Microstructural Characterization Research Articles

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.

Effect of mechanical milling time on powder characteristic, microstructure, and mechanical properties of AA2024/B4C/GNPs hybrid nanocomposites

In this study, hybrid nanocomposites consisting of an AA2024 matrix reinforced with 1 wt% B4C nanoparticles and 1 wt% GNPs were produced using a powder metallurgy method assisted by mechanical milling. This study aimed to systematically investigate the effect of grinding time on powder characteristics (particle size, microhardness, and morphology) as well as microstructure, densification, and mechanical performance to optimize processing conditions for superior material properties. Microstructural characterization of powders and bulk samples were carried out using a SEM device equipped with EDS. The results indicate that with increasing milling time, the particle size significantly decreased, while the particle hardness increased substantially. Additionally, the sample milled for 8 h achieved the highest relative density among the hybrid nanocomposites, reaching a value of 95.3 %. Mechanical tests revealed that after 8 h of milling, the hardness and tensile strength reached peak values of 164 HB and 314 MPa, corresponding to increases of 56 % in hardness and 43 % in tensile strength compared to the unreinforced alloy. The analysis results confirm that the optimal properties were obtained after 8 h under all conditions.

Mechanistic understanding of banded microstructure and its effect on anisotropy of toughness in low carbon-low alloy steel

In this study, the relationship between the anisotropy of toughness and microstructure in low carbon low alloy steel treated by quenching and tempering (QT) heat treatment was investigated with the aid of scanning electron microscope, electron back-scattered diffraction and transmission electron microscope combined with energy disperse spectroscopy techniques. Results show that the impact toughness of the quenched steel plate along the longitudinal and transverse directions are little different. However, after tempering, the longitudinal impact toughness of QT steel plate is improved by 88%, while the transverse impact toughness is slightly decreased, leading to a significant anisotropy of toughness. Microstructural characterizations reveal that banded microstructure with coarse grain size exists along longitudinal direction (i.e., rolling direction) of steel plate, which is attributed to co-segregation of Mn and C and the resulting uneven recrystallization during hot rolling. After tempering, fine and dispersed carbides are precipitated in matrix microstructure, but high-density coarse carbides are formed within banded microstructure. It is suggested that the coarse grains and high-density coarse carbides significantly deteriorate the resistance against crack propagation along banded microstructure, leading to the anisotropy of toughness of QT steel plate. The findings of this study will aid to design metallurgical processes including chemical composition design, hot rolling, and heat treatments to eliminate the anisotropy of toughness of low alloy steels with high strength and toughness.

Enhanced vacuum brazing joining between Ti–48Al–2Cr–2Nb/Ti–22Al–25Nb intermetallic alloys by Zr-free Ti-based filler

This study investigates the microstructure and tensile properties of vacuum-brazed joints of Ti–48Al–2Cr–2Nb (Ti4822) and Ti–22Al–25Nb (Ti2AlNb) intermetallic alloys using Ti-based filler metals, with and without the addition of Zr element. Detailed microstructural characterization of the brazed joints was conducted using Electron Backscatter Diffraction and Transmission Electron Microscopy, identifying various phases and their distributions. The tensile properties were tested at room temperature and at 650 °C, revealing the influence of Zr on the mechanical performance of the joints. The results demonstrated that the microstructure of joints brazed with Zr-containing filler metals exhibited a layered structure with brittle Zr-enriched intermetallic compounds, limiting their mechanical properties. Conversely, Zr-free filler metals yielded more homogeneous and ductile microstructures, significantly improving tensile strength and elongation. The Zr-free joints obtained after holding at 980 °C for 60 min exhibits the highest tensile strength, reaching 368.23 MPa at room-temperature and 293.46 MPa at 650 °C, respectively. These findings provide valuable insights for optimizing brazing processes and filler metal compositions to enhance the performance of TiAl-based intermetallic alloy joints.

