Atom Probe Study of the Miscibility Gap in CuNi Thin Films and Microstructure Development.

Area of Science:

• Materials Science
• Metallurgy
• Physical Chemistry

Background:

• Copper-nickel (CuNi) alloys are technologically important materials.
• Understanding their miscibility is crucial for alloy design and performance.
• Previous studies have yielded unclear results regarding CuNi miscibility.

Purpose of the Study:

• To investigate the miscibility of CuNi alloys using advanced characterization techniques.
• To determine the phase miscibility gap and critical temperature of CuNi alloys.
• To quantify the interdiffusion coefficient in nanocrystalline CuNi microstructures.

Main Methods:

• Preparation of multilayered thin film samples using ion beam sputtering (IBS) and focused ion beam (FIB) shaping.
• Long-term isothermal annealing treatments in a ultra-high vacuum (UHV) furnace at 573, 623, and 673 K.
• Analysis of composition profiles using atom probe tomography (APT) and fitting with a Fourier series to determine the interdiffusion coefficient.

Main Results:

• The effective interdiffusion coefficient was determined as Deff = 1.86 × 10−10 m2/s × exp(−164 kJ/mol/RT).
• Microstructural defects such as grain boundaries and precipitates were observed in nonequilibrium states.
• Experimental evidence for a miscibility gap at 573 K was found, with boundary concentrations of 26 and 66 at% Ni.
• The critical temperature (TC) of the miscibility gap was determined to be 608 K at 45 at% Ni.

Conclusions:

• A distinct miscibility gap exists in CuNi alloys at lower temperatures.
• The critical temperature for the CuNi miscibility gap is approximately 608 K.
• The study provides quantitative data on interdiffusion and phase behavior in CuNi alloys.