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Abstract High temperature, large strain and fast strain rate resulting from the severe plastic deformation will cause local material instability, then physical and chemical reactions such as phase transition, grain redistribution and fracture may occur during this process. This paper presents an in-depth investigation about the material instability and corresponding microstructures during the serrated chip formation of titanium alloy Ti-6.5AL-2Zr-1Mo-1 V by high speed turning. Firstly, intense deformation during high speed cutting was verified. Phase transition under different loading conditions including temperature, strain and strain rate were also explored, followed by the domination of equiaxed α-phase due to suitably localized severe plastic deformation and sufficient cooling. Secondly, criterion for initiation of fracture of material was introduced and applied to chip breaking. Finally, particle redistribution phenomenon was analyzed accordingly and the so-called severe plastic flow was further verified. [ABSTRACT FROM AUTHOR]

This paper presents a simple spatial phase shift shearography based on the Michelson interferometer. A novel digital shearography set-up with a large angle of view, which is based on a 4 f system is demonstrated. In the system, the Michelson interferometer is used as a shearing device to generate a shearing distance by tilting a small angle in one of the two mirrors. In fact spherical wave fronts become plane after going through the first lens in 4 f system. Tilting the mirror in the Michelson interferometer also generates spatial carrier frequency. Sinusoid fitting method is applied to evaluate the phase. This system can generate a phase map of shearography by using only a single image. The effects of shearing angle, the choice of algorithm and comparison result are discussed in detail. The theory and the application are presented. [ABSTRACT FROM AUTHOR]

In this paper, we report the results obtained from the hot compression behaviour of co-spray-formed Al-Si/7075 bimetallic gradient alloys by investigating the five selected layers divided evenly from top to bottom. It was found that with a decrease in the strain rate and an increase in temperature, the hot compression flow stress of deposited alloys decreases gradually, as expected. The relationship between flow stress, temperature and strain rate follows the Arrhenius relationship. The deformation activation energy of the co-spray formed gradient alloy gradually increases from bottom to top in the height direction, which are 100.15, 167.35, 185.54, 208.78 and 220.83 KJ/mol, indicating that the degree of difficulty in the deformation of the alloy is affected by changes in the silicon content of the alloy. Finally, the flow stress constitutive equation is calculated for each layer of alloy material, which is instructive for the subsequent study of the densification process of co-spray-formed gradient alloys. [ABSTRACT FROM AUTHOR]

The simulation of a complete manufacturing process to produce an aero engine case, including forging, rolling, and machining processes, is analyzed via finite element software. The deformation of the turning and drilling processes is quantitatively studied using the energy principles. Firstly, simulations of multi-stage forging of aero engine case and machining-induced residual stress are conducted and verified via the residual stresses test in order to provide the initial elastic strain energy condition prior to machining processes. The effects of blank forging-induced residual stress and machining-induced residual stress on the deformation of titanium alloys aero engine case are investigated. Secondly, a potential energy expression for the machining processes is developed. The predicted results of turning and drilling simulations indicate that there is an optimal process in which the deformation and potential energy decline rapidly compared with the other processes and finally, gradually stabilize at the end of the process. [ABSTRACT FROM AUTHOR]

Abstract: This paper presents a spatial phase-shift digital shearography system based on a modified Michelson Interferometer, which is capable of measuring out-of-plane deformation and its first derivative simultaneously. A reference beam is introduced into the Michelson Interferometer using an optical fiber. Two sheared images from the Michelson Interferometer are combined with the reference beam to generate two holograms and one shearogram. The Fourier Transform method is utilized to calculate the phase difference. To separate the spectrum in the Fourier Domain, the reference beam is tilted a small angle to create a spatial phase shift. An out-of-plane deformation and its first derivative can then be determined simultaneously from a single speckle interferogram by properly selecting filters for the spectrum image. The theory and the experimental results are presented. [Copyright &y& Elsevier]

Abstract: Conventional crystalline materials usually exhibit a ductile to brittle transition behaviour at low temperatures. An increase in the strength is always accompanied by a decrease in the plasticity. Here the authors report on a significant enhancement in both compressive strength and plasticity of a Ti-based bulk metallic glass (BMG) deformed at low temperatures. The ductilization of the BMG system can be evidently attributed to the formation of dense shear bands and the rotation mechanism of shear bands. The cryogenic surroundings can effectively slow down the mobility and diffusion of the atoms and consequently, suppress the nucleation and growth of nanocrystals during the deformation process, allowing the simultaneous improvement in the mechanical responses of the glassy alloy to compressive loading far below the ambient temperature. [Copyright &y& Elsevier]

