Texture Development in a Friction Stir Lap-Welded AZ31B Magnesium Alloy

The present study was aimed at characterizing the microstructure, texture, hardness, and tensile properties of an AZ31B-H24 Mg alloy that was friction stir lap welded (FSLWed) at varying tool rotational rates and welding speeds. Friction stir lap welding (FSLW) resulted in the presence of recrystallized grains and an associated hardness drop in the stir zone (SZ). Microstructural investigation showed that both the AZ31B-H24 Mg base metal (BM) and SZ contained β-Mg₁₇Al₁₂ and Al₈Mn₅ second phase particles. The AZ31B-H24 BM contained a type of basal texture (0001)〈11 \( \overline{2} \) 0〉 with the (0001) plane nearly parallel to the rolled sheet surface and 〈11 \( \overline{2} \) 0〉 directions aligned in the rolling direction. FSLW resulted in the formation of another type of basal texture (0001)〈10 \( \overline{1} \) 0〉 in the SZ, where the basal planes (0001) became slightly tilted toward the transverse direction, and the prismatic planes (10 \( \overline{1} \) 0) and pyramidal planes (10 \( \overline{1} \) 1) exhibited a 30 deg + (n ? 1) × 60 deg rotation (n = 1, 2, 3, …) with respect to the rolled sheet normal direction, due to the shear plastic flow near the pin surface that occurred from the intense local stirring. With increasing tool rotational rate and decreasing welding speed, the maximum intensity of the basal poles (0001) in the SZ decreased due to a higher degree of dynamic recrystallization that led to a weaker or more random texture. The tool rotational rate and welding speed had a strong effect on the failure load of FSLWed joints. A combination of relatively high welding speed (20 mm/s) and low tool rotational rate (1000 rpm) was observed to be capable of achieving a high failure load. This was attributed to the relatively small recrystallized grains and high intensity of the basal poles in the SZ arising from the low heat input as well as the presence of a small hooking defect.     

Anomalous Strain Rate Sensitivity of \{ 10\overline{1}2\} \langle 10\overline{1}\overline{1}\rangle Twinning in a Magnesium Alloy at High Temperature

Anomalous strain rate sensitivity of $ \{ 10\overline{1} 2\} $ { 10 1 ¯ 2 } $ \langle 10\overline{1}\overline{1}\rangle $ 〈 10 1 ¯ 1 ¯ 〉 twinning was observed in a Mg-Al-Mn magnesium alloy during extrusion around 723 K (450 °C). The density of $ \{ 10\overline{1}2\} $ { 10 1 ¯ 2 } $ \langle 10\overline{1}\overline{1}\rangle $ 〈 10 1 ¯ 1 ¯ 〉 twins decreases as the ram speed increases. At 10 mm min^?1, relatively high density twins are activated, but much fewer twins were observed at 30 mm min^?1; at 50 mm min^?1, twins were hardly seen. The negative strain rate sensitivity was ascribed to the interaction of $ \{ 10\overline{1}2\} $ { 10 1 ¯ 2 } $ \langle 10\overline{1}\overline{1}\rangle $ 〈 10 1 ¯ 1 ¯ 〉 twinning with defects.     

Effect of Tungsten on Primary Creep Deformation and Minimum Creep Rate of Reduced Activation Ferritic-Martensitic Steel

