Microstructural Characterization Research Articles

Microstructure and mechanical properties of dissimilar resistance spot welds of TBF and HSLA300 steel sheets

Abstract The welding behavior of the resistance spot welded dissimilar TBF–HSLA300 steel joints under different welding parameters was investigated. TBF steels were used as galvanized or ungalvanized. Microstructural characterization and mechanical tests were performed. Higher heat input resulted in the higher possibility of shrinkage cavities at the weld nugget and also increased the risk of liquid metal embrittlement (LEM) crack in the heat affected zone (HAZ) on galvanized TBF steel sheets. A partial melting zone was observed on HSLA300 side. The welds with ungalvanized TBF sheets had the higher nugget size and indentation. The highest hardness values (over 500 HV0.1) were observed in HAZ on TBF side. The lowest hardness values (below 300 HV0.1) on TBF side were observed in a very narrow softening zone between tempered zone and base metal. The fractures of all spot welds in the tensile shear test occurred on the TBF steel side with the thinner thickness. Low-strength steel sheet have to be sufficiently thicker in order to achieve higher welding strength. Higher welding time led to higher weld strength in the ungalvanized TBF combination. In the galvanized TBF combination, higher heat input led to the drastic decrease in weld strength due to LEM cracks.

Microstructure Evolution of Cold-Rolled Carbide-Free Bainite Steel Sheets During Continuous Annealing Process

A modified carbide-free bainite (CFB) steel has been developed, building on existing alloys for compatibility with commercial continuous annealing lines (CALs), featuring a low austenitization temperature and short overaging time. The microstructural features of such candidate CFB sheets are compared with those of conventional CFB steel sheets that require higher reheating temperatures and longer overaging times. The effects of annealing parameters such as reheating temperatures and overaging temperatures on phase transformation kinetics and microstructure evolution are presented. The annealing process was simulated in a Gleeble thermomechanical processing simulator, and the microstructural characterization was carried out using XRD, SEM, and EBSD. Reconstruction of parent austenite grains from EBSD data did not reveal any variant selection, regardless of changes in the austenitization temperature, overaging temperature, or carbon content. It was observed that the V1–V2 variant pairing is the most common at the lower overaging temperature for reheating at 950 °C; however, this pairing decreases as the isothermal overaging temperature increases, with variant pairings involving low misorientation boundaries—such as V1–V4 and V1–V8—becoming more frequent. Steels with higher carbon content exhibit no significant changes in their variant pairing, regardless of variations in the austenitizing or isothermal temperatures. The XRD results show that the retained austenite fraction is reduced by increasing the isothermal transformation temperature.

Tailoring Wear Properties of Nodular Cast Iron through Induction Hardening Optimization

Abstract The current study investigated the wear performances of GGG60 nodular cast iron under different loads after induction hardening at different powers and durations. The background of this study is the optimization of induction hardening parameters applied to increase the wear resistance of GGG60 nodular cast iron, which is the raw material of parts subjected to high wear loads such as crankshafts, gear systems and flywheels. With the obtained wear results, the induction parameters were optimized by RSM. Induction hardening was treated at four induction powers and two induction durations. Wear tests were conducted using the ball-on-disc method under dry wear conditions for 60 min. Three different wear loads of 10, 20, and 30 N were used. The samples were analyzed in terms of microstructure, hardness, and wear characterization. Subsequently, a RSM model was constructed using the wear results Untreated specimens have significantly lower performance characteristics than treated ones. The hardness, penetration depth, and wear performance indicated a strong relationship with the increase in both induction power and duration. The optimization model presented that the most critical parameter of volume loss is the wear load. In addition, induction power and wear load were found to be significant in the wear rate. The model's prediction capacity for volume loss is satisfactory. Nevertheless, the model's prediction capacity for the wear rate experienced a slight decrease. Conclusions indicate the model can estimate the induction hardening parameters.

