Free Deformation Zone Research Articles

Rolling characteristics of multi-filamentary Bi-2223/AgAu tapes and roller diameter′s effect on transport properties

37-filamentary Bi-2223/ AgAu tapes were fabricated by powder in tube technique. The round wire (φ1.51 mm) were rolled to 0.30 mm tapes by 150 mm, 250 mm and 300 mm roller through flat rolling, respectively. A fundamental understanding of filaments deformation and roll diameter′s effect on critical current properties were systematically investigated. By analyzing the stress distribution on cross section during rolling, it can be understood that the deformation of the filaments at different positions during the rolling of multi-filamentary Bi-2223/AgAu tape is inhomogeneous. According to the deformation extent of filaments, the cross section of the tape can be divided into three areas, namely easy deformation zone, difficult deformation zone and free deformation zone. The average filament width in the free deformation zone is only 65.1 % of the filament width in the easy deformation zone. It can be noticed that the Jc values increase monotonously with increasing roller diameter. Due to more sufficiently deformed filament and flat interfaces, Jc reached the maximum value of 15.7 kA/cm2 on the 300 mm roller sample.

Short-Term Oxidation Behavior, Microstructure Evolution and Compression Behavior of Nickel-Based Superalloy GH4037 in Solid and Semi-Solid States

Semi-solid processing combines the advantages of traditional forging and casting methods, so it has received much attention recently. However, the research on semi-solid behaviors of Nickel-based superalloys has been rarely reported. In order to investigate the behaviors of Nickel-based superalloy at solid and semi-solid states, oxidation experiments, isothermal treatment experiments and deformation experiments of GH4037 alloy were studied. Short-term oxidation experiments of GH4037 alloy were carried out at a solid temperature (1200 °C) and a semi-solid temperature (1360 °C). The results indicated that the oxides formed at 1200 °C were mainly composed of TiO2, Cr2O3 and a small amount of spinels NiCr2O4, while the oxides formed at 1360 °C consisted of the spinels of NiCr2O4, NiWO4 and NiMoO4 besides TiO2 and Cr2O3. Microstructure evolution of GH4037 alloy after semi-solid isothermal treatment at 1370 °C and 1380 °C was studied. The results indicated that semi-solid microstructures consisted of equiaxed solid grains and liquid phases. The average grains size and shape factor of solid grains were affected by melting mechanism and grain growth mechanism. Compression behaviors of GH4037 alloy after compressed at 1200 °C and 1360 °C were investigated. The results indicated that the flow stress of 1360 °C decreased significantly compared to that of 1200 °C. The deformation zones in the specimens were divided into three parts: the difficult deformation zone, the large deformation zone, and the free deformation zone. At 1200 °C, the deformation mechanism was plastic deformation mechanism. At 1360 °C, sliding between solid particles (SS), liquid flow (LF), flow of liquid incorporating solid particles (FLS), plastic deformation of solid particles (PDS) coexisted in the compression specimen.

Electron Backscatter Diffraction Investigation of Heat Deformation Behavior of 2205 Duplex Stainless Steel

Herein, the thermal compression of 2205 duplex stainless steel is simulated using a thermal simulation testing machine at 850–1100 °/0.01 s−1 and 850–1100 °/10 s−1, and the large deformation zone (LDZ) and free deformation zone (FDZ) of the structure are characterized by electron backscatter diffraction (EBSD). The study results show that the stress–strain curve with a strain rate of 10 s−1 hardens continuously. In addition, ferrite undergoes deformation mostly when the strain is less than 0.33, and strain hardening occurs in austenite after the strain reaches 0.33. As a result, the curve ascends and steepens, and secondary hardening occurs. Continuous dynamic recrystallization (CDRX) is distinctly observed in original ferrite grains, whereas the austenite grains are recrystallized discontinuously due to the bulging high‐angle grain boundaries (HAGBs). Meanwhile, the recrystallization fraction in the large deformation region of both ferrite and austenite is significantly higher than that in the free deformation zone. The orientation distribution function (ODF) diagram analysis reveals that ferrite is mainly composed of the rotation cube {001}<111> texture, and austenite mainly consists of the rolled α‐fiber texture, including brass {011}<211>, Gauss {011}<100>, and {011}<111>.