Effect of tungsten on transient creep deformation and minimum creep rate of reduced activation ferritic-martensitic (RAFM) steel has been assessed. Tungsten content in the 9Cr-RAFM steel has been varied between 1 and 2 wt pct, and creep tests were carried out over the stress range of 180 and 260 MPa at 823 K (550 °C). The tempered martensitic steel exhibited primary creep followed by tertiary stage of creep deformation with a minimum in creep deformation rate. The primary creep behavior has been assessed based on the Garofalo relationship, \( \varepsilon = \varepsilon_{\text{o}} + \varepsilon_{\text{T}} [1-\exp (-r^{\prime} \cdot t)] + \dot{\varepsilon }_{\text{m}} \cdot t \) , considering minimum creep rate \( \dot{\varepsilon }_{\text{m}} \) instead of steady-state creep rate \( \dot{\varepsilon }_{\text{s}} \) . The relationships between (i) rate of exhaustion of transient creep r′ with minimum creep rate, (ii) rate of exhaustion of transient creep r′ with time to reach minimum creep rate, and (iii) initial creep rate \( \dot{\varepsilon }_{\text{i}} \) with minimum creep rate revealed that the first-order reaction-rate theory has prevailed throughout the transient region of the RAFM steel having different tungsten contents. The rate of exhaustion of transient creep r′ and minimum creep rate \( \dot{\varepsilon }_{\text{m}} \) decreased, whereas the transient strain ? _T increased with increase in tungsten content. A master transient creep curve of the steels has been developed considering the variation of \( \frac{{\left( {\varepsilon - \varepsilon_{\text{o}} } \right)}}{{\varepsilon_{\text{T}} }} \) with \( \frac{{\dot{\varepsilon }_{\text{m}} \cdot t}}{{\varepsilon_{\text{T}} }} \) . The effect of tungsten on the variation of minimum creep rate with applied stress has been rationalized by invoking the back-stress concept.     

Plastic-Strain-Amplitude Dependence of Dislocation Structures in Cyclically Deformed 〈112〉-Oriented Cu-7 at. pct Al Alloy Single Crystals

Dislocation structures in \( [\overline{1} 12] \) Cu-7 at. pct Al alloy single crystals cyclically deformed at different plastic strain amplitudes were investigated by transmission electron microscope (TEM) and compared with the results of \( [\overline{1} 12] \) Cu single crystals. It is found that the plastic strain amplitude γ _pl has an obvious effect on the slip deformation mode, and consequently on the cyclic hardening behavior of \( [\overline{1} 12] \) Cu-7 at. pct Al alloy single crystals with an intermediate stacking fault energy. For instance, a high slip planarity (i.e., only formation of planar-slip bands) contributes to the occurrence of a gentle cyclic hardening with a much lower saturation stress at a low γ _pl of 4.5 × 10^?4. A mixed planar/wavy-slip mode (e.g., persistent Lüder’s bands/wall-like microstructures) at an intermediate γ _pl of 2.2 × 10^?3 causes an obvious cyclic hardening up to a comparable saturation stress to that for the \( [\overline{1} 12] \) Cu single crystal. In contrast, the deformation mode is dominated by wavy slip (e.g., ill-defined dislocation cells and walls) at the highest γ _pl of 7.2 × 10^?3, causing that its cyclic hardening curve is quite similar to that for the \( [\overline{1} 12] \) Cu single crystal; in this case, a slightly higher saturation stress level than that for the Cu single crystal is reached due to the additional solid solution strengthening.     

Effect of Multi-Scale Thermoelectric Magnetic Convection on Solidification Microstructure in Directionally Solidified Al-Si Alloys Under a Transverse Magnetic Field

The influence of a transverse magnetic field (B < 1 T) on the solidification structure in directionally solidified Al-Si alloys was investigated. Experimental results indicate that the magnetic field caused macrosegregation, dendrite refinement, and a decrease in the length of the mushy zone in both Al-7 wt pct Si alloy and Al-7 wt pct Si-1 wt pct Fe alloys. Moreover, the application of the magnetic field is capable of separating the Fe-rich intermetallic phases from Al-7 wt pct Si-1 wt pct Fe alloy. Thermoelectric magnetic convection (TEMC) was numerically simulated during the directional solidification of Al-Si alloys. The results reveal that the TEMC increases to a maximum ( \( u_{\rm{max} } \) ) when the magnetic field reaches a critical magnetic field strength ( \( B_{\rm{max} } \) ), and then decreases as the magnetic field strength increases further. The TEMC exhibits the multi-scales effects: the \( u_{\rm{max} } \) and \( B_{\rm{max} } \) values are different at various scales, with \( u_{\rm{max} } \) decreasing and \( B_{\rm{max} } \) increasing as the scale decreases. The modification of the solidification structure under the magnetic field should be attributed to the TEMC on the sample and dendrite scales.     

