Tailoring the degradation rate of magnesium-lithium alloy with alloying elements of gadolinium and nickel

Abstract

To explore lightweight degradable materials that are more suitable for fracturing ball, Mg-8Li-4Gd-xNi (x = 0, 0.5, 1, 1.5 wt%) alloys for fracturing ball in petroleum extraction were prepared by vacuum induction melting. The features and formation of long-period stacking ordered (LPSO) doped with gadolinium (Gd) and nickel (Ni) were characterized. And the relationship between the degradation rate of alloys and the structure of LPSO in duplex Mg-Li alloys is investigated. The results show that network 24 R LPSO phase and punctate GdNi3 phase are formed with the addition of Gd and Ni. With the increase of Ni content, the shape of LPSO changes from intermittent network to continuous network and turns into an intermittent network again. The Mg-8Li-4Gd-1.5Ni alloy shows a significant increment in weight loss rate compared with the Mg-8Li-4Gd alloy by 75 times. Atomic force microscope (AFM) results show that the addition of Ni increases the potential difference between the second phase and the β-Li phase from 220 mV to 504 mV. It is difficult for forming LPSO due to higher fault energy when the atomic ratio of Gd to Ni is lower than 4:3, which promotes the LPSO to intermittent network. LPSO and GdNi3 provide higher potentials as cathodes in corrosion, forming a loose and porous corrosion product layer in the alloy. With the increase of Ni content, micro-galvanic corrosion effect is increased which results in a significantly higher corrosion rate of the alloy.