INTRINSIC AND EXTRINSIC METALLURGY

摘要

The intrinsic metallurgy of materials is well understood, forming the basis of physical metallurgy, and leading to the classical concepts of nucleation and growth of phases in a matrix. This highly successful physics has unfortunately generally overlooked the contribution of process metallurgy, in which extrinsic factors in the form of entrainment defects can affect the structure and properties of materials. The limitations of intrinsic metallurgy are seen mainly in the presence of pores and cracks that lead to various kinds of failure in materials, but which cannot be explained by intrinsic mechanisms. For instance solidification as a simple phase change is unable to nucleate a pore or a Griffiths crack (by either homogeneous or heterogeneous nucleation as will be proven) because of the extremely high interatomic forces. Only extrinsically entrained defects can explain these features, and therefore provide understanding of the fundamental causes of failures in tensile, creep, fatigue modes, and probably some if not all, corrosion pitting failures. Furthermore, the assumption of the presence of extrinsic defects in the form of bifilms predicts type 'A' flake, undercooled and spheroidal graphite forms of cast irons, and in Al-Si alloys, unmodified and modified eutectic, and primary silicon forms. An accurate metallurgical understanding of cast and wrought alloys requires both intrinsic and extrinsic contributions.