应变速率对Sn-9Zn共晶合金拉伸性能的影响

Sn—9Zn合金室温的拉伸曲线上存在一个较宽的无加工硬化区域，合金的最大拉伸应力对应变速率敏感，随着应变速率的增加，最大拉伸应力增大，对应变速率与抗拉强度关系的拟合获得了这种合金的应变速率敏感指数为0．097．SEM观察表明，裂纹在棒状Zn与基体的界面处萌生．合金的拉伸断口特征随应变速率的增加从典型的韧窝状延性断裂向半解理脆性断裂过渡。     

23CrNi3Mo钢热塑性行为及断裂机理

利用Gleeble-1500热模拟机进行热拉伸实验,研究了变形温度800~1200℃和应变速率0.002~20 s-1范围内23CrNi3Mo钢热塑性行为及断裂机理。结果表明:23CrNi3Mo钢具有优异的高温塑性。不同的变形温度下,峰值应力随温度线性降低,而随应变速率的增加峰值应力升高。应变速率2 s-1时,热拉伸过程中,高温断裂机制为韧性断裂,断口呈韧窝形貌。随着温度的升高,韧窝直径变小而深度增加。变形温度1050℃时,随应变速率的降低,断裂机制由韧性断裂转变为脆性断裂。应变速率高于0.2 s-1时,断口呈韧窝形貌;而应变速率低于0.2 s-1时,断口呈沿晶断裂形貌。高温拉伸断裂过程中,夹杂物的存在对裂纹的萌生与扩展有一定的影响作用。     

热冲压钢B1500HS在不同应变速率下的氢脆现象研究

通过电化学充氢和不同应变速率拉伸试验,研究应变速率对热冲压钢B1500HS氢脆敏感性的影响。通过微观断口形貌观测,分析不同应变速率下充氢热冲压钢断裂形式的差异,并进一步对其机理进行探究。结果表明,随着应变速率的降低,热冲压钢的强度和塑性损失量逐渐增加,说明慢应变速率下氢脆现象更加明显;慢应变速率下热冲压钢拉伸断口呈准解理状,而快应变速率下则呈现小韧窝状,其断裂形式呈现出由脆性断裂向韧性断裂的转变。分析其原因主要是在慢应变速率下,氢有足够的时间扩散至孔洞、夹杂等缺陷位置,从而促进裂纹的产生和扩展,导致其具有更高的氢脆敏感性。     

Influences of Strain Rates on Fracture Mechanism and Phase Separation in Hf-Based Bulk Metallic Glass

采用INSTRON-5569试验机和分离式霍普金森压力杆对Hf44.5Cu27Ni13.5Ti5Al10大块金属玻璃在不同应变速率下(10-4~103s-1)的压缩断裂行为进行了研究。准静态压缩条件下Hf44.5Cu27Ni13.5Ti5Al10大块金属玻璃不呈现应变速率敏感性,断裂强度值最高可达2400 MPa,动态压缩条件下金属玻璃的屈服强度达到2840 MPa。在断裂面上可观察到涟漪状和周期性条纹结构,涟漪状结构表明宏观为脆性断裂的金属玻璃在微观尺度上属于韧性断裂,周期性条纹结构与动态扩展裂纹前端和弹性波的相互作用有关。高的应变速率导致高的断裂强度和绝热温度,局部区域的绝热升温引起了压缩过程中Al的偏析和扩散,这对剪切带和裂纹的形成起到一定的影响。     

低合金钢FQK400高温拉伸的流变特性

测定了FQK400低合金钢在不同温度、不同速率下的应力-应变曲线,分析了高温应力流变规律,对抗拉强度、峰值应变和拉伸温度、拉伸速率之间的关系进行了数学回归.结果表明,FQK400钢发生动态再结晶的条件是温度在850℃以上、拉伸速率在10×10-3s-1以下.钢的抗拉强度随拉伸温度的提高呈抛物线降低;峰值应变随温度的升高呈抛物线状先降后升,谷值温度为700℃,最大应变随温度的升高先升高后降低,700℃时最高.抗拉强度、峰值应变也随拉伸速率的提高呈抛物线关系上升,而最大应变则随拉伸速率的提高而降低.800℃下、拉伸速率为0.02 s-1以下时为韧性断裂,拉伸速率为0.1 s-1以上时为脆性断裂.     

