Resumo: No Brasil mais de 60% da energia elétrica vem da geração hidrelétrica. Neste tipo de geração, alguns componentes são frequentemente expostos a fenômenos de desgaste, sendo um dos principais a erosão por partículas sólidas. A utilização de revestimentos é uma interessante alternativa para a redução de desgaste, sendo que a aspersão térmica se destaca como uma solução de baixo impacto ao material base do componente. Neste trabalho, uma liga comercial para aplicações anti-desgaste foi aplicada por aspersão térmica a arco elétrico (ASP) em substrato de aço carbono e submetida a tratamentos superficiais de lixamento, polimento e jateamento com esferas de aço (shot peening). Os revestimentos com e sem tratamentos superficiais foram avaliados quanto à morfologia e dureza e então submetidos a ensaios de erosão por jato de lama (slurry jet). Foi verificado que o revestimento tende a apresentar os mesmos mecanismos de erosão de materiais brutos. Além disso, observou-se que o lixamento e polimento reduzem a erosão nos primeiros minutos de ensaio, porém o ganho não compensa a massa perdida na execução dos próprios tratamentos. O shot peening reduziu a resistência à erosão do revestimento.
Abstract: Currently in Brazil, more than 60% of electric energy comes from hydro generation. In hydroelectric generation, some mechanical components are often exposed to wear phenomena, and solid particle erosion is one of the most usual. The use of coatings is an interesting alternative to reduce the wear and thermal spray technology appears as a relevant solution with minimum impact to the component substrate. In this work, a commercial wear resistant alloy was applied on carbon steel substrate by Arc Spray Process (ASP) and subjected to surface finishing of single-step sanding, full polishing and shot peening. Coatings with and without surface treatments were evaluated for morphology and hardness and then subjected to slurry jet erosion tests. The results indicated that the coating tends to present the same erosion mechanisms expected for bulk materials. The surface sanding and polishing reduced the initial wear rates however, it did not compensate the mass loss caused by the finishing processes themselves. The shot peening reduced the erosion resistance of the coating.
AbstractHVOF thermal spray process produces coatings with low porosity and low oxide content, as well as high substrate adhesion. Small variations on the parameters of the HVOF process can generate coatings with different characteristics and properties, which also is chemical composition depended of the alloy. FeMnCrSi alloy is a cavitation resistant class of material with a great potential for HVOF deposition use. The main goal of this article is to study the influence of some HVOF parameters deposition, as standoff distance, powder feed rate and carrier gas pressure on three different alloys. FeMnCrSi experimental alloys with some variations in nickel and boron content were studied. Taguchi experimental design with L9 orthogonal array was used in this work. Porosity, oxide content, tensile adhesion strength and microhardness of the coatings were evaluated. The results indicated that all factors have significant influence on these properties. Chemical composition of the alloys was the most important factor, followed by the carrier gas pressure, standoff distance and powder feed rate. The addition of Ni, produces coatings with lower levels of oxide content and porosity. An experiment with improved parameters was conducted, and a great improvement on the coating properties was observed.