High-temperature deformation behavior of Ti60 titanium alloy

Isothermal compressions of near-alpha Ti60 alloy were carried out on a Gleeble-3800 simulator in the temperature range of 960-1110 °C and strain rate range of 0.001-10.0 s⁻¹. The high-temperature deformation behavior was characterized based on an analysis of the stress-strain behavior, kinetics and processing map. The flow stress behavior revealed greater flow softening in the two-phase field compared with that of single-phase field. In two-phase field, flow softening was caused by break-up and globularization of lamellar α as well as deformation heating during deformation. While in the single-phase field, flow softening was caused by dynamic recovery and recrystallization. Using hyperbolic-sine relationships for the flow stress data, the apparent activation energy was determined to be 653 kJ/mol and 183 kJ/mol for two-phase field and single-phase field, respectively. The processing map exhibited two instability fields: 960-980 °C at 0.3-10 s⁻¹ and 990-1110 °C at 0.58-10 s⁻¹. These fields should be avoided due to the flow localization during the deformation of Ti60 alloy.     

High temperature deformation behavior of a near alpha Ti600 titanium alloy

The high temperature deformation behavior of a near alpha Ti600 titanium alloy was investigated with isothermal compression tests at temperatures ranging from 800 to 1000 °C and strain rates ranging from 0.001 to 10.0 s⁻¹. The apparent activation energy of deformation was calculated to be 620.0 kJ mol⁻¹, and constitutive equation that described the flow stress as a function of the strain rate and deformation temperature was proposed for high temperature deformation of Ti600 titanium alloy in the α + β phase region. The processing map was calculated to evaluate the efficiency of the forging process in the temperatures and strain rates investigated and to recognize the instability regimes. High efficiency values of power dissipation over 55% obtained under the conditions of strain rate lower than 0.01 s⁻¹ and temperature about 920 °C was identified to represent superplastic deformation in this region. Plasticity instability was expected in the regime of strain rate higher than 1 s⁻¹ and the entire temperature range investigated.     

Hot deformation behavior of Cu-bearing antibacterial titanium alloy

We investigated the deformation behavior of a new biomedical Cu-bearing titanium alloy (Ti-645 (Ti-6.06Al-3.75V-4.85Cu, in wt%)) to optimize its microstructure control and the hot-working process. The results showed that true stress–true strain curve of Ti-645 alloy was susceptible to both deformation temperature and strain rate. The microstructure of Ti-645 alloy was significantly changed from equiaxed grain to acicular one with the deformation temperature while a notable decrease in grain size was recorded as well. Dynamic recovery (DRV) and dynamic recrystallization (DRX) obviously existed during the thermal compression of Ti-645 alloy. The apparent activation energies in (α?+?β) phase and β single phase regions were calculated to be 495.21?kJ?mol^?1 and 195.69?kJ?mol^?1, respectively. The processing map showed that the alloy had a large hot-working region whereas the optimum window occurred in the strain rate range of 0.001–0.1?s^?1, and temperature range of 900–960?°C and 1000–1050?°C. The obtained results could provide a technological basis for the design of hot working procedure of Ti-645 alloy to optimize the material design and widen the potential application of Ti-645 alloy in clinic.     

Research on the hot deformation behavior of Ti40 alloy using processing map

The deformation behavior of a Ti40 titanium alloy was investigated with compression tests at different temperatures and strain rates to evaluate the activation energy and to establish the constitutive equation, which reveals the dependence of the flow stress on strain, strain rate and deformation temperature. The tests were carried out in the temperature range between 900 and 1100 °C and at strain rates between 0.01 and 10 s⁻¹. Hot deformation activation energy of the Ti40 alloy was calculated to be about 372.96 kJ/mol. In order to demonstrate the workability of Ti40 alloy further, the processing maps at strain of 0.5 and 0.6 were generated respectively based on the dynamic materials model. It is found that the dynamic recrystallization of Ti40 alloy occurs at the temperatures of 1050-1100 °C and strain rates of 0.01-0.1 s⁻¹, with peak efficiency of power dissipation of 64% occurring at about 1050 °C and 0.01 s⁻¹, indicating that this domain is optimum processing window for hot working. Flow instability domains were noticed at higher stain rate (≥1 s⁻¹) and stain (≥0.6), which located at the upper part of the processing maps. The evidence of deformation in these domains has been identified by the microstructure observations of Ti40 titanium alloy.     

