Consolidation and mechanical properties of Cu46Zr42Al7Y5 metallic glass by spark plasma sintering

https://doi.org/10.1016/j.jnoncrysol.2012.02.027Get rights and content

Abstract

Cu46Zr42Al7Y5 metallic glass with nearly 100% relative density was obtained by spark plasma sintering (SPS) with a diameter of 15 mm, which was larger than the largest size of 10 mm for the as-cast specimen. The fracture strength of the sintered specimen reached 2044 MPa, which was 15% higher than that of the as-cast Cu46Zr42Al7Y5 glassy specimen. The densification and compressive properties of the sintered specimens were related to sintering temperature. Structural changes of the specimens sintered at various sintering temperatures resulted in the difference of macro-mechanical properties.

Highlights

► The largest size of Cu46Zr42Al7Y5 with a diameter of 15 mm was fabricated successfully. ► The highest of strength of sintered specimen is higher than that of as-cast specimen. ► The sintering process was investigated.

Introduction

In recent years bulk metallic glasses (BMGs) have attracted extensive researching interest due to the unique properties, including high mechanical strength, high hardness, superior corrosion resistance and so on[1], [2], [3]. Nevertheless, due to the quite limited glass-forming ability (GFA), the thickness (or diameter) of BMGs is usually small, which restricts its application as engineering material. So exploring alloy systems having high GFA or large critical size is always concerned by BMG researchers. Recently, Cu-based glassy alloys were studied due to their lower cost compared to Zr- and Pd-based BMGs and high GFA. However, the GFA always is limited by the elements of alloys. For example, the critical diameter size of Cu47Zr45Al8 amorphous is 15 mm [4] but the minor addition of Dy can enhance the GFA of Cu-Zr-Al alloys to 20 mm by a copper mold casting method [5]. Therefore, the careful alloy design of the addition of suitable element is necessary for BMG alloys. Generally, a BMGs alloy system should comply with multicomponent systems, significant atomic sizes ratio above 12%, and negative heats of mixing [6]. It means that BMGs with large critical size are always limited in some specific components. To overcome these limitations, powder metallurgical methods have been used to fabricate BMG alloys.

Spark plasma sintering (SPS) technique can sinter powders to full density specimens at relatively low temperatures in a short sintering time [7]. It has been used as one of the promising methods to fabricate BMGs. Xie [8] obtained nearly 100% relative density Ni52.5Nb10Zr15Ti15Pt7.5 bulk metallic glass by SPS and Scudino [9] reported that high-strength Al-based bulk material could be obtained by SPS consolidated glassy powders.

In this work, bulk Cu46Zr42Al7Y5 metallic glassy specimen with larger size and higher strength has been produced by SPS sintering of gas-atomized powders. Comparing with the largest size of 10 mm for Cu46Zr42Al7Y5 specimen fabricated by conventional copper mould casting [10], [11], 15 mm in diameter and highly dense bulk glassy specimen was obtained using the SPS process. Furthermore, its fracture strength was 15% higher than that of as-cast specimen. Therefore, the SPS process shows a promising method to get larger size and higher strength BMGs. Meanwhile, the effect of sintering temperature on the structures and mechanical properties of the sintered specimens were studied.

Section snippets

Experimental procedures

Master ingots of the Cu46Zr42Al7Y5 alloy were prepared by arc melting. In order to obtain Cu46Zr42Al7Y5 glassy powders, the ingots were remelted in a quartz tube using an induction heating coil under vacuum. The melts were injected through a nozzle and atomization by high pressure helium gas. The Cu46Zr42Al7Y5 glassy powders were sieved to below 53 μm and they were sintered in a vacuum condition using a SPS system (Model SPS-3.20MK-IV). The heating rate was 50 K/min (from room temperature to TS-30

Gas-atomized powders

The gas-atomized powders were characterized by SEM, XRD and DSC. The results are shown in Fig. 1, which indicate that the particles of gas-atomized powders have a fully glassy structure. The SEM observation indicates that there is a spherical morphology as well as clean surfaces for the powders, as shown in Fig. 1(a). In order to confirm the structure of the gas-atomized powders, the slow scanning speed of 0.1°/min was used. Fig. 1(b) shows a XRD pattern of the gas-atomized Cu46Zr42Al7Y5 alloy

Discussion

The present experimental results indicate that both the density and mechanical properties are related to the sintering temperature. To understand the temperature influence on the densification, we note that the densification procedure is determined by atomic mobility. The atomic mobility of glassy powders during sintering can be expressed as [12], [13], [14]:n(τT)expΔGmτΔVkTwhere n is the atomic jumping probability, τ is the shear stress, ΔGm is the activation energy of the jumping motion,

Conclusions

Cu46Zr42Al7Y5 bulk metallic glass with nearly full density was fabricated successfully by SPS method using gas-atomized glassy alloy powders. The strength of the specimens is non-linear related to sintering temperatures. A specimen sintered at 653 K possesses the highest density and strength. The results indicate that SPS technique is a promising method for fabricating bulk metallic glass with high strength and large size when sintering temperature, a key sintering parameter, is optimized.

Acknowledgements

This work was supported by the National Nature Science Foundation of China (No. 50771063), Science and Technology Commission of Shanghai Municipality (No. 10JC1407400), the Ph.D. Programs Foundation of Ministry of Education of China (No. 20100073110004).

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