Estudo da influência de adições de prata na cinética de precipitação e no comportamento eletroquímico da liga Cu-6%Al
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Data
2008-01-16
Autores
Carvalho, Thaisa Mary [UNESP]
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Editor
Universidade Estadual Paulista (Unesp)
Resumo
Neste trabalho, estudou-se a influência de adições de 4, 6, 8, 10 e 12% Ag (m/m) na cinética de precipitação e na resistência de polarização da liga Cu-6%Al, utilizando-se análise térmica diferencial (DTA), difratometria de raios X, microscopia eletrônica de varredura (MEV), análise por dispersão de energias de raios X (EDX), medidas de variação da microdureza com a temperatura e o tempo, medidas de potencial em circuito aberto com o tempo (OCP) e curvas de polarização potenciodinâmica (PDS) em solução de NaCl 3,5%(m/v). Os resultados obtidos para as ligas contendo prata foram comparados com aqueles obtidos para as ligas Cu-6%Al. Observou-se que a adição de prata possibilita uma resposta ao tratamento de endurecimento por precipitação nessa liga. A precipitação da prata ocorre preferencialmente nos contornos de grão da fase matriz e o máximo da precipitação foi observado no intervalo de 300 a 500 oC. A formação da fase rica em Ag segue dois processos diferentes, que dependem de concentração de Ag. Para as ligas contendo 4 e 6%Ag a formação de precipitados ocorre por um mecanismo de segunda ordem na velocidade de reação, enquanto que para ligas com 8, 10 e 12%Ag, o mecanismo é de ordem zero. O valor da energia de ativação para o processo de ordem zero foi aproximadamente 50% maior que aquele obtido para o processo de segunda ordem. A análise de variância apresentou uma diferença estatisticamente significativa entre os valores de Rp das ligas estudadas. Esta diferença, indicada pelo teste de Tukey, foi quantificada com intervalos de confiança de 95% para as médias de resistência de polarização populacionais. A resistência à corrosão nessas ligas diminuiu com o aumento da concentração de Ag no sistema. A liga Cu-6%Al (sem adições de Ag) apresentou maior resistência de polarização.
In this work the effect of 4, 6, 8, 10 and 12wt.%Ag addition on the aging characteristics of the Cu-6%Al alloy and the silver precipitation were studied by microhardness changes measurements with temperature and time, differential thermal analysis (DTA), scanning electron microscopy (SEM), energy dispersive X-ray analysis (EDX) and X-ray diffractrometry (XRD). The influence of the Ag content on the alloys corrosion resistance was investigated using electrochemical methods in 3.5%NaCl solution. Open circuit potential (OCP) with time and potentiodynamic direct scanning (PDS) were carried out and the experimental results were analyzed using statistical methods. Regression analysis, variance analysis (one-way ANOVA) and confidence intervals were applied to obtain the different kinetic parameters associated with corrosion resistance for these alloys. The results obtained for the alloys with Ag additions were compared with those obtained for the Cu-6%Al. These results showed that the silver addition enable a response to an age hardening treatment in the Cu-6%Al alloy. The silver precipitation occurs preferentially at the grain boundaries in the matrix, and the precipitation maximum occurred in the temperature range from 300 to 500 oC. The Ag-rich phase formation follows two different processes depending on Ag concentration. For alloys with 4 and 6wt%Ag the precipitation formation occurs as a second-order reaction mechanism while for alloys with 8, 10 and 12wt.%Ag a zero-order reaction was observed. The activation energy value for the zero order process is about 50% larger than that obtained for the second order process. The variance analysis indicated a statistically significant difference between alloys with respect to Rp This difference indicated by the Tukey test was quantified buy confidence intervals of 95 % for the populational polarization resistance averages and the populational corrosion potential. The corrosion resistance in these alloys.
In this work the effect of 4, 6, 8, 10 and 12wt.%Ag addition on the aging characteristics of the Cu-6%Al alloy and the silver precipitation were studied by microhardness changes measurements with temperature and time, differential thermal analysis (DTA), scanning electron microscopy (SEM), energy dispersive X-ray analysis (EDX) and X-ray diffractrometry (XRD). The influence of the Ag content on the alloys corrosion resistance was investigated using electrochemical methods in 3.5%NaCl solution. Open circuit potential (OCP) with time and potentiodynamic direct scanning (PDS) were carried out and the experimental results were analyzed using statistical methods. Regression analysis, variance analysis (one-way ANOVA) and confidence intervals were applied to obtain the different kinetic parameters associated with corrosion resistance for these alloys. The results obtained for the alloys with Ag additions were compared with those obtained for the Cu-6%Al. These results showed that the silver addition enable a response to an age hardening treatment in the Cu-6%Al alloy. The silver precipitation occurs preferentially at the grain boundaries in the matrix, and the precipitation maximum occurred in the temperature range from 300 to 500 oC. The Ag-rich phase formation follows two different processes depending on Ag concentration. For alloys with 4 and 6wt%Ag the precipitation formation occurs as a second-order reaction mechanism while for alloys with 8, 10 and 12wt.%Ag a zero-order reaction was observed. The activation energy value for the zero order process is about 50% larger than that obtained for the second order process. The variance analysis indicated a statistically significant difference between alloys with respect to Rp This difference indicated by the Tukey test was quantified buy confidence intervals of 95 % for the populational polarization resistance averages and the populational corrosion potential. The corrosion resistance in these alloys.
Descrição
Palavras-chave
Físico-química, Ligas de cobre alumínio prata, Cinética de precipitação
Como citar
CARVALHO, Thaisa Mary. Estudo da influência de adições de prata na cinética de precipitação e no comportamento eletroquímico da liga Cu-6%Al. 2008. 58 f. Dissertação (mestrado) - Universidade Estadual Paulista, Instituto de Química, 2008.