Emerging high-entropy alloys (HEAs) exhibit high strength, high ductility and high toughness relative to traditional alloys based on one or two principal elements. The superior mechanical properties are derived from a synergy of multiple deformation mechanisms and their interactions at different stages of plastic straining. It is thus important to uncover the activation and operation of deformation mechanisms in these materials for property optimization and potential structure applications. The present work carried out in-situ tensile deformation of a CrMnFeCoNi HEA at room temperature. The strain hardening rate did not change monotonically during tensile deformation. Surface morphology evolution revealed the effects of massive dislocation activity, activation of multiple slip bands and their interactions on the strain hardening rate. Crack-tip-opening-angle measurements show that the current alloy possesses high fracture toughness. Cracks initiated at dense slip zones and grain boundaries, and propagated gradually, eventually coalescing into main cracks and resulting in final fracture. • The fracture toughness of CrMnFeCoNi HEA was evaluated by the CTOA and the steady-state CTOA was about 20°. • The evolution of the slip bands during tensile deformation was characterized using a series of in-situ experiments. • The relationship between the changes of SHR and surface morphologies of CrMnFeCoNi HEA was established. [ABSTRACT FROM AUTHOR]

Bulk metallic glass composites (BMGCs) reinforced with a B2-CuZr phase exhibit improved ductility. However, the relationship between the macroscopic plastic deformation of BMGCs and the microscopic strain evolution is still poorly understood. Here, we investigated the strain-field evolution of a Cu 44.3 Zr 48 Al 4 Nb 3.7 (at%) BMGC by using an in-situ digital image correlation technique during tensile deformation. The strain-field evolution in the composite containing B2-CuZr particles was analysed and compared to that in a Cu 47 Zr 48 Al 4 Nb 1 BMG. We found that a high degree of shear strain heterogeneity played a key role in the macroscale plastic deformation, which was attributed to the intrinsic structural heterogeneities. These findings have implications for the development of BMGCs with excellent tensile properties. [ABSTRACT FROM AUTHOR]

Highlights: [•] The flow behavior of spray-deposited Al–Zn–Mg–Cu–Zr alloy was investigated. [•] The activation energy for spray-deposited alloy is lower than the as-cast alloy. [•] Fine grains and high solid solubility lead to lower activation energy. [•] Both high temperature and low strain rate promote the formation of DRX. [•] The calculated flow stresses are well consistent with the measured results. [ABSTRACT FROM AUTHOR]

Abstract: In the paper, the deformation of Ti40Zr25Ni3Cu12Be20 bulk metallic glass plate subjected to shear punching has been studied. The fractured surface of the punch-out disks consists of three characteristic zones, namely the deformation band, the fractured zone, and the burr. Vein-like patterns, river-like patterns, and the coexistence of river-like patterns plus radiating cores are found on the fractured surface as the ratio of the punch-head/die clearance to the plate thickness, i.e., the relative clearance, increases because of the changes of the stress states during shear punching. Moreover, with the increase of the relative clearance, more plastic deformation occurs, causing the increase in the height percentages of both deformation band and burr. [Copyright &y& Elsevier]

Abstract: The isothermal deformation of a V-shaped component was simulated by the DEFORMTM process simulation software. The material flow, internal stress and temperature of the billet’s interior were investigated during the process of deforming, and the simulation results showed that bar billet is more suitable than sheet billet for producing the V-shaped component. The real isothermal deformation process was carried out with bar billet, and the microstructure of the shaped component was greatly refined. After heat treatment, the ultimate tensile strength (UTS) of the component can reach 817MPa. The results show that isothermal deformation is a low cost and high efficient compaction technique for produce components from the spray formed Al–Zn–Mg–Cu alloy. [Copyright &y& Elsevier]

