Properties Of Bulk Glassy Alloys Research Articles

Nanocrystallization of Cu-Based Bulk Glassy Alloys upon Annealing

Cu-based bulk glassy alloy is a new amorphous system developed recently, which has large glass forming ability and relatively low cost (Dai et al., 2006; Fu et al., 2008; Kim et al., 2006; Malekana et al., 2010; Zhang & Zhang, 2008). The tensile fracture strength is much higher than crystals, reaching up to 2,000 to 2,400 MPa, with certain ductility. And compared to Zr-based and Pd-based bulk glassy alloys, the strength of Cu-based bulk glassy alloy is also on the top, which can be used as ultra-high strength structural materials in the future. Until now, many researchers in the world have done a lot of deep studies on Cu-based bulk glassy alloy. But as structural materials, the plastic property of prepared Cubased bulk glassy alloy which has lowers plastic property than steel materials also need to be improved. Therefore, it’s an urgent problem to improve the plasticity and toughness of amorphous alloys. Based on the research of bulk glassy alloy, in recent years, the research on the composite material of bulk glassy and nanocrystalline alloy has been carried out (Barekara et al., 2010; Liu et al., 2009; Xie et al., 2008; Yang et al., 2009; Zhang et al., 2013). Because when the nanocrystalline evenly distributed in the bulk glassy alloy matrix, the properties of bulk glassy alloy can be further optimized, while maintaining high strength and improving the lower plastic. So the application field of high strength structural material can be expanded. In this paper, Cu-based bulk glassy alloy was prepared through copper mold casting method. The nanocrystallization of bulk glassy alloy was obtained by annealing. The annealing process, microstructure and properties of the nanocrystallization were investigated. The preparation of Cu-based bulk glassy-nanocrystalline alloy composite materials on the basis of the theory and technology pISSN 2287-5123·eISSN 2287-4445 http://dx.doi.org/10.9729/AM.2016.46.1.32

Recent development and application products of bulk glassy alloys

This paper reviews past developments and present understanding of the glass-forming ability, structure and physical, chemical, mechanical and magnetic properties of bulk glassy alloys (BGA) with the emphasis on recent results obtained since 1990, together with applications of BGA, achieved mainly in Tohoku University. After introducing the fundamental concepts around glassy alloys (GA) in Sections 1 and 2 describes the progress of the study of structural relaxation leading to the discovery of GA with a large supercooled liquid region. Section 3 reviews the history of BGA development, followed by BGA systems and their features in Section 4, and features of glassy structure in Section 5. Sections 6–9 summarize the engineering and standardization of Zr-based BGA, followed by the origins of the development of useful materials on the basis of experimental data on the compositional effect on the fundamental properties of basic ternary and quaternary Zr-based BGA. Sections 10 and 11 include the glass-forming ability and dynamic mechanical properties of Zr-based hypoeutectic BGA and Cu–Zr–Al–Ag BGA. Mechanical properties of Ni- and Zr-based BGA at low temperatures are shown in Section 12, while Section 13 describes the formation and properties of Ni-free Ti-based BGA. Sections 14 and 15 deal with porous Zr-based BGA, including spherical pores and commercialized ferromagnetic and high-strength Fe-based GA, respectively, then Section 16 reviews supercooled liquid formation. Applications for Zr-, Ti- and Fe-based GA are described in Section 17. In conclusion, Section 18 attempts to assess the present knowledge of the structure and physical properties and identify some outstanding problems for future work.

Formation, Thermal Stability and Mechanical Properties of Bulk Glassy Alloys with a Diameter of 20 mm in Zr-(Ti,Nb)-Al-Ni-Cu System

Bulk glassy alloy rods with a diameter of 20 mm were produced for Zr61Ti2Nb2Al7:5Ni10Cu17:5 and Zr60Ti2Nb2Al7:5Ni10Cu18:5 by a tilt casting method. The replacement of Zr by a small amount of Ti and Nb caused a distinct increase in the maximum diameter from 16 mm for Zr65Al7:5Ni10Cu17:5 to 20 mm, accompanying the decrease in liquidus temperature and the increase in reduced glass transition temperature. The primary precipitation phase from supercooled liquid also shows a distinct change, i.e., from coexistent Zr2Cu, Zr2Ni and Zr6NiAl2 phases for the 65%Zr alloy to an icosahedral phase for the 61%Zr and 60%Zr alloys. These results allow us to presume that the enhancement of the glassforming ability is due to an increase in the stability of supercooled liquid against crystallization caused by the development of icosahedral shortrange ordered atomic configurations. The 60%Zr specimens taken from the central and near-surface regions in the transverse cross section at the site which is 15 mm away from the bottom surface of the cast glassy rod with a diameter of 20 mm exhibit good mechanical properties under a compressive deformation mode, i.e., Young’s modulus of 81 GPa, large elastic strain of 0.02, high yield strength of 1610 MPa and distinct plastic strain of 0.012. Besides, a number of shear bands are observed along the maximum shear stress plane on the peripheral surface near the final fracture site. The finding of producing the large scale Zr-based bulk glassy alloys exhibiting reliable mechanical properties is encouraging for future advancement of bulk glassy alloys as a new type of functional material. [doi:10.2320/matertrans.MER2008179]