Effect of Porosity on Tribological Properties of Medical-Grade 316L Stainless Steel Manufactured by Laser-Based Powder Bed Fusion

The potential of laser-based powder bed fusion (L-PBF) technology for producing functional components relies on its capability of maintaining or even improving the mechanical properties of the processed material. This improvement is associated with the microstructure resulting from the high thermal gradient and fast cooling rate. However, this microstructural advantage may be counterbalanced by the lack of full density, which could be tolerated to a certain degree for applications such as biomedical implants and medical equipment. In this study, medical-grade 316L stainless steel specimens with porosities ranging from 1.7 to 9.1% were additively manufactured by L-PBF using different combinations of laser power and scanning speeds. Tribological properties were evaluated by pin-on-disc testing in dry conditions against a silicon nitride test body and analyzed in the context of microstructural characterization by optical and electron microscopy. The results reveal that higher porosity allows for a diminishing wear rate, which is explained by the capacity of the pores to retain wear debris related with the three-body abrasion. This research provides practical insights into the design of medical wear-resistant components, thereby enhancing our understanding of the potential of L-PBF in the fields of materials science and biomedical engineering.

Rigid Fluorescent Indacenetetraone‐Based Semiconducting Polymers via Knoevenagel Condensation

AbstractThe synthesis of new donor‐acceptor polymers is reported through Knoevenagel condensation of indacenetetraone with aromatic dialdehydes. The obtained polymers possess exceptionally rigid planar backbones with a rotational barrier (for single C─C bonds) of 16–20 kcal mol−1, the highest among known conjugated polymers. These structural features confer several unusual properties, including remarkably narrow absorption bands with very high absorption coefficient (up to ≈3×105 cm−1) and efficient fluorescence in the red to near‐IR region (λmax 694–850 nm, quantum yield 10–29%). Systematic spectroscopic, electrical, and microstructural characterization supported by Density Functional Theory (DFT) calculations reveals the effects of heteroatoms and the conjugation lengths on the optoelectronic properties of these materials. The polymers exhibit ambipolar charge transport in field‐effect transistors, which can be tailored to show unipolar p‐type (0.1 cm2 V−1 s−1) and n‐type (0.05 cm2 V−1 s−1) behavior by adjusting the energy levels at the polymer/metal contacts. Additionally, their application is demonstrated as acceptors in all‐polymer organic photovoltaic devices with commercial donor polymers, achieving a power conversion efficiency (PCE) of 11%.

Effect of Hydride Types on the Fracture Behavior of a Novel Zirconium Alloy Under Different Hydrogen-Charging Current Densities.

Hydrogen embrittlement is a critical issue for zirconium alloys, which receives long-term attention in their applications. The formation of brittle hydrides facilitates crack initiation and propagation, thereby significantly reducing the material's ductility. This study investigates the tensile properties and hydride morphology of a novel zirconium alloy under different hydrogen-charging current densities ranging from 0 to 300 mA/cm2, aiming to clarify the influence of hydrides on the fracture behavior of the alloy. The mechanical property results reveal that, as the hydrogen-charging current density increases from 0 to 100 mA/cm2, the maximal elongation decreases from 24.99% to 21.87%. When the current density is further increased from 100 mA/cm2 to 200 mA/cm2, the maximal elongation remains basically unchanged. However, a substantial drop in elongation is observed as the hydrogen-charging current density rises from 200 mA/cm2 to 300 mA/cm2, decreasing from 20.77% to 15.18%, which indicates a marked deterioration in hydrogen embrittlement resistance. Subsequently, phase compositions, fracture morphology, and hydride types in the fracture region of tensile specimens were characterized. The morphology and quantity of hydrides change with increasing hydrogen-charging current density. When the hydrogen-charging current density reaches 100 mA/cm2, the δ-phase hydrides form, which significantly reduces the ductility of the zirconium alloy. At a hydrogen-charging current density of 200 mA/cm2, metastable ζ-phase hydrides are formed, resulting in negligible variations in the alloy's mechanical properties. However, when it comes to 300 mA/cm2, stable δ-phase hydrides with diverse morphologies form, leading to a pronounced degradation in tensile performance. Finally, by integrating mechanical tests with microstructural characterization, the influence of hydrides formed under different hydrogen-charging current densities on the zirconium alloy was analyzed. With increasing hydrogen-charging current density, the maximal elongation of the specimens gradually decreases, while the tensile strength steadily increases. At a hydrogen-charging current density of 300 mA/cm2, a larger amount of hydrides is formed, and the hydride type transitions completely from a mixture of δ-phase and ζ-phase hydrides to entirely δ-phase hydrides. The formation of lath-like δ-phase hydrides induces twinning structures, resulting in further lattice mismatch, which significantly reduces the maximal elongation of the zirconium alloy. Additionally, the morphology of the δ-phase hydrides changes from slender needle-like structures to lath-like structures, leading to a notable increase in internal stress, which in turn further enhances the tensile strength of the specimens.

