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So far, one main shortcoming restricting the wide application of Ti 2 AlNb sheet is the poor ductility. To solve this problem, we hot packed rolled the Ti 2 AlNb compact prepared by spark-plasma-sintering the pre-alloyed powders at the α 2 +B2+O phase field in this work. The sheets were rolled by different thickness reductions and passes. Results showed that the packs made of 304 stainless steel effectively protected the Ti 2 AlNb sheet from cracking, and the obtained sheets had good surface formation quality. B2 grain size and the texture intensity increased with increasing the rolling pass. The sheets rolled by all schemes had excellent ductility and relative high strength without applying any post heat treatment. An extreme high elongation of 13.91% with a tensile strength of 1063.27 MPa was obtained after four rolling passes. The nano O phases had excellent ability to coordinate transformations and account for the excellent ductility of the sheet. The α 2 phases mainly strengthen the strength of the sheet; maintaining its high strength. This work may provide a new insight to develop commercial high ductility Ti 2 AlNb alloys. • Poor room-temperature ductility of Ti 2 AlNb sheet is overcome by hot packed rolling the SPS compact at α 2 +O+B2 phase field. • Elongation of 13.91 % with a strength of 1063.27 MPa is achieved without post heat treatment after four rolling passes. • The reasons underlying the high ductility of Ti 2 AlNb sheet are discussed in detail. [ABSTRACT FROM AUTHOR]

Abstract: Elastic and anelastic properties of TiN/a-Si3N4 and (Ti1−x Al x )N/a-Si3N4 superhard nanocomposite (nc) films prepared by plasma-induced chemical vapor deposition (PCVD), magnetron sputtering and vacuum arc deposition (physical vapor deposition, PVD) have been investigated by mechanical spectroscopy. One internal friction peak with relaxational nature was observed at temperatures around 230–280°C and frequencies about 100Hz for as-deposited films prepared by PVD, while no peak was detected in the films prepared by PCVD whose hardness was as high as 50GPa. A comparison of a series of samples indicates that the peak is higher for films with lower hardness. The activation energy and the pre-exponential factor of the relaxation time are deduced as 0.7–1.0eV and 10−10 to 10−12 s, respectively. The intensity of this peak decreases with increasing annealing temperature. After annealing at 600–750°C, this peak disappears and Young''s modulus increases, in agreement with the increase in the hardness upon the annealing reported earlier. This internal friction peak is suggested to be associated with a thermally activated relaxation process within the interfaces that were not fully developed during the PVD process. [Copyright &y& Elsevier]

Al–1wt%Mn single crystals of {001}〈110〉 orientation have been rolled to 30 and 50% reductions under controlled homogeneous rolling conditions. The local orientations have been measured by the electron back-scattered pattern (EBSP) technique and a semi-automatic TEM method over different scales. EBSP orientation image maps (OIMs) based on the local orientation data and TEM micrographs were used to reveal the deformation structure. It was found that the crystals subdivided into different macroscopic regions across the specimen thickness and significant microstructural difference was observed in regions with different macroscopic orientations. Good agreement was revealed by comparison of the results concerning microstructure and local crystallography obtained from EBSP and TEM measurement. [Copyright &y& Elsevier]

Abstract: In this work a heat treatment procedure was performed on laser clad Ti–6Al–4V, which resulted in a reduction of tensile residual stresses in the clad samples as well and a decrease in the hardness of the clad layer with an increasing heat treatment time. The reduction in the residual stress was attributed to inter-phase stress relaxation brought about by the growth of the β phase. The reduction in hardness was attributed to an increase in the volume fraction of the soft β phase. Both the reduction in residual stress and hardness due to this heat treatment makes it an attractive method to heat treat both laser clad and additively manufactured Ti–6Al–4V components for improved mechanical properties. [Copyright &y& Elsevier]

