Texture Evolution in a Ti-Ta-Nb Alloy Processed by Severe Plastic Deformation

Titanium alloys are extensively used in a variety of applications because of their good mechanical properties, high biocompatibility, and corrosion resistance. Recently, ??-type Ti alloys containing Ta and Nb have received much attention because they feature not only high specific strength but also biocorrosion resistance, no allergic problems, and biocompatibility. A Ti-25Ta-25Nb ??-type titanium alloy was subjected to severe plastic deformation (SPD) processing by accumulative roll bonding and investigated with the aim to observe the texture developed during SPD processing. Texture data expressed by pole figures, inverse pole figures, and orientation distribution functions for the (110), (200), and (211) ??-Ti peaks were obtained by XRD investigations. The results showed that it is possible to obtain high-intensity share texture modes ({001}??110??) and well-developed ?? and ??-fibers; the most important fiber is the ??-fiber ({001} $ \left\langle {1\bar{1}0} \right\rangle $ to {114} $ \left\langle {1\bar{1}0} \right\rangle $ to {112} $ \left\langle {1\bar{1}0} \right\rangle $ ). High-intensity texture along certain crystallographic directions represents a way to obtain materials with high anisotropic properties.     

Quasi-Ternary System Ag2Se-CdSe-Ga2Se3

Phase equilibria in the quasi-ternary system Ag₂Se-CdSe-Ga₂Se₃ were investigated by differential thermal and x-ray phase analysis methods. Phase diagrams of nine vertical sections were constructed. The boundaries of seven single-phase fields were determined which are solid solution ranges of system components and intermediate phases. We constructed the isothermal section at 820 K and the liquidus surface projection, and have determined the position in the system of six invariant processes with the participation of liquid: $ {\text{L}}_{{{\text{U}}_{1} }} + {\upzeta} {\leftrightarrows} {\upbeta} + {\upeta} $ L U 1 + ζ ? β + η (1145 K), $ {\text{L}}_{{{\text{U}}_{ 2} }} + \upzeta \leftrightarrows \upgamma + \upeta $ L U 2 + ζ ? γ + η (1138 K), $ \text{L}_{{U_{3} }} + \upeta \leftrightarrows \updelta + \upgamma $ L U 3 + η ? δ + γ (1113 K), $ {\text{L}}_{{{\text{E}}_{ 1} }} \leftrightarrows \upbeta + \updelta + \upeta $ L E 1 ? β + δ + η (1083 K), $ {\text{L}}_{{{\text{E}}_{ 2} }} \leftrightarrows \upalpha + \upbeta + \upvarepsilon $ L E 2 ? α + β + ε (969 K), $ {\text{L}}_{{{\text{E}}_{ 3} }} \leftrightarrows \upbeta + {\updelta} + \upvarepsilon $ L E 3 ? β + δ + ε (963 K). Two invariant processes in the sub-solidus part, $ \upbeta + \updelta \leftrightarrows \upeta + \uplambda $ β + δ ? η + λ and $ \upbeta + \updelta \leftrightarrows \upvarepsilon + \uplambda $ β + δ ? ε + λ at 968 and 938 K, respectively, were investigated as well.     

The Effect of Texture on the Corrosion Behavior of AZ31?Mg Alloy

Magnesium (Mg) grains show anisotropic corrosion behavior, which implies that the single-phase, hot-rolled Mg alloy AZ31 sheet, if highly textured, will have different corrosion performance depending on its crystallographic orientation of the grains. Its rolling surface, dominated by (0001) basal crystallographic planes, is more corrosion resistant than its cross-section surface, which is mainly composed of $ \{ 10\overline{1} 0\} $ and $ \{ 11\overline{2} 0\} $ prismatic crystallographic planes. Furthermore, grain refinement by hot rolling is beneficial to the overall corrosion resistance of AZ31 because of the dissolution of AlMn(Fe) intermetallic precipitates in the alloy. Surface compressive deformation machining can lead to refined grains and an expected preferred grain orientation, thus improving the corrosion resistance of AZ31 alloy.     

