Long term heating effects at 1173 K and 1273 K on microstructural rejuvenation in various modified alloys based on GTD-111

This research work studied and evaluated the effects of reheat treatment conditions, which consisted of solution treatment at a temperature of 1448 K for 14.4 ks, followed by air cooling and precipitate aging at a temperature of 1118 K for 86.4 ks, on the microstructural rejuvenation or refurbishment of various modified alloys based on the cast nickel base superalloy, GTD-111 with aluminum, nickel and/or cobalt additions after long term heating at temperatures of 1173 K and 1273 K for 1440 ks. From the results obtained, it was found that the reheat treatment conditions applied are more suitable for microstructures after long term heating at a temperature of 1173 K. However, such reheat treatment conditions could not fully return reheat treated microstructures to microstructures similar to those of previous research work. It seems that the selected solutioning temperatures and/or times were not sufficient to completely dissolve all coarse gamma prime particles after long term heating for all samples with alloying additions. Typical size and area fractions of the gamma prime particles of the reheat treated microstructures are very similar to those of the original alloyed ones but with lower values, especially those related to the size of the gamma prime particles.

Effect of Long-Term Aging on Microstructural Restoration in Cast Nickel Base Superalloy, GTD-111

In this research study, the effect of long-term aging after various solutioning temperatures on final microstructure was investigated. The cast nickel base superalloy, GTD-111, usually has standard reheat treatment as follows: solutioning treatment at 1448 - 1478 K for 7.2 ‑ 21.6 ks and aging at 1118 K for 86.4 ks. However, from previous research works, the density of γ՛ phase was not reached the optimum value. Therefore, extension of aging time was performed in the study from 90 to 180, 270, 360, 720, 1080 and 1440 ks in order to increase density or volume fraction of precipitating γ՛ particles. From the results, it was found that longer aging time provided higher values of both area fraction and size of γ՛ particles. However, increase in aging time resulted in the hardness decrease.

Effect of Precipitation Aging Conditions on Microstructural Refurbishment in Cast Nickel Base Superalloy GTD-111

This research study has an aim to evaluate and investigate the effect of various rejuvenation heat treatments on microstructure of long-term serviced cast nickel base superalloy grade GTD-111 used as turbine blade material. The evaluated reheat treatment programs consist of solution treatment at 1195°C for 2, 3, 4 and 5 hours then following with primary aging at 1120◦C for 2 hours and secondary aging at 845°C for 25, 50, 75 and 100 hours, respectively. All reheat treated microstructures were examined and analyzed by SEM and image analyzer. From all obtained results, it was found that the most proper solution treatment duration was 5 hours to provide the most uniform microstructural characteristics, which consist of the uniform distribution of very dense gamma prime particles in the matrix as well as its highest hardness value. Furthermore, when increasing the duration at secondary aging at 845◦C over than 25 hours (which is according to standard heat treatment), such microstructure provided the most gamma prime phase stability comparing to those of other reheat treatment programs.

Effect of Reheat Treatment on Microstructural Refurbishment and Hardness of the As-cast Inconel 738

This work investigates the effect of rejuvenation heat treatment conditions for refurbishment of the long-term serviced gas turbine blades, which were made of as-cast nickel base superalloy grade, Inconel 738. The reheat treatment conditions consist of solutionizing treatments at temperatures of 1,438, 1,458 and 1,478 K for 14.4 ks and aging treatments at temperatures of 1,133, 1,148 and 1,163 K for 43.2, 86.4, 129.6 and 172.8 ks. The results show that increase in aging times results in continuous increase of size and area fraction of gamma prime (γ′) particles. The higher solutionizing temperature leads to the lower area fraction and smaller size of gamma prime particles. Regarding the microstructure characteristics, the most proper reheat treatment condition should be solutionizing at temperature of 1,438 K for 14.4 ks and aging at temperature of 1,133 K for 172.8 ks, which provides the highest area fraction of gamma prime particles in proper size.

New Nickel Based Superalloys Development by Vacuum Arc Melting Process Based on Aluminum Addition of GTD-111

This research objective is to study the microstructural modification by Al additions in cast nickel base superalloy, GTD-111 by means of vacuum arc melting process. The Al additions to the alloy were 1, 2 and 3% by weight. After that, all casted specimens were performed with different reheat treatment conditions, which consist of solutioning temperatures of 1125°C, 1145°C, 1165°C, 1185°C and 1205°C, respectively, for 6 hours following with precipitation aging at 845°C for 24 hours. After all reheat treatments, the microstructures were investigated and analyzed by SEM. From all obtained results, it was founded that the specimens with Al additions for 1-2%wt. following with reheat treatment show the decrease in size of γ’ precipitated particles when increasing solutioning temperatures. 3%wt. of Al addition was too high content resulting in already improper microstructural characteristics. However all obtained data of area fractions of precipitate phase were almost the same. Effect of Al addition and solutioning temperature did not provide any significant effect in this case. The mechanical property behavior: hardness was investigated by using Vickers hardness tester. It was found that the hardness all was very similar and increased with higher solutioning temperatures.

Interdiffusion of Elements in Aluminum 2024 Clad during Reheat Treatment Process at 495°C

Aluminum alloy 2024 is normally strengthened with alloying elements of Cu and Mg. As these elements reduce the corrosion resistance of the materials, a pure Al clad is normally applied. Nevertheless, during ageing at high temperatures, inter-diffusion between elements can occur and causing the recession of the clad. This study investigates the inter-diffusion behavior Al 2024 clad at ageing temperature of 495°C and predicts the clad lifetime due to reheat treatment process. The depletion rate of clad was found at 0.8 μm per-hour of heat treatment. It is predicted that the thickness of the Al 2024 clad will no longer meet with the specifications on heat treatment for 42 hours at 495°C.