Microstructure evolution and hot deformation behavior of Cu−3Ti−0.1Zr alloy with ultra-high strength

The hot compression deformation behavior of Cu–3Ti–0.1Zr alloy with the ultra-high strength and good electrical conductivity was investigated on a Gleeble–3500 thermal-mechanical simulator at temperatures from 700 to 850 °C with the strain rates between 0.001 and 1 s⁻¹. The results show that work hardening, dynamic recovery and dynamic recrystallization occur in the alloy during hot deformation. The hot compression constitutive equation at a true strain of 0.8 is constructed and the apparent activation energy of hot compression deformation Q is about 319.56 kJ/mol. The theoretic flow stress calculated by the constructed constitutive equation is consistent with the experimental result, and the hot processing maps are established based on the dynamic material model. The optimal hot deformation temperature range is between 775 and 850 °C and the strain rate range is between 0.001 and 0.01 s⁻¹.     

Hot working behavior of near alpha titanium alloy analyzed by mechanical testing and processing map

The hot deformation characteristics of the Ti−5.7Al−2.1Sn−3.9Zr−2Mo−0.1Si (Ti-6242S) alloy with an acicular starting microstructure were analyzed using processing map. The uniaxial hot compression tests were performed at temperatures ranging from 850 to 1000 °C and at strain rates of 0.001−1 s⁻¹. The developed processing map was used to determine the safe and unsafe deformation conditions of the alloy in association with the microstructural evolution by SEM and OM. It was recognized that the flow stress revealed differences in flow softening behavior by deformation at 1000 °C compared to the lower deformation temperatures, which was attributed to microstructural changes. The processing map developed for typical strain of 0.7 in two-phase field exhibited high efficiency value of power dissipation of about 55% at 950 °C and 0.001 s⁻¹, basically due to extensive globularization. An increase in strain rate and a decrease in temperature resulted in a decrease in globularization of α lamellae, while α lamellar kinking increased. Eventually, the instability domain of flow behavior was identified in the temperature range of 850−900 °C and at the strain rate higher than 0.01 s⁻¹ reflecting the flow localization and adiabatic shear banding. By considering the power efficiency domains and the microstructural observations, the deformation in the temperature range of 950−1000 °C and strain rate range of 0.001−0.01 s⁻¹ was desirable leading to high efficiencies. It was realized that (950 °C, 0.001 s⁻¹) was the optimum deformation condition for the alloy.     

Hot deformation behavior of novel imitation-gold copper alloy

The hot deformation behavior of a novel imitation-gold copper alloy was investigated with Gleeble–1500 thermo-mechanical simulator in the temperature range of 650–770 °C and strain rate range of 0.001–1.0 s^?1. The hot deformation constitutive equation was established and the thermal activation energy was obtained to be 249.60 kJ/mol. The processing map at a strain of 1.2 was developed. And there are two optimal regions in processing map, namely 650–680 °C, 0.001–0.01 s^?1 and 740–770 °C, 0.01–0.1 s^?1. Optical microscopy was employed to investigate the microstructure evolution of the alloy in the process of deformation. Recrystallized grains and twin crystals were found in microstructures of the hot deformed alloy.     

Cu-Ni-Si-P合金热变形行为及热加工图

采用高温等温压缩试验,对Cu?Ni?Si?P合金在应变速率0.01~5?1、变形温度600~800°C条件下的高温变形行为进行了研究,得出了该合金热压缩变形时的热变形激活能Q和本构方程。根据实验数据与热加工工艺参数构建了该合金的热加工图,利用热加工图对该合金在热变形过程中的热变形工艺参数进行了优化,并利用热加工图分析了该合金的高温组织变化。热变形过程中Cu?Ni?Si?P合金的流变应力随着变形温度的升高而降低,随着应变速率的提高而增大,该合金的动态再结晶温度为700°C。该合金热变形过程中的热变形激活能Q为485.6 kJ/mol。通过分析合金在应变为0.3和0.5时的热加工图得出该合金的安全加工区域的温度为750~800°C,应变速率为0.01~0.1 s?1。通过合金热变形过程中高温显微组织的观察,其组织规律很好地符合热加工图所预测的组织规律。     

