Search

A homogeneous equiaxed‐structure TC21 titanium alloy is hot rolled and annealed for different time ranging from 1 h to 6 h. The grain morphology and texture evolution of α and β phases during annealing are mainly investigated using the electron back‐scattered diffraction characterization. In the early annealing stage, the α grain mainly maintains the elongated morphology generated in the rolling. With increasing annealing time, more and more elongated α grains become equiaxed due to enhanced static recrystallization and boundary splitting. Differently, the β grain exhibits a fully equiaxed morphology all the time due to the sufficient static recrystallization, and get a coarsening with increasing annealing time. The α phase exhibits a (0001) basal texture in the early annealing stage, and then forms a TD‐split texture with increasing annealing time. The β phase exhibits the {001}<110> texture at every annealing time. Based on the analysis about the texture of different grain sizes, the effects of recrystallization nucleation and oriented growth on texture evolution are discussed. It suggests that TD‐split texture in α phase is originated from both the recrystallization nucleation and oriented growth. The formation of {001}<110> texture in β phase is mainly originated from the oriented growth. [ABSTRACT FROM AUTHOR]

Abstract: The growth of individual grains during recrystallization in 96% cold-rolled pure nickel has been followed using electron backscatter pattern maps of the same surface area taken after each of several annealing steps. It was found that the growth is quite complex, with boundaries moving, stopping and moving again. The growth kinetics differ from grain to grain and, on average, cube-oriented grains grow the fastest. The growth of the grains has also been analyzed as a function of boundary misorientation. This analysis shows that there is no significant difference in misorientation distribution between boundaries that move and those that do not. This is contrary to the usual assumption that the boundary mobility and the migration rate depend on the misorientation across a boundary. This observation and the reasons for the faster growth of cube-oriented grains are discussed. [Copyright &y& Elsevier]

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]

The evolution of continuous recrystallization induced by conventional thermomechanical processing and the effect of final annealing temperature on the recrystallized structure have been investigated in a commercial Al-1.2 wt%Mn alloy. Experimental results demonstrate that continuous recrystallization could occur in Al-1.2 wt%Mn processed by thermomechanical processing, resulting in a uniform ultrafine grain structure with 1–2 µm mean grain size. Moreover, final annealing temperature has remarkable influence on the microstructure. A bimodal microstructure with ultrafine grains and coarse grains could be obtained at elevated annealing temperatures. [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]

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]

The bulk stored energy of cold rolled tantalum (Ta, 87% thickness reduction) was measured by differential scanning calorimetry, and related microstructure evolution during the stored energy release was studied by electron backscatter diffraction method. In addition, transmission electron microscopy was employed to reveal the substructure of the deformed Ta. Results showed that the deformed Ta consisted of {1 1 1} texture (<1 1 1> // ND) and {1 0 0} texture (<1 0 0> // ND), and its substructure was characterized by dislocation cells or dense dislocation walls. The total stored energy of as-rolled Ta was about 30.6J/mol, most of which was released by recovery. The release of the stored energy suffered a complicated process and was orientation dependent. Correlative microstructure evolution path during heating referred to (i) recovery of all grains, (ii) primary recrystallization of {111} grains and recovery of {100} grains, and (iii) recrystallization of {100} grains. [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: The effects of an external electric field on cube texture development have been studied by means of electron backscatter pattern technique, using rolled nickel sheets of 99.999% purity. Samples were annealed at 300 °C for different times both without and with an external electric field, of intensity 2000 V/cm. Results show that the application of an external electric field has decreased the volume fraction of cube texture and the grain size of cube oriented grains. [Copyright &y& Elsevier]

Abstract: The effects of an electrical field on recrystallization of Cu have been investigated. A 12° off exact (112) [11] copper single crystal was rolled to 80% reduction. Samples cut from the deformed material were then annealed for 1h at temperatures of between 200°C and 400°C. For each temperature, samples were annealed either with or without the presence of an electrical field of intensity 1500V/cm. The microstructures were investigated in the longitudinal plane by using the electron backscatter pattern technique. Results show that the application of an external electric field might promote the grain growth rate, and also promote the formation of Σ3 twin boundary. [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 development and stability of the cube texture formed during annealing has been investigated, using rolled nickel sheets of 99.95% and 99.999% purity. Microstructure and texture were characterized using electron back-scatter pattern analysis in the scanning electron microscope. The texture following primary recrystallization in both materials showed cube volume fractions of up to 50% and 80% (99.95% and 99.999% Ni respectively). The average grain size of the cube textured grains during recrystallization was larger than for grains of other orientations. For both materials high temperature annealing resulted only in normal grain growth, leading to a significant strengthening of the cube texture. The results are discussed in terms of the relative effects of size, boundary mobility and boundary energy on the process of grain growth. For the 99.999% Ni material an annealing process using a continuous heating ramp to 1200 °C gave a further improvement in the cube texture. [Copyright &y& Elsevier]