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.

The mechanical properties of bulk metallic glasses (BMGs) and their composites have been under intense investigation for many years, owing to their unique combination of high strength and elastic limit. However, because of their highly localized deformation mechanism, BMGs are typically considered to be brittle materials and are not suitable for structural applications. Recently, highlytoughened BMG composites have been created in a Zr-Ti-based system with mechanical properties comparable with highperformance crystalline alloys. In this work, we present a series of low-density, Ti-based BMG composites with combinations of high strength, tensile ductility, and excellent fracture toughness.R ecent progress in ductile-phase-reinforced bulk metallic glass (BMG) composites has demonstrated that with proper design and microstructural control enhanced toughness and tensile ductility can be achieved in 2-phase alloys with a glassy matrix phase that exhibits large glass-forming ability (GFA) (1,2). This work has opened potential structural applications for BMG composites that are not possible in monolithic BMGs, because of shear localization and subsequent catastrophic failure during unconfined loading (2). Although the problems associated with unlimited extension of shear bands and the resulting catastrophic failure seen in monolithic BMGs can be mitigated by adding soft crystalline inclusions to the glass, current BMG matrix composites that exhibit this structure are based on the relatively dense element zirconium (1-4). Reducing the cost and density of current Zr-based composites is beneficial for the commercialization of these new alloys. Low-density components with high toughness and strength could be particularly useful in the aerospace and aeronautics industry as replacements for some crystalline titanium alloy hardware.With this motivation, the current work explores Ti-based (in both weight and atomic percentage) BMG matrix composites with mechanical properties and low density matching or surpassing those of common engineering titanium alloys. Herein, we report BMG composites composed of 42-62 weight percentage (wt%) titanium, with densities ranging from 4.97 to 5.15 g/cm 3 , and all exhibiting at least 5% tensile ductility. We vary the volume fraction of the glass phase from 20% to 70%, investigate aluminum additions to lower density, and report 1 alloy with Ͻ1.0 wt% of beryllium. The current work demonstrates that Ti-based BMG composites are competitive with conventional titanium alloys for some structural applications where high strength and toughness are a necessity.Ti-based, ductile-phase-reinforced matrix composites have been the subject of significant recent research (5)(6)(7)(8)(9)(10)(11)(12)(13)(14). In other systems, nano-crystalline composites have been reported that display significant compressive plasticity (15)(16)(17)(18)(19). These alloys are designed in a similar manner to BMG-matrix composites with the significant difference being that the continuous matrix material is comprised of a nanostruct...

The exceptional processability and large supercooled liquid region of bulk amorphous metals makes them highly promising candidates for thermoplastic processing. We report a lightweight (q = 5.4 g cm -3 ) quaternary glass forming alloy, Over the last two decades, the unique properties of bulk metallic glasses (BMGs), such as high strength, high specific strength, large elastic strain limit, and excellent wear and corrosion resistances along with other remarkable engineering properties have made these materials of significant interest for science and industry. [1][2][3][4][5][6][7][8][9] Researchers have designed families of multi-component systems that form bulk amorphous alloys, [4][5][6][7][8][9] among which Zr-(Vitreloy series), [4] and Pt-based [8] BMGs have been utilized commercially to produce items including sporting goods, electronic casings, medical devices, and fine jewelries. The unique advantages of injection molding, blow molding, microreplication, and other thermoplastic technologies are largely responsible for the widespread uses of plastics such as polyethylene, polyurethane, PVC, etc., in a broad range of engineering applications. Powder injection molding (PIM) of metals represents an effort to apply similar processing to metals, but requires blending of the powder with a plastic binder to achieve net shape forming and subsequent sintering of the powder. Given suitable materials, thermoplastic forming (TPF) would be the method of choice for manufacturing of net shape metallic glass components because TPF decouples the forming and cooling steps by processing glassy material at temperatures above the glass transition temperature (T g ) and below the crystallization temperature (T x ) followed by cooling to ambient temperature. [10,11] Conventional die casting requires rapid quenching to bypass the crystallization nose, which limits the ability to make high quality casts and to create parts with complex geometries. Unfortunately, among the published metallic glasses, only the expensive Pt-, [8] and Pdbased [12,13] glasses have shown good thermoplastic formability.Zr-based metallic glasses, especially the Vitreloy series, are much less expensive than Pt-and Pd-based alloys, have exceptional glass forming ability (GFA), but they are usually strong liquids and low processing viscosities are unattainable in the supercooled liquid region (SCLR) between T g and T x [14,15] . Strain rate effects on viscosity of amorphous alloys have been extensively studied. [16,17] An alloy optimal for TPF should have good glass forming ability, low viscosity (high fragility) in the SCLR, a low processing temperature, and a long processing time at that temperature before crystallization. We studied Be-bearing Zr-Ti based quaternary metallic glasses with compositions in the range of 60 % ≤ Zr+Ti ≤ 70 %. We found that compared with Vitreloys (Zr+Ti = 55 %), T g is lowered, the liquid becomes more fragile, and the SCLR is increased. Two composition regions were found with alloys that exhibit exceptional properties for TPF in ...

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