The aim of this work was to characterize thin interference films grown on the surface of AISI 304 stainless steel for decorative purposes. Films were grown in a sulphochromic solution at room temperature by an alternating pulse current method. The morphology and chemical state of the elements in the films were investigated by field emission scanning electron microscopy (FESEM), atomic force microscopy (AFM), glow discharge optical emission spectrometry (GDOES), and infrared Fourier transform spectroscopy (FTIR). Depth-sensing indentation (DSI) experiments and wear abrasion tests were employed to assess the mechanical resistance of the films. The coloration process resulted in porous thin films which increased the surface roughness of the substrate. The interference films mainly consisted of hydrated chromium oxide containing iron. Increasing film thickness produced different colors and affected the mechanical properties of the coating-substrate system. Thicker films, such as those producing gold and green colors, were softer but more abrasion resistant.
Anodic interference films were grown on stainless steel by an electrochemical process in a 70 g L 21 CrO 3 z500 g L 21 H 2 SO 4 solution at temperatures of 25-75uC. The aim of this research was to assess the influence of temperature on characteristics of this coating. The morphology of the films was assessed through atomic force microscopy, the chemical composition was assessed by X-ray photoelectron spectroscopy, while the mechanical characteristics were assessed by resistance to abrasion wear and nanohardness. The roughness of the films grown at 25uC is less than that of the other temperatures. No significant difference regarding the porosity of the films was detected. A chromium hydroxide was observed on the top of the oxide layer grown on stainless steel. The steel coloured at 75uC presented a lesser hardness compared to the samples grown at 25, 35 and 55uC. The wear resistance increased as the temperature of the film's growth rose, which was inversely proportional to the hardness.
The characterization of architectural coatings grown on the surface of AISI 304 stainless steel by an electrochemical coloration process was realized by multiple techniques. The interference colored coatings were grown in a sulphochromic solution at room temperature by an alternating pulse current method. The morphology and chemical state of the elements in the films were investigated by field emission scanning electron microscopy (FESEM), atomic force microscopy (AFM), glow discharge optical emission spectrometry (GDOES), and infrared Fourier transform spectroscopy (FTIR). Depth-sensing indentation (DSI) experiments and wear abrasion tests were employed to assess the mechanical resistance of the films. The coloration process resulted in porous thin films which increased the surface roughness of the substrate. The interference films mainly consisted of hydrated chromium oxide containing iron. Increasing film thickness produced different colors and affected the mechanical properties of the coating-substrate. ARTICLE TH 38Electrochemical coloration of stainless steel as an alternative for architectural coatings
ResumoEm função da crescente demanda de utilização do aço inoxidável, na arquitetura, como material de revestimento externo e, considerando a preocupação dos ór-gãos de controle ambiental com a poluição no meio urbano, foram avaliados os efeitos da chuva ácida nas condições superficiais do aço inoxidável colorido e na lixiviação de cromo para o ambiente. Para esse estudo, foram realizados, em laboratório, ensaios de imersão de chapas de aço inoxidável colorido e natural em solução simulada de chuva ácida, sendo avaliados a liberação de cromo para a solução e a alteração da aparência superficial das amostras em tempos de exposição de 1, 3, 7, 14 e 28 dias. Nas amostras de aço inoxidável, com e sem coloração, foram medidos a cor e o brilho e, para soluções ácidas remanescentes, foram realizadas análises de cromo total e cromo hexavalente. Os resultados obtidos mostraram que, independente do tempo de contato do aço inoxidá-vel colorido com a solução de chuva ácida, houve preservação da aparência do material, sem alteração das condições superficiais, e o teor de cromo hexavalente na solução se apresentou em níveis muito inferiores aos estabelecidos pelo Conselho de Política Ambiental de Minas Gerais -COPAM. Palavras-chave:Aço inoxidável colorido, aparência superficial, chuva ácida, cromo hexavalente. Abstract
Aços inoxidáveis ABNT 304 foram coloridos em dourado pelo método eletroquímico de corrente pulsada utilizando como eletrólito solução ácida em concentrações de 70 g/L e 250 g/L de cromo, a fim de investigar a influência da concentração de cromo na resistência à corrosão e ao desgaste por abrasão. A caracterização morfológica dos filmes coloridos por interferência foi realizada a partir de imagens adquiridas em um Microscópio de Força Atômica, as quais foram quantificadas a partir de um programa aplicativo de análise de imagens, para determinação da rugosidade e porosidade. O desempenho dos aços inoxidáveis coloridos foi avaliado quanto à resistência à corrosão e abrasão. Para tanto, foram levantadas curvas de polarização potenciodinâmica em solução de NaCl 3% e realizados ensaios de resistência ao desgaste em um equipamento gerador de abrasão para materiais revestidos. Os resultados mostraram que a morfologia do filme de interferência obtido em soluções com 70 g/L e 250 g/L de cromo foi semelhante. Não foi também encontrada diferença significativa no desempenho do aço inoxidável colorido nestas duas concentrações, quanto à abrasão e à corrosão. Os resultados encontrados sugerem que a redução de 72% do cromo no processo de coloração propiciará um ganho de desempenho ambiental e ainda uma economia nos custos de reagentes na produção do aço colorido e no tratamento de efluentes do processo produtivo. palavras-chave: Aço inoxidável colorido; Corrosão; Porosidade; Resistência ao desgaste. evaluation of chromium content on performance of stainless steel obtained by color process electrochemistry abstract AISI 304 stainless steel sheets were colored in gold by an electrochemical alternate pulse current process using acid solutions containing 70 g/L and 250 g/L of chromium. The aim was to investigate the influence of chromium concentration on corrosion and abrasion resistance of colored stainless steel. The morphology of the films was obtained by AFM images processing in order to obtain the film roughness and porosity. The performance of colored stainless steel was evaluated from corrosion and abrasion resistance measurements. The corrosion resistance was determined from potentiodynamic polarization curves in 3% NaCl solution. Dry abrasion resistance tests were performed on an abrasion tester machine for coated materials. It was not observed difference in film morphology for the both chromium concentration. No difference in performance measured by abrasion and corrosion resistance was observed either. The reduction of 72% of chromium in the coloration process results in a great increase in the environmental performance and reagents cost saving for coloration production and for the treatment disposal.
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