Abstract
In this paper, we will develop a strategy for controlling the self-organized critical process using the example of extreme tribological conditions caused by intensive build-up edge (BUE) formation that take place during machining of hard-to-cut austentic superduplex stainless steel SDSS UNS32750. From a tribological viewpoint, machining of this material involves intensive seizure and build-up edge formation at the tool/chip interface, which can result in catastrophic tool failure. Built-up edge is considered to be a very damaging process in the system. The periodical breakage of the build-ups may eventually result in tool tip breakage and, thereby, lead to a catastrophe (complete loss of workability) in the system. The dynamic process of build-up edge formation is similar to an avalanche. It is governed by stick-slip phenomenon during friction and associated with the self-organized critical process. Investigation of wear patterns on the frictional surfaces of cutting tools using Scanning Electron Microscope (SEM), combined with chip undersurface characterization and frictional (cutting) force analyses, confirms this hypothesis. The control of self-organized criticality is accomplished through application of a nano-multilayer TiAl60CrSiYN/TiAlCrN thin film Physical Vapor Deposition (PVD) coating containing elevated aluminum content on a cemented carbide tool. The suggested coating enhanced the formation of protective nano-scale tribo-films on the friction surface under operation. Moreover, machining process optimization contributed to further enhancement of this beneficial process, as evidenced by X-ray Photoelectron Spectroscopy (XPS) studies of tribo-films. This resulted in a reduction of the scale of the build ups leading to overall wear performance improvement. A new thermodynamic analysis is proposed concerning entropy production during friction in machining with buildup edge formation. This model is able to predict various phenomena and shows a good agreement with experimental results. In the presented research we demonstrated a novel experimental approach for controlling self-organized criticality using an example of the machining with buildup edge formation, which is similar to avalanches. This was done through enhanced adaptive performance of the surface engineered tribo-system, in the aim of reducing the scale and frequency of the avalanches.
Highlights
IntroductionMachining of290 hard-to-cut materials with intensive build-up edge formation is a very 2complex
Machining of290 hard-to-cut materials with intensive build-up edge formation is a very 2complexEntropy 2016, 18, of 16 tribological phenomenon
A control strategy of self-organized criticality is presented, using an example of extreme tribological conditions which occur under machining of hard to cut austenitic superduplex stainless steel SDSS UNS32750 associated with intensive build-up edge formation
Summary
Machining of290 hard-to-cut materials with intensive build-up edge formation is a very 2complex. It is known that stick-slip phenomenon is associated with self-organized critical processes [6,7] and has a direct relation to metal cutting [8] To understand this idea in greater detail, we have to consider wear performance of the uncoated cemented carbide cutting tool during machining of one of the most difficult to machine SDSS stainless steel (see Figure 1). This is confirmed in more detail by progressive SEM studies of the worn surface. The goal of this paper is to demonstrate how control of self-organized critical performance could be made through the application of PVD thin film coatings combined with optimization of machining conditions to achieve better adaptive response of the surface engineered nano-material. A combination of thermodynamic modeling and detailed investigation of the coated cutting tool’s wear performance was performed to achieve this goal
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