Why can grain boundaries cause metal failure at high temperatures?

In materials science, grain boundaries are the interfaces where individual crystals (or grains) of varying orientations meet within a solid metal. While these boundaries typically strengthen metals at room temperature, they often become sites of weakness at high temperatures, leading to premature structural failure.12

At elevated temperatures, the cohesion between these crystal grains can diminish, making the boundaries susceptible to fracture. Additionally, grain boundaries can serve as locations for localized corrosion, which further compromises the integrity of the metal. To mitigate these issues, researchers often add specific metals to intermetallic compounds to strengthen the cohesion among the grains where fractures typically develop.31