Nature of negative microplastic deformation in alloys

Autor: V. I. Ivantsov, L. S. Palatnik, Ya. I. Kagan, N. B. Fat'yanova, I. I. Papirov
Rok vydání: 1985
Předmět:
Zdroj: Metal Science and Heat Treatment. 27:450-453
ISSN: 1573-8973
0026-0673
DOI: 10.1007/bf00693287
Popis: According to data of [I], these deformations are associated with structural features of the surface layer in which, after tensile loading, compressive stresses may be induced in consequence of the difference between the properties of the surface and of the base material. The object of the present work is to investigate the microplastic deformation of the corrosion resistant aging alloy 40KhNYu (39-41% Cr; 3.3-3.8% AI;~0.03% C; 0.1% Si and Mn each;~0.6% Fe;~0.02% S;~0.01% P; base nickel) and the physical nature of negative microdeformation when this alloy is subjected to tensile loading. Table 1 presents the mechanical properties of specimens after heat treatment under various conditions. The authors of [5] studied the structure and physical properties of the alloy 40KhNYu after various kinds of heat treatment. After quenching at !150°C (holding for 0.5 h) the microstructure of the alloy is homogeneous and consists of large grains of "quasiequilibrium" supersaturated y1-solid solution on the basis of nickel (ax~ = 0.36 nm). In the process of tempering of the alloy we observe the disintegration of the y~-solution, and at the same time y2-solid solution depleted of alloying elements (ay2 = 0.357 nm), a-phase on the basis of chromium (a a = 0.288 nm), and y'-phase (Ni3AI, ay~ = 0.356 nm) form. With the aid of precision dilatometry it was discovered [5] that the process of aging of the Ni--Cr-AI alloy is steplike and proceeds in two stages: l) the diffusion stage of redistribution of the alloying elements in the lattice of the supersaturated y1-solid solution (its partial ordering); 2) the jumplike disintegration YI ÷ Y~ + ~' + a by diffusionless rearrangement of the crystal ~-lattice in the regions of its partial ordering. The greatest change in volume during the aging process was estimated in specimen 3 of alloy 40KhNYu with practically completely disintegrating ~1-phase. From the data of x-ray crystallographic analysis it may be concluded that the a-phase separated out when the aging process ended (volumetric proportion y~ = 23%); aluminum separated out practically completely in the form of X'-compound [8, p. 136] with yy, ~ 24%. The relative change of volume of specimen 3 of alloy 40KhNYu as a result of the complete disintegration of supersaturated y~solid solution in aging is AV/V~ ~ -1.4%. The corresponding irreversible reduction in length of the specimen in the process of dilatometric investigation is Al/1 = -0.44%, and the change in volume is AV/VxI = 3&l/1 -1.32%, which is in agreement with the data of x-ray crystallographic analysis. The microplasticity of the alloy 40KhNYu was investigated by the method of mechanostatic hysteresis using resistance strain gauges for measuring stresses and deformations [6]. We determined the following characteristics of the materials: the microelastic limit OE, the
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