Residual stress distribution in electron beam-physical vapor deposited ZrO 2 thermal barrier coating layer by raman spec
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dilatantcy with inelastic strain. Some materials that exhibit pressure-dependent flow behavior and a SD have been shown to exhibit strain-induced dilatant behavior.[8,15,21] A number of other mechanisms (e.g., microcracks, residual stresses, internal Bauschinger effects, nonlinear elastic interactions, deformation twinning, interface decohesion at particle/matrix interfaces, and stress interaction with precipitates) could contribute to a SD.[5,7,9,22,23] Theories such as the internal Bauschinger effect and microcracking indicate that the SD will increase with increasing inelastic strain, which was not observed presently. Interface decohesion between the precipitates and the matrix is not likely as these platelets remain coherent to large strains. Furthermore, there is no significant difference between the elastic moduli in tension and compression[1] and the SD persists at strains beyond 2 pct, where the inelastic strains are dominant and nonlinear elastic interactions are negligible. Potential source(s) that require further investigation relate to particle-dislocation interactions and twinning. It is possible that the interaction between coherency strain fields around the particles and the dislocations is different in tension and compression. Deformation twinning has also been observed in IN 718 for high-temperature fatigue[24] and in room-temperature tensile deformation[25] for IN 718 with precipitate sizes that are larger than those in the presently tested alloy. Twinning could contribute to a SD, although one might also expect some pressure dependence to the flow. In the present work, flow in IN 718 appears to be independent of hydrostatic pressure, suggesting that this invariant may be removed from any phenomenological constitutive models under development for this material. Alternate sources of the SD are under investigation. Experimental support was by NASA Glenn Research Center Grant No. NCC3-464 and Reference Metals Company. Equipment support provided by NSF-DMR-PYI-89-58326 and DARPA-ONR-N00013-86-K-0777. The donation by O. Richmond of an oil-based high-pressure apparatus and the compression test fixtures is gratefully acknowledged. REFERENCES 1. C.M. Gil, C.J. Lissenden, and B.A. Lerch: J. Testing Eval., 1999, vol. 27, (5) pp. 327-36. 2. P.W. Bridgman: Studies in Large Plastic Flow and Fracture, McGrawHill, New York, NY, 1952. 3. J.J. Lewandowski and Lowhaphandu: Int. Mater. Rev. 1998, vol. 43 (4), pp. 145-87. 4. W.C. Leslie Sober P.: Trans. ASM, 1967, vol. 60 (3), pp. 459-83. 5. D. Kalish and M.R.J. Cohen: Trans. ASM, 1969, vol. 62 (2), pp. 353-61. 6. G.C. Rauch and W.C. Leslie: Metall. Trans., 1972, vol. 3 (2), pp. 373-85. 7. R. Chait: Scripta Metall., 1973, vol. 7 (4), pp. 351-54. 8. W.A. Spitzig and O. Richmond: Acta Metall., 1984, vol. 32 (3), pp. 457-63. 9. J.P. Hirth and M. Cohen: Metall. Trans., 1970, vol. 1, pp. 3-8. 10. D.C. Drucker: Proc 1st U.S. Nat. Congr. Applied Mechanics (ASME), 1951, pp. 487-91. 11. H.L.I.D. Pugh: Mechanical Behaviour of Materials under
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