Materials Science and Engineering

The high penetration depth and characteristic wavelength of neutrons make neutrons well suited to investigations of materials. Specimens can be studied at temperatures as high as 2000°C or as low as 1.5 K (-272°C). Specimens can also be studied under tensile and compressive loads (up to 45 kN), for standard dog-bone specimens as well as u-bends and compact tension specimens. It is possible to study specimens under load and at elevated temperatures (up to 550°C).

Other environments such as electro-chemical potential and hostile environments have been developed. We also have the ability to examine radioactive samples. We develop new environments to meet user needs, for example a furnace for determining crystallographic texture at elevated temperatures is currently under development, as is an in-situ welding system.

In most cases, measurements can be made non-destructively, leaving the specimen intact for subsequent measurement using other techniques. Special surface preparation is typically not required. Due to the high penetration depth of neutrons, it is relatively easy to create a variety of specimen environments for in-situ experiments. The benefits of these favourable properties is clearly illustrated by the variety of techniques and applications briefly described below.

Residual stress-scanning

Three-dimensional maps of internal residual stress are made non-destructively in engineering components, such as weldments, pipes, rails, bent plates, turbine blades and turbine discs. The technique can be used to evaluate manufacturing processes such as heat treatment, surface modification, forging, straightening and welding. Data are obtained for a wide variety of materials, including steel, aluminum, titanium, zirconium, nickel-based alloys, ceramics and composites. Typically measurements are made in volume elements of order 1 mm³ (but both larger and smaller volume elements have been successfully applied), with typical precisions of ±10 to ±20 MPa.

Crystallographic Texture

Quantitative analysis of the preferred orientations of crystallites is performed to characterize processes that lead to materials with directionally-enhanced properties, such as corrosion resistance, yield strength, creep resistance, elastic stiffness and thermal expansion. Data are obtained for a wide variety of materials, including steel, aluminum, titanium, zirconium, nickel-based alloys, ceramics and composites.

Intergranular Stress Analysis

Polycrystalline materials exhibit constraints amongst neighbouring grains due to directional differences in thermal-expansion, plastic deformation or elastic properties. Thermal and mechanical treatments of materials generate intergranular stresses that may be beneficial or detrimental. Neutron diffraction provides that best method to measure stresses in a minority phase embedded in a matrix. The (hkl)-dependence of residual stresses after plastic deformation or heat-treatment of monolithic materials can also be investigated.

Phase Transitions

Neutron diffraction patterns provide a tool to map out phase diagrams in materials, with straightforward control of environmental parameters such as temperature (270°C to 2000°C), magnetic field (to 9T), pressure (to 3 GPa), atmosphere (oxygen, nitrogen, inert gases, vacuum) and humidity. Phases are identified by characteristic diffraction peaks whose intensities are linked to the state of the material, such as volume fraction of each phase, structure factors of each phase, magnetization, ordering of alloys, etc.

Volume Fraction Analysis

Neutron diffraction patterns are analyzed to determine the volume fractions of components in composite materials, such as graded ceramics, metal-matrix composites and precipitates in alloys. Volume fractions as low as 0.1% can be measured. Data can be acquired as a volume-average of bulk material, or as a non-destructive spatial scan of the interior of a component.

Time-resolved diffraction:

Complete neutron diffraction patterns are acquired as a function of time to investigate the kinetics of processes in engineering materials, such as the growth of precipitates in heat-treated alloys, formation of scale at high temperature and reactions of phases in composites. In vibrating or rotating components, the neutron diffraction pattern can be gated to investigate the response of the material at particular points in each cycle. In some cases the time dependence of strain can also be measured.

Related Information

Read more about Materials Science and Engineering:

Applied Neutron Diffraction for Industry [service]

Applied Neutron Diffraction for Industry [news article]

Innovative Alloys for Autos [news article]

Near-Surface Stress Mapping

Non-destructive Stress Mapping

Institutes:

• NRC Canadian Neutron Beam Centre