\left\{ {10\bar 12} \right\} twinning behavior in magnesium single crystal

In order to investigate $\left\{ {10\bar 12} \right\}$ tensile twinning behavior, the magnesium single crystal was deformed by compressing along the $\left[ {2\bar 1 \bar 10} \right]$ direction at room temperature, as $\left\{ {10\bar 12} \right\}$ tensile twinning easily takes place when the compression direction is perpendicular to the c-axis. Numerous $\left\{ {10\bar 12} \right\}$ primary tensile twins were activated during deformation, and the Schmid factor (SF) criterion was applied to the six $\left\{ {10\bar 12} \right\}$ twin variants. The analysis shows that the majority of the $\left\{ {10\bar 12} \right\}$ primary twins belong to high SF variants, and high SF twin boundaries provided nucleation sites for low SF variants. The $\left\{ {10\bar 12} \right\}$ secondary tensile twins were formed inside the high SF of wide $\left\{ {10\bar 12} \right\}$ primary twin bands, and the basal plane of the $\left\{ {10\bar 12} \right\}$ secondary twin was tilted about 60° with respect to the original parent matrix. In the case of the $\left\{ {10\bar 12} \right\}$ secondary tensile twin, relatively low SF variants were activated while counterparts with higher SF variants were absent.     

Mechanical Properties and Deformation Mechanisms of Mg-Gd-Y-Zr Alloy at Cryogenic and Elevated Temperatures

In this study, mechanical properties and deformation mechanisms of Mg-Gd-Y-Zr alloy at temperatures ranging from 77 K to 523 K have been investigated. The effects of temperature on the mechanical properties, deformation mechanism, and fracture mechanism are discussed. The results show that the strengths of alloy decrease gradually while the elongations increase progressively with increasing temperature. The maximum ultimate tensile strength of the alloy as high as 442 MPa is obtained at 77 K. As the temperature increases from 77 K to 523 K, the ultimate tensile strength of the alloy decreases from 442 MPa to 254 MPa and the elongations increase from 6.3% to 28.9% gradually. The study verifies that the deformation at 77 K is predominated by basal slip and \({{\left\{ {10\bar{1}2} \right\}} \mathord{\left/ {\vphantom {{\left\{ {10\bar{1}2} \right\}} {\left\langle {10\bar{1}1} \right\rangle }}} \right. \kern-0pt} {\left\langle {10\bar{1}1} \right\rangle }}\) deformation twinning system. At 223 K, lots of twins emerge primarily at grain boundaries. At 373 K, all dislocations are proved to be 〈a〉 dislocations. At 523 K, although basal slip is still the dominant deformation mechanism, non-basal slip systems also become activate.     

Effect of Diffusivity on the Pseudospinodal Decomposition of the γ′ Phase in a Ni-Al Alloy

The effect of diffusivity on pseudospinodal decomposition of γ′ (Ni₃Al) phase precipitation was investigated in a Ni-Al alloy using the diffuse interface phase field model. The γ′ phase microstructure, coarsening dynamics and interfacial composition width between the γ and γ′ phases were studied as a function of the diffusivity magnitude. Increasing the diffusivity results in a reduced number of γ′ nuclei, and accelerated growth and coarsening of the γ′ phase. The cube of the γ′ average radius versus time shows a linear relation during coarsening, and the Al concentration in the γ matrix follow the relations \(\Delta c_{\text{Al}}^{\gamma } \sim t^{ - 1/ 3}\) regardless of the diffusivity magnitude. The γ/γ′ interfacial composition width decreases with increased diffusivity and average radius. An obvious Al concentration depleted region is present at the γ/γ′ interface during the nucleation and growth stage of γ′ phase indicates that growth occurs by down-hill diffusion in the matrix γ phase. That combined with the gradual increase in γ′ composition demonstrates that pseudospinodal decomposition is the transformation mechanism.     

