Showing papers on "Superplasticity published in 2011"

Superplastic Deformation of Defect-Free Au Nanowires via Coherent Twin Propagation

Abstract: We report that defect-free Au nanowires show superplasticity on tensile deformation. Evidences from high-resolution electron microscopes indicated that the plastic deformation proceeds layer-by-layer in an atomically coherent fashion to a long distance. Furthermore, the stress–strain curve provides full interpretation of the deformation. After initial superelastic deformation, the nanowire shows superplastic deformation induced by coherent twin propagation, completely reorientating the crystal from to . Uniquely well-disciplined and long-propagating atomic movements deduced here are ascribed to the superb crystallinity as well as the radial confinement of the Au nanowires.

Synthesis of nanocomposites and amorphous alloys by mechanical alloying

Abstract: Mechanical alloying (MA) is a powder metallurgy processing technique that involves repeated cold welding, fracturing, and rewelding of powder particles in a high-energy ball mill. Due to the specific advantages offered by this technique, MA was used to synthesize a variety of advanced materials. This article presents two specific examples of synthesis of nanocomposites containing a high volume fraction of the reinforcement phase in Al and TiAl matrices. It was possible to uniformly disperse 50 vol% of nanometric (50 nm) Al2O3 in Al and achieve high strength and modulus of elasticity. Similarly, it was possible to disperse 60 vol% of Ti5Si3 phase in the γ-TiAl intermetallic. Fully consolidated material showed superplastic behavior at 950 °C and a strain rate of 4 × 10−5 s−1. Amorphous phases were produced by MA of blended elemental powder mixtures in several Fe-based compositions. From the systematic investigations carried out, it was possible to deduce the criteria for glass formation and understand the interesting phenomenon of mechanical crystallization. By conducting some controlled experiments, it was also possible to explain the mechanism of amorphization in these mechanically alloyed powder blends. Other examples of synthesis of advanced materials, e.g., photovoltaic materials and energetic materials, have also been briefly referred to. This article concludes with an indication of the topics that need special attention for further exploitation of these materials.

