Cross-sectional Morphology Research Articles

Effect of beam oscillation frequency on porosity in laser welding of aluminum alloy lap-butt joints

Many investigations into laser oscillations for mitigating severe porosity in aluminum alloys have involved trading off penetration depth, potentially disrupting the porosity suppression mechanism. In this study, an oscillation laser butt-lap welding technique was designed, and the effect of oscillation frequency on cross-section morphologies and porosity rate was investigated while maintaining the constant weld depth. The findings unveiled that heightened oscillation frequencies led to diminished porosity levels, and this pattern remained consistent, even in cases where weld depths were extended. High-frequency laser beam oscillation enhanced the stability of the keyhole, increased the duration of the molten pool existence, and reduced porosity to 0.17%. Thus, this study offered significant insights into the impact of oscillation on laser welding of aluminum alloys.

Mechanical octacalcium phosphate coatings on the plasma electrolytic oxidized pure titanium for bio-implant use

In this study, OCP powder was used for mechanical coating on the plasma electrolytic oxidized (PEO) implant surface to improve bioactivity. PEO treatment was performed on the surface of the implant using a solution mixed with calcium acetate and calcium glycerophosphate, and creates porosity through a pulsed DC power supply. For compositional analysis, energy dispersive X-ray spectrometer analysis was employed to calculate OCP content and X-ray diffractometer analysis was used to confirm the crystal structure. Also, wettability, surface roughness, hardness, elastic modulus, and corrosion resistance testing were performed. Significantly, the reduction in OCP particle size decreased, and pore filling with OCP smaller particles increased as mechanical coating time increased from 0 to 12 h. Surface and cross-sectional morphology showed the presence of OCP on the substrate. Also, surface roughness, contact angles, hardness, and elastic modulus were reduced as mechanical coating time increased. Corrosion resistance was found to be the highest for mechanical OCP coating for 6 h surface treatment on the PEO-treated CW-Ti.

Influence of Anodic Oxidation on the Organizational Structure and Corrosion Resistance of Oxide Film on AZ31B Magnesium Alloy

Magnesium alloys, notably AZ31B, hold promise for lightweight structural applications in the aerospace, automotive, and biomedical sectors due to their excellent strength-to-weight ratios. The broad adoption of these alloys, however, is hindered by their inherent susceptibility to corrosion, reducing durability and functional integrity in corrosive environments. This study explores anodic oxidation as a viable surface treatment to improve the corrosion resistance of the AZ31B magnesium alloy. Focusing on the impact of oxidation voltage on the oxide film’s structural and electrochemical properties, we aim to optimize these characteristics to enhance the alloy’s utility and lifespan significantly. Through detailed analysis of surface and cross-sectional morphologies, film thickness, phase composition, and corrosion resistance, we identify an optimal oxidation voltage of 17.5 V that notably improves the oxide film’s density and corrosion resistance. Through this research, we contribute to the ongoing efforts to overcome the corrosion vulnerability of magnesium alloys, thereby unlocking their full potential in contributing to more sustainable and efficient technological advancements.

Improved corrosion resistance of AZ31B Mg alloy by eco-friendly flash-PEO coatings

The aim of this work was the preparation of an environmentally friendly protective coating on the AZ31B alloy using Flash plasma electrolytic oxidation (F-PEO) process. It was developed with different electrolyte compositions, that determine the morphology and properties of the coatings, this being crucial to understand the anti-corrosion properties. The incorporation of carbonate ions to the electrolyte proved to enhance the electrical response of the F-PEO process, resulting in a more efficient process with an energy reduced consumption of 1.1 kW h m−2μm−1. Surface and cross-sectional morphology analysis of the coatings revealed the presence of isolated pores structure with small pore size (less than 1 µm) that delays the infiltration of aggressive ions towards the substrate. The characterisation by XRD, EDX and Raman spectroscopy showed the presence of amorphous carbonate and phosphate phases in the FPEO-CO layer, that provide a self-restauration effect through a dissolution/reprecipitation mechanism. The lowest value of the corrosion current density was obtained for FPEO-CO coating, 4.60 × 10−7 A·cm−2, together with the highest impedance modulus (f<0.1 Hz), ⁓104 Ω·cm2, two orders of magnitude higher than the AZ31B Mg alloy. Furthermore, the corrosion protection properties of FPEO-CO coating were also analysed through an immersion test in 3.5 wt.% NaCl, confirming the excellent response of the coating for long times up to 336 h (2 weeks). The synergy between a more compact coating and the self-repairing ability of carbonate amorphous species plays a critical role in improving the corrosion resistance properties of the AZ31B Mg alloy, offering an eco-friendly alternative to chromate conversion coatings.

