Microstructural Investigations Research Articles

On the investigation of microstructure and mechanical properties of the AlCoCrFeNi2.1/316 L dissimilar spot-welded joint

On the investigation of microstructure and mechanical properties of the AlCoCrFeNi2.1/316 L dissimilar spot-welded joint

Egg White-Based Gels with Candelilla Wax: A Study of Rheological, Mechanical, Calorimetric and Microstructural Properties

Bigels (BGs) are innovative composite systems that integrate oleogel and hydrogel structures, and are gaining increasing attention for their unique textural and functional properties in food applications. This study evaluated the rheological and mechanical properties of egg white-based bigels incorporating candelilla wax (CW) as an oleogelator. The results indicate that different egg white protein (EWP) (5–10%) concentrations and hydrogel-to-oleogel ratios (20:80 to 80:20) significantly influenced the structural and functional properties of the bigels. Compression testing revealed no significant differences in strength across the tested range; however, higher EWP concentrations enhanced the stability of the BGs. Furthermore, increased candelilla wax oleogel (CWO) content (60%) markedly improved emulsion stability, resulting in superior strength, as confirmed by dynamic light scattering. Rheological studies demonstrated shear-thinning behavior, particularly at higher hydrogel content related to the oleogel (W/O), which exhibited the highest yield stress. Microstructural investigations confirmed the presence of a continuous oleogel phase within the bigels (W/O) and revealed the formation of a complex structure. These findings suggest that a reduced hydrogel-to-oleogel ratio can be utilized across various food systems, opening new possibilities for creating customized food structures with desirable textural and functional attributes.

The Thermomechanical, Functional and Biocompatibility Properties of a Au–Pt–Ge Alloy for PFM Dental Restorations

A high-noble Au–Pt–Ge porcelain-fused-to-metal (PFM) dental alloy without the known adverse metallic elements and with the addition of germanium (Ge) was produced as a more cost-effective alternative to other precious alloying metals, with investigations for determining the functionality and clinical use of this alloy. The thermomechanical, biocompatibility, durability, workability and economic characteristics of the produced dental alloy were investigated. These properties were investigated with in vitro biocompatibility testing on human gingival fibroblasts (HGFs); static immersion testing for metal ion release; DSC analysis; hardness, tensile testing, density and coefficient of thermal expansion (CTE) measurements; metallographic and SEM/EDX microstructure investigations; and finally with the production of a test PFM dental bridge. The results of the thermomechanical testing showed alloy properties suitable for dental restorations and clinical use, with somewhat lower mechanical properties, making the alloy not suitable for extensive multiunit fixed restorations. The microstructure investigations showed segregations of Ge in the homogeneous alloy matrix, which reduce the alloy’s mechanical properties. The produced PFM dental bridge showed excellent workability of the alloy in a dental laboratory setting, as well as a high standard of the final dental restoration. The ion release was negligible, well below any harmful quantities, while the cell viability examination showed significantly higher viability ratings on polished alloy samples as compared to as-cast samples. The results showed that a dental substructure in direct contact with oral tissue and fluids should be highly polished. The performed investigations showed that the produced PFM dental alloy is suitable for clinical use in producing high-quality dental restorations with high biocompatibility for patients prone to metal allergies.

Microstructural and mechanical investigation of dissimilar U-groove weld of IN 718/ASS 304L employing ERNiCr-3 filler

This study investigates the dissimilar welding of Inconel 718 (IN 718) and austenitic stainless steel 304L (ASS 304L) using Gas Tungsten Arc Welding (GTAW) with Ni-based filler ERNiCr-3. IN 718 is valued for its high-temperature stability, oxidation, and corrosion resistance, while ASS 304L offers excellent ductility, formability, and corrosion resistance. The objective is to evaluate the impact of ERNiCr-3 on the weld’s metallurgical and mechanical attributes. The materials, prepared with U-groove edges, were optimized for manual multi-pass welding. Microstructural analysis revealed an austenitic matrix with dispersed Ti(CN) and NbC precipitates, enhancing strength through dispersion-strengthening mechanisms, with no solidification cracking due to Nb presence. FESEM/EDS and colour mapping identified elemental migration and stable carbide formation at the weld interfaces. Mechanical testing revealed uniform hardness within the weld zone and tensile resistance of 510 MPa, underscoring the robustness of ERNiCr-3 weld metal. These results indicate that ERNiCr-3 is highly effective for producing superior quality dissimilar welds amidst IN 718/ASS 304L, making it suitable for applications in elevated-temperature and mechanically demanding environments.