Machine Learning-Assisted Microstructural Quantification of Multiphase Cathode Composites in All-Solid-State Batteries: Correlation with Battery Performance.

Microstructure optimization and high-performance material development are crucial for improving the electrochemical performance of all-solid-state batteries (ASSBs). Researchers frequently record numerous micro-scale or nano-scale electron micrographs for unbiased post-mortem analysis, performance evaluation, and improvement of ASSBs. However, these micrographs are often underutilized and typically analyzed qualitatively without ensuring an accurate representation of the experimental objectives. This study explores machine learning (ML)-based quantitative analysis techniques using electron microscopy images, combined with a stereology-driven linear-intercept concept method and semantic segmentation, to extract quantitative microstructural parameters for optimizing ASSB performance. The applicability of ML-assisted image analytics is demonstrated by employing composite cathodes in ASSBs to achieve unbiased automation and deep semantic segmentation during microstructural characterization. Furthermore, the ramifications of this ML-assisted method are discussed, along with its advantages and disadvantages in battery research.

A Novel Approach for Fabricating In Situ Aluminum Foam‐Filled Carbon Steel Tubes via Hot‐Dip Aluminizing

Herein, a new process combining hot‐dip aluminizing (HDA) technology with melt foaming method is developed to prepare in situ aluminum foam‐filled AISI 1020 tubes with metallurgical bonding which has the advantages of low production cost and wide range of product sizes. Detailed microstructural characterization is performed at the foam/tube interface of in situ foam‐filled tubes (FFTs). Quasistatic compressive experiments are carried out to investigate deformation behavior and mechanical properties of ex situ and in situ FFTs with and without HDA pretreatment (in situ‐HDA FFTs and in situ‐without HDA FFTs). The results indicate that HDA pretreatment effectively improves the wettability between the steel tube and the aluminum melt, enhancing the interfacial bonding quality between the two. Under compressive loading, in situ‐HDA FFTs axially deform in an efficient mixed mode, showing superior energy absorption capability as compared to the empty heat treatment (empty‐HT) tubes. Specifically, in situ‐HDA FFTs have the highest specific energy absorption of an average of 16.6 kJ kg−1 which is 13% higher than the average value of ex situ‐HT FFTs.

Mechanical and microstructural characterization of sisal fiber-reinforced polyester laminate composites for improved durability in automotive applications

This study investigates the effects of fiber concentration and the stacking sequence of laminae on the mechanical properties of a sisal-reinforced polyester composite. The mechanical properties, such as the tensile, flexural, and impact strength were characterized for laminated composite with different fiber concentrations and stacking sequences of lamina after they were processed using the hand layup weaved method. In addition to the mechanical properties, morphological analysis was done. Specimens with different fiber concentrations and stacking sequences were prepared using a manual compression molding technique that provides a flat plate with a thickness of 5 mm. The results showed that 40 wt% of sisal fiber-reinforced composites with 90/0/45 staking sequence have shown the maximum tensile (68.409 MPa), flexural (64.276 MPa), and impact (67.71 MPa) strength, and laminated composite with 90/0/45 staking sequence has shown superior tensile, flexural and impact properties as it compared with randomly oriented and non-woven fiber reinforced composite. The microstructure showed that a better interface adhesion was observed at 40 wt% of fiber and 90/0/45 staking sequence. Therefore, 90/0/45 laminated composite materials can be proposed for engineering applications that require equivalent properties, including automobile front-fender applications.