High temperature deformation and processing map of a NiTi intermetallic alloy

The deformation behavior of a 49.8 Ni-50.2 Ti (at pct) alloy was investigated using the hot compression test in the temperature range of 700 °C–1100 °C, and strain rate of 0.001 s^?1 to 1 s^?1. The hot tensile test of the alloy was also considered to assist explaining the related deformation mechanism within the same temperature range and the strain rate of 0.1 s^?1. The processing map of the alloy was developed to evaluate the efficiency of hot deformation and to identify the instability regions of the flow. The peak efficiency of 24–28% was achieved at temperature range of 900 °C–1000 °C, and strain rates higher than 0.01 s^?1 in the processing map. The hot ductility and the deformation efficiency of the alloy exhibit almost similar variation with temperature, showing maximum at temperature range of 900 °C–1000 °C and minimum at 700 °C and 1100 °C. Besides, the minimum hot ductility lies in the instability regions of the processing map. The peak efficiency of 28% and microstructural analysis suggests that dynamic recovery (DRV) can occur during hot working of the alloy. At strain rates higher than 0.1 s^?1, the peak efficiency domain shifts from the temperature range of 850 °C–1000 °C to lower temperature range of 800 °C–950 °C which is desirable for hot working of the NiTi alloy. The regions of flow instability have been observed at high Z values and at low temperature of 700 °C and low strain rate of 0.001 s^?1. Further instability region has been found at temperature of 1000 °C and strain rates higher than 1 s^?1 and at temperature of 1100 °C and all range of strain rates.     

Hot deformation behavior and microstructural evolution of beta C titanium alloy in β phase field

The hot deformation behavior of beta C titanium alloy in β phase field was investigated by isothermal compression tests on a Gleeble–3800 thermomechanical simulator. The constitutive equation describing the hot deformation behavior was obtained and a processing map was established at the true strain of 0.7. The microstructure was characterized by optical microscopy (OM), scanning electron microscopy (SEM) and electron back-scattered diffraction (EBSD) technique. The results show that the flow stress increases with increasing strain rates, and decreases with increasing experimental temperatures. The calculated apparent activation energy (167 kJ/mol) is close to that of self-diffusion in β titanium. The processing map and microstructure observation exhibit a dynamic recrystallization domain in the temperature range of 900–1000 °C and strain rate range of 0.1–1 s⁻¹. An instability region exists when the strain rate is higher than 1.7 s⁻¹. The microstructure of beta C titanium alloy can be optimized by proper heat treatments after the deformation in the dynamic recrystallization domain.     

60NiTi合金的热压缩变形与显微组织演变（英文）

采用Gleeble-3500热模拟试验机对在变形温度500～650℃和应变速率0.001～1 s^-1条件下的60NiTi合金进行热压缩变形,分析其热变形行为和显微组织,建立变形本构模型,绘制热加工图。结果表明,当压缩温度升高或应变速率降低时,峰值应力减小。合金的热变形激活能为327.89 k J/mol,热加工工艺参数为变形温度600～650℃和应变速率0.005～0.05 s^-1。当变形温度升高时,合金的再结晶程度增大;当应变速率增大时,位错密度和孪晶数量增大,Ni₃Ti相易于聚集;Ni₃Ti析出相有利于诱发合金基体的动态再结晶。动态回复、动态再结晶和孪生是60NiTi合金热变形的主要机制。     

Characterization of mechanisms of hot deformation of as-cast nickel aluminide alloy

