Hot Deformation Temperature Research Articles

Processing map and hot deformation mechanism of novel nickel-free white copper alloy

Hot compression test of a novel nickel-free white alloy Cu–12Mn–15Zn–1.5Al–0.3Ti–0.14B–0.1Ce (mass fraction, %) was conducted on a Gleeble–1500 machine in the temperature range of 600–800 °C and the strain rate range of 0.01–10 s–1. The constitutive equation and hot processing map of the alloy were built up according to its hot deformation behavior and hot working characteristics. The deformation activation energy of the alloy is 203.005 kJ/mol. An instability region appears in the hot deformation temperature of 600–700 °C and the strain rate range of 0.32–10 s–1 when the true strain of the alloy is up to 0.7. Under the optimal hot deformation condition of 800 °C and 10 s–1 the prepared specimen has good surface quality and interior structure. The designed nickel-free alloy has very similar white chromaticity with the traditional white copper alloy (Cu–15Ni–24Zn–1.5Pb), and the color difference between them is less than 1.5, which can hardly be distinguished by human eyes.

Cementite Precipitation of a H21 Tool Steel after Hot Compression and Double Temper

The cementite precipitation behavior in the martensite and banite of the H21 tool steel under high temperature axisymmetric compression test and double temper was investigated. The main purpose on this work is to develop a better understanding regarding the transformation mechanism of bainite and martensite in a H21 tool steel. The selected deformation temperatures were 1100 oC and 1000 oC and the double temper process was carried out at 650 oC for 1 hour respectively. The results showed that the cementite was sensitive to the stress. The applied stress has affected the Fe3C precipitation behaviour by decreasing the number of variants carbides in tempered martensite and decreasing the number of a single variant carbides in tempered lower bainite. The results were in agreement with a displacive mechanism of martensite and bainite transformation. It was also found that hot deformation temperatures selected in this work have the same contribution in decreasing number of variant carbides in tempered martensite and decreasing number of single variant carbides occurred in tempered lower bainite.

Effect of Hot Deformation Parameters on Austenitic Ni – Co – Cr – Mo-Alloy Microstructure Evolution

Physical modeling is provided for hot deformation by torsion of austenitic steel of the system Ni – Co – Cr – Mo using a torsion plastometer. The effect of hot deformation temperature, deformation, and time parameters on microstructure evolution is studied by light microscopy and electron back-scattered diffraction. Results may be used for developing hot plastic deformation regimes for similar alloys.

Microstructure evolution during hot deformation of as cast ESR-CDSed superalloy Rene88DT

The microstructure evolution during hot deformation of directionally solidified disc alloy Rene88DT produced by electroslag remelting continuous directionally solidification (ESR-CDS) was investigated by using optical microscope and electron backscatter diffraction technique. Hot compression tests were conducted at different strains at temperatures ranging from 1060 to 1140°C for strain rates between 0·001 and 1 s−1. Experimental results revealed that the process of dynamic recrystallisation (DRX) in as cast ESR-CDSed Rene88DT alloy can be classified into three periods, namely, incubation, nucleation and growth. Deformation temperature plays a significant role in recrystallisation grain nucleation and migration, which reveals that the size and fraction of DRX grain increases with the increasing temperature. Dynamic softening mechanisms vary depending on the hot deformation temperature. The microstructure evolutions during DRX are characterised in view of subgrain coarsening and strain induced grain boundary migration near the original columnar grain boundary.

Effect of Precipitation on Texture Evolution during Dynamic Recrystallization in Mg-Al-Sn Alloys

In common magnesium alloys, recrystallization is usually not accompanied with a noticeable change of deformation texture resulting in, strong mechanical anisotropy. The aim of this work is to investigate the effect of dynamic or strain induced precipitates on texture evolution during hot deformation of Mg-Al-Sn alloys. Mg-Al-Sn alloys have been designed using thermodynamic modeling software, FactSage, based on forming precipitates at hot deformation temperatures. Two alloys have been chosen in a way that one forms precipitates during the hot deformation process, another does not at a certain temperature. Uniaxial compression has been introduced at different strain rates at this elevated temperature to simulate the hot deformation behaviour. Two alloys have been compared in terms of the intensity of basal texture. It was found that the formation of dynamic precipitates during deformation weakens the texture compared to the case where no precipitates were formed.

