SUPERPLASTICITY OF A WATER-QUENCHED AND TEMPERED 40Cr STEEL

1.IntroductionSuperplasticity possesses many good characteristics such as high elongation, low flow stress and high atom diffusion ability, which make it show good application in metal forming and diffusion bonding of complex shape structure. Up to now, the superplasticity of steel has been more investigated, however the pretreatment in order to obtain fine grain and then superplasticity was often carried out by circular quenchingof typically 3 times and subsequent high-temperature tempering, …     

Effect of electric current pulse on grain growth in superplastic deformation of 2091 Al-Li alloy

1　INTRODUCTIONThecharacteristicthatelectriccurrentpulsepro motesatomdiffusionanddislocationmotionwasgrad uallyrecognizedfromthefailureanalysisonintegrat edcircuitin 1970s[110 ] .Theelectriccurrentpulsewasusedtoincrease plastic property ,improvetheformabilityofless deformablemetals[11,12 ] ,andstudytheeffectsofcurrentpulseonrecrystallization[1318]respectivelyin 1980s .Inthisrespect ,ConradandLaihavedonealotofwork ,inwhichCu ,AlandTiweremainexperimentalmaterialsfordeformationemployedwitha…     

热轧MB8镁合金的超塑性

对热轧MB8(Mg-1.5Mn-0.3Ce)镁合金板材的超塑性进行了研究。高温拉伸实验结果表明,合金在573～723 K及2×10-2～4×10-4s-1应变速率范围内具有良好的超塑性,在673 K及4×10-4s-1条件下得到最大断裂伸长率为441.6%;在723 K时最高应变速率敏感系数m为0.42,此时流变应力仅为6.3 MPa。此外,采用SEM对拉伸试样断口形貌进行了观察,并通过断裂区域显微组织的观察分析了Mg-1.5Mn-0.3Ce镁合金超塑性变形的机制。     

往复挤压ZK60合金的低温准超塑性(英文)

通过2道次往复挤压制备细晶ZK60合金,在443~523K和初始应变速率为3.310-4~3.310-2s-1的范围内测试合金的低温超塑性。结果表明:往复挤压ZK60合金的平均晶粒尺寸约为5.0m,分布于基体内的破碎二次相颗粒和沉淀颗粒尺寸分别为不大于175nm和50nm。该合金具有低温准超塑性,在523K和3.310-4s-1应变速率下伸长率最大,为270%;在443和473K时,应变速率敏感系数m小于0.2;在523K时m为0.42。当温度不高于473K和523K时,超塑性变形激活能分别不高于63.2kJ/mol和110.6kJ/mol。当低于473K时,主要的超塑性流变机制为晶内滑移;在523K时,主要的超塑性变形机制为晶界滑移,由晶界扩散控制的位错蠕变为主要的兼容机制。     

细晶Ti-6Al-4V宽幅板材的超塑性变形机理及组织演变

通过恒应变速率拉伸试验,在1103~1223 K温度范围、3.2×10-4~1×10-2s-1应变速率范围内,研究了Ti-6Al-4V宽幅板材的超塑性,在实验中获得了100%-604%的延伸率。分析了组织演变和变形机理,结果表明,其主要变形机理为晶界滑移,以晶内位错运动和β相的晶内滑移为协调机制。实验中还发现在低温下变形时,Ti-6Al-4V宽幅板材存在各向异性,当在高温下变形时,各向异性不太明显。     

