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NbHfTiVC0.1 refractory high-entropy alloy (RHEA) exhibits excellent comprehensive mechanical properties and demonstrates great potential for applications. However, the mechanical properties need to be improved further. In this work, hot rolling on NbHfTiVC0.1 RHEA at temperatures of 650 °C, 850 °C, and 1050 °C, with total reductions of up to 30%, 50%, 70%, and 80%, was conducted. The microstructure and mechanical property evolution of the samples were further investigated. The hot-rolled samples at 650 °C and 850 °C exhibit a composition consisting of BCC, carbide, and Laves phases, whereas the samples rolled at 1050 °C only consist of BCC and carbide phases. The 650-80 sample displays the highest ultimate tensile strength (1354 MPa), and the 1050-80 sample demonstrates the highest elongation (16%). The highest strength observed in the 650 °C-80% sample can be attributed to the presence of fractured and refined carbides, fine-grains, and the hindrance of dislocation slip by the fine Laves phase. At a higher rolling temperature (1050 °C), the Laves phase disappears, resulting in a reduction in strength but an increase in plasticity. Furthermore, the dislocation slipping mechanism within the BCC matrix also contributes positively to plastic deformation, leading to a notable increase in ductility for the 1050 °C-80% sample. These research findings provide valuable insights into enhancing the strength and ductility simultaneously of NbHfTiVC0.1 RHEA through hot rolling. [ABSTRACT FROM AUTHOR]

Zr-Ti-Nb-Ta alloys were synthesized in parallel via multi-target co-sputtering deposition with physical masking in a pseudo-ternary Ti-Nb-ZrTa alloy system. Sixteen alloys with distinct compositions were obtained. Comprehensive characterization of phase structure, microstructure, Young's modulus, and nanoindentation hardness was undertaken. The Ti-Nb-ZrTa alloys exhibited two typical phase structures: a single-BCC solid-solution structure, and an amorphous structure. Nanoindentation quantification confirmed a Young's modulus ranging from 110 to 130 GPa, alongside nanoindentation hardness spanning 3.6 to 5.0 GPa. The combination of good hardness and a relatively low Young's modulus renders these alloys promising candidates for excellent biomedical materials. This work not only offers an effective method for the high-throughput synthesis of multi-principal element alloys, but also sheds light on a strategy for screening the phase structure and mechanical performance within a given alloy system. [ABSTRACT FROM AUTHOR]

The novel refractory NbMoTiVSix(x = 0,0.25) refractory high‐entropy alloys (RHEAs) with both high strength and good ductility simultaneously by vacuum arc melting are developed. The microstructure evolution, compressive mechanical properties, and strengthening mechanism of the RHEAs with the addition of silicon at 1000 °C are analyzed and discussed. Microstructure observation shows that the NbMoTiV RHEA comprises of a single body‐centered cubic (BCC) phase, whereas the NbMoTiVSi0.25 RHEA consists of a BCC phase and simple multi‐component M5Si3 (M = Nb, Mo, Ti, V) phases. Compressive tests show that the yield and ultimate strength of the NbMoTiVSix(x = 0,0.25) RHEAs at 1000 °C increases from 590 to 931 MPa and from 682 to 1090 MPa with increasing silicon content. The improvement of strength is caused by the dipolar dislocation walls, the pinning effect of the diphasic interface, and a large amount of nano‐silicides phase particles in BCC phase, all of them are the result of silicide formation. [ABSTRACT FROM AUTHOR]

To study the effect of erosion on coal microstructure and its oxidation characteristics, eroded coals were prepared by eroding coal samples in an acidic aqueous solution for 30 days, 90 days and 180 days, respectively. The microcrystalline structure, pore structure and active groups distribution of coal samples were studied using X-ray diffractometer, low-temperature N 2 adsorption and infrared spectra. Temperature-programmed experiment was used to analyze the oxidation characteristics of raw coal and eroded coals. The results reflected that the number of aromatic layers and coalification degree of eroded coal are reduced compared with raw coal. The average pore diameter increases, which promotes oxygen transportation in coal pores. Under the erosion effects, the content of active groups such as hydroxyl (–OH), methylene (–CH 2), and methyl (–CH 3) in coal increases. Eroded coals, especially the coal eroded for 180-day demonstrate more oxygen consumption and CO production than raw coal during the oxidation process, and their apparent activation energies decrease. Besides, the enhancement mechanism of eroded coal's oxidation activity is expounded from the aspects of the increase of active sites and the improvement of pore structure. In brief, erosion effect increases the spontaneous combustion tendency of coal. • The effect of weak acid erosion with different durations on coal oxidation behavior was studied. • Changes of coal physicochemical structure after erosion effect were studied. • The apparent activation energy of eroded coal decreases during low-temperature oxidation. • Mechanism for easier oxidation of dried eroded coal was expounded. [ABSTRACT FROM AUTHOR]