Thermodynamic Modeling and Experimental Measurement of Precipitation Formation during Dynamic Recrystallization for Magnesium Alloys

Magnesium alloys have low formability at room temperature associated with its hexagonal closed pack structure. Formation of precipitates during deformation may pin the grain boundary and reduce the final grain size, which literally means the improvement of formability. The aim of this study is to design magnesium alloys that are capable of forming precipitate during hot deformation. Thermodynamic modeling software, FactSage, has been used to design Mg-Al-Sn alloys based on forming target Mg2Sn precipitate at hot deformation temperatures between 250 and 350oC. Uniaxial compression at elevated temperatures has been performed to simulate the hot deformation behaviour as well as to enhance the formation of precipitates. Strain rates used in this study were in the range of 1.0 to 0.001s-1 for a constant deformation degree of 90%. It was found that the formation of precipitate depends on deformation temperature and strain rate. Measured amounts of precipitate were compared with the calculated equilibrium results from FactSage.

Hot Deformation Behavior of Cu-Ag Alloy for Cu Cladding Al Contact Wire

Cu-Ag alloy is using for Cu Cladding Al Contact Wire, it was formed by continuous extrusion. The flow stress behavior of Cu-Ag alloy for Cu cladding Al contact wire was studied by hot compression experiments using Gleeble-1500 hot simulation machine. The flow stress mathematical models of the Arrhenius relationship of the hyperbolic sine function are established including hot deformation activation energy, deformation temperature and strain rate. The results may be using in numerical simulation for forming.

Study of Dynamic Precipitation during Hot Deformation of Mg-Al-Sn Alloys

The objective of this work is to investigate the effect of dynamic precipitation on the hot deformation behaviour of magnesium. Mg-Al-Sn alloys have been designed using thermodynamic modeling software, FactSage, based on precipitation of Mg2Sn at hot deformation temperatures. Uniaxial compression has been introduced at the temperature range of 250-350 °C to enhance the formation of precipitates. The flow behaviour and microstructural evolvement were studied for a strain rate of 0.01 /sand deformation degree of 90 %. Dynamic recrystallization (DRX) occurs in this study and it is found that the volume percent of dynamic recrystallization and dynamically recrystallized grain size are related to the amount of precipitation formed during deformation. The formation of Mg2Sn precipitates during the dynamic recrystallization process may retard the dynamic recrystallization and slow down the grain growth by precipitation pinning effect at the DRX grain boundaries, resulting in a finer grain size.

Effect of Hot Deformation Temperature on the Restoration Mechanisms and Texture in a High-Cr Ferritic Stainless Steel

The effect of hot deformation temperature on the deformed microstructures and evolution of microstructure and texture of a 21Cr Ti-Nb dual-stabilized ferritic stainless steel was studied using plane strain hot compression tests on a Gleeble 1500 thermomechanical simulator. The deformation was carried out at 550 - 950 °C with a strain of 0.5 at 1 s-1. The compression was followed by fast cooling to room temperature in order to study the deformed microstructures. Some specimens were heated from the deformation stage to either 750 or 950 °C and held for 0 or 30 s in order to study the nucleation process of recrystallization. The electron backscatter diffraction technique was used to analyze the resultant microstructures and textures. Lowering of the deformation temperature increased the rate of static recrystallization (SRX) and decreased the recrystallized grain size. After deformation at 550 and 600 °C and complete SRX, beneficial γ-fibre texture formed presumably as a result of nucleation at in-grain shear bands. SRX after deformation at 750 °C or above led to the formation of harmful α-fibre textures with weak γ-fibre.

Simulation of Dynamic Recrystallization for Ti-6.5Al-3.5Mo-1.5Zr-0.3Si Alloy in β Processed Using Cellular Automaton

The cellular automaton (CA) method coupling fundamental metallurgical principles was used to simulate the dynamic recrystallization (DRX) behavior of Ti-6.5Al-3.5Mo-1.5Zr-0.3Si alloy in β processed. Using physically based rules for the simulation of nucleation and growth phenomena of dynamically recrystallized grains. The effects of hot deformation temperature and true strain on the DRX characteristic of the alloy during β processed was studied, and the results compared with experiments. The predictions show very good agreement with the experimental results for the alloy.

