Removal of heat-formed coating from a titanium alloy using high pressure waterjet: Influence of machining parameters on surface texture and residual stress

© 2015 Elsevier B.V. All rights reserved. Titanium alloys are widely used in the aerospace and medical industries owing to their high strength to weight ratio and outstanding corrosion resistance. A problem for titanium or titanium alloys is the existence of a hard, brittle and oxygen-enriched layer on the surface (so called alpha case). This is usually formed during hot forming processes or after long-term service at elevated temperatures in an open-air environment. With the development of waterjet systems, high pressure waterjet has shown its capability for the removal of such hard and difficult-to-machine coatings. Waterjet machining is usually associated with a surface roughening, which is unwanted for most of aerospace applications, but is beneficial for medical application where fixation is required (e.g. metal orthopedic implants). A potential benefit of waterjet material removal is that the process may introduce compressive residual stress to the machined surface and subsurface layers. In this study, Ti-6Al-4V with an alpha case layer was subjected to plain waterjet impact over a range of parametric conditions, to fully remove the alpha case layer. The resulting surfaces were then analyzed to demonstrate the influence of process parameters on both surface roughness and residual stress measured using X-ray diffraction (XRD)

An assessment of the wear characteristics of microcutting arrays produced from polycrystalline diamond and cubic boron nitride composites

The current methods for manufacturing super-abrasive elements result in a stochastic geometry of abrasives with random three-dimensional abrasive locations. This paper focuses on the evaluation of wear progression/failure characteristics of micro-abrasive arrays made of ultrahard composites (polycrystalline diamond—PCD; polycrystalline cubic boron nitride—PCBN) in cutting/wear tests against silicon dioxide workpiece. Pulsed laser ablation (Nd:YAG laser) has been used to manufacture repeatable patterns of micro-abrasive edges onto microstructurally different PCD/PCBN composites. Opposing to these highly engineered micro-abrasive arrays, conventional electroplated abrasive pads containing diamond and CBN abrasives, respectively, have been chosen as benchmarks and tested under the same conditions. Contact profiling, optical microscopy, and environmental scanning electron microscopy have been employed for the characterization of the abrasive arrays and electroplated tools before/during/after the wear/cutting tests. For the PCD abrasive micro-arrays, the type of grain and binder percentage proved to affect the wear performances due to the different extents of compressive stresses occurring at the grain boundaries. In this respect, the micro-arrays made of PCD with mixed diamond grain sizes have shown slower wear progression when compared to the electroplated diamond pads confirming the combination of the high wear resistance typical of the fine grain and the good shock resistance typical of the coarse grain structures. The micro-arrays made of fine grained diamond abrasives have produced lower contact pressures with the workpiece shaft, confirming a possible application in polishing or grinding. As for the PCBN abrasive micro-arrays, the increase of metallic binder and the presence of metalloids in the medium content-CBN specimens have shown to produce higher contact pressure with the workpiece when compared to the electroplated specimen, causing fracturing as the main wear mechanism; while the PCBN micro-array with purely a metallic binder phase has shown slower wear and lower contact pressure in comparison to the electroplated CBN specimen. Among all of the tested arrays, the mixed grained PCD and the purely metallic binder phase PCBN micro-arrays have shown slower wear when benchmarked to the electroplated pads, giving a possible application of their use in the cutting tool industry

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