Hot deformation behavior and processing map development of AZ110 alloy with and without addition of La-rich Mish Metal

In order to compare the workability of AZ110 alloy with and without addition of La-rich Mish Metal(MM), hot compression tests were performed on a Gleeble-3500 D thermo-mechanical simulator at the deformation temperature range of 473-623 K and strain rate range of 0.001-1 s-1. The flow stress, constitutive relation, DRX kinetic model, processing map and microstructure characterization of the alloys were investigated. The results show that the flow stress is very sensitive to deformation temperature and strain rate, and the peak stress of AZ110 LC(LC = La-rich MM) alloy is higher than that of AZ110 alloy.The hot deformation behavior of the alloys can be accurately predicted by the constitutive relations. The derived constitutive equations show that the calculated activation energy Q and stress exponent n for AZ110 alloy are higher than the calculated values of AZ110 LC alloy. The analysis of DRX kinetic models show that the development of DRX in AZ110 LC alloy is earlier than AZ110 alloy at the same deformation condition. The processing maps show that the workability of AZ110 LC alloy is significantly more excellent than AZ110 alloy and the microstructures are in good agreement with the calculated results.The AZ110 LC alloys can obtain complete DRX microstructure at high strain rate due to its higher stored energy and weak basal texture.     

BT20合金高温变形行为的研究

为实现BT20合金锻造的数值模拟和合理制定其热成形工艺参数,利用Thermecmastor-Z型热模拟试验机对该材料在热成形条件下的变形抗力进行了研究,考察了变形温度、应变速率及变形程度与变形抗力之间的关系,并利用冶金学方法对其进行了分析.结果表明,应变速率和变形温度的变化强烈影响着合金流变应力的大小,流变应力随变形温度升高而降低,随应变速率提高而增大.通过真实σ-ε曲线,回归出可综合反映锻造热力参数对材料成形性能影响的本构方程.     

Constitutive modeling for hot deformation behavior of T24 ferritic steel

Hot compression tests of T24 ferritic steel were carried out using Gleeble-3500 thermo mechanical simulator in the temperature range of 1323-1473 K with the strain rate of 0.01-10 s⁻¹ and the height reduction of 60%. The flow behavior of T24 ferritic steel was characterized based on analysis of the true stress-strain curves. Constitutive equations incorporating the effects of temperature, strain rate and strain have been developed to model the hot deformation behavior of T24 ferritic steel. Material constants α, n, ln A and activation energy Q in the constitutive equations were calculated as a function of strain. The flow stress values of T24 ferritic steel predicted by the proposed constitutive equations show a good agreement with experimental results, which indicated that the developed constitutive equations could give an accurate and precise prediction for the flow stress of T24 ferritic steel.     

Orientation dependent behavior of tensile-creep deformation of hot rolled Ti65 titanium alloy sheet

The mill products like sheet always have one or more severe textures inevitably,and its effect on mechan-ical properties is not a negligible issue.The orientation dependent tensile-creep behavior induced by rolling texture of Ti65 titanium alloy sheet has been systematically investigated at 650℃.There are some anisotropic characteristics between TD and RD of Ti65 sheet.The UTS and TYS of TD are higher than RD at 650℃.Besides,the creep endurance time of TD(172.6-174.5 h)is about three times longer than RD(55.6-65.1 h)at 650℃and 240 MPa.Moreover,the grains are inclined to form Texture Ⅲ(1 2(1)6)[1(2)11]and(01(1)3)[1(2)11]after creep along with TD,but to form Texture I((1)2-(1)0)[10-(1)0]after creep along with RD.Finally,the crack initiation site is different during creep in TD and RD.The reason for anisotropic properties of tensile and creep has been summarized in two aspects:(ⅰ)the change of the SFs(Schmid factors)value between TD and RD;(ⅱ)the difference of creep mechanism between TD(grain boundary sliding)and RD(dislocation slip).Anisotropy of Ti65 sheet should be fully considered to increase structural efficiency in the engineering design and application.     

