Mg-3Al-6Zn-2Y合金的动态压缩性能研究

在0.001、900、1300s-13个应变率下,研究了Mg-3Al-6Zn-2Y合金的压缩性能及微细观变化。结果表明:随应变率增大,合金应变硬化率增大,极限强度与屈服强度增大;强化相Al2Y、Al12Mg17与过渡相MgZn2含量减少;合金产生{1012}<1010>孪生,位错密度增大,出现缠结,并在孪生界面塞集。强化相减少对强度的弱化作用与高密度位错塞集的强化作用相互竞争。     

Mg-3Al-2Zn-2Y合金不同应变率压缩性能研究

在0.001～4800s-1应变率范围,研究了Mg-3Al-2Zn-2Y合金的室温压缩性能。结果表明:合金经1300s-1压缩后,基面与非基面的位错滑移形成平行、弯曲与缠结的混合位错组态;经1800与4800s-1压缩后出现孪生;上述微细观变化导致合金流变应力与极限强度在0.001~1800s-1范围具有应变率强化效应;合金经4800s-1压缩后,出现了以再结晶晶粒与孪生晶粒共同形成的变形局域化区域,导致力学性能比1800s-1时有所下降。     

Ti—47Al—2W—0.5Si抗蠕变合金的高温力学行为和变形机制

研究了Ti-47Al-2W-0.5Si铸造合金的力学行为和变形机制。结果表明,合金的室温－高温屈服强度和650℃蠕变强度都超过LN713LC镍基高温合金的比屈服强度和比蠕变强度,表现出优异的中温力学性能。在蠕变过程中,随着载荷和温度的增加,合金的最小蠕变速率随之增大。可用蠕变方程εm=A（σ/E）^10exP(-420/RT)来描述。位错在界面处繁殖,并在α2/γ层片中缠结和塞积,导致合金的初始蠕变应变速率降低。当位错运动受阻时,可以通过孪生方式使内应力得到缓解。在蠕变第一阶段就可以发生孪生和剪切现象。在高温应力作用下,α2片层发生粗化和相转变。此外,还对合金的实际应用效果进行了考核,并说明了该合金的发展方向。     

钇钕复合合金化对Mg-6Al合金力学性能的影响

研究了Y、Nd复合合金化(Y:Nd=2:1,wt%)对Mg-6Al合金显微组织和力学性能的影响.结果表明,添加稀土元素Y和Nd可显著提高合金从室温至175℃区间的屈服强度和抗拉强度.在Mg-6Al合金中加入总含量为0.9wt%～3.6wt%的Y Nd后,合金的晶粒得到明显细化,且出现Al2Y、Al2Nd高熔点稀土合金相.并探讨了钇钕复合合金化对提高镁铝基合金力学性能的机理:室温下主要是细晶强化机制;高温下则主要是高熔点稀土合金相(Al2Y、Al2Nd)的弥散强化,并由此使热稳定性差的β-Mg17Al12相的数量减少.     

ANTIPHASE DOMAIN BOUNDARY ENERGY OF γ′ [Ni_3(Al,Ti)] PARTICLES WITH VARIOUS Al CONTENTS AND THEIR STRENGTHENING CONTRIBUTION TO A Ni-BASE ALLOY GH99

GH99镍基合金在室温拉伸变形条件下,被位错切割过渡到被位错绕过的γ'[Ni_3(Al,Ti)]质点的临界直径约为60nm.在同样条件下,该合金γ'强化的方式属于被位错切割机制.增加γ'相中Al含量能提高其反相畴界能和增大合金塑性变形的临界分切应力.GH99镍基合金的室温屈服强度理论计算值与实测值很接近.由γ'沉淀强化所贡献的强度占总强度的45％到64％,它随γ'相中Al含量的增多而增大.晶界碳化物强化所贡献的强度很少,只占2—3％。     

不同Al含量γ′相的反相畴界能及其对GH99镍基合金强度的贡献

GH99镍基合金在室温拉伸变形条件下,被位错切割过渡到被位错绕过的γ'[Ni_3(Al,Ti)]质点的临界直径约为60nm.在同样条件下,该合金γ'强化的方式属于被位错切割机制.增加γ'相中Al含量能提高其反相畴界能和增大合金塑性变形的临界分切应力.GH99镍基合金的室温屈服强度理论计算值与实测值很接近.由γ'沉淀强化所贡献的强度占总强度的45％到64％,它随γ'相中Al含量的增多而增大.晶界碳化物强化所贡献的强度很少,只占2—3％。     

