The objective of this Grant Opportunity for Academic Liaison with Industry (GOALI) collaborative research project is to investigate the material substrate-processing interfacial conditions in chemical vapor deposition (CVD)-grown diamond films on cobalt-cemented tungsten-carbide (WC-Co) tools. Coating delamination is the major life-limiting factor to diamond-coated WC-Co cutting tools. Interface engineering, by means of surface treatments and interlayer, and optimum nanocrystalline diamond (NCD) deposition are the key solutions to achieve high-quality diamond coatings for dry machining. This collaborative research will focus on the fundamental mechanisms of interface fabrications, properties and functions to enhance the substrate/coating performance over the life of the cutting tools, and will form joint tasks of modeling, characterization, and optimization of surface conditioning, interlayer interfacial preparations, and subsequent deposition processes. Validation of enhancements to interfacial performance will be demonstrated through machining analysis and wear characterization. In addition, environmental process monitoring, in both coating and dry machining with diamond coated tools, will be conducted with data collected for life-cycle inventory and environmental impact analysis.
If successful, this research will lead to breakthrough of diamond coated tools whose performance is comparable to or better than costly polycrystalline diamond tools. Engineering of interlayer and NCD coating optimization, with material characterizations and performance analysis, will further mature the diamond coated tooling technology for industrial applications. This research will also advance knowledge of interface science, critical to coating system functions, especially in harsh tribological services. The findings gained on interface characteristics and behavior modeling will also offer knowledge transformable to other coating system studies. The proposed program will also synergize universities-industry partnership by providing opportunities for faculty and students to conduct research and gain experiences with production processes in an industrial setting. The collaborations will offer opportunity to students working with industrial colleagues and use of their state-of-the-art equipment facilities.
Tooling costs such as cutting tools for machining operations in the manufacture of numerous parts, e.g., automotive engine blocks, continues to be a large percentage of the overall production costs. Hence, there is an intense interest in developing high performance, and yet cost-effective, cutting tools (i.e., lower wear rate, longer service life) for manufacturing industries. There have been different approaches to improve cutting tools; among them, one is to apply the chemical vapor deposition (CVD) technology to grow a thin diamond film, typically 5 to 30 microns thick, onto a common low-cost carbide tool. Though novel, it is challenging to deposit high-purity well-adherent diamond coatings on carbide tools due to the cobalt binder. In this project, The University of Alabama (UA) collaborated with General Motors R&D and University of South Florida to research the coating-substrate interfacial conditions, one of the most critical issues in diamond coating, in order to improve the machining performance of diamond-coated carbide tools. The major outcomes achieved from this project, by UA, are summarized as follows. (1) An advanced finite element model has been developed and applied to evaluate diamond coating adhesion when subject to scratch testing. The results indicated that (a) a thicker diamond coating will increase resistance of both coating cracking and interface delaminations, and (b) decreasing Young’s modulus of diamond coatings will increase coating cracking resistance, but will decrease coating delamination resistance. (2) Scratch testing was performed on different diamond-coated tools with various interface treatments. For the two types of interlayer materials tested, diamond coatings with the Chromium-interlayer show better adhesion compared to the Titanium-interlayer coatings. (3) Finite element simulations of cutting with a diamond-coated tool were developed, incorporating interface characteristics, to analyze interface mechanical behaviors during cutting. The major results predict that the depth of cut is an important process parameter that may lead to coating delaminations during cutting. (4) The research from this project has been disseminated in several conferences and journal publications. In addition, a seminar of diamond-coated tools, based on this research, was given to the Society of Women Engineering (University of Alabama Chapter), in an attempt of broader disseminations of manufacturing research and its impact to the society. Moreover, the research approaches and results have also been shared with General Motors R&D and University of South Florida.