Abstract: The adiabatic shear bands formed in the zirconium alloy impacted by split Hopkinson pressure bar at a strain rate of about 6000s−1 were characterized systemically by means of a high resolution field emission scanning electron microscope equipped with electron backscatter diffraction probe. The results show that the transformed bands were distinguished on the cross-section view of the impacted specimens, and the ultrafine and equiaxed grains formed in the transformed bands were confirmed. The gradient variation of the grains across the transformed bands from the boundary to the center of the bands was observed, and the grains at the center of the transformed bands were finer than other zones. Based on the characterization of the deformed microstructure adjacent to the transformed bands, the formation mechanism of the ultrafine and equiaxed grains in the transformed bands was revealed, and the rotational dynamic recrystallization mechanism should be responsible for the formation of the ultrafine and equiaxed grains in the transformed bands. According to the collection of the cumulative misorientation at different strain levels, the formation and evolution process of the ultrafine and equiaxed grains in the transformed bands were speculated. The microhardness measurements show that high microhardness value in the transformed bands was obtained because of the grain refining, and the large standard deviation of the microhardness at the center of the transformed bands was confirmed due to the gradient microstructural distribution in the bands. [Copyright &y& Elsevier]

Abstract: The microstructure of a polycrystalline Co annealed at 873K, followed by furnace cooling to room temperature, was studied in this paper. It was found that a small amount of high temperature (above 690K) face centered cubic (FCC) phase is retained after the slow cooling, and there is a Shoji-Nishiyama orientation relationship between the low temperature hexagonal close packed (HCP) and the retained FCC phases. Annealing twins were observed not only in FCC phase but also in HCP phase. A high fraction of special misorientation, was identified in the HCP phase, which was correlated to the phase transformation twins. [Copyright &y& Elsevier]

Commercial purity aluminum (99.5% Al) was deformed by equal channel angular pressing (ECAP) using up to 10 passes using route Bc. The evolution of microstructure and texture was characterized using the electron back scattered pattern technique. By use of the stereological parameter length per unit area (LA), it was found that on average a sub-micron grain size is developed only after 10 passes. Significant heterogeneity exists however in the sample and in some places a sub-micron grain size is not developed even after 10 passes. The texture strength was found to increase with increasing strain over the strain range investigated. Comparison of microstructural evolution with other deformation modes suggests that ECAP is more similar to cyclic extrusion-compression than to cold-rolling. [Copyright &y& Elsevier]

The dependence of flow stress (measured by tensile experiment) on the microstructure is discussed based on the Hall–Petch (H–P) relationship in interstitial-free steel cold-rolled to different reductions of 10–90%. The microstructure was characterized by TEM with semi-automated Kikuchi pattern analysis method. The significant effect of misorientation on the flow stress was found experimentally. The linear dependence of the slope of H–P relation on the average sub(grain) boundary misorientation is derived based on the work hardening dislocation mechanism. The modified H–P relation, i.e. σf=σ0+KH((θav/15)/dsubgrain)0.5 is proposed to describe the effect of average misorientation on flow stress. [Copyright &y& Elsevier]

Aluminum alloy AA1100/AA7075 laminated plates were fabricated from accumulative roll bonding and subsequent cold rolling process. Interface of the Al/Al were carefully characterized by optical microscopy (OM) and scanning electron microscopy (SEM). Mechanical properties of the laminated plates were measured by tensile test. Experimental results showing the critical strain of the onset of plastic instability was acquired with increasing reduction in thickness during cold rolling. It was observed that 7075Al layers were necked and fractured as cold rolling reduction was increased, and the final structure consists of a higher volume fraction of lenticular fragments of the hard phase in 75% reduction. The tensile results demonstrated the fracture phenomenon had a deleterious effect on the strength of laminated plate. Finite element (FEM) analysis of deformation of aluminum composites was carried in order to gain insight into the interface evolution during cold rolling process. It is argued that plastic instabilities were derived from shearing regions with preferential local deformation introduced by the difference in flow properties between the constituent metals. [ABSTRACT FROM AUTHOR]