Ca加入量对Mg-5Al-0.4Zn基铸造合金组织与力学性能的影响

用砂型铸造了不同Ca含量的Mg-5Al-0.4Zn-0.2Mn-Sr-Ti-xCa合金.当x为0.37,0.70,0.93,1.69时,合金相组成为α-Mg,（α＋Al2Ca）共晶和Mg17Al12.当x=2.93时,相组成为α-Mg和（α＋（Mg,Al）2Ca）共晶.随着x增加,合金的室温力学性能（σb和δ）呈下降趋势,但合金在200℃下的强度先升高,后又降低.高温延伸率随x增加而下降.合金200℃下的屈服强度σ0.2,200℃随x的增大而稳步增加.组织的热稳定性分析表明,Ca溶入Mg17Al12相使得其自身的耐热性提高.晶界上耐高温相Al2Ca或（Mg,Al）2Ca的形成,在高温下对晶界具有钉扎作用,并降低了晶界处的溶质扩散速度,使晶界强度提高.TEM分析表明,含Ca合金在200℃拉伸时,（1010）棱柱面和（1121）角锥面上的位错参与了滑移.不同滑移系的位错滑移到晶界时,受到晶界上Al2Ca相阻挡而发生位错塞积.     

AZ91镁合金的动态应力-应变行为及其应变率效应

利用Hopkinson压杆技术对AZ91镁合金进行了冲击压缩实验,分析了该合金在铸态和固溶及时效处理后的动态应力-应变行为及其应变率效应.结果表明：在10^2-10^3s^-1应变率下,随应变率提高,AZ91镁合金在铸态和固溶及时效处理后的应力-应变曲线均具有先升高（正应变率效应）而后下降（负应变率效应）的特性,最大应变也连续增大,且随应变增加,流动应力显著增大.这主要是α-Mg基体的加工硬化、β-Mg17Al12相和Mg-Al-Mn相的晶界强化与沉淀强化、热软化及孔洞或裂纹的产生与发展所致.     

挤压态喷射成形Mg12Al1.5Zn6.5Ca1Nd镁合金组织及力学性能

利用喷射成形技术制备了Mg12Al1.5Zn6.5Ca1Nd镁合金,采用X射线衍射仪(XRD)、扫描电子显微镜(SEM)、透射电子显微镜(TEM)等测试手段,研究了挤压态实验合金的微观组织及力学性能。结果表明:挤压态实验合金组织主要由α-Mg和Al2Ca组成,合金组织为等轴晶,晶粒大小约为2μm,第二相Al2Ca颗粒主要弥散分布在晶界处,颗粒平均尺寸小于1μm;基体内存在位错网及位错塞积,Al2Ca相中存在孪晶结构;合金抗拉强度(σb)、屈服强度(σ0.2)、延伸率(δ)分别为470 MPa、350 MPa、4.7%,主要强化方式为细晶强化、弥散强化、固溶强化;断口存在微孔聚合形成的孔洞,孔洞底部的杂质相或孔洞周围硬脆相与基体之间易萌生微裂纹,合金断裂机制为微孔聚合型沿晶断裂。     

球形SiO2表面Ag纳米粒子生长及其拉曼增强效应

针对粉末冶金铍铝合金开展了微屈服行为的研究;利用SEM、TEM研究了合金在微屈服过程中不同形变量下两相的位错形态变化和断口组织特征.结果表明:合金的微屈服强度较低;铍相在未发生微屈服至发生2个微应变时(2×10-6),位错很难发现;79个微应变时,晶内晶界均出现位错;121个微应变时,位错扩大运动连接成折线状;500个微应变时,位错缠结;拉伸断裂后,晶内的位错线被拉直,晶界附近区域的位错数量减少.与铍相不同,铝相在未屈服前,就已出现少量位错;2个微应变时,基体大面积发生塑性应变;当微应变增至79个时,在外载荷和热残余应力的驱动下,铝域内的位错聚集在界面处,致使位错切入铍相内,降低铍相的形变抗力.铍铝合金的断裂模式为脆性铍相的解理断裂和韧性铝相的韧窝断裂构成的混合型断裂.     

Mg-Al-Ce-Y基压铸合金的微观结构稳定性和力学性能(英文)

为进一步提高Mg-Al-RE基合金的力学性能,采用高压压铸技术制备Mg-3.0Al-1.8Ce-0.3Y-0.2Mn合金,并研究其微观组织、金属间相的热稳定性和合金的力学性能。结果表明:合金由细小的初生α-Mg枝晶和枝晶间的共晶组成。共晶中存在两种金属间相,即Al11(Ce,Y)3和Al2(Ce,Y),其中Al11(Ce,Y)3是主要增强相。研究还表明,Al11(Ce,Y)3的热稳定性是有条件限制的,在200°C时效800h,它基本保持稳定,而在450°C时效800h,绝大部分的Al11(Ce,Y)3发生相分解,转变为Al2(Ce,Y)。添加Ce和Y后,合金强度在室温和200°C下得到明显的提高。合金性能的提高主要归因于Al11(Ce,Y)3的形成对枝晶间区域的增强作用、晶粒细化的影响以及由Y原子造成的固溶强化。     

