Optimum Deformation Temperature Research Articles

Hot Deformation Behavior and Microstructure Evolution of a Graphene/Copper Composite.

Graphene/copper composites are promising in electronic and energy fields due to their superior conductivity, but microstructure control during thermal mechanical processing (TMP) remains a crucial issue for the manufacturing of high-performance graphene/copper composites. In this study, the hot deformation behavior of graphene/copper composites was investigated by isothermal compression tests at deformation temperatures of 700~850 °C and strain rates of 0.01~10 s-1, and a constitutive equation based on the Arrhenius model and hot processing map was established. Results demonstrate that the deformation mechanism of the graphene/copper composites mainly involves dynamic recrystallization (DRX), and such DRX-mediated deformation behavior can be accurately described by the established Arrhenius model. In addition, it was found that the strain rate has a stronger impact on the DRX grain size than the deformation temperature. The optimum deformation temperature and strain rate were determined to be 800 °C and 1 s-1, respectively, with which a uniform microstructure with fine grains can be obtained.

Structure and properties of TiNi shape memory alloy after low-temperature ECAP in shells

The effect of low-temperature equal-channel angular pressing (ECAP) in shells on the structure formation and mechanical and functional properties of a near-equiatomic titanium nickelide (TiNi) shape memory alloy is studied. ECAP with channel intersection angles of 120° and 110° is carried out at temperatures in the 20 °С to 330 °С range after 1 pass. The optimum material for shells is pure iron, which is not destroyed after ECAP down to room temperature. The optimum deformation temperature of ECAP in a shell is determined to be 200 °С. Deformation at low temperatures leads to the premature destruction of TiNi samples. ECAP of the TiNi core in a shell at 200 °С after 1 pass leads to the formation of an elongated, banded martensite structure with a bandwidth of approximately 100 nm. The best combination of mechanical and functional properties is found after ECAP of a TiNi sample with a diameter of 12 mm in core-shell mode at 200 °С followed by the addition of post-deformation annealing at 400 °С for 1 h.

Hot Deformation Analysis and Microstructure Evolution of a Novel Al–Cu–Li Alloy by Isothermal Compression

The hot deformation behavior of a novel Al–Cu–Li alloy is investigated by isothermal compression with a temperature range of 350–510 °C and a strain rate range of 0.001–10 s−1. Constitutive analysis and hot processing maps are used to analyze the influence of deformation parameters on hot deformation behavior, and the related microstructure evolution is characterized by scanning electron microscope (SEM), electron backscatter diffraction (EBSD), and transmission electron microscope (TEM) observations. The results indicate that the microstructure evolution of the alloy during deformation was dominated by dislocation movement and substructure evolution. With the increase in temperature or the decrease in strain rate, the dislocations introduced by deformation gradually transform into dislocation walls and substructures, showing distinct dynamic recovery (DRV) and slight dynamic recrystallization (DRX) characteristics. The degree of DRX is very low, while it is more sensitive to strain rate than temperature. According to the analysis of hot processing maps and microstructure, the optimum deformation temperature and strain rate of the alloy are determined as at least 430 °C and 0.008–0.15 s−1, respectively. These results can be referable for the industrial thermomechanical processing of this novel Al–Cu–Li alloy.

Determination of the optimal temperature regime of plastic deformation of micro alloyed automobile wheel steels

It has been established that hot plastic deformation microalloyed steel 10HFTBch type accelerates the excretion of pearlite and causes structure refinement during subsequent cooling due to an increase of start of new phases’ centers. This leads to the formation of a fine-grained dispersed two-phase structure consisting of ferrite with a high dislocation density and pearlite. It has been determined that at the optimum deformation temperature the prevailing mechanism of structure refinement is the fragmentation of austenitic and ferrite grains of a common initial orientation into misoriented subgrains (fragments) with low-angle dislocation boundaries of deformation origin. A thorough thermokinetic analysis of the course of this process made it possible to determine the optimal temperature regime for plastic deformation for this type of steel, which is 850-900 °C. Plastic deformation increases the range of of pearlite’s transformation existence rates by 2.5 times, it was found that after 30% deformation at 950 °C, pearlite transformation begins at a cooling rate of 5 °C/s, and without deformation – at 2 °C/s