Recovery of waste anode materials in solid oxide fuel cells

This study focuses on the recovery and recycling of production wastes from solid oxide cell (SOC) anode support manufacturing, specifically targeting the state-of-the-art NiO-YSZ (yttria stabilized zirconia) materials. A practical recovery strategy involving a burn-out process to remove additives is developed, followed by milling to manage grain growth and achieve desirable powder properties. The various reclaimed powders obtained after milling at different conditions are subsequently used to fabricate anode support microtubes through extrusion and tape casting coupled with isostatic pressing. Microtubular cells are also constructed on these supports. Comparative analyses of the mechanical and electrochemical performance, along with microstructural investigations, are conducted on supports and cells fabricated from both recovered and commercial powders. The findings indicate that anode supports fabricated from powders recovered through the suggested method exhibit flexural strengths and electrochemical performances comparable to those fabricated from commercial powders, thereby validating the effectiveness of the proposed recovery strategy.

Investigation of formation, microstructure and hardness of Ti-6Al-4V single tracks via Joule-fused filament additive manufacturing

Purpose This paper aims to investigate a novel additive manufacturing (AM) method for titanium alloy using Joule heat as the single heat source to melt TC4 wire, which intends to provide a new low-power, low-cost solution for the processing of titanium alloys. Design/methodology/approach When current flows through the wire and the substrate, Joule heat will be generated to melt the wire and join the wire with the substrate. By stacking the wire layer by layer, finally a part can be formed. The cross-sectional morphology, microstructure and hardness of TC4 single track deposits formed by Joule heat melting wire AM were investigated by various characterization methods. Findings The melting width and melting penetration decreased with the increase of printing speeds. There is no obvious change in single track morphology with the change of printing pressures. The melting width and melting penetration increased with the increase of printing currents. The observation of the internal microstructure of a single track reveals a decrease in grain size as printing speeds increase. The average hardness of the single track was about 363 HV, which is comparable to the hardness of the parts fabricated by selective laser melting process. The printing power is less than 300 W, which is lower than other AM processes. Originality/value This paper provides a novel solution for the processing of titanium alloy parts. Compared with other expensive energy sources, this work only uses an ordinary DC power supply as the energy source. The printing process is simple and the cost is low. The power is much lower than other AM processes.

Weldability and microstructural characterisation of gas tungsten arc welded Al0.3CoCrFeNi high entropy alloy

ABSTRACT High entropy alloys (HEAs) have received significant interest from researchers due to their exciting set of properties such as an optimum combination of strength and ductility. The Al0.3CoCrFeNi alloy has shown promising properties for applications such as structural components in marine environments, cryogenic applications, and antiballistic armour. This study investigates the weldability of Al0.3CoCrFeNi using gas tungsten arc welding (GTAW). GTAW of Al0.3CoCrFeNi results in a higher tensile strength than that of BM. Microstructural investigations were carried out with X- ray diffraction (XRD), scanning electron microscopy (SEM), electron backscattered diffraction (EBSD), accompanied by tensile and hardness testing. The BM and welded samples were found to have yield strengths of 255 MPa and 405 MPa, respectively. However, the welded sample has a lower ductility (20% elongation) than the BM (53% elongation). The high strength and lower ductility of the weld are mainly attributed to the evolution of the BCC/B2 phase and carbide phases in the microstructure of the welded sample. The precipitation of the BCC/B2 phase in the welded sample is a consequence of the lower free energy associated with the B2 phase at intermediate temperatures.

