Four DD26 nickel-based single-crystal superalloys with varying Sn contents (mass fractions of 0%, 0.01%, 0.05%, and 0.10%) were prepared using liquid metal cooling (LMC) directional solidification process. The influence of Sn-amount on the microstructures, as well as the room-temperature tensile properties and stress rupture properties tested under 975 oC/255 MPa was investigated for the as-cast and heat-treated alloys. It was found that there was no significant change in primary dendrite arm spacing, γ/γ′ eutectic content, or the average size and volume fraction of the γ′ phase in DD26 single crystal superalloys with the increase of Sn content. No compounds involving Sn and Ni formed in as-cast alloy, and the Sn segregated around the γ/γ′ eutectic structures in the interdendritic regions. After heat treatment, the segregation of Sn disappeared and Sn distributed uniformly throughout the alloy. No measurable effect on either the tensile properties or the stress rupture performance of DD26 single crystal superalloys was observed with the addition of Sn.
The hot deformation behavior and microstructure evolution of the high-strength nickel-based superalloy GH4151 were systematically studied by isothermal compression test in temperature range from 1120 °C to 1200 °C, by strain rate between 0.001 and 0.1 s-1. Results indicate that at sub-solvus temperatures (1120-1160 °C), low strain rates promote dynamic recrystallization (DRX) and grain refinement, whereas high strain rates suppress DRX due to dislocation accumulation. Whereas, at super-solvus temperatures (1180-1200 °C), the γ′ phase was completely dissolved, and during the thermal compression within the applied strain rate range the alloy underwent complete DRX, and the grain size increases significantly with the rising temperature and decreasing strain rate. Due to the effective pinning effect of the dispersed MC carbides to the grain boundaries, resulting in the enhancement of microstructural uniformity of the alloy. These findings provide meaningful reference for optimizing hot working parameters of GH4151 superalloy to prevent abnormal grain growth or initial melting defects, thereby enhancing its service reliability.
The effect of temperature and strain rate on the tensile deformation behavior of GH4151 nickel-based superalloy was investigated via tensile test at temperatures ranging from 400 oC to 650 oC and strain rates from 0.005 min-1 to 0.02 min-1. Then the variation of microstructure and fracture surface was examined to elucidate the deformation mechanisms and fracture features. The results show that the alloy exhibits the Portevin-Le Chatelier (PLC) effect at 400 oC, which disappears above 500 oC due to accelerated solute atom diffusion. Between 600 and 650 oC, the combined effect of γ′ phase hardening and matrix softening results in the tensile strength reaching a peak at 600 oC, followed by a decrease at 650 oC. At higher temperatures (≥ 600 oC), the fracture surface displays “dagger-shaped” shear features, and the increased density of geometrically necessary dislocations (GNDs) at grain boundaries promotes intergranular cracking. Higher strain rates (0.02 min-1) enhance work hardening and local strain concentration, while lower strain rates (0.005 min-1) facilitate more uniform plastic deformation. This research provides a good reference for optimizing the microstructure control and engineering applications of GH4151 alloy.
The as received 55 mm rod of 316L austenitic stainless steel was first subjected to solution treatment, and then followed by 40% cold rolling, 90% warm rolling, and 90% cold rolling respectively. The above four states of 316L austenitic stainless steel presents tensile strengths ranging from 667 MPa to 1363 MPa. Next, their room-temperature tensile strength and microhardness were measured by means of universal testing machine and micro-hardness tester. The morphology and geometric dimensions of their indentations were observed and measured using laser confocal microscopy. The phase composition, microstructure, and grain size evolution were characterized by X-ray diffraction technology, scanning electron microscopy, transmission electron microscopy, and electron backscatter diffraction. The results indicate that the deformation twins and shear bands appear, and the strain induces martensite phase transformation. The microhardness, tensile strength and strength coefficient of the steels proceeded through different procedures are all enhanced. The hardness indentations of the steels present different pattern types, including the accumulation-type, and different patterns correspond to different hardness-strength relationships, among others, there is a relatively accurate linear relationship between the microhardness and tensile strength for the hardness with accumulation-type indentation pattern, and which was further verified with the data of copper alloys. It is believed that the findings may provide a valuable reference for the prediction and application of the relationship between strength and hardness of metal materials.
Ti-6Al-4V alloy is an ideal material for manufacturing the ultrasonic scalpel rod because of its good acoustic matching performance, low damping, excellent corrosion resistance, outstanding fatigue performance and biocompatibility. The elastic modulus is an important factor affecting the service function of the ultrasonic cutter. Herein, the different annealing heat treatment procedures on the variation in microstructure and elastic modulus of the as-received drawn wire of Ti-6Al-4V alloy with 5.8 mm in diameter was studied aiming to understand the relevant influence mechanism and to acquire the optimal comprehensive performance for the alloy. The results show that for annealing within the temperature range of 560-590 oC, the volume fraction of the α phase increases compared with the as-received material, resulting in an increase in the strength of the alloy. Within the temperature range of 590-830 oC, with the increase of the annealing temperature, the microstructure gradually undergoes recovery, recrystallization and grain growth. The volume fraction of the β phase increases, the elastic modulus of the material decreases, and the yield strength also decreases. Within the temperature range of 830-920 oC, with the increase of the annealing temperature, the volume fraction of the β transformation structure increases, and the secondary α phase precipitates from the β phase. The elastic modulus of the material increases, and the yield strength increases.
