Particle size and orientation effects on softening in a cu matrix containing rod-shaped iron particles
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INTRODUCTION
THEannealing behavior of dispersion hardened alloys after small prestrains, a topic of some practical importance, has been the subject of numerous theoretical and experimental studies. Softening is best considered in terms of an Orowan loop pipe diffusion mechanism. 1-4 For spherical particles this leads to an a-4 dependence of the softening rate, where t~ is the particle radius. For non-spherical particles the same dimensionality must be maintained but the quantity(ies) to be used in place of the particle radius will, in general, be a function of both the particle shape and orientation. Okabe and M o r i 4 have treated this problem theoretically for rodshaped particles. However, as the Cu-mullite alloy used in the experimental portion of their study contained essentially randomly oriented particles, they were unable to confirm the predicted dependence on rod orientation experimentally. a Fe particles are not, of course, truly "non-deformable" in the sense that many oxides are. However, for small strains, both linear work hardening and ct-4 softening kinetics are observed in Cu-aFe alloys: Further, although Orowan loops are not imaged on TEM micrographs of deformed Cu-ctFe specimens, the presence of the loops may be inferred from the appearance and annealing behavior of the Moir6 fringes. 6 This is evidence that discrete Orowan loops do exist but that they tightly wrap the particles and remain at the particle-matrix interface (a supposition also supported by the variation in pipe diffusion activation energy with particle speciesS). Thus, provided we restrict ourselves to small prestrains, the Orowan loop pipe diffusion model should be applicable to softening of Cu-ctFe alloys. We have found that rod-shaped a-Fe particles may be produced in a Cu-Fe alloy by simple thermomechanical treatments. Further, as a result of the initial KurdjumovSachs orientation relationship between the Cu and a-Fe phases (in which an Fe [111] direction aligns with a Cu matrix [110] directionr), these rods are oriented primarily along one, of the six possible, (110) directions in the matrix. Hence by appropriate cutting of tensile specimens to activate various slip systems, the particle axis/slip system orientation relationship can be altered in a controlled manner. Four P.D. FUNKENBUSCH, formerly Visiting Scholar, Department of Materials Science and Engineering, Tokyo Institute of Technology, is Assistant Professor, Department of Mechanical Engineering, University of Rochester, Rochester, NY 14627. T. MORI is Professor, Department of Materials Science and Engineering, Tokyo Institute of Technology, Nagatsuta, Midori-ku, Yokohama, ]apan. Manuscript submitted November 1, 1985, METALLURGICALTRANSACTIONSA
distinct orientation relationships are thus possible and we will designate them as follows: orientation A, 0 = 90 deg and 4' = 0 deg; B, 0 = 90 deg and 4' = 60 deg; C, 0 = 35 deg and 4' = 90 deg; and D, 0 = 35 deg and 4' = 60 deg. Here 0 and 4' are the angles between the particle axis and the slip plane normal and slip dire
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