Influence of surface treatments on highly translucent zirconia: Mechanical, optical properties and bonding performance.

Highly translucent yttria-stabilized zirconia (YSZ) has become more popular due to its enhanced aesthetics. This study aimed to evaluate the influence of traditional air abrasion and a new etching and cleaning agent, Multi Etchant, on the mechanical performance, optical properties, and bond strength of highly translucent zirconia. Specimens of 6YSZ, 5YSZ, 4YSZ&5YSZ, and conventional 3YSZ were fabricated and underwent different surface treatments, including as milled, air abrasion, and Multi Etchant. The chemical, phase, and microstructural characterization of zirconia were analyzed by X-ray fluorescence, X-ray diffraction, scanning electron microscope, and optical profilometer. Furthermore, flexural strength, optical properties, and bond strength of zirconia with resin composite cement before and after three-month water storage were measured. Highly translucent zirconia contained more c-ZrO2 and larger grain sizes (up to 1.85 μm), resulting in higher translucency but lower flexural strength compared to 3YSZ. Air abrasion substantially increased the flexural strength of 3YSZ and improved the bond strength of all zirconia types, with bond strength remaining stable after artificial aging. Multi Etchant did not significantly alter the mechanical or optical properties but enhanced the bond strength of UTML (6YSZ), TT-MT-ML (5YSZ), EZneer (5YSZ), and CER (3YSZ), particularly after water storage. Yttria content variations between highly translucent and conventional zirconia affected mechanical and optical properties but not bond performance. The bonding strategy of air abrasion pretreatment can be effectively extended to highly translucent zirconia. Using an etchant containing adhesive monomer shows clinical potential, as it enhances long-term bond strength without compromising zirconia's durability. The air abrasion parameter of 0.2 MPa for 10 s can be extended from 3YSZ to highly translucent zirconia without impairing its properties. Air abrasion improves the bond strength of highly translucent zirconia.

Assessing Durability and Stability of Calcium Sulfoaluminate Cement-Stabilized Soils Under Cyclic Wet–Dry Conditions

Periodic wet–dry processes are a significant weathering mechanism that can quickly alter a soil’s mechanical characteristics, reducing its resilience and durability. This study investigates the physical and microstructural characterization of stabilized soils through experimental analysis. While the conventional approach to ground improvement involves the application of ordinary Portland cement (OPC) and lime for treating unstable soil, this research explores calcium sulfoaluminate (CSA) cement as an eco-friendly alternative with comparable efficacy and fewer adverse environmental effects. The primary objective is to evaluate the impact of cyclic wet–dry (W–D) events on the durability and stability of CSA cement-treated sand using comprehensive laboratory testing. Various samples were prepared with cement contents of 3%, 5%, 7%, and 10%, corresponding to the optimum moisture content. Stabilized soil specimens underwent testing for unconfined compressive strength (UCS) and ultrasonic pulse velocity (UPV) after curing for 3, 7, 14, and 28 days. Subsequently, these specimens were exposed to zero, one, three, five, and seven W–D cycles. The outcomes show a decrease in the strength and durability index of the soil with a rising number of W–D cycles. However, the decline in the strength and durability of CSA-treated soil samples is significantly mitigated as the CSA content increases from 3% to 10%. The findings indicate that after seven W–D cycles, the UCS value of 10% cemented samples dropped by 14% after 28 days of curing, whereas 3% specimens experienced a 28% loss in strength. Similarly, UCS values for 5% and 7% cement content reduced from 666 kPa to 509 kPa and from 1587 kPa to 1331 kPa, respectively, indicating improved resilience with higher CSA content. The durability index was less affected during the first three cycles, but showed a more pronounced decline after five and seven cycles. For 3% cemented soil, the durability index dropped from 0.95 to 0.71, whereas for 10% cemented soil, it decreased from 0.97 to 0.82 after seven W–D cycles. The scanning electron microscope (SEM) also determines the cement–soil interaction before and after W–D, and it was noted that the pores and cracks increased after each cycle. Based on the findings, it is established that subgrade materials treated with CSA cement demonstrate durability, environmental sustainability, and suitability for integration into road construction projects.

