A new lightweight, refractory high entropy alloy (HEA), CrNbTa
0.25
TiZr, was prepared by arc-melting under a vacuum condition. The as-cast and annealed CrNbTa
0.25
TiZr possessed identical ...dual-phase components: a BCC + a cubic Laves phase. After annealing, the Laves phase matrix in the as-cast alloy was replaced by the BCC phase, possibly due to the diffusion of Cr, which have a much smaller atomic radius than the other principal elements. From a performance perspective, the yield strength significantly increased from 926 MPa of the as-cast HfNbTaTiZr to 1800 MPa and 1500 MPa for as-cast and annealed CrNbTa
0.25
TiZr, while its density (7.25 g/cm
3
) is only 73% of HfNbTaTiZr. The microstructure evolution of the stiff cubic Laves phase is highlighted to unveil the promising strength of the CrNbTa
0.25
TiZr.
Graphic abstract
The phase component, microstructure, and compressive properties of a novel 3d transition metal high entropy alloy, CoCuNiTiV, derived from Fe replaced by V in CoCuNiTiFe alloy, were evaluated in ...as-cast and annealed conditions. The experiments showed that the as-cast alloy possessed a typical BCC + FCC dual-phases, which distinctly varied from the single FCC phase of an adjacent CoCuNiTiFe alloy. The BCC phase takes up the majority acting as the matrix, in which Cu was depleted, and the other elements (i.e., Co, Ni, Ti, and V) were distributed homogenously. Meanwhile, the FCC phase was Cu-rich, and sandwiched in the interval space between the BCC phases forming a net-like framework. After annealing, the matrix bifurcated into two parts: (i) one that remained as the primary BCC phase and (ii) another that decomposed into a Co
2
Ti-type laves phase and a new BCC phase. Meanwhile, the Cu-rich net-like framework is deteriorated forming a series of evenly distributed particles. The yield strength and the fracture strength of the as-cast and annealed alloy are highly similar— about 1674 and 2400 MPa, respectively. The hardness of the annealed alloy (572.9 ± 10.6 HV) was slightly higher than that of the as-cast alloy (530.3 ± 12.2 HV).
Graphic Abstract
A novel 3d transition metal high entropy alloy (TM HEA), CrCuFeTiV, was fabricated by arc-melting under a vacuum condition. Its phase component, microstructure, and compressive properties in the ...as-cast and annealed conditions were carefully investigated. The experimental results showed that the alloys in both conditions consist of one BCC phase (CrV/FeTi-rich regions), one FCC phase (Cu-rich), and one hexagonal Laves phase (Cr
2
Ti). It is suggested that the CrV-rich BCC phase preferentially separates as dendritic centers. Subsequently, the Cr
2
Ti Laves phase and the FeTi-rich BCC phase solidify as a dendritic outer layer. Finally, the FCC Cu-rich phase is squashed into the remaining interdendritic regions. Besides, the yield strength, ultimate strength, and hardness of the as-cast CrCuFeTiV alloy are 1686 MPa, 2205 MPa, and 624 HV, while those for the annealed alloy are 1510 MPa, 2035 MPa, and 618 HV, respectively. The obtained values are the highest among the tabulated five-principle equiatomic Cu-containing 3d TM HEAs. The promising strength-hardness synergy of CrCuFeTiV alloy is likely originated from the majority constitution of the BCC phase and Cr
2
Ti Laves phase.
Graphic Abstract
Two 3d transition metal high-entropy alloys (3d TM HEAs), AlFeNiVCu and AlFeNiVTi, were suction cast under identical conditions into a cylinder copper mould for investigating the compositional ...dependence of phase components, microstructures, and compressive properties. The phase components of the AlFeNiVCu were composed of a BCC FeV-rich dendritic phase, a netlike FCC Cu-rich interdendritic phase, and a uniformly distributed B2 AlNi-rich phase, when Cu substituted by Ti the phase components transformed to two BCC solid solution phases of the AlFeNiVTi. Moreover, an outstanding synergy in strength and ductility (ultimate compressive strength: 1936 MPa, plastic strain: 10.0%) was acquired for the AlFeNiVCu, which was sharply contrast with the typically brittle behaviour at the ultimate strength of 108 MPa for the alloy AlFeNiVTi. The distinctions of phase components and morphology were analysed to uncover the conflict in mechanical performance by Cu and Ti mutual substitution in AlFeNiV-base alloys.
