Hot deformation behavior of Ti-15-3 titanium alloy: a study using processing maps,activation energy map,and Zener–Hollomon parameter map

The hot deformation behavior of Ti-15-3 titanium alloy was investigated by hot compression tests conducted in the temperature range 850–1150 °C and strain rate range 0.001–10 s⁻¹. Using the flow stress data corrected for deformation heating, the activation energy map, processing maps and Zener–Hollomon parameter map were developed to determine the optimum hot-working parameters and to investigate the effects of strain rate and temperature on microstructural evolution of this material. The results show that the safe region for hot deformation occurs in the strain rate range 0.001–0.1 s⁻¹ over the entire temperature range investigated. In this region, the activation energy is ~240 ± 5 kJ/mol and the ln Z values vary in range of 13.9–21 s⁻¹. Stable flow is associated with dynamic recovery and dynamic recrystallization. Also, flow instabilities are observed in the form of localized slip bands and flow localization at strain rates higher than 0.1 s⁻¹ over a wide temperature range. The corresponding ln Z values are larger than 21 s⁻¹. The hot deformation characteristic of Ti-15-3 alloy predicted from the processing maps, activation energy map, and Zener–Hollomon parameter map agrees well with the results of microstructural observations.     

The strain rate and temperature dependence of microstructural evolution of Ti–15Mo–5Zr–3Al alloy

A compressive split-Hopkinson pressure bar apparatus and transmission electron microscopy (TEM) are used to investigate the deformation behaviour and microstructural evolution of Ti–15Mo–5Zr–3Al alloy deformed at strain rates ranging from 8 × 10² s⁻¹ to 8 × 10³ s⁻¹ and temperatures between 25 °C and 900 °C. In general, it is observed that the flow stress increases with increasing strain rate, but decreases with increasing temperature. The microstructural observations reveal that the strengthening effect evident in the deformed alloy is a result, primarily, of dislocations and the formation of α phase. The dislocation density increases with increasing strain rate, but decreases with increasing temperature. Additionally, the square root of the dislocation density varies linearly with the flow stress. The amount of α phase increases with increasing temperature below the β transus temperature. The maximum amount of α phase is formed at a temperature of 700 °C and results in the minimum fracture strain under the current loading conditions.     

Characterization of dynamic recrystallisation in as-homogenized Mg–Zn–Y–Zr alloy using processing map

The hot working behavior of a as-homogenized Mg–Zn–Y–Zr alloy has been investigated in the temperature range 200–400°C and strain rate range 0.0015–7.5 s⁻¹ using processing map. The power dissipation map reveals that a domain of dynamic recrystallisation (DRX) in the temperature range 300–400°C and strain rate range 0.0015–0.15 s⁻¹, with its peak efficiency of 38% at 350°C and 0.0015 s⁻¹, which are the optimum hot working parameters. The apparent activation energy in the hot deformation process is 148 ± 3 KJ/mol that is larger than that of ZK60 alloy because of the obstruction of Y atoms for diffusion. DRX model indicates that DRX of Mg–Zn–Y–Zr alloy is controlled by the rate of nucleation, which is lower one order of magnitude than growth. And the rate of nucleation depends on the process of mechanical recovery by cross-slip of screw dislocations.     

Optimizing the hot-forging process parameters for connecting rods made of PM titanium alloy

In order to optimize the processing parameters of a new low-cost titanium alloy connecting rod made of powder forging, the deformation behavior of an α + β type Ti–1.5Fe–2.25Mo (wt%) alloy produced by elemental powder metallurgy (PM) route was studied using isothermal compression tests. The constitutive equations and a processing map were established to characterize the flow behavior and predict the optimum deformation parameters. The calculated apparent activation energy was 257.73 kJ/mol for deformation in the α + β phase region and 378.01 kJ/mol in the β phase region. Two deformation mechanism domains were found: α + β → β phase transformation and dynamic recrystallization. The results show that the optimum deformation parameters for the present alloy are (700–800 °C, 10^−1.7–1 s⁻¹) and (800–900 °C, 10⁻²–10 s⁻¹). Based on these results, a finite element method (FEM) simulation of the hot-forming of a connecting rod was conducted, and the simulated results have been successfully used in an industrial forging of the connecting rod.     

