Bulk Neutron Diffraction Research Articles

Crystallographic preferred orientation of quartz deformed at granulite conditions: the Kalinjala Shear Zone, Port Neill, South Australia

Crystallographic preferred orientations of quartz aggregates in mylonitic orthogneisses from the highest strained central region of the Kalinjala Shear Zone, Port Neill South Australia, are products of a combination of constrictional and flattening strains. These rocks were deformed under granulite facies peak metamorphic conditions, reaching pressures of ∼1.0 GPa and temperatures of ∼800 ± 50 °C. Neutron diffraction textural and fabric analysis methods reveal a dominant single c-axis maximum parallel to the Y-strain axis. This is accompanied by a symmetric orthorhombic pattern, where the c-axis fabrics and corresponding pole figure densities of {a}, {m}, {r} and {z} planes are arranged around the XY foliation plane. These fabrics from coexisting adjacent layers suggest that the activation of prism-<a> slip is characteristic for these high-temperature deformation conditions. A small asymmetry in the [c], {a} and {m} pole figures suggests a minor component of dextral shearing. The c-axis pattern is weakened where the foliation is dominated by secondary phases, such as concentrations of biotite mica. The opening angles obtained from cross-girdle c-axis patterns produce temperature estimates that are ∼100 °C lower than the peak metamorphic temperature of ∼800 ± 50 °C, but closer to temperatures related to a component of flattening strain. These c-axis patterns are consistent with other structural characteristics and can be related to the late-stage flattening strains during the Kimban Orogeny. KEY POINTS Mylonitic orthogneisses are deformed under granulite facies conditions. Quartz fabrics were measured by bulk neutron diffraction and optical methods. Mylonite c-axis fabrics can be related to the high-temperature deformation and activation of the prism-< a > slip system. Crystal preferred orientations indicate a large component of flattening strain superimposed on the dextral shearing observed in the Kalinjala Shear Zone.

Degradation and onset of plastic anisotropy in marine aluminum alloy due to fire exposure by bulk neutron diffraction and in situ loading

In this paper, the degradation of mechanical properties of marine structural aluminum alloy AA5083 and onset of lattice plastic anisotropy subsequent to fire exposure is investigated. For virgin and fire-exposed samples, microstructural characterization is carried out for the first time and changes in lattice specific strain responses under step and continuous axial deformation are studied using novel bulk neutron diffraction. Peak fitting of raw data yields d-spacing values of reflections of interest and allows for lattice specific strain calculations. A reduction in yield stress from 260MPa in the virgin material to 120MPa in the fire-exposed sample is observed. Virgin material exhibits dynamic strain aging during plastic deformation; this is captured in neutron diffraction measurements. Larger peak broadening for virgin material indicates possible presence of Type II and III residual stresses due to intergranular stress or dislocation stress fields. Stress vs. lattice strain plots show large deviations from linearity post-yield for fire-exposed samples. This is due to strain redistribution among grains as well as grain reorientation. After fire exposure dynamic strain aging does not occur, but individual lattice planes reveal plastic anisotropy in their response to plastic deformation. Results from neutron diffraction, combined with electron backscatter diffraction characterization, provide insight into the yielding mechanisms of AA5083 and effects of fire exposure.

A Comparison of X-Ray and Neutron Diffraction Measurement of Lattice Parameters for the Determination of Residual Stress and Chemical Composition in Zirconium Alloy Tubes

AbstractIntergranular residual stresses can exist in zirconium alloys, especially when there is a large distribution of grain orientations. The stresses result from the anisotropic plasticity and thermal expansion of the hexagonal close-packed crystal structure of α-zirconium. Apart from complicating the characterisation of materials using lattice parameter measurements, the intergranular stresses can significantly affect material behaviour, especially in nuclear reactor environments, and there is therefore a great deal of interest in their measurement.The effects of specimen preparation and surface relaxation on X-ray diffraction measurements of lattice parameters of zirconium alloys have been investigated by comparing bulk neutron diffraction with X-ray diffraction on identical materials. The results show that: (i) intergranular or interphase residual stresses exist in dual-phase Zr-2.5Nb pressure tubes; (ii) the stresses normal to the surface of an X-ray diffraction specimen are not relieved completely when there are intergranular residual stresses in the material. One can conclude that intergranular stresses have to be considered when determining chemical compositions from lattice parameter measurements and also when measuring macroscopic residual stress using X-ray diffraction.