CuZr-based bulk metallic glass and glass matrix composites fabricated by selective laser melting

Monolithic bulk metallic glass and glass matrix composites with a relative density above 98 ％ were produced by processing Cu46Zr46Al8 (at.％) via selective laser melting (SLM).Their microstructures and mechanical properties were systematically examined.B2 CuZr nanocrystals (30-100 nm in diameter) are uniformly dispersed in the glassy matrix when SLM is conducted at an intermediate energy input.These B2 CuZr nanocrystals nucleate the oxygen-stabilized big cube phase during a remelting step.The presence of these nanocrystals increases the structural heterogeneity as indirectly revealed by mircrohardness and nanoindentation measurements.The corresponding maps in combination with calorimetric data indicate that the glassy phase is altered by the processing conditions.Despite the formation of crystals and a high overall free volume content,all additively manufactured samples fail at lower stress than the as-cast glass and without any plastic strain.The inherent brittleness is attributed to the presence of relatively large pores and the increased oxygen content after selective laser melting.     

Mechanical and corrosion behaviour of in situ intermetallic phases reinforced Mg-based glass composite

A (Mg₆₅Cu₁₀Ni₁₀Y₁₀Zn₅)₉₁Zr₉ bulk metallic glass matrix composite, reinforced by in situ formed intermetallic phase, has been fabricated. In contrast to the monolithic Mg-based bulk metallic glasses (BMGs), the composite showed much higher fracture strength of 1039?MPa and a significant plastic strain of more than 5%. Moreover, the effect of in situ formed intermetallic phase on the corrosion behaviour of the composite was also studied. The results indicated that the corrosion resistance of the composite was only slightly lower than that of the monolithic Mg-based BMGs, but still much higher than that of the AZ31 magnesium alloy. This finding gives us a new clue to enhance the mechanical properties and corrosion resistance of Mg-based alloy by designing appropriate metallic glass composites.     

Enhanced tensile plasticity of a CuZr-based bulk metallic glass composite induced by ion irradiation

N⁺ ion irradiation is utilized to tune the structure and mechanical properties of a Cu₄₈Zr_47.2Al₄Nb_0.8 bulk metallic glass composite (BMGC). Ion irradiation increases the disorder near the surface, as probed by neutron diffraction, and, moreover, causes the phase transformation from B2 CuZr to B19’ CuZr martensitic phase in the studied BMGC. The tensile plasticity of the BMGC is dramatically improved after ion irradiation, which results from multiple shear banding on the surface and the martensitic transformation of the B2 to B19’ CuZr martensitic phase. The experimental results are strongly corroborated by complementary molecular dynamic simulations.     

Extrusion properties of a Zr-based bulk metallic glass

The extrusion behavior of Zr_41.2Ti_13.8Cu_12.5Ni₁₀Be_22.5 metallic glasses in the supercooled liquid region was investigated. Good extrusion formability was observed under low strain rates at temperatures higher than 395 °C. The metallic glasses were fully extruded without crystallization and failure within the range of T = 395-415 °C under strain rates from 5 × 10^− 3 s^− 1 to 5 × 10^− 2 s^− 1, and the deformation behavior of the metallic glasses during the extrusion was found to be in a Newtonian viscous flow mode by a strain rate sensitivity of 1.0.     

Mechanical property degradation of a CuZr-based bulk metallic glass composite induced by sub-Tg annealing

The annealing effect at temperatures below glass transition temperature (T_g) on the mechanical behavior of a ductile Cu₄₈Zr₄₈Al₄ bulk metallic glass composite (BMGC) containing a B2-CuZr phase was investigated. It was found that remarkable plasticity and fracture strength degradations of the CuZr-based BMGC occurred with increasing the annealing temperature in the condition without significantly changing the crystalline volume fraction in the BMGC, which were correlated with the annealing-induced microstructure variations. It is expected that the free volume in the glassy matrix of the BMGC still played an important role for its deformation behavior, in despite of the existence of the B2-CuZr phase. The sub-T_g annealing-induced free volume annihilation depressed the shear band generation in the glassy matrix, reduced the synchronous contribution of the “blocking effect” and “deformation-induced martensitic transformation effect” of the B2-CuZr phase to the multiplication of shear bands, resultantly caused the plasticity degradation. The annealing-induced martensitic transformation of the B2-CuZr phase at the temperature close to T_g would further expand the plasticity degradation due to the absence of the “deformation-induced martensitic transformation effect”. Furthermore, the plasticity degradation simultaneously resulted in the fracture strength reduction of the BMGC because its work-hardening-like behavior was conditioned by the plastic deformation ability. The present results indicate that the ductile CuZr-based BMGC reinforced by the B2-CuZr phase similarly suffers from sub-T_g annealing-induced embrittlement, as is the case for most monolithic BMGs.     