Hot Deformation and Processing of Aluminum Alloys

Abstract: Aluminum and Its Alloys Introduction, History, and Applications Crystal Structure and Slip Behavior Starting Point for Analyzing Plastic Forming Alloy Development Alloy and Temper Designations Solidification, Segregation, and Constitutive Particles Aluminum Industry Organization Metal Forming and Deformation Modes Introduction to Metal Forming Industrial Processing Overview Computational Modeling and Simulation Mechanical: Elastic/Plastic Stress/Strain Mechanical: Constitutive Equations Microstructural Development Hot Work Testing Techniques Introduction to Testing Torsion Compression Tension Hot Rolling Extrusion Hot Working of Aluminum DRV, Historical Perspective Steady-State Flow Curves Constitutive Analysis Microstructure Evolution Crystal Rotations, Texture, and Strain-Induced Boundaries GB Serrations Geometric DRX: Grain Refining DRV DRX of Al Alloys GB Sliding and Migration Hot Ductility and Failure Mechanisms Hot Working of Dispersoid and Solute Alloys General Dispersoid Effects Al-Mn Alloys, Can Stock (3000 Series) Al-Fe and Al-Fe-Co Conductor Alloys Al-Si Eutectic Forging Alloys (4000 Series) Mechanical Alloying Rapidly Solidified Alloys Al-Mg Alloys (5000 Series) Al-Mg-Mn Alloys (5000 Series) Hot Ductility of Al-Mg and Al-Mg-Mn Alloys Precipitation Hardening Alloys Introduction: Precipitation Behavior Al-Mg-Si Alloys (6000 Series) Al-Cu-Mg Alloys (2000 Series) Al-Zn-Mg-Cu Alloys (7000 Series) Al-Li-XX Alloys (8000 Series, 2090) Aluminum Matrix Composites Introduction Varieties and Fabrication Hot Deformation Forging Experiments Comparative Extrusion Behavior Comparison of Hot Working of other Metals Face-Centered Cubic Metals (Low SFE) Body-Centered Cubic Metals HCP Metals Workability of Dual Phase Alloys of Ti, Zr, and Fe Summary: Hot Workability of Different Crystal Structures Creep: Strain Rates below 10-4 s-1 Introduction: Objectives and Description Five-Power-Law Creep Diffusional Creep Harper-Dorn Creep Three-Power Law Viscous Glide Creep Creep Behavior of Particle-Strengthened Alloys Creep Fracture: Grain Boundary Sliding Cold Working Introduction Fundamentals of Single-Crystal Plasticity Deformation of Polycrystals Development of Dislocation Substructure: Textures Influence of Solute and SFE Very High Strains: Cyclic Extrusion-Compression Very High Strains by Equal-Channel-Angular Pressing Comparison of Hot and Cold Working Models for Cold and Hot Working Static Restoration, Annealing Introduction SRV after Cold Working SRX after Cold Working SRV after Hot Working SRX after Hot Working SRV and SRX during Hot Forming Schedules Thermomechanical Processing Introduction to Objectives Strengthening Mechanisms Hot Working with Retained Substructure Hot Working with Static Recrystallization Cold Working and Annealing Product Textures Deformation, Precipitation, and Particles Powder Consolidation: Multiphase Materials Superplasticity Introduction to the Phenomenon Fundamentals of Superplasticity Classification of Processes for Refining Microstructure Heavy Cold or Warm Working and SRX Warm Working with cDRX in Superplastic Straining Severe Plastic Deformation at Room Temperature Extrusion Introduction to the Process Control Parameters Insights from FEM Substructures and Microstructures in Extrusions Extrusion Microstructures in Al-Mg and Al-Mg-Mn (5000 Series) Extrusion of Al-Mg-Si Alloys (6000 Series) Extrudability of Al-Zn-Mg Alloys (7000 Series, Cu Free) Extrudability of Al-Zn-Mg-Cu Alloys (7000 Series) Extrudability of Al-Cu-Mg Alloys (2000 Series) Surface Failure in Extrusion Extrudate Properties and Recrystallization Rolling Introduction: The Rolling Process Static Recovery and Recrystallization Hot and Warm Rolling Rolling, DRV, SRV, and SRX: Textures Rod Rolling Particle-Stabilized Wire Torsional Simulation of Rolling Rolling Simulation in Compression Modeling of Rolling Hot and Cold Forging Feedstock Preheat Forging Rate: Press Effects Shape and Fiber Control: Die Type Modeling: Shape and Structure Microstructure Development Properties Comparison to Semisolid Forming

Multi-directional forging of AZ61Mg alloy under decreasing temperature conditions and improvement of its mechanical properties

Abstract: In this study, AZ61Mg alloy was multi-directionally forged (MDFed) up to a maximum cumulative strain of ∑Δ ɛ = 4.0 at a true strain rate of 3 × 10 −3 s −1 . The MDF temperature was decreased pass-by-pass from 623 to 503 K. The average grain size decreased with increasing cumulative strain. After MDF was carried out until ∑Δ ɛ = 4.0, i.e., after five passes, ultrafine grains (UFGs) with an average grain size of 0.8 μm were uniformly evolved. Results revealed that UFG evolution was induced by the combined mechanisms of mechanical twinning, kinking, and continuous dynamic recrystallization. The MDFed AZ61Mg alloy exhibited an excellent balance of strength and ductility at room temperature, i.e., an ultimate tensile strength (UTS) of 440 MPa and plastic strain to fracture of over 20%. In addition, it exhibited superplasticity at elevated temperatures. Because of its superior deformability, the alloy was further made to undergo a cold rolling procedure to achieve up to 20% reduction. The additional thermo-mechanical processes of cold rolling and/or aging successively raised the UTS of the alloy to 550 MPa without much spoiling ductility (plastic strain to fracture of 14%).