Investigation of microstructure and mechanical property evolution in a novel low-cost Ni-free maraging steel based on Mn and C through cold rolling followed by aging

In this work, we investigate the microstructures and mechanical properties evolution on a novel carbon-based maraging steel with the compositions of Fe–10Mn-0.25C–1Cr–2Mo wt%, through hot and cold rolling following by heat treatment. The composition was designed through thermodynamic modelling to achieve a combination of high strength and high tensile elongation through the development of fine tempered martensite with carbide strengthening, and the transformation induced plasticity (TRIP) from the reverted austenite. After hot and cold deformation, a solution treatment at 870 °C followed by quenching gave a martensitic structure with 5% retained austenite. The microstructure and tensile properties were then investigated in detail as a function of ageing time at 510 °C. The kinetics of austenite reversion were much more rapid, with a peak in austenite content after only 5h, giving a maximum volume fraction of ∼26%, with a sharp reduction for longer ageing times. The best tensile properties were obtained after an 8 h age with only ∼16.5% of reverted austenite, which provided a UTS of 1560 MPa (220 MPa contributed by TRIP) and an elongation of 14.5%. While the smallest grain size was attained after 16 h of aging, accompanied by an exceedingly low volume fraction of reverted austenite (∼2.1%) for the TRIP effect, the UTS decreased to 1356 MPa, with a slightly improved elongation of 15.7%. The results show that achieving the optimal mechanical properties requires balancing the volume fraction of reverted austenite for the TRIP effect with the grain size to enhance both strength and ductility.

Functional properties of expanded austenite generated on AISI 316L by plasma nitrocarburizing using different active screen materials

Abstract This study investigates the functional properties of the expanded austenite layers generated on AISI 316L austenitic stainless steel resulting from active screen plasma nitrocarburizing using different active screen materials, i.e. steel or solid carbon. Treatments were conducted at 460 °C for 5 h in a nitrogen-hydrogen feed gas, whereas for the treatments using a steel active screen, methane was added as a carbon precursor. Additionally, the bias plasma conditions applied at the samples were varied between 0 kW and 1.25 kW. Samples were characterized by complementary microstructural and compositional investigations, surface roughness and hardness measurements, pin-on-disk tribological tests as well as potentiodynamic polarization tests in H2SO4 and NaCl electrolytes. The functional properties of the case are discussed based on the contents of nitrogen and carbon in the expanded austenite and their effective diffusion depths. The results show that the usage of a carbon screen generally produces surfaces with uniform layer thickness, high hardness, improved wear resistance and a delayed tendency to pitting corrosion independent of the bias condition applied to the samples. When applying both screen materials at non-biased condition, the general corrosion resistance is slightly reduced under the conditions used, however, the layers generated using the carbon screen have a wear rate that is 3 times lower. It can be concluded that the carbon screen represents a robust treatment variant for austenitic stainless steels to produce sufficiently thick and wear-resistant surface layers in a short treatment duration, which still have the potential to maintain the corrosion resistance in different environments.

S1aUnnotched fatigue behavior of the lased powder bed fused and hot isostatic pressed Inconel 718 at 600 °C

The microstructure and mechanical properties of hot isostatically pressed (HIP) Inconel 718 additively manufactured using the laser beam powder bed fusion (LPBF) process were investigated at 600 °C, with emphasis on the high cycle fatigue behavior evaluated using the rotating bend fatigue tests, and elucidation of the role of γ” precipitate size on the fatigue resistance. Experimental results show that the unnotched fatigue strength (σf) of the peak aged alloy improves only by 7% after HIP, as compared to that of the non-HIP peak aged alloy, despite a significant improvement in the ductility due to HIP. Over-aging the HIP alloy, however, led to a further enhancement (by ∼14%) in σf. Fractographic analyses suggest that the fatigue crack initiation occurs from the intrusions and extrusions on the fracture surface of both versions of the aged alloy. Microstructural investigations reveal the presence of persistent slip bands (PSBs) with different morphologies in peak- and over-aged microstructures. A change in the deformation mechanism due to the size of precipitates was identified to be the reason for the formation of nano-grains (through dynamic recrystallization) within the PSBs of the alloy with a coarse γ” microstructure. In several {110} grains, ∼5 μm thick nanocrystalline grain zones formed on the specimen surface; they completely suppressed the formation of PSBs and enhanced the fatigue resistance of the HIP LPBF IN718 alloy in the over-aged condition.

Investigation of Microstructure and Physical Characteristics of Eco-Friendly Piezoelectric Composite Thin Films Based on Chitosan and Ln2O3-Doped Na0.5Bi0.5TiO3-BaTiO3 Nanoparticles.

