Tool wear performance and surface integrity studies for milling DD5 Ni-based single crystal superalloy

Abstract

Based on the results of slot milling experiments on the DD5 Ni-based single crystal superalloy (001) crystal plane along the [110] crystal direction, in this paper, efforts were devoted to investigate the tool wear process, wear mechanism and failure modes of the physical vapor deposition (PVD)-AlTiN and TiAlN coated tools under dry milling and water-based minimum quantity lubrication (MQL) conditions. The scanning electron microscope (SEM) morphological observation and energy dispersive X-ray spectroscopy (EDX) elements analysis methods were adopted. Moreover, under the water-based MQL condition, the surface integrity such as surface roughness, dimensional and shape accuracy, microhardness and microstructure alteration were researched. The results demonstrated that the tool edge severe adhesion with the work material, induced by the high Al content in the PVD-AlTiN coating caused the catastrophic tool tip fracture. In contrast, the PVD-TiAlN tool displayed a steady and uniform minor flank wear, even though the material peeling and slight chipping also occurred in the final stage. In addition, due to the high effective cooling and lubricating actions of the water-based MQL method, the PVD-TiAlN coated tool demonstrated intact tip geometry; consequently it could be repaired and reused even if the failure criterion was attained. Moreover, as the accumulative milling length and the tool wear increased, all indicators of the surface integrity forehand were deteriorated.