Nanostructured metals and alloys : processing, microstructure, mechanical properties and applications

Abstract: Part 1 Processing of bulk nanostructured metals and alloys: Production of bulk nanostructured metals and alloys by severe plastic deformation (SPD) Bulk nanostructured metals and alloys produced by accumulative roll-bonding Nanocrystalline metals and alloys prepared by mechanical attrition Processing of nanostructured steels by solid reaction Processing of bulk nanocrystalline metals and alloys by electrodeposition Bulk nanocrystalline and nanocomposite alloys produced from amorphous phase Severe plastic deformation and production of nanostructured alloys by machining. Part 2 Microstructure: Deformation structures including twins in nanograined pure metals Microstructure and mechanical properties of nanostructured ferrous alloys by equal-channel angular pressing Characteristic structures and properties of nanostructured metals prepared by plastic deformation. Part 3 Mechanical properties: Strengthening mechanisms in nanocrystalline metals Elastic and plastic deformation in nanocrystalline metals Mechanical properties of multi-scale metallic materials Enhanced ductility and its mechanisms in nanocrystalline metallic materials Mechanical behavior of nanostructured metals based on molecular dynamics computer simulations Surface deformation and mechanical behavior of nanostructured alloys Fatigue behaviour in nanostructured metals Superplastic deformation in nanocrystalline metals and alloys Creep and high temperature deformation in nanostructured metals and alloys. Part 4 Applications: Processing of nanostructured metal and metal-matrix coatings by thermal and cold spraying Nanocoatings for commercial and industrial applications Application of nanostructured steel sheets to automotive body structures Production processes for nanostructured wires, bars and strips Nanostructured plain carbon-manganese (C-Mn) steel sheets by ultra-fast cooling and short interval multi-pass hot rolling.

Developing superplasticity and a deformation mechanism map for the Zn–Al eutectoid alloy processed by high-pressure torsion

Abstract: A Zn–22% Al eutectoid alloy was processed by high-pressure torsion (HPT) for 1, 3 and 5 turns at room temperature to produce an ultrafine grain size of ∼350 nm. Tensile testing at a temperature of 473 K gave excellent superplastic properties with elongations to failure up to a maximum of 1800% at an imposed strain rate of 1.0 × 10 −1 s −1 : this is within the range of high strain rate superplasticity and represents the highest elongation recorded to date for a specimen processed by HPT. It is shown that the experimental data are in excellent agreement with a deformation mechanism map constructed for a temperature of 473 K.

Flow mechanisms in ultrafine-grained metals with an emphasis on superplasticity

Abstract: An analysis was conducted to examine the flow behavior of ultrafine-grained (UFG) metals produced by severe plastic deformation (SPD) processing in equal-channel angular pressing. The results reveal two distinct types of behavior. At elevated temperatures, the analysis shows that superplastic flow is accurately described by the theoretical mechanism developed for coarse-grained metals so that flow in UFG materials may be interpreted using conventional flow mechanisms. By contrast, localized small-scale grain boundary sliding is observed during deformation at low temperatures and this is attributed to the movement of extrinsic dislocations in the non-equilibrium grain boundaries produced by SPD processing.

Superplasticity in a two-phase Mg–8Li–2Zn alloy processed by two-pass extrusion

Abstract: Tensile tests on a two-pass extruded Mg–8Li–2Zn alloy are conducted at 473–593 K, and an initial strain rate of 1.5 × 10 −4 –7.5 × 10 −3 s −1 . The two-pass extruded alloy has refined structure and excellent superplastic properties, with a maximum recorded elongation of 758% at 563 K under an initial strain rate of 1.5 × 10 −4 s −1 . The value of the strain rate sensitivity under the optimum superplastic condition is 0.55, and the activation energy is 90 kJ/mol. These indicate that the dominant deformation mechanism in the two-pass extruded alloy is grain-boundary sliding controlled by grain-boundary diffusion. Coalescence and interlinkage of cavities are the reasons for tensile failure.

