Microstructural Characterization Research Articles

Disclosing Connection Links between Microstructure and Mechanical Performance in Pulsating Current Gas Tungsten Arc Welding of Hastelloy B-2 Superalloy

In this study, welding a Ni-Mo-based superalloy (Hastelloy B-2) was examined in order to characterize the microstructure and mechanical performance of joints along with assessing the effects of current intensity on the microstructure and mechanical responses of different weld zones. The gas tungsten arc welding (GTAW) process was used to weld the samples using ERNiCrMo-2 filler metal. The pulsed current GTAW process was used to weld the superalloy sheets of thickness of 1 mm with background current (Ib) of 20 A and 40 A and peak current (Ip) of 80 A and 60 A. Tensile and Vickers microhardness tests were conducted to evaluate the effect of pulsed current on mechanical properties of the welds along with chemistry and microstructure characterizations. Finally, the fracture surfaces after the tensile test were studied using SEM fractography analysis. The results indicated that increasing Ib and decreasing Ip led to low heat input and high cooling rate resulting in a high thermal gradient. This caused microstructure transition from the columnar dendrites to the coaxial ones in the weld zone; molten metal convection in the fusion zone led to fine grains in the weld zone during welding time. Moreover, a significant decrease in the amount of molybdenum carbides at the interdendritic regions of the weld metal was observed under these conditions. The tensile strength of the weld metal was higher than that of the base metal resulting in the fracture of all welds from the base metal. Additionally, the microhardness results indicated a significant increase for the weld metal compared to both heat-affected zone (HAZ) and base metal. The higher mechanical properties of the weld metal is attributed to the increase in background current and decrease in peak current leading to a fine grain microstructure. Fractography following the tensile test showed a completely ductile fracture.

Exposure behavior and drilling efficiency of basalt fiber composite impregnated diamond bits in hard granite

Impregnated diamond bits (IDBs) are widely used for drilling in hard formations. To improve the drilling efficiency and exposure behavior of IDBs in granite, three types of Cu-based basalt fiber (BF) composite IDBs were designed and prepared by using the medium-frequency induction hot-pressing and sintering method, in which 0 wt.% BF and 25 vol.% diamond were used in 0BF25D IDB, 1 wt.% BF and 25 vol.% diamond were used in 1BF25D IDB, 1 wt.% BF and 20 vol.% diamond were used in 1BF20D IDB. The drilling efficiency of each IDB was tested under different drilling pressures (WOB), and the exposure behavior of IDBs was investigated by scanning electron microscopy and ultra field microstructural characterization. Results show that drilling granite with grade 9 drillability, low drilling pressure can drill successfully with the addition of BF. The average rate of penetration (ROP) of 1BF20D IBD under 6 kN WOB was 4.78 m/h, which was improved by 60%∼80%, energy consumption decreased by 66% for each meter, torque (TOB) decreased, and rotational speed (RPM) was more stable during the drilling process. The addition of BF and reasonable diamond concentration enhanced the holding power of the diamond which promoted the exposure of the diamond. The average exposed height of the diamond in 1BF20D IDB reached 121.2 μm with 22% to 29% of the whole diamond.

Enhancing the Mechanical Properties of Co-Cr Dental Alloys Fabricated by Laser Powder Bed Fusion: Evaluation of Quenching and Annealing as Heat Treatment Methods

Residual stresses and anisotropic structures characterize laser powder bed fusion (L-PBF) products due to rapid thermal changes during fabrication, potentially leading to microcracking and lower strength. Post-heat treatments are crucial for enhancing mechanical properties. Numerous dental technology laboratories worldwide are adopting the new technologies but must invest considerable time and resources to refine them for specific requirements. Our research can assist researchers in identifying thermal processes that enhance the mechanical properties of dental Co-Cr alloys. In this study, high cooling rates (quenching) and annealing after quenching were evaluated for L-PBF Co-Cr dental alloys. Cast samples (standard manufacturing method) were tested as a second reference material. Tensile strength, Vickers hardness, microstructure characterization, and phase identification were performed. Significant differences were found among the L-PBF groups and the cast samples. The lowest tensile strength (707 MPa) and hardness (345 HV) were observed for cast Starbond COS. The highest mechanical properties (1389 MPa, 535 HV) were observed for the samples subjected to the water quenching and reheating methods. XRD analysis revealed that the face-centered cubic (FCC) and hexagonal close-packed (HCP) phases are influenced by the composition and heat treatment. Annealing after quenching improved the microstructure homogeneity and increased the HCP content. L-PBF techniques yielded superior mechanical properties compared to traditional casting methods, offering efficiency and precision. Future research should focus on fatigue properties.

