Variants of face-centered cubic phase in pure hafnium during the HCPFCC phase transformation

In this work, the variants of face-centered cubic (FCC) phase during hexagonal close-packed (HCP) to FCC phase transformation were investigated based on pole fig. (PF) analysis and selected area electron diffraction (SAED) simulations. Results indicated that 12 FCC variants can be generated during both the basal-type (B-type) and prismatic-type (P-type) phase transformations. B-type FCC variants can be further categorized into two groups, and the [1120]HCP//[110]FCC zone axis is optimal for observing all the FCC variants. While the P-type FCC variants can be divided into three groups and the [0001]HCP//[001]FCC zone axis is more favorable for the observation of the three kinds of P-type FCC variants. By using electron backscatter diffraction (EBSD) and transmission electron microscopy (TEM) techniques, both B-type and P-type FCC Hf variants were investigated in pure hafnium. When considering the crystallographic characteristics of B-type FCC, the observed n-ary sumation 3{111} twinlike FCC phase can be considered as two different FCC variants that are parallel to each other and in close contact (here we noted them as Variant-I and variant-II, respectively). While, for the P-type FCC phase, the FCC lamellas with an angle of 60 degrees to each other are the P-type FCC variants with an angle/axis relationship of 60 degrees/[001]FCC, rather than a new potential orientation relationship.