Mechanically robust and uniform aramid nanofiber films fabricated using repeated spin-coating and protonation processes

Aramid nanofiber (ANF) films show promise for various industrial applications, but their applicability has been constrained by the low mechanical properties, which are mainly due to their incomplete packing and non-uniform microstructure. This work introduces an efficient method for significantly improving the mechanical properties of ANF films using repeated spin coating and protonation. The method allows for the preparation of ANF films with highly uniform microstructures and adjustable thicknesses while achieving excellent mechanical properties. These ANF films have a Young's modulus of 6.8 GPa, tensile strength of 310 MPa and hardness of 248 MPa, surpassing those produced using previous methods. A comprehensive analysis of the surface and cross-sectional morphologies, chemical composition, thermal stability, and mechanical properties was also carried out to characterize the film properties.

A NEW TYPE OF PLUG-IN FRICTION-STIR LAP WELDING BASED ON THE 6061-T6 ALUMINUM ALLOY

In this study a new type of plug-in friction-stir lap welding (PFSLW) is proposed to prepare welded joints based on 4-mm-thick 6061-T6 aluminum alloy sheet. The differences in the cross-sectional morphology, microstructure, cross-sectional hardness and shear properties between the PFSLW joint and the normal friction-stir lap-welding (FSLW) joint are discussed. The results show that the cross-sectional morphology of the PFSLW joint has undergone changes. The PFSLW joint has a mechanical interlocking structure on the advancing side that is beneficial to the connection strength of the joint. The grain structure differs at the boundary between the thermo-mechanically affected zone (TMAZ) and the heat-affected zone (HAZ), and the PFSLW joints show a more pronounced bending deformation of the grain organization near the boundary. The microhardness of PFSLW joints was increased in the TMAZ and HAZ areas, and the lowest hardness is further away from the center of the weld. The failure load of the PFSLW joint has been improved, the microcracks part of the PFSLW joint has a ridge-like structure. In addition, the actual welding width of PFSLW joints was improved.

3D porous structure imaging of membranes for medical devices using scanning probe microscopy and electron microscopy: from membrane science points of view.

The evolution of hemodialysis membranes (dialyzer, artificial kidney) was remarkable, since Dow Chemical began manufacturing hollow fiber hemodialyzers in 1968, especially because it involved industrial chemistry, including polymer synthesis and membrane manufacturing process. The development of hemodialysis membranes has brought about the field of medical devices as a major industry. In addition to conventional electron microscopy, scanning probe microscopy (SPM), represented by atomic force microscopy (AFM), has been used in membrane science research on porous membranes for hemodialysis, and membrane science contributes greatly to the hemodialyzer industry. Practical studies of membrane porous structure-function relationship have evolved, and methods for analyzing membrane cross-sectional morphology were developed, such as the ion milling method, which was capable of cutting membrane cross sections on the order of molecular size to obtain smooth surface structures. Recently, following the global pandemic of SARS-CoV-2 infection, many studies on new membranes for extracorporeal membrane oxygenator have been promptly reported, which also utilize membrane science researches. Membrane science is playing a prominent role in membrane-based technologies such as separation and fabrication, for hemodialysis, membrane oxygenator, lithium ion battery separators, lithium recycling, and seawater desalination. These practical studies contribute to the global medical devices industry.

