SEM). According to SEM fractography and SSRT results, the steel showed high SCC susceptibility with a brittle fracture and several secondary cracks without addition of inhibitor, whereas the addition of inhibitor to brine solution was effective to increase the SCC resistance of steel at concentrations of inhibitor of 50 and 100 ppm. A further addition of concentration of inhibitor had a negative effect on the mechanical properties of the steel. Electrochemical measurements results are in accordance with the SCC susceptibility, indicating that corrosion inhibitor film suppressed the anodic and cathodic reactions increasing the resistance to SCC until concentration of 100 ppm. Further addition of inhibitor aggravated the localized corrosion due to local desorption of inhibitor molecules. The Hilbert–Huang transform (HHT) analysis revealed the contribution of different corrosion process contained in the electrochemical current noise (ECN) signals at several inhibitor concentrations.

Development of highly conductive hybrid Ni‐biocarbon‐based polyvinyl alcohol composites for microwave shielding properties

AbstractIn this study a highly flexible microwave shielding material was fabricated by solution casting method utilizing Nickel and biocarbon particles in PVA matrix and characterized for mechanical, magnetic, and microwave shielding properties. The main aim of this study was to prove the significant role of magnetic particles in electromagnetic interference (EMI) shielding along with conductive particles. The results show that the addition of Ni‐biocarbon hybrid particle increases the shielding properties up to 56.5 dB at 20 GHz. The magnetic permeability increased gradually with the inclusion of Ni particles with a highest magnetization, coercivity, and retentivity of 1250 E−6 emu, −9000 G, and 1100 E−6 emu. Similarly the mechanical results show that adding biocarbon enhances the composite's mechanical properties. A highest tensile strength, tear strength, elongation, and hardness are noted as 38, 168 MPa, 18.4%, and 36 Shore‐D. Comparatively, the hardness and elongation% of composite designations contains 3 and 5 vol% of hybrid particles have increased by 9% and 26%, respectively, in comparison to composite containing only 5 vol% of biocarbon with PVA. Scanning electron microscope fractography indicates biocarbon particles reduce voids and improve adhesion. These flexible EMI shielding composites could be used in telecommunication and other wave transmitting devices in engineering applications.

Impact of ultrasonic vibration power and tool pin profile on mechanical and microstructural behaviour of friction stir welded dissimilar aluminium alloy joints

PurposeThe purpose of this paper is to investigate the impact of ultrasonic vibration (UV) and tool pin profile on mechanical properties and microstructural behaviour of AA7075-T651 and AA6061-T6 joints was analysed.Design/methodology/approachThe joints were fabricated using three different tool pin profiles such as cylindrical, square and triangle. For each tool pin profile, two different UV powers of 1.5 kW and 2 kW were used.FindingsOn both the advancing and retreating sides of the weld, the thermo-mechanically affected zone has the lowest microhardness. In all joints, the tensile fracture locations match to the minimum hardness values. Field emission scanning electron microscope fractography of tensile tested specimens reveals heterogeneous modes of brittle, shear and ductile fracture. Three-point bending analysis was performed to determine the ductility and soundness of the weld joint. The acoustic softening effect of UV, as well as the static and dynamic ratio of tool pin profile, plays an important role in determining the material flow and mechanical behaviour of the joint.Practical implicationsDissimilar aluminium joining fascinates many applications like aircraft, aerospace, automobiles, ship building and electronics, where fusion welding is a very intricate process because of the deviation in its physical and chemical properties.Originality/valueFrom this study investigation, it is found that the square pin profiled tool with 2 kW UV power produces metallurgical defect-free and mechanically sound weld with maximum tensile strength, hardness and bending load of 297 MPa, 151HV and 3.82 kN, respectively.

Quasi-ductile to brittle transitional behavior and material properties gradient for additively manufactured SLA acrylate

• Quasi-ductile to brittle transitional behavior investigation of SLA acrylate. • Low curing energy leads to a ductile behavior and clean fracture surface. • High curing energy promotes a brittle behavior and rough fracture surface. • UV-curing creates a thickness-dependent material properties gradient. • Strain rate sensitivity is both a curing- and thickness-dependent variable. This research investigates the correlation between post-curing conditions, thickness, stress–strain, and fracture behaviors of additively manufactured SLA acrylate polymer, utilizing tensile tests and scanning electron microscopic fractography analysis. Due to poor polymerization, low curing energy resulted in a quasi-ductile behavior and low strain rate sensitivity. In contrast, high energy promotes the redistribution of the fracture energy from failure strain to failure stress, leading to increased sensitivity. Furthermore, poorly cured specimens show clean fracture surfaces, contrasting with their quasi-ductile behavior, whereas highly cured specimens present rough surfaces, generally associated with ductile fracture. Therefore, increasing curing energy promotes a transition from a quasi-ductile to an almost perfectly brittle behavior and influences the material's elastic, plastic, and fracture behaviors, which appear to be non-uniform throughout the thickness, especially for thicker structures.

