离子辐照对Zr50.7Cu28Ni9Al12.3非晶合金力学性能的影响

非晶合金有潜力成为新一代核材料,离子辐照对其力学性能的影响决定了其使用价值。在不同剂量的Au离子辐照下,探讨了Zr_(50.7)Cu_(28)Ni_9Al_(12.3)非晶合金力学性能的变化过程。原子力显微镜以及正电子湮没寿命谱分析表明,在离子辐照后,非晶合金的自由体积尺寸增大、密度下降,总自由体积增加。透射电子显微镜分析表明,辐照剂量在达到50 dpa时非晶合金开始有纳米晶析出,随着辐照剂量的增加,纳米晶尺寸在增加、密度变大。纳米压痕试验表明,离子辐照后非晶合金的硬度减小,在高剂量时硬度又有增加的趋势。离子辐照下非晶合金的硬度变化是自由体积以及纳米晶竞争的结果。自由体积使非晶合金软化,纳米晶析出使非晶合金硬化。     

退火工艺对Ce69Al10Cu20Co1非晶合金热稳定性与力学性能的影响

利用X射线衍射分析、差热扫描热分析仪和纳米压痕仪研究退火保温时间对Ce69Al10Cu20Co1非晶热稳定性和力学性能的影响。结果表明:在低于玻璃转变温度以下长时间等温退火,材料仍保持非晶结构,随退火时间的延长,合金的自由体积和缺陷浓度逐渐减少,合金玻璃转化温度逐渐升高,而晶化温度逐渐降低。纳米压痕结果表明,铸态和弛豫态非晶合金在压痕保载曲线均出现明显的蠕变平台,随退火时间延长,由于形成更加致密的堆垛结构,蠕变平台宽度不断减小,而合金的模量和硬度均有提高。     

Zr55块体非晶合金在低频振动场下的微成形能力

通过设计的振动挤压侧向流动方案,对Zr55Cu30Al10Ni5块体非晶合金在过冷液态区的微成形能力进行了研究。利用DEFORM-3D有限元分析软件,对Zr55Cu30Al10Ni5块体非晶合金在振动场作用下的流动变形能力进行了数值模拟分析,在450℃下选取不同振幅38N~760N和不同频率0.1Hz~2.0Hz进行成形实验,测量了非晶合金在横向槽内的流动长度。结果表明,引入振动场可以有效提高非晶合金的微成形能力,随着频率的增大,流动长度明显增大;随着振幅的增大,流动长度先增大后趋向平稳。从材料损耗模量、自由体积理论和表面效应3个方面对该现象进行了分析,表明振动成形是一种提高非晶合金微成形能力的有效方法。     

压痕诱导单晶GaAs非晶相变

利用高分辨电子显微镜观察了(100)GaAs单晶Vickers压痕诱发的形变行为.结果表明,这种材料在Vickers硬度计载荷的作用下产生许多孪晶和堆垛层错,导致发生晶格扭曲,最终诱发晶体的非晶转变.孪晶、层错和晶格扭曲很可能是压痕诱发GaAs非晶转变过程中经历的变形阶段.     

Zr基非晶合金在过冷液相区的高应变速率压缩变形行为

利用Gleeble1500热模拟机研究了Zr41.2Ti13.8Cu12.5Ni10Be22.5非晶合金在过冷液相区内633、653和673K,应变速率分别为2×10-2s-1和2×10-1s-1条件下的单向压缩变形行为.结果表明:在673 K时两种应变速率下,该合金都具有很好的塑性,尤其在2×10-2s-1时流变应力只有74 MPa,非常适于进行超塑性加工.对非晶合金的断口进行了观察,得到柱状非晶合金压缩变形时外观和断口形貌随着变形条件的变化规律.采用自由体积模型对非晶合金的形变和断裂的微观机制进行了分析.     

