Microscopic and crystallographic aspects of retained omega phase in shock-loaded zirconium and its formation mechanism

The α→ω phase transformation products in shock-loaded pure Zr have been investigated. A portion of the ω phase is retained as a metastable phase after the pressure release. The orientation relationship (0001)α//(101l)ω and [1010]α//[112 3]ω observed between the two phases differs from those previously reported in Zr. Based on this orientation relationship a new transformation mechanism is proposed. The defect structures observed in the retained ω phase are in good agreement with those predicted according to the new mechanism.