Development and microstructure optimization of Mg-based metallic glass matrix composites with in situ B2-NiTi dispersoids

In this paper, we designed a novel processing method and successfully developed in situ precipitated B2-NiTi shape-memory-alloy reinforced Mg-based bulk metallic glass matrix composites (BMGMCs). The composites exhibited improved fracture strength in both compressive and flexural modes and large plastic deformation in compressive mode compared with those of its monolithic glassy counterpart. The stress-induced martensitic transformation of B2-NiTi in this system caused the composite to exhibit work-hardening behavior, especially during compression. The microstructure of the composite was optimized by decreasing the size and increasing the volume fraction of the B2-NiTi phase, to obtain better mechanical properties. This novel in situ method is applicable to fabricating various BMGMCs, making it a breakthrough for designing ductile work-hardenable BMGMCs.     

New ductile laminate structure of Ti-alloy/Ti-based metallic glass composite with high specific strength

Bulk laminate structure of Ti-alloy/Ti-based metallic glass composite(MGC) was prepared by melting a preform of alternate stack-up foils in the high vacuum atmosphere. The composite demonstrates a good combination of yield strength(~1618 MPa), plasticity(~4.3%) and specific fracture strength(384 × 10~3 Nmkg~(-1)) in compression. The maintained yield strength results from the unique microstructure composed of the Ti layer, the solution layer with gradient structure and the MGC layer. Such a multilayer structure effectively inhibits the propagation of shear band, leading to the enhanced plasticity. Those extraordinary properities suggest that combining ductile lamella with brittle metallic glass(MG) by such a lay-up method can be an effective way to improve mechanical properties of MG.     

Micro and nano indentation studies on Zr60Cu10Al15Ni15 bulk metallic glass

Partially vitrified Zr₆₀Cu₁₀Al₁₅Ni₁₅ bulk metallic glass has been synthesized using water cooled copper mold drop casting technique. Kinetically favorable microstructures having different morphologies are observed throughout the volume of the bulk metallic glass sample. X-ray diffraction studies indicate formation of hard intermetallic compounds such as Zr₃Al₂ and Zr₂Ni in certain regions along with amorphous structures. Microindentation studies carried out in different regions of the sample reveal microstructure dependent deformation behavior. Highest hardness is observed in the fully crystallized regions compared to pure glassy regions in the same sample. Further nanoindentation in the same sample is used to understand dynamic mechanical properties of microstructures in different regions. The pile-up morphologies around the indent and differences in load–displacement curves provide vital information on deformation behavior of sample in different microstructure sensitive regions.     

Dual magnetic phases in Nd-based bulk metallic glass

Numerous nanocrystals dispersed homogenously in an amorphous matrix were observed in the die-cast cylindrical Nd₅₅Fe₂₈Al₉Ni₈ bulk metallic glass. Most of the nanocrystals are less than 5 nm in size. At room temperature, only one magnetically hard phase was observed. But below room temperature, another magnetically hard phase was also detected. The appearance of the phases was associated with the different exchange coupling effect of the nanocrystalline grains and the amorphous matrix, and the coercivity of the alloy was related to the size of the nanocrystals. It was shown that nanocrytals with a size larger than 1.3 nm might contribute to a larger coercivity of the alloy.     

块体镁基非晶合金及其复合材料研究的新进展

介绍了块体镁基非晶合金及其复合材料的最新研究进展,并简要分析和总结了镁基非晶合金在成分选择和玻璃形成能力(GFA)判据上的新成果,最后针对镁基非晶合金本身存在的问题提出了今后的研究方向建议。     

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 ZrCu-based 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 time-series 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.     