Hot Deformation Behaviour and Constitutive Equation of Mg-9Gd-4Y-2Zn-0.5Zr Alloy

The thermal deformation behaviour of Mg-9Gd-4Y-2Zn-0.5Zr alloy at temperatures of 360–480 °C, strain rates of 0.001–1 s−1 and a maximum deformation degree of 60% was investigated in uniaxial hot compression experiments on a Gleeble 3800 thermomechanical simulator. A constitutive equation suitable for plastic deformation was constructed from the Arrhenius equation. The experimental results indicate that due to work hardening, the flow stress of the alloy rapidly reached peak stress with increased strain in the initial deformation stage and then began to decrease and stabilize, indicating that the deformation behaviour of the alloy conformed to steady-state rheological characteristics. The average deformation activation energy of this alloy was Q = 223.334 kJ·mol−1. Moreover, a processing map based on material dynamic modelling was established, and the law describing the influence of the machining parameters on deformation was obtained. The experimental results indicate that the effects of deformation temperature, strain rate and strain magnitude on the peak dissipation efficiency factor and instability range were highly significant. With the increase in the strain variable, the flow instability range increased gradually, but the coefficient of the peak power dissipation rate decreased gradually. The optimum deformation temperature and strain rate of this alloy during hot working were 400–480 °C and 0.001–0.01 s−1, respectively.

Effects of Tensile Testing Temperature on Mechanical Properties and Deformation Behavior in Medium Mn Steels

In single-phase austenitic steels, the optimum deformation temperature in the tensile test to obtain high tensile strength-elongation balance (TS×El) and work hardening rate (dσ/dε) depends on control of the stability of austenite. In order to clarify the effects of the deformation temperature in complex phase steels containing austenite, in this study, the effects of the tensile testing temperature on mechanical properties and deformation behavior were investigated in detail using steel A and steel B with a chemical composition of 0.15C-0.5Si-5.0Mn (wt%). Steels A and B consisted of ferrite and retained austenite, but contained different volume fractions of retained austenite, namely, 29 % and 17 % as a result of annealing at 660 °C and 620 °C for 2 h, respectively. The stability of the retained austenite of steel B was higher than that of steel A. In steel A, TS×El and dσ/dε achieved their maximum values at 20 °C, decreased from 20 to 100 °C, and then remained almost unchanged at more than 150 °C. On the other hand, in steel B, TS×El and dσ/dε achieved their maximum values at -40 °C, decreased from -40 to 50 °C and remained almost unchanged at more than 100 °C. These results can be explained by the stability of retained austenite and the transformation rate from retained austenite to martensite. It should be noted that control of the stability of retained austenite and the transformation rate from retained austenite to martensite led to an adjustment of the optimum deformation temperature to achieve the high TS×El and dσ/dε in medium Mn steels, in the same manner as in single-phase austenitic steels.

Optimizing Induction Heating of WNiCo Billets Processed via Intensive Plastic Deformation

The aim of the work is to optimize the induction heating regime and propose a suitable deformation temperature for a pre-sintered powder-based tungsten heavy alloy workpiece subsequently processed via rotary swaging. The heating regime is designed with the help of numerical analyses and subsequent experiments. The first part of the study focuses on the theoretic background of the induction heating and comprises the development of a reliable induction heating model via performing electromagnetic simulations in two individual computational software packages (for verification). The second part of the study then involves the optimization of the heating regime using the designed numerical model. Last but not least, the predicted results are compared to the experimentally acquired results, and the optimized heating regime, applicable before experimental rotary swaging of the WNiCo workpiece, is proposed. The results of the microstructure analyses of the workpiece heated to the selected optimum deformation temperature of 900 °C showed that the designed induction heating procedure provided sufficient heating of the bulk of the workpiece (contrary to the lower swaging temperature), as the swaged microstructure featured well-deformed tungsten agglomerates. Furthermore, the analyses documented the high-quality oxidation-free surface of the particular workpiece (contrary to the higher swaging temperature).