CONSTITUTE EQUATIONS OF 40Cr STEEL UNDER SUPERPLASTIC COMPRESSIVE DEFORMATION

The microstructure of 40Cr steel sample and its surface is ultra-fined through salt-bath cyclic quenching and high frequency hardening, then the superplasticity is studied under isothermal superplastic compressive deformation condition. The experimental results indicate that the stress-strain curves are shown to take place obvious superplastic flow characteristic at the temperature of 750-770℃ and at the initial strain rate of (1.7-5.0)×10-4 s-1. Its strain rate sensitivity is 0.30-0.38, the steady superplastic flow stress is 60-70MPa, the superplastic flow activation energy is 198-217kJ/mol, and it is close to α-Fe grain boundary self-diffusion activation energy. The super-plastic compressive constitute equations of this steel are correspondingly set up. Due to the finer microstructure of high frequency hardening, it appears bigger strain rate sensitivity value, smaller the steady superplastic flow stress and the superplastic flow activation energy, so it has better superplastic deformation capabili     

SUPERPLASTICITY IN SiCw／ZK60 COMPOSITE

The superplastic deformation behavior of SiCw/ZK60 composite was investigated at temperatures ranging from 573K to 723K and at initial strain rates ranging from 8.3x10-4s-1 to 8.3x10-2s-1. A maximum elongation of 200% with a m-value of 0.35 was obtained at 613K and a initial strain rate of 1.67x 10-2s-1. The apparent activation energy (98kJ/mol) approximates that for grain boundary diffusion (92kJ/mol) in magnesium. It is proposed that the dominant mechanism of superplastic deformation in the present composite is grain boundary sliding accommodated by diffusional transport, besides, interfacial sliding plays an important role in the superplastic deformation.     

Er、Zr微合金化5083铝合金的超塑性

针对5E83合金(Er、Zr微合金化5083合金),采用超塑性拉伸试验、扫描电镜(SEM)、电子背散射衍射(EBSD)和透射电镜(TEM),探究了Er、Zr微合金元素、晶粒尺寸、变形温度、应变速率对合金超塑性的影响。通过再结晶退火、空冷和水冷的搅拌摩擦加工(FSP),分别获得了晶粒尺寸为7.4、5.2、3.4μm的完全再结晶组织,作为初始状态进行超塑性拉伸。结果表明,初始晶粒尺寸越细小,超塑性伸长率越高。当晶粒尺寸>5μm时,超塑性变形过程晶粒粗化缓慢,细化初始晶粒可显著提高超塑性;而当晶粒尺寸<5μm时,超塑性变形过程晶粒粗化严重,进一步细化初始晶粒对超塑性的提高有限。不同变形温度、应变速率的超塑性拉伸结果显示在变形温度为450～540℃、应变速率为1.67×10^-4～1.67×10^-1 s^-1,超塑性伸长率随变形温度和应变速率的提高呈现先上升后下降再上升的趋势;变形温度为520℃、应变速率为1.67×10^-3 s^-1条件下,水冷FSP态合金获得最大伸长率330%...     

SUPERPLASTICITY OF A SiC_w/2024 Al COMPOSITE MADE BY PRESSURE INFILTRATION

The superplastic characteristics of the β-SiC whisker reinforced 2024 aluminum composite, fabricated by pressure infiltration and hot-rolling after extrusion, were investigated. The composite has a fine grain size of about 1μm, and exhibits a maximum tensile elongation of 370% in the initial strain rate of 3.3×10-3s-1 at 788K.The superplastic deformation mechanism of the composite is thought to be grain boundary (interface) sliding accommodated by grain boundary diffusion of aluminum atom and an appropriate amount of liquid phase.     

Ti40阻燃合金粗晶超塑性变形行为及机理

借助OM、TEM研究了高温条件下Ti40阻燃合金的粗晶超塑性变形行为及机理。结果表明:在920℃下,应变速率为5×10-5～1×10-2s-1的Ti40合金表现出良好的超塑性行为,拉伸延伸率均超过250%,应变速率敏感指数m大于0.3。超塑变形后,粗大的等轴组织细化。TEM分析表明,在变形过程中,位错运动形成亚晶界,亚晶界通过吸收滑移位错形成小角度晶界甚至大角度晶界。Ti40合金的粗晶超塑性是由动态回复和再结晶共同作用的结果。     

