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A different dependence of apparent glass-forming ability (GFA) on casting-atmosphere pressure is observed in a Zr65Al7.5Ni10Cu17.5-xPdx (x=0–17.5) alloy system. Low-Pd alloys (x<12.5) reveal low GFA dependence, while high-Pd ones (x>=12.5) show high GFA dependence on atmosphere pressure applied during casting. The phenomenon is suggested to originate from the fact that for the high-Pd alloys, the transformation region of supercooled-liquid to quasicrystalline phase is located at the low-temperature side of the undercooled-liquid region where the atmosphere-pressure dependence of cooling characteristic coincidently takes place. The on-cooling phase transformation in the alloy system and the cooling mechanism during mold-casting process are discussed comprehensively. [ABSTRACT FROM AUTHOR]

In-situ Ti-reinforced Mg-based (MT-D) and in-situ Ta-reinforced Zr-based (ZT-D) bulk metallic glass matrix composites (BMGMCs) were prepared by a novel dealloying method, which contains an element-selective leaching process in a metallic melt. The BMGMCs exhibit better mechanical properties, including higher fracture strength and larger plastic strain, than their monolithic glassy counterparts or similar BMGMCs by ex-situ dispersing or conventional arc-melting methods. The differences of Young's modulus between the dispersoids and the glassy matrix for these BMGMCs generate stress concentration at the interface, which is considered to suppress the propagation of the single main shear band and initiate multiple shear bands to accommodate the plastic deformation. Furthermore, the fine size of dispersoids for these BMGMCs, caused by low reaction temperature during dealloying in the metallic melt, results in more interfaces with the matrix for further improvement of mechanical properties. In addition, the low reaction temperature can also contribute to less composition fluctuation of the matrix to maintain the glass-forming ability of itself, which can introduce no undesired phases to degrade the mechanical properties. This novel in-situ dealloying method is believed to make a breakthrough in designing ductile BMGMCs with fine-sized secondary particles. [ABSTRACT FROM AUTHOR]

The high-entropy alloy (HEA) design strategy is effective for ultra-coarsening-resistant 3D interconnected materials developed by liquid metal dealloying (LMD). However, the fundamental understanding of the dealloying mechanism and structural evolution of multi-principal elements 3D structured materials is still missing. In this study, the microstructural evolutions of 3D interconnected HEAs in Mg matrix were investigated using two types of multiphase precursors, namely, arc-melted and homogenized ones. The precursors' microstructure greatly influences dealloying kinetics and dealloying mechanisms what, in its turn, determines the final morphology of the 3D interconnected HEAs in Mg matrix. First, the prior fcc phase was dealloyed faster than any other precursor phases at dealloying temperatures from 600 to 900 °C. Second, the dealloying kinetics was faster along precursor grain boundaries (GB) as compared with grain interior. This led to the formation of a unique layered composite structure due to the inhomogeneous dealloying along the fine lamellars' GB of the homogenized precursor. Moreover, governing orientation relationship between precursor and dealloying product depends on the LMD conditions, and it significantly affects the 3D interconnected grain structure. The fundamental understanding of the dealloying mechanisms will pave the way for customized morphology design of the 3D interconnected HEAs in metallic matrix with improved thermal stability and physical properties. [Display omitted] [ABSTRACT FROM AUTHOR]

Abstract: Mg-based bulk metallic glass matrix composite with hcp-Ti powders was fabricated by casting the mixtures of Mg65Cu25Gd10 molten alloy and pure Ti powders into a copper mold. Ti powder was spherical and less than 150μm in diameter, and its volume fraction was controlled from 5 to 40%. Thermal stability of the glassy matrix was maintanied even in the coexistence with the Ti powders. However, Ti dispersoid caused a significant improvement on compressive ductility from 0% plastic deformation for the monolithic glass to 41% plastic deformation for the composite with 40vol.% Ti powders. This is the first success of synthesizing Mg-based alloys with high ultimate strength of ∼900MPa level as well as the large plastic deformation of ∼40%, and suggests a novel guideline to develop Mg-based alloys having high specific strength with high ductility. [Copyright &y& Elsevier]

A new type of Mg-Zn-Cu-Gd-based alloy strengthened by quasicrystal and Laves phase was developed. This alloy exhibits much better creep properties compared to AE42(Mg-4 wt% Al-2 wt% rare-earth) alloy, which is the benchmark creep-resistant magnesium die-casting alloy under the compressive creep condition of 180°C and 80 MPa. The new alloy also exhibits high room-temperature mechanical properties close to that of AZ91 alloy. The good mechanical properties are attributed to the special microstructure; the thermally stable icosahedral quasicrystals phase (i-phase) and Laves phase distributed along the grain boundary as a hard skeleton, and some fine β′1 precipitates distributed homogenously on the matrix. The dislocation morphology after the creep test was studied, and the strengthening mechanism was proposed. [ABSTRACT FROM AUTHOR]

The primary transformation reaction of the Zr65Al7.5Cu27.5 ternary glassy alloy with a low oxygen impurity of approximately 100 mass ppm was investigated. We have discovered the precipitation of the metastable icosahedral phase with a fine grain size of 50-100 nm in diameter accompanying with the formation of stable Zr2Cu phase at the annealing temperatures ranging from 715 to 730 K. The lattice spacing of Zr2Cu phase decreases at higher temperatures, which is attributed to the rearrangement of Zr and Cu in the decomposition of the icosahedral phase. It is suggested that the formation of the icosahedral phase in the primary stage originates from the existence of the quenched-in icosahedral local atomic configuration in the glassy state. [ABSTRACT FROM AUTHOR]