Study on Dynamic Recrystallization Behavior in Deformed Austenite of 52100 Steel by Using JMAK-Model

A Johnson-Mehl-Avrami-Kolmogorov (JMAK)-model was established for dynamic recrystallization in hot deformation process of 52100 steel. The effects of hot deformation temperature, true strain and strain rate on the microstructural evolution of the steel were physically studied by using Gleeble-1500 thermo-mechanical simulator and the experimental results were used for validation of the JMAK-model. Through simulation and experiment, it is found that the predicted results of DRX volume fraction, DRX grain size and average grain size are in good agreement with the experimental ones.

High temperature deformation behavior of Ti–46Al–2Cr–4Nb–0.2Y alloy

Abstract The hot deformation characteristics of cast and hot isostatically pressed Ti–46Al–2Cr–4Nb–0.2Y (at%) alloy in the temperature range of 1100–1250 °C and strain rate range of 0.01–1.0 s−1 using hot compression tests were studied. The processing map of the alloy at true strain of 0.5 was also developed on the basis of the dynamic materials model (DMM). The experimental results show that the flow stress decreases significantly with increasing deformation temperature and decreasing strain rate. Using the kinetic rate equation the stress exponent n and the apparent activation energy of deformation Q were determined as 4.47 and 400.4 kJ mol−1, respectively. The efficiency values of power dissipation of the domain at strain rate below 0.4 s−1 show that the dynamic recrystallization occurring of γ phase in the alloy is easier in the wide deformation temperature range (1100–1250 °C) due to low stacking fault energy. The fraction of new recrystallized grains increased with increasing the hot deformation temperature at a given strain rate. With the increasing of strain rate, the uniformity of microstructure was decreased. The domain defined by the temperature range of 1200–1230 °C and the strain rate range of 0.01–0.05 s−1 which corresponds to a peak efficiency of about 60% is the optimal deformation condition of the alloy. Based on the optimal deformation conditions, a cylindrical sample was near isothermally forged. The microstructure and shape of pancake by forging was in good agreement with the prediction of processing map.

Enhancement in thermoelectric performance of bismuth telluride based alloys by multi-scale microstructural effects

Decoupling of interdependent thermoelectric parameters was considered as a crucial strategy to enhance the thermoelectric performance of bulk materials. Here multi-scale microstructural effects have been introduced by a simple hot deformation process to obtain high-performance n-type bismuth telluride based alloys. Highly preferred orientation enables a significant improvement in in-plane electrical conductivity. The donor-like effect (an interaction of antisite defects and vacancies), which can be adjusted by varying hot deformation temperature, was also considered responsible for the remarkable enhancement in power factor. Besides, the in-plane lattice thermal conductivity was greatly reduced by in situ nanostructures and high-density lattice defects generated during the hot deformation process. The present study experimentally demonstrates a successful combination of microscale texture enhancement, atomic scale lattice defects and donor-like effect and recrystallization induced nanostructures as a new approach to improve thermoelectric properties. These effects led to a maximum ZT of 0.95 for the Bi2Te2Se1 sample hot deformed at 823 K, about 80% improvement over that without hot deformation.

Study on Hot Deformation Behavior and Processing Maps of Cu-0.35Cr-0.15Zr Alloy

The hot deformation behavior of Cu-0.35Cr-0.15Zr (wt.%) alloy was investigated by hot compression tests using a Gleeble-1500D thermal simulator system. The tests were performed under the conditions of 700°С- 820°С temperature and 0.01-10s-1strain rate. The results show that the flow behavior of the studied alloy could be described by the hyperbolic sine constitutive equation, and an active energy of 597.53 kJ/mol was calculated. The processing maps were obtained and analyzed according to the dynamic materials model. The optimum processing parameters of hot deformation of this alloy in the range of this experiment can be attained by the maps. The hot deformation temperature was 800-820°C and the strain rate was 0.01-0.1s-1.The instability zones of flow behavior can also be recognized by the maps.

