Preparation of Cu-based Bulk Metallic Glass Matrix Composites

在 situ 包含的金属性的玻璃(BMG ) 矩阵 composites 形成了的 Cu_(47 )Ti_(34 )Zr_(11 ) Ni_8 体积 TiC 粒子和 delta-TiCu 树突阶段被铜开发模子演员组。composites 的热稳定性和微观结构被调查。房间温度耐压试验表明合成样品展出更高的破裂力量和 0.2 percent-0.5 百分比的不同塑料紧张，把 Ti_(34 ) 与 correspondingCu_(47 ) 的作比较 Zr_(11 ) Ni_8 整体的 BMG。

Ballistic performance of tungsten particle/metallic glass matrix composite long rod

In the present manuscript numerical analysis on the ballistic performance of a tungsten particle/metallic glass matrix(WP/MG) composite rod is conducted by integrating with related experimental investigations. In the corresponding finite element method(FEM) simulations a modified coupled thermomechanical constitutive model is employed to describe the mechanical properties of metallic glass(MG)matrix, and geometrical models of the WP/MG composite rod are established based on its inner structure. The deformation and failure characteristics of the rod and target materials are analyzed in detail,and the influences of various factors on the ballistic performance of the WP/MG composite long rod are discussed. Related analysis demonstrates that the penetrating performance of the WP/MG rod is similar to that of the tungsten fiber/metallic glass matrix(WF/MG) composite long rod, i.e., a "self-sharpening" behavior also occurs during the penetration process, and correspondingly its penetrating capability is better than that of the tungsten heavy alloy(WHA) rod. However, the mass erosion manner of the WP/MG rod is different and the erosion is relatively severe, thus its penetrating capability is a little lower compared with that of the WF/MG one. Moreover, the impact velocity and the target strength have significant influences on the ballistic performance of the WP/MG composite rod, whereas the effect of initial nose shape is very little.

Critical serrated flow features during nanoindentation in La-based bulk metallic glasses

La57.6Al17.5(Cu,Ni)24.9 and La64Al14(Cu,Ni)22 bulk metallic glasses (BMGs) were prepared by copper-mould casting method. Plastic deformation behavior of the two BMGs at various loading rates was studied by nanoindentation. The results showed that the La57.6Al17.5(Cu,Ni)24.9 BMG with a glass transition temperature of 423 K exhibited prominent serrated flow at low loading rates, whereas less pronounced serrated flow at high rates during nanoindentation. In contrast, the La64Al14(Cu,Ni)22 BMG with a glass transition temperature of 401 K exhibited prominent serrated flow at high loading rates. The different rate dependency of serrated flow in the two La-based BMGs is related to the different glass transition temperature, and consequently the degree of viscous flow during indentation at room temperature. A smoother flow occurs in the alloy with relatively lower glass transition temperature, due to the relaxation of stress concentration.

Serration and shear avalanches in a ZrCu based bulk metallic glass composite in different loading methods

In the current research, serrated flow is investigated under tensile and compressive loading in a ZrCubased bulk metallic glass composite (BMGC) that is well known for its plastic deformability, which is higher than that of metallic glasses. Statistical analysis on serrations shows a complex, scale free process, in which shear bands are highly correlated. The distribution of the elastic-energy density stored in each serration event follows a power-law relationship, showing a randomly generated serrated event under both tension and compression tests. The plastic deformation in the temporal space is explored by a timeseries analysis, which is consistent with the trajectory convergent evolution in critical dynamic behavior even in the low strain rate regime in both tests. The results demonstrate that the secondary phase in the BMGC can stabilize the shear band extension and facilitate the critical behavior in the low strain rate regime. This study provides a strong evidence of serrated flow phenomenon in BMGC under tension test, and offers a deep understanding of the correlation between serrations and shear banding in temporal space.

