Dr. Carl Koch

Abstract:

High energy ball milling of powders is an extreme example of severe plastic deformation which can dramatically alter the structure and/or microstructure of materials.  It was first used by John Benjamin and his colleagues in 1966, at what was the International Nickel Company, to obtain uniform distributions of oxide particles to strengthen structural materials like nickel-base superalloys. This method was later extended to produce amorphous alloys from elemental powders [1,2] or the milling of intermetallics [3].  In the synthesis of amorphous alloys from elemental powders (mechanical alloying) or by milling intermetallic compounds (mechanical milling), it was typically found that the microstructure became nanocrystalline before it became amorphous.  Therefore, this suggested a mechanism for the observed amorphization, and also provided a convenient method for preparing nanocrystalline materials. This talk will present a historical perspective on the preparation by ball milling of metastable materials such as amorphous alloys, nanocrystalline materials, quasicrystalline materials [4] and microstructural changes that can have beneficial effects on properties.  Work from the author’s laboratory and from the seminal research in this area by Prof. Ludwig Schultz will be emphasized.