时效硬化

Dislocation-Precipitate Interaction: Bowing of Dislocation Orowan Strengthening Mechanism
(a) The Orowan model. (After E. Orowan, in Internal Stresses in Metals and Alloys (London: Institute of Metals, 1948), p. 451.) (b) Obstruction of dislocation motion by uniformly distributed nonshearing particles in an aluminum alloy (transmission electron microscope) (Courtesy of M. V. Heimendahl.)‫‏‬
Reloading Effect: Formation of Well-Defined Yield Point
Reloading curves after stopping a test for three hours at nominal strains of 0.08, 0.18, and 0.27. The dashed lines indicate the stresses at which the test was stopped. Note the formation of a well-defined yield point in the three cases (Reprinted with permission from M. A. Meyers and J.‫‏‬R.‫‏‬C.‫‏‬Guimar˜aes,‫‏‬Metalurgia – ABM, 34 (1978) 707.)‫‏‬
Βιβλιοθήκη Baidu
Phase Diagrams showing Precipitation Hardening
(a) Phase diagram of the Al-rich end of the Al–Cu system. (b) Phase diagram of the Al-rich end of Al–Li system.
Yield Strength vs. Temperature for Superalloys and TD Nickel
Comparison of yield strength of dispersion-hardened thoria-dispersed (TD) nickel with two nickel-based superalloys strengthened by precipitates (IN-792) and directionally solidified (DS) MAR M 200.
Precipitate-free Zone (top) and Spinodal Decomposition (bottom)
(a) Al–Zn–Mg alloy showing precipitate-free zone along grain boundaries. (b)‫‏‬ Spinodally decomposed Cu–Ni–Fe alloy resulting from aging within the ternary miscibility gap. The light phase is Cu rich, the dark phase, Ni–Fe rich. (Courtesy of G. Thomas.)‫‏‬
Chapter 10 Solid Solution, Precipitation, and Dispersion Strengthening
Forms of Solid Solution
The two basic forms of solid solutions. (a) Substitutional solid solution of zinc in copper to form brass. (b) Interstitial solid solution of carbon in iron to form steel. The interstitial solid-solution carbon atoms are shown in the face-centered cubic form of iron.
Strain Ageing
Dependence of yield stress and ultimate tensile stress on temperature for Inconel 600, a nickel-based superalloy. The hump in the curve due to dynamic strain aging is usually evident only at large strains. (After R. A. Mulford and U. F. Kocks, Acta Met., 27 (1979) 1125.)‫‏‬
Hardness vs. Ageing Temperature in Al-Cu Alloy
Change in hardness with time of various Al–Cu alloys aged at 130 ◦C. (Adapted with permission from H. K. Hardy and T. J. Heal, Prog. Metal Phy., 5 (1954)‫‏‬ 195.)‫‏‬
Precipitation and Dispersion-Hardening
(a) θ precipitates (at grain boundaries) and θ precipitates (in grain interior) in Al–Cu alloy. (Courtesy of K. S. Vecchio.) (b) Al3Li precipitates in Al–Li alloy (TEM, dark field). (Courtesy of K. S. Vecchio.) (c) γ precipitates and aged carbides in a superalloy. (Courtesy of R. N. Orava.)‫‏‬
(a) Schematic stress–strain curve of an annealed low-carbon steel showing the yield-point phenomenon. (b)‫‏‬ Low-carbon steel in a temper-rolled condition and annealed for one hour between 100 ◦C and 34.3 ◦C). (Courtesy of R. Foley.)‫‏‬
Solid Solution Strengthening
(a) Increase in strength, σ, of steel as a function of content of solute. The solid lines represent substitutional solute additions, while the dashed line represents interstitial solute additions. (After F. B. Pickering and T. Gladman, ISI Special Report 81, Iron and Steel Inst., (London: 1963), p. 10). (b) Increase in strength of sapphire (monocrystalline alumina) with small additions of chromium at 1400 ◦C (Adapted from K. P. D. Lagerlof, B. J. Pletka, T. E. Mitchell, and A. H. Heuer, Radiation Effects, 74 (1983) 87.)‫‏‬
Cottrell Atmosphere in Iron
Cottrell atmosphere in iron consisting of an edge dislocation and a row of carbon atoms.
Luders Band Propagation
Propagation of L¨uders band in a tensile sample. v1 and v2 are the velocities of deformation of the specimen and the L¨uders band, respectively.
Serrated Flow: Portevin-La Chatelier Effect
Serrated flow observed in tensile test performed at 650 ◦C in Inconel 718 (a nickel–iron-based superalloy)‫‏‬ solubilized at two temperatures. The undeformed, cold-rolled (19.1% reduction) and shock-loaded (51 GPa peak pressure) conditions are shown. (From M. A. Meyers, Ph.D. dissertation, 1974.)‫‏‬
Different Crystallographic Relationships Between Matrix and Second Phase
Different crystallographic relationships between matrix and second phase. (a) Complete coherency. (b) Coherency with strained, but continuous, lattice planes across the boundary. (c) Semicoherent, partial continuity of lattice planes across the interface. (d) Incoherent equilibrium precipitate, θ; no continuity of lattice planes across the interface.
Interfacial Dislocations at Precipitate
Interfacial dislocations formed in a semicoherent precipitate. (From G. C. Weatherly and R. B. Nicholson, Phil. Mag., 17 (1968), 801.)‫‏‬
Positions of Interstitial Atoms in the Cubic Lattice
(a) Positions of interstitial atoms in the cube. (b)‫‏‬ Carbon atom shown as a producer of a tetragonal distortion.
Elastic Interactions
(r, θ)-coordinates of a solute atom in the strain field of an edge dislocation.
Mechanical Effect Associated with Solid Solutions: Yield Point Formation