Parameter optimization of FSW aviation-grade AA8090 using Taguchi grey relational analysis

PurposeThis paper aims to accomplish friction stir welding (FSW) of Al–Li alloy AA8090 to determine optimal settings of the process parameters for higher tensile strength and higher micro-hardness (MH) to achieve the objective of adequate butt-joint strength.Design/methodology/approachAn empirical relation is implemented to govern the utmost influence parameters, i.e. tool rotation speed (TRS), tool transverse speed (TTS) and dwell time (DT). Taguchi grey relational analysis (GRA) was applied for multi-response optimization of response parameters. The grey relational grades (GRs) have been calculated for both the responses MH and ultimate tensile strength to get optimal parametric settings. The variance test has been performed to check the adequacy of the model.FindingsThe Taguchi L9 orthogonal array design was used in establishing the relation between input parameter and output parameter (tensile and MH). TTS and DT have been predicted to be the two most important parameters that influence the extreme quality features of joints by using friction stir welding. Scanning electron microscopy fractography shows the ductile failure of the welded joints.Originality/valueThe experimental trials provided the followings results, maximum ultimate tensile strength (UTS) of 219 MPa and MH 107.1 HV under 1,400 rpm of TRS, 40 mm/min of TTS and 8 s of DT founded the optimum value through GRA.

Fatigue life, distortion behavior of AA 8011- nano B4C composite using simulated acoustic emission technique – An experimental and statistical appraisal

The high quality AA8011 aluminium alloy dispersed with different percentages of nano-sized B4C (0, 0.5,1 and 1.5 wt%) was fabricated by electromagnetic frequency high energy stir casting technique. The characterization study on metal matrix nanocomposites (MMNC) using Field Emission Scanning Electron Microscope (FESEM), Energy Dispersive Spectrum (EDS), and X-ray Diffraction (XRD) confirmed the morphology and distribution of AA8011 with nano B4C. The microhardness analysis and strength using Vickers hardness testing and Electromechanical Universal Testing Machine, respectively, show significant mechanical properties improvement. The ductility study on Scanning Electron Microscope (SEM) images of the fractured samples reveal the transition from ductile to brittle nature in MMNCs. The online monitoring using Acoustic Emission (AE) during a tensile test indicates the mitigation in crack generation and its propagation. The substantial enhancement in fatigue life by the addition of nano B4C was evidenced by testing at a stress ratio (R = 0.1) and statistically significant (at p < 0.05) by one way Analysis of Variance (ANOVA). The SEM Fractography of fractured fatigue samples discloses the influence of dispersal of nano-sized reinforcements which resist fatigue crack growth. The result demonstrates that AA8011-1.5 % nano B4C composite has improved hardness, higher tensile strength and fatigue strength than the pure matrix due to the addition of the B4C.

Influence of high-intensity horizontal mould vibration on the density, grain refinement and mechanical characteristics of a die cast aluminium alloy (LM21)

The present investigation analysed the effect of mould vibration using an indigenous vibrating setup on the physical, metallurgical and mechanical properties of die cast A308 alloy. The alloy was vibrated at a constant amplitude of 31µm at 75, 100, 125 and 150 Hz. The work aims to generate more nucleation sites during melt solidification by fragmenting dendrites and Si particles. To examine the changes in metallurgical characteristics, α-Al, secondary dendritic arm spacing, length, width and aspect ratio of eutectic Si particles were studied using optical microscopy, scanning electron microscopy and X-ray diffraction analysis. It was observed that the size of α-Al, secondary dendritic arm spacing, length, width and aspect ratio of eutectic Si particles were decreased by 47%, 53%, 65%, 12% and 61%, respectively. Whereas, the shape factor and density of the alloy were enhanced by 25% and 1.62% compared to stationary cast samples because of mechanical vibration treatment at an optimum frequency of 100 Hz. Mechanical testing findings demonstrated a 13%, 20%, 15% and 20% increase in the parameters such as yield strength, ultimate tensile strength, percentage elongation and microhardness at 100 Hz when compared to the stationary cast sample. Grain refinement, uniformity of structure, improvement in the morphology of metallurgical characteristics, decreased porosities and subsequent increase in density were all factors that contributed to the improvement. Tensile test samples with scanning electron microscopy fractography demonstrated transgranular brittle fracture and a few ductile rips.