不同应变速率下5B70铝合金的拉伸断口分析

研究了不同应变速率下5B70铝合金的拉伸断口。结果表明:随着应变速率的增加,合金的断后伸长率下降。断口分析表明,应变速率越低,断口中的韧窝数量多且深度深,表现出明显的高韧性断裂。随着应变速率的增加,出现准解理面,合金偏向于脆性断裂。随着应变速率的增加,合金断口侧面晶粒伸长减小,析出相的数量减少。     

原位反应自发渗透法TiC／AZ91D镁基复合材料及AZ91D镁合金的拉伸变形与断裂行为

利用原位反应自发渗透技术合成了47．5％碳化钛TiC（体积分数，下同）增强AZ91D镁基复合材料，对比研究了该复合材料与铸态镁合金AZ91D基体的室温与高温拉伸变形行为，观察了拉伸断口微观组织形貌，并分析了这两种材料的断裂特征。结果表明，TiC／Mg复合材料具有良好的高温力学性能，在拉伸变形速率为0．001s^-1以及温度为723K，时其拉伸强度可达91．1MPa，而此时相同变形条件下的铸态AZ91D镁合金拉伸断裂强度只有41．1MPa，增幅达120％。而在室温下，镁基复合材料的拉伸断裂强度仅高出基体铸态镁合金23．4％。镁基复合材料的断裂应变较低，高低温时均表现为脆性断裂；而镁合金则由室温下的脆性断裂向高温下的韧性断裂过渡。     

超超临界转子用Inconel 617合金的热塑性

研究了不同温度对Inconel 617合金铸锭高温拉伸热塑性的影响。结果表明,Inconel 617合金在900℃以上有良好的热塑性,拉伸断口有明显的颈缩,断面收缩率均在90%以上。随拉伸温度的升高,颈缩越来越明显,断口韧窝变深,热塑性越来越好。拉伸时发生了局部动态再结晶,随温度升高,再结晶变得充分,高于1200℃拉伸时晶粒快速长大,且断口出现熔融现象。     

TC21钛合金的高温动态拉伸力学行为

在应变速率为0.001～1270s-1、温度为298～1023K条件下对魏氏组织和双态组织的TC21钛合金进行拉伸试验,利用SEM对拉伸试样的断口进行观察。结果表明:TC21钛合金的拉伸力学行为存在显著的温度和应变速率相关性;当应变速率为0.001和0.05s-1的屈服应力—温度曲线存在转折点,且转折点温度随应变速率的增大而升高;当温度低于转折点温度时,相同氧含量的TC21钛合金和多晶纯钛的屈服应力具有相似的温度相关性;微观组织影响屈服应力的幅值和拉伸塑性的大小,但不影响屈服应力的温度相关性和应变速率相关性;除魏氏组织在室温0.001s-1时为穿晶和沿晶混合断裂外,其他工况下的魏氏组织和双态组织均为穿晶韧性断裂;TC21钛合金在拉伸变形过程中未出现绝热剪切带和形变孪晶。     

316L不锈钢应力腐蚀慢应变速率拉伸试验

就316L不锈钢在不同腐蚀环境下的慢拉伸力学性能进行了试验研究。所有试验在恒定应变速率2.4×10-7/s和恒定温度80℃条件下进行,高压釜中为5%Na Cl水溶液,并分别充入CO2和H2S气体。通过改变Cl-的浓度研究Cl-在慢拉伸试验条件下对316L不锈钢的力学性能的影响。试验结果表明,Cl-对316L不锈钢的拉伸力学性能有明显影响,随着Cl-浓度的增加,316L不锈钢的抗拉强度逐渐降低;即Cl-可能是导致316L不锈钢慢拉伸应力腐蚀的关键因素。对316L不锈钢慢拉伸样品断口的SEM微观分析表明,在Cl-的作用下其断裂特性由韧性断裂逐渐转变为脆性断裂,即断口形貌在无Cl-和Cl-浓度较低时有明显的韧窝,为穿晶断裂;而随着Cl-浓度增加,断口形貌为解理性断裂,为沿晶断裂。     

Shear striations and deformation kinetics in highly deformed Zr-based bulk metallic glasses

Detailed microscopic observations of the shear surfaces of a deformed, but unfractured, bulk metallic glass sample reveal a wealth of information on the deformation characteristics, kinetics and influence of temperature during serrated flow. The shear surfaces exhibit shear striations, which are similar to those resulting from viscous-like flow in rock-forming minerals. On the shear surface only a few areas show typical vein patterns, the thicknesses of which are less than those known from fracture surfaces. Combined with estimates for adiabatic heating, this indicates that sufficiently high temperatures are already present during shear banding before fracture, though instigated by non-purely adiabatic effects. A kinetic model based on an energy variable which reflects the structural relaxation ability is proposed that accounts for the occurrence of serrated flow combined with negative strain rate sensitivity, and the transition to non-serrated flow, i.e. positive strain rate sensitivity, below a critical temperature and strain rate.     