Characterization of 3D printed composite for final dental restorations.

This study evaluated the mechanical, optical, microstructural, surface, and adhesive behavior of a 3D printing resin comparing it with a machinable resin composite. Specimens of different sizes and shapes were either printed (Vitality, Smart Dent) or machinable (Grandio Blocs, Voco GmbH) resin composites with similar composition were prepared. Surface and mechanical characterization were performed with Knoop hardness, flexural strength (three-point-bending), and elastic modulus tests. The wear of the tested materials was evaluated against steatite antagonists. The optical properties stability (color change, ΔE00, and translucency, TP00) were observed after staining in red wine. In addition, the bond strength of the resin composites to two resin cement protocols were investigated with microshear bond strength tests at baseline and after thermocycling. Scanning electron microscope (SEM) coupled with Energy-Dispersive X-ray Spectroscopy (EDS) was used for microstructural and chemical characterization. Statistical analyses were performed with t- and ANOVA tests. Hardness values (132.76 (16.32) KH- Machinable and 35.87 (2.78) KH - Printed), flexural strength (172.17 (26.99) MPa - Machinable and 88.69 (8.39) MPa - Printed), color and translucency change (1.86 (0.31)/0.06 - Machinable and 3.73 (0.36)/9,16- Printed), and wear depth (24.97mm (3.60)- Machinable and 7.16mm (2.84) - Printed) were statistically different. Average Regarding bond strength, mean values (MPa) for non-aged and aged groups were respectively 21.76 (6.64) / 31.9 (12.66) for Bifix cement (Voco GmbH, Cuxhaven, Germany) and 26.75 (5.14) / 24.36 (6.85) for Variolink cement (Ivoclar Vivadent, Schaan, Liechtenstein) in Printed and 17.79 (3.89) / 9.01 (3.36) ) for Bifix cement and 22.09 (6.55) / 11.01 (3.77) for Variolink cement in Machinable materials. The material and aging factors did affect bond strength but the cement factor did not (p = 0.202). No statistical differences were observed for mean roughness (Ra) between materials. The better dispersion and larger size of the inorganic particles in the Machinable resin were contrasted with the clustered smaller particles of printed resin, under SEM. The mechanical properties and color stability of the machinable resin were superior to those of the printed resin, probably due to the greater amount and dispersion of inorganic particles in the Mach resin, but bond strength after aging was stronger and more stable in the printed resin. 3D-printed resin composites with similar compositions to machinable resin composites do not necessarily exhibit the same properties, which can impact clinical performance. Understanding these differences can assist manufacturers in improving their materials and help clinicians distinguish between materials appropriate for provisional and final restorations.

Microstructure characterization and corrosion performance of Alloy 625 weld cladding deposited using TWF-GTAW and PTA-P

Microstructure characterization and corrosion performance of Alloy 625 weld cladding deposited using TWF-GTAW and PTA-P