Effects of neutron irradiation and post-irradiation annealing on pop-in crack propagation instabilities in 6061 aluminium alloy

This study analyses the increase of crack propagations instabilities (pop-in) with irradiation during fracture toughness testing of aluminium alloy 6061 alloy after neutron irradiation. The aim is to identify if the crack propagation instabilities are related to microstructural heterogeneities, i.e. weak zones, or if they are linked to a competition between testing machine stiffness and tearing modulus.An in-depth mechanical instability analysis was performed comparing the testing machine stiffness to the tearing moduli of the irradiated materials. For this purpose an experimental program was carried out in the hot cells facility at CEA Saclay to conduct mechanical and microstructural studies, after irradiation in a Material Testing Reactor (mean conventional thermal fluence: 6.8 × 1021 nth.conv.cm−2).The material hardening was quantified in this study using tensile tests after annealing heat treatments. The effect of this hardening on crack propagation instabilities was measured by fracture toughness tests on irradiated and precracked CT12.5 samples. Damage mechanisms were studied by scanning electron microscope fractography and classical ductile fracture micromechanisms were found for all conditions without notable differences between non irradiated and irradiated materials. The evolution of toughness with irradiation and subsequent heat treatments was therefore attributed to the matrix hardening/softening and its effect on nucleation of voids on brittle second phase particles.To investigate experimentally if the crack propagation instabilities were related to the tearing moduli, annealing heat treatments of the irradiated material were applied that softened the material. It was shown that with softening, the number of crack propagation instabilities decreased and eventually the pop-ins disappeared. The instability criteria using J-Δa R-curves of the toughness tests were applied and it was concluded that the increase in pop-ins with irradiation resulted from the decrease of the material tearing modulus and its interaction with the machine stiffness.The toughness test results of the irradiated material of the present study were compared with those of the literature and show very good agreement.

Novel Sustainable Castor Oil-Based Polyurethane Biocomposites Reinforced with Piassava Fiber Powder Waste for High-Performance Coating Floor

The search for new greener materials that contribute to a more sustainable world motivated the present study in which novel biocomposites with 10, 20 and 30 vol% of piassava fiber powder waste reinforcing castor oil-based polyurethane (COPU) intended for a high-performance coated floor (HPCF) were developed. The novel biocomposites were characterized by flexural, Izod impact and wear standard tests as well as Fourier transform infrared spectroscopy (FTIR) and fracture analysis using scanning electron microscopy (SEM). Both flexural modulus and strength displayed marked increases reaching more than 800 and 500%, respectively, compared to plain COPU for 30 vol% piassava powder incorporation. FTIR bands indicated the existence of interaction between the piassava constituents and COPU. However, SEM fractographs disclosed the presence of bubbles attributed to retained gases during the COPU curing. Consequently, the Izod impact resistance showed a 50% decrease while the wear was more than three times accentuated for 30 vol% piassava powder biocomposite. These results met the specified values of corresponding standards and revealed a promising new greener material for HPCFs.

A study on the creep behavior of alloy 709 using in-situ scanning electron microscopy

In this research, an experimental evaluation of creep properties of Alloy 709 in the temperature range of 750–850 °C was undertaken. Alloy 709 is a novel austenitic stainless steel with 20% Cr and 25% Ni by wt% that was developed for application in structural components of nuclear power plants. Creep rupture tests were conducted in an in-situ heating-loading and Scanning Electron Microscope (SEM) unit equipped with Electron Backscatter Diffraction (EBSD) detector and Energy Dispersive Spectroscopy (EDS). “Real-time” creep damage mechanisms of Alloy 709 at various stresses and temperatures using a flat, un-notched sample with continuously reducing cross-section is studied so that the failure and maximum creep damage occurred at the center of the sample where the in-situ SEM imaging could be focused. Accelerated creep tests at temperatures and stresses above service conditions were performed by employing multiple blocks of constant loads where the loads were increased once the sample attained constant creep rate, indicating a secondary creep regime. This technique ensures multiple data points can be obtained from the same test, saves the time required for an otherwise long-term creep test and usage of SEM. Coincident Site Lattice (CSL) boundary maps were collected as control maps before testing, and the grain boundaries were observed during the creep test to understand the effect of grain boundary character on the creep damage mechanism. Void growth, grain boundary separation, and sliding were found to be the main creep mechanisms whose rate is dependent on stress and temperature. Failure mechanisms studied on the fracture surface using SEM fractography were correlated to the sample surface observations to create complementary information to better understand the underline creep mechanism of Alloy 709.