Abstract In the past decades, high Mn Al C lightweight steels have been extensively studied due to their excellent mechanical properties. However, the yield strength is usually less than 1.2 GPa for relative lower carbon content (≤1.2 wt %) steels after the general strengthening process. This study was intended to enhance the yield strength of the steel. For this purpose, a novel heterogenous lamellar microstructure was introduced in lightweight steel with the nominal component of Fe 30Mn 11Al-1.2C (wt. %), which could provide extra back stress strengthening. The microstructure consists of the lamellar fully recrystallized austenite matrix and the small volume fraction (<2%) submicron-sized ferrite which merely distributed in the fine grain layer. The formation process and the underlying strengthening mechanism of the lamellar microstructure were analyzed. Due to the synergistic strengthening of back stress, grain refinement and aging strengthening, ultrahigh yield strength (∼1.4 GPa) and greatest specific yield strength (∼220 MPa g−1 cm3) with good elongation (∼27%) were realized in the present alloy. [ABSTRACT FROM AUTHOR]

Abstract Titanium (Ti)/steel clad plates with interlayer material of interstitial free (IF) steel, vanadium (V) and IF steel + V were successfully fabricated by hot roll bonding method at temperature of 850, 900 and 950 °C. Tensile shear test and tensile test were performed to evaluate the mechanical properties of the Ti/steel clad plates. The interfaces and the fracture surfaces of Ti/steel clad plates were carefully characterized by scanning electron microscopy, energy-dispersive spectroscopy and X-ray diffraction. The results reveal that the interlayer materials have influence on the compounds at the Ti/steel interfaces. Carbides are detected at the interfaces of Ti/steel with single IF steel or V interlayer. The formation of carbides impairs the shear strength of clad plates. σ phases instead of carbides are observed at the interface of Ti/steel clad plate with IF steel + V interlayer, which is beneficial for the tensile shear strength. Rolling temperature also has significant influence on mechanical properties of Ti/steel clad plates. The thickness of σ phase increases with the increase of rolling temperature. Thick σ phases impair the mechanical properties of the Ti/steel clad plate. [ABSTRACT FROM AUTHOR]

By the method of cold rolling, appropriate intermediate annealing and final annealing treatments, the multi-scale lamellar structure of ultrafine grains distributed in ribbons with coarse grains was produced in an Al-1.2Mn alloy, which displayed excellent combination of high strength and good ductility compared to coarse-grained and ultrafine-grained alloys. The high strength of the alloy with multi-scale lamellar structure is attributed to back stress strengthening associated with the formation of geometrically necessary dislocations and the good ductility results from the high strain hardening rate during plastic deformation. Loading-unloading-reloading tests were carried out to measure the back stresses of the alloys. The results show that the back stress of the specimen with multi-scale lamellar structure is much higher than that of the coarse-grained specimen. [ABSTRACT FROM AUTHOR]

Unidirectional rolled (UR) and clock rolled (CR) high purity tantalum sheets were analyzed with an emphasis on the microstructural difference in surface layers. Misorientation characteristics of deformed grains with different orientations are analyzed in detail by visualizing the misorientation angle based on an electron backscatter diffraction dataset. {100}(<100>// normal direction (ND)) grains were found to associate with long-range cumulative orientation changes in CR sample while {111} (<111>// ND) grains were found to contain many micro-shear bands and microbands in UR sample. Then, micro-shear bands and micro-bands were detailedly characterized by transmission electron microscope, and the analysis based on Schmid factor suggested that the primary slip system activated in {111} grains leads to the formation of micro-bands during UR process. Band contrast values were used to evaluate the energy stored in {100} and {111} grains and results showed that the gap of energy between them was narrowed by CR process. Additionally, significant dispersion degree of hardness values indicates the inhomogeneous deformation in UR sample, while different degree in annealed stage indicates the different recrystallization kinetic for UR and CR samples. Upon annealing, nucleation prefers to occur along {111} deformed matrices or {111}-{100} boundaries in UR sample and recrystallization grains are large in size. While nucleation tend to take place in intersected regions in CR sample and recrystallization grains are small, which contributes to the appearance of fine grains in fully recrystallized CR sample. [ABSTRACT FROM AUTHOR]

