Equiatomic CoCrFeNi Thin Films: Defect Driven Texture Transformation and Orientation Relationships

Face centered cubic (fcc) metals deposited onto amorphous substrates reveal a transition from {111} to {001} fiber textures with increasing film thicknesses. This is explained by a competition between surface and elastic strain energy. Similarly, specific orientation relationships evolve for fcc metallic films grown heteroepitaxially on single crystal substrates, which depend on the relative symmetry between the substrate and the film. In the present study, observations on texture formation in fcc metals and binary alloys on an amorphous surface is extended to an equiatomic CoCrFeNi fcc compositionally complex alloy/ high entropy alloy. The change in texture on annealing is discussed based on kinetic and thermodynamic considerations.Further, formation of orientation relationships on a crystalline substrate is investigated. A high density of nanotwins delays grain growth of {111} oriented grains leading to abnormal {001} grain growth even on (0001) oriented single crystalline α-Al2O3 (c-sapphire) substrates. This leads to a new orientation relationship (OR) with respect to the c-sapphire substrate compared to the well-known OR1 ({111}fcc || (0001)Al2O3, <110>fcc||<10-10>fcc) and OR2 ({111}fcc || (0001)Al2O3, <110>fcc||<11-20>fcc) : ({001}fcc || (0001)Al2O3, <100>fcc||<10-10>fcc) referred to as 'OR3'. The rapid high temperature growth of OR3 and OR2 grains in comparison to OR1 grains is discussed. In addition, conditions for the formation of less common orientation relationships {345}fcc || (0001)Al2O3, {236}fcc || (0001)Al2O3, {146}fcc || (0001)Al2O3 and {447}fcc || (0001)Al2O3 are examined in relation to the first and higher order annealing twins in the OR1, OR2 and OR3 grains. The role of growth twins in as-deposited films and deformation twinning in films heat treated at or above 1223 K is discussed in relation to the grain growth behavior of different variants, in addition to elastic strain energy, interface energies, grain boundary mobility and Zener drag due to oxides and pores.