Dynamic recrystallization kinetics and microstructure evolution of an AZ91D magnesium alloy during hot compression

The flow behavior of as-cast AZ91D magnesium alloy was evaluated by isothermal compression tests within the temperatures of 220 °C, 260 °C, 300 °C, 340 °C, and 380 °C, and the strain rates of 0.001, 0.01, 0.1, 1 and 10s−1. Based on the stress-strain curve and hyperbolic sine function, the thermal activation energy and the strain rate sensitivity of the material were determined to be 142.2726 kJ·mol−1 and 0.142, respectively. The S type evolution of the dynamic recrystallization with the increasing strain that dynamic recrystallization (DRX) model obtained from stress and strain data. There was a good consistency between the proposed DRX kinetics model and microstructure observation results. Combining isothermal compression specimens with finite element and scanning electron microscopy (SEM) analysis indicated that the sample can be divided into rarely recrystallized region, partially recrystallized region and completely recrystallized region, which falls within the dense deformation zone, free deformation zone and severe deformation zone, respectively. The different forms of the β-Mg17Al12 phase induced by compression tests were confirmed by SEM. Nucleation mechanisms of the DRX were discussed with reference to the transmission electron microscope (TEM) analysis results.

Deformation behaviour and microstructures of semi-solid A356.2 alloy prepared by radial forging process during high solid fraction compression

Radial forging was introduced to the strain-induced step in the strain-induced melt activation process to prepare high-quality semi-solid A356.2 billet for the high solid fraction compression. Then, the deformation behaviour and microstructures at different compression velocities, temperatures and deformation zones were investigated. The results showed that radial forging can induce enough strain at 60% reduction of area to prepare ideal semi-solid microstructure. The microstructure had no obvious improvement at 75% reduction of area because the distortion energy may be saturated at 60%. During compression tests, the flow stress was sensitive to compression velocity ( Vc) but was insensitive to holding temperature ( Th), and it obeyed the power law [Formula: see text]. The average strain rate sensitivity was 0.2757, and the average apparent activation energy was 254.5 kJ/mol. The compression sample can be divided into hard deformation zone, transition deformation zone, severe deformation zone and free deformation zone. Different zones had different predominant deformation mechanisms which not only affected the morphology of the grains but also codetermined the flow stress. With increasing Vc and Th, the average particle size was increased from hard deformation zone, reached the maximum at severe deformation zone and then decreased at free deformation zone, while the opposite was the case for shape factor. At each deformation zone, the average particle size was increased while the shape factor was decreased with the increasing Vc because higher Vc caused more grains to merge into larger and more irregular grains, while the opposite was the case for the increasing Th because higher Th generated more liquid which helped to isolate the contacted particles and improve their spheroidization degree.

Compression deformation behavior of semisolid Al2O3np reinforced 7075 aluminum matrix composites with high solid fraction

Abstract

FEM Analysis and Experimental Verification of the Integral Forging Process for AP1000 Primary Coolant Pipe

AP1000 primary coolant pipes must be manufactured by integral forging technology according to the designer—Westinghouse Electric Co. The characteristics of these large, special-shaped pipes create nonuniform temperatures, effective stress, and effective strain during shaping of the pipes. This paper presents a three-dimensional finite element simulation (3D FEM) of the integral forging process, and qualitatively evaluates the likelihood of forging defects. By analyzing the evolution histories of the three field variables, we concluded that the initial forging temperature should be strictly controlled within the interval 1123 K to 1423 K (850 °C to 1150 °C) to avoid second-phase precipitation. In the hard deformation zones, small strains do not contribute to recrystallization resulting in coarse grains. Conversely, in the free deformation zone, the large strains can contribute to the dynamic recrystallization, favoring grain refinement and closure of voids. Cracks are likely to appear, however, on the workpiece surface when forging leads to large deformations. Based on the simulation results, an eligible workpiece with good mechanical properties, few macroscopic defects, and favorable grain size has been successfully forged by experiments at an industrial scale, which validates the FEM simulation.

Instability analysis of free deformation zone of cylindrical parts based on hot-granule medium-pressure forming technology

The cylindrical part of sheet metal based on hot-granule medium-pressure forming (HGMF) technology was investigated. The stress functions of the free deformation zone and the fracture instability theory were combined to establish the analytical expression of the critical pressure of punch. The results show that the active friction between the granule medium and the sheet metal, as well as the non-uniform internal pressure presented by the solid granule medium, can obviously improve the forming performance of the sheet metal. The critical pressure of punch increases with the increment of the friction coefficient between the granule medium and sheet metal, as well as the plastic strain ratio, whereas it decreases with the increase of the material-hardening exponent. Furthermore, the impact on the critical pressure from high to low order is the plastic strain ratio, the friction coefficient, and material-hardening exponent. The deep-drawing experiment with HGMF technology on AZ31B magnesium alloy sheet verified the instability theory.

