Transformation Pathway upon Heating of Metastable β Titanium Alloy Ti-15Mo Investigated by Neutron Diffraction

Area of Science:

• Materials Science
• Metallurgy
• Crystallography

Background:

• Metastable beta titanium alloys are critical for various industrial applications.
• Understanding phase transformations in Ti-15Mo alloy is essential for optimizing its properties.
• Thermal treatment significantly influences the microstructure and performance of titanium alloys.

Purpose of the Study:

• To investigate the transformation pathway of metastable beta Ti-15Mo alloy during thermal treatment.
• To analyze the evolution of alpha, beta, and omega phases at different heating rates and aging temperatures.
• To determine the effect of heating rate on the sequence of omega phase dissolution and alpha phase formation.

Main Methods:

• In situ neutron diffraction was employed to monitor phase evolution during thermal treatment.
• Experiments were conducted using two distinct linear heating rates: 1.9 °C/min and 5 °C/min.
• Aging at 450 °C was performed to study phase stability and transformations.

Main Results:

• The study observed that a heating rate of 5 °C/min led to the dissolution of the omega (ω) phase before the formation of the alpha (α) phase.
• At a slower heating rate of 1.9 °C/min, a narrow temperature range exhibiting the coexistence of both alpha (α) and omega (ω) phases was detected.
• Volume fractions and lattice parameters for all observed phases (α, β, and ω) were quantitatively determined.

Conclusions:

• Heating rate critically controls the transformation pathway in Ti-15Mo alloy.
• Faster heating promotes a direct transformation from beta to alpha phase via omega dissolution.
• Slower heating allows for a transient state where alpha and omega phases coexist, impacting alloy properties.