Quantificação de defeitos por processamento digital de imagens em revestimentos obtidos por aspersão térmica.

Abstract

The objective of this work is to quantify defects like pores and cracks in coatings, formed by electric arc thermal spray technique (ASP), using quantitative estereology an digital imaging analysis. Two distinct coatings were obtained by the combination of three wires (a, b and c). Twenty images in secondary eléctron mode were submited to pre-process, segmentation and messuraments steps using the software ImageJ. The coating condition 1 presented 3,81% ± 0,9 of defects and the coating condition 2 presented 3,31% ± 1,42. Both coatings had more cracks than pores, in other words, defects with elongated morphology and form fator smaller than 0,70. These results are consistent with those obtained by other porosity measure techniques, which came up with porosity and defects values about 4%, for these coatings, however, without data for morphology and distribution (Ponte, 2001). Other eleven imagens, using back-scattering (BSE) mode were processed. The process in BSE mode was more practical, faster and came up with resoults similar to those obtaines by the images in SEI mode, such as 3,47 % ± 1,62 in defects for the condition 1, as well as the condition 2 presented 2,76% ± 1,42. It was also noticed that the coatings showed the tendency of having more elongated defects in comparison to the amount of round defects. The Stack process method was also used and was able to reduce work time by 3 hours to 30 minuties, presented equivalent defects measuments to those obtained from the individual analysis, nonetheless they were not the same, due to the process parameters used for all the images are the same, what does not happen in induvial analysis. The variation in chemical composition did not affect the number of pores ou defects and the digital imagin processes presented itself as a reliable technique for pores, cracks and oxide nets quantification.