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1.
《Materials Science & Technology》2013,29(9):1416-1421
AbstractMicrostructure evolution of the homogenised ZK40 magnesium alloy was investigated during compression in the temperature range of 250–400°C and at the strain rate range of 0·01–50 s?1. At a higher strain rate (?10 s?1), dynamic recrystallisation developed extensively at grain boundaries and twins, resulting in a more homogeneous microstructure than the other conditions. The hot deformation characteristics of ZK40 exhibited an abnormal relationship with the strain rate, i.e., the hot workability increased with increasing the strain rate. However, the dynamic recrystallisation grain size was almost the same with increasing the temperature at the strain rate of 10 s?1, while it increased obviously at the strain rates of 20 and 50 s?1. Therefore, hot deformation at the strain rate of 10 s?1 and temperature range of 250–400°C was desirable and feasible for the ZK40 alloy. 相似文献
2.
《Materials Science & Technology》2013,29(12):1429-1438
AbstractMicrostructural evolution and flow behaviour during hot compression of twin roll cast ZK60 magnesium alloy were characterised by employing deformation temperatures of 300, 350 and 400°C and strain rate ranging from 10?3 to 100 s?1. When compressed at 10?3 s?1, all stress–strain curves at different temperatures (300, 350 and 400°C) showed a flow softening behaviour due to active dynamic recrystallisation. When compressed at 10?2 s?1 and elevated temperatures (300, 350 and 400°C), all stress–strain curves showed a flow stress drop after peak stress due to twinning for 300 and 350°C deformation and recrystallisation for 400°C deformation. The balance between shear deformation and recrystallisation resulted in a steady flow behaviour after the true strain reached 0·22. When strain rate increased to 10?1 s?1, a small fraction of dynamic recrystallisation in shear deformation region was responsible for slight flow softening behaviour during compression. A flow hardening appeared due to basal and non-basal slips when deformed at 100 s?1. It is suggested that the flow behaviour during hot compression of twin roll cast ZK60 alloy depends on the separating effect or combined effects of shear deformation, twinning and recrystallisation. 相似文献
3.
《Materials Science & Technology》2013,29(7):607-609
AbstractThe effect of temperature and strain rate on the 0·2% yield strength, ultimate tensile strength, and percentage elongation of M250 maraging steel was investigated under uniaxial tensile conditions in the temperature range from 25 (room temperature) to 550°C and strain rate range 10?4–10?1 S?l. Up to 400°C the steel shows essentially strain rate insensitive behaviour with a gradual decrease in the 0·2% yield strength and ultimate tensile strength. The elongation remains constant at all strain rates up to 300°C. Fractographic analysis indicates that the increasing strain rate induces strain constraint resulting in an increased dimple size. An elongated structure was observed at temperatures above 400°C. X-ray diffraction reveals the presence of reverted austenite in the specimens tested at 550°C.MST/3263 相似文献
4.
《Materials Science & Technology》2013,29(9):705-716
AbstractThe characteristics of the hot deformation of Zr–2·5Nb (wt-%) in the temperature range 650–950°C and in the strain rate range 0·001–100 s?1 have been studied using hot compression testing. Two different preform microstructures: equiaxed (α+β) and β transformed, have been investigated. For this study, the approach of processing maps has been adopted and their interpretation carried out using the dynamic materials model. The efficiency of power dissipation given by [2m/(m+1)], where m is the strain rate sensitivity, is plotted as a function of temperature and strain rate to obtain a processing map. A domain of dynamic recrystallisation has been identified in the maps of equiaxed (α+β) and β transformed preforms. In the case of equiaxed (α+β), the stress–strain curves are steady state and the dynamic recrystallisation domain in the map occurs with a peak efficiency of 45% at 850°C and 0·001 s?1. On the other hand, the β transformed preform exhibits stress–strain curves with continuous flow softening. The corresponding processing map shows a domain of dynamic recrystallisation occurring by the shearing of α platelets followed by globularisation with a peak efficiency of 54% at 750°C and 0·001 s?1. The characteristics of dynamic recrystallisation are analysed on the basis of a simple model which considers the rates of nucleation and growth of recrystallised grains. Calculations show that these two rates are nearly equal and that the nucleation of dynamic recrystallisation is essentially controlled by mechanical recovery involving the cross-slip of screw dislocations. Analysis of flow instabilities using a continuum criterion revealed that Zr–2·5Nb exhibits flow localisation at temperatures lower than 700°C and strain rates higher than 1 s?1.MST/3103 相似文献
5.
