The effect of prior deformation on spinodal age hardening in Cu-15 Ni-8 Sn alloy
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1.0 INTRODUCTION
AGE hardening in Cu-Ni-Sn alloys has been the subject of several recent studies in which a metastable modulated structure produced by aging has been shown to give a significant strengthening effect. 1"3In the Cu-15 Ni-8 Sn alloy the modulated structure can be produced by aging at temperatures below 723 K. 4 A yield strength increase of up to 450 MPa occurs with the modulated structure formation where the modulation wavelength lies between 3.5 and l0 nm. The moduated structure is subsequently replaced by a discontinuous cellular transformation which originates at grain boundaries and in highly deformed regions. A survey of these transformations, as well as a correlation between modulation wavelength and yield-strength, can be found in Ref. 4. The details of these transformation processes affect the mechanical property response of the alloy during age hardening. Since prior cold rolling is used to attain higher strength, it is important to understand the effect of deformation on structure development. In the present paper, further details on the modulated structure and its development with time, temperature and prior deformation are given. The effects of deformation on the development of modulated structure and tin-rich phase ordering are assessed. 2.0 EXPERIMENTAL PROCEDURES 2.1 Material The alloy was produced and processed commercially in two lots whose compositions are given in Table I. The material in Lot No. 1 was provided in the form of rectangular stock which was cold-rolled by 50 pet to a thickness of 2.9 mm (0.114 in.). It was solution annealed
STEPHEN SPOONER is Professor of Metallurgy, Metallurgy Program, Georgia Institute of Technology, Atlanta, GA 30332, and BRUCE G. LEFEVRE is Member of Technical Staff, Bell Laboratories, 2000 N.E. Expressway, Norcross, GA 30071. Manuscript submitted July 20, 1979.
and recrystallized at 875 ~ for 1 h and water quenched. Most of the material was then cold-rolled to produce stock having 20, 40, 60 and 80 pet reduction. The material of Lot No. 2 was provided as cold-rolled strip which was solution heat-treated for 1 h, water quenched and cold-rolled 78 pct to a thickness of 0.64 mm (0.025 in.). This material was either aged directly or resolution heat-treated and aged.
2.2 Transmission Electron Microscopy Transmission electron microscopy (TEM) and selected area diffraction (SAD) were used to characterize the morphology and precipitated phase structure in aged material which were either undeformed or deformed prior to aging. A JEOL 100C equipped with a high-angle, double-tilt metallurgical stage were used in this investigation. Alloy foils were punched and then prepared by electropolishing with refrigerated methanol--33 pct nitric acid solution.
2.3 X-Ray Diffraction A G E XRD-5 diffractometer equipped with a doubly bent LiF monochromator5 was used to record sideband intensity profiles associated with the (200} and (220} Bragg reflections. All X-ray samples were wet polished with abrasive papers down to 600 grit and then macroetched with a concentrated
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