Optimization of forging process parameters of Ti600 alloy by using processing map

Abstract: The hot deformation behavior of Ti600 titanium alloy has been studied using the processing map technique. Compression test with gleeble-1500 thermal simulator were performed in the temperature range of 800–1100 °C and the strain rate range of 0.001–10 s −1 . The flow stress data obtained from the test were used to develop processing map according to dynamic material model and Prasad's instability criterion. In the processing map, the variation of the efficiency of the power dissipation is plotted as a function of temperature and strain rate. The map exhibits two domains of dynamic recrystallization occurring at the temperature range of 800–950 °C in the strain rate of 0.003–1 s −1 and the temperature range of 970–1070 °C in the strain rate range of 0.03–1 s −1 , respectively. Moreover, the superplastic of Ti600 alloy occurs at low strain rate ranges of 0.001–0.01 s −1 and high temperature range of 930–1100 °C with the peak efficiency higher than 60%, which are the optimum domain for hot working of Ti600 titanium alloy. The instability domain (flow localization and adiabatic shear) of flow behavior can also be recognized at the temperature range of 800–950 °C in the strain rate of 0.03–10 s −1 and the temperature range of 1070–1100 °C in the strain rate of 1–10 s −1 . The evidences of deformation in these domains were identified and validated through microstructure observations.

Hot deformation behavior of Cu–8.0Ni–1.8Si–0.15Mg alloy

Abstract: The hot deformation of Cu–8.0Ni–1.8Si–0.15Mg (wt.%) alloy sample was carried out on a Gleeble-1500 thermo-simulator with various strain rates at different deformation temperatures. The thermal deformation activation energy Q was calculated and hot compression constitutive equation has been established. Metallomicroscopy was employed to analyze the microstructures evolution of the alloy during deformation. The working hardening, the dynamic recovery and the dynamic recrystallization play important roles to affect the plastic deformation behaviors of the alloy at different temperature regions. The processing map of the alloy has been established.

Superplastic Behavior of Ti-6Al-4V-0.1B Alloy (Preprint)

Abstract: : The superplastic behavior of Ti-6Al-4V-0.1B sheet was evaluated. The strain rate sensitivity (m) is 0.47 in the temperature range 775-900 C and at strain rate ( ) = 10-5 to 10-3 s-1. The material exhibits tensile elongations 200% in the temperature range 725-950 C at = 3 10-4 s-1. The optimum superplastic forming temperature is 900 C, which is similar to conventional Ti-6Al-4V. However, a lower flow stress is needed in the case of Ti-6Al-4V-0.1B. The superplastic deformation mechanism is suggested from estimates of activation energy to be grain boundary sliding (GBS) accommodated by dislocation motion along grain boundaries at = 10-4 s-1 and is diffusion-controlled dislocation climb at = 10-3 s-1. Microstructural observations also confirm that GBS is the operating deformation mechanism at 900 C and = 3 10-4 s-1.

Superplastic-like forming of non-superplastic AA5083 combined with mechanical pre-forming

Abstract: Superplastic forming has been considered as an attractive process in the automotive and aerospace industries. However, the disadvantages of slow forming rate, high-temperature requirement, poor thickness distribution, and expensive base material have hindered its widespread use for high production volume. In this paper, the non-superplastic grade of 5083 aluminum alloy (AA5083) sheets with thickness of 3 mm was employed in a superplastic-like forming process, which is a combination of drawing (mechanical pre-forming) and superplastic forming (blow forming). Experimental trials were conducted to verify the possibility of improving the forming rate and lowering the process temperature. The blank was firstly pre-formed during the mechanical pre-forming phase. As a result, some part of material along the flange area was introduced inside the deformation cavity in advance of the blow forming phase. Secondly, argon gas was applied on the sheet, which would be deformed to come into contact with the inner die surface at the end of pressure cycle. It took only 8 min for the blow forming phase, and the process achieved an almost fully formed part at 400°C. The minimum thickness occurred at the inward corners, and the maximum thinning of the formed part was 54%. Grain growth and cavitation were found from the microstructure observations.

