Simultaneous high stiffness and metal-like superelasticity in TiB2–Ni coatings revealed by in-situ TEM nanoindentation

Abstract

Titanium diboride (TiB2) coatings possess excellent functional and structural properties, including high hardness, good abrasion resistance, superior thermal conductivity and outstanding electrical properties. However, the intrinsic brittleness of ceramics severely restricts their application in load-bearing and impact-resistant components. It is therefore highly desirable to improve ductility without sacrificing stiffness. In this study, TiB2–Ni coatings with Ni contents of 4 at.% and 20 at.% were prepared by magnetron co-sputtering from TiB2 and Ni targets. In-situ transmission electron microscopy (TEM) nanoindentation revealed that the 20 at.% Ni coating exhibits an elastic recovery rate of 86% while retaining a high hardness of 35 GPa, demonstrating that metal-like superelasticity and ceramic-like stiffness can be simultaneously realized. High-resolution TEM analysis revealed a homogeneous amorphous Ti–Ni alloy structure with short-range order, which accommodates reversible deformation via shear transformation zone activity, while the percolating TiB2 crystalline skeleton retains the high stiffness. In-situ observation further revealed that crack propagation occurs via layer-by-layer tearing rather than catastrophic brittle fracture. These results provide direct evidence and an instructive design strategy for ceramic coatings that combine high strength, high toughness, and superelasticity.