Structure stability of AA3003 alloy with ultra-fine grain size

The study on the structure stability of AA3003 alloy produced by an intense plastic straining process named accumulative roll bonding (ARB) has been conducted. The results show that continuous recrystallization took place in the ARBed 3003 alloy with increasing the annealing time at 250°C and increasing the annealing temperature to 275°C. While, discontinuous recrystallization began in some regions after 300°C annealing, and nearly finished after 400°C annealing. Furthermore, an unusual tensile behavior was observed in this alloy after annealing at 250–275°C. The Hall-Petch dependence was observed in the plot of microhardness versus d ^–1/2 of the ARBed 3003 alloy, but its dependence slope was changed. The ultra-fine grains (<1 m) formed in the ARBed 3003 alloy can be stable until annealing at 250°C for 1 h, and the fine grains (<2 m) can be stable until annealing at 275°C for 1 h. Therefore, grain structure formed in the ARBed 3003 alloys after intense plastic strain is reasonably stable. In addition, the mechanism of structure stability and mechanical behavior were also discussed.     

Thermal stability of undoped polycrystalline silicon layers on antimony and boron-doped substrates

The structure of as-deposited and annealed polycrystalline silicon layers has been investigated by scanning electron microscopy and x-ray diffraction. The structure of intentionally undoped layers prepared by low pressure chemical vapor deposition at a temperature of 640 °C was found to be stable upon annealing at temperatures lower than about 900 °C. On the other hand, primary recrystallization of the layers has been observed during annealing at temperatures in the range of 900 to 1150 °C. Isochronal annealing revealed the activation energy for the primary recrystallization of undoped layers as 0.6 eV. The activation energy for diffusion of silicon self-interstitials along the grain boundaries was calculated to be 2.2 eV. The difference in grain-growth process was observed for the undoped layers grown either (i) on lightly boron-doped substrate or (ii) on the substrate heavily doped with antimony. The different grain-growth mechanism was found to be a consequence of antimony diffusion into the polycrystalline layer.     

Effect of post-weld heat treatment on the microstructure and plastic deformation behavior of friction stir welded 2024

To improve the plasticity of friction stir welded joints for plastic processing applications, post-weld heat treatment (PWHT) of 2024-O aluminum alloy friction stir welding joints was carried out at annealing temperatures from 250 °C to 450 °C with an interval of 50 °C for 2 h, followed by cooling to 200 °C in the furnace. The effect of PWHT on the microstructure and plastic deformation behavior of the joints was investigated. It was found that the fine-equiaxed grains are stable and retained in the nugget of the joints even after annealing at 450 °C for 2 h. However, the grains in the thermo-mechanically affected zone (TMAZ) of the joints become coarse and equiaxed as annealing temperature increases. The plastic deformation of as-welded joint is very heterogeneous. In contrast, the plastic deformation of PWHT joint is relatively homogeneous by both the nugget and the base material showing large deformation. The decrease in elongation of as-welded joints is completely recovered by PWHT. The high ductility of the joint is mainly attributed to the retention of the fine-equiaxed grains in the nugget during PWHT.     

Strain-softening behavior of an Fe-6.5 wt%Si alloy during warm deformation and its applications

An Fe-6.5 wt%Si alloy with columnar grains was compressed at a temperature below its recrystallization temperature. The Vickers hardness and structure of the alloy before and after deformation were investigated. The results showed that with an increase in the degree of deformation, Vickers hardness of the alloy initially increased rapidly and then decreased slowly, indicating that the alloy had a strain-softening behavior after a large deformation. Meanwhile, the work-hardening exponent of the alloy decreased significantly. Transmission electron microscopy confirmed that the decrease of the order degree was responsible for the strain-softening behavior of the deformed alloy. Applying its softening behavior, the Fe-6.5 wt%Si alloy with columnar grains was rolled at 400 °C and then at room temperature. An Fe-6.5 wt%Si thin strip with thickness of 0.20 mm was fabricated. The surface of the strip was bright and had no obvious edge cracks.     

