Investigation of mechanical properties and in vitro corrosion of bulk nanostructured metal produced by equal channel angular pressing

• Published in: AIP conference proceedings 2022-06, Vol.2454 (1)
• Main Authors: Zahari, Zahiruddeen Salam, Shri, Dayangku Noorfazidah Awang, Yamamoto, Akiko
• Format: Article
• Language: English
• Subjects: Austenitic stainless steels; Cell culture; Corrosion; Diamond pyramid hardness tests; Electrolytes; Equal channel angular pressing; Grain size; Heat treatment; Mechanical properties; Metallurgy; Optical microscopes; Stainless steel
• ISSN: 0094-243X; 1551-7616
• DOI: 10.1063/5.0078675

ECAP(Equal Channel Angular Pressing) process on 316L stainless steel was done in this study using two different channel angles 120° and 126° after all samples were heat treated. There were three experiments ran in this study optical microscope analysis, hardness test and electrochemical measurement for three conditions samples which are before ECAP (BE), 120° ECAP and 126° ECAP. Metallurgical optical microscope was used to analyse the changing in grain size. The hardness test is examined using Wilson Vickers Hardness Test Machine with 100 gf load subjected on the samples about 10 seconds. Electrochemical measurements are done to observe the corrosion behavior of the samples. Two electrolytes were used during the test which are 0.9%NaCl and E-MEM+10%NCS cell culture medium solution. An incubator is used during the experiment for the samples experience a real human body environment (37°C) in two conditions which is for 0.9%NaCl and 5% CO2 for cell culture medium on 316L stainless steel. As a result, optical analysis shows that the grain size for both 120° ECAP and 126° ECAP samples had refined with an elongated grain compared to BE for both materials. However, 120° ECAP shows a slightly better refinement grain size than 126° ECAP. Besides, in hardness test results, the 126° ECAP shows the increment value of Vickers hardness from others. 120° ECAP and 126° ECAP has 27.67% and 28.84% hardness increment, respectively. Meanwhile, for electrochemical tests show that ECAP influences the corrosion properties of 316L stainless steel. Current density(Icorr) is reduced by 120° ECAP (24.6±4.9 nA/cm2 and 37.6±24.3 nA/cm2) and 126° ECAP (107.0±82.0 nA/cm2 and 56.6±27.2 nA/cm2) in both conditions tested (0.9%NaCl and E-MEM+10%NCS) , but 120° ECAP improves better than 126° ECAP for both conditions(lower results values). The reduction of Icorr by ECAP process is smaller in cell culture medium than 0.9% NaCl. As a conclusion, 120° ECAP shows the best performance in these three testing but almost to 126° ECAP results. Therefore, by increasing small value of ECAP die angle will not obviously change the mechanical properties and corrosion behavior outcomes in fact the ECAP pressing force become lower.