Effect of bias voltage on the structural properties of WN/NbN nanolayer coatings deposited by cathodic-arc evaporation

In this work, WN/NbN nanolaminate coatings were synthesized by cathodic-arc physical vapor deposition (CA-PVD) technique on a stainless-steel substrate. The paper reports the microstructure, cross-sectional morphology, surface roughness, and adhesion strength changes caused by variations in the absolute values of the negative substrate bias voltage, Us , in the 50-200 V range. Synthesized coatings were analyzed by Grazing incidence X-ray diffraction (GI-XRD), scanning transmission electron microscopy (STEM), scanning electron microscopy (SEM), laser scanning confocal microscopy (LSCM), and Daimler-Benz test. The phase analysis revealed that multilayer coatings had complex polycrystalline microstructure. They consisted of face-cantered cubic (fcc) β-W2N, fcc δ-NbN, and hexagonal ε-NbN phases. The total thickness and surface roughness had a descending trend with an increase in the absolute value of the negative bias voltage. Moreover, the WN/NbN coating deposited at Us = -50 V demonstrated the best adhesion strength to the substrate, suitable for protective coatings.

Structure and mechanical properties of TiCN-ZrCN multilayer coatings

The present study is focused on the design, deposition and characterization of nanoscale multilayer TiCN/ZrCN coatings obtained by cathodic-arc PVD technique. The multilayer coatings with the bilayer period’s thickness of 12 nm, 20 nm and 32 nm were deposited on stainless steel and high-speed steel substrates at temperature of 320°C in a mixture of N2 and CH4 gases. Scanning electron microscopy equipped with energy dispersive x-ray spectroscopy, was employed to investigate the top surface morphology, cross-sectional morphology, bilayer thickness and structure of the coatings. Mechanical properties were investigated via Calotester, Nanoindentation tester, Scratch tester and Tribometer. The SEM/EDS cross-sectional analysis revealed a columnar morphology and well expressed multi-layered periodic structure. All the multilayer samples demonstrated an increase in hardness and well fracture resistance ability in comparison to TiCN and ZrCN monolayer coatings. The highest nanohardness of 41GPa and better wear resistance for the coatings with bilayer period of 12 nm was determined. The results of the study show that a reduction in the thickness of the individual sub-layers has a significant impact on the mechanical properties of the coatings.

Development and evaluation of Bauhinia Kockiana extract-incorporated sago starch intelligent film strips for real-time freshness monitoring of coconut milk

The aim of this work was to fabricate an intelligent film using sago starch incorporated with the natural source of anthocyanins from the Bauhinia Kockiana flower and use it to monitor the freshness of coconut milk. The films were developed using the casting method that included the addition of the different concentrations (0, 5, 10, 15 mg) of Bauhinia Kockiana extract (BKE) obtained using a solvent. The anthocyanin content of Bauhinia Kockiana was 262.17 ± 9.28 mg/100 g of fresh flowers. The spectral characteristics of BKE solutions, cross-section morphology, physiochemical, barrier, and mechanical properties, and the colour variations of films in different pH buffers were investigated. Films having the highest BKE concentration demonstrated the roughest structure and highest thickness (0.16 mm), moisture content (9.72 %), swelling index (435.83 %), water solubility (31.20 %), and elongation at break (262.32 %) compared to the other films. While monitoring the freshness of coconut milk for 16 h, BKE15 showed remarkable visible colour changes (from beige to dark brown), and the pH of coconut milk dropped from 6.21 to 4.56. Therefore, sago starch film incorporated with BKE has excellent potential to act as an intelligent pH film in monitoring the freshness of coconut milk.

Effect of ultrasonic power density on the quality of fresh wet noodles

In order to enhance the production efficiency in the flour products industry by reducing dough resting time, this study investigated the impact of different ultrasonic densities on starch, protein hydration, and gluten network formation in fresh wet noodles using the ultrasound. The sensory quality, secondary structure, and cross-sectional morphology of the dough were also analyzed. Compared to the control group, the results demonstrate that treatment with an ultrasonic power density of 66 W/L improves the texture of wheat dough, as well as the hydration of starch and protein, the hardness of fresh wet noodles decreased by 14.19 %, and tensile force significantly increased by 33.43 %. Furthermore, Fourier-transform infrared spectroscopy (FTIR) analysis indicated a significant increase in the content of α-helix and an overall increase in the content of β-sheet due to ultrasonic vibration treatment. To summarize, the implementation of ultrasonic treatment exhibits promising potential in reducing the resting processing period while concurrently elevating the overall quality of freshly prepared wet noodles. This is primarily achieved by augmenting the texture, heightening the hydration levels of starch and protein constituents, as well as modifying the gluten network structure.