Hot deformation of AA6082-T4 aluminum alloy

High-temperature tensile deformation of 6082-T4 Al alloy was conducted in the range of 623–773 K at various strain rates in the range of 5 × 10⁻⁵ to 2 × 10⁻² s⁻¹. Stress dependence of the strain rate revealed a stress exponent, n of 7 throughout the ranges of temperatures and strain rates tested. This stress exponent is higher than what is usually observed in Al–Mg alloys under similar experimental conditions, which implies the presence of threshold stress. This behavior results from dislocation interaction with second phase particles (Mg₂Si). The experimental threshold stress values were calculated, based on the finding that creep rate is viscous glide controlled, based on creep tests conducted on binary Al–1Mg at 673 K, that gave n a value of 3. The threshold stress (σ _o) values were seen to decrease exponentially with temperature. The apparent activation energy for 6082-T4 was calculated to be about 245 kJ mol⁻¹, which is higher than the activation energy for self-diffusion in Al (Q _d = 143 kJ mol⁻¹) and for the diffusion of Mg in Al (115–130 kJ mol⁻¹). By incorporating the threshold stress in the analysis, the true activation energy was calculated to be about 107 kJ mol⁻¹. Analysis of strain rate dependence in terms of the effective stress (σ − σ _o) using normalized parameters, revealed a single type of deformation behavior. A plot of normalized strain rate () versus normalized effective stress (σ − σ _o)/G, on a double logarithmic scale, gave an n value of 3. Ehab A. El-Danaf—on leave from the Department of Mechanical Design and Production, College of Engineering, Cairo University, Egypt.     

Deformation behavior of an Al–Cu–Mg–Mn–Zr alloy during hot compression

Deformation behavior of an Al–Cu–Mg–Mn–Zr alloy during hot compression was characterized in present work by high-temperature testing and transmission electron microscope (TEM) studies. The true stress–true strain curves exhibited a peak stress at a critical stain. The peak stress decreased with increasing deformation temperature and decreasing strain rate, which can be described by Zener–Hollomon (Z) parameter in hyperbolic sine function with the deformation activation energy 277.8 kJ/mol. The processing map revealed the existence of an optimum hot-working regime between 390 and 420 °C, under strain rates ranging from 0.1 to 1 s⁻¹. The main softening mechanism of the alloy was dynamic recovery at high lnZ value; continuous dynamic recrystallization (DRX) occurred as deformed at low lnZ value. The dynamic precipitation of Al₃Zr and Al₂₀Cu₂Mn₃ dispersoids during hot deformation restrained DRX and increased the hot deformation activation energy of the alloy.     

Creep behavior of AZ31 magnesium alloy in low temperature range between 423 K and 473 K

The deformation behavior of coarse-grained AZ31 magnesium alloy was examined in creep at low temperatures below 0.5 T _m and low strain rates below 5 × 10⁻⁴ s⁻¹. The creep test was conducted in the temperature range between 423 and 473 K (0.46–0.51 T _m) under various constant stresses covering the strain rate range 5 × 10⁻⁸ s⁻¹–5 × 10⁻⁴ s⁻¹. All of the creep curves exhibited two types depending on stress level. At low stress (σ/G < 4 × 10³), the creep curve was typical of class I behavior. However, at high stresses (σ/G > 4 × 10³), the creep curve was typical of class II. At the low stress level, deformation could be well described by solute drag creep whereas at the high stress level, deformation could be well described by dislocation climb creep associated with pipe diffusion or lattice diffusion. The transition of deformation mechanism from solute drag creep to dislocation climb creep, on the other hand, could be explained in terms of solute-atmosphere-breakaway concept.     

