The effect of oxygen on the microstructural evolution in crystallized Cu–Zr–Al metallic glasses

• The effect of oxygen content in crystallized Cu-rich CuZrAl glasses is characterized.
• B2–CuZr forms at lower temperatures in samples with higher oxygen contents.
• The precipitation of L21 Cu2ZrAl phase inside B2 grains is observed and discussed.
• The experimental orientation relationship between the B2 and B19′ phases is reported.

Cu–45Zr–8Al and Cu–44.1Zr–7.8Al–2Y metallic glass ribbons were prepared by melt spinning and heat treated at two different temperatures followed by microstructural characterization by SEM and TEM. The compositions were selected to better understand the effect that oxygen has in the sequence and morphology of the phases formed during devitrification. A novel microstructure consisting of the Heusler Cu2ZrAl phase precipitated inside a B2–CuZr matrix that has shape memory properties was produced. It is proposed that this novel microstructure may be used to prepare samples with improved shape memory responses. The known cube–cube relationship between the Heusler and B2 phases also provides direct evidence about the orientation relationship between the martensite and the parent B2 austenite and the results are in contrast to what is reported in the literature. The results also confirm that oxygen dissolved in these alloys leads to the formation of the B2–CuZr phase at lower temperatures than comparable low oxygen alloys.