A new methodology for investigating the weld joint microstructure and micro-hardness of the austenitic stainless steel clad plate made by SMAW/GTAW multi-pass welding process: part III – clad layer case study

In this study, the influence of repeated thermal cycling during multi-pass welding on the microstructural transformations and mechanical properties of austenitic stainless clad-steel plates (ASCSPs) was investigated, with a particular focus on the clad layer. A novel methodology was employed, involving the complete filling of the groove length and gradually shortening subsequent passes. Microstructural characterization of various zones within the welded joint was conducted using optical microscopy. The results demonstrated that repeated thermal cycles during multi-pass welding caused significant microstructural changes in the weld metal clad layer (WM-CL), including the transformation from columnar to equiaxed grains and the evolution of δ-ferrite morphology from dendritic to skeletal. Additionally, the ferrite number decreased from 8.5 ± 2 in the sixth pass to 2 ± 0.5 in the ninth pass, correlating with increased heat input (HI) from 15.5 kJ/cm to 25.8 kJ/cm and repeated thermal cycling. Furthermore, the heat-affected zone (HAZ) exhibited coarse-grained polygonal austenite near the fusion line, with recrystallization attributed to the high thermal input. Micro-hardness measurements showed a reduction from 320 HV in the sixth pass to 195 HV in the ninth pass, linked to alloying element diffusion and ferrite content reduction. The findings highlight the importance of controlling thermal cycles and HI during multi-pass welding to optimize the microstructural stability and mechanical properties of ASCSP welded joints. These results provide valuable insights for improving the performance of ASCSP in industrial applications.

A Novel Ceramic Reinforced Metal Matrix Composite (Cu–Ni/TiC–CaF2): Fabrication, Microstructure, Mechanical and Tribological Characterization

A Novel Ceramic Reinforced Metal Matrix Composite (Cu–Ni/TiC–CaF2): Fabrication, Microstructure, Mechanical and Tribological Characterization

Mechanical Testing and Microstructural Characterization of Bimetallic Structure of Austenitic Steel Fabricated via Wire plus Arc Additive Manufacturing

Mechanical Testing and Microstructural Characterization of Bimetallic Structure of Austenitic Steel Fabricated via Wire plus Arc Additive Manufacturing

Exploiting the Electrostatic Binding of Ruthenium Hexamine Molecular Redox Nanowires onto DNA/OGCN Biohybrid Electrodes toward the Electrochemical Detection of COVID-19.

The Coronavirus Disease 2019 (COVID-19) recently emerged as a life-threatening global pandemic that has ravaged millions of lives. The affected patients are known to frequently register numerous comorbidities induced by COVID-19 such as diabetes, asthma, cardiac arrest, hypertension, and neurodegenerative diseases, to name a few. The expensiveness and probability of false negative results of conventional screening tests often delay timely diagnosis and treatment. In such cases, the deployment of a suitable biosensing platform can readily expedite the rapid diagnosis process for enhanced patient outcomes. We report the development of an electrochemical genosensor based on DNA/OGCN (DNA/oxygenated graphitic carbon nitride) nanohybrids for the quantification of severe acute respiratory syndrome-coronavirus-2 (SARS-CoV-2) DNA─the key biomarker for COVID-19. This is achieved by exploiting the molecular nanowire-formation capability of the [Ru(NH3)6]2+/3+ redox probe onto the DNA phosphate backbone via electrostatic interactions. The microstructural characterization of OGCN was performed using scanning electron microscopy (SEM) coupled with an energy-dispersive X-ray (EDX) module, X-ray diffraction (XRD), and Fourier transform infrared spectroscopy. The electrochemical analyses were performed using cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS), while the analytical performance of the sensor was evaluated using square wave voltammetry (SWV). The developed sensor exhibited a wide linear detection range within 10 fM-10 μM, with a limit of detection (LoD) of ∼7.23 fM with a high degree of selectivity toward SARS-CoV-2 target DNA, thereby indicating its potential to be employed in a point-of-care scenario toward providing affordable healthcare to the global populace.