Abstract: Al–10.66Zn–2.48Mg–1.41Cu–0.17Zr–0.17Sc (wt.%) alloy prepared by spray deposition was processed with different hot deformation followed by heat treatment. The mechanical properties and microstructure evolution were investigated. The results indicate that uniform ultimate tensile strength of 774MPa, yield strength of 734MPa and elongation of 13.7% are obtained with two-step hot deformation, which increase by 2.7%, 3.82% and 95% compared with one-step hot deformation. Microstructural observations show that increase of elongation is mainly ascribed to high volume fraction of smaller precipitates and reduction of stress concentration areas as a result of disappearance of the coarse second phases. The fractured tensile specimens with two-step hot deformation exhibit dimple fractographic features. Improvement of strength is attributed to the precipitation strengthening and dispersed strengthening. [Copyright &y& Elsevier]

Melt-extracted amorphous Co68.15Fe4.35Si12.25B15.25 microwires were drawn at ambient temperature into different diameters and the dependence of tensile properties and microstructural evolution on the degree of deformation was investigated. The cold-drawn wire with 51% area cross-section reduction exhibits a tensile ductility of 1.64%, with a tensile strength exceeding 4000MPa. Deformation-induced Co-rich nanocrystals were observed in the cold-drawn wires and proved to be capable of arresting the quick extension of shear bands and leading to the enhanced global plasticity of the microwires. [ABSTRACT FROM AUTHOR]

Abstract: The effect of cooling rate on the mechanical behaviors of a Ti-based bulk metallic glass has been studied using nanoindentation technique. It is found that the hardness increases, while the plastic deformation capacity gradually decreases from the edge to the center of the sample. The variation of the structural uniformity within the as-cast glassy sample may account for the cooling rate dependence of mechanical performance. [Copyright &y& Elsevier]

• CrMnFeCoNi HEA exhibits excellent mechanical properties at cryogenic temperatures. • Enhanced yield strength of the alloy stems from the larger lattice distortion. • High dislocation density and nano-twins lead to the high SHR. • Lower deformation temperature pronouncedly decreased SFE. Here, the evolution of the deformation mechanism of the well-known CrMnFeCoNi high entropy alloy (HEA) under a cryogenic temperature was investigated via using transmission electron microscopy characterization after compressive experiments. It is found that, in contrast to the dominate mechanism of dislocation slip at 298 K, the deformation mode of the studied HEA at 123 K can be divided into two stages: (i) at the initial plastic stage, the plasticity is mainly induced by the planar dislocation glide; and (ii) at the late plastic stage, the combination of dislocation hardening and mechanical twinning facilitates high strength for the studied alloy. These findings are helpful to understand the temperature dependent deformation mechanism of high entropy alloys. [ABSTRACT FROM AUTHOR]

In this study, the effect of cryogenic testing temperatures on the deformation behavior of a CuZr-based bulk metallic glass composite (BMGC) has been investigated using in situ high energy X-ray diffraction. The yield strength and work-hardenability of the studied BMGC show an increasing trend from 298 K to 153 K. A higher yield strength at a lower temperature can be attributed to the larger difference in the volume shrinkage between the crystalline phase and the amorphous matrix. The increasing martensitic transformation degree of the crystalline phase from 298 K to 153 K results in the enhanced work-hardenability. These results lead to a better understanding of the temperature dependence of phase-transformation induced plasticity in CuZr-based BMGCs. ga1 • The yield strength of the BMGC shows an increasing trend from 298 K to 153 K. • The increase of the work-hardenability is attributed to martensitic transformation. • Martensitic transformation degree is higher at a lower temperature. [ABSTRACT FROM AUTHOR]

Abstract: Compressive deformation behaviors of a cast Ti40Zr25Ni3Cu12Be20 bulk metallic glass in the test temperatures ranging from 428 to 658K were examined in a broad range of strain rates from 1.3×10−4 to 3×10−2 s−1. The alloy studied exhibits an extraordinary compressive superplastic formability within the supercooled liquid region, typically evidenced by a large compressive strain up to 0.83. The superplastic flow behaviors are strongly dependent on the test temperatures and applied strain rates. At low temperatures or high strain rates, the viscosity measured is found to dramatically decrease with increasing strain rate (i.e., non-Newtonian flow) and a stress overshoot is detected in the first steps of strain. At low strain rates or high test temperatures, the studied glass exhibits a Newtonian flow behavior. The value of activation volume increases with increasing test temperatures. [ABSTRACT FROM AUTHOR]