Formation and mechanical properties of bulk Cu-Ti-Zr-Ni metallic glasses with high glass forming ability

Bulk amorphous Cu52.5Ti30Zr11.5Ni6 and Cu53.1Ti31.4Zr9.5Ni6 alloys with a high glass forming ability can be quenched into single amorphous rods with a diameter of 5 mm, and exhibit a high fracture strength of 2 212 MPa and 2 184 MPa under compressive condition, respectively. The stress—strain curves show nearly 2% elastic strain limit, yet display no appreciable macroscopic plastic deformation prior to the catastrophic fracture due to highly localized shear bands. The present work shows clearly evidence of molten droplets besides well-developed vein patterns typical of bulk metallic glasses on the fracture surface, suggesting that localized melting induced by adiabatic heating may occur during the final failure event.     

Effects of Laser Quenching on Impact Toughness and Fracture Morphologies of 40CrNiMo High Strength Steel

The surface of 40CrNiMo steel was quenched with a CO₂ laser, Charpy impact test was conducted at temperatures of 20, 0, and ?20 °C, and the impact absorption energies were measured. The fracture morphologies were observed with SEM, and the influence of microhardness, residual stress, and retained austenite on mechanical behavior of impact fracture after laser quenching was discussed. The results show that the hardened layer depth is more than 1 mm after laser quenching, and hardness is about 480-500 HV. The fracture morphology of the sample is dimple rupture at a temperature of 20 °C; with the lower temperature the fracture dimples become smaller. At a temperature of ?20 °C, the fracture morphologies change from ductile to brittle, which is mainly cleavage fracture. The increase in surface hardness, production of compressive residual stress, and existence of retained austenite after laser quenching are the main mechanisms of increasing impact toughness.     

Zr55Al10Ni5Cu30块状非晶合金的高温压缩断裂

利用Gleeble1500热模拟试验机研究了Zr55Al10Ni5Cu30块状非晶合金的高温压缩断裂，在室温情况下，在块状非晶合金断面的脉纹壁上出现了带有锯齿形边缘的裂口，在高温情况下，Zr55Al10Ni5Cu30块状非晶合金的宏观断面变得粗糙不平并出现了台阶，随着实验温度的不断上升，断面粘性流动特性变得更加明显，断面出现了大面积类似流动熔体凝固后的特征结构，塑性形变产生的最大剪切面的绝热温升或熔比是块状非晶合金中部粘性流动的原因。     

HEAT CAPACITIES OF Fe_（40）Ni_（40）B_（20） GLASSY ALLOY MEASURED BY ENTHALPY METHOD

ＨＥＡＴＣＡＰＡＣＩＴＩＥＳＯＦＦｅ_（４０）Ｎｉ_（４０）Ｂ_（２０）ＧＬＡＳＳＹＡＬＬＯＹＭＥＡＳＵＲＥＤＢＹＥＮＴＨＡＬＰＹＭＥＴＨＯＤ￥ＪＩＡＮＧＱｉｎｇ;ＺＨＡＯＭｉｎｇ;ＬＩＪｉａｎｃｈｅｎ（ＪｉｌｉｎＵｎｉｖｅｒｓｉｔｙｏｆＴｅｃｈｎｏｌ?..     

硅元素对炉生铁皮界面微观结构的影响研究

钢铁板带产品生产中发现,随着Si含量的增加,红铁皮缺陷比例增加,热卷表面质量下降。红铁皮产生的原因主要与Fe2SiO4的液相温度有关,但目前对富Si相熔融的微观特征研究鲜少报道。本文通过热重模拟实验,研究分析了加热温度、保温时间和钢中Si含量等因素对铁皮界面结构的影响。研究发现：Si质量分数为0.15%时,基体与铁皮界面无典型的富Si颗粒带,Si质量分数大于0.50%时,界面富集层明显;低温模拟试样富Si层为颗粒带,高温下为网状形貌;进一步观察高温模拟试样,界面处存在富Si层锚状侵入形貌,其形成原因为Fe2SiO4相高于1 170 ℃时为液相,其渗透和流动性更强,在钢基体内部裂纹和晶界等缺陷处加速氧化,此结构为高Si钢炉生铁皮难以除去的关键。     