Dislocation and Structural Studies at Metal–Metallic Glass Interface at Low Temperature

In this paper, molecular dynamics (MD) simulation deformation studies on the Al (metal)–Cu₅₀Zr₅₀ (metallic glass) model interface is carried out based on cohesive zone model. The interface is subjected to mode-I loading at a strain rate of 10⁹ s^?1 and temperature of 100 K. The dislocations reactions and evolution of dislocation densities during the deformation have been investigated. Atomic interactions between Al, Cu and Zr atoms are modeled using EAM (embedded atom method) potential, and a timestep of 0.002 ps is used for performing the MD simulations. A circular crack and rectangular notch are introduced at the interface to investigate the effect on the deformation behavior and fracture. Further, scale size effect is also investigated. The structural changes and evolution of dislocation density are also examined. It is found that the dominant deformation mechanism is by Shockley partial dislocation nucleation. Amorphization is observed in the Al regions close to the interface and occurs at a lower strain in the presence of a crack. The total dislocation density is found to be maximum after the first yield in both the perfect and defect interface models and is highest in the case of perfect interface with a density of 6.31 × 10¹⁷ m^?2. In the perfect and circular crack defect interface models, it is observed that the fraction of Shockley partial dislocation density decreases, whereas that of strain rod dislocations increases with increase in strain.     

Influence of pulse impact on properties of liquid phase pulse impact diffusion welding SiCp/AlSi7Mg and its welding mechanism

Abstract

The influence of pulse impact on the microstructure and properties of welded joints of aluminium matrix composite SiC_p/AlSi7Mg by liquid phase pulse impact diffusion welding (LPPIDW) and its welding mechanism had been studied. It showed that during LPPIDW, under the effect of pulse impact, the interface state between SiC particle and matrix was prominent, the initial pernicious contact state of reinforcement particles had been changed from reinforcement (SiC)/reinforcement (SiC) to reinforcement (SiC)/matrix/reinforcement (SiC), and the harmful microstructure or brittle phase was restrained from the welded joint. Moreover, the density of dislocation in the matrix neighbouring to and away from the interface was higher than that of its parent composite and the dislocation entwisted each other intensively. Furthermore, the deformation mainly occurred in the matrix grain and the matrices around SiC particles engendering intensive aberration offered a high density nucleus area for matrix crystal in favour of forming nanograins, which improved the properties of welded joints distinctly, resulting in welding the composite successfully. Consequently, the tensile strength of the welded joints was up to 179 MPa, which was ～74˙6% of the strength of SiC_p/AlSi7Mg (as stir cast), and its corresponding radial deformation was less than 3%, suitable for the demand of deformation of welded specimens.     

应变速率对高氮奥氏体钢拉伸变形的影响

采用金相及透射电子显微镜对高氮奥氏体Fe-20Mn-19Cr-0. 6N钢在应变速率范围为3×10^-6～1 s^-1条件下的拉伸变形行为进行了研究。研究结果表明:N元素的固溶强化作用和促使位错平面滑移阻碍位错运动机制是高氮奥氏体钢的重要应变硬化机制,同时,随着应变速率的提升,这种强化机制不断提升,而应变诱导孪生机制不断削弱。随着应变速率的提升,高氮奥氏体钢的抗拉强度和屈服强度均呈逐步上升的趋势,断后伸长率则逐步下降。屈服强度提升超过60%,而抗拉强度提升仅10%。随着应变速率的提升,基体变形程度逐步下降,材料的位错密度和滑移带密度逐步下降。     

In situ TEM observation of dislocation motion in thermally strained Al nanowires

Al thin films deposited epitaxially on (0001) -Al₂O₃ substrates, have been thinned cross-sectionally to form Al nanowires. The Al wires, consisting of two Σ3 twin variants, have been strained in situ by differential thermal expansion between the Al wires and the Al₂O₃ substrate during transmission electron microscopy heating. Dynamical observations show that maximum dislocation activity occurs in the first heating cycle up to 400°C, with decreasing activity during further cycles. The {111} Al || (0001) -Al₂O₃ interface acts as a source of dislocation half-loops. The motion of threading dislocations along the wires generates long trailing dislocation segments parallel to, and offset from, the {111} Al || (0001) -Al₂O₃ interface. Dislocation multiplication occurs by the reaction of half-loops and extended threading dislocation segments at the wire boundaries and substrate interface. The Σ3 twin grains bisecting the wires are observed to be stable during thermal cycling to 400°C, and their { } boundaries are weak pinning sites.     

