No abstract

A detailed transmission electron microscopy study of oxide and oxygencontaining phase formation during the sliding wear of metals, composites and coatings is provided. A wide range of different materials types are reported in order to compare and contrast their oxidational wear behaviour: a low carbon stainless steel, a H21 tool steel containing 7% TiC particles, a 17% Cr white iron, an Al-Si / 30%SiC composite, an Al-alloy (6092)-15% Ni3Al composite and finally a 3rd generation TiAlN/CrN 'superhard' multilayer coating. For the ferrous alloys, nanoscale oxides and oxygen-containing phases were formed that exhibited excellent adhesion to the substrate. In all cases, an increase in oxide coverage of the surface was associated with a decrease in Lancaster wear coefficient. The oxide at the surface of the 316L and H21+7%TiC was found to deform with the substrate, forming a mechanically mixed layer that enhanced surface wear resistance. Evidence of oxidational wear is presented for the wear of the A-Si-30%SiCcomposite, but this did not give a beneficial effect in wear, a result of the brittle nature of the oxide that resulted in detachment of fine (150nm) thick fragments. The worn surface of the Al-alloy (6092)-15%Ni3Al and TiAlN/CrN coating was characterized by reaction with the counterface and subsequent oxidation, the product of which enhanced wear resistance. The observations are related to the classical theory of oxidational wear.

No abstract

The theory of time-modulated circular arrays in respect of generating orbital angular momentum (OAM) beams at harmonic frequencies is analysed. Without using expensive phase shifters in phased arrays, beam steering for OAM beams is achieved using switches connected to array elements. The model of an eight-element time-controlled circular array is derived with the method of time-modulation beam steering techniques. Simulation results show that beam steering for OAM beams is realised, which indicates the effectiveness of the proposed method.

No abstract