Quantifying the recrystallization of cold rolled AA 3015 aluminum alloy by X-ray diffraction

The recrystallization kinetics of continuous cast (CC) AA 3015 aluminum alloy with and without pre-treatment has been investigated by X-ray diffraction and measurements of hardness. The variation in texture volume fractions with annealing time reflects better the progress of recrystallization. The JMAK exponent and the activation energy for recrystallization derived from texture data are in good agreement with those from hardness data. Monitoring the change of texture volume fractions during annealing is shown to be a feasible method of determining the recrystallization kinetics of aluminum alloys. The recrystallization kinetics and recrystallization texture of CC AA 3015 aluminum alloy are strongly affected by concurrent precipitation. Concurrent precipitation significantly retards the recrystallization of CC AA 3015 aluminum alloy, decreases the JMAK exponent, enhances the activation energy for recrystallization, and results in a strong P recrystallization texture.     

Research on the hot deformation behavior of Ti40 alloy using processing map

The deformation behavior of a Ti40 titanium alloy was investigated with compression tests at different temperatures and strain rates to evaluate the activation energy and to establish the constitutive equation, which reveals the dependence of the flow stress on strain, strain rate and deformation temperature. The tests were carried out in the temperature range between 900 and 1100 °C and at strain rates between 0.01 and 10 s⁻¹. Hot deformation activation energy of the Ti40 alloy was calculated to be about 372.96 kJ/mol. In order to demonstrate the workability of Ti40 alloy further, the processing maps at strain of 0.5 and 0.6 were generated respectively based on the dynamic materials model. It is found that the dynamic recrystallization of Ti40 alloy occurs at the temperatures of 1050-1100 °C and strain rates of 0.01-0.1 s⁻¹, with peak efficiency of power dissipation of 64% occurring at about 1050 °C and 0.01 s⁻¹, indicating that this domain is optimum processing window for hot working. Flow instability domains were noticed at higher stain rate (≥1 s⁻¹) and stain (≥0.6), which located at the upper part of the processing maps. The evidence of deformation in these domains has been identified by the microstructure observations of Ti40 titanium alloy.     

Hot ductility of a Fe–Ni–Co alloy in cast and wrought conditions

The hot ductility of Fe–29Ni–17Co alloy was studied in both cast and wrought conditions by hot tensile tests over temperature range of 900–1250 °C and at strain rates of 0.001–1 s⁻¹. Over the studied temperature range, the wrought alloy represented higher elongation and reduction in area as compared to the cast alloy. Dynamic recrystallization was found responsible for the higher hot ductility of the wrought alloy and the improvement of hot ductility of the cast alloy at high temperatures. At temperature range of 1000–1150 °C the wrought alloy exhibited a hot ductility drop while a similar trough was not observed in case of the cast alloy. It was also found that at temperatures of 1150–1250 °C the best hot ductility is achieved in both cases of cast and wrought alloy. The experimental data of flow stress were constitutively analyzed and the apparent activation energy of deformation was estimated to be 344 kJ/mol.     

Effects of annealing and deforming temperature on microstructure and deformation characteristics of Ti–Ni–V shape memory alloy

Effects of annealing temperature T_an and deforming temperature T_d on microstructure and deformation characteristics of Ti–50.8Ni–0.5V (atomic fraction, %) shape memory alloy were investigated by means of optical microscopy and tensile test. With increasing T_an, the microstructure of Ti–50.8Ni–0.5V alloy wire changes from fiber style to equiaxed grain, and the recrystallization temperature of the alloy is about 580 °C; the critical stress for stress-induced martensite σ_M of the alloy decreases first and then increases, and the minimum value 382 MPa is got at T_an = 450 °C; the residual strain ?_R first increases, then decreases, and then increases, and its maximum value 2.5% is reached at T_an = 450 °C. With increasing T_d, a transformation from shape memory effect (SME) to superelasticity (SE) occurs in the alloy annealed at different temperatures, and the SME → SE transformation temperature was affected by T_an; the σ_M of the alloy increases linearly; the ?_R of the alloy annealed at 350–600 °C decreases first and then tends to constant, while that of the alloy annealed at 650 °C and 700 °C decreases first and then increases. To get an excellent SE at room temperature for Ti–50.8Ni–0.5V alloy, T_an should be 500–600 °C.     

