The Surface Quality of Hipped Gamma Titanium Aluminide Bar after Turning
This paper reports a study of the surface morphology and integrity of HIPped Ti-48A1-2Mn-2Nb bars after turning. The machining experiments were carried out using statistically designed tests to investigate the effect of a range of cutting conditions and different cemented carbide tool grades on surface finish. Cracks and cavities were found in the machined surfaces after turning under roughing and semi-finishing conditions which is a matter of concern considering the low ductility of this material and the likely significance of defects on brittle failure. It was found that the cracks were associated with microstructural features such as γ lamellae or γ grain boundaries and originated from the deformed layer observed at the surface under all machining conditions. The depth of cracks was found to vary with depth-of-cut and feed rate and their cause is probably dependent on surface temperatures and stresses generated in machining. Microhardness measurements indicated that there was a hardened layer at the surface.
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