半固态Al-4Cu-Mg合金的变形行为及组织演化

以热模拟压缩实验为基础,研究了变形工艺参数(包括变形温度、应变速率和变形程度)对半固态Al-4Cu-Mg合金变形力学行为和微观组织的影响.研究结果表明:半固态Al-4Cu-Mg合金的流变应力峰值对变形温度和应变速率的变化比较敏感;变形温度和应变速率对稳态流动应力影响较小.应变速率对流变应力峰值的影响与变形温度有关.变形工艺参数对微观组织的影响为:随着变形温度的升高和应变速率的减小,α相晶粒平均尺寸增大,半固态Al-4Cu-Mg合金变形后的组织仍保持近球状组织,这与变形过程中固态α相的流动方式有关.     

铸态Ti-46Al-6(Cr, Nb, Si, B)合金的高温流变行为及其组织演变

以3次真空自耗熔炼的Ti-46Al-6(Cr,Nb,Si,B)(at%)(以下简称G4合金)合金为对象,采用恒温等应变速率热模拟压缩试验研究G4合金在1050～1250℃及0.001～1s-1应变速率下的高温流变行为和组织演变。结果表明,在高温变形过程中,G4合金呈现先硬化后软化的流变行为特征,组织由粗大的铸态γ+γ/α2近片层组织演变为细小的近等轴γ+α2组织;造成G4合金流变软化和组织演变的主要原因是动态再结晶(DRX)。变形温度和应变速率是影响G4合金高温流变和组织演变的2个主要因素。铸态G4合金在高温下的变形机制以γ/α2层片晶团的扭折、弯曲、球化和DRX以及γ晶粒的拉长、破碎和DRX为主,孪生变形也起到了一定的辅助作用。其最佳高温塑性变形温度为1150℃,应变速率应不大于0.1s-1。     

LZ61镁锂合金热变形行为及微观组织研究

通过熔炼得到了铸态LZ61镁锂合金,对其进行了热压缩变形行为研究,分析了变形温度及应变速率对其热变形行为的影响,并建立了本构方程。结果表明,合金的应变速率敏感指数m=0.218,平均热变形激活能Q=99.21kJ/mol,合金的流变曲线均属于动态再结晶型,流变应力随着温度升高(应变速率降低)而减小。温度及应变速率对合金的动态再结晶影响显著;显微组织的变化证明了动态回复和动态再结晶的发生。铸态合金组织由α-Mg相基体及弥散分布在晶界上的β相组成。经热压缩后,在相同温度下,随着应变速率降低,组织由粗细相间的晶粒转变为细小均匀的再结晶晶粒。在同一应变速率下,随着温度升高,再结晶区域逐渐增大,晶粒明显细化。     

Ti-5Al-5Mo-5V-1Cr-1Fe合金的高温塑性变形行为

在Gleeble-1500热模拟机上对Ti-5Al-5Mo-5V-1Cr-1Fe合金进行高温热压缩实验,研究该合金在变形温度为750~900℃、应变速率为0.001~1 s 1条件下的流变应力行为。利用光学显微镜分析合金在不同变形条件下的组织演化规律。结果表明:合金的流变应力随着应变速率的增大和变形温度的降低而增大;流变应力随着应变的增加而增大,出现峰值后逐渐趋于平稳;变形过程中的流变应力可用Arrhenius双曲正弦本构关系来描述,平均变形激活能为454.2 kJ/mol;各种变形条件均可细化原始晶粒尺寸。随着温度的升高和应变速率的降低,合金的主要软化机制由动态回复逐渐变为动态再结晶;在(α+β)相区变形(750~850℃)时,α相对β晶粒的动态再结晶的发生起到阻碍作用。     

环轧态Ti40钛合金热变形组织演变及本构关系研究

针对环轧态Ti40钛合金,进行等温恒应变速率高温压缩变形实验,研究合金在应变速率0. 001～1 s~(-1),温度950～1100℃范围变形过程中流变应力和微观组织演变行为,并通过流变应力曲线拟合计算建立合金该变形条件下的流变应力本构方程。实验结果表明:流变应力随着应变量的增加急速升高而后突降,同时流变应力随着应变速率增大而增大,这与位错密度增殖和运动密切相关;当合金变形温度一定时,随着应变速率变小,内部组织发生动态再结晶,平均晶粒尺寸得到细化;但当应变速率一定时,合金在较低应变速率(0. 001 s~(-1))变形时,需适当控制变形温度,才能得到晶粒更细小的均匀组织。     