The hot deformation behavior of as-cast Ni₃Al alloy has been characterized on the basis of its flow stress variation obtained by isothermal constant true strain rate compression testing in the temperature range 1100–1250°C and strain rate range 0.001–10 s⁻¹. The mechanisms of hot working have been evaluated using four generations of materials modeling techniques, which included shape of stress–strain curves, kinetic analysis, processing maps and dynamical systems approach. The material exhibited a steady-state flow behavior at slower strain rates but flow softening associated sometimes with broad oscillations, was observed at higher strain rates. The flow stress data did not obey the kinetic rate equation over the entire regime of testing but a good fit has been obtained in the intermediate range of temperatures (1150–1200°C). In this range, a stress exponent value of 6.5 and an apparent activation energy of about 750 kJ/mol have been evaluated. Microstructural investigations have shown that the matrix γ′ phase undergoes dynamic recovery in the presence of harder γ colonies The processing maps revealed four different domains out of which three are interpreted to represent cracking processes. The fourth domain, which has a peak efficiency of about 44%, occurred at 1250°C/0.001 s⁻¹. Microstructural observations revealed that this domain represents dynamic recrystallization (DRX) of γ phase and is desirable for hot working the material. The material exhibits flow instabilities when deformed in the intermediate temperature regime at strain rates higher than 1 s⁻¹ and these are manifested as shear localization.     

Hot deformation mechanisms in Ti-5.5Al-1Fe alloy

The mechanisms of hot deformation in the alloy Ti-5.5Al-1Fe have been studied in the temperature range 750 to 1150 °C and with the true strain rate varying from 0.001 to 100 s⁻¹ by means of isothermal compression tests. At temperatures below β transus and low strain rates, the alloy exhibited steady-state flow behavior, while, at high strain rates, either continuous flow softening or work hardening followed by flow softening was observed. In the β region, the deformation behavior is characterized by steady-state behavior at low strain rates, yield drops at intermediate strain rates, and oscillations at high strain rates. The processing maps revealed two domains. (1) In the temperature range 750 to 1050 °C and at strain rates lower than 0.01 s⁻¹, the material exhibits fine-grained superplasticity. The apparent activation energy for superplastic deformation is estimated to be about 328 kJ/mole. The optimum conditions for superplasticity are 825 °C and 0.001 s⁻¹. (2) In the β region, a domain occurs at temperatures above 1100 °C and at strain rates from 0.001 to 0.1 s⁻¹ with its peak efficiency of 47% occurring at 1150 °C and 0.01 s¹. On the basis of kinetic analysis, tensile ductility, and grain size variation, this domain is interpreted to represent dynamic recrystallization (DRX) of β phase. The apparent activation energy for DRX is estimated to be 238 kJ/mole. The grain size (d) is linearly dependent on the Zener-Hollomon parameter (Z) per the equation

Superplastic behavior of a TiAl-based alloy

Superplastic behavior under the conditions of a temperature range from 850 to 1075°C and strain rates varying from 8×10⁻⁵ to 1×10⁻³ s⁻¹ was investigated for Ti–33Al–3Cr–0.5Mo (wt%) alloy with a very fine grain size obtained by the multi-step thermal mechanical treatment. The results show that the TiAl-based alloy with a hot-deformed fine grain size possesses good superplasticity. It exhibits a strain rate sensitivity coefficient of 0.9 at a strain rate of 3×10⁻⁵ s⁻¹ and temperature from 1000 to 1075°C. Moreover, the strain rate sensitivity coefficient is stable during the hot deformation, and a tensile elongation of 517% was obtained at 1075°C and a strain rate of 8×10⁻⁵ s⁻¹. The superplastic behavior of the present fine-grained TiAl-based alloy can be explained by the local strain hardening and high m value during the tensile deformation. Microstructure evolution in the superplastic deformation was also discussed.     