Constitutive modeling of hot deformation behavior of H62 brass

The hot deformation behaviors of H62 brass are investigated by isothermal compression tests on a Gleeble 1500 thermal-mechanics simulator in the temperature range of 650-800 °C and the strain rate range of 0.01-10 s⁻¹. Most of the stress-strain curves exhibit a single peak stress, indicating a typical dynamic recrystallization (DRX) behavior of the alloy. Further microstructural observation confirms the occurrence of DRX behavior and the β → α phase transformation of H62 brass under the deformation conditions. A new constitutive equation coupling flow stress with strain, strain rate and deformation temperature is developed on the basis of the Arrhenius-type equation, in which the Zener-Hollomon parameter is modified by considering the compensation of the strain rate. In the constitutive equation, the material constants α, n, Q and A are found to be functions of the strain. The flow stress predicted by the constitutive equation shows good agreement with the experimental stress, which validates the efficiency of the constitutive equation in describing the deformation behavior of the material.     

Hot deformation and processing maps of extruded ZE41A magnesium alloy

The hot deformation behavior and microstructure evolution of extruded ZE41A magnesium alloy has been studied using the processing map. The compression tests were conducted in the temperature range of 250–450 °C and the strain rate range of 0.001–1.0 s⁻¹ to establish the processing map. The dynamic recrystallization (DRX) and instability zones were identified and validated through micrographs. The observations were performed in order to describe the behavior of the material under hot forming operation in terms of material damage and micro-structural modification.     

基于热加工图的7075铝合金热塑性变形工艺参数优化识别

在Gleeble-1500热模拟试验机上进行多组热压缩试验,得到7075铝合金在成形温度573～723K,应变速率0.01～10s-1下的真应力-应变数据,用此数据作为计算应变速率敏感指数（m值）、功率耗散因子（η值）、失稳判据（ξ（ε.）值）三重判据的基本模型。通过三重判据构建包含应变在内的7075铝合金热加工图,并观察试样变形后的微观组织来验证热加工图,最终判断该合金在试验范围内的最佳变形参数。结果表明7075铝合金热加工的安全区集中在高温低应变速率区,并随着应变的增加,η值逐渐增加;通过金相观察,稳定变形区,材料由于变形发生动态再结晶而使晶粒细化;不稳定变形区,裂纹伴随着流动位错带的产生而被发现,因此可以通过包含应变的热加工图所确定的最佳工艺参数来保证无缺陷的7075铝合金锻件。     

Hot deformation behavior and microstructure evolution of twin-roll-cast Mg–2.9Al–0.9Zn alloy: A study with processing map

The hot deformation behavior and microstructure evolution of twin-roll-cast of Mg–2.9Al–0.9Zn–0.4Mn (AZ31) alloy has been studied using the processing map. The tensile tests were conducted in the temperature range of 150–400 °C and the strain rate range of 0.0004–4 s⁻¹ to establish the processing map. The different efficiency domains and flow instability region corresponding to various microstructural characteristics have been identified as follows: (i) the continuous dynamic recrystallization (CDRX) domain in the range of 200–280 °C/≤0.004 s⁻¹ with fine grains which provides a potential for warm deformation such as deep drawing; (ii) the discontinuous dynamic recrystallization (DDRX) domain around 400 °C at high strain rate (0.4 s⁻¹ and above) with excellent elongation which can be utilized for forging, extrusion and rolling; (iii) the grain boundary sliding (GBS) domain at slow strain rate (below 0.004 s⁻¹) above 350 °C appears abundant of cavities, which result in fracture and reduce the ductility of the adopted material; and (iv) the flow instability region which locates at the upper left of the processing map shows the metallographic feature of flow localization.     

