Effects Of Minor Addition Rare Earth Elements On Glass-forming Ability And Corrosion Resistance Of Cu-based Metallic Glasses

Bulk metallic glasses (BMGs) with unique properties have aroused great interests in materials and engineering over the past decades. Minor addition or micro-alloying technique is one of the most widely used way to improve the properties and structure of metallic materials. It also plays an effective role in formation of BMGs. In this paper, the rare earth elements (RE) were used as minor addition materials in Cu- based BMG, and its influences on the Glass-forming Ability (GFA), thermal stability and corrosion behaviors were studied.First, the rare earth elements(Y,Ce,Sm,La) were used as minor alloy elements, and a series of (Cu₅₀Zr₄₅Al₅)100-xREx alloys were designed. The alloy samples were prepared by suction-cast technology. The microstructure of the samples were studied by X-ray diffraction (XRD) and opitical microscope (OM). The results showed that a minor addition of RE, the samples remained fully metallic glasses, but Cu10Zr7, CuZr and Zr2Cu phases precipitated with the increasing addition of RE.The Glass-forming Ability and thermal stability of Cu-based BMGs were investigated by differential scanning calorimetry (DSC) and differential thermal analysis (DTA). Because the RE elements have similar atomic size, chemical and physical properties, they have large atomic mismatch and negative heat of mixing with the main components of the based alloy, proper addition of RE can improve the GFA and thermal stability of Cu-based BMGs. The DSC and DTA results showed that when Y, Sm, La≤2 at.%, The Trg(Trg=Tg/Tl) ranged from 0.595 to 0.615, theγ(γ=Tx/( Tg+ Tl)) ranged from 0.402 to 0.410 and Tx ranged from 55K to 66K respectively, which means the alloys have good Glass-forming Ability and thermal stability. The GFA and thermal stability began decreasing when the amount of Y, Sm, La exceeded 2 at.%. The addition of Ce decreased the thermal stability, but had not much effects on the Glass-forming Ability.The BMGs have high corrosion resisitance because of their special structure. The corrosion behaviors of Cu-Zr-Al-RE bulk metallic glasses were investigated in 3.5% NaCl solution by electrochemical method. The results showed that the Ec of Cu-Zr-Al-RE BMGs ranged from -480mV to -530mV, the ic ranged from 6μA/cm2 to 20μA/cm2. The Ec was deteriorated with the addition of Y. The Ec reached the lowest level( -533mV) when the amount of Y was 3 at.%. The ic shifted slightly with the addition of Y. The ic was increased with increasing addition of Ce. The alloys exhibited higher corrosion resisitance than the based alloy Cu₅₀Zr₄₅Al₅ (Ec=-487mV, ic=16.8μA/ cm2)when Ce≤3 at.%,. Minor addition of Sm and La decreased the ic, but did not have much influences on the Ec.Compared with Zr55Cu30Al10Ni5(Ec=-500mV,ic=12.6nA/cm2), the Cu-Zr-Al-RE bulk metallic glasses alloys did not exhibit excellent corrosion resistance, which showed that the addition of RE elements did not have benefit effects on the corrosion resistance of Cu-based alloys. It means that besides the microstructure, the kinds and content of minor addition elements are another important reason on the corrosion behavior of Cu-based BMGs. Cu-Zr-Al-RE bulk metallic glasses showed good resistance to pitting corrosion. When the alloys were full amorphous, the corrosion behavior was uniform corrosion. Local corrosion happened while the samples were partly amorphous.