Aging treatments under three temperatures were performed to investigate the aging hardening response of high carbon high manganese austenitic Fe-30Mn-10Al-2C steel. The dramatic differences in hardness and microstructure were observed after aging under different temperatures. The aging treated at 500 ℃ had a typical aging hardness curve and the hardening response originated from the precipitation of κ-carbide, which plays an important role in performance improvement. When aging was conducted at 700 ℃, there was no significant change in hardness because a balance between aging hardening and high-temperature softening was built. On the contrary, the aging under 600 ℃ exhibited novel continuous increase in hardness and dramatic secondary hardening due to the formation of β-Mn which had an intrinsic high hardness. In addition, the β-Mn was also found after aging for long time under other temperatures. Unfortunately, the formation of β-Mn distributed along γ grain boundaries led to serious brittle fracture. For further investigation and application, the β-Mn transformation behavior was discussed based on the diffusion and redistribution of elements. Considering the dramatic difference in the formation kinetics of β-Mn depending on aging temperature, the diagram of β-Mn transformation was achieved to obtain optimized aging conditions. [ABSTRACT FROM AUTHOR]

The influence of preferential orientation (namely cube texture) on annealing twins in a cold rolled (95% thickness reduction) pure nickel has been investigated during isothermal annealing at low temperature. The results reveal that the cube oriented grains in cube related twinning (CT) regions have larger average boundary migration rate in comparison with grains in non-cube related twinning (NCT) regions. However, the twin density is always lower in CT regions than that in NCT regions. This is contrary to the growth accident model that suggests that twin density was proportional to the grain boundary velocity and grain boundary distance. It can be interpreted by the fact of the selective nucleation and growth mechanism for cube oriented grains which are less dependent on annealing twinning during recrystallization. Furthermore, during grain growth the average length of annealing twin boundary segments has a significant increment, which is probably attributed to lengthening of low energy twin boundaries along with the migration of other neighboring boundaries. [ABSTRACT FROM AUTHOR]

It is urgent to develop new copper alloys for future fusion reactors (e.g. DEMO and CFETR). This work involved the design and fabrication of an alloy, Cu-0.8Cr-0.12Zr-(0.05Si), with increasing high-temperature softening resistance by thermo-mechanical treatment. The influence mechanism of Si on its mechanical properties and softening resistance at high temperature was investigated. The peak-aged Cu–Cr–Zr alloy containing Si exhibits higher ultimate tensile strength of 622 MPa, yield strength of 588 MPa with a considerable elongation of 17% and electrical conductivity of 76% IACS. The dislocation and Orowan strengthening trigged for finer Cr precipitates are proven to be the main reasons for the improvement in strength. Moreover, the increase in elongation originates from the deformation twins due to the lower stacking fault energy, as confirmed by the first principles. Meanwhile, the addition of Si can significantly improve the high-temperature softening resistance of the alloy. The main reason is that the growth of Cr precipitates is suppressed by adding Si, and its pinning effect on the boundary is better, thereby inhibiting the occurrence of recrystallization. [ABSTRACT FROM AUTHOR]

The effect of pre-aging and peak-aging treatments prior to cryorolling on the microstructure and mechanical properties of 6016 Al alloys were investigated by hardness measurements, tensile tests, differential scanning calorimetry (DSC) and transmission electron microscopy (TEM). The results showed that high density of dislocation was induced by cryorolling with 80% thickness reduction. The pre-aging treatment enabled the alloy to have stronger work hardening effect during cryorolling and higher precipitation potential during subsequent aging than the peak-aging treatment. This was due to that the pre-aging enhanced the dislocations accumulating in the cryorolling of pre-aged specimen, and promoted the secondary precipitation during subsequent aging after cryorolling. Meanwhile, the yield strength and ultimate tensile strength of the pre-aged specimen subjected to cryorolling and subsequent aging significantly increased by 72% and 50%, respectively, while the ductility remained similar, as compared to the conventional peak-aged specimen. [ABSTRACT FROM AUTHOR]

An investigation on the evolution of annealing twins in a cold rolled (95% thickness reduction) high-purity nickel was reported as a function of annealing temperature. Electron backscattered diffraction (EBSD) analysis revealed that both the grain boundaries migration and the formation of cube texture promoted the proportion of Σ3 boundaries during recrystallization. Moreover, further increasing annealing temperatures showed that the frequency of annealing twins markedly decreases due to encountering of the growing cube-oriented grains one another during grain growth to form new LAGBs. [ABSTRACT FROM AUTHOR]