This paper investigates the synthesis and characterization of eco-friendly piezoelectric composite thin films composed of chitosan and Ln2O3-doped Na0.5Bi0.5TiO3-BaTiO3 (NBT-BT) nanoparticles. The films were fabricated using a solution-casting technique, successfully embedding the particles into the chitosan matrix, which resulted in enhanced piezoelectric properties compared to pure chitosan. Characterization methods, such as photoluminescence spectroscopy and piezo-response force microscopy (PFM) which revealed strong electromechanical responses, with notable improvements in piezoelectric performance due to the inclusion of NBT-BT nanoparticles. X-ray diffraction (XRD) analysis revealed a pure perovskite phase with the space group R3c for NBT-BT and NBT-BT-Ln particles. Scanning electron microscopy (SEM) images showed a non-uniform distribution of NBT-BT particles within the chitosan matrix. The results also suggest that the incorporation of rare earth elements further enhances the electrical and piezoelectric properties of the composites, highlighting their potential in flexible and smart device applications. Overall, these findings underscore the potential of chitosan-based composites in addressing environmental concerns while offering effective solutions for energy harvesting and biomedical applications.

The Influence of Surface Segregation on the Anodizing of AlSi11Cu2(Fe) Diecastings

A positive segregation is usually formed on the casting surfaces produced by high-pressure die casting (HPDC). In diecast Al-Si-Cu alloy components, this segregation shows a higher content of Si compared to the nominal composition of the alloy and it drastically affects the anodizing response of the casting surface. In the present work, HPDC components were produced by AlSi11Cu2(Fe) alloy, grit-blasted, and then anodized in a sulfuric acid electrolyte at the temperature of -4.5°C. Before the anodizing process, some regions of the casting were also milled, in order to completely remove the surface segregation. Microstructural investigations were carried out on grit-blasted and milled surfaces to characterize the initial substrates before anodizing, and to study their effect on the growth of the anodic layer. Scratch and wear tests were also performed to investigate the surface mechanical properties after anodizing. The results show that the surface segregation and the rough surface present on grit-blasted substrate leads to the formation of a thin and homogeneous anodic layer. On the contrary, a thicker and scalloped oxide film is formed on the milled surfaces. After anodizing, grit-blasted surfaces show lower wear and scratch resistance than milled substrates. The presence of surface segregation prevents the thickening of the anodic layer, negatively affecting the surface wear resistance due to the reduced oxide thickness.

Mechanical Properties and Microstructural Characteristics of Steel Pipes after Long-Time Hydrogen Exposure

There are three possibilities to transport hydrogen by high pressure pipeline (i) blending hydrogen into the existing natural gas pipeline system, (ii) after checking the integrity, using the natural gas transporting pipeline system to transport hydrogen, (iii) building a new pipeline system to transport pure hydrogen. In all three cases should be known the behaviour of the pipe material and its welded joints influenced under high pressure hydrogen. For this aim pipeline sections made of P355NH base material were investigated without and with hydrogen exposure, where the exposure time was 41 days. Gas metal arc welding and hybrid tungsten arc welding / gas metal arc welding were applied for preparation of the girth weld joints. Tensile, three point bending and hardness tests, furthermore microstructural investigations were performed both on base materials and girth welds of the pipeline sections. The testing results were analysed and compared with each other (base material vs. welded joints, without exposure vs. with exposure) and with limit values can be found in the literature. Conclusions were drawn on the behaviour of the investigated pipe material and its welded joints.

Tensile strength of friction stir additive manufactured laminated AA 6061/TiC/GS composites

Abstract With the fast progress of industrial manufacturing, friction stir additive manufacturing has fascinated wide-ranging consideration in the industry due to high material consumption rate. Friction stir additive manufacturing (FSAM), a newly developed solid-phase additive manufacturing technique was employed to fabricate AA6061/TiC/GS composite. The process parameters like tool rotational speed, transverse speed, tool tilt angle and type of tools used in friction stir additive manufacturing were analyzed. Taguchi’s L16 orthogonal array and ANOVA method was used to find the optimum process parameters for the tensile strength. Development characteristics of stirred zone, recrystallization and mixing of reinforced particles will significantly improve the mechanical properties of the fabricated composites. Microstructural investigation and fractography was done by using optical microscopy and scanning electron microscopy (SEM). Corrosion, wear behavior and elemental analysis through EDS was also performed for the fabricated material. The maximum tensile strength of 385.74 MPa was attained under optimal parameters of the tool rotational speed 1,200 rpm, transverse speed 55 mm min−1, and tool tilt angle of 1° for scrolled tapered octagonal tool pin. The findings of the linear regression model showed a minor variance between model and experimental values. Prominent results of the experiment were compared by few other researcher’s findings working in similar area.