Hot workability of a NiTiCu shape memory alloy with acicular martensite phase based on processing maps

Hot deformation behavior and processing maps of Ni₄₅Ti₅₀Cu₅ (at.%) shape memory alloy (SMA), which possesses acicular martensite phase at room temperature, were investigated systematically based on isothermal compression tests at the temperatures ranging from 600 to 1000 °C and the strain rates ranging from 0.0005 to 0.5 s⁻¹. The flow stresses of the studied alloy were found to be dependent on the strain rate as well as the temperature. Processing maps at strains of 0.3, 0.6 and 0.9 were constructed on the basis of dynamic material model (DMM) theory by using the flow stresses obtained from compression tests. According to the processing maps, flow instability was found to mainly occur in the region with high strain rate and the scope of instability region was found to increase with the increase in the true strain. Based on the combination of processing map and microstructural observations, microstructural defects were found in the alloy samples deformed in the instability regions and the parameters suitable for hot working of the studied alloy were determined as the temperatures ranging from 750 to 850 °C and the strain rates ranging from 0.0005 to 0.001s⁻¹.     

Processing maps for hot working of a P/M iron aluminide alloy

The hot working behavior of a Fe–24 wt.% Al iron aluminide alloy processed by the powder metallurgy route has been studied in the temperature range 750–1150°C and strain rate range 0.001–100 s⁻¹ by establishing processing maps at different strains in the range 0.1–0.5. The features in the processing maps have changed with strain suggesting that the mechanisms of hot deformation are evolving with strain. Early in the deformation (strain of 0.1), the map exhibited a single domain with a peak efficiency of power dissipation of about 44% occurring at about 1100°C and a strain rate of about 0.03 s⁻¹. This domain represents dynamic recrystallization (DRX) of the initial material possibly causing a substantial grain refinement. With increasing strain, a bifurcation has occurred giving rise to two domains: (1) at strain rates lower than about 0.1 s⁻¹ and temperatures above 1000°C, superplastic deformation has occurred, and (2) at strain rates higher than about 10 s⁻¹ and temperatures above 1125°C, DRX has occurred. The material exhibited flow localization at lower temperatures and higher strain rates. On the basis of the processing maps, the optimum processing routes available for hot working of this material are outlined.     

Characterization of hot deformation and microstructure evolution of a new metastable β titanium alloy

The hot deformation characteristics of as-forged Ti?3.5Al?5Mo?6V?3Cr?2Sn?0.5Fe?0.1B?0.1C alloy within a temperature range from 750 to 910 °C and a strain rate range from 0.001 to 1 s^?1 were investigated by hot compression tests. The stress?strain curves show that the flow stress decreases with the increase of temperature and the decrease of strain rate. The microstructure is sensitive to deformation parameters. The dynamic recrystallization (DRX) grains appear while the temperature reaches 790 °C at a constant strain rate of 0.001 s^?1 and strain rate is not higher than 0.1 s^?1 at a constant temperature of 910 °C. The work-hardening rate θ is calculated and it is found that DRX prefers to happen at high temperature and low strain rate. The constitutive equation and processing map were obtained. The average activation energy of the alloy is 242.78 kJ/mol and there are few unstable regions on the processing map, which indicates excellent hot workability. At the strain rate of 0.1 s^?1, the stress?strain curves show an abnormal shape where there are two stress peaks simultaneously. This can be attributed to the alternation of hardening effect, which results from the continuous dynamic recrystallization (CDRX) and the rotation of DRX grains, and dynamic softening mechanism.     

Optimization of thermal processing parameters of Ti555211 alloy using processing maps based on Murty criterion

