Influence Of Deformation Temperature Research Articles

Deformation Characteristics and Mechanism of Martensitic Stainless Steel during Thixoforming

Semi-solid billet of 9Cr18 martensitic stainless steel with globular grains was made by a wavelike sloping plate experimental device, and hot compression tests were carried out in the semi-solid state of 9Cr18 semi-solid billet on Gleeble-1500 thermal simulation testing machine at the temperatures of 1250°C ~1300°C and the strain rates of 0.1 s-1~5.0 s-1to investigate the effects of thixoforming parameters on its deformation characteristics and mechanism. According to the true stress-strain curves obtained from the test, the influence of deformation temperature and strain rate on 9Cr18 semi-solid billet deformation resistance was investigated, and the deformation resistance model of specimen with coexistence of solid and liquid phases was established. In this paper, it was found that deformation mechanism changed because of different deformation temperature and strain rate. Dynamic recrystallization occured at 1250°C in different phases separately. So that big fine recrystallized grains were achieved at the soft primary austenite region while small recrystallized grains were achieved at the hard solidified liquid region. The melted metal would be extruded from the centre of the specimen to the free surface completely when the temperature was higher than 1275°C. And then specimen became FGM (functionally graded materials), with phases and properties graded distribution perpendicular to the stress direction. When thixoforming temperature reached 1300 °C, martensitic transformation occurred after rapid cooling. The mathematics models of the relation between stress and temperatures, fraction of solid, deformation rates and deformation degree of 9Cr18 semi-solid billet were regressed and established based on the dates attained from the compression deformation experiments. The R value was 0.991, and the RMSE value was 3.57.

Effect of temperature and strain on the formation of elongated fine grained structure in middle carbon steel during large plastic deformation

The influence of deformation temperature and strain rate on the mechanisms of elongated fine grain (EFG) formation in the medium-carbon steel was studied. Compression tests were carried out at the temperatures in range of 673-973K at three different strain rates: 10−2, 1.3*10−3 and 10−4 s−1. Presence of two temperature intervals with different dominant mechanisms of deformation was identified: low temperature (673-823K) interval and high temperature (873-973K) interval. Microstructure evolution during deformation at strain rate of 1.3*10−3 s−1 and different temperatures was studied. Also was investigated the microstructure and mechanical properties of steel after warm plastic deformation. EFG structure formation in steel by caliber rolling at temperatures 673 and 773K on strain ε ~ 1.1 results in a significant increase of toughness, including at low temperatures, while improving strength.

Influence of deformation temperature on texture evolution in HPT deformed NiAl

NiAl is an intermetallic compound with a brittle-to-ductile transition temperature at about 300°C and ambient pressure. At standard conditions, it is very difficult to deform, but fracture stress and fracture strain are increased under high hydrostatic pressure. On account of this, deformation at low temperatures is only possible at high hydrostatic pressure, as for instance used in high pressure torsion. In order to study the influence of temperature on texture evolution, small discs of polycrystalline NiAl were deformed by high pressure torsion at temperatures ranging from room temperature to 500°C. At room temperature, a typical shear texture of body centred cubic metals is found, while at 500°C a strong oblique cube component dominates. These textures can be well simulated with the viscoplastic self-consistent polycrystal deformation model using the primary and secondary slip systems activated at low and high temperatures. The oblique cube component is a dynamic recrystallization component.

Influence of Deformation Temperature on γ-α Phase Transformation in Nb–Ti Microalloyed Steel during Continuous Cooling

The dynamic continuous-cooling-transformation (CCT) diagrams of Nb–Ti microalloyed steel for four different deformation temperatures of 850, 900, 950 and 975°C were plotted by means of a combined method of dilatometry and metallography. The influence of deformation temperature on continuous cooling transformation behavior and transformation microstructure was elucidated. The reason that the polygonal ferrite transformation field is shifted to the right and moved down as the deformation temperature is increased and the progress of transformation for lowest continuous cooling rate of 0.5°C/s was obviously retarded at the lowest deformation temperature of 850°C was discussed in details based on transformation kinetics and strain-induced precipitation kinetics, respectively. Moreover, the polygonal ferrite grain size for lowest continuous cooling rate of 0.5°C/s can be significantly refined from approx. 15.4 μm to 9.4 μm as the deformation temperature is reduced from 975°C to 850°C. In addition, the empirical equation to calculate γ-α phase transformation start temperature was established, and the calculated Ar3 temperatures are in good agreement with measured ones.

