Hypergravity-exacerbated cracking in high-speed rotating 7075 aluminum blades

Abstract

On Earth, high-speed rotating blades and rotors experience hypergravity, which is mainly derived from centrifugal force. Aluminum alloys are widely used in high-speed rotating machines. In particular, 7075 aluminum has excellent properties, providing it with great potential for application in high-temperature rotating parts. In this work, the cracking behavior and microstructural evolution characteristics of high-speed rotating blades under different stresses were studied. A specifically designed instrument and blades with multiple necks were assembled, and the stress was tuned by adding weight to the blade tip. Each rotating blade cracked on its root neck, indicating that the gradient hypergravitational force decreased from the root to the tip. The degree of high-temperature cracking obviously increased with a sawtooth-like tip, but the degree of low-temperature cracking did not obviously increase with a smooth tip. A comparison under a constant uniaxial force required a greatly increased ultimate cracking strength that was approximately 10–18 times greater than that under hypergravitational force at the same temperature. Force analysis indicated that the coupling of hypergravitational forces in the normal direction and torsional forces in the tangential direction accelerated cracking. A uniaxial force caused grains to extend along the blade direction. However, a tangential force cut these extended grains to accelerate cracking and grain refining. In this study, real-world simulated service conditions for commercial alloys rotating at high speeds and a new understanding of the mechanical properties of alloys under various severe conditions were provided.

Keywords

• Hypergravity
• 7075 aluminum alloy
• Microstructure
• Thermal crack
• High-speed rotation