Microstructure and mechanical properties of metallic glass/metallic glass composites

We report microstructure and mechanical properties of bulk metallic glass (BMG)/metallic glass composites fabricated by mechanical alloying with subsequent consolidation process. The microstructural investigations of a bulk composite reveal that a submicron-scale layered structure with irregular interfaces consists of three amorphous phases in tornado-like morphology. Based on these results, poor plasticity of the metallic glass composite can be understood possibly due to the irregular interfacial morphology of the submicron-scale heterogeneous amorphous phases throughout the materials.     

Microstructural tailoring and improvement of mechanical properties in CuZr-based bulk metallic glass composites

A strategy for homogenizing the B2 CuZr phase in CuZr-based bulk metallic glass (BMG) composites based on inoculation is presented. The sizes and distribution of B2 CuZr particles can be effectively homogenized by Ta additions in rapidly solidified Cu₄₇Zr_48?xAl₅Ta_x (0 ≤ x ≤ 1, at.%) alloys. Mechanisms of the homogenizing effect were investigated by analyzing the microstructures of the composites as well as the nucleation and growth processes of the B2 CuZr phase. Mechanical properties of the alloys were significantly improved by the uniform B2 CuZr particles under both compression and tension. The inhibition on the propagation of shear bands and cracks by the ductile crystals and deformation-induced martensitic transformation of the B2 phase was proved to account for the superior tensile properties. Fracture mechanisms were proposed to correlate the tensile fracture behaviors to microstructural features of the alloys. Furthermore, the tensile plastic strain was quantitatively modeled by using the empirical microstructural element body approach as well as percolation theory. This study has important implications for the development and structural applications of high-performance BMG composites.     

不锈钢网增强锆基非晶复合材料的压铸制备及力学性能研究

全程真空压铸技术的快速发展为大块非晶合金的工业化应用提供了可能,受到了广泛关注。但是,非晶合金的室温脆性限制了压铸结构件在一些关键领域的应用。本论文利用压铸工艺高速充型及高压凝固的特性,通过在Vit1锆基非晶合金中引入304不锈钢网叠层焊接制造的骨架,成功制备出了不同体积分数晶态相增强的非晶复合材料,并系统研究了不锈钢网体积分数对力学性能的影响。研究结果表明,不锈钢网在非晶基体中均匀分布,与非晶合金存在冶金界面结合。力学性能测试显示,随着不锈钢编织网的引入,室温脆性的压铸Vit1块体金属玻璃的塑性得到了显著提升。随着不锈钢网目数增大(对应晶态相体积分数增大),非晶复合材料的塑性呈增大的趋势,但是,当目数超过200时,过细的孔洞会导致骨架局部区域无法填充,恶化性能。当晶态相的体积分数为53.7％时,断裂应变达到最大值,约为10％左右,其值高于传统不锈钢纤维增韧的Zr基非晶复合材料。韧化机制分析表明,压铸非晶合金出现脆-延性转变的根本原因是不锈钢网对剪切带扩展进行高效抑制,促进剪切带的增殖和萌生,减少宏观塑性变形的局域化。本研究为非晶复合材料的结构设计提供了新的思路,对于促进非晶合金的更广泛应用具有重要的工程价值。     

Effect of Al addition on formation and mechanical properties of Mg-Cu-Gd bulk metallic glass

The effect of partial substitution of Al for Cu on the glass forming ability（GFA） and mechanical properties of Mg65Cu25-xAlxGd10 （x=0, 1, 3 and 5, molar fraction, %） alloys were studied by X-ray diffi-actometry（XRD）, differential scanning calorimetry（DSC） and uniaxial compression test. The result reveals that GFA of the alloys changes slightly with increasing x from 0 to 3, and then abruptly decreases with x increasing up to 5. The plasticity can be greatly improved with appropriate substitution of Cu by A1 （3%, molar fraction） in Mg65Cu25Gd10 bulk metallic glass, and the resultant fracture strength, total strain to failure, and plastic strain are 898 MPa, 2.19% and 0.2%, respectively.     

