Amorphous martensite in β-Ti alloys

Area of Science:

• Materials Science
• Crystallography
• Solid-state Physics

Background:

• Martensitic transformations are displacive lattice changes driven by rigidity instability.
• Conventional titanium alloys undergo martensitic transformations upon cooling.

Purpose of the Study:

• To investigate the cooling-induced phase transformation in Ti-Zr-Cu-Fe alloys.
• To explore the mechanism of solid-state amorphization in these alloys.
• To establish a link between martensitic transformations and inverse melting.

Main Methods:

• Experimental observation of phase transformations in Ti-Zr-Cu-Fe alloys during cooling.
• Analysis of lattice shear, distortion, and phase morphology.
• Investigation of the reversibility and cooling rate dependence of the transformation.

Main Results:

• Cooling of Ti-Zr-Cu-Fe alloys results in the formation of an intragranular amorphous phase, not martensite.
• The amorphous phase exhibits lenticular plates with a defined orientation relationship to the parent β-Ti crystal.
• The solid-state amorphization process is reversible, cooling rate independent, and linked to elastic softening and lattice shear.

Conclusions:

• A novel solid-state amorphization mechanism is identified in Ti-Zr-Cu-Fe alloys.
• The study establishes an experimental link between martensitic transformations and congruent inverse melting.
• Elastic softening and local lattice shear are identified as unifying mechanisms for both phenomena.