Influence of milling on surface integrity of Ti6Al4V-study of the metallurgical characteristics: microstructure and microhardness

The quality of titanium alloy parts in the aeronautical field demands high reliability, which is largely related to surface integrity. Surface integrity is generally defined by three parameters: a geometric parameter, a mechanical parameter and a metallurgical parameter. The present article addresses the influence of milling on the metallurgical parameter for a surface milled in Ti6Al4V material, focusing in particular on the microstructure and microhardness. Observation of the machined surface from a macroscopic perspective highlight an orange peel phenomenon. This effect is the combined result of redeposition and crushing of the milled material. No plastically deformed layer or lengthening of the grains was observed under the milled surface. As far as microhardness is concerned, a slightly softened region was observed under the milled surface. A diffusion of vanadium from the beta phase to the alpha phase was also noted, but with no change in microstructure.