On microscopic plastic instabilities in metal machining chips
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Aluminum At. Pct 2 4 6 8 Avg.(Ref. 2)
D Wt Pct
cm2/sec • 10+9
0.93 1.88 2.85 3.84
1.2 1.5 1.5 t.1 0.3
t h e r e f o r e , a s i m i l a r r e l a t i o n s h i p e x i s t s b e t w e e n RAI(X) and c o n c e n t r a t i o n . T h e diffusion p r o f i l e f o r the N i - 4 . 8 A I : T D - N i is r e plotted in Fig. 4 where changes in molar volume with composition are taken into account by expressing concentration of aluminum in moles per cu cm with aid of the lattice parameter data from PearsonJ From this profile the interdiffusion coefficient, /~, was calculated as a function of composition by application of the standard Boltzman-Matano analysis. The results of these calculations are shown in Table II for selected concentration; the averaged/~ obtained by extrapolation of data in Ref. 2 is also given in this table. 1. J. D. Whittenberger:Diffusion in Thoriated and Nonthoriated Ni and Ni-Cr Alloys at 1260~ NASA TN D-6797. 2. M. M. P. Jansen and G. D. Rieck: Trans. TMS-AIME, 1967, vol. 239, pp. 137285. 3. W. B. Pearson:A Handbook of Lattice Spacings and Structures of Metals and Alloys, p. 378, Pergamon Press Inc., New York, 1958.
On Microscopic Plastic Instabilities in Metal Machining Chips J. TEMPLE
BLACK
SINCE the original papers by Zener and Holloman ~ and Zener, 2 the adiabatic shear phenomena has been repeatedly proposed in the literature 3-5 as the failure mechanism in large strain, high strain rate modes of plastic deformation. It has been proposed that at high strain rates, a marked temperature rise can occur in a localized region due to adiabatic heating. This localized heating softens the metal so that additional plastic deformation is concentrated on macrescopieally well-defined planes and a shear type failure occurs. While an increase in hardness has been noted in the shear zones, it is difficult to obtain information on the resultant defect structures of the shear zones which can, in turn, be related to the deformation process and it has therefore, been difficult to postulate theoretical models to describe this phenomena. The purpose of this note is to point out that the chips J. TEMPLE BLACK is Assistant Professor, Mechanical Engineering Department, University of Vermont, Burlington, Vt. until June 1, 1972. After July 1, 1972, he will be Associate Professor of Industrial Engineering, Univ. of Rhode Island, Kingston, R. I. Manuscript submitted November 22, 1971. 2012-VOLUME 3, JULY 1972
Fig. 1--SEM micrograph of the top surface of a chip machined by orthogonal cutting conditions. The material is electrolytic tough pitch copper, chip thickness 40pm, cut at 200 SPM with a 6 deg rake, high speed steel tool. The average lamella (L) width is 2pro. Flow around second phase particles (P) and cross slip (CS) is observed. The shear fronts (SF) lie perpendicular to the tooling marks (TM) placed in the material during the previous pass of the tool over the workpiece. Marker = 10pm. p r o d u c e d by the m e t a l cutting mode of p l a s t i c d e f o r m a tion u n d e r g o a p l a s t i c i n s t a b
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