Low-Velocity Impact Behaviors of B4C/SiC Hybrid Ceramic Reinforced Al6061 Based Composites: An Experimental and Numerical Study

This study studied the low-velocity impact behavior of silicon carbide (SiC), boron carbide (B4C), and hybrid B4C/SiC reinforced aluminum 6061 alloy (Al 6061) matrix composites experimentally and numerically. The effect of hybridization, reinforcement volume fraction, and reinforcement type on low-velocity impact was investigated. 16 different metal-matrix composite materials were manufactured for the study, including 9 hybrid samples, 6 non-hybrid samples for each reinforcing ceramic particle, and 1 unreinforced sample. The powder metallurgy - hot press method was used in experimental production and then low-velocity impact tests were carried out. Numerical study was carried out using the non-linear finite element method (FEM). A Python algorithm running on ABAQUS/Explicit was utilized to determine ceramic particle distribution based on volume fraction, hybridization ratio, and random particle arrangement. The Johnson-Cook Plasticity Model was used for the non-linear relationship between stress and strain in the Al 6061 metal-matrix during impact. The results were interpreted with the contact force-time, contact force-displacement, and energy-time data obtained from low-velocity impact tests. In addition, the amount of collapse that occurred during the impact was measured and compared, and finally, SEM/EDX analysis was performed for the microstructure characterizations of the composite sample. Impact tests revealed that the collapse of composite samples ranged from 3.06mm to 3.58mm, with the unreinforced S6 sample collapsing 4.18mm, indicating that increased reinforcement elements reduce ductility, while a lower B4C ratio or higher SiC ratio in hybrid composites leads to greater collapse. Keeping the hybridization rate constant while increasing the reinforcement ratio leads to an increase in contact force and a decrease in contact time. Hybrid composites exhibited higher stiffness as SiC content increased, while B4C reinforced non-hybrid composites showed more significant stiffness. There is good agreement between the numerical and experimental results. Non-hybrid samples have a better match between numerical predictions and experimental results than hybrid samples.

Enhancing microstructure, nanomechanical and tribological properties of TiAl alloy processed by spark plasma sintering with Si3N4 ceramic particulates addition

TiAl matrix composites reinforced with varying weight fractions of Si3N4 ceramic particles were successfully fabricated by the spark plasma sintering method. The microstructure, nanomechanical and tribological properties of the sintered composites were investigated. The microstructural characterization revealed the evolution of a quasi-continuous and continuous network structure consisting of minor fractions of in-situ formed Ti2AlN, unreacted Si3N4 ceramic particles and dominant Ti5Si3 intermetallic phases within the TiAl matrix at Si3N4 content above 1.5 wt%. The in-situ precipitated phases enhanced the nanomechanical and tribological properties of the composites. The 7Si3N4/TiAl composite displayed the best nanomechanical properties, including nanohardness, elastic modulus, and H/Er ratio among the sintered samples. The specific wear rate of the composites decreases with increasing reinforcement content. 7Si3N4/TiAl composite exhibited the lowest specific wear rate of 0.38 ± 0.55 10-4 mm3/Nm, representing a 95.6% improvement in wear resistance compared to the unreinforced pure TiAl alloy. The improved wear performance of the composites was attributed to their load-bearing capacity and wear resistance of the hard, in-situ Ti2AlN, Ti5Si3 and unreacted Si3N4 particles in the TiAl matrix. The composites displayed a transition from adhesive wear to predominantly abrasive wear where the hard Si3N4 particles prevented direct metal-to-metal contact and facilitated the formation of a protective tribolayer, resulting in enhanced wear resistance. Hence, the developed Si3N4/TiAl composites are suitable for various structural and tribological applications.

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.

Strength analysis and microstructural characterization of calcined red mud based-geopolymer concrete modified with slag and phosphogypsum

This research aims to comprehensively investigate the combined use of calcined red mud (RM), calcium sulfate dihydrate (CSD), and ground granulated blast furnace slag (GGBFS) in geopolymer concrete (GC), demonstrating how their optimized proportions improve GC's fresh, mechanical, durability, and microstructural properties. This study investigated the influence of partially replacing calcined red mud (RM) with GGBFS and Phosphogypsum or CSD in GC. The test program included tests on the fresh, mechanical, and durability properties of these blends, including slump value, compressive strength, ultrasonic pulse velocity, water absorption and porosity, rapid chloride penetration, electrical resistivity, mass loss due to freeze-thaw cycles, and resistance to sulfate attack. Material characterization of the GC blends was conducted using scanning electron microscopy (SEM), X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), thermogravimetric analysis (TGA), and differential thermogravimetric analysis (DTG). One-way ANOVA analysis was also used to examine the significance of variation between the results due to the replacement of calcined RM with GGBFS and CSD. The results showed that the mix R40-G45-C15, with 40% calcined red mud, 45% GGBFS, and 15% CSD, demonstrated the highest density at 2401 kg/m³, 15.93% greater than the R70-G15-C15 mix, and achieved a compressive strength 73.40% higher at 28 days. Additionally, R40-G45-C15 showed superior durability, with water absorption and porosity reductions of 87.42% and 83.86%, an 85.78% reduction in charge passed at 7 days, and a 40.94% lower mass loss from freeze-thaw cycles compared to R70-G15-C15. SEM analysis confirmed the formation of N–A–S–H and C–A–S–H gels in the blends, contributing to improved density and strength. XRD tests indicated the nominated peaks of calcite, quartz, and portlandite in the blends, with increased portlandite intensity due to higher RM content. These results indicate that partially substituting the calcined RM with CSD and GGBFS in GC could be a viable alternative option, offering potential contributions to sustainable construction with improved structural performances.