马氏体TiAl合金的热变形行为

为研究马氏体TiAl合金的热变形行为,对Ti-42.1Al-8.3V合金进行1320 ℃油淬,得到马氏体,然后利用Gleeble-1500D热模拟试验机研究了马氏体在变形温度为1000~1150 ℃、应变速率为0.001~1 s^-1下的热变形行为。利用背散射电子成像(BSE)和背散射衍射(EBSD)研究了热变形参数对TiAl合金显微组织的影响,通过分析真应力-真应变曲线,结合双曲正弦方程建立了本构方程。结果表明,马氏体TiAl合金的流变应力曲线符合动态再结晶特征,峰值应力随着变形温度的降低和应变速率的增大而增大;通过计算得到n为2.175,变形激活能Q为595.79 kJ/mol,并构建了马氏体TiAl合金的本构方程;在热变形后,TiAl合金中近等边三角形排布的马氏体转变成α₂/γ片层结构。随着变形温度的升高和应变速率的减小,α₂/γ片层逐步被再结晶晶粒替代,最后在变形温度为1100 ℃、应变速率为0.001 s^-1条件下全部转化为等轴晶。另外,随着应变速率的降低和变形温度的升高,晶粒充分长大,逐渐粗化。     

Al-Cu-Mg-Ag合金热压缩变形的流变应力行为和显微组织

采用热模拟实验对Al-Cu-Mg-Ag耐热铝合金进行热压缩实验,研究合金在热压缩变形中的流变应力行为和变形组织.结果表明:Al-Cu-Mg-Ag耐热铝合金在热压缩变形中的流变应力随着温度的升高而减小,随着应变速率的增大而增大;该合金的热压缩变形流变应力行为可用双曲正弦形式的本构方程来描述,其变形激活能为196.27 kJ/mol;在变形温度较高或应变速率较低的合金中发生部分再结晶,并且在合金组织中存在大量的位错和亚晶;随着温度的升高和应变速率的降低,合金中拉长的晶粒发生粗化,亚晶尺寸增大,位错密度减小,合金的主要软化机制逐步由动态回复转变为动态再结晶.     

内燃机用IN718镍基合金热变形动态组织性能分析

对锻态IN718镍合金在不同工艺参数下进行了热压缩实验。采用OM、SEM和TEM分析方法,研究了不同热变形条件下IN718合金组织的结构变化规律。研究结果表明:IN718合金的流变应力随着应变的增大而增大,是典型的有动态再结晶塑性流变过程。在各个热变形工艺条件下,合金表现出显著的峰值现象,当温度上升或者应变速率变小后都会引起峰值应力的下降。合金在1050℃下生成了许多细小的再结晶晶粒,当热处理温度上升后,合金的平均晶粒尺寸更大。当应变速率增大后,合金晶粒尺寸不断减小。1080℃下以0. 001 s~(-1)应变速率使试样发生塑性变形时,晶粒中的细小γ'相可以对位错运动起到明显的抑制作用。     

半固态7050铝合金热压缩变形行为

在Gleeble-3500热模拟机上对半固态7050铝合金进行了高温热压缩试验,研究了该合金在变形温度为420～465℃、应变速率为0.001～0.100s-1条件下的流变应力行为以及变形过程中的显微组织。结果表明,流变应力在变形初期随着应变的增大迅速增大,出现峰值应力后逐渐平稳,流变应力随着应变速率的增大而增大,随着变形温度的升高而下降;流变应力可以用双曲线正弦形式的关系来描述,通过线性拟合计算出该材料的形变激活能等参数,获得流变应力的本构方程。随着变形温度升高和应变速率降低,合金中拉长的晶粒变大,合金热压缩变形的主要软化机制为动态再结晶。     