Effect of pre-existing shear bands on mechanical properties and serration behaviors in bulk metallic glasses

Pre-existing（multiple）shear bands were introduced into the ductile Zr56Co28Al16 and Zr65Ni10Cu15Al10bulk metallic glasses（BMGs）through the lateral-deformation,respectively.It was found that the pre-exiting shear bands can further enhance the compressive plasticity of ductile BMGs.According to the serration analysis on the plastic deformation of the as-cast and the pre-deformed samples,the serration events in the stress-strain curves during deformation display a self-organized critical（SOC）behavior.Compared with the as-cast BMGs,a larger power-law scaling exponent calculated based on serrated flow behaviors becomes larger for the pre-deformed BMGs,implying that the shear banding stability of BMGs is effectively enhanced.This should be caused by the pronounced interactions of shear bands during plastic deformation for the pre-deformed BMGs.However,by introducing a large amount of multiple shear bands into the glassy matrix,it also becomes easier for shear bands to propagate along the pre-existing shear bands,leading to a lower cut-off elastic energy density for the pre-deformed BMGs.More multiple shear bands with stronger interactions for the pre-deformed BMGs could provide a larger chance to activate the shear-band cracking but less local elastic energies are remained for the subsequent crack-linking.

Fracture toughness of a rejuvenated β-Ti reinforced bulk metallic glass matrix composite

A β-Ti dendrite reinforced Zr-based bulk metallic glass composite(BMGC) was found to be brittle when cast in a large size. The reasons for the embrittlement and the effectiveness of the cryothermal cycling(CTC) treatment in restoring the mode I fracture toughness are examined. Plasticity in all the CTC treated BMGC is estimated from the distribution and occurrence of pop-ins in nanoindentation tests and by measuring the magnitude of enthalpy of relaxation(△H_(rel)) via differential scanning calorimetry(DSC). This is further validated by examining the strain-to-failure(ε_(f)) in compression tests. Mode I fracture behaviour of the as-cast embrittled BMGC and the CTC treated BMGC, which exhibits maximum plasticity, is examined. Results show that both BMGCs are equally brittle and exhibit 5 times lower notch toughness(K_(QJ))than their tougher counterpart. Post-facto imaging of the side surfaces reveals the absence of notch-tip plasticity in both BMGCs. The lack of notch tip plasticity of CTC treated BMGC, despite exhibiting signatures of plasticity in nanoindentation and higher △Hrelis rationalized by reassessing the origin of pop-ins in nanoindentation tests and describing the variations in chemical and topological short range ordering during CTC, respectively. Implications of these results in terms of improving the fracture toughness of structurally relaxed BMGCs via CTC are discussed.

In-situ Dendrite/Metallic Glass Matrix Composites:A Review

The advanced fabrication of in-situ dendrite/metallic glass matrix （MGM） composites is reviewed. Herein, the semi- solid processing and Bridgman solidification are two methods, which can make the dendrites homogeneously dispersed within the metallic glass matrix. Upon quasi-static compressive loading at room temperature, almost all the in-situ composites exhibit improved plasticity, due to the effective block to the fast propagation of shear bands. Upon quasi-static tensile loading at room temperature, although the composites possess tensile ductility, the inhomogeneous deformation and associated softening dominates. High volume-fractioned dendrites and network structures make in-situ composites distinguishingly plastic upon dynamic compression. In-situ composite exhibits high tensile strength and softening （necking） in the supercooled liquid region, since the presence of high volume-fractioned dendrites lowers the rheology of the viscous glass matrix at high temperatures. At cryogenic temperatures, a distinguishingly-increased maximum strength is available; however, a ductile-to-brittle transition seems to be present by lowering the temperature. Besides, improved tension-tension fatigue limit of 473 MPa and four-point-bending fatigue limit of 567 MPa are gained for Zr58.5Ti14.3Nb5.2Cu6.1Ni4.9Be11.0 MGM composites. High volume-fraction dendrites within the glass matrix induce increased effectiveness on the blunting and propagating resistance of the fatigue-crack tip. The fracture toughness of in-situ composites is comparable to those of the toughest steels and crystalline Ti alloys. During steady-state crack-growth, the confinement of damage by in-situ dendrites results in enhancement of the toughness.

Deformation behavior of Ta wire-reinforced Zr-based bulk metallic glass composites

A Ta wire-reinforced Zr-based bulk metallic glass composite with a new type of structure was prepared successfully by the method of liquid metal infiltration. Ta wires distribute uniformly in the metallic glass matrix in the form of spirals. The composite exhibits two yield stages under compressive stress, and the samples are compressed into thin pancakes. The micro-cracks originate at the interface between the Ta wire and the metallic glass matrix and propagate perpendicularly to the interface, which then induce multiple shear bands in the metallic glass matrix due to the stress concentration. Shear cracks form in the metallic glass matrix during the continued loading process as a result of the interaction of shear bands. Deformation bands of Ta wires occur under the impact of shear bands. The local stress fields in the composite are changed obviously due to the introduction of the spiral-formed reinforcements. The investigation of the deformation behavior and mechanism suggests a new method for the application of bulk metallic glass composites as the structural materials.