Unravelling the dominant influence of microsegregation on creep rupture behaviour of additively manufactured inconel 718

This investigation focuses on unravelling the dominant influence of microsegregation and microstructure altered due to heat treatment cycle variation on creep rupture behaviour of additively manufactured Inconel 718 (AM-IN718). Two microstructural variants differing in the fraction of recrystallized grains while δ-phase being absent, were produced. A typical heat treatment (HT) cycle includes the stress-relieving of the as-built specimens at 980 °C, followed by solution treatment at 1080 °C (STA1080, a partially recrystallized microstructural variant) or 1150 °C (STA1150, a fully recrystallized microstructural variant), and double ageing (soaking at 720 °C for 8h and subsequent furnace cooling, followed by 8h at 620 °C and air cooling).Detailed microstructural characterization of two microstructural variants through correlative microscopy revealed a prevalent existence of Nb-rich precipitate-free zones (PFZ) in STA1080 than in STA1150. Creep characterization of the two microstructural variants in the temperature range of 625–675 °C and at 500–750 MPa demonstrated superior creep resistance in STA1150. The correlation of kinetic analysis and comprehensive post-deformation microstructural characterization suggests grain boundary cavitation as the main damage/softening mechanism and the reason for the difference in creep rupture behaviour between the two microstructural variants. The long-term exposure heat treatment methodology demonstrates that PFZs are the major influencing factor responsible for microsegregation-dependent creep rupture behaviour. Interestingly, the presence of the δ phase within PFZs appeared to retard cavity coalescence and failure during creep, despite its usual detrimental role in creep resistance.

A novel process for simultaneously improving the strength and plasticity of 18Ni(350) maraging steel

A novel process involving cold deformation, cyclic solution, and two-step aging is developed for simultaneously improving the strength and plasticity of 18Ni(350) maraging steel. The strengthening and toughening mechanisms are elucidated by microstructural characterization and tensile property measurements. Cold deformation and cyclic solution refine the final martensite grains. In addition, two-step aging ensures the formation of numerous fine precipitates and a small amount of fine reversed austenite. Ultra-high strength is achieved by a combination of solid-solution, grain refinement, dislocation, and precipitation strengthening, with the latter having the largest contribution. Compared with the traditional process, the UTS and elongation are increased by 9.13% and 22.83%, respectively, to 2511 MPa and 5.81%, demonstrating the effectiveness of this novel process.

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.

Optimizing weld strength and microstructure in CP-titanium and 304 stainless steel friction welds with chromium interlayer

This study investigates the effect of a Cr-interlayer on the hardness and friction-welded joint strength between CP-titanium and 304 stainless steel. Rotary friction welding, with its adjustable parameters such as upset pressure, is the preferred method for this dissimilar joint. Due to the difference between these two base metals, a metallic interlayer like chromium, is crucial for controlling the formation of intermetallic compounds (IMCs). Welding was conducted at three different upset pressures, both with and without the Cr-interlayer. Tensile and microhardness tests were performed, complemented by phase analysis and microstructural characterization using XRD and SEM. Our findings reveal that employing a chromium layer and higher upset pressures enhances strength while reducing the presence of brittle IMCs in the welds. At the CP-titanium side, dynamic recrystallization occurs due to increased heat generation at the interface and strain occurred by materials flow, facilitating IMC formation, especially evident at 250 MPa upset pressure. Interestingly, relatively higher strength at 150 MPa is attributed to the absence of IMCs. Conversely, higher strength results at 350 MPa due to from the flow of softened material, effectively purging IMCs from the weld zone. Notably, both β-titanium and chromium-based IMCs form in the presence of the chromium interlayer, resulting in decreased joint hardness and increased overall ductility. In conclusion, our study's findings contribute to bridging the gap between theoretical strength and practical application, significantly advancing joint performance.

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.