高速冲击拉伸条件下低硅TRIP钢的延伸率特性

对低硅HSLA -TRIP钢在室温条件下 5 0 0s-1～ 1 70 0S-1应变率范围内的动态拉伸性能进行了研究。实验结果表明 ,随应变率增大 ,钢的均匀延伸率 (eu)下降、总延伸率(et)和能量吸收值增加 ,但强度 (σb)保持不变或略有提高 ,能量吸收的增幅随应变率增大而变缓。分析认为 :残余奥氏体在颈缩发生前的较完全转变有利于提高均匀延伸率 ;高应变率下能量吸收值的提高可能由两个原因造成 :一是大应变下的奥氏体相变推迟断裂的发生 ;二是动态拉伸中的绝热温升有利于总延伸率的提高。     

应变速率对Ti/Mg基非晶双连续相复合材料力学行为的影响

采用真空压力浸渗技术了制备金属Ti/Mg基非晶双连续相复合材料,系统研究了其准静态和动态力学行为。并借助XRD、SEM等技术分析了该复合材料的结构和断口形貌。研究发现,该复合材料具有优异的综合力学性能,强度优于基体Mg基非晶合金和增强相Ti骨架。动态载荷下,应变速率的变化对复合材料的性能和断口形貌具有显著的影响,随应变速率的增大,复合材料的强度逐渐升高,断口上非晶相的粘滞流变现象更加明显。     

Microstructure Evolution and Strain-Dependent Constitutive Modeling to Predict the Flow Behavior of 20Cr–24Ni–6Mo Super-Austenitic Stainless Steel During Hot Deformation

Hot compression tests were carried out with specimens of 20 Cr–24 Ni–6 Mo super-austenitic stainless steel at strain rate from 0.01 to 10 s~(-1) in the temperature range from 950 to 1150 °C, and flow behavior was analyzed. Microstructure analysis indicated that dynamic recrystallization(DRX) behavior was more sensitive to the temperature than strain rate, and full DRX was obtained when the specimen deformed at 1150 °C. When the temperature reduced to 1050 °C, full DRX was completed at the highest strain rate 10 s~(-1) rather than at the lowest strain rate 0.01 s~(-1) because the adiabatic heating was pronounced at higher strain rate. In addition, flow behavior reflected in flow curves was inconsistent with the actual microstructural evolution during hot deformation, especially at higher strain rates and lower temperatures. Therefore, flow curves were revised in consideration of the effects of adiabatic heating and friction during hot deformation. The results showed that adiabatic heating became greater with the increase of strain level, strain rate and the decrease of temperature, while the frictional effect cannot be neglected at high strain level. Moreover, based on the revised flow curves, strain-dependent constitutive modeling was developed and verified by comparing the predicted data with the experimental data and the modified data. The result suggested that the developed constitutive modeling can more adequately predict the flow behavior reflected by corrected flow curves than that reflected by experimental flow curves, even though some difference existed at 950 °C and0.01 s~(-1). The main reason was that plenty of precipitates generated at this deformation condition and affected the DRX behavior and deformation behavior, eventually resulted in dramatic increase of deformation resistance.     

Deformation and fracture behaviors of Co-based metallic glass and its composite with dendrites

Microstructures and mechanical properties of Co-based metallic glass with nominal composition of Co₄₃Fe₂₀Ta_5.5B_31.5 (at.%) cast at the different cooling rates were investigated. When cooling rate is low enough, some dendritic crystalline phases were in situ precipitated from the glass matrix, forming the Co-based metallic glass composite with dendrites. Macroscopically, the fully amorphous samples often split apart or were broken into some particles, displaying a fragmentation failure mode. The size of particles became larger with the decrease in cooling rate. But, strength reduces slightly. Besides, the composites with dendrites show a small compressive plasticity, plus local melting behaviors with vein-like structure on the fracture surfaces. Furthermore, the effects of cooling rate on microstructures, deformation and fracture behaviors were discussed systemically. It is proposed that the fragmentation mechanism can be attributed to the inherent brittle character and high stress concentrations around the free volume. And the local melting behavior is due to the more receiving elastic energy and local shearing.