Stress relaxation and the structure size-dependence of plastic deformation in nanotwinned copper

Stress-relaxation experiments were performed on nanotwinned Cu to characterize the twin size-dependence of the activation volume and mobile dislocation density. We find that the variation of activation volume as a function of twin lamellae thickness can be captured well by a Hall–Petch-type relation. This structure size-dependence is interpreted to arise from a transition of the rate-controlling mechanism from intra-twin to twin boundary-mediated processes with decreasing twin thickness. Furthermore, we find that the exhaustion rate of mobile dislocations reduces with decreasing twin thickness. Such a twin size-dependence is attributed to the increased strain-hardening rate associated with a high density of coherent twin boundaries. Our results demonstrate that twin boundary-mediated dislocation processes can effectively promote the strain hardening and preserve mobile dislocations, leading to ultrahigh strength while retaining ductility in nanotwinned Cu.     

Microstructures and mechanical properties of BP/7A04 Al matrix composites

The microstructures and interface structures of basalt particle reinforced 7A04 Al matrix composites (BP/7A04 Al) were analyzed by using OM, TEM, SEM and EDS, and the mechanical properties of 7A04 Al alloy were compared with those of BP/7A04 Al matrix composites. The results show that the basalt particles are dispersed in the Al matrix and form a strong bonding interface with the Al matrix. SiO₂ at the edge of the basalt particles is continuously replaced by Al₂O₃ formed in the reaction, forming a high-temperature reaction layer with a thickness of several tens of nanometers, and Al₂O₃ strengthens the bonding interface between basalt particles and Al matrix. The dispersed basalt particles promote the dislocation multiplication, vacancy formation and precipitation of the matrix, and the precipitated phases mainly consist of plate-like η (MgZn₂) phase and bright white band-shaped or ellipsoidal T (Al₂Mg₃Zn₃) phase. The bonding interface, high dislocation density and dispersion strengthening phase significantly improve the mechanical properties of the composites. The yield strength and ultimate tensile strength of BP/7A04 Al matrix composites are up to 665 and 699 MPa, which increase by 11.4% and 10.9% respectively compared with 7A04 Al alloy without basalt particles.     

应变速率对含空洞的镁孪晶界面塑性变形机制的影响

利用嵌入原子势的分子动力学模拟,研究了应变速率对含空洞的镁孪晶界面塑性变形机制的影响。结果表明,塑性变形的主要形式包括不全位错、滑移带和堆垛层错;应变速率不会改变试样的杨氏模量,应变速率愈大屈服应力愈大;随着应变速率增大,位错和滑移带的数量增加,堆垛层错的数目先增加后减小,位错运动自由行程的平均长度减小;随着变形进行,位错源不断产生新位错,导致位错密度提高;高应变速率时,晶界处容易形成应力集中,并会有微裂纹产生。     

Al2O3,TiB2粒子增强铝基复合材料的动态压缩性能和高温蠕变性能

对ＴｉＯ２－Ａｌ－Ｂ和ＴｉＯ２－Ａｌ－Ｂ２Ｏ３体系制备的两种Ａｌ２Ｏ３和ＴｉＢ２原位粒子增强铝基复合材料进行了动态压缩试验和高温拉伸蠕变试验。动态压缩试验表明,随着应变速率的提高,复合材料的强度和初始加工硬化率明显增加。然而,复合材料中含有的条状Ａｌ３Ｔｉ对复合材料的动态机械响应基本没有影响。透射电镜观察表明,在高应变速率下两种复合材料强度和初始加工硬化率的明显提高可由复合材料基体中位错密度的显著     

FATIGUE BEHAVIOUR OF SiC_p/6061Al COMPOSITE

The fatigue of SiC_p/6061Al composite containing 15 v.-% SiC particles has been compared with 6061Al alloy.Dislocation structure and microprocess of fatigue crack initiation and propagation in the composite have been investigated by using SEM and TEM.The results in- dicate that the fatigue strength at 10~7 cycles of the composite is 196 MPa,i.e.about 25% higher than matrix alloy.The voids and microcracks initiated at and near the interface be- tween SiC_p and matrix,where has a higher density of dislocations,will propagate and link up to form the fatigue crack.It is an important evidence to note that the dislocation channels where screw dislocation can travel are formed near interface and corner region of SiC_o in the composite subjected to fatigue stress(σ_(max)=274 MPa N=2.4×10~5 cycles),demonstrating the relationship between fatigue crack initiation and dislocation movement in the SiC particles reinforced 6061 Al alloy composite.