| Abstract | 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 due to the formation of large brittle regions or low melting point and volatile eutectics. An example is the production of thick coatings of the copper-indium-gallium (CIG) system on plates or tubes, as they are required in the fabrication of the CIGS(Se) absorber layer of thin film photovoltaic solar modules on an industrial-scale. At the relevant compositions, extended solidification intervals, such as in casting, 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. Shrinkage effect further promote porosity. The equilibrium phase diagrams even allow the retention of pure Ga and the In-Ga eutectic, essentially liquid materials at room temperature and highly undesirable for the application. On the other hand, 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. |
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