Abstract: High-purity nickel samples with different volume fractions of initial cube textures were cold rolled to 96% reduction and subsequently annealed at different temperatures. The survived cube orientation fractions in the cold-rolled samples were found to be in proportion to the volume fraction of the initial cube texture. The initial cube fraction could affect the recrystallization process significantly, which showed some huge differences in the case of low temperature annealing from that of high temperature annealing. [Copyright &y& Elsevier]

Abstract: A detailed investigation of the microstructure and mechanical properties has been conducted in pure nickel deformed to high strains using accumulative roll bonding (ARB). Samples have been investigated after different numbers of ARB cycles and the results have been compared with data for nickel processed by other deformation techniques, with particular focus on conventional rolling. It is found that the structural evolution in ARB-processed nickel is rapid at low strains followed by a slower evolution as the strain approaches ultrahigh levels. Comparing samples processed by ARB and by conventional rolling to an identical nominal strain, the microstructure after ARB is more refined and contains a greater fraction of high angle boundaries. This enhanced refinement is attributed to the geometric accumulation of shear-strain influenced volumes as a result of the ARB process and large-draught rolling conditions. Based on the observations, it is suggested that the key strengthening mechanisms in deformed nickel are grain boundary and dislocation boundary strengthening, and that the strength–microstructure relationship can be expressed by a single parameter equation: σ−σ 0=k 2 d av −0.5, where k 2 is a constant and d av is the average boundary spacing in the deformed microstructure. [Copyright &y& Elsevier]

Abstract: Samples of the magnesium alloy AZ31 have been deformed by compression to strains of 5% and 10% and microstructural observations made to investigate the activation of specific extension twin variants. The twinning has been analyzed on a grain-by-grain basis for more than 260 grains to determine both the number of extension twin variants in each grain, and the volume fraction of each. At 5% strain approx. 30% of the grains contain twins corresponding to variants with the third or lower ranked Schmid factor, with the fraction increasing to 40% after 10% compression. A grain size effect is also observed in that smaller grains are less likely to contain lower ranked twin variants. For both 5% and 10% compression no clear relationship exists between the volume fraction of each twin variant in a given grain population and the Schmid factor for the twin variant. A positive linear relationship can be defined, however, between the maximum twinning fraction that a twin variant can reach and its Schmid factor. [Copyright &y& Elsevier]

Abstract: The twinning and slip system activities during compression testing at room temperature and 150°C have been investigated for an AZ31 magnesium alloy. The samples, which were cut from a rolled sheet, were compressed with the compression axis taken at different angles to the sheet normal direction. The electron backscatter diffraction technique in the scanning electron microscope was used to investigate the local texture and microstructure evolution. The plastic deformation of magnesium is controlled by both twinning and slip during deformation. Extensive twinning takes place when the sample is loaded perpendicular to the basal plane normals (BPNs). A high work-hardening rate, with very little twinning, is observed for samples loaded parallel to the BPNs. The main features of the stress–strain curves can be explained based on the microstructural and texture data. [Copyright &y& Elsevier]

Abstract: The relationship between crystallographic orientation and the deformation microstructure formed during cold-rolling to high strains (up to ɛ vM =4.5) has been investigated. The starting material was Ni (99.96% purity) with a coarse initial average grain size (approximately 500μm). Microstructural characterization was carried out using a combination of electron channeling contrast imaging and electron back-scatter diffraction orientation mapping. An orientation dependence of the deformation microstructure was observed even at the highest strain examined. A large increase in the average boundary misorientation is found at strains above ɛ vM =1.8 for regions with the {112}〈111〉 and {123}〈634〉 orientations. This increase accompanies the structural transition from a medium strain microstructure to a high strain lamellar microstructure. In contrast, the average misorientation in regions of {110}〈112〉 orientation increases only slowly even up to the highest strain examined. [Copyright &y& Elsevier]

