Segregation behavior at grain boundary of Mg Zn Al Ca Sr alloys was calculated by using the grain boundary phase model based on the Hillert s parallel tangential construction to Gibbs energy. The correlations between the calculated segregations and literature values of their maximum texture intensity and Erichsen value were investigated. The Zn addition in Mg Ca alloys kept a certain Ca concentration in hcp phase regardless of Ca 2 Mg 6 Zn 3 precipitation. The addition of Al and Zn in Mg Ca alloys promoted the Ca segregation. However, the Al addition in Mg Ca alloys signi cantly decreased Ca concentration in hcp phase due to precipitation of Al Mg Ca compound phases. According to the comparison between the calculated segregation Ca and Sr and literature values of maximum texture intensity, the Ca and Sr segregation in grain boundary promoted a decrease of texture intensity of the alloys. The decrease of the texture intensity of Mg Al Ca and Mg Zn Sr alloys were relatively small because of the precipitates formation. The negative correlation coef cient of −0.85 was obtained between the calculated grain boundary segregation of Ca at the rolling temperature and the literature values of maximum texture intensity. It was estimated that the large amount of Ca segregation at grain boundary region in Mg Zn Ca alloys is obtained by rolling at just below the melting point of Ca 2 Mg 6 Zn 3 phase in the three phase region hcp, C14 and Ca 2 Mg 6 Zn 3 on the phase diagram.
NKH71 is a Re free nickel based single crystal superalloy. The long term creep strength of this alloy is superior to that of the practical used 2 nd generation superalloy, CMSX 4, containing Re but the short term creep strength is inferior to that of CMSX 4. This may be caused by the initial microstructure before creep. In order to arrange the initial morphology of the g′phase in NKH71, eight kinds of processes in heat treatment are carried out. After a series of heat treatments, each specimen is examined with scanning electron microscopy (SEM) and transmission electron microscopy (TEM). From SEM, it is found that the initial morphology of the g′ phase is different by the cooling rate after solution treatment and temperatures of 1 st step aging. It is also found by TEM that dislocation density at the interface between the g and g′ phase is different. In order to make clear the origin of the morphological difference in the each heat treatment, the phase field simulation is carried out on the basis of Gibbs free energy calculated using thermodynamic date of Ni Al binary system.
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