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    Effects of bismuth (bi) additions on microstructure and mechanical properties of AZ91 alloy
    (TANGER Ltd., 2015) Elen, L.; Zengin, H.; Turen, Y.; Turan, M.E.; Sun, Y.; Ahlatci, H.
    In this study, the effects of bismuth additions of 0.2, 0.5 and 1 wt% on microstructure and mechanical properties of AZ91 alloy were examined. A permanent mold casting procedure was carried out to produce the alloy billets under a mixed gas atmosphere of SF6 and CO2. Microstructural investigations showed that Mg3Bi2 intermetallic phases were formed in all the samples and it coarsened with increasing amount of Bi in AZ91 alloy. Furthermore, a finer dispersion of Mg17Al12 intermetallic phases was observed in the structures as the amount of Bi in AZ91 increased. It was also showed that increasing Bi addition increased the hardness of AZ91 alloy. However, the highest hardness value was found for the alloy having 0.5wt% Bi addition that means high amount of Bi can decrease the hardness of AZ91 alloy. On the other, there were no considerable changes in the tensile strengths and yield strengths of the alloys as the amount of Bi increased although a slight increase in both strengths were observed with increasing amount of Bi. Percent elongation at break showed a decrease as Bi addition increased.
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    Residual stress measurement in rails by destructive and non destructive method
    (TANGER Ltd., 2015) Turan, M.E.; Ozcelik, S.; Zengin, H.; Ahlatci, H.; Turen, Y.; Tozlu, I.; Sun, Y.
    Residual stress is an elastic stress in remaining part after the various stages of production. If residual stress values in rails are known, mechanical properties of rails and their effects in railway can be predicted. For this purpose, residual stresses of rails which had same casting number were measured by cutting and X-ray diffraction method in this study. Five rails were used for measurement. Firstly, according to the EN 13674-1 which is railway rails standard, strain gauge that is an electrical apparatus were used and one meter long rails were cut. After cutting, Hooke law was applied and residual stress values of rails were found. The residual stress values were around between 115 MPa and 180 MPa. In addition to standard residual stress measurement, X-ray diffraction method was used to compare between destructive and nondestructive techniques. Five specimens were taken from five rails in the appropriate size for X-ray device. In this method stress values were around between 200 and 400 MPa. After residual stress measurement, Brinell's hardness test was applied to three samples and microstructure of rail which has biggest residual stress value was examined by SEM. The results show that, residual stress values in cutting method were different from X-ray diffraction method and residual stress could affect the rails hardness.