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

APPLICATION OF ARTIFICIAL NEURAL NETWORK FOR PREDICTION OF SUPERPLASTIC BEHAVIOUR IN NiAl ALLOYS

Chemical composition, grain size, and processing conditions such as temperature and strain rate have important influence on superplasticity of NiAl alloys, which would allow the optimization of these parameters in order to achieve the desired combination of properties. In this work, the optimal superplastic deformation conditions of NiAl alloys were studied by using artificial neural networks (ANN). The standard multilayer feedforward networks were trained and tested using comprehensive datasets from previous experimentally works on the as-extruded NiAl, NiAl-25Cr, NiAl-20Fe-Y(Ce), NiAl-30Fe-Y, NiAl-9Mo, NiAl-P alloys. Different effects are modeled, including the influence of the alloying elements on the superplastic, and the influence of deformation temperature, strain rate and grain size on the elongations during the superplastic tensile tests. The artificial neural network models are combined with computer programmers for optimization of the inputs in order to achieve desirable combination of outputs. Good performances of the neural networks are achieved. Results of this research propose a range of strain rate and temperature within which the NiAl alloy possesses superplasticity with larger elongations, although the deformation temperature and strain rate of superplastic alloys alternately influence each other within the range. These models are convenient and powerful tools for practical applications in superplastic prediction in NiAl alloys.

Unique Recovery Behavior in Amorphous Shape‐Memory Polymer Networks

AbstractShape‐memory polymers (SMPs) have emerged as a multi‐functional materials platform and have been proposed for a variety of applications ranging from simple actuators to biomedical devices. The shape‐memory cycle is demonstrated through a three‐step process of programming, storage, and recovery. In this paper, recent findings that associate each step of the shape‐memory cycle to unique recovery behavior are highlighted. The article focuses on the influence of deformation temperature, long‐term storage (physical aging), partially constrained recovery, and mechanically driven recovery with respect to shape‐memory behavior. magnified image

Intelligent method to develop constitutive relationship of Ti–6Al–2Zr–1Mo–1V alloy

The isothermal compression tests were carried out in the Thermecmastor-Z thermo-simulator at temperatures of 800, 850, 900, 950, 1000 and 1050 °C and the strain rates of 0.01, 0.1, 1 and 10 s−1. The influence of deformation temperature and strain rate on the flow stress of Ti–6Al–2Zr–1Mo–1V alloy was studied. Based on the experimental data sets, the high temperature deformation behavior of Ti–6Al–2Zr–1Mo–1V alloy was presented using the intelligent method of artificial neural network (ANN). The results indicate that the predicted flow stress values by ANN model is quite consistent with the experimental results, which implies that the artificial neural network is an effective tool for studying the hot deformation behavior of the present alloy. In addition, the development of graphical user interface is implemented using Visual Basic programming language.

High Temperature Deformation Behavior of Fe-9Ni-C Alloy

AbstractThe high temperature deformation behavior of the 9Ni steel has been studied by the Gleeble-3500 tester. The relationship between deformation resistance and deformation degree, deformation temperature and deformation rate was revealed. The results show that when the deformation degree is less than 0.2, the deformation resistance increases by about 70 to 200 MPa, while the deformation degree varied between 0.2 and 0.4, the deformation resistance increases by about 30–40 MPa, when the deformation degree is larger than 0.4, the deformation resistance increases slowly, some become stable gradually. The influence of deformation temperature on deformation resistance is larger, and deformation resistance at higher temperature is about 160 MPa smaller than at lower temperature. Higher deformation rate leads to larger deformation resistance. The deformation resistance increases about 70 to 110 MPa with the increase of the deformation rate. A new and highly accurate mathematical model of the steel was established to describe the deformation behavior during rolling.

Flow Stress and Critical Dynamic Recrystallization Behavior of Cu–Fe16Mn0.6C High Manganese TWIP Steel

AbstractThe true stress–strain curve of Cu–Fe16Mn0.6C twinning induced plasticity (TWIP) steel was studied with a compression test on Thermecmastor‐Z thermal simulator at a temperature range of 850–1150°C and strain rate range of 0.03–30 s−1. The influence of deformation temperature and strain rate on high‐temperature flow stress and critical recrystallization behavior of the TWIP steel was investigated. It is concluded that the peak flow stress of Cu–Fe16Mn0.6C under high‐temperature deformation decreases as the temperature increases but increases with the strain rate. Meanwhile at strain rate of 0.03 and 30 s−1 obvious peak stresses are observed which demonstrates the dynamic recrystallization. The constitutive equation of Cu–Fe16Mn0.6C under high temperature deformation is calculated by linear regression method. The activation energy is 505 kJ mol−1. The relationship between critical strain of dynamic revrystallization and Zener–Hollomon parameter is determined by the curve between strain‐hardening rate and flow stress.

