Microstructure and properties of spray atomized and deposited superalloys

Spray atomization and deposition or Spray Forming (SF) has been a newly emerging science and technology in the field of materials development and production. SF makes it possible to combine the atomization of molten metals (Rapid Solidification) and the deposition of atomized droplets (Dynamic Droplets Compaction) into one metallurgical operation to produce directly from liquid metal near-net shaped preform materials that have uniform chemical composition, refined grain and microstructure and improved properties. At BIAM, fundamental work on the research and development of SF superalloys has been going on since 1990, A spray atomization and deposition facility has been designed and built with a strong vacuum evacuation system and minor leakage chamber. Inside the chamber a special designed water cooled multifunctional substrate/collector has been installed. The problem of contamination by the ceramic inclusions has been satisfactorily solved. A series of Ni-base superalloys such as K403, K405, K417, GH95, and the intermetallic alloys IC-218, IC-6 etc, have been spray atomized and deposited. Various experiments and tests have been conducted on the samples taken from the disk-shaped performs (psi 220-250x50m/m) and column-shaped billets (psi 170x150m/m) including macrostructure inspection on vertically sectioned slices, density measurements, microstructure examination by optical SEM or TEM, X-ray diffraction, HIP, hot deformation behavior and mechanical testing. On the basis of results from the investigation, the following conclusions can be made: Spray formed superalloy materials have low oxygen content, homogeneous chemistry, refined microstructure and improved forgebility. HIP eliminates microporosity to make the preforms fully dense, which reduces the scatter of mechanical properties. The properties of SF superalloys may be adjusted through hot deformation and subsequent heat treatment to meet the specific requirements of a particular applications.