In this work, the biomedical applicability and physical properties of magnesium-based metallic glass/polycaprolactone (PCL) composites are explored. The composites were fabricated via mechanical alloying and subsequent coextrusion. The coextrusion process was carried out at a temperature near to the supercooled liquid region of the metallic glass and the viscous region of the polymer. The structures, as well as thermal and mechanical properties of the obtained samples were characterized, and in vivo investigations were undertaken. The composite samples possess acceptable thermal and mechanical properties. Tensile tests indicate the ability of the composites to withstand more than 100% deformation. In vivo studies reveal that the composites are biologically compatible and could be promising for biomedical applications. [ABSTRACT FROM AUTHOR]

Even though the Mg-based bulk metallic glasses (BMGs) have shown superior anti-corrosion properties compared with their crystalline counterparts, the brittleness of them limits the widespread application of these materials. In the present study, we have firstly introduced porous NiTi shape memory alloy particles into an Mg-Zn-Ca BMG by the direct adding method. This composite showed both improved compressive strength and corrosion resistance in Hank's solutions than its monolithic glassy counterpart. The NiTi dispersoids among the matrix were likely to hinder the main shear band propagation, and also acted as the corrosion barriers. Furthermore, the porous nature of present added particle could further increase the interface areas, which should enhance the reinforcing effects compared with solid ones. This low-cost, high-anticorrosive composite was a good candidate as an engineering material. [ABSTRACT FROM AUTHOR]

In the present letter we compare the thermal conductivities of Cu- and Ni-based alloys in relation with their cooling rates and glass-forming abilities. The cooling rates obtained for Cu- and Ni-based bulk glass-forming alloys are found to scale with the thermal conductivities of the base elements. Relatively low thermal conductivity of Ni-based alloy compared to the Cu-based one explains its lower glass-forming ability. The results also indicate that the thermal conductivity of the molten alloy should be also used as an indicator of the glass-forming ability among the other factors. [ABSTRACT FROM AUTHOR]

In the present study TiNb/Zr 55 Cu 30 Al 10 Ni 5 with various fraction additions were fabricated by spark plasma sintering successfully. The interface between the TiNb and the glassy matrix was investigated by nanoindentation. The results indicate that there is a good bonding between them. Therefore, the strength and plastic strain are improved due to introduction of TiNb. In order to study the improved plastic deformation of the composites, the FEM (Finite Element Method) was adopted. It is observed that more shear bands are formed around the TiNb particles. The shear bands form and propagate at the interface of the TiNb and the glassy matrix due to the misfit of their Young's modulus, therefore, the plastic strain is improved. [ABSTRACT FROM AUTHOR]

Abstract: The high strength metastable Ti–Fe–Co alloys were produced by arc-melting in the shape of distorted semi-spherical ingots with the dimensions of about 25–30mm in diameter and 7–10mm in height. The structure of the hypereutectic Ti–Fe–Co alloys (at Fe/Co ratio ≥1) studied by X-ray diffractometry and scanning electron microscopy consisted of the primary dendrites of an ordered cP2 Ti(Fe, Co) compound and an eutectic consisting of the cP2 Ti(Fe, Co) compound and a disordered BCC cI2 β-Ti solid solution. The strongest Ti–Fe–Co alloys have a hypereutectic structure and exhibit a high strength exceeding 2000MPa and a plastic deformation of about 15%. The quaternary Ti67Fe14Co14Sn5 alloy exhibits a high strength of 1830MPa and the largest plastic strain of 24%. The deformation behavior and the fractography of Ti–Fe–Co and Ti–Fe–Co–Sn alloys are studied in detail. The formation of a composite-like structure with hard carcass of the intermetallic phase in the relatively soft eutectic matrix enabled both high strength and ductility. The accommodation deformation can be explained by the intergranular sliding of the primary Ti(Fe, Co) dendrites in the softer eutectic matrix. Rough primary dendrites and eutectic rods of the cP2 intermetallic phase act as efficient barriers for shear strain and cracks propagation, while fine eutectic rods of submicron size are quite effortlessly cut by deformation bands and cracks. It is shown that the high strength and ductility values for Ti-based alloys can be achieved without using the injection mould casting or rapid solidification procedure. [Copyright &y& Elsevier]

Abstract: A Mg3Cu3Gd bulk metallic glass matrix composite with porous α-Ti dispersoids was prepared by dealloying in a metallic melt. The in situ formed α-Ti dispersoids had a pore-size of ∼500nm, which was imparted from the Ti2Cu precipitate in the prealloy. Pore size was therefore controllable through the cooling rate of the prealloy preparation. Plasticity was not improved apparently, however the maximum fracture stress under four point bending mode increased from 217MPa for the monolithic counterpart to 387MPa. This was due to the optimal relationship where dispersoid size (L)≈dispersoid interval distance (S)≈process zone size (R p ). This was achieved locally within and around the porous Ti dispersoids, and helped improve the toughness and ductility. [Copyright &y& Elsevier]