变形参数对Ti-22Al-24Nb合金高温流动应力及组织影响

采用Gleeble-3500热模拟试验机研究了Ti-22Al-24Nb合金在温度为900～1 110℃和应变速率为0.01～10s~(-1)条件下的高温流动应力及微观组织,分析了应变速率和变形温度对高温流动应力及热变形组织的影响。结果表明,变形温度和应变速率对Ti-22Al-24Nb合金的流动应力随变形温度的升高而降低,随应变速率的增加而升高。在α_2+B_2两相区,高应变速率下(6)ε≥1.0s~(-1))进行变形时,合金显微组织发生局部塑性流动和绝热剪切。在B_2单相区,低应变速率(6)ε≤0.1s~(-1))进行变形时,有明显的动态再结晶晶粒产生。高应变速率下,原始B_2相晶粒被明显拉长,晶界多呈不连续状态;低应变速率下变形时,随变形温度升高,合金易发生动态再结晶,当变形温度高于990℃时出现明显的动态再结晶特征;高应变速率下变形时,晶界模糊,随变形温度降低,晶界几乎全部消失,合金易发生局部塑性流动和绝热剪切。     

7150铝合金高温热压缩变形流变应力行为

在Gleeble-1500热模拟机上对7150铝合金进行高温热压缩实验,研究该合金在变形温度为300~450 ℃和应变速率为0.01～10 s~(-1) 条件下的流变应力行为.结果表明:流变应力在变形初期随着应变的增加而增大,出现峰值后逐渐趋于平稳;峰值应力随着温度的升高而减小,随着应变速率的增大而增大;可用包含Zener-Hollomon参数的Arrhenius双曲正弦关系来描述合金的热流变行为,其变形激活能为226.698 8 kJ/mol;随着温度的升高和应变速率的降低,合金中拉长的晶粒发生粗化,亚晶尺寸增大,再结晶晶粒在晶界交叉处出现并且晶粒数量逐渐增加;合金热压缩变形的主要软化机制由动态回复逐步转变为动态再结晶.     

120°模具室温ECAP制备工业纯钛的热压缩变形行为

在Gleeble-1500热模拟机上对室温120°模具等径弯曲通道变形(ECAP)制备的平均晶粒尺寸为200nm的工业纯钛(CP-Ti)进行等温变速压缩实验,研究超细晶(UFG)工业纯钛在变形温度为298～673K和应变速率为10-3～100s-1条件下的流变行为。利用透射电子显微镜分析超细晶工业纯钛在不同变形条件下的组织演化规律。结果表明:流变应力在变形初期随应变的增加而增大,出现峰值后逐渐趋于平稳;峰值应力随温度的升高而减小,随应变速率的增大而增大;随变形温度的升高和应变速率的降低,应变速率敏感性指数m增加,晶粒粗化,亚晶尺寸增大,再结晶晶粒数量逐渐增加;超细晶工业纯钛热压缩变形的主要软化机制随变形温度的升高和应变速率的降低由动态回复逐步转变为动态再结晶。     

Flow Behavior and Microstructures of Inconel 625 Superalloy at the Elevated Temperature

The deformation behavior of Inconel 625 superalloy was investigated by means of hot compression tests. The flow stress curves were obtained in the temperature and strain rate ranges of 950-1200 ℃ and 0.01-10 s-1, respectively. Optical microscopy was used to evaluate the microstructural evolution of the alloy under different conditions examined. The results show that the flow stress decreases with decreasing strain rate and increasing temperature, and the activation energy is about 654.502 kJ/mol. Microstructure observations show that with increasing temperature, the sizes and volume fraction of dynamic recrystallization (DRX) grains increase. The strain has no remarkably effect on the sizes of DRX grains, but with increasing strain the volume fraction of DRX grains increases. During hot compression of Inconel 625 superalloy at elevated temperature, the occurrence of DRX was the main softening mechanism. The DRX mechanism of Inconel 625 superalloy can be mainly attributed to the discontinuous dynamic recrystallization (DDRX).     

Ti-47Al-2Cr-0.2Mo合金多道次热塑性变形行为

采用Gleeble-1500热模拟实验机及光学显微镜和透射电子显微镜研究了Ti-47Al-2Cr-0.2Mo(原子分数,%)合金在2.5 s-1,1050～1150℃,道次保温时间分别为1 min、5 min、10 min条件下的多道次热压缩变形行为及其组织演化规律。结果表明,增大道次变形量,合金软化率增大;随着道次间保温时间的延长,合金软化率逐渐增大;变形及保温温度升高,合金软化率提高。动态和亚动态再结晶是合金发生软化的主要原因。再结晶优先发生于层片晶团边界处。随着变形温度升高,γ晶粒内的孪生增多。经过热压缩变形后,组织被细化和均匀化。位错和孪生是主要的变形机制。     

High temperature deformation behavior of near γ-phase high Nb-containing TiAl alloy