Orientation relationships between the icosahedral phase and β solid solution in quasicrystal-forming quenched Al61Cu26Fe13 alloys

Electron microscopy has been used to study orientation relationships (ORs) and stable misorientations between corresponding directions of the icosahedral ι phase and the β phase (CsCl type structure) of the solid solution in quenched two-phase Al₆₁Cu₂₆Fe₁₃ alloys with a dendritic structure. Calculated values of the azimuthal misorientations have been obtained for the directions of the reciprocal lattices of the ι and β phases in diffraction patterns A5 _l ,[113]_β; A2 _l , [111]A5_β for the basic $OR[110]_\beta \left\| {A5_l , [\bar 11\bar 1]_\beta } \right\|A2_l $ and close orientation conditions such as $[110]_\beta \left\| {A5_l , [\bar 110]_\beta } \right\|A2_l ; [11\bar 1]_\beta \left\| {A3_l , [\bar 110]_\beta } \right\|A2_l ; [111]_\beta \left\| {A2_l , [\bar 110]_\beta } \right\|A2_l $ . Two possible mechanisms of stabilization of the azimuthal misorientations revealed are discussed; first, the realization of the $OR[111]_\beta \left\| {A2_l , [\bar 110]_\beta } \right\|A2_l $ in quenched Al-Cu-Fe alloys and, second, the stability of the arising misorientations as a result of the formation of a layer with a modulated icosahedral structure at the boundaries between the β and gi phases.     

Metal Dusting of Nickel–Aluminium Alloys

Alloys of γ-Ni(Al), γ–γ′ Ni(Al)–Ni₃Al, γ′–Ni₃Al and β-NiAl were exposed in 1 h cycles to a carbon-supersaturated CO–H₂–H₂O gas mixture (a _C = 36.7, ${{p_{{\rm O}_2}}} $  = 2.83 × 10^?26 atm) at 650 °C and an overall pressure of 1 atm. It was found that all alloys except β-NiAl had been attacked by metal dusting, leaving a layered structure of nickel particles, graphite and catalytically grown nano-sized carbon filaments as the corrosion product. Carbon uptake and metal wastage rates were slowed with increasing aluminium content for the single-phase alloys. However, the γ–γ′ two phase alloy had the overall highest metal loss rate. Surface morphologies reflected uniform attack for the γ and γ–γ′ alloys, whereas on γ′ a pitting type of attack was observed. Amorphous alumina formation was identified on the surface of the γ′ and β alloys, and is thought to be the major factor providing protection against dusting attack.     

Modeling the Correlation of Composition-Processing-Property for TC11 Titanium Alloy Based on Principal Component Analysis and Artificial Neural Network

In the present investigation, the correlation of composition-processing-property for TC11 titanium alloy was established using principal component analysis (PCA) and artificial neural network (ANN) based on the experimental datasets obtained from the forging experiments. During the PCA step, the feature vector is extracted by calculating the eigenvalue of correlation coefficient matrix for training dataset, and the dimension of input variables is reduced from 11 to 6 features. Thus, PCA offers an efficient method to characterize the data with a high degree of dimensionality reduction. During the ANN step, the principal components were chosen as the input parameters and the mechanical properties as the output parameters, including the ultimate tensile strength ( $ \upsigma_{\text{b}} $ ), yield strength ( $ \upsigma_{0.2} $ ), elongation ( $ \updelta $ ), and reduction of area (??). The training of ANN model was conducted using back-propagation learning algorithm. The results clearly present ideal agreement between the predicted value of PCA-ANN model and experimental value, indicating that the established model is a powerful tool to construct the correlation of composition-processing-property for TC11 titanium alloy. More importantly, the integrated method of PCA and ANN is also able to be utilized as the mechanical property prediction for the other alloys.     

