Turbine and compressor wheels and buckets in gas power plants that are typically used like peak-plants are running under high temperature and high mechanical strain. A wheel of the axial compressor of a heavy duty gas turbine was considered for Residual Stresses determination by Neutron Diffraction and for a SANS investigation of nanostructures in correspondence of specific positions individualized from a precedent FEM analysis, to perform comparative studies of the expected changes of the precipitate distribution with the results of the Residual Stresses investigation.
Constitutive material: NiCrMoV steel (with reference to the ASTM A 471- type 2 norms), usually adopted in the manufacturing of forged components for gas turbines. Exercise temperature: ≤300°C.

Residual Stresses determination by Neutron Diffraction
• Measurements performed along radial, hoop and axial directions of each considered point - reference to Fe (110)
• Adopted incident beam size = 4 x 5 mm2; Diffracted beam size 5 x 6 mm2; Wavelength λ = 5.14 Å; Interplanar distance d0 = 3.58687 Å, calculated by measuring a powder obtained from standard reference material
Results:
• Hoop RS, in general, higher than radial ones, and in the range ~ 50÷200 MPa, reaching their max value in the location 19 (σ19hoop = 190,7 MPa).
• Radial RS in the range ~ 10÷130 MPa, showing their max value in the same location 19 (σ19rad = 128,7 MPa) and their min. values in the contiguous locations 3, 6 and 26. RS firstly due to the manufacturing process, and changed, successively, by the operating cycles fatigue and thermal effects.
• Both consequences, including the Δσ between different locations, can represent a life-time limiting factor.
• Publications: M. Rogante, G. Török, G. F. Ceschini, L. Tognarelli, I. Füzesy, L. Rosta, Physica B: Condensed Matter, 350/1-3S (2004) pp. E479-E481; M. Rogante, in: Proc. 1st Italian Workshop for Industry: Applicazioni Industriali delle Tecniche Neutroniche® - AITN 2008, Rogante Engineering (Ed.), Civitanova Marche, Italy (2008), pp. 40-120.

SANS investigation
Used range of momentum transfer: q = (4p×/l)sin(q/2) = 0.01-0.1 Å-1 corresponding a usual scale of precipitates r~1/q~10-100 Å.
Results:
• The material possesses an isotropic nanostructure composed of: tiny domains (precipitates, diameter ~ 200-300 Å); concentration N»(1-3)×1014 cm-3; volume fraction j » 0.1-0.2 %; total area of interface St » 0.2-0.4 m2.
• The SANS-data testify the material having a low concentration of nano-defects, as compared to steels after thermal treatment, where an intense formation is induced of precipitates which volume fraction exceeded ~ 1 %.
• Publication: M. Rogante, G. F. Ceschini, L. Tognarelli, E. Rétfalvi, V. T. Lebedev, J. Mat. & Design, 26/3 (2005) 191-195; M. Rogante, in: Proc. 1st Italian Workshop for Industry: Applicazioni Industriali delle Tecniche Neutroniche® - AITN 2008, Rogante Engineering (Ed.), Civitanova Marche, Italy (2008), pp. 40-120.

NMI3 project
RII3-CT-2003-505925

Keywords Material Sciences