چكيده به لاتين
Nickel base superalloys, which are designed and manufactured to work in acute conditions, have relatively good properties in these conditions. However, by applying suitable heat treatment, the properties of these alloys can be altered and improved, so in this research, the mechanical properties of the 3 nickel base superalloy Inconel 718+ (an alloy containing a standard boron (B1) alloy, an alloy containing The excess boron element (B2) and a standard boron containing zirconium (B3) alloy are improved by applying a number of heat treatment cycles. In the first part of this study, in addition to standard heat treatment, 4 different design cycle heat treatment (T1, T2, T3 and T4) were designed and applied on an alloy containing extra amount of boron (B2). Then, the microstructural changes resulting from this heat treatment were investigated and its effect on some of the mechanical properties of the alloy was studied. The design of heat treatment cycles has been designed to create different microstructures in the alloy. The results of microstructural studies showed that B2T1 and B2T2 samples, in addition to secondary coarse gamma prim particles ,contains a different volume fraction of tertiary gamma prime particles of less than 30 nm. The B2T3 and B2T4 heat treatment cycles are designed to have all the gamma prim particles in these two samples have dimensions close to those of tertiary gamma prime particles in B2T1 and B2T2 samples. The results of mechanical experiments on these four samples show that a sample with a higher volume fraction of small particles of gamma-prim has better tensile properties and rupture stress than other samples and standard specimens.
In the second part of the present study, the optimal heat treatment of the first part (T3), which resulted in increasing the tensile properties and the rupture stress, was selected as the optimal heat treatment cycle and applied on B1 alloy and B3 alloy, and then the microstructures were obtained by optical microscope and electron microscope was investigated. The results of these studies showed that boron and zirconium had a slight effect on the average grain size of the samples, but after applying the same heat treatment, the hardness of the alloys containing boron and zirconium (B2T3 and B3T3 samples) compared to the base alloy (sample B1T3) has increased. The results of the tensile test on these specimens showed that the yield strength of the B2T3 and B3T3 alloy increased by 8 and 6 percent, respectively, than the B1T3 alloy. Also, the increase in the length of B2T3 and B3T3 samples decreased by 18 percent and increased by 6 percent, respectively, than the B1T3 alloy.
The results of rupture stress tests on B1T3, B2T3 and B3T3 samples showed that the rupture stress of these samples was 48, 74 and 53 hours, respectively. This increase in life, especially in the B2T3 sample, could be due to an increase in the fractional volume of gamma prim particles in these specimens. In addition, the increase in the amount of B and Zr + B in the chemical composition of the IN 718+ alloy has caused the content of these two elements to be further segregated in the boundary, reducing the movement or stopping of the boundaries in these two samples. This may have helped to extend the life of these two samples.
