جستجوی مقالات مرتبط با کلیدواژه « ni-base superalloy » در نشریات گروه « فنی و مهندسی »

In this research, Inconel 738LC as the base metal was joined by wide gap brazing (WGB) using the mixture of Amdry718 as high temperature particle (HTP) and BNi-2 as low temperature particle (LTP). By using Amdry 718, the brazing temperature can be increased and porosity reduced significantly due to higher melting point temperature than base metal. The effect of mixture ratio on the microstructure and the mechanical properties was studied. The amount of the LPT in the mixture was 30, 40, and 50 percent. By decreasing the LTP ratio, the amount of eutectic phase and the blocky boride in the solid diffusion zone (SDZ) decreased markedly. The joint width increased by increasing the amount of LTP. There were two distinct regions in the joint/base interface. Due to the diffusion of B into the base, adjacent to the joint, the grain boundary melted and created a region including both the isothermal solidification zone (ISZ) and SDZ. By getting away from the joint, the content of B reduced by the grain-boundary diffusion. It was observed that aging did not have a significant effect on the amount and distribution of eutectic phases and blocky borides, however, the morphology of these phases changed slightly. Moreover, aging had a small effect on hardness making the hardness of different phases more uniform.

Solidification microporosity forms within dendritic space of gas turbine blades at large section in investment casting. Microporosity content more than permissible limit significantly reduces mechanical properties of turbine blades at the service conditions. In these work effects of Hot Isostatic pressing (HIP) followed by standard heat treatment cycle process on microstructural characteristics such as grain boundaries serration, microporosity content and mechanical properties of Ni-base superalloy IN738LC have been investigated by optical, Scanning Electron Microscopy (SEM) and practical experiments. The results of studies have shown that hot isostatic pressing provides more serration at grain boundary and could mostly eliminate or reduce microporosity, was generated during solidification by means of sintering. HIP is able also to improve creep life and ductility but has no effect on yield stress at tensile experiment.

In this study the effects of diameter variation in Bridgman directional solidification technique on structure of Ni-base superalloy GTD-111 has been investigated. So the samples with diameters of 22 and 29 mm were selected that at 5 mm/min withdrawal rate were directed. Thus the effect of this variation on structure contain density of grains, deviation orientation, primary and secondary dendrite arm spacing, volume fraction of γ-γ' eutectic, the number of freckle and average size of γ' particle were evaluated. It was observed increasing diameter cause density of grains decreased but the deviation orientation, primary and secondary dendrite arm spacing, volume fraction of γ-γ' eutectic, the number of freckle and average size of γ' particle increased. Therefore, the review of the alloy structure revealed that by increasing the diameter due to reduced cooling rate, the possibility of inappropriate structure increases. Therefore, it was suggested that in directional casting of large section in Bridgeman method, the decrease of cooling rate should be compensated by increasing the optimal withdrawal rate.

In this study the effect of Bridgman technique withdrawal rate on structure of Ni-base superalloy GTD-111 has been investigated. So the withdrawal rate 2.5, 5 and 10 mm/min selected and effect of this variation on structure contain density of grains, deviation orientation, primary and secondary dendrite arm spacing were evaluated. It was observed increasing withdrawal rate cause density of grains increased but the deviation orientation, primary and secondary dendrite arm spacing decreased. It was also observed that by increasing the withdrawal rate, at first the number of freckle decrease and then increase. Thus, this result was obtained with investigation of alloy structure that by the increasing the withdrawal rate of a limit, risk of formation the freckle increase in alloy structure and this has a negative effect on the directional structure. This issue was observed in 10 mm/min withdrawal rate.