《Materials Science & Technology》2013,29(1):453-457
AbstractThe hot deformation behaviour and microstructural evolution in Ti–6Al–2Zr–1Mo–1V alloys have been studied using isothermal hot compression tests. The processing map was developed at a true strain of 0·7 in the temperature range 750–950°C and strain rate range 0·001–10 s?1. The corresponding microstructures were characterised by means of a metallurgical microscope. Globularisation of lamellae occurring to a greater extent in the range 780–880°C and 0·001–0·01 s?1 had a peak power dissipation efficiency of 58% at about 850°C and 0·001 s?1. The specimens deformed in 750–880°C and 0·01–10 s?1 showed an instability region of processing map, whereas the specimens deformed in 880–950°C and 1–10 s?1 indicated three kinds of flow instabilities, i.e. macro shear cracks, prior beta boundary cracks and flow localisation bands. 相似文献
6.
《Materials Science & Technology》2013,29(3):300-308
AbstractThe deformation behaviour of a 20Cr–25Ni superaustenitic stainless steel (SASS) with initial microstructure of columnar dendrites was investigated using the hot compression method at temperatures of 1000–1200°C and strain rates of 0·01–10 s?1. It was found that the flow stress was strongly dependent on the applied temperature and strain rate. The constitutive equation relating to the flow stress, temperature and stain rate was proposed for hot deformation of this material, and the apparent activation energy of deformation was calculated to be 516·7 kJ mol?1. Based on the dynamic materials model and the Murty’s instability criterion, the variations of dissipation efficiency and instability factor with processing parameters were studied. The processing map, combined with the instability map and the dissipation map, was constructed to demonstrate the relationship between hot workability and microstructural evolution. The stability region for hot processing was inferred accurately from the map. The optimum hot working domains were identified in the respective ranges of the temperature and the strain rate of 1025–1120°C and 0·01–0·03 s?1 or 1140–1200°C and 0·08–1 s?1, where the material produced many more equiaxed recrystallised grains. Moreover, instability regimes that should be avoided in the actual working were also identified by the processing map. The corresponding instability was associated with localised flow, adiabatic shear band, microcracking and free surface cracks. 相似文献
7.
《Materials Science & Technology》2013,29(6):1067-1072
AbstractThe 7075 aluminium alloy is one of the most important engineering alloys utilised extensively in aircraft and transportation industries due to its high specific strength. In the present research, the flow behaviour of this alloy has been investigated using hot compression test at strain rates of 0·001, 0·01, 0·1 and 1 s?1 and temperatures of 350, 400 and 450°C. The results reveal that dynamic softening occurred in these temperatures and strain rates. The activation energy, strain rate sensitivity and two constitutive equations (hyperbolic sine law and the power law) are derived from the results. It is shown that the hyperbolic sine law has a better agreement with the experimental results. 相似文献
8.
《Materials Science & Technology》2013,29(6):617-624
AbstractIn this, the second of four papers devoted to the isothermal forging of intermetallic compounds, the Ti3 Al based alloy Superalpha-2 has been deformed in compression at constant strain rate, over temperature and strain rate ranges of 900–1050°C and 0·0003–0·035 s-1, respectively. Calculation of the material property parameters suggests that this material deforms via dynamic recrystallisation of the B2 phase. Microstructural examination has shown that isothermal forging generates non-equilibrium microstructures. Deformation modelling has been successful in predicting the forging behaviour. Finally, the possibility of explosive grain growth immediately after forging raises questions as to whether the mechanical properties of this material can usefully be controlled by isothermal forging. 相似文献
9.