High Temperature Deformation Behavior and Microstructure Preparation of Cu-Ni-Si-P Alloy

The hot deformation behavior of Cu-Ni-Si-P alloy have been investigated by means of isothermal compression tests on a Gleeble-1500D thermal mechanical simulator in the temperature ranges of 873-1073 K and strain rate ranges of 0.01-5s-1. The results show that the dynamic recryatallization occurs in Cu-Ni-Si-P alloy during hot deformation. The peak stress during hot deformation can be described by the hyperbolic sine function. The influence of deformation temperature and strain rate on the peak stress can be represented using the Zener-Hollomon parameter. Moreover, the activation energy for hot deformation of Cu-Ni-Si-P alloy is determined to be 485.6 kJ / mol within the investigated ranges of deformation temperature and strain rate. The constitutive equation of the Cu-Ni-Si-P alloy is also established. Keywords: Cu-Ni-Si-P alloy; Hot deformation; Dynamic recrystallization; Zener-Hollomon parameter.

Critical Strain Model of Cr4 Steel for Heavy Supporting Roller

Critical strain is the basis to determine whether the dynamic recrystallization occurs during hot deformation process, it is important for designers to control hot forming process and microstructure of final product. In order to investigate the influence of deformation temperature and strain rate on critical strain of Cr4 steel, hot compression simulation experiment was conducted for Cr4 steel in the temperature range of 750～1200°C and strain rate of 0.002～5S-1 by means of Gleeble−1500D thermo-simulation machine. The results showed that the critical strain increase with decreasing deformation temperature and increasing strain rate. Based on the experimental data and regression analysis method, the mathematical model of the critical strain of Cr4 steel is constructed. The critical strain model provides data support to predict the dynamic recrystallization during Cr4 heavy supporting roller hot forging process.

Hot deformation behavior and microstructure evolution of spray formed GH738 superalloy

In order to evaluate the deformation characteristics of spray formed superalloy GH738, the hot compression test was conducted on Gleeble-3500 thermal mechanical simulator at a temperature range of 960–1120 °C, and a strain rates range of 0.1, 1.0 s−1 with engineering strain 50%. The flow stress data at various hot working conditions was obtained, and the influence of deformation temperature and strain rate on the microstructure evolution of spray formed GH738 was analyzed. The result shows that, the flow stress improves with the increasing of strain rate and the decreasing of temperature, the yield drop is observed on true stress-strain curves at strain rate of 1.0 s−1. The temperature and strain rate have a strongly effect on dynamic recrystallization. Higher temperature could efficiently promote the process of dynamic recrystallization, as the increment of temperature, the dynamic recrystallization grain size shows the tendency of growth. Higher strain rate is better for grain refinement.

Dynamic Strain-Induced Ferrite Transformation during Hot Compression of Low Carbon Si-Mn Steels

The dynamic strain-induced transformation (DSIT) of austenite to ferrite was investigated under different undercooling conditions using three low carbon Si-Mn steels. The undercooling of austenite (ΔT) was controlled by varying the cooling rate between austenitization and deformation temperatures. Uniform DSIT ferrite grains (∼2.3 μm) were produced at a relatively high deformation temperature above 840°C using a low carbon high Si steel (0.077C-0.97Mn-1.35Si, mass%) in connection with a larger ΔT. The critical conditions for DSIT were determined based on the flow stress-strain curves measured during hot compression tests. Influence of deformation temperature on DSIT of low carbon Si-added steel was also discussed.

Corrosion Behaviors of Two Types of Commercial Stainless Steel after Plastic Deformation

The influence of deformation temperature, strain rate and alloying elements such as chromium, nickel, copper, on corrosion resistance of a 304 stainless steel after plastic deformation was investigated. The techniques employed were tensile test at room and elevated temperature, deep drawing tests at various strain rates, X-ray diffraction test and potentiodynamic and cyclic polarization, metallography by optical and scanning electron microscopy. Results showed that chromium, nickel and copper had a significant effect on corrosion resistance of steel after plastic deformation. It was observed that corrosion resistance after plastic deformation was a function of deformation temperature and alloying elements.

Rate Independent and Rate Dependent Structural Evolution during Severe Plastic Deformation

High pressure torsion (HPT) deformation enables the grain refinement of bulk materials until a saturation region is reached where no further microstructural refinement can be observed. The influence of deformation temperature, alloying and strain rate on the saturation region was examined by using pure aluminum, an Al-1 mass%Mg alloy and an Al-3 mass%Mg alloy. The deformation temperature was varied between � 196 � C and 450 � C. Both, temperature and alloying exhibit a pronounced influence on the saturation microstructure. The measurements reveal either a rate independent behavior of the structural evolution at low temperatures and a rate dependent behavior of the structural evolution at high temperatures. Two different processes are proposed to be the reason for the saturation at low and high homologous temperatures.