Effects of solution treatment on the microstructure and mechanical properties of Al–Cu–Mg–Ag alloy

The effects of solution treatment on the microstructure and mechanical properties of Al–Cu–Mg–Ag alloy were studied by optical microscopy (OM), scanning electron microscopy (SEM), energy dispersive X-ray (EDX), differential scanning calorimeter (DSC), transmission electron microscopy (TEM) and tensile test, respectively. The results show that the mechanical property increases and then decreases with increasing the solution temperature. And the residual phases are dissolved into the matrix gradually, the number fraction of the precipitation and the size of recrystallized grains increase. Compared to the solution temperature, the solution holding time has less effect on the microstructure and the mechanical properties of Al–Cu–Mg–Ag alloy. The overburnt temperature of Al–Cu–Mg–Ag alloy is 525 °C. The yield strength and the elongation get the best when the alloy is solution treated at 515 °C for 1.5 h, is 504 MPa and 12.2% respectively. The fracture mechanism of the samples is ductile fracture.     

High-temperature deformation behavior of Ti60 titanium alloy

Isothermal compressions of near-alpha Ti60 alloy were carried out on a Gleeble-3800 simulator in the temperature range of 960-1110 °C and strain rate range of 0.001-10.0 s⁻¹. The high-temperature deformation behavior was characterized based on an analysis of the stress-strain behavior, kinetics and processing map. The flow stress behavior revealed greater flow softening in the two-phase field compared with that of single-phase field. In two-phase field, flow softening was caused by break-up and globularization of lamellar α as well as deformation heating during deformation. While in the single-phase field, flow softening was caused by dynamic recovery and recrystallization. Using hyperbolic-sine relationships for the flow stress data, the apparent activation energy was determined to be 653 kJ/mol and 183 kJ/mol for two-phase field and single-phase field, respectively. The processing map exhibited two instability fields: 960-980 °C at 0.3-10 s⁻¹ and 990-1110 °C at 0.58-10 s⁻¹. These fields should be avoided due to the flow localization during the deformation of Ti60 alloy.     

Thermomechanical treatment for enhancing gamma fiber component in recrystallization texture of copper-bearing bake hardening steel

A two-step rolling-annealing process has been developed to increase the 〈1 1 1〉//ND (γ fiber) component in the recrystallization texture of a copper-bearing bake hardening steel. The two step process comprises the first rolling by a low reduction in thickness and subsequent annealing at 780 °C, followed by the second rolling by a high reduction and subsequent annealing at 780 °C. The first rolling process aims at seeding the γ fiber oriented grains, so that they can grow at the expense of differently oriented grains developed in the second rolling process. In this way the density of γ fiber component in the recrystallization texture of the bake hardening steel much increases compared with that in the conventional one-step rolling-annealing process.     

Effect of grain size and orientation on the initial permeability of 36 wt % Ni-Fe alloys

The effect of grain size and grain orientation on the initial permeability of a 36 wt % Ni-Fe alloy with additions of molybdenum, chromium and copper is reported. The initial permeability was found to increase with annealing temperature between 600° C and approximately 900° C due to the formation of a (1 2 3) [4 1 ¯2] primary recrystallization texture. Increasing the annealing temperature in the range 900 to 1100° C led to progressively lower permeabilities due to the growth of randomly oriented abnormal grains within the textured matrix. It is suggested that an increase in the misorientation between adjacent grains gives rise to an increase in the local magnetostatic energy, leading to much stronger pinning of magnetic domain walls, with a consequent decrease in permeability. Annealing at temperatures above 1100° C tends to increase the permeability, because of the increase in grain size.     