“Cutting effect” of needles on the raindrop characteristics

Plant leaves (both in the canopy and on the land surface) can substantially alter raindrop characteristics, which link to rainfall evaporation, infiltration, raindrop energy, and land surface erosion. The effect varies depending on the leaf morphology. Because of the magnitude difference between needle diameter (∼1 mm) and raindrops (up to ∼8 mm), there should be a “cutting effect” of the needle on falling raindrops. However, no study has beem performed to address how this effect alters raindrop characteristics. In this study, we investigated the effect using artificial water drops, high-speed photography, and staining method in the laboratory. Masson pine (Pinus massoniana Lamb.) needles were collected from the field including fresh green needles (FGN) withered yellow needles (WYN) partially decomposed needles (PDN). The needle properties (i.e., surface repellency, cross-section morphology, and flexural stiffness) were measured to determine the factor controlling the cutting effect. Results showed that after the cutting effect, one raindrop could be cut into up to 12 small raindrops. Their velocities owned a bimodal distribution. Compared to the diameter before the cutting effect occurred, the raindrop diameter decreased by an average of 59 %, and the raindrop velocity decreased by an average of 19 %. This caused a substantial decrease in the raindrop energy (∼85 %). The cutting effect included three sub-processes: collision, splitting, and interception. Our analysis suggested that the splitting process was the main reason for the cutting effect to reduce raindrop energy. The cutting effect was affected by the needle properties and raindrop falling heights. The cutting effect was enhanced when the needle developed from FGN and WYN to PDN. The cutting effect was positively related to the falling height of raindrops. Changes in the raindrop characteristics due to the cutting effect should enhance rainfall evaporation and infiltration and thus decrease soil erosion, which needs to be evaluated in further studies.

Superior toughness of thermal barrier coating caused by co-doping of trivalent and pentavalent oxides

The zirconia-based thermal barrier coating co-doped with trivalent and pentavalent oxides was deposited on DD 90 single crystal superalloy using air plasma spraying. The coating is composed of cubic and tetragonal phases denoted by bi-phase solid solution (BPS) ceramic coating. The microstructure, cross-sectional morphology, and cracks evolution of BPS coatings, before and after 1200 °C thermal cycling, were investigated compared with 8YSZ coating. The BPS coating is intact after 250 thermal cycles, and the phase constitution is consistent with as-sprayed state. On the contrary, the brittle monoclinic phase can be observed in the thermal cycled 8YSZ coating, and severe exfoliation occurred. The propagation and splitting of the cracks are inhibited by the randomly distributed nanocrystalline clusters, and the cracks are inclined to grow longitudinally, which are beneficial to improve the toughness and thermal shock resistance of thermal barrier coating.

Exploring the Influence of the Deposition Parameters on the Properties of NiTi Shape Memory Alloy Films with High Nickel Content

NiTi shape memory alloy films were prepared by magnetron sputtering using a compound NiTi target and varying deposition parameters, such as power density, pressure, and deposition time. To promote crystallization, the films were heat treated at a temperature of 400 °C for 1 h. For the characterization, scanning electron microscopy, energy dispersive X-ray spectroscopy, atomic force microscopy, synchrotron X-ray diffraction, and nanoindentation techniques were used on both as-deposited and heat-treated films. Apart from the morphology and hardness of the as-deposited films that depend on the deposition pressure, the power applied to the target and the deposition pressure did not seem to significantly influence the characteristics of the NiTi films studied. After heat treatment, austenitic (B2) crystalline superelastic films with exceptionally high nickel content (~60 at.%) and vein-line cross-section morphology were produced. The crystallization of the films resulted in an increase in hardness, Young’s modulus, and elastic recovery.

