MICROSTRUCTURAL ANALYSIS AND MACHINABILITY IMPROVEMENT OF UDIMET 720 VIA CRYOGENIC MILLING

The objective of this research is to improve the milling process performance for Udimet 720. In order to do so, both material microstructure and tool failure conditions are studied with different milling processes, such as cryogenic-assisted machining and conventional milling. To gain an understanding of the mechanism behind the smearing and plucking phenomena, which are used as a measure of quality and also a limiting factor to machining speed, the post machined microstructure has been investigated. The dynamic forces of machining, chip morphology, microstructure, deformation layer, and maximum cutting velocity are considered for the optimization of the milling process of Udimet 720. The tool life during milling of Udimet 720 is also determined under two different machining arrangements with an oil-base coolant and cryogenic cooling. In cryogenic milling, it has been discovered through these experiments, that there exists a concentration of gamma phase in the material. The experimental cryogenic milling process has yielded positive results by increasing the maximum cutting velocity from 10m/min to 120m/min. This is over an 1100% increase in the machinability of Udimet 720. Microstructural analysis confirmed these findings that the smearing and plucking mechanisms are retarded by the slowing or elimination of the diffusion process.