High temperature compressive deformation behaviors of a high Nb-containing PM-TiAl alloy (Ti–45Al–7Nb-0.3 W, at.%) were investigated at temperatures ranging from 1050 °C to 1200 °C, and strain rates from 0.001 s⁻¹ to 1 s⁻¹. The microstructure mainly consists of γ phase. The data obtained from the flow curves were employed to develop the constitutive equation, and the apparent activation energy (Q) was determined to be 414 kJ mol⁻¹. The size of the dynamically recrystallized grains (DRX) decreased with the increasing value of Zener–Hollomon (Z) parameter. A processing map was constructed on the basis of the flow stress, and the condition of intermediate Z (1150 °C, 0.1 s⁻¹) was determined to be the optimum hot forging parameter for industrial productions. DRX was observed under all the deformation conditions. At high Z and intermediate Z condition, dislocation climbing and twinning accompanied by DRX can act as the main deformation mechanisms. At low Z condition, DRX becomes the dominant softening mechanism, accompanied by the bending of lamellar colonies as well as the broken of γ grains and α₂ grains.     

DYNAMIC RECOVERY AND DYNAMIC RECRYSTALLIZATION OF 7005 ALUMINIUM ALLOY DURING HOT COMPRESSION

1.IntrottionItiswellknownthatworkhardeninganddynathecsofteningbehavescontradictorilydur-lughotworkingofmaterials.DislocationgenerationandintersectionsOfdislocationsduringI)lasticdeformationleadstoworkhardening,WhilesofteningismainlysuPPliedbydynamoicrecoveryand/ordynamicrecrystallization,whichresultsfromcoalescence,annihilationandreconstmctionofdislocationsbycross--slipandclilnhwiththeaidofaPPliedstressandthermal..ti.ati..Lll2}.However,completeannihilationofdislocationsreqUirescross--slipa…     

Microstructural instability in surface layer of a high Nb-TiAl alloy processed by shot peening following high temperature exposure

Microstructural instability induced by shot peening was investigated in a Ti-45Al-8.5Nb-(W, B, Y) alloy following high temperature exposure. After shot peening and thermal exposure at 1000 °C for 300 h, fine grains are formed in the outermost (FG layer). Underneath, coarse grains (CG layer) are formed. The FG layer is composed of completely recrystallized γ grains. The CG layer is composed of incompletely recrystallized γ grains, where the critical strain for recrystallization is not reached. During long term thermal exposure, α₂ lamellae can undergo dissolution, precipitation and growth. After thermal exposure for 300 h, large α₂ grains precipitated at the γ/γ interface or inside the γ grains in both FG and CG layers. The precipitated α₂ particles almost have the same orientation with primary α₂ lamellae, indicating that nearly no recrystallization phenomena occur for α₂ phase. So the γ lamella is easier to recrystallize than that of α₂ lamella at the same temperature and residual strain.     

The effects of long-term air exposure on the stability of lamellar TiAl alloys

The thermal stability of fine-grained and coarse-grained lamellar TiAl alloys was studied at 700°C in air. Both α₂ and γ lamellae were altered markedly after 1000- and 3000-h exposure. Three types of decomposition were found: (a) parallel decomposition of coarse α₂ into bunches of very fine α₂+γ lamellae, (b) perpendicular decomposition of fine γ (or γ+α₂) lamellae into short-ranged γ domains or (γ+α₂) grains and (c) perpendicular decomposition of fine α₂ lamellae into short-ranged α₂/γ grains. All three types are still at an intermediate stage after 3000-h exposure and neither break-up of lamellae nor globularisation of segments was observed. The thermal stability of microstructural constituents in increasing order was found to be: thick α₂, thin α₂, thin γ, and thick γ lamellae. Tensile properties were affected by these changes and the extent was found to vary from alloy to alloy.     

挤压开坯后TiAl合金高温变形过程中的微观组织演变

采用Gleeble-1500热模拟机对经挤压开坯后的TiAl合金进行热压缩变形,研究热变形参数对合金微观组织的影响。结果表明,随着变形量的增加,γ相首先在晶界处发生再结晶并长大,α2相发生拉长、分解和球化,组织得到了细化;变形温度和应变速率对组织影响显著,提高变形温度和降低应变速率,可有效提高组织均匀性。对微观组织进行定量金相统计分析,得到了TiAl合金动态再结晶组织演化模型。