Designing metallic glass matrix composites with high toughness and tensile ductility

Abstract

The selection and design of modern high-performance structural engineering materials is driven by optimizing combinations of mechanical properties such as strength, ductility, toughness, elasticity and requirements for predictable and graceful (non-catastrophic) failure in service. Highly processable bulk metallic glasses (BMGs) are a new class of engineering materials and have attracted significant technological interest. Although many BMGs exhibit high strength and show substantial fracture toughness, they lack ductility and fail in an apparently brittle manner in unconstrained loading geometries. For instance, some BMGs exhibit significant plastic deformation in compression or bending tests, but all exhibit negligible plasticity (<0.5% strain) in uniaxial tension. To overcome brittle failure in tension, BMG-matrix composites have been introduced. The inhomogeneous microstructure with isolated dendrites in a BMG matrix stabilizes the glass against the catastrophic failure associated with unlimited extension of a shear band and results in enhanced global plasticity and more graceful failure. Tensile strengths of approximately 1 GPa, tensile ductility of approximately 2-3 per cent, and an enhanced mode I fracture toughness of K(1C) approximately 40 MPa m(1/2) were reported. Building on this approach, we have developed 'designed composites' by matching fundamental mechanical and microstructural length scales. Here, we report titanium-zirconium-based BMG composites with room-temperature tensile ductility exceeding 10 per cent, yield strengths of 1.2-1.5 GPa, K(1C) up to approximately 170 MPa m(1/2), and fracture energies for crack propagation as high as G(1C) approximately 340 kJ m(-2). The K(1C) and G(1C) values equal or surpass those achievable in the toughest titanium or steel alloys, placing BMG composites among the toughest known materials.

Thickness-Dependent Strain Rate Sensitivity of Nanolayers via the Nanoindentation Technique

“…Therefore, the SRS should be similar to the single layer Cu. However, when h is smaller, the and would be close to 0.5 due to the co-deformation of crystalline phase and amorphous phase (the two phases share the deformation equally) [8,13], and the SRS would be closer to the single-layer amorphous film based on Equation (6). Figure 6b is a schematic showing the different deformation mechanisms at different h. When h > 100 nm, Cu layers deform plastically due to its low strength and accommodate most of the strain, and thus Cu/a-CuNb multilayers have an apparent SRS value similar to that of the single layer Cu film.…”

“…That means the key in this study is to determine how the displacement is distributed. In Equation (6), both the SRS and the percentage of plastic deformation accommodated by the crystalline ( ) and amorphous ( ) layers should change with the change of h. For the SRS of Cu/a-CuNb multilayers, we take the previously measured SRS of the 1.5 μm Cu film (m = 0.048, assuming that m does not change in this regime) into Equation (6) and treat ma as a value close to zero, then we can qualitatively discuss the relationship between m and h. As shown in Figure 6a, the modeled curve (dashed line) indicates the evolution of co-deformation of both Cu and a-CuNb. In addition, the SRS of a-CuNb, Cu, their average value (dotted lines) and Cu/a-CuNb are also plotted on the graph.…”

“…Metallic glasses (MGs) exhibit high strength, excellent abrasion and corrosion resistance [4], but they are generally brittle due to the shear band (SB) controlled-deformation mechanisms therefore the SRS is close to zero [5]. Prior studies have shown that adding a crystalline phase to the amorphous matrix can increase the toughness/plasticity of ZrTi-based MGs [6] and crystalline/amorphous (C/A) multilayers [7][8][9][10][11][12][13][14]. For the C/A multilayer composites, their thermally-activated plastic deformation mechanisms can also be revealed by quantifying their SRS.…”

Properties of Bulk Metallic Glasses

“…Сплавы Cu-Zr-Al-Co [97,98] и Сu-Zr-Al [99] показывают деформационное упрочнение вслед-ствие мартенситного превращения при деформа-ции. Наиболее успешные результаты получены в сплавах на основе Zr, содержащих бериллий -элемент с низкой технологичностью (может обра-зовывать токсичный оксид), который затрудняет формирование интерметаллических соединений и обуславливает получение граничного твердого раствора в дендритной форме [100]. Данные сплавы показали высокую пластичность на растяжение.…”

Tuning plasticity of in-situ dendrite metallic glass composites via the dendrite-volume-fraction-dependent shear banding

“…Uncontrolled shear banding can incur catastrophic failure with very limit ductility [6,10], impeding wide applications of BMGs as structural materials. An effective way to solve this bottle-neck problem is to develop BMG composites by in-situ introducing crystalline second phases [11][12][13][14][15][16][17][18][19][20][21]. It is expected that these crystalline phases facilitate shear band nucleation at their interfaces with the glass matrix, and meanwhile act as obstacles to shear band propagation into cracks due to their relatively high shear-band toughness [22,23].…”