Influence of a Discontinuous Process Strategy on Microstructure and Microhardness in Drilling Inconel 718

Abstract

Nickel-base alloys are proven materials in the fields of the aerospace and oil industry, which is due to their characteristic material properties of high temperature strength, high toughness and good oxidation resistance. These properties are beneficial to applications in technical components in general. However, they also represent challenges for machining. Especially while drilling Inconel 718, high temperatures occur in the chip-formation zone that implicate high thermal load in the material and thus, influence the surface integrity, for example, by causing white layers. Hence, the development of strategies to improve the ability to supply cutting edges with cooling lubricant is becoming increasingly important. In this context, an alternative process design, the discontinuous drilling, takes place, characterized by a periodic interruption of feed motion and thus, chip formation. A minor retraction movement from the contact zone enables the cooling lubricant to reach the cutting edges and to reduce their thermal load. In comparison to the conventional process of drilling Inconel 718, the effects of discontinuous drilling with varying numbers of interruptions on the resulting surface integrity and further parameters of drilling qualities are analyzed. Thereby, the prevention of process-related phase transformations due to thermal impact was discovered when a discontinuous drilling strategy was implemented.