退火温度对Mg61Cu28Gd11块体非晶结构与性能的影响

对Mg61Cu28Gd11块体非晶在其玻璃转变温度以下温度(325、350、375和400 K)等温退火1 h,用X射线衍射仪(XRD)、差热扫描量热仪(DSC)、纳米压痕仪、扫描电子显微镜(SEM)、显微维氏硬度计等分析研究了低温退火对其热稳定性、微区力学性能及变形的影响,并分析了塑性变形机理.结果表明,低温退火后非晶原子的短程有序性增加,非晶结构的稳定性变差,并在400K发生部分晶化.同时,在325～375 K范围内,显微硬度和弹性模量E随退火温度的升高而增大,塑性变形量Dn和最大压入深度Dmax减小;400 K退火后,由于少量析出的晶体相与压头下新产生的自由体积相互作用,合金抵抗变形能力减弱,显微硬度和弹性模量E降低,Dn和Dmax提高.     

蒸发法制备Ni－Ti纳米非晶合金粒子

采用气相蒸发法制备纳米量级的Ｎｉ－Ｔｉ非晶合金粒子，研究了各种因素对Ｎｉ－Ｔｉ纳米非晶合金粒子形成的影响，并用透射电子显微镜，高分辨电子显微镜，Ｘ射线衍射仪和能谱等多种手段对纳米非晶合金粒子进行了表征．结果表明，当粒子成分在共晶区Ｎｉ（４０）Ｔｉ（６０）附近时，容易形成非晶；较低惰性气体压力和较高蒸发温度有利于Ｎｉ－Ｔｉ纳米非晶粒子的形成．     

Zr基大块非晶合金的微区变形及力学性能

利用纳米压痕仪、扫描电镜等研究了Zr基大块非晶合金在纳米压痕条件下的变形及力学性能。Zr基大块非晶合金在纳米压头作用下以弹性-塑性方式变形，载荷-位移曲线及压痕周边多重剪切带(堆起或波纹状)的特征证明了塑性变形的存在。冷却速度、第二相及退火等因素影响非晶合金的压痕硬度HV和弹性模量E，冷却速度小的试样或部位(如试样中心)的HV，E值略高；离第二相(W丝)越近，HV，E值越高；退火处理提高非晶的HV，E值，同时退火与第二相还明显改变压痕周边的变形状态及塑性变形量的大小，退火显著减小塑性变形量，使压痕周边凹陷，而第二相使压痕堆起消失。对塑性变形机理进行了初步分析。     

块体非晶合金剪切带的原子力纳米压痕行为

通过原子力显微镜(AFM)纳米压痕实验研究传统纳米压痕实验形成的Fe基非晶合金剪切带区域及未变形区域的变形;结合压痕形貌实时原位观测,探讨块体非晶合金塑性变形局域化的原因.结果表明最大载荷44.6μN下,材料的剪切带、剪切带间和未变形区域的AFM纳米压痕残余面积分别为3274.7、2976.5和2879.2nm2,对应的硬度分别为13.62、14.98和15.49GPa,剪切带区域的硬度值比未变形区域的硬度值降低了约10%,说明塑性变形过程中,过剩自由体积的产生使剪切带结构发生软化.     

Zr41Ti14Cu12.5Ni10Be22.5块体非晶合金结构自由体积周围化学环境的研究

采用X射线衍射(XRD)、正电子湮没技术(PAT)-多普勒展宽谱,研究Zr41Ti14Cu12.5Ni10Be22.5块体非晶合金及其过冷液相区结构自由体积周围的元素分布.结果表明:原始制备的Zr41Ti14Cu12.5Ni10Be22.5块体非晶合金其结构自由体积周围主要富集Zr原子,在过冷液相区(T＝400 ℃)等温退火后,在该合金结构自由体积周围探测到Zr、Ti和Be原子.     

镁基大块非晶合金在过冷液相区流变行为本构关系

研究了Mg60Cu30Y10大块非晶合金在过冷液相区的流变行为.结果表明:随着温度升高和应变速率增加,平衡态的牛顿流转变为非平衡态的非牛顿流;其流变行为对于温度和应变速率非常敏感.由粘度与应变速率的关系,根据Arrhenius型VFT方程,确定了流动应力、应变速率和温度的关系.Mg60Cu30Y10大块非晶合金在过冷液相区的流变性能依赖于温度与变形速率,其微观机制可由自由体积模型解释,为大块非晶合金流变成形工艺的实现提供理论依据:温度高于玻璃转变温度以后,自由体积的增加使非晶合金变形过程中能够移动的原子数目随之增加,自由体积周围的原子沿外力的作用方向移动,即宏观上的塑性流变行为.应变速率增加,由热激活引起的自由体积增加不能满足更多原子流变所需的空间体积,导致牛顿流向非牛顿流转变.     

