What could be a cause of cracks perpendicular to the leading edge of a first stage single turbine blade?

The presence of cracks perpendicular to the leading edge of a first stage single turbine blade can often be attributed to over-temperature conditions. In turbine engines, excessive temperatures can lead to material weakening and, subsequently, failure. The leading edge of a turbine blade is subject to high thermal and mechanical stresses due to the intense environment in which it operates, particularly during the combustion process.

When a blade experiences over-temperature, it may exceed the material's safe operational limits, causing microstructural changes such as grain growth, which can reduce the blade's ability to withstand stress. As the blade continues to operate under these extreme conditions, the combination of thermal expansion and mechanical stress can initiate and propagate cracks. These cracks tend to originate near high-stress areas, such as the leading edge, and their orientation can indicate that they are a result of thermal fatigue or other heat-related failures.

While manufacturing defects, normal wear and tear, and improper installation can contribute to blade issues, these factors typically do not present the same direct correlation to crack formation in the manner seen with thermal over-stressing. Thus, over-temperature stands out as the most plausible cause of such specific crack patterns in turbine blades.