Residual Stresses Assessment in Coated Materials: Complementarity between Neutron and X-Ray Techniques

Abstract

The residual stress (RS) status induced in the substrate of coated materials by the coating process plays frequently a major role in lending the component’s characteristics. RS assessment can give, thus, a substantial contribution in justifying different cases of failure or else bad performance of coated components due to e.g. the coating delamination or to other occurrences which are not simply interpretable via the conventional mechanical tests or microstructure analyses. The adoption of both neutron diffraction (ND) and X-ray diffraction (XRD) techniques has revealed its usefulness in assessing the RS values in proximity of the coating interface area, respectively, without any layer removal or hole drilling at the extreme surface. In this paper, some real cases of RS determination in coated materials by using these techniques and exploiting their complementarity are described. ND, in particular, is very suitable for crucial applications, where a much different stress situation than that assessed by XRD could be present at some depth below the surface. The results achieved can yield trends adoptable in monitoring of the coating features.

Feasibility Study for Neutron Beam Investigation of the Turin Shroud

“…X-ray diffraction and ND have already shown their complementarity in a variety of cases, e.g. see [45]. Among the various complementarities, hydrogen scattering can be highlighted: it is rather weak for X-rays, while it is strong for neutrons.…”

Residual stress determination by neutron diffraction in a car gear-shaft made of 20NiCrMo2 alloyed case hardening steel

“…In the case of RS measurements the main advantage of ND over other methods is that they can provide required information in the range of the depth from several tenths of millimetres up to several centimetres. As the XRD technique, in fact, according to the atomic number of the investigated material allows measuring surface RS only to a depth of several tens of micrometres both non-destructive diffraction methods can supplement each other when permitting RS investigations from the extreme surface to deep without any layer removal or hole drilling [14].…”

Nanostructural Investigation of Case Hardened Steels for Speed Gears Applications by Small-Angle Neutron Scattering (SANS)

“…Consequently, further complementary investigation techniques are suggested. The results obtained by adopting neutron techniques in materials characterization have often proved their strong support for better understanding of material characteristics and behaviour [2][3][4]. SANS, in particular, provides key data to complement the analytical and crystallographic information, which are crucial to comprehend the structural basis for the chemical and physical properties of materials.…”