MICROSTRUCTURE AND WEAR BEHAVIOR CHARACTERIZATION OF STIR-CAST ALUMINUM 6063 ALLOY AND ITS FOAM: A COMPARATIVE STUDY

In this research work, aluminum 6063 alloy foam was synthesized through stir casting using varying amounts of titanium hydride as a foaming agent. A comparative microstructural and wear behavior analysis of stir-cast aluminum 6063 alloy and its foam is presented. The oxide and aluminide phases present as intermetallic compounds in the stir-cast aluminum 6063 alloy foam ensure the stability of the synthesized foam. In order to optimize the effect of wear parameters on the tribological properties of stir-cast aluminum 6063 alloy foam, the L933 orthogonal array (OA) was designed and modeled statistically. The tribological properties of stir-cast aluminum 6063 alloy and its foam were evaluated by pin-on-disc tests. The optimal tribological properties of the synthesized foam are 0.29 coefficient of friction, 8.6 N frictional force, and 0.00025 mm3/N-m specific wear rate. The tribological properties of stir-cast aluminum 6063 alloy foam are superior to those of aluminum 6063 alloy and comparable to other aluminum foams described in the literature.

Comparative Study of High-Cycle Fatigue and Failure Mechanisms in Ultrahigh-Strength CrNiMoWMnV Low-Alloy Steels

This study provides a thorough analysis of the fatigue resistance of two low-alloy ultrahigh-strength steels (UHSSs): Steel A (fully martensitic) and Steel B (martensitic–bainitic). The investigation focused on the fatigue behaviour, damage mechanisms, and failure modes across different microstructures. Fatigue strength was determined through fully reversed tension–compression stress-controlled fatigue tests. Microstructural evolution, fracture surface characteristics, and crack-initiation mechanisms were investigated using laser scanning confocal microscopy and scanning electron microscopy. Microindentation hardness (HIT) tests were conducted to examine the cyclic hardening and softening of the steels. The experimental results revealed that Steel A exhibited superior fatigue resistance compared to Steel B, with fatigue limits of 550 and 500 MPa, respectively. Fracture surface analysis identified non-metallic inclusions (NMIs) comprising the complex MnO-SiO2 as critical sites for crack initiation during cyclic loading in both steels. The HIT results after fatigue indicated significant cyclic softening for Steel A, with HIT values decreasing from 7.7 ± 0.36 to 5.66 ± 0.26 GPa. In contrast, Steel B exhibited slight cyclic hardening, with HIT values increasing from 5.24 ± 0.23 to 5.41 ± 0.31 GPa. Furthermore, the martensitic steel demonstrated superior yield and tensile strengths of 1145 and 1870 MPa, respectively. Analysis of the fatigue behaviour revealed the superior fatigue resistance of martensitic steel. The complex morphology and shape of the NMIs, examined using the 3D microstructure characterisation technique, demonstrated their role as stress concentrators, leading to localised plastic deformation and crack initiation.

Mechanical and micro-structural characterization of biodegradable coir fiber–glass sheet–charcoal reinforced polymer composite: an experimental approach

In the present investigation, the combined influence of coir, glass fibers and charcoal content on the mechanical properties of epoxy-based hybrid composites has been explored, providing insights for the potential development of advanced materials with tailored performance characteristics. Through a systematic analysis of the mechanical properties (tensile strength, Young's modulus, flexural strength, flexural modulus, and Brinell hardness number), various composite formulations were evaluated to discern their performance characteristics. The study reveals significant variations in mechanical properties across different composite configurations, highlighting the critical role of fiber type and charcoal content in determining the materials’ performance. Notably, composites featuring alternating layers of glass and coir fibers exhibit superior tensile and flexural strengths, underscoring the synergistic effects of hybridization. Conversely, the introduction of charcoal as a reinforcement agent leads to deterioration in the mechanical properties, indicating a trade-off between the reinforcement and other desirable attributes. These findings offer valuable insights for the strategic design and engineering of advanced materials tailored to specific applications, paving the way for the development of high-performance epoxy-based hybrid composites with enhanced mechanical properties and durability.

