In situ observations of grain growth and recovery in cold sprayed Ni-Y2O3 and CP-Ni coatings using hot-stage TEM

Cold spray is a severe plastic deformation-based processing technique. The material undergoes extreme environments and a large energy can be assumed to be stored in material in form of strain, dislocations, and vacancies. The thermal stability and structural integrity of cermet coatings processed by cold spray for elevated temperature applications are rather important but not well understood. Here, commercially pure-Ni (CP-Ni) and Ni-Y(2)O(3 )cermet coatings were fabricated and annealed by an in-situ hot-stage transmission electron microscopy (TEM) technique to investigate and compare the microstructural evolution of these two materials including strain relaxation, sub grain boundary and grain boundary motion which as otherwise impossible to probe using ex situ annealing. The as-deposited CP-Ni exhibits crystallized ultra-fine grains (UFG), while the Ni-Y2O3 coatings show a combination of nanocrystalline (NC) and UFG grains and a non-uniform distribution of Y2O3 in the Ni matrix. The hot-stage TEM results show a decreased strain contrast and limited grain growth for both materials annealed at 350 ? for 2 h. When the materials are continuously heated from 25 ? to 800 ? in 19 min, the presence of nano Y2O3 particles shows pinning effects at grain boundaries, resulting in improved thermal stability of Ni-Y2O3 coatings compared with CP-Ni coatings.

Automated summary

In this study, the microstructural evolution of commercially pure nickel and nickel-yttria cermet coatings was investigated using in-situ hot-stage transmission electron microscopy. It was found that the nickel-yttria coatings exhibited better thermal stability compared to the pure nickel coatings.