Carbide precipitation behavior is greatly improved for AerMet100 steel by high frequency electropulsing assisted aging (EAA). As a result, the EAA hardening efficiency of AerMet100 remarkably increased by ∼10 times compared with that of conventional furnace ageing. Fracture elongation exceeds 18% within 10 times of EAA peak aging time.

NiAl intermetallic compounds have attracted the attention of researchers in the field of high-temperature structural materials, but their poor room-temperature ductility and insufficient high-temperature strength crying out for solutions have hindered their practical application. To solve these problems, a novel 3-dimensional network structure-reinforced NiAl-based composite was designed by hot presing sintering sinter with pre-alloyed powders. The 3-dimensional network structure was composed of discrete nearly spherical HfO2 and rod-shaped HfRe2. The mechanical properties of the composites were closely correlated with the distribution of the 3-dimensional network structure in the matrix, which was controlled by the sintering temperature and holding time. A microstructure with a desirable 3-dimensional network structure distribution and the best comprehensive mechanical properties was produced at 1375 degrees C/60 min. The microstructural evolution along with the strengthening and toughening mechanisms were discussed in detail. The increase in the high-temperature strength was mainly attributed to the pinning effect of the 3-dimensional network structure on dislocations and the restraining effect on the sliding and rotation between the matrix grains, while the increase in room-temperature ductility was mainly due to the grain refinement and hindering of crack propagation by the 3-dimensional network structure. In this paper, the development of a novel low-density NiAl-based composite with a 3-dimensional network structure improved both the strength and ductility, providing design ideas for the application of NiAl-based materials.

The mechanical behavior and microstructure evolution of Al-Mg-Li alloys under the effect of electric current was investigated using an electropulsing-assisted uniaxial tensile (EAUT) test combined with microstructure observations. It was found that the localized Joule heating-induced microscale high temperature at the grain boundaries in the necking zone significantly accelerated the grain boundary weakening when necking occurred, which resulted in rapid intergranular fracture and relevant decrease in elongation. Electropulsing induced continuous dynamic recrystallization (CDRX) in the both side layers and the discontinuous dynamic recrystallization (DDRX) in the intermediate layers of the Al-Mg-Li sheet during EAUT testing at 460 degrees C and higher, promoting the formation of newly near-equiaxed recrystallized grains and weakening of beta-fiber texture components. For the conventional high temperature tensile test, only a small amount of recrystallized grains formed along the grain boundaries of the coarse parent grains under the control of DDRX. The occurrence of CDRX during EAUT was substantially attributed to the promoted effect of electropulsing on dislocation glide and climb, which resulted from the combined effect of microscale localized Joule heating around dislocations and the electro-induced enhancement effect on vacancy diffusion. (c) 2021 Elsevier B.V. All rights reserved.

The precipitation of homogeneous nanoscale HfRe2 in NiAl grains was achieved by strain-induced precipitation at 1000 degrees C with a strain rate of 0.001 s-1. HfRe2 could not be precipitated under separate heating at 1000 degrees C, as the deformation increased, HfRe2 began to precipitate and gradually increased in size due to Ostwald ripening. The increase in hardness confirmed the occurrence of precipitation processes. A detailed discussion of the phase composition of the precipitates and their orientation relationship with the matrix was performed. The lattice mismatch at the NiAl(111)//HfRe2(2 7 5 5.36)perpendicular to HfRe2[2 7 5 3] interface was calculated to be only 3.90% based on the Bramfitt two-dimensional lattice mismatch theory, which demonstrated that HfRe2 could precipitate with NiAl as a heterogeneous nucleus.

For high-temperature structural materials such as NiAl, the selection of appropriate mechanical properties to meet the room-temperature ductility and high-temperature strength required for practical engineering applications is a pressing issue. To address this issue, novel NiAl-based composites reinforced by 3-dimensional network structure were prepared using pre-alloyed powders sieved into five different particle size ranges. All composites in this paper had excellent mechanical properties as the 3-dimensional network structure could improve both room-temperature ductility and high-temperature strength. Due to almost each powders grew into one grain during the hot pressing sintering process and the grains did not grew further caused by the hindrance of the 3-dimensional network structure, the particle size of the original powders and the grain size of the composites showed an obvious linear relationship. The relationship among original powder particle size, grain size and mechanical properties of the NiAl-based composites was established by fitting method, and the fitted equations were validated with an average deviation of 2.45%, so that quasi-quantitative control of the mechanical properties could be achieved by designing the original powder particle size. This work allowed both room and high temperature mechanical properties of NiAl to be improved and quasi-quantitative control over them, which provided a new idea for the design of composites.