Commercial purity aluminum (99.5%) was fabricated by equal channel angular pressing (ECAP) up to total accumulated strains of approx. 10. The annealing behavior of material deformed to total strains of approx. 1 and 10 was investigated, using heat treatments of 2 h at various temperatures from 100 to 500 °C. The microstructure of the annealed materials was characterized using the electron back-scatter pattern technique. A number of parameters were determined including the distribution and average values of both the boundary spacings and misorientations. For samples deformed to a total strain of 1, annealing resulted in discontinuous recrystallization. For samples deformed to a total strain of 10, annealing resulted in microstructures exhibiting characteristics of both uniform coarsening and, in a number of places, of discontinuous recrystallization. An attempt was made, based on the boundary spacing distributions, to separate these two components. The grain size after annealing was still however small, being just 6.4 μm after 2 h at 300 °C. [Copyright &y& Elsevier]

The recent investigations testified that the dislocation played a crucial role in the Portevin-Le Chatelier (PLC) effect. In this work, dislocation was induced through rolling with 28% (R28%), 50% (R50%) and 80% (R80%) thickness reductions in friction stir processed (FSP) Al–3Mg–0.2Sc alloy, and the plastic instability was investigated by the multifractal framework. Different PLC types could be interpreted by the mechanism of the balance between strain localization of deformation bands and plastic relaxation. It was found that more chaotic or non-regular dislocation system led to more complex PLC types. According to the microstructural results, the chaos of dislocation was R50% > R80% > R28%. And this qualitative description was quantitatively expressed as Θ R50% = 1.42Θ R80% = 1.44Θ R28% in terms of the singularity spectrum width Θ by the multifractal analysis method. The multifractal results were not only consistent with the mechanism, but also transformed the comparison from qualitative to quantitative. Finally, the linear function linked between deformation and holistic dynamic strain aging (DSA) was discovered, showing that the holistic DSA decreased with the increase of rolling reductions. [ABSTRACT FROM AUTHOR]

A strategy was developed to circumvent the trade-off between the yield strength and strain hardening capability in Fe–30Mn–11Al–1.2C low-density steel by coupling two-step aging and intermediate pre-strain processes. The improvement of strain hardening capability is attributed to the non-shearable intragranular DO 3 particles. [ABSTRACT FROM AUTHOR]

The effect of warm rolling on precipitation and mechanical properties of a cryorolled Al-Zn-Mg-Cu sheet was investigated by hardness measurements, tensile tests, Electron backscatter diffraction, X-ray diffraction, transmission electron microscopy and atom probe tomography. The strength of the alloy subjected to cryorolling followed by warm rolling was higher than that of the alloy subjected to only cryorolling with the same total thickness reduction. Besides, the warm rolled alloy exhibited a better combination of strength and ductility compared to the cryorolled alloy after peak aging. Microstructural results demonstrated that warm rolling facilitated the formation of fine strengthening phases uniformly distributed in the matrix while cryorolling caused a mixture of fine and coarse precipitates during artificial aging. [ABSTRACT FROM AUTHOR]

This study presents a method to obtain aluminum alloy laminated composites with high yield strength and good ductility through a multiscale coarse/ultrafine-grained design, which are fabricated by accumulative roll bonding (ARB) and subsequent annealing treatment. Experimental results showed that an outstanding combination of strength and ductility was achieved in 1100/7075 Al alloy laminated composites after annealing at 300 °C for 60 min. Deviation between experimental and predicted results from stress-strain curves indicated that an extra strengthening effect was present in the laminated metal composites. Moreover, to analyze the effect of the magnitude of mechanical incompatibility on the mechanical properties during deformation, laminated metal composites with constituent layers possessing different flow properties were comparatively studied. Laminated metal composites with multiscale grain size distributions were obtained using different rolling strain paths and annealing treatments, which was attributed to differences in the recrystallization of constituent metals. It was determined that cross rolling, compared with direct rolling, gave rise to more effective improvements in the mechanical properties after annealing treatments due to higher mechanical incompatibility across the interface. For the Al alloy laminated composites, the difference in flow properties between the constituent layers plays an important role in additional interfacial strengthening by appropriate collocation of component strengths. During tensile deformation, a high density of geometrically necessary dislocations (GNDs) was distributed in the interface of the soft layer due to the mechanical incompatibility across the interface. The high yield strength with a multiscale interfacial structure is attributed to the back stress strengthening associated with the formation of GNDs and the good ductility results from the high strain hardening rate during plastic deformation. [ABSTRACT FROM AUTHOR]