Study of \{ 11\bar{2} 1\} Twinning in α-Ti by EBSD and Laue Microdiffraction

Activity of the $ \{ 11\bar{2} 1\} \langle \bar{1} \bar{1} 26 \rangle $ extension twinning (T2) mode was analyzed in a commercial purity Ti sample after 2 pct tensile strain imposed by four-point bending. The sample had a moderate c-axis fiber texture parallel to the tensile axis. Compared with the many $ \{ 10\bar{1} 2\} \langle \bar{1} 011 \rangle $ extension (T1) twins that formed in 6 pct of the grains, T2 twins were identified in 0.25 pct of the grains by scanning electron microscopy (SEM) and electron backscattered diffraction (EBSD) maps. Most of the T2 twins exhibited irregular twin boundaries (TBs) on one side of the twin. High-resolution EBSD revealed both intermediate orientations at some matrix/twin interfaces and substantial lattice rotation within some T2 twins. Interactions between matrix 〈c + a〉 dislocations $ \frac{1}{3} \langle 1\bar{2} 13 \rangle $ and a $ \{ 11\bar{2} 1\} $ T2 twin were investigated by combining SEM/EBSD slip trace characterization and Laue microdiffraction peak streak analysis. 〈c + a〉 dislocations that originally glided on a pyramidal plane in the matrix were found on other planes in both the matrix and the twin, which was attributed to extensive cross-slip of the screw component, whose Burgers vector was parallel to the twinning plane. On the other hand, thickening of the twin could engulf some pile-up edge components in front of the TB. During this process, these 〈c + a〉 dislocations transmuted from a pyramidal plane $ (0\bar{1} 11) $ in the matrix to a prismatic plane $ (\bar{1} 010)_{\text{T}} $ in the twin lattice. Finally, possible mechanisms for the nucleation and growth of T2 twins will be discussed.     

Crystallographic Reconstruction Study of the Effects of Finish Rolling Temperature on the Variant Selection During Bainite Transformation in C-Mn High-Strength Steels

The effect of finish rolling temperature on the austenite-(γ) to-bainite (α) phase transformation is quantitatively investigated in high-strength C-Mn steels using an alternative crystallographic γ reconstruction procedure, which can be directly applied to experimental electron backscatter diffraction mappings. In particular, the current study aims to clarify the respective contributions of the γ conditioning during the hot rolling and the variant selection during the phase transformation to the inherited texture. The results confirm that the sample finish rolled at the lowest temperature [1102 K (829 °C)] exhibits the sharpest transformation texture. It is shown that this sharp texture is exclusively due to a strong variant selection from parent brass {110} \( \left\langle {1\bar{1}2} \right\rangle \) , S {213} \( \left\langle {\bar{3}\bar{6}4} \right\rangle \) and Goss {110}〈001〉 grains, whereas the variant selection from the copper {112} \( \left\langle {\bar{1}\bar{1}1} \right\rangle \) grains is insensitive to the finish rolling temperature. In addition, a statistical variant selection analysis proves that the habit planes of the selected variants do not systematically correspond to the predicted active γ slip planes using the Taylor model. In contrast, a correlation between the Bain group to which the selected variants belong and the finish rolling temperature is clearly revealed, regardless of the parent orientation. These results are discussed in terms of polygranular accommodation mechanisms, especially in view of the observed development in the hot-rolled samples of high-angle grain boundaries with misorientation axes between 〈111〉γ and 〈110〉γ.     

First Order Pyramidal Slip of 1/3\ \langle 1\bar{2}10\rangle Screw Dislocations in Zirconium

Atomistic simulations, based either on an empirical interatomic potential or on ab initio calculations, are used to study the pyramidal glide of a \(1/3\ \langle 1\bar{2}10\rangle \) screw dislocation in hexagonal close-packed zirconium. Generalized stacking fault calculations reveal a metastable stacking fault in the first order pyramidal \(\lbrace 10\bar{1}1 \rbrace \) plane, which corresponds to an elementary pyramidal twin. This fault is at the origin of a metastable configuration of the screw dislocation in zirconium, which spontaneously appears when the dislocation glides in the pyramidal plane.     

