Equicohesion: Intermediate Temperature Transition of the Grain Size Effect in the Nickel-Base Superalloy PM 3030

Abstract

The intermediate temperature transition of the grain size effect on the yield strength of PM 3030 is investigated using compression tests from room temperature to 1200°C. It is found that grain boundary strengthening is strong at low temperature which is consistent with conventional Hall-Petch hardening. However, the grain boundary contribution to strength diminishes exponentially at intermediate temperature and vanishes at the equicohesion point. Above the equicohesion point, finer grain structure leads to material softening primarily due to grain boundary diffusion and deformation processes. Maximum softening occurs at T soft-max which is about 70% of the melting point, then decreases logarithmically with further increase in temperature, and vanishes at the melting point. This can well be rationalized by the overwhelming dominance of volume diffusion over grain boundary diffusion at temperatures close to the melting point, which decreases the impact of grain size on material strength. An exponential transition from the Hall-Petch behavior to the diffusion-based behavior provides an overall better fit of test data as compared to a linear transition. This study provides a contribution to the understanding of equicohesion and variation of the grain size effect on material strength and can be particularly crucial for components used at intermediate temperature.

Microstructure and mechanical properties of γ΄ strengthened Co–Ni–Al–W-base ODS alloys

“…A significant drop in strength has been observed in the temperature range of 600e700 C, indicating the switch-over from low-temperature to high-temperature deformation mechanisms. This transition can be attributed to the pronounced drop in grain boundary strengthening effect [26,27]. It is inferred that the contribution of grain boundary strengthening to material strength drops significantly in the temperature range of 600e700 C. As the temperature reached beyond 700 C, the compression yield strength of 40Ni alloy becomes comparable to that of Coe9.3Ale10.4W alloy, indicating the insufficient demonstration of the superior high-temperature mechanical properties of Co-base ODS alloys.…”

Correlation between Microstructure and Mechanical Properties of Heat-Treated Novel Powder Metallurgy Superalloy

“…However, with the testing temperature increasing, brittle fracture occurred for SL. It has been well-known that deformation transforms from slipping to grain boundary sliding when deformed at a high temperature [31,[45][46][47]. It can be seen from Figure 5a,d that some pores were produced near fracture after deformation at 550 • C. With deformation temperature increasing, pores are more prevalent near fracture, which can be clearly observed in Figures 6 and 7a,d.…”

“…A similar phenomenon was also observed by Kozar et al [30]; that is, the sub-solvus heat-treated IN100 superalloy exhibited superior mechanical performance to the super-solvus one at a low temperature (<600 • C). This was generally ascribed to the low mean free path of dislocations in fine grains at a low temperature, also known as the Hall-Petch relationship [30][31][32]. However, it must be mentioned that next generation PM superalloy have to function at a higher temperature (>850 • C), at which grain boundary sliding will dominate the deformation [31,[33][34][35].…”

“…This was generally ascribed to the low mean free path of dislocations in fine grains at a low temperature, also known as the Hall-Petch relationship [30][31][32]. However, it must be mentioned that next generation PM superalloy have to function at a higher temperature (>850 • C), at which grain boundary sliding will dominate the deformation [31,[33][34][35]. Additionally, finegrained alloys have an occurrence of grain boundary sliding at high temperatures and are generally associated with decreased strength compared to alloys with large grains [36,37].…”

Assessment of Substrate and TBC Damage Effects on Resonance Frequencies for Blade Health Monitoring

“…The drop is strongest at 1155 K due to a transition in mechanical behavior of the blade from primarily dislocation slip at lower temperature to mainly easier creep deformation processes at higher temperatures. This transition leads to a strong decrease in material resistance to deformation, particularly in yield strength (van Dyke & Nganbe, 2021; Nganbe & Fahim, 2010;Nganbe, 2014;Nganbe, 2009). Consequently, the energy dissipation properties and damping behavior of the blade change, leading to lower natural frequencies.…”