This study demonstrates the complete closure of a crack and subsequent materials healing via a solid-state process upon application of high-density electric current pulses. This novel method leverages the simultaneous generation of a high-temperature field near the crack tip, a compressive stress zone induced by temperature gradients, and a significant electromagnetic force acting in Mode I, all arising from the flow of electric current around the crack. Finite element-based analysis is employed to optimize the process parameters, ensuring the dominance of the compressive stress field over the tensile electromagnetic force near the crack tip. Conjugate experiments demonstrate that fatigue-induced edge cracks in a metallic material (e.g., SS 316) can be fully healed by applying electric current pulses with extended pulse-width (e.g., 200 ms) and high densities (e.g., 10(6-)10(8) A/m(2)). Detailed microstructural analysis of the healed region reveals micro-void-free complete bonding between the crack faces, characterized by a narrow strip (<100 mu m width) featuring small, recrystallized grains. The observed boundary migration, entrapment of cavities inside grains, and partial alignment of dislocation substructures across the original crack confirm the solid-state diffusion bonding responsible for the materials healing. The yield strength, ductility and fatigue life of the "healed" material are commendable and can be significantly improved to mimic those of as-received material after solutionizing heat treatment. Overall, this study introduces a novel method for controlled crack closure and materials healing in in-service components, offering the potential to extend their operational life significantly.

IN740H, a Ni-based superalloy comprising a low volume fraction of γ′, is a promising material for superheater and reheater components in advanced ultra-supercritical (AUSC) power plants. Here, its tensile deformation behavior across a temperature range of 25–800 °C and strain rates of 10−3 to 10−5 s−1 was investigated. Distinct stress-strain curve serrations, consistent with dynamic strain aging (DSA), were predominantly observed between 400 and 600 °C. At lower temperatures and strain rates, Type E serrations appeared, which transitioned to Type B and then to Type B + C serrations with increasing temperature. At 600 °C, Type B serrations emerged at high strain rates, gradually transforming into Type B + C serrations as rates decreased before disappearing at lower rates. Notably, the alloy displayed negative strain rate sensitivity in the DSA regime. Furthermore, the alloy also showed yield strength anomaly (YSA), wherein the yield strength decreased initially with temperature, followed by an increase above a specific temperature. Fractography reveals a transition from transgranular dimple fracture behavior to intergranular fracture behavior with an increase in temperature. Post-deformation electron backscatter diffraction analysis indicated predominant grain alignment along {100} and {111} planes, such that {111}-oriented grains exhibited a lower Schmidt factor and the formation of fewer sub-grain boundaries. This work comprehensively characterizes DSA and YSA in IN740H in the temperature range relevant to AUSC power plants, thereby providing much-needed information to assess its potential suitability for applications under harsh conditions.

Examination of microstructural evolution and mechanical properties of the laser powder bed fusion (LPBF)-processed Inconel 939 (IN939) after direct aging (DA) and solutionizing (S) followed by aging (SA) may enable the development of strategies for optimizing the microstructure with excellent mechanical properties. Herein, the samples that were solutionized followed by water quenching and two-step aging showed commendable room temperature mechanical properties with 0.2

Here, we investigate the effect of high-pressure torsion (HPT), a severe plastic deformation process, on the mechanical properties, corrosion, and cytotoxicity of Mg–6Zn–0.2Ce alloy, a candidate material for bioresorbable bone implants. This alloy was processed by quasi-constrained HPT by applying a pressure of 6 GPa at room temperature for 1, 2, and 5 turns. Samples processed to two turns of HPT showed the smallest grain size, the highest strength that was approximately five times higher than the as-received coarse-grained sample and a reduction in the ductility. Electrochemical impedance spectroscopy and potentiodynamic polarization demonstrated the highest corrosion resistance for the Mg-alloy processed for two turns of HPT; however, accelerated degradation due to pitting corrosion was observed after immersion in simulated body fluid for 3 days. Nevertheless, all HPT-processed samples showed lower corrosion rates in all corrosion tests compared to their annealed counterparts. Finally, cell culture revealed good cytocompatibility without any noticeable changes in cytotoxicity following HPT processing. Overall, HPT for two turns showed enhanced strength and reduced corrosion rates without loss in cytocompatibility for the Mg–6Zn–0.2Ce alloy, making it a promising strategy to enhance the performance of the alloy as a bioresorbable orthopedic biomaterial. This work highlights the potential of HPT as a viable technique to improve the biomedical performance of Mg alloys for engineering next-generation biomedical implants.

The bolometer is developed using single-walled carbon nanotubes (SWCNT) anchored with semiconductor nanoparticles of cadmium sulfide, stannous disulfide, and zinc oxide (ZnO). The bolometric responses were recorded at varying temperatures from 10 K to room temperature. The anchored SWCNTs provided a higher temperature coefficient of resistance (TCR) than pristine SWCNTs. The largest TCR is recorded from SWCNTs/ZnO (-0.11%/K) at room temperature, which is 200% higher than pristine SWCNTs. The largest photoresponsivities of SWCNTs/ZnO under near-infrared (NIR) and wide wavelength source (200-1200 nm) illuminations are 5.06 and 37.51 mV/W, respectively. The extraordinary performance of SWCNTs/ZnO stands out at similar to 17 x 10(4)% under IR illumination. The study presents a significant advancement in the development of high-performance SWCNT bolometric materials by anchoring with semiconductor nanoparticles.

IN740H, a Ni-based superalloy comprising a low-volume fraction of γ′, is a candidate material to be used over long periods at high temperatures and stresses, as conditions prevalent in advanced ultra-supercritical (AUSC) powerplants. In this study, IN740H has been tested at temperatures above 700 °C to gain mechanistic insights into its high-temperature creep behavior. The material showed classic signatures of the presence of threshold stress, marked by observation of a high apparent creep stress exponent, n, (e.g., 10 at 750 °C) and a high apparent activation energy for creep, Qc (e.g., ∼545 kJ/mol), along with a rapid increase in n at lower stresses. Accounting for the threshold stress led to a decrease in the values of n and Qc to 4 and 280 kJ/mol, respectively. Furthermore, the transmission electron microscopy and atomic scale compositional analysis reveal the pinning of dislocations at γ-γ′ interface and segregation of Co, Cr and Mo atoms in the regions of γ-γ′ interface rich in dislocations. The above combination of n and Qc and the observation of dislocation pinning at the γ-γ′ interface indicate the dislocation climb over γ′ as the dominant creep mechanism in this γ′-lean Ni-based superalloy, with the detachment of dislocations from the γ-γ′ interface, augmented by the segregation of Co, Cr and Mo, as the mechanism responsible for the realization of the threshold stress. This work, thus, provides a new impetus to research on the long-term structural integrity of γ′-lean Ni-based superalloys exposed to extreme service conditions.