Synthesis of Zr-based bulk metallic glass-crystalline aluminum alloy composite by co-extrusion

The effects of co-extrusion conditions like extrusion temperature and deformation rate on the fabrication of a Zr-based bulk metallic glass-Al clad material were investigated under the extrusion ratio of 5.06. The ranges of extrusion temperature and deformation rate were varied from 658 to 703 K and from 10^− 3 to 10^− 1 mm/s, respectively. Both macroscopic and microstructural characterizations reveal that sound materials compatibility could be obtained under the low deformation rate-low temperature within supercooled liquid region combination, showing homogeneous distribution of the rate of cross-sectional area between core and sleeve without crack or intermetallic compound in the vicinity of the interface.     

Numerical study of shear banding evolution in bulk metallic glass composites

In this article, a systematic simulation was performed to demonstrate the detailed shear banding evolution in bulk metallic glass (BMG) composites subjected to the tension, and the relation between microstructures and tensile ductility was therefore elucidated. Free volume was adopted as an internal state variable to characterize the shear banding nucleation, growth and coalescence in BMG matrix with the help of free volume theory, which was incorporated into ABAQUS finite element method (FEM) code as a user material subroutine. The present numerical method was firstly verified by comparing with the corresponding experimental results, and then parameter analyses were conducted to discuss the impacts of particle volume fraction, particle shape, particle orientation and particle yielding strength on the enhancement efficiency of the tensile ductility of BMG composites.     

Enhanced plasticity of Zr-based bulk metallic glass composite by in situ formed β-Zr dendritics

A Zr_56.2Ti_13.8Nb_5.0Cu_6.9Ni_5.6Be_12.5 bulk metallic glass composite with enhanced plasticity by in situ formed bcc β-Zr solid solution was prepared by water quenching. The ductile β phase with a volume fraction of about 30% possesses a developed dendritic morphology. The composite exhibits a pure plastic strain of 10.2% combined with a large elastic strain limit of 2% and a high ultimate strength of 1778 MPa upon room-temperature compression. Microscopic observation shows numbers of wave-like shear bands distributed on the surface of the compressive samples. Translated from Acta Metallurgica Sinica, 2006, 42(3): 331–336 [译自: 金属学报]     

Plastic deformation of a Zr-based bulk metallic glass fabricated by selective laser melting

Fully amorphous Zr_52.5Cu_17.9Ni_14.6Al₁₀Ti₅ bulk metallic glass(BMG) samples with a relative density exceeding 98% were fabricated via selective laser melting(SLM).High fracture stresses of around1700 MPa and a reproducible plastic strain of about 0.5% were obtained for cylindrical SLM samples.The analysis of the observed serrations during compressive loading implies that the shear-band dynamics in the additively manufactured samples distinctly differ from those of the as-cast glass.This phenomenon appears to originate from the presence of uniformly dispersed spherical pores as well as from the more pronounced heterogeneity of the glass itself as revealed by instrumented indentation.Despite these heterogeneities,the shear bands are straight and form in the plane of maximum shear stress.Additive manufacturing,hence,might not only allow for producing large BMG samples with complex geometries but also for manipulating their deformation behaviour through tailoring porosity and structural heterogeneity.     

An experimental study on grinding of Zr-based bulk metallic glass

There are limited studies in the literature about machinability of bulk metallic glass(BMG).As a novel and promising structural material,BMG material machining characteristics need to be verified before its utilization.In this paper,the effects of cutting speed,feed rate,depth of cut,abrasive particle size/type on the BMG grinding in dry conditions were experimentally investigated.The experimental evaluations were carried out using cubic boron nitride(CBN) and Al_2O_3 cup wheel grinding tools.The parameters were evaluated along with the results of cutting force,temperature and surface roughness measurements,X-ray,scanning electron microscope(SEM)and surface roughness analyse.The results demonstrated that the grinding forces reduced with the increasing cutting speed as specific grinding energy increased.The effect of feed rate was opposite to the cutting speed effect,and increasing feed rate caused higher grinding forces and substantially lower specific energy.Some voids like cracks parallel to the grinding direction were observed at the edge of the grinding tracks.The present investigations on ground surface and grinding chips morphologies showed that material removal and surface formation of the BMG were mainly due to the ductile chip formation and ploughing as well as brittle fracture of some particles from the edge of the tracks.The roughness values obtained with the CBN wheels were found to be acceptable for the grinding operation of the structural materials and were in the range of 0.34-0.58 μm.This study also demonstrates that conventional Al_2O_3 wheel is not suitable for grinding of the BMG in dry conditions.     