Isothermal compression testing of Ti555211 titanium alloys was carried out at deformation temperatures from 750 to 950 °C in 50 °C intervals with a strain rate of0.001–1.000 s~(-1). The high-temperature deformation behavior of the Ti555211 alloy was characterized by analysis of stress–strain behavior, kinetics and processing maps. A constitutive equation was formulated to describe the flow stress as a function of deformation temperature and strain rate, and the calculated apparent activation energies are found to be 454.50 and 207.52 k J mol~(-1)in the a b-phase and b-phase regions, respectively. A processing map based on the Murty instability criterion was developed at a strain of 0.7. The maps exhibit two domains of peak efficiency from 750 to 950 °C. A *60 % peak efficiency occurs at 800–850 °C/0.001–0.010 s~(-1). The other peak efficiency of *60 % occurs at C950 °C/0.001–0.010 s~(-1), which can be considered to be the optimum condition for high-temperature working of this alloy.However, at strain rates of higher than 1.000 s~(-1)and deformation temperatures of 750 and 950 °C, clear process flow lines and bands of flow localization occur in the hightemperature deformation process, which should be avoided in Ti555211 alloy hot processing. The mechanism in stability domain and instability domain was also discussed.     

Deformation behavior and processing maps of Mg-Zn-Y alloy containing I phase at elevated temperatures

The microstructure and mechanical properties of extruded Mg-Zn alloy containing Y element were investigated in temperature range of 300–450 °C and strain rate range of 0.001–1 s^?1 through hot compression tests. Processing maps were used to indicate optimum conditions and instability zones for hot deformation of alloys. For Mg-Zn and Mg-Zn-Y alloys, peak stress, temperature and strain rate were related by hyperbolic sine function, and activation energies were obtained to be 177 and 236 kJ/mol, respectively. Flow curves showed that the addition of Y element led to increase in peak stress and decrease in peak strain, and indicated that DRX started at lower strains in Mg-Zn-Y alloy than in Mg-Zn alloy. The stability domains of Mg-Zn-Y alloy were indicated in two domains as 1) 300 °C, 0.001 s^?1; 350 °C, 0.01–0.1 s^?1 and 400 °C, 0.01 s^?1 and 2) 450 °C, 0.01–0.1 s^?1. Microstructural observations showed that DRX was the main restoration mechanism for alloys, and fully dynamic recrystallization of Mg-Zn-Y alloy was observed at 450 °C. The instability domain in Mg-Zn-Y alloy was located significantly at high strain rates. In addition, the instability zone width of Mg-Zn and Mg-Zn-Y alloys increased with increasing strain, and cracks, twins and severe deformation were considered in these regions.     

Hot working characteristics of HEXed PM nickel-based superalloy during hot compression

To study the hot deformation behavior of a new powder metallurgy nickel-based superalloy, hot compression tests were conducted in the temperature range of 1020–1110 °C with the strain rates of 0.001–1 s⁻¹. It is found that the flow stress of the superalloy decreases with increasing temperature and decreasing strain rate. An accurate constitutive equation is established using a hyperbolic-sine type expression. Moreover, processing map of the alloy is constructed to optimize its hot forging parameters. Three domains of dynamic recrystallization stability and instability regions are identified from the processing map at a strain of 0.7, respectively. The adiabatic shear band, intergranular crack and a combination of intergranular crack and wedge crack are demonstrated to be responsible for the instabilities. Comprehensively analyzing the processing map and microstructure, the optimal isothermal forging conditions for the superalloy is determined to be t=1075–1105 °C and =10⁻³–10^−2.8 s⁻¹.     

Hot deformation behaviour and microstructure control in AlCrCuNiFeCo high entropy alloy

An AlCrCuNiFeCo high entropy alloy (HEA), which has simple face centered cubic (FCC) and body centered cubic (BCC) solid solution phases as the microstructural constituents, was processed and its high temperature deformation behaviour was examined as a function of temperature (700–1030 °C) and strain rate (10⁻³–10⁻¹ s⁻¹), so as to identify the optimum thermo-mechanical processing (TMP) conditions for hot working of this alloy. For this purpose, power dissipation efficiency and deformation instability maps utilizing that the dynamic materials model pioneered by Prasad and co-workers have been generated and examined. Various deformation mechanisms, which operate in different temperature–strain rate regimes, were identified with the aid of the maps and complementary microstructural analysis of the deformed specimens. Results indicate two distinct deformation domains within the range of experimental conditions examined, with the combination of 1000 °C/10⁻³ s⁻¹ and 1030 °C/10⁻² s⁻¹ being the optimum for hot working. Flow instabilities associated with adiabatic shear banding, or localized plastic flow, and or cracking were found for 700–730 °C/10⁻³–10⁻¹ s⁻¹ and 750–860 °C/10^−1.4–10⁻¹ s⁻¹ combinations. A constitutive equation that describes the flow stress of AlCrCuNiFeCo alloy as a function of strain rate and deformation temperature was also determined.     

