Design of Comb Crack Resistant Milling Inserts: A Comparison of Stresses, Crack Propagation, and Deformation Behavior between Ti(C,N)/α-Al2O3 and Zr(C,N)/α-Al2O3 CVD Coatings

Maiara Moreno,Flavio Soldera,Idriss El Azhari,Haroldo Pinto,José García,Daniel Apel,Wei Wan,Frank Mücklich,Matthias Meixner

doi:10.3390/cryst11050493

Abstract

Investigations on comb crack resistance of milling inserts coated with chemical vapor deposition (CVD) Ti(C,N)/α-Al2O3 and Zr(C,N)/α-Al2O3 showed a distinct wear evolution in both systems. Wear studies revealed that the appearance of comb cracks is connected to the initial CVD cooling crack network. Micropillar compression tests indicated a brittle intergranular fracture mechanism for the Ti(C,N) layer and a transgranular fracture accompanied with signs of plastic deformation for the Zr(C,N) coating. Additionally, for the Zr(C,N) based system, a compressive stress condition in the temperature range of interest (200–600 °C) was determined by in-situ synchrotron X-ray diffraction. The set of residual compressive stresses together with the ability of the Zr(C,N) layer to deform plastically are key features that explain the enhanced resistance to comb crack wear of the Zr(C,N) based system in milling of cast iron.

Highlights

Cemented carbides coated with wear resistant layers deposited either by physical or chemical vapor deposition (PVD or CVD) are predominant cost-effective tools for machining of automotive parts and aerospace components [1]
The results of this work show that the wear development and comb crack resistance of milling inserts cannot be attributed to a main factor, but to the linking between the residual stresses behavior, deformation behavior and physical or chemical characteristic of the coating/carbide systems
The comb crack resistance differs considerably if the Ti(C,N) intermediate layer is replaced by a Zr(C,N) layer in the carbonitride/α-Al2O3 CVD system

Summary

Introduction

Cemented carbides coated with wear resistant layers deposited either by physical or chemical vapor deposition (PVD or CVD) are predominant cost-effective tools for machining of automotive parts and aerospace components [1] Machining involves processes such as turning or milling, where interrupted cutting condition causes faster degradation of the cutting edge and reduced tool life. A main drawback of CVD coating systems is the presence of a network of microcracks formed during the cooling step of the CVD process after deposition at high temperature [5] This network of cracks stems from the difference in coefficient of thermal expansion (CTE) between the cemented carbide and the coating layers, which generates tensile stresses above the yield strength of the films, leading to crack formation and relaxation of stresses [6].

Methods

Results

Conclusion