金属玻璃基复合材料的微结构效应

基于自由体积理论和Ramberg-Osgood模型,并利用ABAQUS软件,建立颗粒随机分布代表性体积单元模型,模拟了Ti_(64.5)Zr_(14.5)V_(18.5)Cu_(2.5)颗粒增韧Ti基金属玻璃基复合材料在单轴拉伸状态下的微结构效应,讨论了颗粒的体积分数、团聚数目、长径比、定位取向和界面对金属玻璃韧性的影响。结果表明:提高颗粒体积分数能显著提高复合材料的塑性,但部分牺牲了复合材料的强度;增大颗粒长径比能够增强复合材料的塑性和屈服强度;使颗粒的取向与荷载方向成90°或0°,不仅增强了复合材料的塑性,而且与其他排布相比也增强了复合材料的强度;减少团聚数目至2个以下,能明显减少金属玻璃基复合材料的塑性和强度的损失,使团聚中颗粒与荷载成90°,却能改善复合材料的塑性和强度;在颗粒增韧金属玻璃基复合材料中加入零厚度界面,能观察到在主剪切带上颗粒和基体在界面处脱粘,得到与实验现象更加吻合的结果。通过上述的研究能够很好地理解复合材料的微结构效应,并有利于材料的设计。     

Diffusion bonding of Zr55Cu30Ni5Al10 bulk metallic glass to Cu with Al as transition layer

In this work we demonstrate the diffusion bonding of Zr₅₅Cu₃₀Ni₅Al₁₀ bulk metallic glass (BMG) to aluminum and copper alloy. The process parameters including temperature, pressure and time are investigated experimentally, and we obtain appropriate ones for accomplishing diffusion bonding of the BMG to aluminum alloy successfully. Then we present a two-step diffusion bonding process to bond the BMG to copper alloy by using aluminum alloy as transition layers, and achieve a five-layer bonded joint of BMG/Al/Cu/Al/BMG. The mechanical properties of the multilayer joint are examined. The hardness of the BMG in the joint is enhanced while the bending strength decreases significantly compared with the as-received BMG. Besides, the crystalline metals alleviate and block the extension of cracks in the BMG, which results in the joint fracturing in an explosion-proof glass manner, dissimilar to rupturing in a catastrophic manner that is always happened in the BMGs. Therefore, diffusion bonding of BMG to crystalline metals is a promising way to extend its application.     

形状记忆合金的力学及界面参数和体积分数对大块金属玻璃基复合材料增韧的影响

采用考虑塑性的超弹性材料模型和基于损伤塑性的准脆性材料模型,建立了三维单胞有限元模型,模拟了形状记忆合金颗粒增韧大块金属玻璃基复合材料的单调拉伸行为。讨论了形状记忆合金的力学参数、体积分数、界面厚度和界面材料参数对金属玻璃增韧效果的影响。结果表明:提高形状记忆合金的相变应变和马氏体塑性屈服应力将显著提高形状记忆合金颗粒增韧大块金属玻璃基复合材料的拉伸失效应变;形状记忆合金弹性模量超过50.0GPa、马氏体塑性屈服应力超过1.8GPa后,复合材料的拉伸失效应变变化不大。能同时兼顾失效应变和失效应力的形状记忆合金体积分数为15%左右。复合材料界面弹性模量和界面屈服应力的增加将提高复合材料的失效应力,但对失效应变影响不大;复合材料界面厚度的增加在提高失效应变的同时,也降低了复合材料的失效应力。     

Dynamic fracture of berylium-bearing bulk metallic glass systems: A cross-technique comparison

We report on a detailed comparison between two different experimental techniques used to measure the dynamic initiation fracture toughness of a bulk metallic glass system (Vitreloy-1) and its β-phase composite. Both the coherent gradient sensing interferometry (CGS) and one-point impact techniques reveal very similar trends in the relationship for Vitreloy-1. A drastic increase in initiation toughness with the stress intensity rate is observed. By contrast, the one-point impact method shows a relative rate-insensitivity for the of the β-phase composite. The results are rationalized through a detailed characterization of the failure mechanisms.