Tensile and impact-toughness behaviour of cryorolled Al 7075 alloy

The effects of cryorolling and optimum heat treatment (short annealing + ageing) on tensile and impact-toughness behaviour of Al 7075 alloy have been investigated in the present work. The Al 7075 alloy was rolled for different thickness reductions (40% and 70%) at cryogenic (liquid nitrogen) temperature and its mechanical properties were studied by using tensile testing, hardness, and Charpy impact testing. The microstructural characterization of the alloy was carried out by using field emission scanning electron microscopy (FE-SEM). The cryorolled Al alloy after 70% thickness reduction exhibits ultrafine grain structure as observed from its FE-SEM micrographs. It is observed that the yield strength and impact toughness of the cryorolled material up to 70% thickness reduction have increased by 108% and 60% respectively compared to the starting material. The improved tensile strength and impact toughness of the cryorolled Al alloy is due to grain refinement, grain fragments with high angle boundaries, and ultrafine grain formation by multiple cryorolling passes. Scanning electron microscopy (SEM) analysis of the fracture surfaces of impact testing carried out on the samples in the temperature range of −200 to 100 °C exhibits ductile to brittle transition. cryorolled samples were subjected to short annealing for 5 min at, 170 °C, and 150 °C followed by ageing at 140 °C and 120 °C for both 40% and 70% reduced samples. The combined effect of short annealing and ageing, improved the strength and ductility of cryorolled samples, which is due to precipitation hardening and subgrain coarsening mechanism respectively. On the otherhand, impact strength of the cryorolled Al alloy has decreased due to high strain rate involved during impact loading.     

Microstructure of electroplated Cu(Ag) alloy thin films

Electroplated Cu(Ag) alloy thin films are potential candidates for future electronic devices in terms of lifetime and reliability compared to copper as the state of the art interconnect material. In the present paper we focus on the microstructure of Cu(Ag) alloy films considering the grain evolution as well as silver incorporation and segregation. We show that Ag alloying addition prevents room temperature recrystallization. Thermally induced grain growth occurs mainly between 180 °C and 330 °C. Silver can be incorporated as solid solution into the Cu matrix by up to 0.8 at.% after annealing and even in higher concentrations in the as-deposited state, which is significantly above the equilibrium solubility limit. Precipitations are formed by the continuous mode and can be mainly found at the film surface but also inside the Cu(Ag) grains as ball-shaped particles. Based on our results a reliability improvement is expected by mechanical strengthening due to alloying effects while maintaining a low electrical resistivity and a {111} fiber texture.     

Influence of intermediate annealing on final Goss texture formation in low temperature reheated Fe-3%Si steel

The precipitation behavior of inhibitors and their influence on final Goss texture formation in grain-oriented electrical steels produced by compact strip processing technology with a reheating temperature lower than 1200 °C were investigated under two distinct intermediate annealing methods: conventional intermediate recrystallization annealing and a new intermediate decarburizing and recrystallization annealing method without final decarburizing after the second cold rolling. The initiation of secondary recrystallization, the distributions of second phase particles, the final Goss texture, and the grain structure were observed. The new technology could maintain higher inhibitor densities because the deformed matrix could provide higher site densities for inhibitor nucleation before secondary recrystallization, resulting in a relatively higher inhibition effect of the second phase particles. The new technology could also compensate for the disadvantages of fewer inhibitors induced by fewer dissolved Mn and S elements in the matrix during lower reheating temperature for hot rolling. The final sheet produced after the secondary recrystallization annealing obtained stronger Goss texture, larger grain size, and better magnetic properties.     

A comparative analysis of tensile and impact-toughness behavior of cold-worked and annealed 7075 aluminum alloy

The present research reports comparative analysis of effects of cold working (CW) and annealing on tensile and impact-toughness behavior of 7075 Al alloy. Cold-rolled samples were annealed at various temperatures in the range of 225–345 °C for 5 min. A remarkable increase in ductility and impact toughness was observed when specimens were annealed at temperatures above 265 °C for 5 min. It was also found that cold rolling has a profound effect on strength anisotropy that enhances with amount of % CW. The maximum strengths were observed in the transverse direction in the investigated alloy. Cold rolling has been found to impart a significant effect on decreasing the impact toughness of alloy that enhance with amount of % CW; this loss in impact energy could not be compensated by recrystallization process. It has also been shown that impact test can be considered as a simple method for measurement of toughness and plastic anisotropy in sheet and plate. The analysis of the fracture surfaces with the scanning electron microscope presented dimpled morphology for the failure ductile mechanism in starting material and fibrous structure with some quasi-cleavage regions in cold-rolled samples, corresponding to the ductile to brittle fracture mechanism.     