Micro-Defects-Related Low Cycle Fatigue Mechanical Model of the Nuclear-Grade S30408 Stainless Steel.

Continuous and interrupted low cycle fatigue tests were conducted on nuclear-grade S30408 stainless steel under different stress conditions at room temperature. Vickers hardness testing and microstructure characterization were performed on the fatigue samples with different fatigue states. The evolutionary mechanism of the microstructure defects in materials under fatigue cyclic loading was discussed. The traditional Basquin formula was used to predict the fatigue life of these fatigue samples. At the same time, a quantitative mechanical model related to the characteristic micro-defects parameter KAM and the Vickers hardness (Hv) was established for the S30408 stainless steel during the low cycle fatigue damage process, and the prediction accuracy of the Vickers hardness is greater than 90%, which is significant and useful for the fatigue life prediction of the 304 stainless steels used in nuclear systems and the safe operation of the reactors.

Significant reduction of anisotropy in stress relaxation aging and mechanical properties improvement for 2195 Al-Cu-Li alloy subjected to plastic loading

Although the plastic loading can enhance creep deformation and yield strength, the anisotropic Stress Relaxation Aging (SRA) behavior and mechanism under plastic loading remain unclear, which presents a significant challenge in accurately shaping aluminum alloy panels. In this study, the SRA behavior of 2195-T4 Al-Cu-Li alloys were thoroughly studied under initial loading stresses within the elastic (210/250 MPa) and plastic (380/420 MPa) ranges at 180 ℃ by stress relaxation and tensile tests as well as microstructure characterization. The findings reveal that compared with those under elastic loadings, in-plane anisotropy (IPA) values of the stress relaxation amount, yield strength and fracture elongation under plastic loadings are reduced by 60%-80%, 70%-90% and 72%-89%, respectively. Similarly, IPA values of precipitate size in grains and Precipitation-Free Zones (PFZ) width at grain boundaries under plastic loading decrease by 31.4% and 94.4% respectively. These results indicate plastic loading significantly weakens the anisotropic SRA behavior, owing to numerous uniformly distributed fine T1 phases and small IPA values of both T1 precipitates size and PFZ width in various loading directions. Compared with those of elastic loading-aged alloys, yield strength of plastic loading-aged alloys shows high strength-ductility because of the combined effect of closely dispersed fine T1 precipitates, narrowed PFZ and numerous sheared and rotated T1 phases at different locations during tensile process. The uniformly distributed larger Kernel Average Misorientation (KAM) and Schmidt factor values of the plastic loading-aged alloy, as well as the cross-slip generated, also help to enhance the strength and ductility of the alloy.

Experimental bilayer zirconia systems after aging: Mechanical, optical, and microstructural characterization.