Microstructural Investigation and Mechanical Properties of Resistance Spot Welding Joints of Mild Steel Sheets

Due to its high productivity, low cost, and increased work efficiency, resistance spot welding (RSW) can instantly join two or more steel sheets and it is widely used in the automotive industry and lately in the manufacturing of thin-walled cold-formed steel constructions. However, the RSW of zinc-coated mild steel sheets presents metallurgical challenges, especially when different thickness combinations are used. Therefore, in the present paper a resistance welding machine was used which uses direct current (MFDC) inverter technology combined with SMART AUTOSET technology to weld S250 GD and S350 GD galvanised mild steel sheets with different thicknesses. It is well known that, due to the elevated temperature that occurs during the welding process, followed by rapid cooling, defects such as cracking, porosity, lack of fusion, and an increased amount of brittle phases affect the welding quality. Therefore, the influence of the RSW process parameters established by an automatic sequence on the nugget geometry, microstructure, and mechanical properties was investigated. The phase transformations that took place during the heating-cooling cycle were analysed in detail through metallographic studies. The results showed that the microstructure of the weld nuggets was similar, characterised by columnar grains elongated in the direction of heat evacuation. Nevertheless, there were differences in terms of phase dispersion, defects and mechanical properties that have been linked to the RSW process parameters.

Recrystallization Behavior of Computationally Optimized Low‐Alloy Steel at Various Temperatures and Strain Rates

The dynamic recrystallization (DRX) behavior of SA508‐III steel, a critical material for reactor pressure vessels (RPVs) normally treated by hot forging, is thoroughly examined in this article. In the investigation, elevated temperatures and the coarsening of metallic phases and carbides are revealed to contribute to the degradation of the steel's strength–toughness relationship. Utilizing computational thermodynamics, the stability of secondary phases, including carbides and brittle inclusions, is simulated to enable precise phase equilibrium calculations and accurate prediction of key mechanical properties such as yield strength, tensile strength, and hardness. These simulations facilitated targeted modifications to the alloy composition to enhance the steel's strength and hardenability under high‐temperature, high‐pressure conditions. In this study, alloy composition and processing parameters within the CALculation of PHAse Diagram framework, utilizing the ThermoCalc and JMatPro software packages, are optimized. In the microstructural investigations conducted under various isothermal deformation conditions (1173–1473 K) and strain rates (0.001–1 s−1), it is demonstrated that DRX mechanisms led to varied grain size developments, with a critical strain rate identified at 0.01 s−1 during high‐temperature deformations. In these findings, significant insights are provided into optimizing the mechanical performance of SA508‐III steel for RPV applications.

Investigation of Microhardness, Microstructural, Tribological, and Thermal Properties of Al7075/TiO2/Kaoline Hybrid Metal Matrix Composites Produced by Powder Metallurgy Process

The shift from traditional, single‐component metals and alloys continues, and researchers are currently investigating alternative materials. This evolution has led to the creation of innovative materials, including hybrid metal‐matrix composites. The present study aims to investigate the microstructural, surface morphological, and thermal properties of a novel Al7075/TiO2/Kaoline hybrid metal‐matrix composite prepared using high‐energy ball milling and sintering methods. In this study, phases related to the composite components are formed depending on the milling time, no undesirable phase is formed, but the peak intensities decreas as the milling time increases. Particle size increases from 63 to 215 μm with increasing milling time. Increasing the kaoline reinforcement ratio and sintering temperature increases the microhardness from 62.27 ± 2 to 75.83 ± 2 HV, and reduces the friction coefficient from 0.82 ± 0.01 to 0.62 ± 0.01. The wear rate of the composite without kaoline addition is 2.1 (mm3 m−1) × 10−3, while with 6 wt% kaoline addition, it decreases to 1.5 (mm3 m−1) × 10−3. There are no cracks in the composite other than plastic deformation due to sintering and wear. Peaks indicating endothermic and exothermic reactions during continuous heating occurr in the 635–750 °C temperature range.

