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Local melting to design strong and plastically deformable bulk metallic glass composites

View Article: PubMed Central - PubMed

ABSTRACT

Recently, CuZr-based bulk metallic glass (BMG) composites reinforced by the TRIP (transformation-induced plasticity) effect have been explored in attempt to accomplish an optimal of trade-off between strength and ductility. However, the design of such BMG composites with advanced mechanical properties still remains a big challenge for materials engineering. In this work, we proposed a technique of instantaneously and locally arc-melting BMG plate to artificially induce the precipitation of B2 crystals in the glassy matrix and then to tune mechanical properties. Through adjusting local melting process parameters (i.e. input powers, local melting positions, and distances between the electrode and amorphous plate), the size, volume fraction, and distribution of B2 crystals were well tailored and the corresponding formation mechanism was clearly clarified. The resultant BMG composites exhibit large compressive plasticity and high strength together with obvious work-hardening ability. This compelling approach could be of great significance for the steady development of metastable CuZr-based alloys with excellent mechanical properties.

No MeSH data available.


Schematic of the local electric arc melting (a) and distribution of Young’s modulus in Cu47Zr47Al6 plates: as-cast (b) and after electric-arc treatment for the glassy matrix (c), heat-affected zone (d) and molten zone (e).
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f3: Schematic of the local electric arc melting (a) and distribution of Young’s modulus in Cu47Zr47Al6 plates: as-cast (b) and after electric-arc treatment for the glassy matrix (c), heat-affected zone (d) and molten zone (e).

Mentions: The electric arc local melting process is schematically illustrated in Fig. 3a. Once the electric arc is induced to the amorphous plate, it melts locally. The generated heat is dissipated by the convection, radiation, and heating the surrounding glassy matrix, respectively212223242526. A part of the generated heat would be consumed the neighbouring argon atmosphere in the convection and radiation manners (see the blue line in Fig. 3a). However, most of the generated heat can be dissipated by the material itself in a conduction way during local melting, while the heated material itself also can loss some heat in a radiation manner from the surface (see the orange line in Fig. 3a). The surface of the melt is deformed due to the induced arc pressure (Fig. 3a)212223242526, which causes that the final surface topology is not flat (Fig. 1a and b). Such a surface topography might result in the formation of residual stresses, negatively affecting the fabricated composite. However, this layer can be removed by polishing. Moreover, the Lorenz force induced by the electric arc can also drive the flow of the melt212223242526. Previous experimental and simulation results have shown that the temperature field of a molten pool and the liquid metal in the molten pool exhibit a radial gradient272829, resulting in a similar crystallization direction (blue arrows in Fig. 2(h)). Usually, the maximum temperature of the molten pool is larger than 1500 K21–29. This is certainly higher than the onset temperature and the final temperature of the melting for Cu47Zr47Al6 BMG which are 1150 ± 2 K and 1174 ± 2 K, respectively9. After removing the electric arc molten pool is rapidly quenched due to its small dimensions and cooling the plate by supporting water-cooled cooper block. Although the present cooling rate is higher than that of about 4 K/s reported for arc melting30, it is probably somewhat lower than the quenching speed of 200–770 K/s required preventing decomposition of the high-temperature B2 CuZr phase into the stable CuZr2 and Cu10Zr7 phases3132. Therefore, a small amount of Cu10Zr7 crystals is formed under a high arc melting current. Furthermore, CuZr martensities are induced within B2 crystals due to the thermal stress during quenching1033. Naturally, the present cooling rate is not sufficient to quench the melts into a fully amorphous state, but this is also not aimed.


Local melting to design strong and plastically deformable bulk metallic glass composites
Schematic of the local electric arc melting (a) and distribution of Young’s modulus in Cu47Zr47Al6 plates: as-cast (b) and after electric-arc treatment for the glassy matrix (c), heat-affected zone (d) and molten zone (e).
© Copyright Policy - open-access
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC5304197&req=5

f3: Schematic of the local electric arc melting (a) and distribution of Young’s modulus in Cu47Zr47Al6 plates: as-cast (b) and after electric-arc treatment for the glassy matrix (c), heat-affected zone (d) and molten zone (e).
Mentions: The electric arc local melting process is schematically illustrated in Fig. 3a. Once the electric arc is induced to the amorphous plate, it melts locally. The generated heat is dissipated by the convection, radiation, and heating the surrounding glassy matrix, respectively212223242526. A part of the generated heat would be consumed the neighbouring argon atmosphere in the convection and radiation manners (see the blue line in Fig. 3a). However, most of the generated heat can be dissipated by the material itself in a conduction way during local melting, while the heated material itself also can loss some heat in a radiation manner from the surface (see the orange line in Fig. 3a). The surface of the melt is deformed due to the induced arc pressure (Fig. 3a)212223242526, which causes that the final surface topology is not flat (Fig. 1a and b). Such a surface topography might result in the formation of residual stresses, negatively affecting the fabricated composite. However, this layer can be removed by polishing. Moreover, the Lorenz force induced by the electric arc can also drive the flow of the melt212223242526. Previous experimental and simulation results have shown that the temperature field of a molten pool and the liquid metal in the molten pool exhibit a radial gradient272829, resulting in a similar crystallization direction (blue arrows in Fig. 2(h)). Usually, the maximum temperature of the molten pool is larger than 1500 K21–29. This is certainly higher than the onset temperature and the final temperature of the melting for Cu47Zr47Al6 BMG which are 1150 ± 2 K and 1174 ± 2 K, respectively9. After removing the electric arc molten pool is rapidly quenched due to its small dimensions and cooling the plate by supporting water-cooled cooper block. Although the present cooling rate is higher than that of about 4 K/s reported for arc melting30, it is probably somewhat lower than the quenching speed of 200–770 K/s required preventing decomposition of the high-temperature B2 CuZr phase into the stable CuZr2 and Cu10Zr7 phases3132. Therefore, a small amount of Cu10Zr7 crystals is formed under a high arc melting current. Furthermore, CuZr martensities are induced within B2 crystals due to the thermal stress during quenching1033. Naturally, the present cooling rate is not sufficient to quench the melts into a fully amorphous state, but this is also not aimed.

View Article: PubMed Central - PubMed

ABSTRACT

Recently, CuZr-based bulk metallic glass (BMG) composites reinforced by the TRIP (transformation-induced plasticity) effect have been explored in attempt to accomplish an optimal of trade-off between strength and ductility. However, the design of such BMG composites with advanced mechanical properties still remains a big challenge for materials engineering. In this work, we proposed a technique of instantaneously and locally arc-melting BMG plate to artificially induce the precipitation of B2 crystals in the glassy matrix and then to tune mechanical properties. Through adjusting local melting process parameters (i.e. input powers, local melting positions, and distances between the electrode and amorphous plate), the size, volume fraction, and distribution of B2 crystals were well tailored and the corresponding formation mechanism was clearly clarified. The resultant BMG composites exhibit large compressive plasticity and high strength together with obvious work-hardening ability. This compelling approach could be of great significance for the steady development of metastable CuZr-based alloys with excellent mechanical properties.

No MeSH data available.