Caracterização mecânica e tribológica do aço ferramenta ABNT H13 com tratamento híbrido de modificação de superfície com usinagem por descarga elétrica e revestimento TiAlN PVD

Abstract

High productivity and performance requirements are continuously required by the tooling and mechanical components industry, among which, attain the level of hardness necessary for higher wear resistance and improve the load bearing capacity of steel substrates. To meet this demand, hybrid treatments consisted of conventional nitriding and coating are applied. However, adhesion at the coating-substrate interface can be affected by the presence of a compound layer or recast layer, which can destabilize. Another aspect, which is also able to influence the wear is the manufacturing parameters, which can contribute to answer the challenges of producing more uniform surface layers, in the emerging process of surface modification by die-sinking electrical discharge machining (SM-SEDM). Hence, the aim of this work was to produce hybrid systems: MS-EDM, with higher uniformity and hardened depth of the altered metal zone (AMZ), and subsequent deposition of the TiAlN coating by physical vapor deposition (PVD), on AISI H13 steel substrates, as received and hardened and tempered (H&T), for tribological evaluation. To enable the application of SM-EDM, the electric discharge machining (EDM) machine was previously adapted to work with aqueous dielectric fluids. The influence of pulse duration (TON) and pulse interval (TOFF) times on the layers produced by SM-EDM was investigated. In order to characterize the systems, chemical analysis, microhardness tests, adhesion of the coating by Rockwell C hardness test, X-ray diffraction (XRD), optical microscopy, scanning electron microscopy (SEM), X-ray fluorescence and profilometry were performed. Wear was assessed by microscale sliding and abrasion tests. There is an evident influence of the SM-EDM process parameters on the uniformity and thickness of the layers produced. The thickest AMZ obtained was 53.2 ± 5.5 μm when TON and TOFF of 500 μs were used, while the smallest thickness of 31.0 ± 4.6 μm was obtained with both TON and TOFF of 100 μs. The hybrid treatment of SM-EDM and TiAlN PVD provided improved sliding wear resistance by four to six times compared to systems nitrided by SM-EDM only, as well as provided lower abrasion wear. This performance gain can be explained by the increase in hardness (e.g., five times compared to AISI H13H&T steel), which in turn is influenced by the phase difference, Fe11N, TiN and TiO. The obtained results showed that the hybrid systems have the potential to improve the tribological properties of surfaces in contact conditions by sliding and also by abrasion.