《Materials Science & Technology》2013,29(10):907-914
AbstractThe influence of C on hot ductility in the temperature range 600–1000°C has been examined for three C contents (0·1, 0·4, and 0·75 wt-%). Using a strain rate of 3 × 10?3 s?1, tensile specimens were heated to 1330°C before cooling to the test temperature. For the 0·4%C steel, two further strain rates of 3 × 10?2 and 3 × 10?4 s?1 were examined. At the strain rate of 3 × 10?3 s?1, increasing the C content shifted the low ductility trough to lower temperatures in accordance with the trough being controlled by the γ–α transformation. Thin films of the softer deformation induced ferrite formed around the γ grain boundaries and allowed strain concentration to occur. Recovery to higher ductility at high temperatures occurred when these films could no longer form (i.e. above Ae3) and dynamic recrystallisation was possible. The thin films of deformation induced ferrite suppressed dynamic recrystallisation in these coarse grained steels when tested at low strain rates. Recovery of ductility at the low temperature side of the trough in the 0·1%C steel corresponded to the presence of a large volume fraction of ferrite, this being the more ductile phase. For the 0·4%C steel decreasing the strain rate to 3 × 10?4 s?1 resulted in a very wide trough – extended to both higher and lower temperatures compared with the other strain rates. The high temperature extension was due to grain boundary sliding in the γ. Recovery of the ductility only occurred when dynamic recrystallisation was possible and this occurred at high temperatures. At the low temperature end, thin films of deformation induced ferrite were present and recovery did not occur until the temperature was sufficiently low to prevent strain concentration from occurring at the boundaries. Of the two intergranular modes of failure grain boundary sliding produced superior ductility. At the higher strain rates there was less grain boundary sliding, which led to a lower temperature for dynamic recrystallisation. Higher strain rates also increased the rate of work hardening of deformation induced ferrite, reducing the strain concentration at the boundaries. Ductility started to recover immediately below Ae3, resulting in very narrow troughs. Finally, it was shown that the 2% strain that occurs during the straightening operation in continuous casting is sufficient to form deformation induced ferrite in steel containing 0·1%C.MST/1809 相似文献
10.
《Materials Science & Technology》2013,29(5):377-383
AbstractThe hot deformation characteristics of IN 600 nickel alloy are studied using hot compression testing in the temperature range 850–1200°C and strain rate range 0·001–100 s?l. A processing map for hot working is developed on the basis of the data obtained, using the principles of dynamic materials modelling. The map exhibits a single domain with a peak efficiency of power dissipation of 48% occurring at 1200°C and 0·2 s?1, at which the material undergoes dynamic recrystallisation (DRX). These are the optimum conditions for hot working of IN 600. At strain rates higher than 1 s?1, the material exhibits flow localisation and its microstructure consists of localised bands of fine recrystallised grains. The presence of iron in the Ni–Cr alloy narrows the DRX domain owing to a higher temperature required for carbide dissolution, which is essential for the occurrence of DRX. The efficiency of DRX in Ni–Cr is, however, enhanced by iron addition.MST/1856 相似文献
11.
《Materials Science & Technology》2013,29(7):1149-1156
AbstractIn the present work, the formation of ultrafine grained ferrite has been studied by applying suitable thermomechanical treatment. A high amount of deformation (~80%) at varying strain rates (0·01–10 s?1) was applied in the temperature range of Ar3 to Ac3 followed by water quenching. This treatment resulted in a two-phase ferrite–martensite microstructure as compared to fully martensite structure after quenching without deformation. The formation of ultrafine ferrite (?3 μm) during deformation was favourable at a lower temperature and a slower strain rate. A maximum ~50% ferrite formed during deformation at 780°C with a strain rate of 0·01 s?1. Experimental rolling with a high strain (~1·3) with finish rolling temperature just above Ar3 (~750°C) resulted in fine ferrite–pearlite of ?3 μm, and the properties showed a high value of strength as compared to steels rolled in a conventional way. Dual phase microstructure (ferrite and martensite) was produced after partial austenisation to 780°C followed by quenching in water, and this resulted in an excellent combination of properties (high ultimate tensile strength, low yield strength/ultimate tensile strength, high elongation and high n values). 相似文献
12.