INVESTIGATION ON DRY SLIDING WEAR BEHAVIOR OF TITANIUM DIOXIDE-REINFORCED MAGNESIUM MATRIX COMPOSITE

In this work, the dry sliding wear behaviors of pure monolithic magnesium and magnesium–titanium dioxide (Mg–TiO2) composites were studied using pin-on-disc tribometer against an oil-hardened nonshrinking die steel (OHNS) counter-disc with a normal load of 0.5–2[Formula: see text]kg and a sliding velocity of 1.5–2.5[Formula: see text][Formula: see text] with the sliding distance and wear track diameter of 1500[Formula: see text]m and 90[Formula: see text]mm, respectively. The pin samples were characterized for their microstructural, nanomechanical and tribological properties such as wear rate, coefficient of friction and wear fractographs. Scanning electron microscopy (SEM) was used to analyze the worn-out surfaces of each pin sample in order to identify the different types of wear and wear mechanisms and the chemical constituents of each element were quantified by energy-dispersive spectroscopy. The influence of TiO2 reinforcements on the nanomechanical behavior was studied by nanoindentation technique. As compared with pure Mg, the nanoindentation strengths of Mg–1.5TiO2, Mg–2.5TiO2 and Mg–5TiO2 composites were found to increase by 11.9%, 22.2% and 35.8%, respectively, which was due to the addition of TiO2 particles and also due to the good bonding at the interface of TiO2 and magnesium particles. From the wear test results, a significant change in wear rate was observed with the change in normal load than that of sliding speed, whereas a significant change in coefficient of friction was noticed with the changes in both normal load and sliding velocity. The dominant wear mechanisms involved under the testing conditions were identified through plotting the contour maps and SEM fractographs. Also, from the fractographs it was noticed that delamination and plowing effect have been the significant wear mechanisms observed during low wear rate of samples, whereas melting, delamination and oxidation wear have been observed during high wear rate of pure Mg and its composites.

Effect of multipass cold plastic deformation and heat treatment on the mechanical properties of C250 marageing steel for aerospace applications

The present investigation is aimed to reduce the cost of production of various components fabricated by using cold rolled C250 marageing steel in the aerospace applications like landing gears of aeroplane and spacecraft. As cast C250 marageing steel was forged and solution annealed as per the specification of the customer. Forged C250 steel was cold rolled from 15 to 300%. Microstructure analysis revealed that grains got refined and elongated in the direction of cold working. Cold drawing increases the hardness, tensile strength and yield strength. However, loss in ductility and impact strength was observed. Scanning electron microscope fractographs of tensile and impact samples showed elongation of the dimples in cold working direction. The increase in cold working reduces the size of dimples indicating the transformation of fracture nature from the ductile-to-brittle regime. At higher cold working, &gt;170% led to intergranular tearing and resulted in a loss of impact and mechanical properties of the steel. Further, cryogenic treatment of cold rolled C250 steel delayed ageing causing increase in tensile and yield strength with a marginal loss in ductility. The cost estimation of C250 steel revealed a significant cost saving (Indian Rupees [INR] 7500/1000 kg) for components made from different diameters of cold rolled steel over the solution annealed steel.

Analysis of the Root Causes of Damage to the Edges of Tank Manholes on the Main Deck of Handy-Size Bulk Carriers.

This study analyzes the root causes of cracks in the deck plating around tank manholes. Four handy-size bulk carriers built in one shipyard were analyzed. In all cases, deck cracks were found near manholes, and the average time from the commencement of operation until the occurrence of cracks was 1356 days. Due to this short wear-life of the vessel’s structural material, the authors believed that it was unlikely to be caused by corrosion fatigue. The authors hypothesized that main decks cracked around manholes because of very poor-quality welded joints and poor-quality steel (large amounts of non-metallic impurities) used to make the manholes. In order to verify this hypothesis, on each of the vessels, material samples were collected from near the cracks and then examined thoroughly. Each sample was subjected to the macroscopic examination of the natural surfaces of cracks and their vicinity, microscopic examination of the material, mechanical property tests, and scanning electron microscope fractography for samples obtained after impact tests. The examination and test results were used to draw detailed conclusions for each case study. The general conclusions based on examination of the whole damage population validated the authors’ hypothesis that main decks cracked around manholes because of very poor-quality welded joints and poor-quality steel used to make the manholes.

CVN impact energy and fracture characteristics correlations with different oxide nanoparticles improving submerged arc welds

The main aim of this research is to correlate the toughness improvement with fracture features of tested Charpy V-Notch impact specimens obtained from submerged arc welds enriched by different oxide nanoparticles (TiO2, SiO2, Al2O3 and Mn2O3). Through Scanning Electron Microscopy (SEM) fractography, fracture features were determined, which are the shear fracture percent, the loading angle, as well as the diameter of dimples and the width of cleavage sheets at ductile and brittle fracture regions, respectively. It was observed an increase of the Charpy V-Notch impact energy with the decrease of loading angle and the average diameter of dimples, as well as with the increase of its shear fractures percents. Moreover, it was correlated the increase of Acicular Ferrite surface density with the decrease of width of cleavage sheets. Thus, the toughness of the submerged arc welds can be improved by adding TiO2, SiO2, Al2O3 or Mn2O3 nanoparticles.