Hot working of Ti-17 titanium alloy with lamellar starting structure using 3-D processing maps

Isothermal compression of Ti-17 titanium alloy with lamellar starting structure at the deformation temperatures ranging from 780 °C to 860 °C, the strain rates ranging from 0.001 to 10 s⁻¹, and the height reductions ranging from 15% to 75% with an interval 15% were carried out. Based on experimental results, 3-D processing maps including strain were developed and used to identify various microstructural mechanisms and distinguish the safe and unsafe domains. The processing maps exhibit two maximum power dissipation efficiency domains and dynamic globularization takes place in this two domains. The first domain occurs at 800–860 °C and at strain rates lower than 0.01 s⁻¹, and the second occurs at 780–800 °C and at strain rates lower than 0.01 s⁻¹. With the increasing of the strains, the values of maximum power dissipation efficiency in this two domains increase. One flow instability domain due to adiabatic shear bands and lamellar kinking occurs at strain rates higher than 0.487 s⁻¹, lower temperature, and higher strain above 0.2. The instability deformation region increases with increasing strain, strain rate, and decreasing temperature.     

Constitutive modeling for hot deformation behavior of ZA27 alloy

The hot deformation behavior of ZA27 alloy was investigated in the temperature range of 473–523 K with the strain rates in the range of 0.01–5 s⁻¹ and the height reduction of 60 % on Gleeble-1500 thermo mechanical simulator. Based on the experimental results, constitutive equations incorporating the effects of temperature, strain rate, and strain have been developed to model the hot deformation behavior of ZA27 alloy. Material constants, α, n, ln A, and activation energy Q in the constitutive equations were calculated as a function of strain. The results showed that the stress–strain curves of ZA27 alloy predicted by the constitutive equations are in good agreement with experimental results, which validates the efficiency of the constitutive equations in describing the hot deformation behavior of the material.     

Processing maps for Fe–24Ni–11Cr–3Ti–1Mo superalloy

Hot deformation characteristics of a Fe-base superalloy were studied at various temperatures from 1000–1200°C under strain rates from 0·001–1 s^− 1 using hot compression tests. Processing maps for hot working are developed on the basis of the variations of efficiency of power dissipation with temperature and strain rate and interpreted by a dynamic materials model. Hot deformation equation was given to characterize the dependence of peak stress on deformation temperature and strain rate. Hot deformation apparent activation energy of the Fe–24Ni–11Cr–1Mo–3Ti superalloy was determined to be about 499 kJ/mol. The processing maps obtained in a strain range of 0·1–0·7 were essentially similar, indicating that strain has no significant influence on it. The processing maps exhibited a clear domain with a maximum of about 40–48% at about 1150°C and 0·001 s^− 1.     

Rate-dependent deformation of Sn–3.5Ag lead-free solder

Compression experiments on bulk Sn-3.5Ag lead-free solder specimens have been carried out to help formulate the material constitutive behaviour of this alloy using the concept of an evolving internal stress. Tests covered the temperature range 0–125 °C and fixed strain rates between 3 × 10⁻⁷–3 × 10⁻³ s⁻¹. Flow behaviour was found to be compatible with that for a deforming a tin-rich matrix (stress exponent n = 7, activation energy Q = 46.7 kJ/mol) in which the external applied stress is reduced by an internal back stress due to the presence of precipitate phase particles. Stress–strain curves have been satisfactorily modelled using rate equations incorporating linear hardening and diffusion-controlled recovery. Comparison with supplementary tension and creep experiments, and with data from other researchers, indicates that inconsistencies in reported flow behaviour is most likely to be due to variations in initial microstructure rather than the nature of the applied loading.     