C. Dharmendra K. P. Rao Y. V. R. K. Prasad N. Hort K. U. Kainer 《Journal of Materials Science》2013,48(15):5236-5246
Hot deformation behavior of as-cast TX32 (Mg–3Sn–2Ca) alloy has been studied in uniaxial compression in the temperature and strain rate ranges of 300–500 °C and 0.0003–10 s?1 with a view to characterize the evolution of microstructure and texture. On the basis of the temperature and strain rate dependence of flow stress, a processing map has been developed and the crystallographic orientation information on the deformed specimens has been obtained from electron back scatter diffraction micro-texture analysis. The processing map revealed two domains of dynamic recrystallization in the temperature and strain rate ranges of (1) 300–350 °C and 0.0003–0.001 s?1 and (2) 390–500 °C and 0.005–0.6 s?1. Specimens deformed at peak in Domain 1 exhibited maximum intensity of basal poles located at about 35–45° to the compression axis while those deformed at peak in Domain 2 showed near-random texture. Schmid factor analysis of different slip systems operating in the two domains suggests that basal + prismatic slip causes the basal texture in Domain 1 while second-order pyramidal slip randomizes the texture in Domain 2. 相似文献
13.
《Materials Science & Technology》2013,29(9):908-912
AbstractThe characteristics of serrated yielding (the Portevin–Le Chatelier effect) in a Nb–V dual phase steel have been studied in the temperature range 85–210°C at strain rates between 1·2 × 10?5 and 1·2 × 10?2 s?1. Serrated yielding was found to initiate only after a critical strain ?c was reached. The strain between two successive serrations ??s increases almost linearly with strain, while the stress drop ?σc increases with strain up to ?σmax, then decreases. The exponent β in the mobile dislocation density–plastic strain relationship (ρm= ?β) is 1·09 in the temperature range 85–140°C and 1·34 in the temperature range 140–210°C. The results also indicate that in the same temperature ranges there are two values of activation energy for type A serrations, i.e. 79 and 119 kJ mol?1 respectively. The results are discussed in terms of substitutional–interstitial solute atom interaction and changes of concentration of interstitial atoms.MST/934 相似文献
14.
S. Gall M. Huppmann H. M. Mayer S. Müller W. Reimers 《Journal of Materials Science》2013,48(1):473-480
The plastic deformation and recrystallization behavior of the commercial magnesium alloys AZ31 and ME21 were analyzed in a wide temperature range. Using the conventional hyperbolic sine equation the flow stress dependence on temperature and strain rate was modeled. The activation energy for plastic deformation significantly increased with increasing temperature and delivered values above 180 kJmol?1 for both alloys in the very high-temperature regime (400–550 °C). At lower temperatures (250–400 °C) the activation energy of the AZ31 alloy was approximately 108 kJmol?1 considering the peak stress as well as 120 kJmol?1 considering the flow stress at a strain of 0.5. The stress exponent varied in a range between 4.5 and 6.5. During the high-temperature compression tests a partial recrystallized microstructure was formed, which was distinctly different in AZ31 compared to ME21 due to the different onset of dynamic recrystallization (DRX) mechanisms. 相似文献
15.
《Materials Science & Technology》2013,29(9):1088-1094
AbstractThe authors present a study on the hot formability of 7020 aluminium alloy. Isothermal hot compression tests of solid cylindrical specimens were performed in the temperature range of 300–550°C and the strain rate range of 0·001–10 s–1. Stress–strain curves obtained from the experiment data are fitted using the Sellars–Tegart constitutive equation to obtain the constitutive parameters. Using the dynamic material model, the authors develop a processing map based on the flow stress data. The map shows that the parameters suitable for hot working are a temperature range of 450–550°C and a strain rate range of 0·001–0·1 s–1. This parameter range is where the efficiency of power dissipation is above 27% and where dynamic recrystallisation occurs. Unstable regions to be avoided in hot forming are deduced from an instability condition. The processing map is validated by comparing the microstructures of deformed compression specimens. 相似文献
16.