Mechanical properties of a Ni 60Pd 20P 17B 3 bulk glassy alloy at cryogenic temperatures

Little is known about mechanical properties of bulk glassy alloys (BGAs) at cryogenic temperatures. In this study, we investigated the effects of temperature and strain rate on the mechanical properties of a Ni 60Pd 20P 17B 3 BGA. Compression tests were performed at temperatures of 295, 223, 173 and 77 K and at strain rates from 5 × 10 −5 to 5 × 10 −3 s −1. Measurements of the elastic parameters were also made at temperatures from 91 to 371 K. It is found that both the maximum compressive stress and plastic strain to failure increase with decreasing testing temperature. The Young and shear moduli, and Debye temperature monotonically increase with decreasing temperature, while Poisson’s ratio decreases, indicating that the BGA becomes rigid and the effective atomic distance decreases at cryogenic temperatures. The mechanism reflecting the changes in the maximum compressive stress and plastic strain with temperature is discussed.

Influences of Temperature and Strain Rate on Mechanical Behavior of a Cu<SUB>45</SUB>Zr<SUB>45</SUB>Al<SUB>5</SUB>Ag<SUB>5</SUB> Bulk Glassy Alloy

Since the invention of bulk glassy alloys, a number of studies have been performed at ambient temperatures or above. However, little is known about mechanical properties of bulk glassy alloys at cryogenic temperatures. In this study, we investigated the effects of temperature and strain rate on the mechanical properties of a Cu45Zr45Al5Ag5 bulk glassy alloy fabricated by high pressure die casting methods. Compression tests were performed for the Cu45Zr45Al5Ag5 bulk glassy alloy rods with a diameter of 3 mm at temperatures of 298, 223, 173 and 77 K and at strain rates from 5 10 5 to 5 10 3 s 1 . It is found that the maximum compressive stress and plastic strain to failure increase monotonically with decreasing testing temperature. Multiple shear bands are observed on the side surface of the specimen deformed plastically at cryogenic temperatures. The maximum compressive stress and plastic strain are almost independent of strain rate. The reason for the changes in the maximum compressive stress and plastic strain with temperature and strain rate is discussed. [doi:10.2320/matertrans.MBW200734]

Synthesis of Ti-Based Glassy Alloy/Hydroxyapatite Composite by Spark Plasma Sintering

The spark plasma sintering process has been used to fabricate Ti40Zr10Cu36Pd14 glassy alloy/hydroxyapatite composites. XRD, DSC, SEM and compression testes were used to examine the microstructure and properties of the composites. No crystallization was observed in the glassy alloy matrix. The glass transition temperature (Tg) is independent of the HA addition and the onset temperature of crystallization (Tx) slightly decreases with increasing HA content. The sintered composite exhibited reduced value of Young's moduli as compared with the as-cast Ti40Zr10Cu36Pd14 bulk glassy alloy. (doi:10.2320/matertrans.MBW200716) Since bulk glassy alloys were synthesized for the first time by a copper mold casting process in the late 1980's, 1) a number of bulk glassy alloys in Mg-, La-, Zr-, Pd-, Ti, Fe-, Co-, Ni- and Cu-based systems have been developed. 2) Unique properties of bulk glassy alloys make them extremely attractive for biomedical applications. Recently, bulk glassy alloy composites have attracted much attention due to their improved characteristics. Most of researches for bulk glassy alloy composites have been focused on the improvement of mechanical properties, especially for ductility. 3-5) Hydroxyapatite (HA), which is a main mineral constituent of teeth and bone, has an excellent biocompatibility with hard tissue, skin and muscle tissue. Moreover, HA does not exhibit any cytoxic effects and can directly bond to human bone. 6-8) A number of studies have been reported on HA coating on Ti metal and Ti-alloys for improving the surface bioactivity. 9-12) However, the HA coatings often flake off as a result of poor ceramic/metal interface bonding. 13) The problems mentioned above may be solved by fabrication of metal/HA composites. Some papers have been published on the preparing of Ti/HA composite materials. 14-16) As a novel rapid sintering technique, the use of a spark plasma sintering (SPS) technique enables the sintering of high quality materials within a short time by controlling the spacing between powder particles, electrical energy and sintering pressure. The SPS includes various phenomena: 17) (a) electrical breakdown of surface oxide film and removal of contaminated layer on particle surface by spark generation and sputtering effect; (b) destruction of surface oxide film and neck formation between powder particles; (c) focused current and Joule heat at the neck; and (d) enhanced migration of atom or ion by the difference in temperature between neck and particle core as well as by electrical field, and neck growth. The phenomena provide advantages which cannot be obtained using the conventional sintering process. The sintering can be carried out at a lower temperature and in a shorter time as compared with the conventional sintering process. Consequently, the SPS can be applied to materials which are required to suppress crystallization and grain growth, such as glassy alloys. 17)

