Complex Metal-Intermetallic Composites by Cold Spray Deposition: A Copper-Indium-Gallium (CIG) Example

 

 

Cold spray offers unique possibilities in processing intermetallic-forming or phase-segregating metallic alloys, which are difficult to address by classical melt-metallurgical processes such as casting or thermal spraying. An example is the production of thick coatings of the copper-indium-gallium (CIG) system, as used in the fabrication of the CIGS(Se) thin film photovoltaic solar modules. At the relevant compositions, extended solidification intervals create material segregation into large brittle CuGa₂-type regions intermixed in an indium-rich matrix rendering the cast non-uniform and fragile with high internal stresses. The equilibrium phase diagrams even allow pure Ga and the In-Ga eutectic, essentially liquid materials and highly undesirable for the application.   Using rapid solidification by gas atomizing the Cu-In-Ga to produce cold spray powder promotes a fine-scaled and uniform phase distribution and microstructure of Cu(In,Ga) ,CuIn and In. By decoupling the material synthesis from the forming process, this phase distribution can be fully preserved in the cold spray deposition process to advantageously fabricate the coatings for that application.

This presentation will discuss the development of the parameter space for cold spray CIG at the NRC. Properties and performance of optimized coatings and assemblies will be shown. The relationship between feedstock characteristics and processability will be addressed.