Effects of C and La on the Tensile Property and Hot Working Characteristics of CoCrFeMnNi High-Entropy Alloy

CoCrFeMnNi high-entropy alloy series were cast by magnetic suspension vacuum melting furnace. They were forged at 1160°C and annealed at different temperatures. Gleeble3800 thermal deformation simulation testing machine was used to conduct thermal compression simulation to research the hot workability of the alloy. The results show that the microstructures of these alloys are made up of solid solution with face-centered-cubic structure and white granular precipitate M23C6. The addition of C and La increases the elongation of CoCrFeMnNi high-entropy alloy forged without annealing by 1.32 times. Annealing deteriorates the tensile properties of these alloys. The constitutive equation and thermal processing diagram of the alloy are established according to the results of thermal simulation. The addition of C and La reduces the flow stress of CoCrFeMnNi high-entropy alloy, but significantly reduces the instability region of thermoplastic deformation. The optimized thermal process parameters are as following: ①CoCrFeMnNi, when the range of the deformation temperature and the strain rate are respectively 900~1040°C and 0.01~0.025s−1, the optimum deformation temperature is 1040~1100°C, and the strain rate is in the range of 0.013~0.033s−1; ②CoCrFeMnNiC0.007La0.0004, when the range of the deformation temperature and the strain rate are respectively 1000~1080°C and 0.31~1s−1, the optimum deformation temperature is 1080~1100°C, and the strain rate is 0.01~0.025s−1.

Superplasticity of Ti-6Al-4V Titanium Alloy: Microstructure Evolution and Constitutive Modelling.

Determining a desirable strain rate-temperature range for superplasticity and elongation-to-failure are critical concerns during the prediction of superplastic forming processes in α + β titanium-based alloys. This paper studies the superplastic deformation behaviour and related microstructural evolution of conventionally processed sheets of Ti-6Al-4V alloy in a strain rate range of 10–5–10–2 s–1 and a temperature range of 750–900 °C. Thermo-Calc calculation and microstructural analysis of the as-annealed samples were done in order to determine the α/β ratio and the grain size of the phases prior to the superplastic deformation. The strain rate ranges, which corresponds to the superplastic behaviour with strain rate sensitivity index m ˃ 0.3, are identified by step-by-step decreasing strain rate tests for various temperatures. Results of the uniaxial isothermal tensile tests at a constant strain rate range of 3 × 10−4–3 × 10−3 s−1 and a temperature range of 800–900 °C are presented and discussed. The experimental stress-strain data are utilized to construct constitutive models, with the purpose of predicting the flow stress behaviour of this alloy. The cross-validation approach is used to examine the predictability of the constructed models. The models exhibit excellent approximation and predictability of the flow behaviour of the studied alloy. Strain-induced changes in the grain structure are investigated by scanning electron microscopy and electron backscattered diffraction. Particular attention is paid to the comparison between the deformation behaviour and the microstructural evolution at 825 °C and 875 °C. Maximum elongation-to-failure of 635% and low residual cavitation were observed after a strain of 1.8 at 1 × 10−3 s−1 and 825 °C. This temperature provides 23 ± 4% β phase and a highly stable grain structure of both phases. The optimum deformation temperature obtained for the studied alloy is 825 °C, which is considered a comparatively low deformation temperature for the studied Ti-6Al-4V alloy.

Achieving bimodal microstructure and enhanced tensile properties of Mg–9Al–1Zn alloy by tailoring deformation temperature during hard plate rolling (HPR)

In the present work, we investigated the influence of deformation temperature on the formation of a bimodal microstructure and tensile properties of a Mg–9Al–1Zn (AZ91) alloy processed by a single pass hard plate rolling (HPR) with a thickness reduction of 55% followed by a short time annealing. Microstructural examinations by electron backscatter diffraction (EBSD) reveal that there exists a narrow deformation temperature window, i.e. it is only feasible to achieve a desired bimodal grain structure in the AZ91 alloy when HPRed at ∼350 °C. It is mainly because that partial dynamic recrystallization (DRX) occurs easily in the sample HPRed at ∼ 350 °C, facilitating the formation of a bimodal microstructure consisting of coarse un–recrystallized grains (>∼70 μm) and fine recrystallized grains (<∼5 μm). In contrast, reducing deformation temperature to ∼300 °C results in a coarse unrecrystallized microstructure containing substantial sub structure, while elevating the deformation temperature to ∼400 °C leads to an almost uniform recrystallized grain structure. Especially, the formation mechanism for the bimodal grain structure at the optimum deformation temperature is explored in terms of Schmidt factors analysis for basal slips (SFbasal) for grains of different size scales. Moreover, the 350 °C HPRed AZ91 sample exhibits a better combination of strength (ultimate tensile strength = ∼374 MPa) and ductility (elongation = ∼19.6%), as compared to the 300 and 400 °C samples. It is mainly attributed to the typical bimodal grain structure and the relatively high SFbasal featured by the fine recrystallized grains as well as the nanometer spherical particles distributing in fine grain interiors.

