Abstract
The relationship between the wear process and the adaptive response of the coated cutting tool to external stimuli is demonstrated in this review paper. The goal of the featured case studies is to achieve control over the behavior of the tool/workpiece tribo-system, using an example of severe tribological conditions present under machining with intensive built-up edge (BUE) formation. The built-ups developed during the machining process are dynamic structures with a dual role. On one hand they exhibit protective functions but, on the other hand, the process of built-up edge formation is similar to an avalanche. Periodical growth and breakage of BUE eventually leads to tooltip failure and catastrophe of the entire tribo-system. The process of BUE formation is governed by the stick–slip phenomenon occurring at the chip/tool interface which is associated with the self-organized critical process (SOC). This process could be potentially brought under control through the engineered adaptive response of the tribo-system, with the goal of reducing the scale and frequency of the occurring avalanches (built-ups). A number of multiscale frictional processes could be used to achieve this task. Such processes are associated with the strongly non-equilibrium process of self-organization during friction (nano-scale tribo-films formation) as well as physical–chemical and mechanical processes that develop on a microscopic scale inside the coating layer and the carbide substrate. Various strategies for achieving control over wear behavior are presented in this paper using specific machining case studies of several hard-to-cut materials such as stainless steels, titanium alloy (TiAl6V4), compacted graphitic iron (CGI), each of which typically undergoes strong built-up edge formation. Various categories of hard coatings deposited by different physical vapor deposition (PVD) and chemical vapor deposition (CVD) methods are applied on cutting tools and the results of their tribological and wear performance studies are presented. Future research trends are outlined as well.
Highlights
Adaptive response to external stimuli is mostly observed and studied in natural systems [1]
Machining of various hard to machine materials usually occurs alongside intense built-up edge (BUE) formation
Metal cutting with BUE formation is associated with the stick–slip phenomenon at the tool/chip interface and constitutes a self-organized critical (SOC) process
Summary
Adaptive response to external stimuli is mostly observed and studied in natural systems [1]. Due to the enhanced ability of the CrN coating to form thermal barrier Cr2O3 tribo-films under operation, the intensity of crater wear is strongly diminished and tool life is increased (Figure 9) This substantially improves the tribological performance, resulting in the formation of more curled chips in the tool with a CrN coating (Figure 12a). It was demonstrated that superior wear performance and longer tool life can be attributed to a surface engineered carbide material with an optimal combination of the coating/substrate properties as a whole [8] Such a structure has the potential to present adaptive response on two scales: nano- and micro. Under severe frictional conditions associated with self-organized critical performance (i.e., strong built-up edge formation), the mechanical properties which determine the overall resistance of the coated carbide tool to severe external impact have a direct effect on the length of tool life (Table 1) [8]. The second type is high entropy alloy coatings [63], whose combination of protective/lubrication characteristics with beneficial micro-mechanical properties is responsible for their superior wear performance during machining with BUE formation
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