Abstract: The hot deformation behavior of Zn82.7–Al10.2–Cu2.1 (in wt.%) was investigated by means of hot compression tests in the temperature range of 180–330°C and strain rate range of 0.01–10s−1. Processing maps were developed on the basis of experimental data and using the principles of the dynamic materials model (DMM). The results show that the maximum stress decreases with decreasing strain rate and increasing temperature, and that the activation energy is about 141.895kJ/mol. It is found that the strain has insignificant effect on the power dissipation maps. The maps exhibit two domains. The first domain occurs in the temperature range of 218–270°C and strain rate range of 0.04–1.2s−1 with the peak efficiency of 0.53. The second domain occurs in the temperature range of 290–330°C and strain rate range of 0.01–0.18s−1 with the peak efficiency of 0.58. Microstructural observations reveal that the partial dynamic recrystallization (DRX) of the Zn-rich phase occurs in the first domain and the full DRX of that occurs in the second domain. The dendritic structure is partially fragmented and elongated within the eutectic matrix and some initial laminar Al-rich phase is transformed into a spherical shape in the two domains. The large regime of flow instability is observed at the higher strain rates and all the tested temperatures with strain higher than 0.3. It expands when strain is increased. The flow instability predicted by processing maps is manifested as adiabatic shear bands, micro-cracks and macro-shear cracks. [Copyright &y& Elsevier]

Abstract: The hot deformation behavior of Inconel 690 has been investigated by means of hot compression tests in the temperature range of 950–1200°C and strain rate range of 0.001–10s−1. The results show that the maximum stress decreases with decreasing strain rate and increasing temperature, and the activation energy is about 380.215kJ/mol. Processing maps developed on the basis of experimental data and using the principles of the dynamic materials model exhibited two domains. The first domain occurs in the temperature range of 970–1120°C and strain rate range of 0.03–3.3s−1, with a peak efficiency of power dissipation of 0.39. The second domain occurs in the temperature range of 1150–1200°C and strain rate range of 0.003–0.1s−1, with a peak efficiency of power dissipation of about 0.37. Microstructural observations revealed that the full dynamic recrystallization (DRX) occurred in these two domains. In the first domain, the undissolved carbides assisted in nucleating DRX and restricted the coarsening of the full DRX grains and the refined grains were obtained. A small regime of flow instability was noticed at low temperature and high strain rate. [Copyright &y& Elsevier]

Abstract: Hot compressions tests of Inconel 625 superalloy were conducted using a Gleeble-1500 simulator at different strains between 900°C and 1200°C with a strain rate of 0.1s−1. Optical microscope, transmission electron microscope and electron backscatter diffraction technique were employed to investigate the microstructure evolution and nucleation mechanisms of dynamic recrystallization. It was found that both the size and fraction of dynamically recrystallized grains increase with increasing deformation temperature. However, the size of dynamically recrystallized grains almost remains constant with increasing deformation strain. The dominant nucleation mechanism of dynamic recrystallization in Inconel 625 superalloy deformed at 1150°C is the discontinuous dynamic recrystallization, which is characterized by the bulging of the original grain boundaries accompanied with twining. The continuous dynamic recrystallization characterized by progressive subgrain rotation occurs simultaneously in dynamic recrystallization process, although it can only be considered as an assistant nucleation mechanism at the early stage of hot deformation. [Copyright &y& Elsevier]