Current research on van der Waals heterostructure-based optoelectronic devices has predominantly focused on two-dimensional (2D) material systems, whereas investigations into the integration of multiferroic thin films with 2D materials within van der Waals heterostructures remain limited. In this study, a hybrid WSe2/BiFeO3(BFO)/quasi-two-dimensional electron gas (Q2DEG) heterostructure was successfully fabricated by combining pulsed laser deposition (PLD) with Ar+-ion bombardment-assisted (AIBA) techniques. A low-temperature chargeable photoconductivity (CPC) effect was achieved, with the operational retention temperature extended up to 60 K. The results demonstrate that after 30 s of illumination using a 405 nm laser, the peak current of stored photogenerated carriers released upon application of a bias voltage in the dark state reaches 250 μA. Moreover, under a fixed bias voltage of +4 V and at low temperature of 20 K, the device exhibits stable and repeatable switching behavior under varying laser irradiation conditions. Both the photocurrent magnitude and on/off ratio can be synergistically modulated through control of light intensity and wavelength. The CPC effect further demonstrates broad spectral responsivity (405-808 nm), enhanced performance at low temperatures, and robustness against external magnetic field interference. This work not only advances the fundamental understanding of photogenerated carrier separation, storage, and transport mechanisms at multiferroic-2D material interfaces but also establishes a critical materials and device platform for the development of high-performance non-volatile optical memory and neuromorphic computing technologies.
Fretting wear between Zr-2.5Nb pressure tubes and bearing pads occurs inevitably owing to flow induced vibration during the operation of heavy water reactor, which can be regarded as one of the main failure forms of pressure tubes. The fretting wear behavior between Zr-2.5Nb pressure tubes and bearing pads under two typical vibration conditions in a simulated water of primary loop for heavy water reactor was investigated. The wear degree, wear mechanism and material degradation form of the pressure tube were analyzed. The results showed that the main wear mechanism of the pressure tube was abrasive wear, and the sub-mechanism was micro-ploughing. Abrasive wear of the pressure tube was aggravated under severe vibration condition, resulting in a serious damage of the pressure tube. In addition, the formation mechanisms of abrasives and grooves were discussed in detail.
A composite material (PPy-GO) film with high selectivity for permeability was prepared on an anion exchange membrane (AEM) via co-deposition method with polypyrrole (PPy) and graphene oxide (GO) as raw material, resulting in a new type of composite anion exchange membrane, while the "carbon catalysis" effect of GO also played a significant role during the process. The surface morphology and physicochemical properties of the membrane were characterized using scanning electron microscopy, energy-dispersive X-ray spectroscopy, Fourier transform infrared spectroscopy, and X-ray photoelectron spectroscopy, so that to determine the optimal conditions for the co-deposition of PPy-GO on the membrane surface. The results show that with the increasing GO concentration, the water content and ion exchange capacity of the modified membrane increased, while the contact angle significantly decreased. An appropriate increase in the NaCl solution concentration was found to be beneficial for improving the modification effect. The current density in the range of 1-5 mA/cm2 had a positive impact on the performance of the modified membrane. Under optimized deposition conditions (current density of 5 mA/cm2, PPy:GO ratio of 2:1, 0.3 mol/L NaCl, deposition time of 20 min), compared to the unmodified membrane, the PPy-GO modified membrane exhibited an increase in ion exchange capacity by 0.85 mmol/g, a decrease in contact angle by 42.7°, a reduction in membrane resistance by 3.58 Ω, and a 4.66% increase in selectivity for permeability.
To concurrently improve thermal conductivity (TC) and mechanical properties, cast Mg-xCe-1Al (x = 0.4, 0.7, 1.0) alloys were prepared, followed by solid solution treatment at 580 oC for 12 h (T4) and aging treatment at 200 oC for 24 h (T6). The phase constituents, mechanical properties and thermal conductivity of the alloys in different states were determined by using X-ray diffraction (XRD), scanning electron microscopy (SEM), computer-controlled material testing machine and laser thermal conductivity meter. The results show that with the increase of Ce content of the as cast alloys, the TC of the alloy increases from 106.00 W/(m·K) to 120.65 W/(m·K), while the ultimate tensile strength (UTS) firstly rises and then decreases, and reach the maximum value of 180.67 MPa at the Ce content of 0.7%. After T6 treatment, the alloy with the Ce content of 0.7% shows the maximum TC and UTS (TC = 126.02 W/(m·K), UTS = 192.52 MPa). The strengthening mechanisms of TC and UTS were discussed, in terms of the variations of the amount and size of Al-Ce intermetallic phase and the content of Al solute atoms.
