Understanding Interfacial Reactions in Ti-Ni Diffusion Couple

Area of Science:

• Materials Science
• Physical Chemistry
• Metallurgy

Background:

• Understanding diffusion in binary metal systems is crucial for materials development.
• Titanium-nickel (Ti-Ni) alloys are known for their unique properties, including shape memory effects.

Purpose of the Study:

• To investigate the diffusion phenomenon in the Ti-Ni binary system at 1173 K.
• To identify intermetallic compounds formed and determine their diffusion coefficients.

Main Methods:

• Microstructure and texture analysis were performed.
• Nucleation surface energy was analytically estimated.
• Marker experiments using thoria particles were conducted.
• The Wagner method was employed to calculate diffusion coefficients.

Main Results:

• Three stable intermetallic compounds (Ti2Ni, TiNi, TiNi3) and two metastable compounds (Ti3Ni4, Ti2Ni3) were identified in the diffusion zone.
• Marker experiments confirmed Ti2Ni as the initial phase to form at the Ti-Ni interface.
• Integrated diffusion coefficients at 1173 K were determined: 3.53 × 10^-12 m²/s for Ti2Ni, 1.81 × 10^-14 m²/s for TiNi, and 6.2 × 10^-15 m²/s for TiNi3.

Conclusions:

• The study elucidates the complex phase formation during Ti-Ni diffusion at elevated temperatures.
• Ti2Ni plays a primary role in the initial stages of diffusion in the Ti-Ni system.
• Quantitative diffusion data provide valuable insights for predicting Ti-Ni alloy behavior and optimizing processing.