Tribological properties of graphite- and ZrC-reinforced bulk metallic glass composites

The influence of second-phase reinforcement on the micro-tribological properties of Zr_52.5Cu_17.9Ni_14.6Al₁₀Ti₅ (Vit 105) was investigated by ball-on-disc tests. It was found that monolithic amorphous Vit 105 displays a coefficient of friction (COF) similar to that of 100Cr6 bearing steel. Further, it was seen that adding a low volume content of graphite and especially of ZrC generates a significant decrease in the COF, of up to 50%. Amorphous Vit 105 and its graphite-/ZrC-reinforced composites typically display two regimes of COF. After 100–500 revolutions it drops to about 2/3 of the starting value, and jumps back up to the initial COF are also observed. These transitions take place within the space of about 10 revolutions and are accompanied by a significant change in wear track depth. Investigation of the wear rate indicates that the graphite-/ZrC-reinforced bulk metallic glass composites display an even lower wear rate than 100Cr6 bearing steel.     

Microstructure and mechanical properties of Mg-Cu-Y-Zn bulk metallic glass matrix composites prepared in low vacuum

Mg-Cu-Y-Zn bulk metallic glasses(BMG) and in situ bulk metallic glass matrix composites were prepared by copper mold casting under the low vacuum with the argon atmosphere,and the raw materials used in preparing the Mg-Cu-Y-Zn alloys were commercially pure materials.The microstructures of the bulk samples were analyzed by X-ray diffractometer(XRD) and the thermal stability of samples was investigated by using a differential scanning calorimeter(DSC).The thermal stability of sample prepared with commercia...     

Zr基非晶合金多孔材料的制备与性能

采用液态金属渗流法制备直径为6 mm 的Zr基块体多孔非晶合金,采用扫描电镜(SEM)和X射线衍射仪(XRD)分析多孔材料的结构、形貌、断口特征和相组成,同时对多孔非晶合金的孔隙结构和力学特点进行分析.结果表明:采用CaC2作为孔隙支撑材料,能够制备出孔隙分布均匀、孔隙直径为0.2～0.8 mm的多孔非晶合金,其密度和孔隙率分别为3.57 g/cm3和47%.压缩力学性能实验表明:该多孔非晶合金的应力-应变曲线具有锯齿状变化规律,应力逐渐降低,其最大强度和应变分别为383 MPa和18.6%,应变量远大于单相非晶合金的应变量.     

In-situ synthesis and mechanical properties of Zr-based bulk metallic glass matrix composites manipulated by nitrogen additions

Our study investigates in-situ synthesis and mechanical properties of Zr-based bulk metallic glass (BMG) matrix composites via arc plasma-induced accelerated displacement reaction (APADR) process. The aluminum nitride precursor under arc plasma-induced ultra-high temperature results in higher contents of dissolved nitrogen as well as precipitation of zirconium nitride (ZrN) particles in a Zr-based amorphous matrix. The nitrogen in the matrix results in a decrease of crystallization resistance (lower T_x and reduced glass-forming ability), but an increase of mechanical stability (a decrease of strain burst sizes). In particular, in-situ formed ZrN, which exhibits a homogeneous distribution and strong interfacial bonding with the matrix, causes an increase in compressive fracture strength and significant plastic deformation in the composite compared with the monolithic BMG. The formation of multiple shear bands and the enhancement of shear band interactions by the dissolved nitrogen as well as the in-situ formed ZrN particles were carefully confirmed by a statistical analysis on serrated flows. These results give us a guideline on how to manipulate nitrogen contents and fabricate in-situ BMG matrix composites with improved mechanical properties via APADR process.     

Optimized interface and mechanical properties of W fiber/Zr-based bulk metallic glass composites by minor Nb addition

W fiber/Zr-based bulk metallic glass composites were prepared by melt infiltration casting and the interface reaction in composites was studied in detail. It was found that minor Nb addition to the matrix can suppress the interface peritectic reaction and optimize the interface structure in W fiber/Zr-based bulk metallic glass composites. Taking the interface characteristics of composites and glass forming ability of the matrix into account, an optimized alloy Zr₄₇Ti₁₃Cu₁₁Ni₁₀Be₁₆Nb₃ was selected as a new metallic glass matrix. The interface in the W fiber/Zr₄₇Ti₁₃Cu₁₁Ni₁₀Be₁₆Nb₃ bulk metallic glass composite has excellent interface bonding, and the compressive strength of 70% W fiber/Zr₄₇Ti₁₃Cu₁₁Ni₁₀Be₁₆Nb₃ metallic glass composite is 2.6 GPa, 58% higher than the unreinfored matrix. Multiple shear band formation in the matrix, which results from the interaction between W fiber and the matrix, can answer for the high ultimate fraction strength and excellent plastic deformation of the composite.     