Two 3d transition metal high-entropy alloys, AlCrCuFeX (X = Ti, V), were prepared by a vacuum arc-melting, and their phase components, microstructures, and compressive properties were investigated. ...The phase components of the alloy with X = V were the BCC + FCC dual-phases, while that of the X = Ti alloy was composed of a multi-phase structure (2BCC + FCC + Laves + L2
1
). Core–shell structural dendrites, together with discontinuous inter-dendrites formed in the X = Ti alloy, while netlike inter-dendrites surrounded the cellular dendrites in the X = V alloy. Moreover, the X = V alloy possessed a good synergy in strength and plasticity (ultimate strength: 2138 MPa, plastic strain: 7.1%) due to the ameliorating role of the netlike Cu-rich FCC inter-dendrites on the crack extension, while cleavage fracture mechanism for the X = Ti alloy caused by CrTi-rich Laves phase deteriorated its strength and ductility. The high hardness of the AlCrCuFeX alloys with X = Ti and V reaches 714 ± 27 and 565 ± 22 HV, significantly larger than 495 ± 15 HV of the alloy with X = Ni.
A novel 3d transition metal high-entropy alloy, Al0.5CrCuNiV, was prepared by vacuum arc-melting. Its phase component, microstructure, and compressive properties in as-cast and as-homogenized ...conditions were investigated. The results show the Al0.5CrCuNiV alloys either in the as-cast or as-homogenized conditions mainly compose of one FCC, two BCC and one ordered B2 phases. The incorporation of the BCC phases significantly enhanced the yield and ultimate compressive strength up to 1763 and 2336 MPa in the as-cast condition, which is stronger than the most of the single FCC phase 3d transition metal high-entropy alloys. Moreover, in the present work, we uncovered the deterioration of the strength through homogenized treatment is due to the decreasing effect of solid solution strength stemming from the increasing Cu concentration in the FCC Cu-rich regions from 49.7 ± 1.1 at. % to 72.8 ± 6.4 at. %. Further, the elongation of the as-cast and as-homogenized alloys are 13.8% and 15.7%.
•High-entropy alloy Al0.5CrCuNiV was designed by the incorporation of V in AlCrCuNi.•Incorporation of V changed single phase structure of base alloy to multiple phases.•High strength with promising ductility was acquired in as-cast and as-homogenized states.
Structural diversity, like chemical composition and morphology, is an important originating point of various mechanical properties. The exploration of these properties has been motivated by the ...fertile compositional constituents of multicomponent alloys/high-entropy alloys (HEAs). Herein, hierarchical Cu-rich precipitates embedded in a BCC matrix were found and highlighted in an equimolar CoFeTiVCu HEA. The Cu-rich precipitates were branched into two main classifications: nanoscale particles and micron lath/irregular shapes. Among them, the nanoparticles were almost evenly distributed in the overall region, which was attributed to the dramatically decreased solubility of Cu in the BCC matrix as the temperature decreased and that Cu quickly diffused. Alternatively, the others formed directly from the Cu-rich liquid during the solidification process. These kinds of hierarchical precipitates, combined with the great solid solution strengthening in the BCC matrix, gave rise to an excellent combination of strength and plasticity, specifically a yield strength, fracture strength, and compressive plasticity as high as 1.9 GPa, 2.2 GPa, and 7%, respectively.
Graphical Abstract
BiFeO3 is a ferroelectric with a Curie temperature of 830 °C, however, its piezoelectric performance at high temperature remains unclear. The current work reveals a disappearance/recovery of ...piezoelectricity in BiFeO3 at elevated temperature and upon cooling. In particular, that temperature is strongly frequency‐dependent and ranges from 280 to 430 °C between 0.5 and 140 Hz, respectively. Meanwhile, in situ and ex situ X‐ray diffraction and piezoresponse microscope analysis demonstrate thermally‐resistant domain texture to temperatures as high as 750 °C. This demonstrates that the piezoelectricity of BiFeO3 is strongly influenced by its resistance/conductance variations due to charge carrier motion limiting the operational frequency. The investigation enhances the understanding of BiFeO3 complex piezoelectric behavior at various temperatures, offering insights into its potential applications.
BiFeO3 lead‐free ceramics exhibit a disappearance of piezoelectricity in BiFeO3 upon heating to ≈300–450 °C, and this temperature increases with increasing measuring frequency. Remarkably, the piezoelectricity recovers upon cooling. These behaviors are attributed to its significant electrical leakage but outstanding thermal resistance of its poled state to very high temperature approaching its Curie point of 830 °C.
This paper reported the alloying effects in the non-isothermal crystallization of as-cast bulk metallic glasses. Three kinds of Al, Ni and Si elements with minor quantity of 0.5 at% were individually ...added into a base Cu
55
Zr
37
Ti
8
bulk metallic glass. Differential scanning calorimetry was utilized to characterize the crystalline processes during heating, and Johnson–Mehl–Avrami equation was adopted to determine and evaluate the crystallization kinetic parameters. The results disclose that alloying processing with 0.5 at% of Al, Ni and Si elements altered the crystallization kinetic behaviors. Alloying with 0.5 at% of Ni performs more remarkable constraint on the nucleation and growth of the crystallization with regard to alloying with the same quantity of Al and Si elements in the base bulk metallic glass and favors the suppression of crystallization.