Interaction Between Basal Slip and a Mg17Al12 Precipitate in Magnesium

We performed molecular dynamics simulations and investigated interactions between a Mg₁₇Al₁₂ precipitate and a basal dislocation in magnesium. Modified embedded-atom method potentials for multiple-component systems were used in our simulations. The simulation results show that the basal dislocation is able to shear through the matrix and the precipitate/matrix interface, without creating a loop around the precipitate. The precipitate is only elastically deformed by the external shear strain. This interaction can be considered an extreme case of the Orowan mechanism when the strength of the precipitate/matrix interface is weak. Cross slip of the basal dislocation was observed when the precipitate size was 3.0 nm. The dislocation changed its slip plane to another basal plane via the \( (01\overline{1} 0) \) prismatic and the \( (0\overline{1} 11) \) pyramidal planes, creating jogs on these non-basal planes. The jogs had low mobility and debris was created when the jogs were dragged forward by the Shockley partial dislocations.     

Enrichment Mechanism of Phosphate in CaO-SiO2-FeO-Fe2O3-P2O5 Steelmaking Slags

The phosphate-enrichment behavior has experimentally been investigated in CaO-SiO₂-FeO-Fe₂O₃-P₂O₅ steelmaking slags. The reaction ability of structural units in the slags has been represented the mass action concentration \( N_{i} \) from the developed ion and molecule coexistence theory (IMCT)- \( N_{i} \) model based on the IMCT. The defined enrichment possibility \( N_{{{\text{c}}i{\text{ {-}c}}j}} \) and enrichment degree \( R_{{{\text{c}}i{\text{{-}c}}j}} \) of solid solutions containing P₂O₅ from the developed IMCT- \( N_{i} \) model have been verified from the experimental results. The effects of binary basicity, the mass percentage ratio \( {{ ( {\text{pct Fe}}_{t} {\text{O)}}} \mathord{\left/ {\vphantom {{ ( {\text{pct Fe}}_{t} {\text{O)}}} { ( {\text{pct CaO)}}}}} \right. \kern-0pt} { ( {\text{pct CaO)}}}} \) , and mass percentage of P₂O₅ in the initial slags on phosphate-enrichment behavior in the slags has also been discussed. The results show that the P₂O₅ component can easily be bonded by CaO to form tricalcium phosphate 3 CaO·P₂O₅, and the formed 3CaO·P₂O₅ can react with the produced dicalcium silicate 2CaO·SiO₂ to generate solid-solution 2CaO·SiO₂-3CaO·P₂O₅ under fixed cooling conditions. The maximum value of the defined enrichment degree \( R_{{{\text{C}}_{ 2} {\text{S{-}}} {\text{C}}_{ 3} {\text{P}}}} \) of solid-solution 2CaO·SiO₂-3CaO·P₂O₅ is obtained as 0.844 under conditions of binary basicity as 2.5 and the mass percentage ratio \( {{ ( {\text{pct Fe}}_{t} {\text{O)}}} \mathord{\left/ {\vphantom {{ ( {\text{pct Fe}}_{t} {\text{O)}}} { ( {\text{pct CaO)}}}}} \right. \kern-0pt} { ( {\text{pct CaO)}}}} \) as 0.955 at fixed cooling conditions.     

