Neutrons in Practical Metallurgy

Abstract

The virtues of slow neutrons as unique probes of the microscopic structure of materials are proven to the extent that industrial use is now made of neutron studies to aid alloy development. Since most metals have low absorption cross-sections for neutrons and scattering mean paths of the order of a centimetre, penetration of the neutron beam through most metals is easy and facilitates “in situ” studies of annealing effects, texture and residual stress. In many cases combinations of SANS and wide angle diffraction results are required to characterise the microscopic transformations. Studies of the development of the hardening phases in commercial alloys are described to illustrate this point. In each case a simple model for the kinetics of the process is found to be applicable. Radiation can cause pressure vessel steels to harden and embrittle if the copper content is too high. This has been known for many years but the inhomogeneities causing the effect are difficult to observe and characterise. A systematic investigation by the SANS technique of a large number of samples of a pressure vessel steel with differing concentrations of minority components is presented. A close correlation between SANS due to 30 A defects, copper content and radiation hardening is found. The nature of the defect is discussed. It would be both efficient and accurate to be able to observe SANS, wide angle diffraction, texture and macroscopic stress simultaneously. A multifacility based on a pulsed neutron source has been designed for this purpose.