Metallurgy without Bifilms: No More Fractures

Abstract

There is growing evidence that the failure by cracking of nearly all solid metals, whether cast or wrought, is probably in most cases initiated by casting defects; entrained oxides known as bifilms which are the Griffith cracks necessary to initiate failure. Because bifilms are practically universally present in metals, the few examples of metals and alloys without bifilms, such as ductile iron, Hadfield Manganese Steel and Ni superalloy single crystals, appear to have unusually good properties, being unusually resistant to failure by cracking. Boron containing steels, and carbon steels deoxidised with CaSi might also be candidates. They indicate the potential for all metals and alloys if cast well. Current metallurgical thinking is required to recognize the current near-ubiquitous presence of bifilms in metals and the future casting technologies required for their avoidance. Uncracked and uncrackable metals having high strength, together with high ductility and toughness, should and could be the norm.