Prediction of hot deformation behavior of Al–5.9%Cu–0.5%Mg alloys with trace additions of Sn

High temperature deformation behavior of Al–5.9wt%Cu–0.5wt%Mg alloys containing trace amounts (from 0 to 0.1 wt%) of Sn was studied by hot compression tests conducted at various temperatures and strain rates. The peak flow stress of the alloys increased with increase in strain rate and decrease in deformation temperature. The peak stress could be correlated with temperature and strain rate by a suitable hyperbolic-sine constitutive equation. The activation energy for hot deformation of the alloy without Sn content was observed to be 183.4 kJ mol⁻¹ which increased to 225.5 kJ mol⁻¹ due to 0.08 wt% of Sn addition. The Zener-Hollomon parameter (Z) was determined at various deforming conditions. The tendency of dynamic recrystallization increased with low Z values, corresponding to low strain rate and high temperature. The peak flow stresses at various processing conditions have been predicted by the constitutive modeling and correlated with the experimental results with fairly good accuracy. It was possible to predict 80, 75, 100, 100, 90, and 85% of the peak stress values within an error less than ±13%, for the investigated alloys. With addition of Sn content >0.04 wt%, peak flow stress increased significantly for all strain rate and temperature combinations. Scanning electron microscope revealed two types of second phases at the grain boundary of the undeformed alloy matrix, one being an Al–Cu–Si–Fe–Mn phase while the other identified as CuAl₂. The high strength and flow stress value of the alloy with 0.06 wt% of Sn content, may be attributed to the variation in amount, composition, and morphology of the Al–Cu–Si–Fe–Mn phase, as well as to the lower value of activation energy for precipitation reaction, as revealed from differential scanning calorimetric studies.     

Compressive deformation behavior of Al 2024 alloy using 2D and 4D processing maps

The hot deformation behavior of Al 2024 was studied by isothermal hot compression tests in the temperature range of 250–500 °C and strain rate range of 10⁻³ to 10² s⁻¹ in a computer-controlled 50 kN servo-hydraulic universal testing machine (UTM). The results show that the flow stress of Al 2024 alloy increases with strain rate and decreases after a peak value, indicating dynamic recovery and recrystallization. The processing map exhibits two domains of optimum efficiency for hot deformation at different strains, including the low strain rate domain at 500 °C and between 10⁻² and 10⁻¹ s⁻¹ and the high strain rate domain in 250 and 300 °C in the strain rate range of 10¹ to 10² s⁻¹. An attempt has been made in this article to generate a new hybrid 4D process map which illustrates contours of power dissipation and instability in the 3D space of strain rate, temperature, and strain.     

Fabrication of dense β-calcium orthophosphate with submicrometer-sized grains and its high-temperature superplastic deformation

High-density β-calcium orthophosphate (β-Ca₃(PO₄)₂, also called β-tricalcium phosphate: β-TCP) ceramics with submicrometer-sized grains were fabricated using a pulse-current pressure firing route. The maximum relative density of the β-TCP compacts was 98.7% at 1050 °C and this was accompanied by a translucent appearance. The mean grain size of the β-TCP compacts increased slightly with temperature to reach 0.78 μm at 1000 °C. However, upon further increasing the firing temperature to 1050 °C the mean grain size increased significantly to 1.6 μm. The extent of plastic deformation during tensile testing was examined at temperatures between 900 and 1100 °C using a strain rate in the range 9.26 × 10⁻⁵ to 4.44 × 10⁻⁴ s⁻¹. The maximum tensile strain achieved was 145% for a test temperature of 1000 °C and strain rate of 1.48 × 10⁻⁴ s⁻¹ and this was attributed to the relatively high density and small grain size.     

Diffusion coefficient of Fe<Superscript>2+</Superscript> in single-crystal ZnSe

The diffusion coefficient of Fe in single-crystal ZnSe has been measured in the temperature range 886–995°C. The 995°C diffusion coefficient is (47 ± 5) × 10⁻¹¹ cm²/s, and the average activation energy for Fe diffusion is 2.9 ± 0.3 eV.     

