Mechanical integrity of coated cutting tools used for machining metallic alloys
Tutor / Supervisor
Student
Segorbe Serra, Paula
Document type
Master thesis
Date
2024
rights
Restricted access - confidentiality agreement
Publisher
Universitat Politècnica de Catalunya
UPCommons
Abstract
There is an ongoing effort to improve the service life of cutting tools for machining aerospace materials, such as titanium and aluminum alloys. Although the design and coated materials for cutting tools have been widely studied and optimized along the last years, new requirements need to be accomplished since the additive manufacturing (commonly referred to as 3D printing) and subsequent post-printing processes has been introduced into the aerospace sector. In this regard, the surface finishing operation of complex shape and thin-walled 3D components could significantly reduce the life of cutting tools, due to the presence of complex loading conditions produced by unexpected vibrations. A coating composed by an interlayer of ¿¿(¿, ¿) followed by a top layer of ¿¿2¿3 is one the most used CVD bi-layer system specifically designed for cutting operations of titanium alloys. Nowadays, manufacturers of cutting tools explore the alternative of applying mechanical post-treatment processes after coating deposition, in an effort to reduce the premature failure of these tools. Take into account this scenario, the aim of this study is to document the micromechanisms of damage resulting from contact loading applied on coated system subjected to blasting and/or shot peening post-treatment processes. Coated system consisted in a bi-layer ¿¿ (¿, ¿)/ ¿¿2¿3 deposited on a cemented carbide with 7 wt% of Co binder. Two different bi-layer thickness were evaluated. Spherical indentation under monotonic loading condition was used to evaluate the contact resistance to crack appearance on coated samples surface. Advanced microscopy techniques were used to analyze the micro-cracking patterns achieved at the edge of residual imprints. Results shown that post-treatments could induced changes in surface roughness, and even more in the crack appearance under contact loading conditions. Thicker coatings provide higher resistance to crack nucleation, but post-processes such as SP and WB are necessary to optimize tool performance. Moreover, the combination of both micro-mechanical treatments presented the best overall resistance to crack initiation and propagation, despite some surface defects.