Microstructure and mechanical properties of a novel Zr-based bulk metallic glass composite

Zr48.5Cu46.5Al5 bulk metallic glass (BMG) com- posites with diameters of 3 and 4 mm were prepared through suction casting in an arc melting furnace by modulating the alloy composition around the monothetic BMG composition of the high glass forming ability. Microstructural charac- terization reveals that the composites contain micron-sized CuZr phase with martensite structure, as well as nano-sized Zr2Cu crystalline particles and Cu10Zr7 plate-like phase em- bedded in an amorphous matrix. Room temperature com- pression tests showed that the composites exhibited signifi- cant strain hardening and obvious plastic strain of 7.7% for 3 mm and 6.4% for 4 mm diameter samples, respectively.

Interactions of Shear Bands in a Ductile Metallic Glass

Shear bands play a key role in the plastic deformation of metallic glasses（MGs）.Even though there are extensive studies on the initiation and propagation of shear bands,the interactions among them have not been systematically studied yet.The interactions between the primary shear bands（PSBs）and secondary shear bands（SSBs）in a ductile Zr-based MG were studied.The residual stress near PSBs can deflect the propagation direction and reduce the propagation velocity of SSBs,which contributes to the plasticity and toughness of the MG.It was demonstrated that the probability and strength of the interactions between PSBs and SSBs would become stronger for MGs with larger Young′s modulus and smaller shear modulus,i.e.,larger Poisson′s ratio.These results are valuable in understanding the plastic deformation of MGs and may be helpful in designing new MGs with desirable mechanical properties.

Statistical analysis on strain-rate effects during serrations in a Zr-based bulk metallic glass

By means of statistical analysis,the deformation mechanisms taking place in elastic loading and plastic shearing stages during serrated flows on the stress-strain curves for bulk metallic glasses were studied comprehensively.Normalized serration number presented a linear increasing tendency with the decrease of applied strain rates due to the reduction of free volumes.An excellent plastic deformation was illustrated from the influences of structure arrangement with activation energy.By using mean-field theory（MFT）,maximum elastic-energy density at different strain rates could be predicted by MFT besides maximum stress drops during serrations.These results were helpful for understanding the serrated flow behavior or designing decent schemes to improve the plasticity of bulk metallic glasses at room temperature.

Rate Dependence of Serrated Flow and Its Effect on Shear Stability of Bulk Metallic Glasses

The rate dependence of serrated flow and its effects on the stability of shear banding were systematically investigated in a prototypic bulk metallic glass.It was found that with the increase of external strain rate,the serrated flow is gradually suppressed and could completely disappear at a critical strain rate.The serration size,characterized by the mean stress drop amplitude,decreases inversely with the strain rate,while the waiting time for serration decreases with the strain rate in a power-law manner.The rate dependence of the serrated flow has important effects on the dynamics and stability of shear banding process,and leads to an optimal plasticity achieved around the critical strain rate for the disappearance of serrated flow.These results are discussed and interpreted in terms of the microscopic deformation theory and the stick-slip dynamics of shear banding for bulk metallic glasses.

Effect of the cooling rate on plastic deformability of a Zr-based bulk metallic glass

The present work found the plastic deformability of Zr65Cu17.5Ni10Al7.5 BMG dependent on the cooling rate during the formation from the molten state alloy. The deformation behavior in the compression test of φ 2 mm Zr65Cu17.5Ni10Al7.5 BMGs as-cast or lathed from different sizes as-cast samples was characterized, and they exhibited different plastic strains. The compressive plastic strain increases with the decreasing diameter of the as-cast specimens, i.e. with increasing the cooling rate. It is suggested that free volume content in the BMGs, which is related to the cooling rate during the rapid solidification, could play an important role in the deformation process of the BMGs.

Deformation behavior of Fe-based bulk metallic glass during nanoindentation

Fe-based bulk metallic glasses (BMGs) normally exhibit super high strength but significant brittleness at ambient temperature. Therefore,it is difficult to investigate the plastic deformation behavior and mechanism in these alloys through conven-tional tensile and compressive tests due to lack of distinct macroscopic plastic strain. In this work,the deformation behavior of Fe52Cr15Mo9Er3C15B6 BMG was in-vestigated through instrumented nanoindentation and uniaxial compressive tests. The results show that serrated flow,the typical plastic deformation feature of BMGs,could not be found in as-cast and partially crystallized samples during nanoinden-tation. In addition,the deformation behavior and mechanical properties of the alloy are insensitive to the applied loading rate. The mechanism for the appearance of the peculiar deformation behavior in the Fe-based BMG is discussed in terms of the temporal and spatial characteristics of shear banding during nanoindentation.