Wear behavior of Fe-based bulk metallic glass composites

Composite samples comprising Fe-based metallic glass particles and the crystalline Ni matrix were produced. Wear behavior was investigated by a pin-on-disc type tester using hardened steel as the counter material. It was concluded that the wear mechanism depended on the volume fraction of crystalline nickel in the composites. The transition from the brittle fracture to the adhesive wear was observed by increasing the volume fraction of ductile Ni in the composites.     

Notch toughness of Fe-based bulk metallic glass and composites

The notch fracture toughness of Fe₇₅Mo₅P₁₀C_8.3B_1.7 monolithic bulk metallic glass (BMG) and Fe₇₇Mo₅P₉C_7.5B_1.5 and Fe₇₉Mo₅P₈C_6.7B_1.3 BMG matrix composites with α-Fe as reinforcing phase, fabricated by suction mould casting, were evaluated. It was found that the monolithic BMG has a toughness of 27 MPa m^1/2, while the Fe₇₇Mo₅P₉C_7.5B_1.5 BMG composite reinforced by single α-Fe dendrite phase exhibits a higher toughness of nearly 40 MPa m^1/2. However, for the Fe₇₉Mo₅P₈C_6.7B_1.3 alloy with more dendrites, the toughness decreased up to 25 MPa m^1/2. Microstructure investigation reveals that the simultaneous formation of Fe-Mo-P hard brittle phase apart from α-Fe dendrites in the Fe₇₉Mo₅P₈C_6.7B_1.3 alloy is the reason for the degradation of the fracture toughness.     

Designing bulk metallic glass and glass matrix composites in martensitic alloys

To circumvent the limited plasticity of bulk metallic glasses (BMGs), heterogeneous materials with glassy matrix and different type and length-scale of heterogeneities (micrometer-sized second phase particles or fibers, nanocrystals in a glassy matrix, phase separated regions, variations in short-range order by clustering) have been reported. We developed bulk metallic glasses and glass matrix composites in martensitic Zr–Cu-base alloys. Large plasticity can be obtained from microstructure consisting of either a glassy structure, or for alloys with martensitic second phase embedded in a glassy matrix. This type of glasses and glass–matrix composites are able to achieve high strength together with pronounced work-hardening. We explore the possibilities to synthesize such in situ composite microstructures based on shape memory alloys (“M-Glasses”) through metal mold casting.     

Glass formation,thermal and mechanical properties of ZrCuAlNi bulk metallic glasses

The glass forming ability, thermal and mechanical properties of some ZrCuAlNi bulk metallic glasses were analyzed. The compositions of the alloys were theoretically determined with the dense packing and kinetic fragility index models. Cylindrical and conical ingots were produced by copper mould suction-casting under Ar atmosphere. The conical ingots were characterized by means of X-ray diffraction in order to determine the glassy structure. It was found that both alloys have a critical glassy diameter, D_c, of 3 mm. Thermal behaviours were investigated by differential scanning calorimetry at heating rates of 0.5, 0.67 and 0.83 K/s. The gamma parameter γ, supercooled liquid region ΔT_x, and reduced glass transition temperature T_rg, of the experimentally obtained glasses indicated high glass forming ability. The glassy compositions showed a fragility index of ～40 GPa. The compression test of the investigated alloys was carried out at a strain rate of 0.016 s^?1, obtaining a elastic modulus of ～83 GPa, total deformation of ～5%, yield strength of 1.6 GPa and hardness of 4 GPa. It was concluded that the use of the dense packing and kinetic fragility index models helped to predict glass-forming compositions in the family alloy investigated.     

Y元素添加对CuZrAl块体金属玻璃的结构和力学性能的影响(英文)

研究添加Y元素对CuZrAl块体金属玻璃的结构和力学性能的影响。结果表明,添加Y元素提高CuZrAl体系的玻璃形成能力,而且由于添加Y元素可以降低该体系的结合能,从而降低其断裂强度。Cu45Zr48Al7块体金属玻璃的断裂表面主要呈脉状,而Cu46Zr42Al7Y5块体金属玻璃的断裂表面则很平滑。TEM观察表明,Cu45Zr48Al7的微观结构为非晶基体中含有纳米相,然而Cu46Zr42Al7Y5块体金属玻璃为全非晶结构。     

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.     

