Improvement of the Interfacial Fatigue Strength and Milling Behavior of Diamond Coated Tools via Appropriate Annealing

Abstract

This article deals with the potential to reduce the amount of the residual stresses in the diamond films on cemented carbide inserts for improving their effective interfacial fatigue strength and thus their wear resistance. In this context, nano-crystalline diamond coatings (NCD) were deposited on cemented carbide inserts. A portion of these coated tools were annealed in vacuum for decreasing the amount of residual stresses in the film structure. The annealing temperature was appropriately selected for keeping the substrate strength properties invariable after the coating annealing. Inclined impact tests at ambient temperature on the untreated and heat-treated diamond coated tools were conducted for evaluating their effective interfacial fatigue strength. Depending upon the impact load, after a certain number of impacts, damages in the film-substrate interface develop, resulting in coating detachment and lifting. Via appropriate FEM (Finite Element Method)-evaluation of the impact imprints, the residual stresses in the diamond film structure were determined. Milling experiments were conducted for evaluating the cutting performance of the coated tools using aluminum foam as workpiece material. A correlation between the interfacial fatigue strength of diamond coatings and their residual stresses affected by annealings contributed to the explanation of the attained cutting results.

Optimization of Crystalline Diamond Coating Structure Architecture for Improving Adhesion and Cutting Performance in Milling with Cemented Carbide Inserts

“…Crystalline diamond coatings (CDCs) on cemented carbide inserts are widely used in various cutting applications, especially for aluminum alloys, carbon-fiber-reinforced composite materials, etc. [1][2][3][4][5]. Such coatings are characterized by high compressive residual stresses in their structures, significantly affecting the interfacial fatigue strength [6,7].…”

Effect of Coating Thickness on Abrasion and Cutting Performance of NCD-Coated Ball Endmills on Graphite Machining

“…Hence, NCD coated tools are, relatively, more advantageous in precision cutting [ 3 , 4 ]. Thus, many studies have attempted to improve the lifespan of NCD-coated tools [ 4 , 5 , 6 , 7 , 8 , 9 ]. The coating thickness changes the cutting-edge radius and coating surface, which affect the geometric precision of the tool.…”

“…According to Qin [ 5 ], there is a lack of research that analyzes the impact of the coating thickness on the lifespan and cutting performance of the tools. Moreover, recent studies are primarily focused on developing new coating materials and improving the process [ 4 , 7 , 8 , 9 ].…”

“…Additionally, it was suggested that the lifespan and surface quality improved by maintaining the ductile-machining mode of tools, but premature delamination limited its application in micro-milling of ceramics. Skordaris [ 7 ], Hodroj [ 8 ], and Lu [ 9 ] reported on effects used to improve the interfacial fatigue strength and wear resistance of NCD coatings, such as the use of films annealed in a vacuum [ 7 ], tantalum or zirconium nitride-molybdenum bilayers used as interlayers [ 8 ], or the change of the basic properties of NCD coatings by doping boron at various concentrations [ 9 ]. Similar to this this, several researchers experimentally assessed the mechanical properties of the diamond using diamond-coated cutting tools or coated specimens, but an in-depth analysis of the impact of coating thickness has yet to be performed.…”

Special Issue: Current Research in Thin Film Deposition: Applications, Theory, Processing, and Characterisation

“…Finally, and staying on the topic of tribological coatings, Skordaris et al [34] describe the reduction in residual stresses in 5 µm-thick nanocrystalline diamond coatings deposited on cemented carbide insert tools, via an optimised annealing process. This results in an impressive enhancement of fatigue strength and milling performance of such tools, increasing the components' service life by up to four times that of a non-annealed coated tool.…”