Comparative TEM investigation on the precipitation behaviors in Cu–15wt%Sn alloy

The decomposition and precipitation behaviors of a quenched Cu–15wt%Sn alloy as a function of aging temperature were investigated using transmission electron microscopy (TEM). Focused ion beam (FIB) was employed to assist TEM specimen preparation. At 300 °C, the decomposition of the supersaturated α′ phase occurred at grain boundaries, displaying a cellular morphology. The lamellae were found with ζ and α phases, rather than with the equilibrium ε and α phases. The ζ and α phases exhibit a well-defined orientation relationship (OR) as $ (1\bar{1}0)_{\alpha } //(0001)_{\zeta } ,\;[11\bar{2}]_{\alpha } //[\bar{1}2\bar{1}0]_{\zeta } $ . On the other hand, at 320 °C, only incipient lamellar structures of several micron meters were observed, which were composed of the δ and α phases. At the same time, abundant intragranular precipitation of the ε phase in the form of platelets was observed, and OR as $ (1\bar{1}1)_{\alpha } //(001)_{\varepsilon } , $ [110] _α //[100] _ε exists between ε phase and the α phase. These contrasting precipitation behaviors are discussed from the viewpoint of crystallographic coherency of these phases.     

Characterization of crystallographic properties of GaN thin film using automated crystal orientation mapping with TEM

The GaN thin film deposited on an amorphous glass substrate was analyzed by using transmission electron microscopy with a new automated crystal orientation mapping tool. Film deposition was made at 600°C for 4 h by the hyperthermal neutral beam (HNB) source. Columnar crystals oriented to the [0001] direction without significant disordering were clearly observed. Electron diffraction patterns indicated that the crystals have mainly two different zone axes, [2 $\bar 1$ $\bar 1$ 0] and [10 $\bar 1$ 0]. This crystallographic and microstructural information provides the guidance for future works for the HNB source to obtain GaN thin films of higher quality on amorphous substrates.     

The role of a preceding chemical reaction and reactive clusters in phase transitions of intermetallic compounds

By means of chemical and X-ray phase analysis with the use of a rotating disc electrode, it is found that the dissolution of Mg-Cu and In-Bi intermetallic compounds proceeds via magnesium ionization and subsequent $Mg_2 Cu\xrightarrow[{ - Mg^{2 + } }]{}MgCu_2 $ and $In_2 Bi\xrightarrow[{ - In^{3 + } }]{}InBi$ InBi phase regrouping. It is postulated that the process is accompanied by the formation of a defective crystal lattice and the appearance of reactive clusters, which interact to produce, at first, nuclei of a new phase and, then, the crystal lattice of a new intermetallic compound that is enriched in the electrochemically less active component.     

Crystallographic peculiarities of the eutectoid and martensite structures in the U–1.5 % Mo alloy

Using electron microscopy, samples of U–1.5 wt % Mo alloy with a partial structure of eutectoid, which consists of alternating plates of α phase depleted of molybdenum (α-U) and ordered γ’ phase (U₂Mo), have been studied. The structures of a eutectoid and martensite have been obtained by the quenching of samples characterized by delayed cooling from 1000°C. It has been shown that, in the eutectoid, the constant orientation relationships (ORs) are observed between the α-U and U₂Mo phases, namely, \({\left[ {100} \right]_\alpha }{\left\| {\left[ {331} \right]} \right._{\gamma '}},\;{\left( {010} \right)_\alpha }{\left\| {\left( {11\bar 6} \right)} \right._{\gamma '}},\;{\left( {010} \right)_\alpha }{\left\| {\left( {\bar 110} \right)} \right._{\gamma '}}\) These relationships are similar to the ORs observed in the martensite between an orthorhombic α’ martensite and initial bcc γ phase that have been found in low alloys of U–Nb, U–Zr, U–Mo and experimentally confirmed in this work. It has been established that, in the γ’ phase, principal axes a, b, c remain parallel to the principal axes of the matrix γ phase. However, its axis of tetragonality c has the only nonequivalent crystallographic direction at which the plates in the eutectoid colonies that are parallel to the planes of atomic ordering of the γ’ phase have interphase boundaries of \((001)_{\gamma '} ||(130)_\alpha \).     