For the purpose of obtaining a niobium-microalloyed steel with a preferable ultrafine-grained ferrite microstructure, a thermomechanical controlled processing (TMCP) strategy that included a hot shear deformation conducted near the local phase transformation temperature and a subsequent cooling process is proposed. As a large plastic strain was enforced by the simple hot shear deformation, severe plastic deformation (SPD) of the niobium-microalloyed steel was realized. The proposed TMCP strategy was simulated physically on a Thermecmastor-Z compression machine combined with a multi-type cooling system. Various cooling rates of different cooling methods resulted in reconstructive and displacive phase transformations from γ-Fe to α-Fe and led to different microstructural morphologies. In addition to phase transformations, the precipitation of carbides, grain growth, plastic deformation, discontinuous dynamic recrystallization (dDRX) of retained austenite grains, and continuous dynamic recrystallization (cDRX) of ferrite grains occurred during hot shear and subsequent cooling. The effects of the strain rate and forming temperature on the microstructural and textural evolution of niobium-microalloyed steel during hot shear and subsequent cooling were investigated and discussed. A niobium-microalloyed steel with a homogenous ultrafine-grained ferrite microstructure and intense γ-fiber texture was fabricated when the forming temperature, strain rate of hot shear deformation, and cooling rate of subsequent mist cooling were 1073 K, 20 s−1, and 10 K·s-1, respectively.

The hot deformation behavior and microstructure evolution of the new NiAl-9%HfO2 composite synthesized by hot pressing sintering were researched by hot compression tests at temperatures of 1250-1400 degrees C and strain rates of 10(-3)-10(-1) s(-1) under a true strain of 0.693. The Arrhenius constitutive model was established on account of the stress-strain curves corrected by friction and adiabatic. The processing maps were also developed and the features of microstructure inferred by the processing map were corresponded to the microstructure observation. The optimum hot deformation processing window was 1300-1350 degrees C/0.03-0.01 s(-1). In addition, the microstructure evolution and the softening mechanism during hot deformation were discussed in detail. Based on the room-temperature compression test, the samples deformed at 1350 degrees C with a strain rate of 0.03 s(-1) exhibited the highest performance with the yield strength and ultimate compression deformation increasing by 22.6% and 52.2% compared with the original samples, respectively. This work provided more theoretical guidance for the hot processing of NiAl-based composites and further promoted their application.

In mechanical engineering and intelligent manufacturing research area, excellent surface quality and dimensional accuracy at the macro level for products manufactured by means of information and intelligent technology are desired, at the same time, their controls of microstructure and properties at the microscopic scale are also of great concern. Tantalum-tungsten (Ta-W) alloy components are widely used in high temperatures, ballistics, and aerospace fields due to their advantages of high density, high plasticity, and good corrosion resistance. Therefore, in this paper, by studying the influence of processing parameters of heat treatment on microstructure and properties in cold forging deformation, tantalum-tungsten alloy components with homogeneous and fine-grained microstructure as well as excellent mechanical properties can be successfully achieved. Results show that the average grain size of Ta-W alloy components reaches the minimum when annealed at 1300 °C for 60 min, which is less than 25 μm. The recrystallization process of Ta-W alloy components with a reduction of 74% has completed at the annealing temperature of 1300 °C, and apparently grain growth occurs when the annealing temperature reaches 1400 °C. With the increase of annealing temperature paremeters, the microhardness of Ta-W alloy components decreases at first then slightly increases. The increase of microhardness at 1400 °C is likely due to the tendency of refractory metals to oxidize at high temperatures. After annealing treatment, the deformation of Ta-W alloy components shows obvious elastic-plastic deformation behavior, and its elongation reaches a maximum value of 46%.

