Superfunctional materials are defined as materials with specific properties being superior to the functions of engineering materials. Numerous studies introduced severe plastic deformation (SPD) as ...an effective process to improve the functional and mechanical properties of various metallic and non-metallic materials. Moreover, the concept of ultra-SPD-introducing shear strains over 1000 to reduce the thickness of sheared phases to levels comparable to atomic distances-was recently utilized to synthesize novel superfunctional materials. In this article, the application of ultra-SPD for controlling atomic diffusion and phase transformation and synthesizing new materials with superfunctional properties is discussed. The main properties achieved by ultra-SPD include: (i) high-temperature thermal stability in new immiscible age-hardenable aluminum alloys; (ii) room-temperature superplasticity for the first time in magnesium and aluminum alloys; (iii) high strength and high plasticity in nanograined intermetallics; (iv) low elastic modulus and high hardness in biocompatible binary and high-entropy alloys; (v) superconductivity and high strength in the Nb-Ti alloys; (vi) room-temperature hydrogen storage for the first time in magnesium alloys; and (vii) superior photocatalytic hydrogen production, oxygen production, and carbon dioxide conversion on high-entropy oxides and oxynitrides as a new family of photocatalysts.
High-pressure torsion (HPT) method currently receives much attention as a severe plastic deformation (SPD) technique mainly because of the reports of Prof. Ruslan Z. Valiev and his co-workers in ...1988. They reported the efficiency of the method in creating ultrafine-grained (UFG) structures with predominantly high-angle grain boundaries, which started the new age of nanoSPD materials with novel properties. The HPT method was first introduced by Prof. Percy W. Bridgman in 1935. Bridgman pioneered application of high torsional shearing stress combined with high hydrostatic pressure to many different kinds of materials such as pure elements, metallic materials, glasses, geological materials (rocks and minerals), biological materials, polymers and many different kinds of organic and inorganic compounds. This paper reviews the findings of Bridgman and his successors from 1935 to 1988 using the HPT method and summarizes their historical importance in recent advancement of materials, properties, phase transformations and HPT machine designs.
Following the introduction of high-entropy alloys (HEAs) with five or more principal elements, dual-phase HEAs have recently received significant attention due to their promising mechanical ...properties. Theoretical simulations suggest that unique mechanical properties of these alloys arise due to the contribution of localized phase transformation and diverse microstructural behavior of two phases under plastic deformation. In this study, phase transformations and microstructural evolution in a dual-phase AlFeCoNiCu alloy is investigated experimentally during plastic deformation using the high-pressure torsion (HPT) method. The two BCC and FCC phases exhibit diverse behaviors under plastic straining. The FCC phase with low stacking fault energy forms numerous nanotwins and stacking faults and its lattice is expanded by 3 vol%. The BCC phase accumulates dislocations, and its lattice is contracted by 5 vol%. These diverse microstructural/structural evolutions, which are partly consistent with the predictions of theoretical simulations, lead to a high microhardness of 495 Hv in this dual-phase HEA.
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•Effect of strain on microstructure and structure of a dual-phase high-entropy alloy is studied.•AlFeCoNiCu with the BCC+FCC structure is strained by high-pressure torsion.•Lattice contraction and dislocation accumulation occur in BCC by straining.•Lattice expansion and formation of twins and stacking faults occur in FCC by straining.•These microstructural/structural evolutions in two phases lead to high hardness.
•A new dual-phase high-entropy alloy, AlCrFeCoNiNb, is developed.•Grains are refined to an average size of 10 nm by high-pressure torsion processing.•The dislocations within nanograins are trapped ...due to lattice distortion.•Ultra-high hardness of 1030 Hv is achieved in this nanograined alloy.
High-entropy alloys (HEAs) usually show higher hardness compared to conventional alloys due to the presence of five or more principal metals in the solid-solution form, but there are significant efforts for further enhancing the hardness of these alloys. In this study, three strategies are combined to achieve one of the highest hardness levels reported for metallic alloys: (i) solution hardening by the concept of multi-principal element alloys, (ii) grain refinement by severe plastic deformation via the high-pressure torsion method, and (iii) introduction of dual phases to hinder dynamic recrystallization and enhance interface hardening. An ultrahigh hardness of 1030 Hv is achieved by the introduction of nanograins in a dual-phase (cubic + hexagonal) HEA, AlCrFeCoNiNb. Such a high hardness is not only due to the formation of nanograins with an average size of 10 nm, but also due to the generation of dislocations, interfaces and spinodal-like elemental decomposition.
► Metals with low melting points (In, Sn, Pb, Zn) were processed by high-pressure torsion (HPT). ► An unusual softening behavior was observed in these metals after processing by HPT. ► The ...hardness-strain behavior is represented by homologous temperature in HPTed metals. ► The steady-state grain size is significantly influenced by homologous temperature. ► The effect of stacking fault energy on grain size is minor at a given homologous temperature.
High purity metals with low melting temperatures such as indium (99.999%), tin (99.9%), lead (99%), zinc (99.99%) and aluminum (99.99%) were processed using high-pressure torsion (HPT). An unusual softening behavior was observed in all these metals after processing by HPT at room temperature. Pure copper (99.99%) and palladium (99.95%) were used to simulate the softening behavior due to a thermal effect by processing and subsequently holding at the temperatures equivalent to room temperature of pure Al. It is shown that a hardness peak appears in any metal by static softening after processing by HPT at a homologous temperature of 0.32 which is equivalent to room temperature of pure Al. The contribution of dynamic softening on hardness decrease becomes more important as the homologous temperature and stacking fault energy increase. Microstructural examinations indicate that, although the stacking fault energy influences the rate of the microstructural evolution, the homologous temperature appears to be a dominant parameter to determine the steady-state grain size after processing by HPT.
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