非晶合金中剪切温升的研究进展

区别于传统的晶态金属材料,非晶合金(BMGs)不具备长程有序结构,其塑性变形载体为剪切带。剪切带一旦形成,便很快发展成为裂纹,引发材料的灾难性断裂。剪切不稳定性的研究有助于非晶合金塑性变形机理的理解,并可为非晶合金塑性变形能力的提高提供设计思路。近年来,基于非晶合金的结构特点,科研工作者努力探究非晶合金的剪切不稳定性,主要提出了结构软化诱导的剪切不稳定性和热软化引发的剪切不稳定性两种机制。本文重点总结了非晶合金中剪切温升的研究进展,介绍了测试应变速率、外部约束、试验机刚度和测试温度对剪切温升的影响,指明非晶合金中剪切引入的热远低于玻璃转变温度,暗示热软化对剪切不稳定性的影响是微弱的。本文最后对非晶合金中剪切不稳定性机制的研究方向进行了展望。

半固态等温热处理对Zr基非晶复合材料塑性变形机制的影响

通过添加不同体积分数的Nb,本工作设计了一系列Zr基非晶复合材料,主要研究了Nb含量对铸态、半固态非晶复合材料的微观组织及塑性性能的影响。结果表明:非晶复合材料塑性应变量随晶体相(β-Zr相)体积分数增加而呈现S型增强规律。半固态等温处理后的非晶复合材料塑性提升,但其塑性增长率随Nb含量增加而减小。当D C(当量直径)/X(平均自由程间距)≥0.65时,β-Zr相体积分数出现最小临界阈值35%,此时材料塑性开始迅速提升;D C/X≥1.5时,β-Zr相体积分数超过54%后,材料塑性保持稳定,进一步说明非晶复合材料塑性与β-Zr相体积分数有关。

Serration Behavior in Zr-Cu-Al Glass-forming Systems

The metallic glass matrix composites（MGMCs）and bulk metallic glasses（BMGs）were studied by statistical analysis during plastic deformation at the strain rates of 2×10^-2,2×10^-3,and 2×10^-4 s^-1,respectively.No serration events occur in both MGMCs and BMGs during compression tests at the strain rate of 2×10^-2 s^-1.When deformed at the strain rate of 2×10^-3 s^-1,the BMG displays a larger plasticity,which is due to the larger serration events followed by a series of small serrations caused by the continuous movement of free volume.The amplitudes and elastic-energy densities increase with increasing the strain rates owing to many serrations in MGMCs.It is deduced that the Young′s modulus decreases from the normalized stress drop and fluctuations are observed on stressstrain curves,which is attributed to a lower coefficient according to the stick-slip model.

钨丝增强ZrAlNiCuSi块体非晶复合材料及其塑性行为

采用渗流铸造法制备出了钨丝增强ZrAlNiCuSi块体非晶复合材料,在压缩条件下复合材料表现出弹性-完全塑性的应力-应变行为,和未复合的大块非晶相比,总应变量提高600％以上.非晶复合材料塑性提高的原因是钨丝阻碍了非晶基体剪切带的滑移,诱发多个剪切带的产生,同时滑移的面积增大的结果.复合材料的破坏方式与钨丝体积分数有关,在体积分数小于40％时一般为剪切破坏,大于60％时为纵向劈裂破坏,介于（40-60）％之间时,在钨丝与界面结合良好的情况下,趋于剪切破坏,否则为劈裂的破坏方式.

体积分数对W_f/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。

内生枝晶增塑锆基块体金属玻璃复合材料

利用熔体水淬法制备了内生bccβ-Zr固溶体增塑的Zr56．2Ti13．8Nb5．0Cu6．9Ni5．6Be12.5块体金属玻璃基体复合材料．β相呈发达的树枝状,体积分数约为30％．室温单轴压缩时,复合材料失效前的纯塑性应变达到10．2％,并具有2．0％的弹性应变极限和1788 MPa的极限断裂强度．显微观察表明,压缩变形后的试样表面均匀分布着大量波浪形剪切带．