Fe-based bulk metallic glass composites without any metalloid elements

Glass-formation of Fe-based bulk metallic glasses (BMGs) and their composites is strongly dependent on their metalloid content. A good Fe-based glass former usually needs a metalloid content of ～20 at.% or above; however, the high content of the metalloids usually has side-effects on the performance of the alloys. In this paper, we developed a series of metalloid-free Fe-based BMG matrix composites with a diameter of more than 10 mm in the Fe–Co–La–Ce–Al–Cu system. During cooling, phase separation took place, i.e. Fe-rich and Fe-depleted liquids formed. Upon subsequent cooling, the body-centered cubic (bcc)-Fe(Co, Al) solid solution and Ce(Fe, Co)₂ intermetallic phase precipitated out of the Fe-rich liquid and the remaining Co–La–Ce–Al–Cu liquid was eventually vitrified to form the amorphous matrix. Due to elemental partitioning, it was found that, for a given Fe content, there exists an optimum compositional range for Co and Ce so that a large fraction of the glassy matrix can form. In addition, the final microstructure of the current composites was strongly dependent on the cooling rates applied: excessively fast cooling rates restricted the diffusion and precipitation of the Fe atoms, which reduced formation of the glassy matrix.     

Cu50 Zr42 Al8块体金属玻璃的组织和力学性能

采用悬浮熔炼-铜模吸铸法制备了Cu50Zr42Al8块体金属玻璃,研究了其楔形试样的组织演变.随着熔体凝固过程中冷却速度的变化,楔形试样中存在表面全非晶区,中心晶体区以及二者之间的过渡区域,并确定Cu50Zr42Al8块体金属玻璃临界尺寸为4.8 mm.分别考察了φ4 mm铸态完全非晶棒和φ5 mm非晶复合棒的力学性能.φ4 mm非晶棒的压缩断裂强度,弹性应变和塑性应变分别为2260 MPa,2.0%,0.4%,几乎没有塑性变形.而φ5 mm铸态非晶复合棒的屈服强度、断裂强度分别为1670MPa、1849 MPa,弹性应变和塑性应变分别为1.6%和1.9%.非晶基体中存在的马氏体相CuZr和正交晶相Cu10Zr7的竞争影响了非晶复合棒的最终力学行为.     

Formation,microstructure and properties of long-period order structure reinforced Mg-based bulk metallic glass composites

In situ Mg–Cu–Y–Zn bulk metallic glass (BMG) matrix composites, in which Mg solid solution flakes of 0.5–1 μm thickness and 2–10 μm length are dispersed, have been prepared by copper mold casting. The Mg flakes are characterized as a long-period order structure (LOS), i.e. periodic arrays of six close-packed planes distorted from the ideal hexagonal lattice of 6H-type. The formation mechanism of LOS is interpreted as the precipitation of the leading phase of the eutectic reaction above the glass transition temperature. In comparison with monolithic Mg-based BMG alloys, the composites with an LOS exhibit significant improvement in mechanical properties, e.g. a compressive plastic strain of ∼18% and ultimate strength of ∼1.2 GPa, have been measured in Mg₈₁Cu_9.3Y_4.7Zn₅ alloy. It is suggested that the enhancement of the mechanical properties of the composites can be attributed to the generation of multiple shear bands and the deformation of the LOS.     

CuTiZrCo块体非晶合金的形成及磁性能

采用铜模吸铸工艺制备出直径为3 mm的Cu50.4Ti27.1Zr16.2Co6.3和Cu50.9Ti27.4Zr16.4Co5.3非晶圆棒,用X射线衍射、差示扫描量热仪、扫描电子显微镜、能谱分析仪和振动样品磁强计研究非晶合金的热稳定性、结构组织、相成分和磁性能。结果表明:当升温速率为20℃/min时,该两种非晶合金的过冷液相区分别为59 K和41 K;在磁性元素含量较小的铜合金体系中,小范围变化Co含量对饱和磁化强度的影响不大;样品直径由3 mm增大到5 mm时,非晶基体中会析出较多形状不规则富Co和Ti的混合相,使样品的饱和磁化强度Ms明显增大。