Fabrication and characterization of austenite-ferrite stainless steel bimetals by twin wire arc additive manufacturing

In this work, gas metal arc welding (GMAW) based twin wire arc additive manufacturing (TWAAM) system has been employed to deposit to wire materials simultaneously to fabricate austenite-ferrite stainless steel (AFSS) bimetal of austenite stainless steel (SS304L) and ferrite stainless steel (SS430L). A combination of high voltage and wire feed with low torch speed and gas flow resulted in optimal deposition as determined through response surface analysis based on experimental data of single-track bimetal bead on plate depositions. Mechanical and microstructural characterization of the AFSS bimetal was carried out using tensile test, hardness tests, fractography, SEM with EDS, and phase analysis. Tensile properties of the AFSS bimetal were seen to improved with the yield strength of 343 MPa, ultimate strength of 613 MPa and elongation of 67%, and a hardness value of 225 HV. The interface of the AFSS bimetal was found defects free and microstructures contained both austenite and ferrite phases with higher amounts of Ni-content. The fracture morphology of the fabricated AFSS bimetal was seen to contain dimple sizes lying between that of individual steels and resulted in higher elongation than that of the pure ferrite steel. This study demonstrated defects free fabrication of bimetallic structures with unique microstructural features and enhanced mechanical properties.

Investigating the Effects of Boron Nitride on Mechanical Properties of CoCrFeNiMn Composites

High‐entropy alloys (HEAs) are gaining attention for their exceptional properties but achieving precision and surface quality in powder metallurgy (PM) can be challenging. This study investigates the mechanical properties of CoCrFeNiMn HEAs produced through the flake powder metallurgy (FPM) technique and laser powder bed fusion (LPBF) preservative industrial, which established outstanding antiwear properties. To assess the enhancement of mechanical behavior and wear resistance by incorporating boron nitride (BN) into CoCrFeNiMn composites is fabricated via FPM. By incorporating BN into the composites, the mechanical behavior is significantly enhanced, leading to improved resistance against wear. Furthermore, the study delivers comprehensions into the serration behavior microstructure and shear localization in a high‐strain‐rate‐deformed CoCrFeMnNi entropy‐high alloy produces through metallurgy in powder. The serration behavior of the CoCrFeMnNi HEA is discussed concerning strain rate and temperature. Accordingly, the study employs the LPBF technique to fabricate the CoCrFeMnNi alloy from the prepared flakes. Microstructural characterization using scanning electron microscopy and X‐ray diffraction techniques to explore phase distribution, grain size, and possible segregation in the CoCrFeMnNi alloy produced through FPM‐LPBF is performed. In this particular investigation, a gradient microstructure is achieved through fusion in a laser‐powder bed of CoCrFeMnNi HEA onto highly deformed equal‐atomic HEA sheets. The resulting combination of partially recrystallized regions, exhibiting elevated yield strength, and fully recrystallized regions, demonstrates enhanced strain hardenability and elongation, and yields superior mechanical properties. The results obtained from the FPM‐LPBF CoCrFeMnNi alloy will be compared with those of conventionally processed CoCrFeMnNi to highlight the advantages and improvements achieved through the proposed method. The study findings reveal that the fundamental understanding of HEAs’ behavior under LPBF with FPM affords valuable insights into optimizing the processing parameters and achieving superior mechanical attributes.

Stepwise Optimization of Thermoelectric Performance in n‐Type SnS

AbstractTin sulfide (SnS) has been developed as an earth‐abundant and eco‐friendly compound that exhibits promising thermoelectric (TE) performance. While significant achievements are achieved in p‐type SnS, the development of its n‐type counterpart remains at a nascent stage, making it rather essential for developing n‐type SnS to ensure good compatibility in SnS‐based TE devices. In this study, Br is selected as the aliovalent dopant for realizing n‐type transport in SnS. Subsequently, isoelectronic Se alloying and vacancy compensation are utilized to further promote the TE performance for n‐type SnS. Se alloying can effectively narrow the bandgap of SnS for enhancing carrier concentration and diminishing thermal conductivity by strain and mass field fluctuations, while the excess Sn further compensates intrinsic Sn vacancies, thus optimizing carrier concentration and mobility simultaneously. These results are well verified by microstructure characterization and defect formation energy calculations. Consequently, the maximum ZT value of ≈0.7 and quality factor B of ≈1.02 at 823 K can be obtained after stepwise optimization, which is currently the highest value for n‐type SnS thermoelectrics. This study presents a significant progress for n‐type SnS and lays an important foundation for constructing all‐SnS‐based TE devices.