THE HOT DEFORMATION BEHAVIOR AND DYNAMIC RECRYSTALLIZATION MODEL OF 35CrMo STEEL

The isothermal single-stage compression of 35CrMo structural steel has been carried out by using Gleeble 1500 simulator at the temperature range of 950℃ to 1150℃ and strain rate range of 0.01s-1 to 10s-1. The effect of hot deformation parameters, such as strain rate, deformed temperature and initial grain size on the flow stress behavior was investigated. The activation energy of tested alloy was calculated, which is 378.16kJ/mol; The relationships between the peak stress (σp), the peak stain (εp), the critical strain (εc) and Z parameter were established. The micro structure evolution shows the pre-existing austenite grain boundaries constitute the principal nucleation sites for dynamic recrystallization (DRX), and the initial austenite grain size affects the grain size of DRX slightly. The kinetic mathematical model of DRX of 35CrMo is: XDRX=1-exp(-3.23-2.28) and Ddyn = 2.252× 10Z-0.22.     

脉冲电流对2091Al-Li合金超塑变形机理的影响

分析了脉冲电流对２０９１Ａｌ－Ｌｉ合金超塑变形中晶内位错滑移、晶界位错滑移及原子扩散的影响。研究表明,脉冲电流促进位错滑移及增殖,降低原子扩散激活能,加速位错在晶界上的攀移,从而提高了超塑变形在高应变速率下的可能性。据此,建立了施加脉冲电流条件下的超塑变形速率方程。     

挤压铸造铝基复合材料的高应变速率超塑性

用挤压铸造、挤压比仅为１０∶１的挤压以及进一步的轧制成功地制备了具有高应变速率超塑性行为的βＳｉＣ晶须增强ＬＹ１２复合材料。该复合材料晶粒细小,约为２μｍ;在温度为８０３Ｋ和初始应变速率为１．１×１０－１ｓ－１时,延伸率达３５０％,应变速率敏感系数ｍ值约为０．３５;超塑性变形的主要机制是细小晶粒的晶界滑动,适当的微量液相有利于该复合材料的高应变速率超塑性。     

Superplasticity and diffusion bonding of magnesium alloy ZK60

1 INTRODUCTIONRecently , the use of magnesium alloys asstructural materials has significantlyincreased,forits good damping capacity , di mension stability ,machinability and lowcasting costs . But magnesi-umalloys normally exhibit lowductility near roomtemperature because of their HCP structure .Therefore ,it is necessary to i mprove the ductilityof these alloys for their use as structural compo-nents[1 3].In manufacturing,superplastic forming is of-ten combined with diffusion bonding, w…     

LZ91镁锂合金板材的超塑性气胀成形研究

本文利用热拉伸实验、气胀成形实验、金相分析和扫描电镜观察,研究LZ91镁锂合金板材的超塑性、气胀成形性能及其组织结构。结果表明:在热拉伸变形温度为573 K、应变速率为0.001 s-1时,其伸长率可达343.7 %,应变速率敏感指数为0.697,轧制态的LZ91合金板材表现出优良的超塑性;在胀形温度573 K,胀形气压0.06 MPa条件下,板材成形高度为51.14 mm,高径比达1.279,说明该镁锂合金板材具有良好的超塑性成形潜力;在热拉伸变形和超塑性气胀成形过程中,均有动态再结晶现象产生,可有效提高该合金的塑性成形能力;在拉伸断口和胀形件破裂处断口均存在典型的超塑性空洞形貌特征,说明两者的主要变形机制均为晶界滑移,且合金超塑性失效的主要原因是空洞的长大和连接。     