To characterize two experimental zirconia bilayer materials compared to their monolithic controls, before and after hydrothermal aging. Commercial zirconia powders were utilized to fabricate two bilayer materials: 3Y-TZP+ 5Y-PSZ (3Y+5Y/BI) and 4Y-PSZ+ 5Y-PSZ (4Y+5Y/BI), alongside control groups 3Y-TZP (3Y/C), 4Y-PSZ (4Y/C), and 5Y-PSZ (5Y/C). Compacted specimens were sintered (1550 °C- 2 h, 3 °C/min), and half of them underwent hydrothermal aging (134 °C-20h, 2.2 bar). Characterizations were performed through scanning-electron microscopy (SEM), X-ray diffraction (XRD), Raman spectroscopy, reflectance tests and biaxial flexural strength test (ISO:6872). Weibull statistics were applied to determine the characteristic strength and Weibull modulus. Grain size and optical properties were analyzed using two-way ANOVA followed by the Tukey test. Degradation regions and monoclinic phase were observed at aged 3Y-TZP and 4Y-PSZ surfaces. Significant differences were observed in the evaluation of optical properties between the bilayer and control groups. The bilayer materials presented intermediate characteristic strength values compared to their controls and aging significantly increased the strength of some groups. Experimental bilayer materials presented lower mechanical properties than monolithic controls, 3Y/C and 4Y/C. Hydrothermal aging increased the characteristic strength of bilayered and monolithic controls, except for 5Y-PSZ. Both experimental bilayer systems, as well as monolithic controls, met the ISO 6872:2015 requirements for single-unit crowns (100 MPa), 3-unit fixed dental prostheses (FDPs) up to premolars (300 MPa), and 3-unit FDPs involving molars (500 MPa). However, for FDPs with four or more units, only monolithic 3Y-TZP and 4Y-PSZ, and bilayered 3Y+5Y met the required minimum flexural strength (≥800 MPa).

Achieving improved dynamic mechanical properties in twinning-dominated titanium alloys

Structural materials with low densities and high-strain-rate properties are of significant importance for the armor applications. Titanium and titanium alloys offer great potential in this regard but typically suffer from localized instability deformation during dynamic loadings. Here, we show that enhanced dynamic mechanical properties are attained in a twinning-dominated titanium alloy Ti-15Mo during split Hopkinson pressure bar tests. Under these tests, the solution treated specimens exhibit superior strain hardening capabilities compared to those of the solution treated plus aging specimens. Benefiting from this, the formation of the adiabatic shear bands (ASBs) and the subsequent material failure are delayed. The deformation-producing heat calculation suggests that the temperature rise is not a major origin of the adiabatic shearing. Yet, the strain localization associated with the non-uniform plastic deformation accounts for more. Microstructural characterizations indicate that the {332}<113> twinning, acting as a predominant deformation mode, improves the strain hardening capabilities of the Ti-15Mo alloy. With the increased strain rate, the increasing trend of the twin density gradually decreases, resulting in the grain boundary separations or even the formation of the ASBs at 4060 /s. The ASB’s shear zone has a density of dynamically recrystallized β grains with maximal hardness but poor strain hardening capability, while the adjacent transition zone experiences a highly localized shear deformation accompanied by the ASB widening. On the basis of these results, the impacts of the twinning on the microstructures and mechanical properties of the Ti-15Mo/Ti-15Mo laminated target plates after penetration experiments are discussed. We believe that titanium alloys with distinguished twinning effect can inspire their widespread applications in military fields.

Microstructural characterization and mechanical properties of inertia friction welded FGH96 joints

It is considerable to describe comprehensively the synergy effects of grain morphology and γ′ phase on mechanical properties in FGH96 inertia friction welded (IFWed) joints. Herein, the high-strength joining of the precipitation strengthened FGH96 superalloy was successfully realized by inertia friction welding. The evolution of grain morphology and γ′ phase, as well as the mechanical properties at room temperature (RT) and 750 ℃ were systematically investigated. It was discovered that fine equiaxed crystals were observed in the central of the bonding interface due to the dynamic recrystallization. The γ′ phase was progressively dissolved from the base material (BM) to the weld interface, resulting in the gradual flattening of grain boundaries. The evolution of the grain and γ′ phase exhibited a key role on the microhardness of IFWed joint. The impact toughness of joint at RT exceeded that of BM. The tensile strength of joint at RT reached 1514MPa, showing 94.8% of that of BM, with the fracture occurring in heat-affected zone. The tensile strength was 1223MPa at 750 °C, showing 96.3% of that of BM, with the fracture occurring in weld nugget zone. The tensile fractures subject to both RT and 750 °C were characterized by ductile fracture.