Hot deformation behavior of an extruded Mg-Li-Zn-RE alloy

A new Mg-7.8%Li-4.6%Zn-0.96%Ce-0.85%Y-0.30%Zr alloy has been developed. α phase, β phase and RE-containing intermetallics formed in the alloy. It is found that the alloy can easily be extruded at 260 °C with σ_0.2 = 256 MPa, σ_b = 260 MPa and δ = 14%. Hot deformation behavior of the extruded alloy was studied using the processing map technique. Compression tests were conducted in the temperature range of 250-450 °C and strain rate range of 0.001-10 s⁻¹ and the flow stress data obtained from the tests were used to develop the processing map. The different efficiency domains and flow instability region corresponding to various microstructural characteristics have been identified as follows: (1) Domain I occurs in the temperature range of 250-275 °C and strain rate range of 1-10 s⁻¹, with a peak efficiency of about 50% at 250 °C/10 s⁻¹. Incomplete DRX process has occurred in β phase and DRX process hardly occurs in α phase; (2) Domain II occurs in the temperature range of 250-275 ?C and strain rate range of 0.001-0.003 s⁻¹, with a peak efficiency of about 42% at 250 °C/0.001 s ⁻¹. Incomplete DRX process has occurred in β phase and α phase; (3) Domain III occurs in the temperature range of 400-450 °C and strain rate range of 1-10 s⁻¹, with a peak efficiency of about 42% at 450 °C/10 s⁻¹. Complete DRX process has occurred in β phase and α phase. No cracking, cavity and band of flow localization are observed in flow instability region. The optimum parameters for hot working of the alloy are 250 °C/10 s⁻¹ and 250 °C/0.001 s⁻¹, at which fine dynamic recrystallization microstructure will be achieved. RE-containing intermetallics and α phase accelerate the DRX process in β phase. The softer β phase reduces the driving force for DRX process in α phase, so DRX process in α phase is retarded.     

Prediction of the flow stress of Al6061 at hot deformation conditions

Isothermal compression tests were carried out on Al6061 using a Gleeble-1500 thermal simulator at temperatures ranging from 573 to 723 K and strain rates from 0.5 to 30 s⁻¹. The flow stress of Al6061 was characterized based on an analysis of the true stress-true strain curves. A mathematical mode coupling flow stress with strain, strain rate and temperature for Al6061 has been proposed by using a hyperbolic sinusoidal type equation. The material constant α is 0.01 MPa⁻¹ in the model, whereas other material constants n, lnA and Q are found to be functions of strain. The predicted results from this proposed model are found to be in good agreement with the experimental flow stress curves which can be used to predict the required deformation forces in hot deformation processes.     

TB6合金热压缩变形行为研究

本文主要研究了热变形过程中变形温度、应变速率对TB6合金组织性能的影响。研究表明流动应力随应变速率的升高而增大,随变形温度的升高而减小。而变形温度对流动应力的影响程度与应变速率的大小有关。     

Hot compressive deformation behavior of the as-quenched A357 aluminum alloy

The objective of the present work was to establish an accurate thermal-stress mathematical model of the quenching operation for A357 (Al–7Si–0.6Mg) alloy and to investigate the deformation behavior of this alloy. Isothermal compression tests of as-quenched A357 alloy were performed in the temperature range of 350–500 °C and at the strain rate range of 0.001–1 s⁻¹. Experimental results show that the flow stress of as-quenched A357 alloy decreases with the increase of temperature and the decrease of strain rate. Based on the hyperbolic sine equation, a constitutive equation is a relation between 0.2 pct yield stress and deformation conditions (strain rate and deformation temperature) was established. The corresponding hot deformation activation energy (Q) for as-quenched A357 alloy is 252.095 kJ/mol. Under the different small strains (≤0.01), the constitutive equation parameters of as-quenched A357 alloy were calculated. Values of flow stress calculated by constitutive equation were in a very good agreement with experimental results. Therefore, it can be used as an accurate thermal-stress model to solve the problems of quench distortion of parts.     