The role of magnesium oxide addition in densification of AlON transparent ceramics by pressureless sintering

AbstractPressureless sintering processing was adopted to fabricate transparent aluminum oxynitride (AlON) ceramics by using magnesium oxide (MgO) as a sintering additive into synthetic single phased aluminum oxynitride powder. Under the condition of adding 0.6 wt% magnesium oxide, the relative density of aluminum oxynitride ceramics increased from 98.67% with no addition to 99.9% after being held at 1800°C for 24 h, coupled by a reducing of average grain size from 190 µm to 130 µm. The optical linear transmittance of the AlON ceramic sample (thickness 1.2 mm) reached 84.2% at the wavelength of 1100 nm. The microstructural characterizations by energy dispersive spectroscopy and atom probe tomography indicated that the doping Mg element was uniformly dispersed inside aluminum oxynitride grains of as‐sintered ceramics. It was demonstrated that magnesium oxide played a key role in inhibiting the movement of grain boundaries, eliminating pores, leading to the fully densification of aluminum oxynitride ceramics.

What can machine learning help with microstructure-informed materials modeling and design?

AbstractMachine learning (ML) techniques have been widely employed as effective tools in addressing various engineering challenges in recent years, particularly for the challenging task of microstructure-informed materials modeling. This work provides a comprehensive review of the current ML-assisted and data-driven advancements in this field, including microstructure characterization and reconstruction, multiscale simulation, correlations among process, microstructure, and properties, as well as microstructure optimization and inverse design. It outlines the achievements of existing research through best practices and suggests potential avenues for future investigations. Moreover, it prepares the readers with educative instructions of basic knowledge and an overview on ML, microstructure descriptors, and ML-assisted material modeling, lowering the interdisciplinary hurdles. It should help to stimulate and attract more research attention to the rapidly growing field of ML-based modeling and design of microstructured materials. Graphical abstract

Microstructural and hardness characterization of stainless steel 316-Inconel 718 multimaterial developed by wire-based Directed Energy Deposition

Microstructural and hardness characterization of stainless steel 316-Inconel 718 multimaterial developed by wire-based Directed Energy Deposition

Accurate quantification of dislocation loops in complex functional alloys enabled by deep learning image analysis

In-depth statistics of individual defects observed during transmission electron microscopy (TEM) experiments are essential for the thorough characterization of materials. In this study, we aim to quantitatively characterize the population of dislocation loops in ion-irradiated CrFeMnNi alloys. To this end, we propose an efficient guideline to prepare TEM micrographs dataset for deep learning analysis, adapted for accurate characterization of microstructures produced by thousands of overlapping defects, a very common situation in TEM images, unfeasible by previous existing methods. To reduce human effort, we annotate only a few images and complement the database through a two-step process: initially, singular value decomposition to normalize image background, followed by a controlled data augmentation. The performed analysis provides precise quantitative information about the number of loops of different types, as well as their spatial distribution, their size, and the inter-object distances. These characteristics provide insights into the nucleation, mobility, and growth of dislocation loops, as well as the elastic anisotropy of the material. Our results emphasize how accurate analysis of complex microstructures can provide insights into the physical properties of materials and open up many perspectives for attaining quantitative information on materials properties based solely on their image analysis.

Alumina ceramic insulation layer for strain sensor fabricated by direct laser deposition

ABSTRACT Strain sensors are often used to monitor the use of critical components. The bond strength between the strain sensor and the gear teeth is particularly critical. There is a problem of insufficient bond strength between separated strain sensors and parts. The strain sensor is prone to loosening and flaking in the working environment. Therefore, a method of preparing the ceramic insulation layer of the strain sensor by direct laser deposition (DLD) is proposed. The effects of laser scanning trajectories, laser power, and scanning speed on forming quality were investigated experimentally. In addition, the phase analysis, microstructure characterization, and insulation properties of the insulating layers prepared at different overlap rates were researched. The research shows that the ceramic insulation layer has good insulation properties and hardness. The maximum hardness can reach 2405.74MPa, and the insulation resistance increases with the number of layers. The surface of the ceramic insulation layer is dense and has no cracks.

