Fine Structure in Multi-Phase Zr₈Ni 21 -Zr₇Ni 10 -Zr₂Ni₇ Alloy Revealed by Transmission Electron Microscope

• Published in: Materials 2015-07, Vol.8 (7), p.4618
• Main Authors: Shen, Haoting, Bendersky, Leonid A, Young, Kwo, Nei, Jean
• Format: Article
• Language: English
• ISSN: 1996-1944; 1996-1944
• DOI: 10.3390/ma8074618

The microstructure of an annealed alloy with a Zr₈Ni composition was studied by both scanning electron microscopy (SEM) and transmission electron microscopy (TEM). The presence of three phases, Zr₈Ni , Zr₂Ni₇, and Zr₇Ni , was confirmed by SEM/X-ray energy dispersive spectroscopy compositional mapping and TEM electron diffraction. Distribution of the phases and their morphology can be linked to a multi-phase structure formed by a sequence of reactions: (1) L → Zr₂Ni₇ + L'; (2) peritectic Zr₂Ni₇ + L' → Zr₂Ni₇ + Zr₈Ni + L"; (3) eutectic L" → Zr₈Ni + Zr₇Ni . The effect of annealing at 960 °C, which was intended to convert a cast structure into a single-phase Zr₈Ni structure, was only moderate and the resulting alloy was still multi-phased. TEM and crystallographic analysis of the Zr₂Ni₇ phase show a high density of planar (001) defects that were explained as low-energy boundaries between rotational variants and stacking faults. The crystallographic features arise from the pseudo-hexagonal structure of Zr₂Ni₇. This highly defective Zr₂Ni₇ phase was identified as the source of the broad X-ray diffraction peaks at around 38.4° and 44.6° when a Cu-K was used as the radiation source.