The Influence of Viscous Flow Deformation on the Thermal Stability and Hardness of ZrCuAlNi Bulk Glassy Alloy

We investigated the thermal stability and hardness of a Zr55Cu30Al10Ni5 bulk glassy alloy after isothermal viscous flow deformation in the supercooled liquid region. The influence of deformation temperature, holding time and initial strain rate on the thermal stability and hardness of aZ r 55Cu30Al10Ni5 bulk glassy alloy subjected to the high temperature compression test was examined by differential scanning calorimetry (DSC) and with a Vickers micro-hardness tester. The results showed that the incubation time for isothermal annealing crystallization reduced during the viscous flow deformation. Thermal stability of supercooled liquid decreased after viscous flow deformation. As the deformation temperature increased, the SCL region decreases. At lower temperatures below 713 K the structural relaxation occurred, resulting in a slight increase in hardness. The crystallization at higher temperatures of over 723 K caused a rapid increase in hardness. The supercooled liquid region decreased and the hardness increased with increasing deformation time. Higher strain rate resulted in larger deformation in the same deformation time, and had slight influence on the thermal stability and hardness of the Zr55Cu30Al10Ni5 glassy alloy. When the Zr55Cu30Al10Ni5 bulk glassy alloy was compressed for 300 s with an initial strain rate of 3:3 � 10 � 3 s � 1 at the temperatures of 723 K, nanocrystallization occurred, and the grain size was evaluated to be smaller than 5 nm. [doi:10.2320/matertrans.MJ200712]

Influence of deformation temperature on the ferrite grain refinement in a low carbon Nb–Ti microalloyed steel

Grain refinement is one of the effective methods to develop new generation low carbon microalloyed steels possessing excellent combination of mechanical properties. In the present work, the microstructural evolution and ferrite grain refinement at various deformation temperatures were investigated using single pass isothermal hot compression experiments for a low carbon Nb–Ti microalloyed steel. The physical processes that occurred during deformation were discussed by observing the optical microstructure and analyzing the stress–strain responses. The results show that there is a close relation between the microstructural evolution and true stress–true strain responses during the deformation. Microstructural observation indicates that very fine ferrite grains of about 1.8–3 μm are obtained by deformation at 830–845 °C, about Ar 3 ± 10 °C. The obtained stress–strain curves suggest the occurrence of strain-induced dynamic transformation (SIDT) of γ to α at this deformation temperature range.

Craze Formation in Long Chain Branched Poly(Styrene) as Revealed by In Situ Transmission Electron Microscopy: Influence of Deformation Temperature

The craze structure of linear and long chain branched poly(styrene) (PS) was investigated as a function of temperature by means of in situ transmission electron microscopy (TEM). At room temperature, high entanglement density and a degree of molecular mobility result in homogeneous crazes for branched PS and fine fibrillated crazes for linear PS. With increasing temperature up to near (but still below) the glass transition temperature, the mobility of polymer chains increases, longer units of macromolecules are mobile, and disentanglement becomes more probable. This behavior results in a transition from the formation of homogeneous crazes to fibrillated crazes in long chain branched PS, and in the formation of coarser fibrils and greater distances between the fibrils in both linear and long chain branched PS. The increase in the deformation rate has the opposite effect on the craze structure compared to the temperature increase. After breaking the craze fibrils, a high stress concentration is suddenly produced in the active zone, at the tip of the craze, and the entanglements act as chemical cross-links in the short time available which restricts the mobility of polymer chains, reduces disentanglement, and hence increases the probability of homogeneous crazes formation.

Influence of deformation temperature on shape memory effect of Fe–Mn–Si–Ni–Cr alloy

The phase transformation hypocrisy-elasticity behaviour and the shape memory completeness of four Fe–Mn–Si–Ni–Cr alloys deformed at different temperatures are reported. An incomplete phase transformation hypocrisy-elasticity caused by the γ→ε martensite reversible transformation is exhibited in an Fe–14Mn–5Si–9Cr–5Ni alloy at 473 K. The shape recovery completeness of four alloys depends on the difference between Md and Mεs, TN temperatures and the stacking fault energy of the parent phase. It is practically meaningful that a quite high net recovery strain can be obtained in Alloys 2 and 4 by the addition of the rare earth Cerium and Nitrogen elements when pre-strained at 300 and 77 K, respectively. The net recovery strain is 4.3% in Alloy 2 and 4.6% in Alloy 4, respectively, at pre-strain 5.3%.