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Phase transformations in engineering materials are inevitably related to mechanical behavior and are often precursors to residual stress and distortion. Neutron scattering in general is a valuable tool for studying their effects, and pulsed neutrons are of special value, because of the inherently comprehensive crystallographic coverage they provide in each measurement. At the Manuel Lujan neutron scattering center several different research programs have addressed the relationships between phase transformation/mechanical behavior and residual strains. Three disparate examples are presented: 1) stress induced transformation in a NiTi shape memory alloy, 2) cryogenically induced transformation in a quenched 5180 steel, and 3) time resolved evolution of strain induced martensite in 304 stainless steel. In each case a brief description of the principal result will be discussed in the context of using neutrons for the measurement.

The neutron intensity transmitted through polycrystalline material exhibits sudden well defined increases whenever the neutron wavelength ceases to fulfil the Bragg coherent scattering condition for a specific subset of lattice planes. Since in the transmitted beam all diffracted neutrons are absent, the so-called Bragg edges build up very rapidly, because diffraction of neutrons into the full solid angle contributes to their presence. High peak-intensity neutron bursts may be detected using the current-mode technique, opening up the possibility to do both transient and stroboscopic measurements. This new method is relevant to different research areas, like transient phase transformation, melting and solidification, dynamic stress influence or materials under extreme environmental conditions. Progress has been made in rapid data acquisition and analysis as well as temperature measurement by resonance doping.

High-resolution neutron diffraction has become a powerful method to determine strains caused by residual stresses in polycrystalline materials on a microstructural scale, measuring distorted lattice plane distances to within an accuracy of better than 0.5 X 10-4. The method implies very good knowledge of the equivalent undistorted (stress-free) lattice parameters in order to avoid systematic errors. Lattice parameters can also be affected by material composition, so that one can arrive at false values even under stress-free conditions. This has led the authors to use neutrons to measure both lattice distances by neutron time-of- flight (TOF) and chemical composition by prompt-gamma analysis non-destructively at the same time. Aluminum-copper alloys with copper contents between 0.08 and 4.98 weight% have been investigated as model substances, because the aluminum lattice contracts with increasing copper solute.© (1995) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.