Hot Compression Deformation Behavior and Microstructural Evolution of Al-7.5Zn-1.5Mg-0.2Cu-0.2Zr Alloy

Hot compression tests of as-homogenized Al-7.5Zn-1.5Mg-0.2Cu-0.2Zr alloy were carried out on Gleeble-3500 thermal simulation machine at the temperature ranging from 350°C to 550°C and strain rate ranging from 0.001s-1 to 10s-1. Processing maps were established on the basis of dynamic material model, and the microstructure was studied using electron back scattered diffraction (EBSD) technique. The results showed that the peak stress and steady flow stress decrease with decreasing strain rate or increasing deformation temperature. There are one peak efficiency domain and one flow instability domain in the processing maps. The flow instability domain which exists in high-strain-rate region becomes larger with increasing strain. Shear bands occur at 45° toward the compression axis at grain interiors and meanwhile flow localization occurs. The optimum deformation temperature and strain rate ranges from 450°C to 500°C and 0.003s-1 to 0.1s-1, respectively, with high power dissipation efficiency of 34-39%.

Evolution of Dynamically Recrystallized Grains in Steel SCM435

An MMS-200 high-temperature test complex is used to study dynamic recrystallization in steel SCM435. The effect of temperature and strain rate on recrystallized grain size is studied metallographically. Results show that strain parameters have a complicated effect on the number of average grain size, and also on the number of largest and smallest grains. The optimum deformation temperature providing formation of fine and uniform grains increases with an increase in strain rate. On the basis of analyzing the sizes of dynamically recrystallized grains in steel SCM435 a model is developed for calculating average grain size in the temperature range 850–1050°C.

Plastic Formability and Auto Demonstration Parts of Mg-Nd-Zn-Zr Magnesium Alloy

Mg-3.0Nd-0.2Zn-0.4Zr (wt.%, NZ30K) alloy shows middle strength and high toughness, potentially being applied as a wrought alloy. In this paper, this alloy is first successfully cast into some billets in a diameter of 100mm by direct chill (DC) casting. The optimal casting temperature is 700°C and casting speed is 90mm/min. Then, the deformability of NZ30K alloy billets was modeled by using uniaxial tensile and compression tests at different process parameters. The results show that the optimum deformation temperature of the as-cast NZ30K alloy is between 350 and 400 °C and strain ratio ranges from 0.01 to 1 s-1. Finally some round and rectangular tubes (which are also bent and weld into a support frame for an auto instrument panel) are successfully extruded, and an end cover for auto transmission case is successfully forged. Both the extruded and forged demo parts show good mechanical properties. The maximum ultimate tensile strength, yield strength and elongation of the T5 state alloy are 323 MPa, 318MPa and 11.2%, respectively.

Strain rate sensitivity of a high strain rate superplastic TiN p/2014 Al composite

The effects of deformation temperature and strain in hot rolling deformation on strain rate sensitivity of the TiN p/2014 Al composite were studied by tensile tests conducted out at 773, 798, 818 and 838 K with the strain rates from 1.7 ×10 −3 to 1.7 × 10 0 s −1. It is shown that the curves of m value of the TiN p/2014Al composite deformed at different temperatures can be divided into two stages with the variation of strain rate, and the critical strain rates are 10 −1 s −1. The optimum deformation temperature of the TiN p/2014 Al composite is near incipient melting temperature of 816 K and the optimum strain rate is a little higher than the critical strain rate. The effect of deformation temperature on strain rate sensitivity is relative to liquid phase helper accommodation. The effect of strain in hot rolling deformation on strain rate sensitivity attributes to change of microstructure and deformation mechanism.

