Point Defects in Materials Part I: Behavior and Characteristics in Different Material Classes
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y by a monovacancy mechanism since the enthalpy of formation of a selfinterstitial atbm, the [100] split form, also called the dumbbell form, is too large to be compatible with the activation enthalpy for self-diffusion in copper. It is now well established that the latter is given by the sum of the enthalpy of formation and the enthalpy of migration of a monovacancy in many face-centered-cubic (fec), bodycentered-cubic (bec), and hexagonal-closepacked (hep) metals. Huntington empriasizes the importance of the now classic Kirkendall marker experiments (1947) in demonstrating that neither the direct interchange nor Zener's ring mechanism (1950) is consistent with a Kirkendall marker shift; the markers always move into the side rich in the faster diffusing élément with a displacement proportional to the square root of the time. He also points out that the classic quenching and annealing experiments, pioneered by Kaufman and Koehler (1952,1955), yield both the enthalpy of formation and the enthalpy of migration of a monovacancy, though under nonequilibrium conditions, and that the sum of thèse two enthalpies is equal to the activation energy for selfdiffusion, as measured by the radioactive tracer technique, in pure gold. Huntington discusses the élégant experiments pioneered by Simmons and Balluffi
(1960 to 1963) on the fec metals aluminum, copper, gold, and silver. The SimmonsBalluffi experiment yields the fractional net change in the point defect population under thermodynamic equilibrium conditions, and simultaneously demonstrates— without any assumptions —which point defect is the dominant one. For thèse fec metals, the Simmons-Balluffi experiment demonstrated conclusively that the vacancy is the dominant point defect at elevated températures, thus proving that vacancies médiate self-diffusion in thèse metals. Huntington further discusses substitutional impurity diffusion in metals, and reviews the séminal contributions of Lazurus (1954) and LeClaire (1962, 1964) to our physical understanding of this problem. Historically, radiation damage produced by energetic particle bombardment (fast neutrons, deuterons, or 1 MeV électrons) was used to create Frenkel pairs (a vacancy plus a self-interstitial atom) in order to generate self-interstitial atoms in sufficient concentrations to study them. Electronirradiation experiments (Meecham and Brinkman in 1954, Corbett, Smith and Walker in 1959, and Sosin and Brinkman in 1960) at 4.2 K demonstrated that the radiation damage produced at this température was much greater than the damage produced at room température, and upon subséquent annealing of a spécimen irradiated at 4.2 K, the amount of recovery was extensive. A séminal model developed by Corbett, Smith and Walker (1959) — and presently called the one-interstitial model—attributes the low température (or Stage I) recovery behavior to the [100] split or dumbbell self-interstitial and Stage III recovery to the monovacancy in fec metals. A great deal of research since the mid1960s has vindicated this model in the fec and b
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