Effect of the diffusion annealing process and cooling rate on the microstructure of Zr/Ti layered materials

Layered materials are of great interest in aerospace and automotive engineering fields due to their superior performance. In the present work, Zr/Ti layered materials were fabricated by hot-rolling and diffusion annealing. Diffusion annealing for various times followed by cooling with different rates were carried out to tailor the microstructure. Scanning and transmission electron microscopes (SEM and TEM), energy dispersive spectrometer and electron backscatter diffraction (EBSD) were used to study the microstructure of the fabricated Zr/Ti layered material. In addition to the Zr layer and Ti layer, diffusion layers are formed after the diffusion annealing. The layer thickness and the microstructure of the diffusion layer are significantly affected by the diffusion annealing. Micron-scaled face-centered-cubic (FCC) phase and {10−12} 〈−1011〉 twins are observed in the Zr layer. The orientation relationship between the FCC phase and the matrix is determined as {0001}_HCP // {111}_FCC and 〈11−20〉 _HCP // 〈110〉_FCC. Combined with finite element model (FEM) simulation, the formation of the FCC phase and {10–12} 〈1011〉 twins is mainly attributed to the interlayer stress, which is caused by the difference in thermal expansion coefficients between different layers.