Phase Composition Effects on Dynamic Behavior and Strain Rate Sensitivity in Metastable β-Ti Alloys

Area of Science:

• Materials Science
• Mechanical Engineering
• Metallurgy

Background:

• Metastable beta-titanium (β-Ti) alloys are crucial in aerospace and biomedical applications due to their unique properties.
• Understanding their mechanical behavior under dynamic loading is essential for predicting performance and ensuring safety.
• The influence of phase composition and microstructure on the strain rate sensitivity of these alloys requires further investigation.

Purpose of the Study:

• To investigate the dynamic mechanical behaviors and deformation mechanisms of α-β metastable β-Ti alloys.
• To compare the effects of different microstructures (equiaxed vs. lamellar) on mechanical properties and strain rate sensitivity.
• To elucidate the role of phase composition in dictating the dynamic response of Ti-45551 alloy.

Main Methods:

• High strain rate tension tests were performed using a split Hopkinson tension bar.
• Two distinct microstructures, bimodal equiaxed αₚ + β and lamellar α<0xE2><0x82><0x9B> + β, were created via controlled hot working and thermal processing.
• Microstructure characterizations were conducted to analyze deformation mechanisms.

Main Results:

• Both quasi-static and dynamic loading revealed dislocation nucleation, motion, tangling, and pile-ups at α/β interfaces as primary deformation modes.
• A positive strain rate dependence was observed for both strength and ductility, linked to dislocation activation in the α + β Ti-45551 alloy.
• Deformation twinning became a significant mechanism in equiaxed αₚ + β microstructures under dynamic loading, but was suppressed in lamellar α<0xE2><0x82><0x9B> + β due to nano phase size.

Conclusions:

• The mechanical behaviors and strain rate sensitivity of metastable β-Ti alloys are strongly dependent on their phase composition and microstructure.
• Deformation twinning plays a critical role in the dynamic response of equiaxed microstructures, while lamellar structures exhibit different behaviors.
• These findings provide valuable insights for designing and processing titanium alloys for high-strain-rate applications.