High-temperature deformation resistance and forming behavior of two-step SIMA-processed 6066 alloy

The aims of this study were to investigate the effects of a modified two-step strain-induced melt activation (SIMA) process on the high temperature formability of 6066 Al alloy, and to understand the compressive and tensile properties of the alloy such processed. For these purposes, the forming test which compressed a cylindrical rod into a screw nut was conducted at 550°C, while the compressive and tensile tests were conducted at 550°C and the vicinity. The high-temperature tensile data show that phases on globule boundaries can cause the SIMA-processed alloy to break by integranular fracture, and thus the tensile ductility cannot compete with the alloy in hot-extruded condition to have dynamic recrystallization during tensile deformation. The high-temperature compression test shows that the flow resistance can be decreased by the SIMA process to the level lower than that of the fully annealed alloy. In terms of compressive microstructure, the SIMA-processed alloy is composed of three zones: (1) large deformation zone with flattened structure in specimen center, (2) free deformation zone with globular grain structure near the top and bottom edges, and (3) a transition zone between the above two zones. Finally, the forming test shows that SIMA process can decrease flow resistance by about 25–30%. When a SIMA-processed alloy has sufficient liquid fraction and appropriate globule size, its ability of metal flowing can be significantly increased to have superior high-temperature formability.

5083铝合金热压缩过程的有限元模拟研究

采用Gleeble-3800热模拟试验机对5083铝合金进行热压缩实验，并利用有限元分析软件DEFOM-3D对5083铝合金在变形温度为400℃应变速率为1 s−1，变形温度为400℃应变速率为10 s−1，变形温度为500℃应变速率为1 s−1条件下热压缩过程进行数值模拟，利用后处理程序，分析了合金内部的应变场、应变速率场、应力场和温度场变化。研究表明：5083铝合金热压缩过程具有明显的变形不均匀性，试样分为易变形区、难变形区和自由变形区；为了合理预测再结晶晶粒尺寸，需对实验数据进行修正。 The hot compression of 5083 aluminum alloy was carried out on Gleeble-3800 thermal simulator. The hot compression process at a strain rate of 1 s−1 and temperature 400˚C, strain rate of 10 s−1 and temperature 400˚C, strain rate of 1 s−1 and temperature 500˚C of 5083 aluminum alloy was simulated in the finite element analysis software DEFOM-3D. The variation and distribution of strain, strain rate, stress and temperature in the compressed work piece were analyzed by the post-processing procedures. The results show that the hot compression of 5083 aluminum alloy exhibits a nonuniform characteristic and the specimen is divided into easy deformation zone, hard deformation zone and the free deformation zone. The temperature has gone up during the hot de-formation process, and the experimental data need to be modified in order to reasonably predict recrystallization grain size.

Deformation characteristic of semi-solid ZCuSn10 copper alloy during isothermal compression

The compression tests were carried out by Gleeble-1500 thermo-mechanical simulator with samples of semi-solid ZCuSn10 alloy prepared by strain-induced melt activation (SIMA) process. The original microstructure and the deformation temperature of semi-solid ZCuSn10 alloy are different. The strain is 0.2, and the strain rate is 1 s−1 for the compression test. The results show that when the semi-solid ZCuSn10 alloy was prepared by SIMA process, the liquid fraction of semi-solid microstructure increases, and the solid grain is smaller, more uniform and more inclined to be round as the rolling pre-deformation increasing. The results also indicate that the deformation resistance of ZCuSn10 alloy in semi-solid state decreases with the deformation temperature increasing or the solid fraction of original microstructure decreasing. The stress–strain curves of the isothermal compression can be divided into quasi-elastic deformation stage and plastic deformation stage, and there are three deformation zones in the samples after isothermal compression, namely the difficult deformation zone, the large deformation zone and the free deformation zone. In the three deformation zones, the main deformation mechanism is flow of liquid incorporating solid particles (FLS) mechanism, plastic deformation of solid particles (PDS) mechanism and liquid flow (LF) combining with FLS mechanism, respectively.

