Formation of 3D Cr₂C through solid state reaction-mediated Al extraction within Cr₂AlC/Cu thin films

Area of Science:

• Materials Science
• Solid-State Chemistry

Background:

• MAX phases are a unique class of ternary carbides and nitrides with desirable properties.
• Extracting specific elements from MAX phases can be challenging using traditional methods.

Purpose of the Study:

• To report a novel chemical etching-free method for forming chromium carbide (Cr2C).
• To investigate the transformation of Cr2AlC MAX phase thin films into Cr2C.
• To analyze the diffusion of aluminum and its effect on the MAX phase structure.

Main Methods:

• Deposition of Cr2AlC/Cu assemblies on sapphire substrates via magnetron sputtering.
• Vacuum annealing of the deposited assemblies.
• Characterization of the resulting carbide grains using transmission electron microscopy.
• Comparison of experimental interatomic distances with ab initio calculations.

Main Results:

• Aluminum successfully diffused from the Cr2AlC MAX phase into the copper layer.
• Formation of Al4Cu9 intermetallic compound observed.
• Collapse of the MAX phase structure into Cr2C grains.
• Experimental interatomic distances for Cr2C grains closely matched theoretical predictions.

Conclusions:

• A viable chemical etching-free method for producing Cr2C from Cr2AlC was demonstrated.
• Aluminum diffusion is the key mechanism driving the MAX phase transformation.
• The study validates theoretical predictions for the Cr2C phase equilibrium volume.