微量添加Fe元素对CuZrAl块体金属玻璃的结构和力学性能的影响(英文)

使用水淬法制备含微量Fe元素的CuZrAl块体金属玻璃。使用X射线衍射(XRD)检测其结构;采用DSC研究Fe元素的添加对块体金属玻璃热稳定性的影响,微量添加Fe元素显著拓宽了过冷液相区。Cu44Zr48Al7Fe块体金属玻璃的塑性应变约为1.5%。使用透射电子显微镜(TEM)观察其微观结构,结果发现,添加1%～2%Fe(摩尔分数)的CuZrAl合金中出现了相分离的富CuZr非晶相。     

Mg-Cu-Y块体金属玻璃的塑性变形特性

通过对Mg-Cu-Y块体金属玻璃在深过冷液体区间塑性变形特性的研究，探讨了影响其塑性变形的因素及其影响规律。结果表明，加载温度和时间均对其塑性变形有明显的影响，在深过冷液体区间，要达到合适的变形量，加载温度和时间必须适中；Mg-Cu-Y块体金属玻璃在压缩条件下能够发生流变，较好地复制模具表面的显微形貌。同时，在加载条件下，Mg-Cu-Y块体金属玻璃更容易发生晶化。     

Zr_(65)Al_(7.5)Ni_(10)Cu_(12.5)Ag_5非晶合金压痕下方剪切带形貌的研究

以Zr65Al7.5Ni10Cu12.5Ag5块体非晶合金作为研究对象,采用界面压痕技术和扫描电子显微镜,分别对铸态、轧制态以及轧制-退火态试样压痕下方的剪切带形貌进行了研究。实验结果表明,铸态试样以半圆形剪切带为主,同时存在少量的射线状剪切带,并且形貌比较规则;轧制态试样的剪切带形貌变得很不规则,很难分辨半圆形和射线状剪切带,并且随着变形量的增加,剪切带形貌的不规则程度增加;轧制-退火态试样中重新出现了规则的半圆形和射线状剪切带,变形量对剪切带形貌几乎没有影响。这些结果说明,轧制态试样压痕下方剪切带形貌不规则的主要原因是轧制变形使剪切带中自由体积含量显著增加。     

块状非晶态合金Zr65Al7.5Ni10Cu17.5的室温单轴压缩断裂行为

利用IUTM和SEM研究了Zr65Al7 5Ni10Cu17.5块状非晶合金的室温单轴压缩变形和断裂行为.该合金的室温压缩变形过程主要表现为弹性和塑性变形,并且塑性变形阶段没有加工硬化现象.宏观形貌观察发现样品形成与压缩方向呈约45°的变形带.塑性变形以剪切带粘性流层相对滑动的方式进行,在变形过程中形成脉络状断面形貌.裂纹于塑性变形积累到一定程度之后,在切变变形较大的区域表面形成.裂纹从萌生、扩展到断裂,时间极短.流变积累和应力集中综合作用的结果导致断裂.     

体积分数对Wf／Zr基非晶复合材料准静态压缩特性的影响

系统研究了体积分数对钨丝增强Zr基非晶复合材料力学性能的影响。结果显示，在钨丝体积分数〈50％时，复合材料以剪切方式断裂为主，压缩强度和塑性应变随着体积分数的增加而增加；在体积分数≥50％时，复合材料以弯曲和劈开方式断裂为主，压缩强度随着体积分数的增加而继续增加，而塑性应变则开始降低。分析表明，钨丝体积分数的变化通过影响剪切带的形成而引起材料的力学性能发生变化。     

Interpretation of viscous deformation of Zr-based bulk metallic glass alloys based on Nabarro-Herring creep model