Comparative investigation of composition, microstructure and property influences on electrocatalysis of two representative cathodes: BaCo0.4Fe0.4Zr0.1Y0.1O3-δ versus Ba0.5Sr0.5Co0.8Fe0.2O3-δ

BaCo0.4Fe0.4Zr0.1Y0.1O3-δ (BCFZY) and Ba0.5Sr0.5Co0.8Fe0.2O3-δ (BSCF) perovskites are two representative high-performance cathode materials for intermediate-temperature solid oxide fuel cells (IT-SOFCs). Here, symmetric cell tests demonstrate that polarization resistance values of BCFZY cathode are only 0.21–0.29 times those of BSCF cathode at 740–660 °C, and 0.21–0.26 times those of BSCF cathode at the oxygen partial pressures of 1.00–0.10 atm. Distribution of relaxation times (DRT) is applied to detect individual electrode processes overlapped in impedance spectra, which finds that the dominant processes of oxygen dissociation, subsequent species transfer and reduction on BCFZY cathode are superior to those of BSCF cathode. By temperature-programmed desorption of oxygen (O2-TPD), thermal expansion coefficient (TEC) measurements, scanning electron micrograph (SEM) and energy dispersive spectra measurements, the strong oxygen combination ability with higher activation energy of oxygen desorption (Ed = 84 kJ mol-1), peculiar surface state with evident nano-particle structure, more matchable TEC (19.0 × 10-6 K−1) and excellent interfacial connection with the electrolyte are observed on BCFZY cathode to account for its distinctive catalysis, as compared to BSCF cathode (Ed = 68 kJ mol-1, TEC = 24.2 × 10-6 K−1).

Effect of laser drilling process on combustor liner effusion hole quality

Abstract Effusion cooling is one of the significant cooling technologies in combustor liners in terms of cooling efficiency and weight reduction. However, effusion cooling technology is difficult to manufacture. In fact this technology requires laser-drilling of thousands of tiny holes with shallow angles on a sheet metal with a thickness generally varying between 0.5 to 1.5 mm. In addition, the use of thermal barrier coating is common in gas turbine engines and is one more challenge for the drilling process. In order to obtain more efficient gas turbine engines, the inlet temperature keeps increasing in the last decades, which induces the combustion chamber to operate in a hotter environment. Therefore, efficient cooling technology is needed, even if it is hard to manufacture. For laser drilling, several parameters have to be explored to obtain acceptable holes. This study includes the microstructure investigations of the holes produced with different laser parameters and the optimal laser parameters determined according to the microstructure of six different effusion cooling hole configurations. The results show that laser process differences affect the metal substrate microstructure and thermal barrier coating structure. Drilling method, peak power, number of pulses, gas type and pressure value have a significant effect on the hole geometry and its microstructure.

Morphology engineering of low-temperature-synthesized aluminum nitride

We have developed an aluminum nitride (AlN) manufacturing method that operates below the melting point of aluminum. To examine the nucleation and growth mechanisms of AlN during the synthesis process, we used a variety of characterization techniques, including high-resolution transmission electron microscopy and rapid Fourier transform, which highlighted the development of its single-crystal and polycrystalline forms. The microstructural investigation showed that nitridation began with forming AlN shells on the surface of aluminum particles. Subsequently, volume nitridation occurred by transforming a single aluminum particle into either polycrystalline AlN with a columnar structure or single-crystal AlN. In addition, various interesting morphologies were observed during the microstructural investigation of low-temperature synthesized AlN, including truncated dodecahedrons, nanowires, particles, pillars, plates, and other polyhedral shapes. The study's microstructural findings provide crucial data on the AlN particle formation process, offering valuable insights expected to deepen understanding and expand the applications of AlN. Therefore, the consequence of this study is expected to make a meaningful contribution to understanding the formation mechanism of the particle type of AlN.