Superplastic behavior of coarse-grained Al–Mg–Zn alloys

In the present study, the superplastic behavior of five Al–Mg–Zn alloys in coarse grain size condition has been studied. The alloys were melted, cast into ingots and hot rolled. The grain size of the rolled samples was 69, 45, 40, 30 and 35 μm. Tensile test specimens were machined from the hot rolled plate in the rolling direction. Strain-rate-change (SCR) tests at temperatures between 300 and 450 °C and strain rates between 1 × 10⁻⁴ and 1 × 10⁻¹ s⁻¹ were carried out to determine the strain rate sensitivity of the flow stress. Finally, elongation-to-failure tests were conducted at those temperatures and strain rates, where the alloys showed high strain rate sensitivity. A maximal elongation of 400% was obtained for the 3.89 wt.% Zn alloy. The results are explained in terms of solute drag creep as the principal deformation mechanism.     

Quasi-static and dynamic compressive behaviour of poly(methyl methacrylate) and polystyrene at temperatures from 293 K to 363 K

Flow stress, Young’s Modulus, energy and strain of fracture of poly(methyl methacrylate) (PMMA) and polystyrene (PS) were studied under compressive loading at strain rates of 10⁻⁴–10 s⁻¹ and temperatures from 293 K to temperatures ∼20 K below T _g. It was found that the energy of fracture shows an increase in the quasi-static strain rate (10⁻⁴–10⁻³ s⁻¹) region and becomes constant in the low strain rate (10⁻²–10 s⁻¹) region, while the strain of fracture shows a slow decrease with rate over the strain rate range tested. The activation energies and volumes of PMMA and PS at yield stress, 20% and 30% strain were evaluated using Eyring’s theory of viscous flow. ΔG was found to be constant for all strain rates and strains for both PMMA and PS. The activation volume for both materials increased as a function of strain.     

Superplastic deformation of sheet test pieces machined from Ti-6Al-4V bar

Sheet tensile test pieces were machined in three orientations from edge textured Ti-6Al-4V bar and tested at temperatures in the range 800 to 975‡ C and at strain rates of 3 × 10⁻⁴ and 1.5×10⁻³ sec⁻¹. Bands of contiguous alpha grains aligned in the rolling direction caused local variations in the flow stress, strain to necking, strain rate sensitivity, plastic strain ratio values and surface roughness. Texture effects were only detected at the lowest test temperature (800‡C) and highest strain rate (1.5×10⁻³ sec⁻¹).     

Effects of dynamic strain aging on mechanical properties of SA508 class 3 reactor pressure vessel steel

An as-received reactor pressure vessel (RPV) steel SA508 class 3 (SA508 Cl.3) has been subjected to uniaxial tension tests in the strain-rate range of 6.67 × 10⁻⁵ s⁻¹ to 1.2 × 10⁻² s⁻¹ and the temperature range of 298 K to 673 K to investigate the effects of temperature and strain rate on its mechanical properties. It was found that the region of dynamic strain aging (DSA) was in the temperature range of 523–623 K at a strain rate of 1.2 × 10⁻³ s⁻¹, 473–573 K at 1.2 × 10⁻⁴ s⁻¹, and 473–573 K at 6.67 × 10⁻⁵ s⁻¹, respectively. Serrated stress–strain behaviors, predominately consisting of type A, B, and C, have been observed in these temperatures and strain-rate ranges. The solutes responsible for DSA have been identified to be carbon and nitrogen, and nitrogen atoms play a more important role. The relative DSA mechanisms for this RPV steel are discussed.     

Tensile deformation of a Mg–2.54Nd–0.26Zn–0.32Zr alloy at elevated temperature

The engineering stress versus engineering strain curves for a Mg–2.54Nd–0.26Zn–0.32Zr cast alloy were measured by Gleeble-1500D thermo-simulation machine in the temperature range of room temperature to 400 °C at initial strain rates of 10⁻⁴–10⁻² s⁻¹. The effects of strain rate on stress, elongation to facture, and section shrinkage were analyzed. The fractograph morphologies were investigated by using SEM. It was found that strain rate has little effect on engineering stress for the Mg–2.54Nd–0.26Zn–0.32Zr alloy when tested at below 250 °C. When tested at above 250 °C, low strain rate resulted in decreased engineering stress, increased elongation to fracture, and section shrinkage. The fracture mode is cleavage fracture with elongated dimple below 250 °C and changes to typical ductile failure when tested above 250 °C.