Extracting ductile cast iron microstructure parameters from fracture surfaces: A deep learning based instance segmentation approach

This study investigates the deep-learning based microstructural analysis from SEM images of ductile cast iron fracture surfaces. A Mask R-CNN model was trained, achieving 70% precision and 75% recall in graphite particle detection. Combined with a fracture surface reconstruction using the.4-quadrant backscattered electron signal, key parameters, including the particle size, shape and distance were extracted accurately. Compared to micrograph analysis, following probabilistic simulations showed the impact of the higher microstructural variance for the fracture surfaces on crack initiation, leading to higher scatter and elevated crack resistance curves. This highlights the potential of deep-learning based analysis for comprehensive microstructural characterization.

The Dependence of Electrochemical Behavior and Discharge Performance on the Zn/Gd Ratio of Mg-Li-Zn-Gd Anodes for Mg-Air Batteries

In this study, the electrochemical performance and discharge behavior of Mg-Li-Zn-Gd alloys with α-Mg and β-Li-based anode material are investigated, with the aim to improve the anode performance of Mg-air batteries. The experimental anode alloys with detailed Mg-8Li-xZn-yGd (x = 1, 2, 3; y = 1, 2, 3 wt.%) components are prepared, and extrusion deformation is carried out on these alloys. Simultaneously, scanning electron microscope (SEM), X-ray diffractometer (XRD), electrochemical workstation, and constant current discharge systems are applied for microstructure characterization, corrosion, and discharge performance testing. The results show that the experimental alloys are composed of an α-Mg and β-Li dual matrix, with W-Mg3Gd2Zn3, Mg3Gd, and MgLiZn second phases. Meanwhile, extrusion deformation promotes the recrystallization process through the particle-induced nucleation mechanism. The corrosion resistance is improved with the increasing Zn/Gd ratio, and the extruded Mg-8Li-2Zn-1Gd (LZG821) alloy exhibits the optimum corrosion resistance, with a corrosion rate of 0.493 mm·year−1. In addition, the extruded Mg-8Li-1Zn-1Gd (LZG811) alloy has the optimal discharge performance, with a discharge specific capacity of 1371.04 mA·g−1 at a current density of 40 mA∙cm−2, and its anode efficiency reaches nearly 70%. The poorer discharge properties of the Mg-8Li-2Zn-1Gd (LZG821) and Mg-8Li-2Zn-3Gd (LZG823) alloys are attributed to their refined grains, which could bring severe intergranular corrosion while increasing the grain boundary density.

Understanding the grain refinement and residual stress formation mechanisms of a Ni-based alloy during machining processes

Ni-based alloys are important materials for many industries, microstructure of the sub-surface regions of these alloys can be refined during machining processes, affecting both their machinability and service performance. Several mechanisms have been proposed to explain the machining-induced microstructure refinement of these alloys, however, sound evidences to support them are still lacking. In this research, microstructure characterization with an emphasis on the micro-texture and defects was conducted on milled surfaces of a Ni-based alloy, to promote in-depth understanding of the grain-refinement process. A nano-crystalline layer consisted a topmost region with randomly-orientated grains and annealing nano-twins and a textured region beneath it with deformed microstructure was observed in the cross-section of the alloy with the help of high resolution orientation determination techniques. These observations provide additional evidences to support the recrystallization induced grain-refinement mechanism of the nano-grains. It is also suggested that recrystallization was a by-product of the shear deformation occurred during the milling process, supported by the observation of the clear boundary between the nano-grain layer and its beneath deformed region. The deformed region was refined as a result of mechanical twining and twin-intersections, leading to significant fluctuations of the residuals stresses.

Experimental Study of the Microstructural Characterization of Microbial Induced Calcite Precipitation (MICP) Bio-Cement Concrete

Experimental Study of the Microstructural Characterization of Microbial Induced Calcite Precipitation (MICP) Bio-Cement Concrete