The MPAW of Ti-3Al-2.5V Thin Sheets and Its Effects on Mechanical and Microstructural Properties

This research work deals with joining of Ti-3Al-2.5V titanium alloy thin sheets by means of microplasma arc welding (MPAW). An experimental set-up was developed to produce specimens welded in butt joint under controlled welding parameters, such as voltage, current, travel speed, and shielding gas flow rate. The performance of MPAW process was examined by mechanical properties tests and microstructural characterization. Results show that tensile strength and elongation of the welded specimens for a range of specific input heat are comparable to those of the base material (BM). Scanning electron microscopy (SEM) images of the fracture surface presented characteristics of ductile rupture. Studies on microstructure morphology of the specimens at the fusion zone (FZ) and heat-affected zone (HAZ) reveal occurrence of phase transformation from high temperature β phase to acicular $ \alpha^{\prime} $ phase, while the BM is of equiaxed α with intergranular β. An increasing variation in hardness was measured at the HAZ and FZ, which can be attributed to the presence of acicular $ \alpha^{\prime} $ phase and decreasing the amount of β phase at these regions. Based on the experimental results, it can be stated that MPAW process is an effective method for joining Ti-3Al-2.5V thin sheets provided appropriate welding parameters are used.     

Microstructure of Co precipitation strengthened B2-ordered NiAl

A transmission electron microscopy investigation on the phase decomposition of B2-ordered (Ni,Co)Al supersaturated with Ni and Co has revealed the precipitation of (Ni,Co)₂Al which has not been expected from the reported equilibrium phase diagram. The (Ni,Co)₂Al phase has a hexagonal structure and takes a rodlike shape with the long axis of the rod parallel to the 〈111〉 directions of the B2 matrix. By aging at temperatures below 873 K, a long period superlattice structure appears in the hexagonal (Ni,Co)₂Al phase. The orientation relationship between the (Ni,Co)₂Al precipitates and the B2-(Ni,Co)Al matrix is found to be (0001)_p//(111)_B2 and [ $ \bar 1 $ 2 $ \bar 1 $ 0]_p//[ $ \bar 1 $ 10]_B2, where the suffix p and B2 denote the (Ni,Co)₂Al precipitate and the B2-(Ni,Co)Al matrix, respectively. (Ni,Co)Al hardens appreciably by the fine precipitation of the (Ni,Co)₂Al phase.     

Kinetic Study of the Solid-State Transformation of Vacuum-Plasma-Sprayed Ti-6Al-4V Alloy

Because of the nature of the plasma spraying process, the physical and mechanical properties of vacuum-plasma-sprayed structures of Ti-6Al-4V alloy are completely different from those of conventionally manufactured alloys such as bulk materials from casting and forging. To obtain desired mechanical and physical properties, vacancy and internal defects must be reduced, splat boundaries must be eliminated, and optimal phase compositions should be obtained through postdeposition heat treatments. To determine appropriate heat treatment processes, one needs to study the kinetic behavior of the as-sprayed microstructure at elevated temperatures. In the current study, the kinetics of the solid transformations found in Ti-6Al-4V alloys produced during the vacuum plasma spraying process was studied based on the Johnson-Mehl-Avrami theory. For the kinetic behavior of this alloy, the nonconstant temperature dependence of the transformation rate constant exhibits an irregularity at 900 °C, marking a change in the transformation mechanism. For the lower-temperature (<900 °C) curves, the constant gradient indicates a lack of change in the transformation mechanism, including homogeneous nucleation, with growth of α phase. For higher temperatures (>900 °C), a gradient change indicates a change in the transformation mechanism. The first mechanism was the formation of α-phase grain boundary, and the second mechanism was α-plate nucleation and growth from grain boundaries. The value of the transformation rate constant in the kinetics study of as-sprayed Ti-6Al-4V alloy was much higher than for material produced by the casting method. Using the results obtained from the kinetics of the $ \upbeta \to \upalpha + \upbeta $ phase transformation at different constant temperatures, a time–temperature–transformation (TTT) diagram for as-sprayed Ti-6Al-4V alloy was developed.     

