Joe McGeough

Surface Modification for Orthopaedic Titanium Alloy by Wide-Area Electron Beam

Abstract Wide-area electron beam (WAEB) irradiation was proposed as a new surface-finishing process for orthopaedic titanium alloy products. The surface roughness could be reduced from Rz = 10 μm to Rz = 0.7 μm all over the wide circular surface within a diameter of 60 mm in just a few minutes under optimum electron beam conditions. In this paper, the surface structure and the surface characteristics of WAEB-irradiated surface are discussed. The crystal grain size becomes small and the microstructure in the surface vicinity changes under WAEB irradiation. The corrosion resistance and the repellency can be improved simultaneously with the surface smoothing. Therefore, the WAEB irradiation method enables highly efficient surface smoothing and surface modification of orthopaedic titanium alloy.

Observation of craters formed by single pulse discharge by stacking cross sectional shapes: comparison of craters in liquid and air

This paper describes the results of comparing craters formed by single pulse discharge in liquid and in air at comparatively short pulse durations. Investigations were conducted by stacking cross-sectional shapes that the authors developed to clarify the volumes of resolidified metal and molten metal at the crater. In liquid, most of the resolidified layer remained at the bottom of the crater or in its vicinity. In air, the resolidified layer existed only at the downstream side of the high-speed gas flow. The removal ratio was found to be minus in liquid as most of the molten material remained on the crater. In air, more than 70 per cent of the molten material was removed at pulse durations above 2.5 µs. Thermal analysis results indicate that about 26 per cent of the discharge energy was used for melting the workpiece regardless of the pulse duration in liquid. In air, the discharge energy was found to decrease with longer pulse durations (i.e. from 20 to 10 per cent for 2.5 to 2.8 µs) due to the decrease in the heat flux in the workpiece as a result of the arc column being moved at high speed by the high-speed gas flow in the discharge gap.

Unconventional Cutting Technologies in Orthopaedic Surgery

In this paper, unconventional methods of cutting based on ultrasonics, laser, and water jet mechanisms that might be used in orthopaedic surgery are discussed. Their advantages include no or little contact with bone or tissue that is to be cut, the application of much less mechanical force compared to traditional techniques, and reduction in localised heat effect in the region undergoing surgical cutting. A critical analysis is performed to identify their limitations and merits.