Henara Lillian Costa

On the abrasive wear of zirconias

Abstract Zirconia ceramics with different dopants, used to retain the tetragonal phase metastably, were evaluated to determine the effect of the difference in degree of transformability on the abrasive wear behavior. The abrasive wear tests, carried out on a multiple abrasive wear tester, showed that for two-body and three-body configurations the wear rate increases for higher normal loads and abrasive grain sizes. The specimen with low degree of transformability presented the worst behavior in every configuration owing to its low fracture toughness. For the three-body configuration, the specimen with intermediate degree of transformability presented the best behavior; this was associated with its higher hardness and flexural strength. For two-body abrasive tests, the change in wear severity conditions led to an inversion of wear behavior of the specimens with a high degree of transformability. The results obtained were associated with the microstructure generated, the physical and mechanical properties and the tetragonal to monoclinic transformation rates, since the stress induced transformation could be inhibited owing to the temperature developed in the contact between the zirconia sample and the abrasive material. Finally, the comparison between zirconia and white cast iron wear behavior under two different conditions revealed that the performance of zirconias was favorable only for low severity wear conditions and for intermediate and high degrees of transformability.

Influence of Layer Thickness on the Properties of Multifunctional Tribological Coatings

Multifunctional coatings, widely used in tribological applications, have their properties strongly influenced by the interaction of the system coating/substrate. The use of multi-layered coatings has been pointed out as a solution for the problem of high internal stresses that can be generated in coated systems, in particular in the case of soft substrates. In multilayered coatings, a decrease in the stress gradient between substrate and coating improves adhesion. Moreover, the thickness of the coating has shown a strong influence on the tribological behavior of the coated system. This paper, through widely used and efficient techniques, seeks to assess the influence of the thickness of different layers (DLC and CrN) on the response of a multifunctional coating. Si-rich DLC and CrN multi-layered coatings with different thicknesses were deposited on a steel substrate (AISI 1020) by Plasma Enhanced Magnetron Sputtering (PECVD). Scanning electron microscopy (SEM) and Raman spectroscopy (RS) were used in order to characterize the chemical composition and microstructure of the coatings. Instrumented indentation and scratch test techniques were used to measure hardness, elastic modulus, and adhesion of each layer. Critical loads were determined by visual analysis, using SEM in conjunction with the curves obtained in the scratch tests. The evaluation of the effect of the thicknesses of the layers allowed an optimized design of the multifunctional coated systems with improved durability.Copyright

Influence of layer thickness on sliding wear of multifunctional tribological coatings

Purpose – This paper aims to analyse the influence of the thickness of different layers [diamond-like-carbon (DLC) and chromium nitride (CrN)] on the sliding wear behaviour of a multifunctional coating on AISI 1020 substrates. When small and cheap components need to be manufactured in large scale, they are often produced using soft metals, such as unhardened low carbon steels and pure iron. Design/methodology/approach – Two families, one with thicker films and the other with thinner films, were deposited onto a soft carbon steel substrate by plasma-enhanced chemical vapour deposition (PECVD). Reciprocating linear tests with incremental loading assessed the durability of the coatings. In addition, friction coefficient and wear rates of both specimens and counterbodies were measured at a constant load. Findings – Thinner layers presented lower sliding wear rates (four-five times lower) for both specimens and counterbodies, less spalling and protective tribolayers on the wear tracks. Originality/value – Alth...

Life of cutlery cutting tools: effects of surface finish

Purpose The progressive wear of cutting tools used in industrial cutlery production results in excessive burr formation and reduces tool service life. This paper aims to investigate the effects of the sheet surface finish on tool wear and service life during blanking. Design/methodology/approach Two alternative surface finish techniques were proposed and initially implemented under laboratorial conditions and compared with conventional acid pickling. Those surface finish techniques were then implemented on an industrial scale to improve the service life of cutting tools. Industrial blanking tests characterized the effect of sheet surface finish on tool life. Findings In the first technique, called skin pass, an additional mechanical pass under controlled conditions reduced the height of the surface peaks and resulted in partial embedding of the carbides into the surface. The second technique, called electrochemical pickling, removed solely the surface carbides, leaving behind a smoother surface without carbides. Real industrial blanking tests identified that the use of skin pass reduced burr formation and increased tool life by around 300 per cent when compared with conventional acid pickling. With electrochemical pickling, burr formation was further reduced and tool life increased further by 300 per cent when compared with skin pass. Research limitations/implications First, this work proposes an alternative surface finishing technique (electrochemical pickling) to be used after annealing of stainless steel. Second, the work clearly shows the presence of protruding surface carbides when conventional surface finishing techniques are used, which do not exist after acid pickling. Practical implications When electrochemical pickling is implemented on an industrial scale, the life of blanking tools is substantially improved. Originality/value Although the sheet surface finish is widely recognized to affect metalforming processes, the literature lacks studies on the effect of sheet surface finish on tool wear during blanking. First, this work proposes an alternative surface finishing technique (electrochemical pickling) to be used after annealing of stainless steel. Second, the work clearly shows the presence of protruding surface carbides when conventional surface finishing techniques are used, which do not exist after acid pickling. Third, when electrochemical pickling is implemented on an industrial scale, the life of blanking tools is substantially improved.