An improvement of thermoelectric properties for Mg3Bi2/Mg2Sn nanocomposite films by the phase interface

Mg3Bi2/Mg2Sn nanocomposite films were prepared on single Si substrate using high pure metal Mg, Mg3Bi2 and Mg2Sn target by alternately sputtering. The phase composition of the deposited Mg3Bi2/Mg2Sn films was analyzed by X-ray diffraction patterns. The surface and cross-sectional morphology of the deposited Mg3Bi2/Mg2Sn films was observed by scanning electron microscope. The content and distribution of elements in the deposited Mg3Bi2/Mg2Sn films were measured by an energy dispersive spectroscopy. The Seebeck coefficient and electrical conductivity of the deposited films was measured by Seebeck coefficient/resistance analysis system. The carrier concentration and carrier mobility of the sample was measured and calculated by Hall experiments. Results showed that the Mg3Bi2/Mg2Sn films were composed of Mg3Bi2, Mg2Sn and a few of metal Mg phase. The carrier (hole) concentration and Seebeck coefficient gradually increased, but the mobility and electrical conductivity decreased with increasing the Mg2Sn phase content in deposited films. As a result of the competition between the electrical conductivity and the Seebeck coefficient, the power factor first increased, reached a maximum value of 1.20 mW·m−1·K−2 at 155 °C, and then decreased. The deposited Mg3Bi2/Mg2Sn nanocomposite films with 6.5 at.% Sn possessed the highest power factor in measured temperature range. The power factor of deposited Mg3Bi2 films can be effectively improved by adding moderate Mg2Sn phase and forming Mg3Bi2/Mg2Sn nanocomposite films.

In situ formation of micro arc oxidation ceramic coating on refractory high entropy alloy

Micro arc oxidation (MAO) coatings were in situ prefabricated on refractory high entropy alloys (RHEAs). We systematically studied the evolution of the surface and cross-sectional morphologies and composition of the MAO ceramic coatings on AlTiCrVZr substrate with oxidation time. It was found that the surface elements in AlTiCrVZr exhibit competitive oxidation behavior during the MAO process. The inner layer of the MAO ceramic coating was mainly composed of ceramic oxides of the substrate elements, and the outer layer primarily consisted of ceramic oxides formed by the solute ions. Finally, we propose a growth model of the ceramic oxide coatings based on the formation mechanism of the MAO ceramic coating and the physical and chemical properties of the ceramic oxides formed by the principal elements in the RHEAs.

4D printing of porous PLA-TPU structures: effect of applied deformation, loading mode and infill pattern on the shape memory performance

For the first time, the synergy of shape memory polymer (SMP) blending, 4D printing, and cold programming (CP) are investigated for improving the functionality of the shape memory effect (SME), increasing medical applications of porous structures, direct programming, and removing current limitations. Porous PLA-TPU structures with different printing patterns and applied deformation were CPed under constrained and non-constrained compression modes at room temperature and were recovered in the rubbery phase. The shape fixity and shape recovery ratios were calculated and the cross-section morphology was examined with scanning electron microscopy (SEM). The shape fixity values were in the range of 39.75%–71.27%, while almost complete shape recovery ratios (100%) were observed for all porous samples. Low shape fixity ratios can be justified due to the existence of two steps of spring-back and structure relaxation after unloading in cold programming, resulting from elastic and viscoelastic behavior. The glass transition temperature of the PLA-TPU blend was 69 °C and shifted to raw materials, indicating the possibility of some interaction between the two components. SEM images showed the uniform distribution of TPU particles and matrix-droplet morphology in the PLA-TPU blend. After printing, TPU droplets were stretched and the sea-island morphology was observed in some segments.