LY12合金粗晶材料的超塑性变形机制

采用单轴拉伸对LYl2粗晶材料进行超塑性研究，温度一定时，在较高和较低的应变速率下都得到了大延伸率，而处于中间应变速率的试样延伸率较低。SEM断口分析表明，晶界上产生的粘性物质对粗晶超塑性行为有决定性影响。在高应变速率下，晶界上粘性层很薄，被粘性层包围着的晶粒和亚结构在相互挤压和相对转动中容易细化，有利于超塑性变形能力的提高且不易产生孔洞，室温性能良好；低应变速率下，大多晶界上都有粘性物质包围且粘性层厚度增大，粘性物质的增多使超塑性变形能力增强，但易产生孔洞，使室温性能恶化；而中间应变速率区间，晶粒细化程度不够，晶界上末产生较多粘性物质，有少量孔洞产生且变形能力较差。     

超轻双相镁锂合金的超塑性、显微组织演变与变形机理

采用熔铸、大变形轧制(加工率大于92%)和硝酸盐浴退火方法制备Mg-7.83%Li 合金与Mg-8.42%Li合金细晶板材,研究合金的超塑性、显微组织、空洞与断裂形貌和变形机制.计算α相(5.7%Li)和β相(11%Li)的扩散系数和Gibbs自由能,讨论573 K时超塑性晶粒长大的原因.结果表明:Mg-7.83Li和Mg-8.42Li合金分别获得850%和920%的最大超塑性;Mg-7.83Li合金在573 K时发生了显著的超塑性晶粒长大;在573 K和1.67×10~(-3) s~(-1)条件下制备的Mg-8.42Li合金中的空洞较少,且在变形区中随机而孤立地分布.断裂形貌观察发现Mg-8.42Li合金在573 K和5×10~(-4) s~(-1)条件下发生穿晶断裂;Mg-7.83Li合金在573 K和1.67×10~(-3) s~(-1)条件下发生沿晶界韧窝断裂.归一化实验数据与考虑位错数量的变形机制图对比表明合金超塑性变形机制为晶格扩散控制的位错调节的晶界滑移.     

SiCp增强2024铝基复合材料超塑性的研究

对搅拌铸造法制备的SiCp/2024Al复合材料超塑性的预处理、力学行为、微观结构及变形机制进行了研究,结果表明,合适的强烈塑性变形是改善复合材料组织进而提高超塑性的有效方法:经小挤压、热轧和冷轧后,在温度为823K、初始应变速率为 1.1×10-3 s-1的拉伸变形条件下,超塑延伸率为405%,超塑变形机制为晶粒的适度长大、动态连续再结晶和适当的微量液相共同协调的晶界滑动:液相不是该复合材料展现超塑性的必要条件。     

High strain rate superplasticity of rolled AZ91 magnesium alloy

The high strain rate superplastic deformation properties and characteristics of a rolled AZ91 magnesium alloy at temperatures ranging from 623 to 698 K（0.67Tm-0.76Tm） and high strain rates ranging from 10^-3 to 1 s^-1 were investigated.The rolled AZ91 magnesium alloy possesses excellent superplasticity with the maximum elongation of 455% at 623 K and a strain rate of 10-3 s-1,and its strain rate sensitivity m is high up to 0.64.The dominant deformation mechanism responsible for the high strain rate superplasticity is still grain boundary sliding（GBS）,and the dislocation creep mechanism is considered as the main accommodation mechanism.     

Superplasticity of a SiC particulate-reinforced 6A02AI matrix composite

The superplastic characteristics of a 15% (volume fraction) SiCp (14 μm)/6A02A1 composite, fabricated by stirring casting and cold-rolling after extrusion with a low extrusion ratio of 10:1 and hot-rolling, were investigated. The composite exhibits a tensile elongation of 250% at an initial strain rate of 8.9 x 10-4 s-l and at 833 K where an appropriate amount of liquid phase is presented in the composite. The superplastic deformation is uniform and the strain hardening exponent 2is as high as 1.6. The fracture surface is intergranual and the superplastic deformation mechanism of the composite is considered to be grain boundary (interface) sliding accommodated by an appropriate amount of liquid phase.