Research on the hot deformation behavior and graphite morphology of spheroidal graphite cast iron at high strain rate

The hot deformation behavior of spheroidal graphite cast iron (SGCI) was investigated quantitatively from 600 °C to 950 °C at high strain rate of 10 s −1 by compression tests on a Gleeble-1500 simulator. The results show that the peak strain increases gradually with increasing deformation temperatures in the range of 600–800 °C and decreases when the temperature is raised to 800 °C and above. The optimum deformation temperature range is determined at 700–900 °C. The graphite particles become spindles or flakes after deformation, even some graphite collapse in the compressed specimens with about 0.7 peak strains. The graphite area fraction decreases as the temperature increases, at the same time, the high peak strain promotes the dissolving of carbon.

Superplastic deformation behaviour of friction stir processed 7075Al alloy

Commercial 7075Al rolled plates were subjected to friction stir processing (FSP) with different processing parameters, resulting in two fine-grained 7075Al alloys with a grain size of 3.8 and 7.5 μm. Heat treatment at 490 °C for 1 h showed that the fine grain microstructures were stable at high temperatures. Superplastic investigations in the temperature range of 420–530 °C and strain rate range of 1×10 −3–1×10 −1 s −1 demonstrated that a decrease in grain size resulted in significantly enhanced superplasticity and a shift to higher optimum strain rate and lower optimum deformation temperature. For the 3.8 μm 7075Al alloy, superplastic elongations of >1250% were obtained at 480 °C in the strain rate range of 3×10 −3–3×10 −2 s −1, whereas the 7.5 μm 7075Al alloy exhibited a maximum ductility of 1042% at 500 °C and 3×10 −3 s −1. The analyses of the superplastic data for the two alloys revealed a stress exponent of 2, an inverse grain size dependence of 2, and an activation energy close to that for grain boundary self-diffusion. This indicates that grain boundary sliding is the main deformation mechanism for the FSP 7075Al. This was verified by SEM examinations on the surfaces of deformed specimens.

Hot deformation behaviour and grain refinement of intermetallic compound Ni 3Al

The paper describes the preparation of Ni 3Al-based intermetallic compounds and investigations of their structures in the ascast, worked, and annealed states. The performed experimental works approved a possibility of hot working of the highly brittle polycrystalline intermetallic compound Ni 3Al with large grain cast structure. The facility of originating the recrystallization seems to be surprising in such a material. On the other hand, the growth of recrystallization nuclei is strongly retarded. The case is further complicated by the fact of heterogeneous deformation in the microvolume. Microalloying with boron or zirconium influenced the original structure parameters as well as the optimum deformation temperature. Simultaneously the probability of a transgranular cleavage fracture increased. For the stoichiometric Ni 3Al intermetallic compound the optimum deformation temperature 1150 °C has been assessed. At temperature 1250 °C, the alloy Ni 3Al + 0,1 at. % B manifested the best plasticity. The special type of rotary working combined with friction heating gave the best results from point of view of obtaining a fully recrystallized region.

Superplastic deformation characteristics of two microduplex titanium alloys

A comparison of the superplastic deformation behaviour of Ti-6Al-4V (wt%) between 760 and 940‡ C and Ti-6Al-2Sn-4Zr-2Mo between 820 and 970‡ C has been carried out on sheet materials possessing similar as-received microstructures. High tensile elongations were obtained with maximum values being recorded at 880‡ C for Ti-6Al-4V (Ti-6/4) and at 940‡ C for Ti-6Al-2Sn-4Zr-2Mo (Ti-6/2/4/2), under which conditions both alloys possessed aΒ phase proportion of approximately 0.40. For a given deformation temperature the Ti-6/4 alloy had a slightly lower flow stress than the Ti-6/2/4/2, and this was attributed to the lowerΒ phase proportion in the latter alloy. However, at the respective optimum deformation temperatures the Ti-6/2/4/2 alloy had the lower flow stress. The results show that suitably processed Ti-6/2/4/2 alloy is capable of withstanding substantial superplastic strains at relatively low flow stresses, although the optimum deformation temperature is higher for this alloy than for Ti-6/4 material possessing a similar microstructure.

Thermomechanical treatment of boring chisels

1. Thermomechanical treatment increases the working life of chisels by 20–30% in cutting quenched steel. 2. The optimum deformation temperature of the head of the chisel is 500° C. Cooling below 500°C decreases the ductility of the metal and leads to the formation of cracks during deformation. 3. The effect of thermomechanical treatment consists in the change of the fine structure of the steel and in the type and distribution of dislocations.