Superplastic-like viscous deformation of bulk metallic glass alloys around the glass transition temperature (Tg) was analyzed based on the Nabarro-Herring creep model, a classical creep model, where the diffusional motion of atoms or vacancies through the lattice (atomic configuration) is considered. The amorphous matrix of bulk metallic glasses that has a randomly-packed atomic configuration was assumed to behave in a manner similar to the grain boundary in polycrystalline metals so as to approximate the diffusivity of the major constituent element. In spite of rough approximation of the parameters in the Nabarro-Herring creep equation, a reasonable value of the diffusion path (d) could be obtained from the experimentally-obtained metal flow data, including the steady state stress and the strain rate. Due to the absence of vacancy sources such as grain boundaries in homogeneous metallic glasses, the diffusion path, which, in polycrystalline materials, generally is the average distance between vacancy sources such as grain boundaries, was considered in this work as the average distance between tunneling centers in bulk metallic glass alloys. The calculated diffusion path was comparable to the density of tunneling centers around Tg, proposed by M. H. Cohen and G. S. Grest based on free volume theory. The calculated diffusion path showed monotonous decrease with temperature over Tg for Zr-based bulk metallic glass alloys. Based on this analysis, a schematic model for viscous deformation of bulk metallic glass was proposed.     

钨颗粒增强大块非晶复合材料

利用不锈钢管水淬法制备出直径为10mm、钨颗粒体积分数达60％的非晶基复合材料。RXD分析表明，除元素W峰外，没有发现其它晶态相的析出。单轴压缩实验表明，复合材料能大幅度提高非晶合金的塑性应变。对非晶复合材料塑性变形机理进行了讨论。     

On the structural relaxation of bulk metallic glass under warm deformation

The influence of both isothermal annealing and warm deformation on the structural relaxation behavior of Zr₄₄Ti₁₁Cu_9.8Ni_10.2Be₂₅ (LM1B) bulk metallic glass (BMG) was investigated. The structurally relaxed samples were obtained from warm extrusion to introduce different amounts of free volume annihilation. We employed density measurements as well as differential scanning calorimetry to study free volume changes in these structurally relaxed samples. The results demonstrated that isothermal annealing within the supercooled liquid region (SLR) caused annihilation of free volume by ～0.1%, but a small amount of in situ deformation promoted the annihilation process. In contrast to the conventional belief that annealing induced embrittlement caused by the reduction of free volume and densification, it is interesting to note that, in this study, when material was relaxed at the mid-temperature within the SLR (673 K for LM1B) plastic strain actually increased as compared to the as-received counterpart. This indicates that proper warm deformation can improve the room temperature plasticity of BMG as a result of subtle atomic-scale structural changes.     

High Temperature Deformation Behavior of High Strength and Toughness Ti-Ni Base Bulk Metallic Glass CompositesEI北大核心CSCD

Room-temperature brittleness and strain-softening during deformation of bulk metallic glasses, and limited processability of shape memory alloys have been stumbling blocks for their advanced functional structural applications. To solve the key scientific problems, a new shape memory bulk metallic glass based composite, through the approach using transformation-induced plasticity (TRIP) effect of shape memory alloys to enhance both ductility and work-hardening capability of metallic glasses, and superplasticity of bulk metallic glass in supercooled liquid region to realize near net forming, was developed in this work. And the Ti-Ni base bulk metallic glass composites (BMGCs) rods were prepared by the levitation suspend melting-water cooled Cu mold process. Microstructure, thermal behavior, mechanical properties and high temperature deformation behavior of the alloy were investigated. The results show that the as-cast alloy microstructure consists of amorphous matrix, undercooled austenite and thermally-induced martensite. Besides, the size of the crystal phase precipitated on the amorphous matrix in-creases from the surface to the inside. The alloy exhibits excellent comprehensive mechanical properties at room temperature. The yield strength, fracture strength and the plastic strain of alloy are up to 1286 MPa, 2256 MPa and 12.2%, respectively. Under compressive loading in the supercooled liquid region, the composite exhibits approximate Newtonian behavior at lower strain rate in higher deformation temperature, and the optimum deformation temperature is T>480 degrees C and the intersection part with supercooled liquid region (SLR). When the temperature is 560 degrees C and the strain rate is 5x10(-4) s(-1), the stress sensitivity index m and the energy dissipation rate Psi are 0.81 and 0.895, respectively. Furthermore, the volume of activation is quantified to characterize the rheological behavior.