Kinetics of copper sulfidation at temperatures 570–1123 K

The kinetics of copper sulfidation have been studied as a function of temperature (570–1120 K) by the use of the modified Wagner's pellet method. It has been found that sulfidation follows a parabolic rate law with different activation energies in the low- and high-temperature ranges: $$k_{p}^{'} = 10.2 exp - (70 \pm 4)[kJ/mole]/RT (570 - 780 K)$$ and $$k_{p}^{'} = 1.69 \times 10^{ - 3} exp - (13 \pm 1.0)[kJ/mole]/RT (780 - 1120 K)$$ Using thermodynamic data as well as interfacial chemical potentials and ionic conductivity, the parabolic rate constants of sulfidation of copper have been calculated with good agreement with experimental results. Parabolic rate constants of sulfidation have been used to calculate average self-diffusion coefficients of copper in Cu₂S, the temperature dependence of which is as follows: $$\bar D_{Cu} = 8.76 \times 10^{ - 4} exp - (22.4 \pm 1)[kJ/mole]/RT$$      

Sulfidation properties of an Fe-26.4Cr-8Al-6Mn alloy at 973 and 1073 K in H2S-H2 atmospheres,10^{ - 4} \leqslant {\text{P}}_{{\text{S}}_{\text{2}} } \leqslant 10^2 {\text{Pa}}

The sulfidation behavior of an Fe-26.4Cr-8Al-6Mn (at.%) alloy in H₂S-H₂ atmospheres, \(10^{ - 4} \leqslant {\text{P}}_{{\text{S}}_{\text{2}} } \leqslant 10^2 {\text{Pa}}\) .     

Secondary recrystallization in Fe-3% Si alloy with (110)[001] single-component texture

After the primary recrystallization of a preliminarily deformed (110)[001] single crystal, the texture also has the preferred (110)[001] orientation. Furthermore, the texture contains weak orientations, a major part of which is formed at the sample surface and can be described by a spectrum of scattered orientations {120}〈210〉…{351}〈103〉. A further heating leads to two concurrent processes taking place in the samples, i.e., the normal growth of Goss grains and secondary recrystallization. Abnormally grown crystals are represented by a quartet of orientations related with the initial Goss orientation by a rotation around [011], [01 $\bar 1$ ], [101], and [10 $\bar 1$ ] axes at an angle of ～30°. The crystallographic relationship between the initial and final grain orientations can be explained by their closeness to special misorientations as follows: Σ9, Σ19a, Σ27a, and Σ33a (rotation around 〈110〉 axes to close angles).     

Effect of nitrogen and stacking-fault energy on twinning in [ \bar 1 11] single crystals of austenitic stainless steels

The dependence of critical shear stresses for twinning τ _cr ^tw on the stacking-fault energy γ₀, the nitrogen concentration C _N (wt %), and the test temperature has been studied for [ $ \bar 1 $ 11] single crystals of austenitic stainless steels upon tensile deformation. It is shown that τ _cr ^tw ～ γ₀/b ₁ in nitrogen-free steels, while it exhibits a nonmonotonic dependence on the nitrogen concentration C _N in nitrogen-alloyed steels. An increase in τ _cr ^tw at C _N = 0.3 wt % and its decrease at C _N ≥ 0.5–0.7 wt % are determined by the competition of two contributions to τ _cr ^tw , namely, a decrease in γ₀ and a solid-solution hardening with increasing nitrogen concentration.