Crystallographic Orientation of the ε → α′ Martensitic (Athermal) Transformation in a FeMnAlSi Steel

The presence of athermal ε- and α-martensite (α′) in the as-cast structure of a Fe-0.08C-1.95Si-15.1Mn-1.4Al-0.017N alloy has been revealed by electron backscattered diffraction analysis. The alloy exhibited two athermal martensitic transformations described by γ → α′ and γ → ε → α′. The Shoji–Nishiyama orientation relationship was observed between γ-austenite and ε-martensite, while α-martensite nucleated from γ-austenite exhibited a Kurdjumov–Sachs orientation relationship. Six crystallographic variants of α-martensite consisting of three twin-related variant pairs were observed in ε-bands. A planar parallelism of {0001}ε || {110}α′ and a directional relation of \( \left\langle {1\bar{1} 1} \right\rangle \alpha ' \) lying within 1 deg of \( \left\langle {\bar{1} 2\bar{1} 0} \right\rangle \varepsilon \) existed for these variants.     

Atomic Structures of [0\bar{1}10] Symmetric Tilt Grain Boundaries in Hexagonal Close-Packed (hcp) Crystals

Molecular dynamics simulation and interface defect theory are used to determine the relaxed equilibrium atomic structures of symmetric tilt grain boundaries (STGBs) in hexagonal close-packed (hcp) crystals with a $ [0\bar{1}10] $ tilt axis. STGBs of all possible rotation angles ?? from 0?deg to 90?deg are found to have an ordered atomic structure. They correspond either to a coherent, defect-free boundary or to a tilt wall containing an array of distinct and discrete intrinsic grain boundary dislocations (GBDs). The STGBs adopt one of six base structures, $ P_{B}^{(i)} $ , i?=?1, ??, 6, and the Burgers vector of the GBDs is related to the interplanar spacing of the base structure on which it lies. The base structures correspond to the basal plane (???=?0?deg, $ P_{B}^{(1)} $ ); one of four minimum-energy, coherent boundaries, $ (\bar{2}111),\;(\bar{2}112),\;(\bar{2}114) $ , and $ (\bar{2}116)\;\left( {P_{B}^{(2)} - P_{B}^{(5)} } \right) $ ; and the $ \left( {11\bar{2}0} \right) $ plane (???=?90?deg, $ P_{B}^{(6)} $ ). Based on these features, STGBs can be classified into one of six possible structural sets, wherein STGBs belonging to the same set i contain the same base boundary structure $ P_{B}^{(i)} $ and an array of GBDs with the same Burgers vector $ b_{\text{GB}}^{(i)} $ , which vary only in spacing and sign with ??. This classification is shown to apply to both Mg and Ti, two metals with different c/a ratios and employing different interatomic potentials in simulation. We use a simple model to forecast the misorientation range of each set for hcp crystals of general c/a ratio, the predictions of which are shown to agree well with the molecular dynamics (MD) simulations for Mg and Ti.     

A Thermodynamic Model for Representation Reaction Abilities of Structural Units in Fe-S Binary Melts Based on the Atom-Molecule Coexistence Theory