Effect of microalloying (Ca, Sr, and Ce) on elevated temperature tensile behavior of AZ31 magnesium sheet alloy

Abstract: The effect of microalloying with calcium, strontium, and cerium on the microstructure and the elevated temperature deformation behavior of magnesium sheet alloy AZ31 was investigated. Base composition and microalloyed AZ31 materials were cast and rolled into wrought sheet by an identical thermo-mechanical process. A series of hot tensile tests (temperatures of 300 °C, 400 °C, and 450 °C; constant true strain rates of 0.1 s−1, 0.01 s−1, 0.001 s−1, and 0.0003 s−1) were performed to characterize the deformation behavior of the sheet alloys. Interrupted tensile tests were used to study microstructural evolution with strain. A well-dispersed and thermally stable second phase produced by microalloying refines, stabilizes the grain structure, and significantly enhances hot formability of AZ31 sheet. The enhancement is most pronounced under deformation conditions of 450 °C and; 0.0003 s−1 strain rate, with tensile elongation increasing from 347% for the base alloy, to 406% with Ca only, 437% with Ca and Ce, and 552% with Ca, Sr and Ce for microalloyed AZ31 alloys. The second phase particles resist grain coarsening, promote grain boundary sliding, retard strain localization or necking, and postpone cavitation to higher strain levels to achieve this improvement in formability.

Thermal Shock Response of Fine and Ultra Fine Grained Tungsten Based Materials

Abstract: In this work, the focus is on the thermal shock analysis of fine- and ultra-fine-grained tungsten-based materials doped with 0.5–1.1 wt% TiC that showed in previous studies improved ductility at low temperatures and also performed well when exposed to neutrons and ions (H/He). Herein, the resistance of the material to crack formation is evaluated by applying edge-localized mode-like loads (n=100) with an energy density of 1 MJ m-2 at various temperatures up to 150 °C by means of an electron beam facility. The results indicate that the cracking threshold is significantly reduced even down to room temperature when the oxygen content is reduced and the combination of grain size, TiC particle size and distribution of TiC-particles to almost each grain boundary reaches its optimum. This is achieved by a post-manufacturing treatment of the material at 1650 °C using the material's superplasticity caused by grain boundary sliding at this temperature, which changes the material's microstructure from ultra-fine grains surrounded by weak grain boundaries to fine grains with significantly strengthened grain boundaries.

Microstructure and mechanical properties of ZA62 Mg alloy by equal-channel angular pressing

Abstract: The Mg–6Zn–2Al alloy was processed by ECAP and microstructure and mechanical properties of the alloy before and after ECAP were studied. The results revealed that the microstructure of the ZA62 alloy was successfully refined after two-step ECAP (2 passes at 473 K and 2–8 passes at 423 K). The course bulk interphase of Mg51Zn20 was crushed into fine particles and mixed with fine matrix grains forming “stripes” in the microstructure after the second step of ECAP extrusion. A bimodal microstructure of small grains of the matrix with size of ∼0.5 μm in the stripes and large grains of the matrix with size of ∼2 μm out of stripes was observed in the microstructure of samples after 4–8 passes of ECAP extrusion at the second step. The mechanical properties of the alloy studied were significantly improved after ECAP and the highest yield strength and elongation at room temperature were obtained at the samples after 4 and 8 ECAP passes at the second step, respectively. Tensile tests carried out at temperature of 473 K to 573 K and strain rate of 1 × 10−3 s−1 to 3 × 10−2 s−1 revealed that the alloy after 8 ECAP passes at the second step showed superplasticity and the highest elongation and strain rate sensitivity (m-value) reached 520% and 0.45, respectively.

Effect of eutectic particles on the grain size control and the superplasticity of aluminium alloys

Abstract: Aluminium alloys containing eutectic particles of the Al–Ni, Al–Mg–Si, Al–Ni–Ce and Al–Cu–Ce systems are investigated. The particles which control grain growth and stimulate grain nucleation are studied. The Zener–Smith law about dependence between grain size and particle parameters is confirmed and experimental coefficients are found. Experimental coefficients of the Zener–Smith equation obtained in this study depend on the particle size and differ from theoretical coefficients proposed by Zener and Smith. Some alloys with grain size about 3 μm demonstrate very good superplasticity indicators, namely: the strain rate sensitivity index m = 0.5–0.6 and the elongation over 400% at constant strain rate 5 × 10 −3 s −1 .