Papers by Keyword: Hot Compression Test

Abstract: In this work the texture evolution of a near β Ti-3Zr-2Sn-3Mo-25Nb (TLM) biomedical titanium alloy in hot compression at different deformation temperatures from 750°C to 850°C has been investigated. The XRD examination shows that the samples of hot deformation consist of β phase only. The development of texture has been explained in terms of orientation distribution functions (ODFs) of α and γ fibres. Compared with cold compression of TLM alloy, the texture changes obviously with the increase of deformation temperature. The {111}<110> texture shows the feature that weaken firstly and then strengthen, while the {111}<112> texture shows an opposite tendency. Specifically, the prominent texture components change to the {111}<110> and {111}<112> at the deformation temperature of 850°C, which are the same texture type and the nearly level of orientation density with the starting materials.

Abstract: Dynamic recrystallization (DRX) characteristics of an 5182 Al alloy was investigated at temperatures ranging from 673 K-773 K and constant strain rates of 0.01 s^-1, 0.1 s^-1, 1 s^-1, 10 s^-1, and 50 s^-1. The average grain size of the as-casted alloy was 160 μm and was refined to 20 μm via deformation at 773 K, 50 s^-1 to a strain level of 0.5 (40%). The true stress-strain curves were determined and divided into two main groups based on the temperatures and strain rates. The activation energy of the DRX in the examined aluminum alloys was calculated, being 175,87 kJ/mol. During the crystallization process compound phases were crystallized along the border of initial grains due to the great content of Mg, Mn and Fe. It was deduced from the metallography examination that most of the new grains formed via necklacing mechanism from the mentioned borders during the DRX.

Abstract: Isothermal forging is a near-net shape forming technology for manufacturing complex titanium alloy components. In order to characterize the workability of Ti-6Al-4V alloy during isothermal forging process, the material properties of Ti-6Al-4V alloy were investigated by isothermal compression tests under different strain rate-temperature, where the temperature range is 850~1000 °C and strain rate range is 0.001~0.05s⁻¹. The obtained flow stress-strain data was used to develop the Arrhenius constitutive model of which material constants considered the compensation of strain. The developed constitutive model was used to simulate the isothermal forging process of Ti-6Al-4V alloy component by finite element (FE) based numerical method. The metal flow and potential defect locations were predicted by numerical simulation. Furthermore, the relevant simulation results were compared with the product in industrial workshop to demonstrate the validity of material constitutive model. Keywords: Isothermal forging; Ti-6Al-4V alloy; Hot compression test; Arrhenius constitutive model; FE analysis; Model validation;

Abstract: The dynamic recrystallization (DRX) of N08028 corrosion resistant alloy was investigated by hot compression tests which were performed at the deformation temperatures from 1000°C to 1200°C and strain rate from 0.01s^-1 to 1s^-1 on a Gleeble-1500 thermo-mechanical simulator. The stress-strain curves at all strain rates showed the characteristics of DRX and exhibited a peak in the flow stress before reaching steady state. The microstructures after deformation demonstrated that DRX took place in all specimens. The results show that DRX occurs more easily with the decrease of strain rate and the increase of deformation temperature. By regression analysis, the activation energy in the entire range of deformation conditions, and the relationship of critical strain as well as strain for 50% DRX with deformation conditions were determined. A good agreement between the experimental and predicted results shows that the proposed DRX kinetic equations can give an accurate estimate of the DRX behavior in hot deformed N08028 corrosion resistant alloy.

Abstract: This paper presents an investigation about the occurrence of the dynamic recrystallization (DRX) during hot forming. Two 7075 aluminum alloy samples in different initial states were examined by compression tests at temperatures between 573 K and 723 K and constant strain rates ranging from 0.002 to 2 (s-1) with the maximum strain of 0.5 mm/mm. The activation energies of the examined aluminium were calculated, being 137.7 kJ/mol and 142.4 kJ/mol. The critical stresses and strains for the initiation of the dynamic recrystallization were determined using a numerical method based on the changes of the work hardening rate (θ) as a function of the flow stress (σ) or a strain (ε), respectively. Based on the micrographs taken after the deformations it was revealed that in some cases only dinamyc recovery (DRV) whereas in others DRX occurred under the applied examination conditions. The critical stress which belongs to the onset of the DRX or the DRV depend on the temperature, the strain rate, and the initial grain size. The critical and maximal stresses and the corresponding strain values at different conditions were determined. In the examined range of deformation, temperature and strain rate, the critical rations are σ_c/σ_p= (0.93-0.99) and εc/ εp = (0.3-0.74), respectively.