新型无镍白色铜合金的热加工图及其热变形机制(英文)

采用Gleeble-1500热模拟实验机在温度为600~800°C、应变速率为0.01~10 s-1的热变形条件下对新型无镍白色Cu-12Mn-15Zn-1.5Al-0.3Ti-0.14B-0.1Ce(质量分数,%)合金进行热压缩模拟实验;根据该合金热变形行为及热加工特征,建立该合金热变形的本构方程和热加工图。该合金热变形过程中变形激活能为203.005 k J/mol。当真应变为0.7时,合金热加工图中存在一个失稳区,此区域的变形温度为600~700°C,应变速率为0.32~10 s-1。在较适宜的热变形条件(800°C、10 s-1)下获得的合金具有良好的表面质量和内部组织。同时,该无镍合金具有与传统镍白铜Cu-15Ni-24Zn-1.5Pb合金相近似的白色色度和肉眼不易察觉的色差(小于1.5)。     

Mechanical Behavior and Microstructure Evolution of Bearing Steel 52100 During Warm Compression

High-performance bearing steel requires a fine and homogeneous structure of carbide particles. Direct deformation spheroidizing of bearing steel in a dual-phase zone can contribute to achieving this important structure. In this work, warm compression testing of 52100 bearing steel was performed at temperatures in the range of 650–850°C and at strain rates of 0.1–10.0 s^?1. The effect of deformation temperatures on mechanical behavior and microstructure evolution was investigated to determine the warm deformation temperature window. The effect of deformation rates on microstructure evolution and metal flow softening behavior of the warm compression was analyzed and discussed. Experimental results showed that the temperature range from 750°C to 800°C should be regarded as the critical range separating warm and hot deformation. Warm deformation at temperatures in the range of 650–750°C promoted carbide spheroidization, and this was determined to be the warm deformation temperature window. Metal flow softening during the warm deformation was caused by carbide spheroidization.     

The optimal determination of forging process parameters for Ti–6.5Al–3.5Mo–1.5Zr–0.3Si alloy with thick lamellar microstructure in two phase field based on P-map

The deformation behavior of Ti–6.5Al–3.5Mo–1.5Zr–0.3Si alloy with thick lamellar α microstructure is investigated by using the Processing-map (P-map). The results show that the P-map can predict the regime of flow instability and reveal deformation mechanisms well. Through analyzing P-maps and observing the microstructure evolution of Ti–6.5Al–3.5Mo–1.5Zr–0.3Si alloy in forging process, the phenomena of flow instability are found to occur at the temperature and strain rate ranges of (750–880 °C, 0.005–10.0 s^?1) and (880–950 °C, 0.17–10.0 s^?1), which include macrocracks, adiabatic shear bands and prior β boundary cavities. The preferable temperature and strain rate for hot working of the Ti-alloy are (790–900 °C, 0.001–0.003 s^?1) and (900–950 °C, 0.001–0.017 s^?1). In these two deformation domains, the globularization of α lamellae occurs, and the combination of the globularization of α lamellae and α + β → β phase transformation happen, respectively. For forging of Ti–6.5Al–3.5Mo–1.5Zr–0.3Si alloy in α + β phase field, the optimum temperature can be selected from the temperature range of 850–950 °C and the optimum stain rate is 0.001 s^?1 based on the volume fraction of α phase for obtaining the needed properties of forgings in design of forging processes.