Formation of V2Zr in MA-SPS process of V–4Cr–4Ti alloy when using ZrO2 vials

Abstract

In this work, a series of V–4Cr–4Ti alloy and powders were prepared using mechanical alloying and spark plasma sintering. X-ray diffraction, transmission electron microscopy, selected area electron diffraction and energy dispersive spectrometer were used to characterize the morphology and microstructure. Some unknow peaks were appeared in XRD spectrum, which had a high correlation with ZrO2 milling balls and vials. TEM results shown that a part of these unknown peaks resulting from ZrO2 particles peeled from milling balls and vials. Other peaks were Laves phase V2Zr formatted in SPS process under a sintering temperature of 1350 °C or higher. Contrast experiment proved the stability of ZrO2 at 1150 °C. Thermodynamic calculation showed that the lowest temperature for the formation of V2Zr was 1380 °C. This temperature could be lower due to the inhomogeneous current distribution in SPS process. Thus, when using ZrO2 milling balls and vials, SPS sintering at 1150 °C was more suitable for V-based alloy to avoid the formation of V2Zr and the dissolution of oxygen.