چكيده به لاتين
A286 Fe-Ni superalloy is one of the most practical compounds in gas turbine industries. The formation of precipitates reduces the mechanical properties and performance of the superalloy. The present study investigates the formation conditions of phase with a variation of A286 chemical composition. In this regards, 6 types of the alloy with varying in Al, Ti, and Nb elements were produced via the VIM method and named Nb0, Nb15, Nb25, Nb30, Nb35, and Nb40. Homogenization, hot rolling, and dissolution annealing were applied to the alloys. Then, the alloys were heat-treated at 650 to 900 ºC for 2 to 30 h. The microstructural evolution, especially the amount of and , was analyzed by optical microscopy, SEM, DTA, and XRD techniques. In addition, the mechanical properties were investigated via hardness and hot tensile tests at 650 ºC. The microstructural studies indicated that firstly appeared in all of the aging temperatures, and then, precipitates formed either directly or from transformation. Although none of precipitates was observed at 650 and 720 ºC, increasing temperature up to 840 ºC maximized the amount of precipitates, and then the precipitates disappeared at 900 ºC. According to microstructural evolution, the amount of precipitates reduced from Nb0 (control sample) to Nb30, and increased in Nb35 and Nb40. The maximum amount of precipitates was observed at 840 ºC in Nb0, Nb30, and Nb40, as 6.4, 4.8, and 7.5, respectively. Result analysis showed that the minimum fraction of precipitates attributed to Nb30, and thermodynamical and kinetical models evaluated and proved this event. The mechanical evaluation indicated that hardness and hot tensile strength improved from Nb0 to Nb30, from 864 MPa to 972 MPa, respectively. In summary, the study showed that the targeted selection of Nb, Ti, and Al in the optimum alloy (Nb30) increased the amount and stability of precipitates, reduced the formation of precipitates during aging, and improved hardnes and hot tensile properties.
