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M7C3 carbide [M: metallic element] is the primary reinforcement in white cast irons. Further improving its properties for maximized benefits is highly desired. However, no clear clues are available to guide the modification. Through atomic force microscopy in-situ analysis and first-principles calculations, we demonstrate that (Fe,Cr)7C3 carbide's strength is governed by its metallic bond component. We theoretically prove that M7C3 carbide is tailorable by partially replacing its metallic elements with substitutes selected based on their work function as an indicator. This study provides an insight into the electronic origin of carbide's mechanical behaviour, helping guide developing high-performance M7C3 carbides.

Duplex stainless steels have excellent corrosion resistance due to their two-phase microstructure and electrically insulating passive film. Nevertheless, hydrogen charging causes deterioration of the corrosion protection mechanisms, resulting in increased pitting susceptibility. In this study, current-sensing atomic force microscopy was used to investigate the electrical properties of the passive film formed on 2507 duplex stainless steel before hydrogen charging. Results were compared with optical images of pitting corrosion initiation after hydrogen charging and FeCl3 exposure. Highest passive film conductivity and current density were seen at grain boundaries, indicating poor passive film development and high pitting probability. High conductivity was also observed on the passive film located at the adjacent austenite phase, alluding to favorable conditions for pitting corrosion propagation. Phases were identified by magnetic force microscopy, while pit initiation with subsequent propagation after hydrogen charging and FeCl3 exposure was observed using optical microscopy. Pitting corrosion initiated at grain boundaries and propagated into the austenite grains. This study identified the pitting initiation and propagation mechanisms in 2507 duplex stainless steel.

The crystallographic anisotropy of the electric current or conductance, adhesive force, elastic modulus, and deformation magnitude of alpha brass were investigated through property mapping using an atomic force microscope. Surface electron work functions of differently oriented grains in the brass were also analyzed using atomic force microscopy. The mapped surface properties are closely related to the electron work function; the work function reflects the surface activity, which is itself dependent on the surface energy. The anisotropy of the properties is closely correlated to the in situ measured surface electron work function. It is demonstrated that crystallographic planes with higher electron work functions exhibit lower current, smaller adhesive forces, larger elastic moduli and smaller deformation magnitudes. Efforts are made to understand the relationships by connecting the properties with surface energy and electron work function. The dependence of the properties on crystallographic orientation can be elucidated by considering the surface electron behavior using electron work function as a novel probing parameter.

High-Cr cast irons (HCCIs) have demonstrated excellent performance during various industrial processes involving mining, oil sand slurry handling, and manufacturing. Attempts have been made to extend concentration ranges of carbon and chromium up to a higher level, e.g., 6%C and 35%Cr or higher. However, it is not clear how the Cr content influences properties of carbide, ( F e , C r ) 7 C 3 , and the ferrous matrix, and thus the performance of HCCIs during wear processes, e.g., slurry erosion for oil sand transport. In this study, we investigated how the chromium content, in the range of 5–35%Cr, affected the performance of HCCIs with 5%C during erosion tests in slurries at two pH levels and four velocities. In particular, local mechanical properties and electron work function which is a measure of electrochemical stability were analyzed for both carbides and the ferrous matrix in the HCCIs using a micro-indenter and a multi-mode atomic force microscope. First-principles calculation was conducted to understand mechanisms responsible for the observed phenomena.

Electron work function (EWF) is a promising parameter for guiding structural materials design. This parameter is intrinsically correlated to the metallic bond strength and stability, on which mechanical and electrochemical properties of metals depend. However, whether EWF can reflect overall properties of a multiphase alloy remains a question. This is a main barrier to the application of EWF in material design towards the development of an alternative or complementary metallurgical framework: “electronic metallurgy”. In this article, using high-Cr cast irons as a sample material, we demonstrate that the apparent EWF does carry the information on integrated electron behavior and overall properties of multiphase alloys. The charge relocation due to the formation of a dipole layer at interphase boundary plays a crucial role in this matter.

This paper demonstrates the hydrogen-induced phase transformation and the associated pitting nucleation sites of 2507 duplex stainless steel using scanning Kelvin probe force microscopy and magnetic force microscopy. The low potential sites in Volta potential images, which are considered as the pitting nucleation sites, are strongly dependent on the hydrogen-induced phase transformation. They firstly initiate on the magnetic martensite laths in the austenite phase or at the ferrite/austenite boundaries, and then appear near the needle-shaped microtwins in the ferrite phase, because of the difference in physicochemical properties of hydrogen-induced phase transformation microstructures.

A poor interface or defected interfacial segment may trigger interfacial cracking, loss of physical and mechanical functions, and eventual failure of entire material system. Here we show a novel method to diagnose local interphase boundary based on interfacial electron work function (EWF) and its gradient across the interface, which can be analyzed using a nano-Kelvin probe with atomic force microscope. It is demonstrated that a strong interface has its electron work function gradually changed across the interface, while a weaker one shows a steeper change in EWF across the interface. Both experimental and theoretical analyses show that the interfacial work function gradient is a measure of the interaction between two sides of the interface. The effectiveness of this method is demonstrated by analyzing sample metal-metal and metal-ceramic interfaces.

Local electron work function, adhesive force, modulus and deformation of ferrite and austenite phases in a duplex stainless steel were analyzed by scanning force microscopy. It is demonstrated that the austenite has a higher electron work function than the ferrite, corresponding to higher modulus, smaller deformation and larger adhesive force. Relevant first-principles calculations were conducted to elucidate the mechanism behind. It is demonstrated that the difference in the properties between austenite and ferrite is intrinsically related to their electron work functions.

Titanium dioxide (TiO2) nanotubes are promising for a wide variety of potential applications in energy, biomedical and environmental sectors. However, their low mechanical strength and wide band gap limit their widespread technological use. This article reports our recent efforts to increase the mechanical strength of TiO2 nanotubes with lowered band gap by immobilizing a peptide of D-amino K122-4 (D) onto the nanotubes. Topographies and chemical compositions of the peptide-coated and uncoated TiO2 nanotubular arrays were characterized by scanning electron microscopy and X-ray photoelectron spectroscopy (XPS). Properties of the peptide-coated and uncoated TiO2 nanotubular arrays, including hardness, elastic modulus, electron work function and photocurrent, were evaluated using micromechanical probe, Kelvin Probe and electrochemical system. Effect of the peptide on surface conductivity was also investigated through current mapping and I–V curve analysis with conductive atomic force microscopy. It is demonstrated that the peptide coating simultaneously enhances the mechanical strength, photocatalytic and electrical properties of TiO2 nanotubes.