A thermodynamic model for calculating the mass action concentrations of structural units in Fe-S binary melts based on the atom-molecule coexistence theory, i.e., AMCT-N _i model, has been developed and verified through a comparison with the reported activities of both S and Fe in Fe-S binary melts with changing mole fraction $ x_{\text{S}} $ of S from 0.0?to 0.095?at temperatures of 1773?K, 1823?K, and 1873?K (1500 °C, 1550 °C, and 1600 °C) from the literature. The calculated mass action concentration $ N_{\text{S}} $ of S is much smaller than the reported activity $ a_{\text{R, S}} $ of S in Fe-S binary melts with changing mole fraction $ x_{\text{S}} $ of S from 0.0?to 0.095. The calculated mass action concentration $ N_{\text{S}} $ of S can correlate the reliable 1:1?corresponding relationship with the reported activity $ a_{\text{R, S}} $ or $ a_{\%,\text {S}} $ of S through the introduced transformation coefficients with absolutely mathematical meaning or through the defined comprehensive mass action concentration of total S with explicitly physicochemical meaning. The calculated mass action concentrations $ N_{i} $ of structural units from the developed AMCT-N _i thermodynamic model can be applied to describe or predict the reaction abilities of structural units in Fe-S binary melts. The reaction abilities of Fe and S show a competitive relationship each other in Fe-S binary melts in a temperature range from 1773?K to 1873?K (1500 °C to 1600 °C). The calculated mass action concentration $ N_{{{\text{FeS}}_{ 2} }} $ of FeS_2?is very small and can be ignored because FeS_2?can be incongruently decomposed above 1016?K (743 °C). The very small values for the calculated mass action concentrations $ N_{{{\text{FeS}}_{ 2} }} $ of FeS_2?in a range of mole fraction $ x_{\text{S}} $ of S from 0.0?to 1.0?as well as a maximum value for the calculated mass action concentration $ N_{\text{FeS}} $ of FeS with mole fraction $ x_{\text{S}} $ of S as 0.5?are coincident with diagram phase of Fe-S binary melts. A spindle-type relationship between the calculated mass action concentration $ N_{i} $ and the calculated equilibrium mole number $ n_{i} $ can be found for FeS and FeS_2?in Fe-S binary melts. The Raoultian activity coefficient $ \gamma_{S}^{0} $ of S relative to pure liquid S(l) as standard state and the infinitely dilute solution as reference state in Fe-S binary melts can be determined as 1.0045?in a temperature range from 1773?K to 1873?K (1500 °C to 1600 °C). The standard molar Gibbs free energy change $ \Updelta_{\text{sol}} G_{{{\text{m, S }}({\text{l}}) \to [{\text{S}}]_{{ \, [{\text{pct \, S}}] = 1.0}} }}^{{\Uptheta,\%}} $ of dissolving liquid S for forming [pct S] as 1.0?in Fe-S binary melts relative to 1?mass percentage of S as standard state can be formulated as $ \Updelta_{\text{sol}} G_{{{\text{m, S }}({\text{l}}) \to [{\text{S}}]_{{ \, [{\text{pct \, S] }} = \, 1.0}} }}^{{\Uptheta,\, \%}} \,\, = -0.219\,-\,33.70T\,\,\left( {\text{J/mol}} \right).$      

Effect of temperature and shear direction on yield stress by {11\bar 22}〈\overline {11} 23〉 slip in HCP metals23〉 slip in HCP metals

The yield shear stress τ _y due to {11 $\bar 2$ 2}〈 $\overline {11} $ 23〉 second-order pyramidal slip system in cadmium, zinc, and magnesium hcp crystals increased with increasing temperature. This result is interpreted by two thermally activated processes as follows: (1) the dissociation of a (c+a) edge dislocation with a Burgers vector of 1/3〈 $\overline {11} $ 23〉 into a c sessile dislocation and an a glissile basal dislocation, and the subsequent immobilization of the (c+a) edge dislocation; (2) consequently, the double-cross slip of (c+a) screw dislocations must be activated thermally by an increment of applied stress to increase propagation velocity of slip band width. Moreover, τ _y is affected strongly by a direction of applied shear force due to second-order pyramidal slip in zinc as well as in cadmium. The anomalous behaviors of yielding would be caused by the nonsymmetrical core structure of the (c + a) dislocation due to the lattice heterogeneity in hcp metals.     

An Insight into Slag Structure from Sulphide Capacities

The molar sulphide capacities $ C_{\text{S}}^{'} $ ?=?(mol?pct?S) ( $ P_{{{\text{O}}_{2} }} /P_{{{\text{S}}_{2} }} $ )^1/2 on four binary systems, MgO-SiO₂, CaO-SiO₂, MnO-SiO₂ and FeO-SiO₂ are elucidated so as to compare the magnitudes of the basicities of four metallic oxides and to estimate the temperature dependencies of the basicities of metallic oxides. The enthalpy changes of the reaction?2O^??=?O?+?O^2?, viz. the silicate polymerization reaction (denoted as $ \Updelta H_{(8)}^{^\circ } $ ) have been calculated from the slopes of the log $ C_{\text{S}}^{'} $ vs 1/T curves for four binary silicates. The $ \Updelta H_{(8)}^{^\circ } $ value is considered in the present work to be an index of the basicity of silicate melts. The basicities obtained on the basis of the $ \Updelta H_{(8)}^{^\circ } $ values are in the order MgO?<?CaO?<?MnO?<?FeO, which are determined by two effects; (i) ionicity of chemical bonds between metallic and oxygen ions and (ii) clustering of metallic oxides in silicates. It is also found that the basicity of the FeO-SiO₂ system is larger at higher temperatures.     

