Room-temperature strength of the interfacial bond between silica inclusions and iron

The strength of the interface between iron (Fe) and individual spherical silica (SiO2) inclusions of 5±1 μm diameter is measured by means of in-situ micro-cantilever bending tests conducted under displacement control within a scanning electron microscope, using a wedge indenter tip. Attention is paid to ensure that reported data are not affected by either the electron beam during in-situ testing or by focused ion beam milling, used to produce the cantilevers. For the latter, a simple yet effective strategy, validated using finite element modeling, is devised to shift the peak interfacial stress towards the beam center, thereby relocating the fracture initiation position away from potential FIB-induced artefacts at the beam edge. All bend beams tested fractured along the Fe/SiO2 interface, with no visible evidence of silica microcracking or iron plastic deformation. The rapidly cooled iron matrix features a submicron ferrite grain size, causing its yield strength to exceed 1 GPa. Using classical Euler-Bernoulli beam theory, the estimated Fe/SiO2 interfacial tensile strength yields values ranging from 0.9 to 2.3 GPa, proving that SiO2 inclusions are strongly bonded to the Fe matrix at room-temperature. There is, thus, potential for engineering inclusion-containing Fe-based alloys that, under monotonic loading conditions, do not compromise the mechanical integrity of the ferrous matrix.