Flow stress and ductility of AA7075-T6 aluminum alloy at low deformation temperatures

The present investigation has been conducted in order to develop a rational approach able to describe the changes in flow stress of AA7075-T6 aluminum alloy with deformation temperature and strain rate, when this material is deformed at temperatures in the range of 123-298 K at strain rates in the range of 4 × 10⁻⁴ to 5 × 10⁻² s⁻¹. The constitutive formulation that has been advanced to accomplish these objectives represents a simplified form of the mechanical threshold stress (flow stress at 0 K) model developed at Los Alamos National Laboratory (Los Alamos, New Mexico, USA). Thus, it is assumed that the current flow stress of the material arises from both athermal and thermal barriers to dislocation motion. In the present case, the effect of three thermal barriers has been considered: solid solution, precipitation hardening and work-hardening. The first two effects do not evolve during plastic deformation, whereas the last one is considered as an evolutionary component of the flow stress. Such an evolution is described by means of the hardening law earlier advanced by Estrin and Mecking (1984) [20]. The law is implemented in differential form and is integrated numerically in order to update the changes in strain rate that occur during tensile tests carried out both at constant and variable crosshead speed. The extrapolation of the hardening components from 0 K to finite temperatures is accomplished by means of the model earlier advanced by Kocks (1976) [19]. The results illustrate that the constitutive formulation developed in this way is able to describe quite accurately both the flow stress and work-hardening rate of the material, as well as temperature and strain rate history effects that are present when deformation conditions change in the course of plastic deformation. The evaluation of the ductility of the alloy indicates that the changes in this property are mainly determined by deformation temperature rather by strain rate. When deformation temperature decreases from 298 to 123 K, ductility also decreases from ∼35 to 24%. However, despite these relatively small variations, significant changes in the fracture morphology could be observed on the fracture surfaces of the examined specimens, with the predominance of a mixed ductile-brittle mechanism at lower temperatures.     

挤压态AZ40镁合金热变形行为及热加工图分析

采用Gleeble-3500热模拟试验机对挤压态AZ40合金进行热压缩实验,分析压缩后不同温度真应力-应变曲线的变化趋势,得到流变应力受变形温度和应变速率等因素的影响规律;在双曲正弦关系的基础上构造挤压态AZ40合金的本构方程,在动态材料模型(DMM)基础上建立挤压态AZ40合金的热加工图,从而确定挤压态AZ40镁合金的热变形加工范围.结果表明:明显的动态再结晶是挤压态AZ40镁合金流变曲线的特点,在压缩过程中,随变形温度的升高,挤压态AZ40镁合金的峰值应力减小;随应变速率升高,挤压态AZ40镁合金的峰值应力增大.当变形温度相同时,动态再结晶晶粒比例随着应变速率的升高而降低;当应变速率相同时,动态再结晶晶粒大小随着变形温度的升高而增大.粗大的未再结晶晶粒有明显的<1010>‖ND和<21-1-0>‖ND两种取向,而再结晶晶粒取向随机;通过热加工图及组织分析,确定了最佳的加工工艺为T=573 K,ε·=0.1 s-1.     

TA12钛合金热变形微观组织演变及变形参数优化

在应变速率为0.01~10 s-1,变形温度为870~1 070℃,最大变形量为80%的条件下,利用Gleeble-3800热模拟机对TA12合金高温压缩变形行为进行研究。依据实验结果绘制真应力-应变曲线,分析变形参数与组织的关系。同时把应力-应变曲线作为计算应变速率敏感指数m、功率耗散因子η、失稳判据ξ的底层数据,研究应变速率、变形温度、变形量共同存在对应变速率敏感指数m、功率耗散因子η的影响,绘制失稳图对失稳区域进行识别,并将功率耗散图和失稳图叠加构建热加工图。结果表明,在变形温度较低时,温度的影响主要表现为α相形态和数量的变化,在变形温度较高时,主要表现为β晶粒粗化;应变速率的影响主要表现在变形时间上;较高的η和ξ区域为良好加工区域,较低的η和ξ的失稳变形参数区域为加工避免区域。本批次合金适宜加工参数为温度910~970℃,应变速率0.01~0.3 s-1。