Improved mechanical properties of bulk glassy alloys containing spherical pores

For future extension of application fields for bulk glassy alloys, it is important to develop a new type of glassy alloys which exhibit simultaneously high strength, low Young's modulus, large elastic elongation, high ductility, high corrosion resistance, low density, high specific surface area, etc. Considering that bulk glassy alloys in non-ferrous metal base systems possess unique characteristics of high strength, low Young's modulus, large elastic elongation, high fracture toughness and high corrosion resistance, they are expected to become an important candidate material for structural applications. One of the ways to develop a new material with the above-described properties is to fabricate ductile bulk glassy alloys containing open or closed pores in a wide range of volume fraction. Mechanical properties of closed-pore type porous bulk glassy alloys are presented. Moreover, in the present work, we review our recent work on the porous glassy Pd 42.5Cu 30Ni 7.5P 20 alloys and present an analysis of stress concentration around spherical pores.

Formation, thermal and mechanical properties of bulk glassy alloys in Zr–Al–Co and Zr–Al–Co–Cu systems

New Zr-based bulk glassy alloys in Zr–Al–Co and Zr–Al–Co–Cu systems were developed. The largest supercooled liquid region is upto 64 K for the Zr55Al20Co25 alloy and 80 K for the Zr55Al20Co20Cu5 alloy, respectively. Glassy rods with a diameter of 3 mm for the Zr55Al20Co25 alloy and 5 mm for the Zr55Al20Co20Cu5 alloy can be prepared by copper-mold casting. Glassy Zr55Al20Co20Cu5 sheet with a thickness of 2 mm was also formed by squeeze copper-mold casting. The bulk glassy Zr55Al20Co20Cu5 alloy exhibits Young’s modulus of 92 GPa, elastic limit of 2.1%, tensile strength of 1960 MPa, compressive fracture strength of 2200 MPa, and compressive plastic strain of 0.6%. The tensile strength value is considerably higher than those for the other Zr-based bulk glassy alloys reported upto date. The synthesis of the new Zr-based bulk glassy alloys with high glass-forming ability and high tensile strength approaching 2000 MPa is expected to result in a future extension of application fields as a high strength material.

Formation, Thermal Stability and Mechanical Properties of Ca-Based Bulk Glassy Alloys

New bulk glassy alloys were formed in the Ca–Mg–Cu system by the copper mold casting method. The maximum rod diameter (dmax) for the formation of a glassy phase was 2 mm for Ca67Mg19Cu14 and above 4 mm for Ca57Mg19Cu24. The glass transition temperature (Tg), crystallization temperature (Tx), supercooled liquid region (ΔTx=Tx−Tg) and reduced glass transition temperature (Tg⁄Tm) are 387 K, 407 K, 20 K and 0.60, respectively, for the former alloy and 404 K, 440 K, 36 K and 0.64, respectively, for the latter alloy. There is a tendency for dmax to increase with increasing ΔTx and Tg⁄Tm. Young’s modulus (E) and compressive fracture strength are 38 GPa and 545 MPa, respectively, for the Ca57Mg19Cu24 alloy rod with a diameter of 2 mm. The success of synthesizing bulk glassy alloys in the simple metal (Ca) base system makes it important as a basic alloy system for examining fundamental chemical and physical properties of bulk glassy alloys.

Recent Progress in Bulk Glassy Alloys

For thousands of years, metallic alloys have been among the most important materials used by mankind, and their importance as engineering materials remains as great now as ever. Without exception, all bulk metallic alloys used to date consist of crystalline materials with three-dimensional periodic atomic configurations. The instability of the liquid phase of metallic alloys below melting temperature had been thought to be a universal phenomenon, making the formation of a crystalline phase of the bulk metallic alloy unavoidable. In order to prevent transition from a liquid to a crystalline phase, extremely high cooling rates of the order 10 6 K/s are required and the alloys exhibiting critical cooling rates of 10 5 to 10 7 K/s are known as amorphous/glass forming alloys. 1, 2) As a result of the requirement for rapid cooling, amorphous alloys have usually been produced in a thin sheet form with thicknesses below 0.05 mm. The conventionally accepted concept that the supercooled liquid phase of metallic alloys is always unstable has been broken through by the recent successes in forming bulk glassy alloys in a number of transition metal-based alloy systems using the copper mold casting technique. 3‐5) In recent years, studies of the stabilization of metallic supercooled liquid and the resulting bulk glassy alloys have been significant not only for fundamental science but for engineering applications as well. In this paper we review our recent results on the formation and properties of bulk glassy alloys.