Tea-Sung Jun

Residual stress characterization in 12%-Cr steel friction stir welds by neutron diffraction

In the present paper we report the results of a study into friction stir welds made in 12.7 mm-thick 12%-Cr steel plates. Residual stress measurements were performed using angle-dispersive neutron diffraction. Complete characterization of the three-dimensional residual stress state in friction stir weld samples was obtained by analysing diffracted peaks; peak broadening for identifying the regions of severe plastic deformation and the associated residual strain (eigenstrain) acting as the source of residual stress and peak shifting for evaluating residual elastic strains in the welded component. Three different methods were used to address the key issue of determining the d0 variation across the weld. The comb (or matchstick) method was compared with two other approaches: the balance method, and the zero traction method. It was found that a combination of the comb and the zero traction methods allows reliable residual strain/stress distributions.

Analysis of Preferred Orientations in Linear Friction Welded (LFW) Aluminium Alloy Specimens using “One-shot” Multi-element Energy Dispersive Synchrotron X-ray Diffraction

pole figures obtained after ODF calculation were obtained. These are presented and discussed. The results show that the thermalmechanical processes that occur during the LFW process lead to significant modification of the orientation distribution, but cause only moderate changes in the texture index.

S201 INVITED—A STUDY OF RESIDUAL STRESSES IN VACUUM PLASMA SPRAYED TUNGSTEN COATINGS

Thick tungsten coatings are potential plasma facing materials in fusion reactors but the coefficient of thermal expansion (CTE) mismatch between W and Cu or steel substrates leads to large thermally induced stresses and premature failure. While inter-layers can be used to grade and distribute stresses away from a discrete planar tungsten-steel interface, in the present study an alternative approach was used based on patterning of the interface with repeating mm-scale 3D features or “sculptures”. Up to 2mm thick W coatings were manufactured directly on water-cooled patterned substrates using vacuum plasma spraying (VPS), without any inter-layers. Synchrotron-based white beam, high energy Xray diffraction measurements [1] of lattice parameters was used to obtain maps of residual strains and stresses in the VPS tungsten. Residual elastic lattice strains were deduced from energy-dispersive diffraction profiles collected by two detectors mounted in the horizontal and vertical diffraction planes, providing information about lattice strains in two nearly perpendicular directions lying in the plane of the coating. On the basis of these data, maps of residual stresses in the VPS coatings were constructed. The findings are discussed in the context of the geometry of the substrate-coating interface and any inelastic processes operating to relieve and manage successfully the thermal expansion mismatch induced stresses.

High energy white beam x-ray diffraction studies of residual strains in engineering components

In order to predict the durability of engineering components and improve performance, it is mandatory to understand residual stresses. The last decade has witnessed a significant increase of residual stress evaluation using diffraction of penetrating radiation, such as neutrons or high energy X‐rays. They provide a powerful non‐destructive method for determining the level of residual stresses in engineering components through precise characterisation of interplanar crystal lattice spacing. The unique non‐destructive nature of these measurement techniques is particularly beneficial in the context of engineering design, since it allows the evaluation of a variety of structural and deformational parameters inside real components without material removal, or at worst with minimal interference. However, while most real engineering components have complex shape and are often large in size, leading to measurement and interpretation difficulties, since experimental facilities usually have limited space for mounting the sample, limited sample travel range, limited loading capacity of the sample positioning system, etc. Consequently, samples often have to be sectioned, requiring appropriate corrections on measured data; or facilities must be improved. Our research group has contributed to the development of engineering applications of high‐energy X‐ray diffraction methods for residual stress evaluation, both at synchrotron sources and in the lab setting, including multiple detector setup, large engineering component manipulation and measurement at the UK Synchrotron Radiation Source (SRS Daresbury), and in our lab at Oxford. A nickel base superalloy combustion casing and a large MIG welded Al alloy plate were successfully studied.In order to predict the durability of engineering components and improve performance, it is mandatory to understand residual stresses. The last decade has witnessed a significant increase of residual stress evaluation using diffraction of penetrating radiation, such as neutrons or high energy X‐rays. They provide a powerful non‐destructive method for determining the level of residual stresses in engineering components through precise characterisation of interplanar crystal lattice spacing. The unique non‐destructive nature of these measurement techniques is particularly beneficial in the context of engineering design, since it allows the evaluation of a variety of structural and deformational parameters inside real components without material removal, or at worst with minimal interference. However, while most real engineering components have complex shape and are often large in size, leading to measurement and interpretation difficulties, since experimental facilities usually have limited space for mounti...