Avaliação de insertos de metal duro revestidos com TiN pelo processo de gaiola catódica rotatória

Abstract

The demand for increased production in machining industry has led to research that promote the improvement of cutting tools performance. Thus, increasingly, they support the harsh conditions imposed by the machining process. However, as good as the adopted cutting parameters are set, the tool will wear out due to tribological applications of the system and will need replacement, interrupting production. This motivated the coating process of the cutting tools with films that confer them properties that, together with the material of its substrate, extends its useful life. Such coatings are generally performed in a static manner, resulting in the need for more than one deposition treatment to assure that an insert is completely coated.Plasma deposition techniques as ASPN (Active Screen Plasma Nitriding) solve these drawbacks and still allow optimal control of deposited phases. The Cathodic Cage Plasma Nitriding (CCPN) process, developed based on ASPN, promotes better adhesion of the coating to the substrate without the need for pre-cleaning and besides allow good control of the deposited phases for the production of ions and, consequently, the hollow cathode effect. But this technique still has the limitation of not allowing the tridimentional application of the coating on all surfaces of the sample, a practice commonly applied to carbide inserts for machining process. This research aims to propose a new way of coating deposition to these tools by the application of Rotary Cathodic Cage Plasma Nitriding (RCCPN). This novel deposition technique based on CCPN, enables all sample surfaces to receive the film during the same treatment, due to rotation of cage around the reactor axis, which promotes better uniformity to the deposited layer, besides it enables the treatment in batches. Therefore, cemented carbide inserts were coated by RCCPN process, keeping current, voltage, pressure, and proportion of gas fixed and varying only the treatment time. These were led to turning tests, as well as characterization by microhardness Vickers, XRD with oblique incidence angle and SEM/EDS to evaluate the mechanical properties of the coating and its adhesion to the substrate, as well as the uniformity of deposited film. As a result it was possible to obtain layers of more uniform deposited films than those observed in CCPN treatment, with hardness values 40% higher that the measures in uncoated inserts.