Dissolution corrosion of FeCrAl alloy exposed to oxygen-depleted lead–bismuth eutectic containing Ni impurities at 600 ℃

FeCrAl alloy is one of the potential candidates of structural materials due to its high strength, low radiation swelling and good oxidation resistance for the application of lead-cooled fast reactors (LFRs). Particularly, FeCrAl alloy can form protective Al-containing oxide scales after exposure to liquid oxygen-rich Pb and lead–bismuth eutectic (LBE) at 400–800 ℃, showing better performance than traditional commercial stainless steels such as T91, 316L and 15-15Ti. Given the possibility that oxygen in liquid metal could be consumed and not be supplied timely in some quasi-static regions of the actual coolant circuit, to figure out the corrosion behavior of FeCrAl alloy in oxygen-depleted LBE is necessary. In this work, the commercial FeCrAl alloy was exposed to static liquid LBE containing Ni impurities with 10−9 wt% oxygen concentration at 600 ℃ for up to 5000 h, and the surface and cross-sectional morphology of the samples was characterized and analysed. It is found that FeCrAl alloy underwent severe dissolution corrosion, and the maximum penetration depth of LBE reached 161.4 μm after the test for 5000 h; PbBi infiltrated into alloy matrix along the GBs and selectively leached Al from the affected grains. Besides, an interesting discovery is the Cr-rich thin layer at LBE/matrix interface and Ni3Al precipitates in LBE penetration front which should be attributed to the deposition of impurity elements dissolved in liquid LBE during the cooling process.

Preparation and properties of modified POD membranes by polycarboxylic acids copolymerization

A series of X-POD polymers were prepared by condensation reaction of terephthalic dihydrazide and four different polycarboxylic acids in polyphosphoric acid (PPA) as solvent, and the corresponding membranes were formed by phase inversion method. The modified X-POD polymer structures have changed from linear structure to multidimensional network structure, which has great influence on the quality and performance of the membranes. The membrane structures were characterized by FTIR, and the thermal stability of the samples was determined by Thermogravimetric analysis (TGA) and differential scanning calorimeter (DSC). The ultraviolet transmittance and fluorescence properties of membranes were tested by ultraviolet spectrophotometer. The crystallinity and orientation of the samples were observed by X-ray diffraction (XRD). The surface and cross-sectional morphology of the membranes were evaluated by scanning electron microscope (SEM). Additionally, the oxidation and water absorption properties of the membranes were collected, and the mechanical properties of the membranes were tested. Overall, X-POD membranes show good mechanical properties, chemical inertness and thermal stability. The quality and mechanical properties of X-POD membranes demonstrated varying degrees of improvement. Notably, the mechanical properties of II-POD and III-POD membranes were enhanced by 244.52% and 203.66%, respectively. X-POD membranes exhibit high strength and excellent toughness, rendering them a highly promising material for membrane applications in the market.

Study on the role of chromium addition on sliding wear and corrosion resistance of high-manganese steel coating fabricated by wire arc additive manufacturing

Guide shoe made of steel is an important component of coalcutter and rail transport to sustain forward direction. However, the guide shoe suffers from wear failure due to the heavy load and fatigue. Preparing wear-resistance coating on the worn surface is a practical and economic technology to elongate longevity. High manganese steel is a candidate material with excellent wear resistance. In this study, high-manganese (HiMn) and high-manganese medium-chromium (HiMnMeCr) coatings are fabricated by using wire arc additive manufacturing (WAAM) to investigate the role of Cr addition on the microstructure and resistance to wear and corrosion by analyzing the microstructure morphology, wear rate, coefficient of friction, surface and cross-sectional morphology of the wear track, and electrochemical behavior by using sliding wear test and electrochemical experiment. The experimental results obtained by using the counterface material of ZrO2 showed that Cr addition changed the microstructure constitutes of WAAMed HiMn coating from biphasic austenite + martensite to single austenite. The addition of Cr elongated the running-in period of the wear process and weakened the wear resistance of the WAAMed HiMnMeCr coating due to the work-hardening effect induced by the severe plastic deformation of austenite. At loads of 50 and 100 N, the primary wear mechanism for the HiMn coating was a complex mode of abrasive and adhesive wear. The wear mechanism transformed into a single adhesive wear at a load of 120 N. However, the primary wear mechanism of the HiMnMeCr coatings was abrasive wear at all tested loads. The electrochemical experiment (pote ntiodynamic curves and EIS analysis) shows that the corrosion resistance of HiMnMeCr coating was better than that of HiMn coating, indicating that the addition of Cr enhanced the corrosion resistance of the WAAMed HiMn steel by the passivation effect of Cr. This study will provide a fundamental theory for the fabrication of wear-resistance coating by using WAAM.