A new approach for in-situ synthesis of nano-HfO2 reinforced NiAl intermetallics was proposed for the prepa-ration of a new NiAl-based composite material that is expected to function at 1200 degrees C. The phase composition, microstructure and mechanical properties of NiAl-HfO2 composites prepared by hot pressing sintering with Ni, Al, Hf and O-2 as starting materials were studied. The composites with NiAl as the matrix and nearly spherical or capsule-shaped HfO2 with an average size of 80.19 nm as the dispersion strengthening phase were designed and prepared. The results indicated that the addition of HfO2 significantly increased the high-temperature strength and slightly improved the room-temperature plasticity of the NiAl matrix due to the design of the appropriate content, size and distribution of HfO2. The NiAl-9HfO(2) (in wt.%) exhibited the most excellent mechanical properties with the compressive yield strength of 351.1 MPa at 1200 degrees C as well as the compressive yield strength of 1316.8 MPa and ultimate compression deformation of 25.8% at room temperature. The strengthening and toughening mechanisms of HfO2 on NiAl matrix were discussed in details, and the Orowan strengthening mechanism was emphasized.

The combined processing of electropulsing assisted recrystallization annealing (EARA) and electropulsing assisted ageing (EAA) was designed as an efficient environmental-friendly route to optimize the microstructure and mechanical properties of a cold rolled Al-Mg-Li alloy. The EARA treatment could rapidly complete the recrystallization and texture weakening of the cold rolled alloy within tens of seconds, which was mainly due to the promotion effect induced by electropulsing. The electropulsing promoted the climb of dislocations by accelerating the diffusion of vacancies, further resulting in the rapid continuous microstructure evolution from cold deformed structure to substructure and recrystallized grains. After the subsequent EAA treatment, the mechanical properties of the alloy were improved remarkably due to the combination of the precipitation strengthening of delta' phase, grain refinement and texture modification. The 66.7% cold rolled alloy treated by EARA + EAA exhibited the most excellent mechanical properties with the yield strength of 355.3 MPa, ultimate tensile strength of 527.2 MPa and elongation of 10.9%. Besides, the anisotropy of mechanical properties was weakened substantially due to the grain refinement and texture weakening. The mechanism of electropulsing induced rapid recrystallization and the effect mechanism of microstructure on mechanical properties were discussed in detail. (C) 2019 Elsevier B.V. All rights reserved.

Outstanding combination of strength and ductility of the Al-Mg-Li alloy could be achieved using the efficient and energy saving route of cold rolling combined with two steps of electropulsing assisted treatment (EAT), namely, the electropulsing assisted recrystallization annealing (EARA) and electropulsing assisted ageing (EAA). It was found that the EARA tremendously promoted the recrystallization behavior of the cold rolled alloy, leading to the grain refinement and texture weakening. Besides, the following EAA accelerated the coarsening of the strengthening δ′ phase. As a result, there was a remarkable improvement in strength and ductility, among which the increase in strength was mainly due to the combined effect of precipitation of δ′ phase and grain refinement, while the increase in elongation was mainly attributed to the grain refinement and texture modification. The rapid recrystallization during EARA was substantially attributed to the promotion effect of electropulsing on dislocation climb, which further resulted from not only the higher diffusion coefficient of vacancies under the application of electropulsing but also the another diffusion flux of vacancies induced by electro-migration.

The electropulsing treatment (EPT) combined with pre-deformation, an environmentally-friendly and efficient method, was designed as a novel ageing process for improving the mechanical properties of the 5A90 Al-Li alloy. Compared with the conventional ageing treatment, the EPT could remarkably shorten the peak ageing time of the alloy by enhancing the coarsening of δ′-Al3Li strengthening precipitates. Particularly, the combination of EPT and pre-deformation could increase the strength of the alloy dramatically with a slight decrease in elongation by increasing the size and volume fraction of δ′ phase. The increase in strength was attributed to the combination of the coarsening of δ′ precipitates induced by electropulsing, the Ostwald ripening process promoted by pipe diffusion and the localized Joule heating effect contributing to the diffusion, while the decrease in elongation mainly resulted from the formation of coarse β-Al3Mg2 phase particles accelerated by electropulsing. Based on the diffusion kinetics, the associated mechanisms including the coarsening of δ′ precipitates induced by interaction between the electropulsing and vacancies, the promoting effect of pipe diffusion on the Ostwald ripening process and the influence of localized Joule heating were discussed theoretically and schematically.