《Materials Science & Technology》2013,29(4):501-504
AbstractThe behaviour of 17-4 precipitation hardening (PH) stainless steel was studied using the hot compression test at temperatures of 950–1150°C with strain rates of 0·001–10 s?1. The stress–strain curves were plotted by considering the effect of friction. The work hardening rate versus stress curves were used to reveal whether or not dynamic recrystallisation (DRX) occurred. Using the constitutive equations, the activation energy of hot working for 17-4 PH stainless steel was determined as 337 kJ mol?1. The effect of Zener–Hollomon parameter Z on the peak stress and strain was studied using the power law relation. The normalised critical stress and strain for initiation of DRX were found to be 0·89 and 0·47 respectively. Moreover, these behaviours were compared to other steels. 相似文献
17.
《Materials Science & Technology》2013,29(2):136-144
AbstractSpecimens of wrought Waspaloy have been reheated to above the γ' solvus temperature and tested in plane-strain compression at constant equivalent tensile strain rates in the range 0.5–50 s?1, and at initial test temperatures in the range 960–1070°C. The majority of tests were conducted with the tools and test environment at 850°C. Dynamic recrystallization was observed under all test conditions, but was only complete by the strain limit of 2·7 in tests at the highest temperatures. Static (metadynamic) recrystallization initiated rapidly after deformation. Flow stress, either at the peak or at a constant strain, is related exponentially to strain rate, and gives an activation energy of 475 kJ mol?1 when related to the instantaneous temperature, which changed rapidly during deformation. For practical purposes, the stress-strain-strain-rate-temperature relationships may be treated as equations of state.MST/96 相似文献
18.
《Materials Science & Technology》2013,29(8):944-954
AbstractFatigue tests under constant amplitude load were conducted on compact tension specimens of SA533B3 steels with four levels of sulphur content at different temperatures. A modified capacitance type crack opening displacement (COD) gauge was shown to be suitable for fatigue crack length measurement at high temperatures. Test results obtained with different measurement techniques show good consistency. The observation that the Young's moduli measured at a strain rate of 4 × 10?3 s?1 for the SA533B3 steels at 150 and 300°C do not decrease with increasing temperature seems to be related to the presence of dynamic strain aging. The fatigue crack growth rates at 150 and 300°C are about two and half times slower than those tested at 400°C because dynamic strain aging prevails at 150 and 300°C. Fractographic examination results suggest that inclusions embedded in secondary cracks enhanced the fatigue crack initiation rather than the fatigue crack growth. 相似文献
19.
《Materials Science & Technology》2013,29(1):24-29
Abstract316LN is a type of austenitic stainless steel whose grain refinement only depends on hot deformation. The true stress–strain curves of 316LN were obtained by means of hot compression experiments conducted at a temperature range of 900–1200°C and at a strain rate range of 0·001–10 s?1. The influence of deformation parameters on the microstructure of 316LN was analysed. Both the constitutive equation for 316LN and the model of grain size after dynamic recrystallisation were established, and the effect of different deformation conditions on the microstructure was analysed. The results show that the suitable working region is the one with a relatively higher deformation temperature and a lower strain rate, in which the dynamic recrystallisation is finely conducted. Moreover, the working region that should be avoided during hot deformation was indicated. 相似文献
20.
《Materials Science & Technology》2013,29(12):1191-1199
AbstractTorsion tests at strain rates of 10?3, 0·16, and 1 s?1 and at temperatures between 850 and 1100°C have been carried out on an aluminium killed mild steel after either heating directly to the testing temperature or soaking for 30 min at 1200°C, then cooling the specimen to the testing temperature. During direct heating, a dispersion of small AlN particles was present and after soaking a coarser distribution of AlN particles was observed. Compared with the latter, the former microstructure seriously retarded the completion of dynamic recrystallisation. The effect of the two different particle distributions was examined for the following parameters: peak and steady state stress, peak strain, and dynamically recrystallised grain size. The retardation of completion of dynamic recrystallisation has the additional effect of impairing the hot ductility.MST/997 相似文献