Mechanical property and structure relationships in hard coatings for cutting tools

Abstract

The trends in the use of hard protective coatings in WC–Co metal cutting inserts are reviewed in light of recent evaluations of mechanical and structure-sensitive properties such as elevated temperature microhardness, microfracture toughness, and internal stress. A better understanding of the role of hard coatings has evolved due to development of reliable methods to measure mechanical properties of thin coatings (of the order of 5 μ thick). There are intrinsic differences in the microstructure and residual stress state of chemical and physical vapor deposited (CVD and PVD) hard coatings. High compressive residual stress and fine grain size in PVD coatings contribute to increased microhardness and microfracture toughness. However, these benefits are reduced at high temperatures. Certain well-known structure/property concepts in bulk materials are shown to be applicable to hard coatings, which aid in interpretations of metal cutting wear behavior.

Cloud-enabled prognosis for manufacturing

“…Lau et al [108] proposed a relationship between tool geometry, i.e., rake angle and clearance angle, and the Taylor Constant. Also, experiments by Quinto [166] and Oxley [154] indicated that the cutting temperature dominates the tool life. It is straightforward and convenient to predict tool life using Taylor's basic equation and its extended version.…”

Experimental support for a model-based prediction of tool wear

“…The hardness data of the coatings and cementite are collected from the literature [10,17,18]. The temperature-dependent hardness for three coatings (TiN, TiCN and alumina) and the abrasive (cementite) are also collected and presented in Table 2.…”

Multiphase Nano-Composite Coatings for Achieving Energy Optimization

“…By varying the t/D ratio within the coating, the number of interfaces will be altered and hence mechanical properties like crack propagation and the hardness. All these architectures are applicable to different machining conditions [7][8][9]. At UES a TiAlN based bi-layered coating has been developed to enhance the cutting tool life in titanium machining application [10].…”