Microstructure and Properties of T2 Copper Tube Produced by Severe Hot Rolling

In this study, the microstructure evolution as well as mechanical properties of T2 copper tube during severe hot rolling has been investigated. Owing to the severe hot rolling deformation and high rolling temperature, the microstructure of T2 copper tube evolved from initial cast structure into relatively homogenous and equiaxed grains during the process, which was testified through the results of optical microscope observation. Besides, the microhardness measurements were taken, from which the results gained were in correspondence to the microstructure transformation.

Effect of hot deformation temperature on the magnetic and mechanical properties of Nd–Fe–B magnets prepared by spark plasma sintering

The magnetic and mechanical properties of Nd–Fe–B magnets at different hot deformation temperatures have been investigated. The results showed that the optimum magnetic and mechanical properties and the highest crystallographic alignment of Nd–Fe–B magnets were obtained at 700 °C, and the possible reasons were analyzed. The microstructures show that abnormal grain growth is not observed at 650 °C; there exist many small spherical grains, and these small grains do not align during die upsetting. The average size of the grains and the volume fraction of coarse grains increase with increase in deformation temperature. The coarse grains do not align during die upsetting, and the non-alignment regions enlarge with increase in deformation temperature.

Influence of hydrogen content on hot deformation behavior and microstructural evolution of Ti600 alloy

Abstract Isothermal hot compression tests of a Ti600 alloy after hydrogenation were carried out over the temperature range of 760 to 880 °C and strain rate range of 0.01 to 10 s−1. The influence of hydrogen content was studied on the flow stress and activation energy of deformation. The microstructural changes were examined by transmission electron microscopy (TEM). The results show that the addition of 0.3% hydrogen in Ti600 alloy can decrease the hot deformation temperature by 80 °C and increase the deformation strain rate by two orders of magnitude. Both the flow stress and activation energy of deformation of Ti600 alloy decrease gradually with increasing hydrogen content in the hydrogen range of 0 to 0.3%. TEM observation suggests that dynamic recrystallization (DRX) is promoted after hydrogenation. Hydrides δ (fcc structure) exist in the specimens with 0.3% and 0.5% hydrogen, and the hydrides tend to be broken up and twisted with increasing hydrogen content after deformation. The mechanism of hydrogen reduced flow stress of Ti600 alloy has been discussed in detail.

Structure and properties of aluminum alloy 1421 after equal-channel angular pressing and isothermal rolling

Sheets from the aluminum alloy 1421 with an ultrafine-grained (UFG) structure and a weak crystallographic texture were prepared by the method of equal-channel angular pressing (ECAP) through a die with channels of a rectangular cross section and by subsequent isothermal rolling. Both operations were carried out at a temperature of 325°C. It is shown that severe plastic deformation (SPD) leads to the formation of a completely recrystallized uniform microstructure with an average grain size of 1.6 µm in the alloy. At room temperature the alloy 1421 demonstrates high static strength (σu = 545 MPa, σ0.2 = 370 MPa) in the absence of a significant anisotropy. At temperatures of hot deformation, the alloy showed ultrahigh elongations under superplasticity (SP) conditions. At a temperature of 450°C and initial deformation rate of 1.4 × 10−2 s−1 the maximum elongation at fracture was ∼2700%. At static annealing at a temperature of SP deformation, the UFG structure formed in the process of SPD remains stable. The SP deformation is accompanied by an insignificant grain growth and pore formation.

Optimization of mechanical properties of a micro alloyed steel

In this work, the effect of hot deformation temperature on microstructure and mechanical properties of micro alloyed steel was studied. The results indicated that by decreasing the deformation temperature final microstructure is refined and the volume fraction of grain boundary ferrite is increased and some pearlite is produced. Therefore both the yield strength and ultimate tensile strength is increased, while the toughness is preserved in comparison to a ferritic–pearlitic microstructure. Also a model was developed to relate the deformation condition to the volume fraction of acicular ferrite at mixed microstructure.

Viscoplastic model for the strain resistance of 08Kh18N10T steel at a hot-deformation temperature

The viscoplastic model of the strain resistance of a metal developed earlier is shown to be applied to austenitic corrosion-resistant 08Kh18N10T steel with the fcc lattice at a hot-deformation temperature of 1150°C. Metallographic examination supports dynamic recrystallization occurring at this deformation temperature.