The development of new coatings in the last years contributed to the improvements of machining industry. In general, it is known that the performance of drilling tools increases with the application of a proper coating, and it is worth remembering that the adhesion is an important condition for the success of any coating. This work presents a performance of cemented carbide cutting tool coated with diamond-like carbon (DLC). The deposition of the coating used in this study has been done using plasma enhanced chemical vapor deposition system. Suitable adhesion between film and the substrate did not occur in the initial deposition parameters tested. To enhance adhesion of the film, an intermediate silicon layer has been added. To evaluate this adhesion, VDI 3198 standard adhesion test was used. Spectra analyses collected using Raman backscattering spectroscopy have been used to characterize the composition and structural information of the film. The silicon layer was evaluated using atomic force microscopy. Drilling tests were performed using workpieces casting in aluminum alloy (SA-323) and roundness, radial deviation, deviation of diameter and roughness of geometries changes were measured as a function of the number of holes produced. The results showed that the DLC coating improves the tool performance, which subsequently improves the drilling quality.
Abstract. The presence of surface and subsurface residual stresses in steel components has a significant influence on fatigue resistance. In the present work, surface modification of AISI 9254 steel coil springs by heat treatment and multiple shot-peening procedures was investigated. Samples were characterized in the as-coiled, quenched, quenched and tempered, as well as submitted to single and double shot peening treatments. Depth resolved residual stress profiles were determined by X-ray diffraction combined with electrolytic dissolution of the steel. Fracture analysis was performed subsequent to fatigue tests by scanning electron microscopy. It was possible to show that double shot peening led to an increase in compressive stresses in the immediate sub-surface region, which improved fatigue resistance relative to the other tested conditions.
IntroductionIn automotive suspension systems, the springs perform the important tasks of supporting vehicle weight and absorbing kinetic energy transmitted from the track to the automobile in the form of elastic strain. Common materials for automotive suspensions are medium carbon steels containing Si, Cr and Mn additions, which offer elevated ductility, strength and hardenability [1]. Given the nature of their operation, automotive springs require excellent fatigue resistance, which is strongly influenced by material surface conditions since fatigue cracks usually nucleate and grow in surface or sub-surface regions. For this reason, various surface treatments are currently applied in the automotive industry with the objective of improving component life or reducing weight by increase in performance [2,3].An important surface modification technique widely employed for increasing fatigue properties of automotive components is shot peening. In shot peening the component is bombarded with high velocity shots of a hard material causing plastic deformation at the surface and sub-surface regions. As a consequence, the material undergoes strain-hardening, which increases yield strength at the surface, and the imposition of compressive residual stresses [4] which hinder crack nucleation and growth increasing fatigue resistance, as attested by numerous researchers [5][6][7][8][9][10][11]. Furthermore, shot peening is a highly flexible process that can be applied to components with various geometries and also increases resistance to stress corrosion cracking, fretting and erosion [12].Although the role of shot peening in enhancing fatigue resistance by the generation of compressive residual stresses is well understood, detailed investigations on the relation of process parameters and component performance are less common [13]. For instance, it is still matter of debate whether the major benefits to fatigue performance are due to the compressive residual stress field itself or rather to changes in the microstructure of shot peened components [14]. Recent works directed towards incorporating shot-peening effects in predictive fatigue life models have also highlighted the need for det...
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