Neutron diffraction measurements of intergranular strains in MONEL-400
- PDF / 539,246 Bytes
- 12 Pages / 612 x 792 pts (letter) Page_size
- 52 Downloads / 226 Views
INTRODUCTION
MEASUREMENTS of residual stress by diffraction methods are of high value to the engineer, since they avoid destructive methods of stress analysis in expensive components. Neutron diffraction, in particular, permits the measurement of stress at depth by virtue of the high penetration of thermal neutrons through most engineering materials. Diffraction methods are not without uncertainties in interpretation, which arise from the fact that plastic deformation in metals is anisotropic. Thus, a given crystal orientation will deform by different amounts depending, in a discontinuous way, on the angle the orientation makes with the stress axis. Similarly, different crystallographic orientations ([h, k, l], where h, k, and l are Miller indices) in a polycrystalline aggregate aligned parallel to the stress axis undergo different plastic deformations. The former case gives rise to deviations from linear behavior of strain with sin2 c (for example, Reference 1) where c is the deviation from normal incidence on the surface. The latter gives rise to differences in strains and stresses obtained with different crystal reflections. Measurements of residual strains in bent INCOLOY 800 steam generator tubes[2] gave a clear example of this effect. Similar behavior is shown for bent MONEL* 400 steam *INCOLOY and MONEL are trademarks of INCO Alloys International, Huntington, WV.
generator tubing in Figure 1. The (002) reflection gives strains which are twice as large as those for (111) in the region close to the neutral axis of the bent tube. The strains near the top of the bent tube are tensile for (002) and compressive for (111). A naive interpretation of the results would suggest that the uniaxial stress field is tensile for (002) and compressive for (111), which is an absurd conclusion. The present measurements were, therefore, undertaken to clarify the character of the measured stresses in MONEL-400 tubing
T.M. HOLDEN, formerly Senior Research Officer with AECL, Chalk River Laboratories, is Senior Research Officer, Steacie Institute for Molecular Science, Neutron Program for Materials Research, Chalk River, ON, Canada K0J 1J0. A.P. CLARKE, Systems Researcher, is with Microsoft Inc., Seattle, WA 98052. R.A. HOLT, Program Manager, is with Reactor Materials Research, AECL, Chalk River Laboratories, Chalk River, ON, Canada K0J 1J0. Manuscript submitted August 7, 1996. METALLURGICAL AND MATERIALS TRANSACTIONS A
and to permit a consistent analysis to be made of the data. This article reports neutron diffraction measurements of the evolution of lattice strain in the face-centered cubic (fcc) CuNi alloy MONEL-400 during in situ tensile testing. The lattice parameter measurements give the lattice strain response to the externally applied stress field for different crystal orientations in the elastic regime, i.e., the diffraction elastic constants, which may be critically compared with theoretical models. More important however, the deviations from linearity of the lattice strain response above the yield point give the interg
Data Loading...
