In situ transmission electron microscopy investigation of quasicrystal-crystal transformations in Mg–Zn–Y alloys

•Quasicrystal-to-crystal transformation sequence in Mg–Zn–Y alloys was determined.•H phase Zn3MgY and W phase Zn3Mg3Y2 nucleated on icosahedral quasicrystal Zn6Mg3Y.•Growth of both H and W phase is controlled by diffusion.•The close relationship between building units plays a key role in the transformation. Evolution of icosahedral quasicrystals (IQC) in Mg–Zn–Y alloys during annealing was investigated by in situ transmission electron microscopy (TEM), in combination with differential thermal analysis and X-ray diffraction. In bulk samples, the IQC phase transformed to face-centered cubic phase W and hexagonal phase H at 720K and 727K, respectively. In TEM samples, IQC started to transform to W at 673K and H at 688K during heating, and H transformed to W at 623K on cooling. Quantitative analysis of the in situ transformation process reveals that growth of both H and W is controlled by diffusion, agreeing with the Avrami’s model. The transformed products have specific orientation relationships with the parent phases: 3-foldIQC//[0001]H//[111]W and 2-foldIQC//112¯0]H//[01¯1]W. The specific orientation relationships are attributed to close structural correlation among icosahedron, distorted icosahedron and cuboctahedron in IQC, H and W phases. The close structure relationship among IQC, H and W phases on the unit-cell level plays an important role in the phase transformations.