Process of back pressure deep drawing with solid granule medium on sheet metal

The experimental die apparatus of the solid granules medium forming on sheet metal was designed and manufactured. Typical parts, such as conical, parabolic, cylindrical and square-box-shaped components, were successfully trial-produced as well. According to the analysis of the changing trends of the cross-section shape and the wall thickness during the process, it can be found that the shape of the free deformation zone of the sheet metal, which is the most critical thinning area, can be described as an approximately spherical cap. According to this forming feature, back pressure deep drawing technology with solid granules medium on sheet metal was proposed to restrain drastic thinning at the bottom of the part through the joint friction effect of solid granules medium, the back pressure tringle and the sheet metal. Therefore, the deep drawing limit of the sheet metal is significantly improved. In order to fabricate thin-walled rotary parts with great drawing ratio and complex cross-sections, a finite element model based on the material property test of the solid granules medium was established to optimize the scheme of the back pressure deep drawing. The effects on the forming performance of sheet metal from back pressure load and the approach of blank holding control were analyzed through this model.

INFLUENCE OF DEFORMATION TEMPERATURE ON HOT DEFORMATION BEHAVIOR OF COLD SPRAYED 304 STAINLESS STEEL COATING MATERIAL

The dense 304 stainless steel coating material was fabricated by cold spraying tech- nology. The influence of deformation temperature on hot deformation behavior of cold sprayed 304 stainless steel coating material was investigated by thermo-mechanical simulator. The re- sults showed that deformation resistance of cold sprayed 304 stainless steel coating material re- duced with the increment of deformation temperature. The steady-state deformation resistance reduced from 315.4 MPa to 187.9 MPa when deformation temperature increased from 1000 to 1150 with deformation rate 20 s 1 and deformation reduction 17.5%. The microsturcture of de- formation sample might be divided into easy, difficult and free deformation zones. The area of easy deformation zone increased and area of difficult deformation zone decreased when deformation temper- ature increased from 1000 to 1150 . Recrystallization occurred at free deformation zone without cracking at 1150 . DSC curve showed that phase transition of cold sprayed 304 stainless steel coating material occurred at 1237—1265 . The microhardness of cold sprayed 304 stainless steel coating ma- terial was 313.3 HV0.2, which was relatively high. The microhardness of deformation samples reduced from 332.8 HV0.2 to 244.8 HV0.2 as the deformation temperature increased from 1000 to 1150 with deformation rate 20 s 1 and deformation reduction 50%. The hot temperature deformation

Experimental study of the tube axial compression forming process with free dieless deformation

The tube axial compression forming process with a fillet die can be developed into an advanced precision forming process with high quality, high efficiency, low consumption and good flexibility for size changing. With the help of this process, a tubular blank can be formed into a complicated part that is difficult to be manufactured by any other technique. In this process, there is a free deformation zone under dieless control, and the precision of the part made by this process depends fundamentally on the shape of the free deformation zone. Therefore it is necessary to understand the mechanism of the free deformation. However, up to now, it appears that there have not been any studies reported in the literature on the mechanism of the free deformation. In this paper, based on the method of orthogonal design, experimental research on the process is reported for tubular blanks of such parameters as LF2M Ø30×1, Ø32×1, Ø42×1, LF21M Ø42×1, with die fillet radii of 2.75, 3.0, 3.5 and 4.5, using graphite lubricant. The results of the research will offer guidance in the practical application of the tube axial compression forming process.

Measurement of contact pressures in tube rolling

An attempt is made to explain some of the phenomena occurring in the longitudinal rolling of tube through two grooved rolls by the use of specially developed pin load-cells, which measured the pressure distribution on one roll surface. Observations were made also of the shape of the free and contact zones enabling the length of the arc of contact to be measured. These are compared with values calculated for a variety of rolling parameters. Solutions to some problems associated with pin load-cells are given. The principal conclusions are that (1) a free deformation zone occurs which results in a reduction in the length of the arc of contact by about 30%, (2) there are regions in contact with the roll surface where the neutral point lies outside the deformation zone. The industrial significance of these results is that uncontrolled deformation is now known to exist upstream of a stand. Also, the control of the shape of the tube is less than would be imagined from a geometrial reconstruction of the press. Consequently mill designers cannot estimate the performance of the pass soley from the geometrical deformation zone. To assist them it is shown that the actual arc of contact is about 1/√2 time the value expected from the geometry of the pass. It was found also that (3) the most reliable results are obtained when the pins are arranged to protrude above the surface of the roll by a small specified distance, and (4) the performance of the pin load-cells, of the design which was finally adopted, was not affected significantly by the presence of small amounts of extruded metal in the annular clearance between the roll and the pin. Thus, the findings of this investigation provide a contribution to the understanding of the mechanics of longitudinal tube-rolling for both industrial and research engineers.