Revealing the interfacial plasticity and shear strength of a TiB2-strengthened high-modulus low-density steel

Abstract

The TiB2-strengthened high-modulus low-density steel, fabricated by eutectic solidification, has been considered as a potential advanced high strength steel grade for lightweight automotive applications. In the present work, a novel experimental procedure based on nanoindentation compression is designed to probe the deformation behavior and shear strength of the interface between the steel matrix and the TiB2 particles, which are important microstructure properties determining the macroscopic mechanical properties of the present high-modulus low-density steel. Specimens with wedge-shaped TiB2 particles attached to the steel matrix are fabricated using focused ion beam milling and are subjected to compression tests using a nanoindenter with a flat tip. Microstructural analysis after the compression test shows that, prior to the interface debonding, a large strain gradient occurs in the steel matrix near the interface, leading to the formation of lamellar dislocation substructures. Finite element (FE) simulations are also carried out in the present work to simulate the deformation behavior of the interface. The simulations are in good agreement with the experimental observations. Based on the nanoindentation compression tests as well as the FE simulations, the intrinsic interfacial shear strength is determined to be as high as ∼700 MPa for the present steel. This large interfacial shear strength explains why the particles are difficult to be detached during deformation, which is the main mechanism responsible for the excellent tensile ductility of the present steel.