Influence of thermomechanical treatment on the hardening mechanisms and structural changes of a cast Cu–6.6 wt.%Ag alloy

Investigations were carried out on the cast samples of Cu–6.6 wt.%Ag alloy, as well as pure copper samples, for the sake of comparison. Cast samples of copper and alloy were subjected to the same thermomechanical treatment. The thermomechanical treatment included the homogenized annealing, prefinal cold rolling, solution annealing, final cold rolling with a final reduction of 20%, 40% and 60% as well as the isochronal and isothermal annealing up to the recrystallization temperature. Influence of thermomechanical treatment on the hardening mechanisms and structural changes of cast Cu–6.6 wt.%Ag alloy has been investigated for the hardness and electrical conductivity measurements as well as optical microscopy. The study has shown that the anneal hardening effect appeared on the cast Cu–6.6 wt.%Ag alloy in the temperature range of 160–400 °C and was followed by an increase in the hardness and electrical conductivity.     

Effect of temperature on deformation behavior and microstructures of TC11 titanium alloy

The isothermal compression deformation behavior of TC11 titanium alloy with beta microstructure was studied between 750 °C and 1100 °C under the strain rate ranging from 0.001 s⁻¹ to 10 s⁻¹ by THERMECMASTOR-Z simulator. In addition, the effect of temperature on microstructure was observed using optical microscope. The results showed that the temperature greatly affected the flow stress and microstructure of TC11 titanium alloy cooled from beta phase region in air. During hot deformation of TC11 titanium alloy, the steady state flow characteristic was observed at higher temperature or lower strain rate. In the α + β phase region, spheroidization fraction of α lamellar decreased with increasing temperature, while in near-β and β phase regions, dynamic recrystallization fraction increased with increasing temperature in all strain rates except at the strain rate of 0.001 s⁻¹.     

Formation and thermal stability of aluminium nanoparticles synthesized via yttrium ion implantation into sapphire

Yttrium ion implantation of 1 1 2 3 alumina resulted in the formation of metallic aluminium–yttrium, face centred cubic (a0=0.41 nm) spherical nanocrystals ( 12 nm in diameter) embedded in an amorphous matrix. A fluence of 5×1016Y+/cm2 implanted at ambient temperature and accelerating energies of 150 or 170 keV yielded this result. Crystalline nanoparticles were not present in the amorphous matrix for implantations done with identical conditions but lower energy (100 keV). Substrates implanted at 150 keV were annealed in laboratory air for times ranging from 20 to 90 min and temperatures ranging from 1000 to 1400°C. A clear progression of morphologies resulted from these annealing treatments. A 1000°C, 90 min anneal produced 13% recrystallization of the amorphous region and induced the formation of crystallites of a metastable Y–Al alloy. An 1100°C, 90 min anneal demonstrated 40% recrystallization of the amorphous region, accompanied by the formation of partially aligned internal grains of Y2O3. Electron diffraction shows that the Y–Al alloy crystallites which formed in the 1000°C anneal are also present at 1100°C. A highest temperature anneal of 1400°C, 60 min induced essentially complete recrystallization of the amorphous phase, the dissolution of the metastable Y–Al alloy, the retention of the internal yttria grains, and the formation of partially oriented external grains of yttria resulting from the segregation of yttrium to the substrate surface.     

A gradual annealing of amorphous sputtered indium tin oxide: Crystalline structure and electrical characteristics

Thin films of amorphous indium tin oxide were deposited by soft sputtering. The film was gradually annealed in air at temperatures from 110 °C to 150 °C. Its structural and electrical properties were monitored in order to get a better understanding of the annealing process. Firstly, carrier density decreases by oxygen intake. Crystallization speeds up at 150 °C, with a 2.5 D growth of crystallites. The preferred orientations come from sputtering induced seeds. Then, the carrier density increases again due to tin activation. Meanwhile, the carrier mobility is more damaged by the low temperature annealing in air than by a standard annealing in a reducing atmosphere. Thus, tin oxide segregation is suspected at grain boundaries.