The electropulsing assisted ageing (EAA) processing was proposed as a novel energy-saving heat treatment processing for ageing, and how it influenced the microstructure evolution and mechanical properties of an Al-Mg-Li alloy was investigated in this paper. The mechanical properties and deformation behavior of the alloy were closely correlated with the precipitation and coarsening of the δ′ precipitates. Compared with the conventional ageing (CA), the EAA could accelerate the coarsening of the δ′ precipitates owing to the combination of the electro-migration offering another δ′ precipitate growth coefficient and the enhancement of diffusion due to the interaction between the vacancies and drift electrons, which lowered the ageing temperature for reaching peak-strength under the same ageing time. Besides the strength increased as the coarsening of the δ′ precipitates, the elongation and fracture mode were associated with the volume fraction of the δ′ phase. The easier occurrence of planer slip in the case of the higher volume fraction of the δ′ phase resulted in the low elongation and brittle intergranular fracture of the under-aged and peak-aged alloys, but the slight increase in elongation and reduction of intergranular cracks when the over-ageing occurred. The associated mechanism were discussed in detail.

gamma-TiAl based alloys are promising materials for high-temperature components in aerospace applications. To enable good mechanical characteristics with optimized microstructures via a low-cost green manufacturing technology, alloys were fabricated via spark plasma sintering by adopting pre-alloyed powders and followed by pulse current assisted isothermal forging (PCAIF). The sintering temperature determined the phase transformation behavior and thus resulted in typical near gamma, duplex, near lamella, and fully lamella microstructures. Additionally, the multiscale microstructure which derived from the occurrence of dynamic recrystallization (DRX) in deformed powders during the densification process and the original powder boundaries (OPBs) deteriorated their mechanical properties, and could not be eliminated thoroughly by optimizing sintering parameters. After PCAIF, typical near gamma, duplex, and near lamella microstructures were obtained with increasing forging temperature. Particularly, the multiscale microstructure and OPBs were eliminated due to the collective occurrence of DRX. Therefore, when tensile tested at 800 degrees C, the fracture mechanism transformed from fracturing at the interface of multiscale microstructure or OPBs due to the stress concentration between the zone with large and small grain size into the micro-void development at the interfaces of deformation twin groups and the DRX grains, thus improved the elongation significantly.

In order to solve the difficulty in producing Al-Li alloy 5A90, the heating characteristics of sheet 5A90 heated by pulse current were studied by the theoretical analysis and experimental test.It is found that the sheet 5A90 can be heated to 300 ℃ in two minutes by pulse current of 10 A?mm-2.Then, the mechanical properties of sheet 5A90 at high temperature were tested by uniaxial tensile test.The results show that the elongation of sheet 5A90 can reach 63.4% at 300 ℃.Furthermore, based on the study of heating characteristics and mechanical properties, the forming process of workpiece 5A90 is designed, and the stringer 5A90 is successfully formed by the process of pulse current assisted thermoforming.Finally, the dimensional accuracy of the workpiece meets the design requirements and the surface quality is good without cracks and scratches.The pulse current assisted thermoforming technology provides a simple and efficient way for the forming of Al-Li alloy 5A90 parts with thin-wall.

Al-Li alloy with advantages of low density, high specific strength etc.is the desirable material to realize the weight loss for aircraft structure, which shows strong competitiveness and broad application prospect in the field of aerospace and aviation.The advanced electrical heating forming technology is an effective way to improve the formability of light alloy.Therefore, the formability of Al-Li alloy 5A90 was studied by high temperature tensile experiment.And the best forming temperature of Al-Li alloy 5A90 sheet is 340 ℃.Then, the appropriate current density of Al-Li alloy 5A90 sheet under heating is 10 A·mm-2, which is obtained by the current resistance heating experiment.Furthermore, the device of current resistance heating forming for Al-Li alloy 5A90 stringers was designed and produced to solve the problem of poor formability at room temperature.The Al-Li alloy 5A90 stringers were formed by the current resistance heating forming process to meet the requirements, and the influences of temperature, lubrication and other factors on the quality of Al-Li alloy 5A90 stringers were analyzed.Thus, the new current resistance heating forming process and corresponding devices for sheets have great significance in practical application.