In this work, cold drawing deformation was applied aiming to achieve a good combination of strength and electrical conductivity of Cu–20Fe alloy, and also such underlying mechanisms for microstructure evolution and strengthening, as well as variation in conductivity were clarified. It is also found that both Cu matrix grains and Fe-rich dendrites can be significantly refined and transformed into fibrous structure with increasing of drawing strain. The average size of Cu grains and thickness of Fe fiber are 0.47 ± 0.05 μm and 25 ± 5 nm, respectively for alloy subjected to the drawing strain of η = 5.78. In addition, the Fe dendrites exhibit a strong <110> fiber texture, while the corresponding Cu matrix forms a <111> fiber texture. It is demonstrated that the excellent properties with the yield strength of 1173 MPa and the electrical conductivity of 41 %IACS can be reached for cold-drawn Cu–20Fe alloy. In addition, the quantitative analysis on strengthening contributions shows that the high strength of as-drawn Cu–20Fe alloy is dominantly originated from high-density Fe fibers. Meanwhile, the lower electrical conductivity is ascribed to the high solute Fe content and high-density Cu/Fe heterogeneous phase interface. • The microstructure evolution and properties of Cu–20Fe alloys at different drawing strains were clearly elucidated. • The Cu–Fe dual-phase co-deformation behavior during drawing deformation process was described. • A strengthening model of Cu–Fe dual phase alloy under severe plastic deformation was established. • The Cu–20Fe alloy achieves a good combination of mechanical and electrical properties at drawing strain of η = 5.78. [ABSTRACT FROM AUTHOR]

A refractory high entropy alloy (RHEA) NbHfTiV was selected as the master alloy and carbon element was introduced to synthesize the novel NbHfTiVC x RHEAs (x = 0, 0.1, 0.2, 0.3), which perform outstanding strength and excellent ductility simultaneously. Phase identification, microstructure evolution, and mechanical properties were systematically analyzed. The results show that the primary MC-type carbides and nano-precipitate carbides are generated in the BCC matrix phase with the addition of carbon. The primary carbides evolve from solid spheroid (x = 0.1) to sandwich-like pattern (x = 0.2, 0.3), and grain size is significantly refined from 537 µm (x = 0) to 25 µm (x = 0.3). Compressive tests show that the yield strength increases from 958 MPa to 1115 MPa, and the fracture mechanism is changed from ductile fracture to ductile and brittle mixed fracture with carbon content increasing. Meanwhile, the atomic size mismatch and elastic mismatch of the matrix phase reduce with carbon content increasing, which could decrease the lattice distortion degree and soften the matrix phase. [Display omitted] • Carbides (FCC-MC) are generated in BCC matrix with the addition of carbon. • After adding carbon, the grain size is greatly refined from 537 to 25 µm. • Increasing carbon content release severe lattice-distorted and soften the matrix. • Yield strength of NbHfTiVC x RHEAs increase from 958 (C 0) to 1115 MPa (C 0.3). [ABSTRACT FROM AUTHOR]

In the present study, the effect of C micro-alloying on microstructure evolution and properties of metastable immiscible Cu-20Fe alloy was comprehensively investigated. Experimental results indicate that the microstructure of Cu-Fe alloy is extremely sensitive to the C content. It was found that obvious liquid-liquid phase separation (LLPS) behavior is observed in Cu-20Fe alloy after C micro-alloying, and the tendency of LLPS is enhanced with increasing C content. The calculation of ΔScc(0) suggests that C atoms preferentially pair with free Fe atoms to form new Fe (C) atomic clusters, thus resulting in the enhancement of bonding of the like-atom pairs. In addition, the quasi-binary phase diagram calculation further reveals the existence of a stable miscibility gap for C-containing alloys, and the temperature interval of miscibility gap is significantly enlarged with increasing C content. Meanwhile, the interface energy between two liquids formed by LLPS also slightly increases as C content increasing. These above reasons should be responsible for the microstructure evolution of Cu-20Fe-xC alloys. In addition, the C micro-alloying deteriorates the soft magnetic properties of Cu-Fe alloys to a certain extent, whereas improves its corresponding wear-resistance. • The microstructure evolution and solidification behavior of Cu-20Fe-xC alloys were clearly elucidated. • The calculation of ΔScc(0) indicates that C atoms preferentially pair with free Fe atoms to form new Fe(C) atomic cluster. • Phase calculation indicates that the metastable miscibility gap of Cu-20Fe alloy is stabilized by the introduction of C. • The addition of appropriate amount C enhances the wear-resistance of Cu-20Fe alloy. [ABSTRACT FROM AUTHOR]