Effects of Cooling Rate and Solute Content on the Grain Refinement of Mg-Gd-Y Alloys by Aluminum

The effect of Al additions on grain refinement of Mg-Gd-Y alloys with different solute contents at different cooling rates has been investigated. For all alloys, significant grain refinement was due to the formation of Al₂(Gd _x Y_1?x ) nucleant particles. The number density and size distribution of Al₂(Gd _x Y_1?x ) were affected by both solute content and the cooling rate. Grain sizes (d _gs) of Mg-Gd-Y base alloys and of Mg-Gd-Y-Al alloys were related to solute content (defined by the growth restriction factor, Q), cooling rate ( \( \dot{T} \) ), and area number density (ρ _ns) and size (d _p) of nucleant particles that can be activated. It is found that grain sizes of Mg-Gd-Y base alloys follow the relationship \( d_{\text{gs}} = a + \frac{b}{{Q\sqrt {\dot{T}} }} \) , while grain sizes of Al-refined samples follow the relationship \( d_{\text{gs}} = \frac{a'}{{\sqrt {\rho {}_{\text{ns}}} }} + \frac{b'}{{\sqrt {\dot{T}} Qd_{\text{p}} }} \) , where a, b, a′, and b′ were constants. In addition, the grain refinement effect of Al additions was more susceptible to solute content and the cooling rate than that of Zr which is regarded as the most efficient grain refiner for Mg alloys.     

Texture Evolution During Cross Rolling and Annealing of High-Purity Nickel

Evolution of texture during cross rolling and subsequent annealing was studied in high-purity nickel. For this purpose nickel samples were subjected to multipass cross rolling up to 90 pct reduction in thickness followed by annealing at different temperatures ranging between 673 K and 1073 K (400 °C and 800 °C). Cross rolling was carried out by rotating the samples about the normal direction (ND) by 90 deg interchanging the rolling direction and transverse direction (TD) between each consecutive pass. The development of microstructure and texture was characterized using X-ray and electron backscattered diffraction (EBSD) techniques. The deformation texture was characterized by the presence of strong brass ({110}〈112〉) and ND-rotated brass ({011}〈21 $ \overline{13} $ 13〉)) orientations. Upon annealing at 673 K (400 °C), ND||[111] fiber could be observed in the microtexture which originated from the twin formation of the recrystallized TD-rotated cube ({027}〈0 $ \overline{7} $ 2〉) grains. The fiber was weakened after annealing at 1073 K (800 °C) because of the decreased propensity for twin formation, and the microtexture was found to be weak and diffused. EBSD studies on early recrystallization stages indicated the absence of preferential nucleation of cube grains being in agreement with a weak cube texture formation in annealed cross-rolled high-purity nickel.     

Plastic deformation of titanium at elevated temperatures

The deformation of iodide titanium single crystals containing 200 to 250 ppm O, was studied in compression at temperatures from 25° to 800°C. Reduction of about 5 pct along thec axis was accommodated almost entirely by \(\left\{ {11\bar 22} \right\}\) twinning from 25° to 300°C, and above 400°C by \(\left\{ {10\bar 11} \right\}\) twinning in combination with c+a slip. The stress for \(\left\{ {11\bar 22} \right\}\) twinning increased with increasing temperature, and twin formation was accompanied by a load drop, while the stress for \(\left\{ {10\bar 11} \right\}\) twinning decreased with increasing temperature and twinning was not accompanied by a load drop. Crystals reduced normal to thec axis deformed by a combination of prism slip and \(\left\{ {10\bar 12} \right\}\) twinning at 25°C and by prism slip alone above 500°C.