Abstract: The constitutive equation in hot working for Al 7075 aluminum alloy was obtained employing experimental data of stress-strain curve, in a wide range of temperature (250-450°C) and strain rate (0.002-2 s-1). The influence of temperature and strain rate on the deformation behavior is represented by the equation proposed by Sellar and McTegart, all material parameters are considered as function of equivalent strain. The force-height data was corrected with interpolation method in the way to eliminate the error at the measurement. To verify the constitutive equation two parameter were calculated average absolute relative error (AARE=6.42) and correlation coefficient (R=0.998), for the same purpose the measuring and calculated flow curve are plotted together, the results shows that the constitutive equation obtained is good describing the behavior of the material.

Abstract: In order to obtain a refined and uniform microstructure in the final billet, the radial forging process needs to be optimized and controlled with various process parameters such as temperature of ingot and die, die size, ram speed, upset ratio, etc. Grain size control is one of the most effective ways for the control of mechanical properties. The change in grain size is significantly related with strain, strain rate and temperature of forged part. To understand material properties and to analyze stability and instability area of forged workpiece, hot compression test of Ti-6Al-4V was carried out within the strain-rate range 10-2 to 10 s-1, and the temperature range 800 to 1100oC. And dynamic material map of Ti-6Al-4V was tabulated. In this study, a three-dimensional rigid-plastic finite element method(FEM) was used to analyze the radial forging process, focusing on the effects of feed rate and rotation angle for appropriate forging pass schedule. And the simulation result was confirmed with dynamic material model of Ti-6Al-4V. The optimal combination of feed rate and rotation angle has been determined by quantifying the radius profile in the longitudinal direction, roundness of the product and uniform strain distribution.

Abstract: The high-temperature deformation resistance of X120 pipeline steel was studied under different deformation temperature and different deformation rate through the hot compression test on the Gleeble-3500 thermal/mechanics simulation test machine. The influence of deformation degree, deformation temperature and deformation rate on deformation resistance was thoroughly investigated. The deformation resistance of X120 pipeline steel increased slowly when deformation degree was higher than 0.2. With the increase of deformation temperature, the work-hardening effect was weakened, so the deformation resistance decreased. And the deformation rate had dual influences on the deformation resistance, including the effect of temperature and time. Based on the experiment data, the parameters in the mathematical model were regressed by using SPSS (Statistic Package for Social Science), and the mathematical model of the deformation resistance of X120 pipeline steel was established finally. Through the regression analysis, the model had been proved to have great matching precision.

Abstract: The aim of the paper is to determine the influence of hot deformation conditions on σ-ε curves and microstructure evolution of new-developed high-manganese C-Mn-Si-Al-Nb austenitic steel. The force-energetic parameters of hot-working were determined in continuous and multi-stage compression tests performed in a temperature range of 850 to 1100°C by the use of the Gleeble 3800 thermomechanical simulator. Evaluation of processes controlling work-hardening were identified by microstructure observations of the specimens water-quenched after various conditions of plastic deformation. Multi-stage compression tests with true strain of 0.29 permit to use the dynamic and metadynamic recrystallization for forming the fine-grained, austenite microstructure of steel in the whole range of deformation temperature.

Abstract: The material constitutive behaviour and microstructure of Aluminium alloys 6082 and 7449 were studied with the Gleeble hot compression test. The novel aspect of the work is that the testing was done at high strain-rates and at temperatures within 5 K of the solidus. The results indicated that the strength was maintained up to near solidus temperatures, with no dramatic strength reduction being observed. There was however, a distinct change in the slope observed with the 7449 results around 720 K. The experimental results were then fit to the Zener-Holloman equation, which describes the relationship between the material flow stress, temperature and strain-rates. The material microstructure of the hot compression test samples was analysed, and the averaged grain size was calculated to compare with friction stir weld nuggets. This will be used to infer the processing conditions that exist in the dynamically recrystallized weld nugget. Finally, a simple model was used to understand how processing conditions affected the deformation behaviour.