H. E. Kissinger

Amorphous phase formation in irradiated intermetallic compounds

Abstract A variety of intermetallic compounds have been irradiated with high energy ions to determine the criteria for an amorphous transformation. Those compounds with limited compositional range or solubility tend to become amorphous during irradiation, whereas those compounds with wide solubility tend to remain crystalline. This solubility criterion is consistent with the concept that a critical defect density which will result in a greater free energy of the crystal phase than the free energy of the amorphous phase is necessary for the amorphous transformation. This critical defect density is lower in those compounds that become amorphous. The ionicity criterion of Naguib and Kelly does not work for these intermetallic compounds, but the temperature criterion is probably valid and is, in fact, directly related to the proposed solubility criterion.

Production of voids in nickel with high energy selenium ions

Abstract Irradiation of high purity (99.9 wt %) nickel at 525 °C with 6 to 11 MeV selenium ions produced voids in the metal. In general, the size and number density of the voids increased with displacement damage up to approximately 50 displacements per atom (dpa). Irradiation to higher displacement densities caused a slight reduction in the average size and a continued increase in the number density of voids. The resultant swelling was found to increase as the 1.45 power of the displaced atom density until approximately 50 dpa. The volume change appears to saturate at approximately 4–5% in the 100–400 dpa range. A face centered cubic superlattice of voids was discovered in nickel which had been irradiated to 400 dpa.

MICROSTRUCTURAL ANALYSIS OF NEUTRON-IRRADIATED TITANIUM AND RHENIUM.

Abstract The defect structure in α-titanium and rhenium irradiated with neutrons at 0.4T m (T m = absolute melting temperature) has been analyzed using transmission electron microscopy. In rhenium, the vacancies agglomerate into voids whereas in titanium, vacancy dislocation loops lying on the prism planes are the only vacancy type defects observed. In both metals, dislocation segments and network fragments are the main evidence of interstitial type defects. The presence of dislocation loops rather than voids in titanium irradiated at this temperature is an anamalous result when compared to results on other similarly irradiated pure metals. Possible explanations for the preferential formation of loops rather than voids in the titanium are discussed.

Fluence and temperature dependence of swelling in irradiated molybdenum

Abstract Volume changes have been analyzed in molybdenum which has been neutron irradiated to various fluences over the temperature range 50 to 1300°C. This data together with all previously reported data has been compiled into a three-dimensional plot of swelling versus temperature versus fluence. Significant low temperature swelling, 400°C. The nature of the dislocation and void microstructure at high irradiation temperatures are analyzed quantitatively as a function of irradiation temperature and the results are reasonably consistent with a recent model of Brailsford and Bullough. The same model is also consistent with an observed trend towards saturation in the void swelling at high fluences at the low temperature end of the void region.

Characterization and annealing behavior of voids in neutron-irradiated nickel☆

Transmission electron microscopy (TEM) and small angle scattering (SAS) techniques were used to determine the size and density of voids in high purity nickel that had been irradiated to 3 × 1021n/cm2 (>0.1 MeV) at 450°C and subsequently annealed for 2 hr at 650, 800, 900, 975, 1050 and 1150°C. The as-irradiated material contained 1.8 × 1014 truncated octahedral voids cm3 whose average size was 400 A. TEM revealed that the dissolution of the voids during high temperature anneals was rather inhomogeneous with those voids nearest the grain boundaries disappearing first. This resulted in a grain boundary denuded zone whose width depended on temperature, varying from 1 μ at 650°C to 15 μ at 975°C and complete “denuding” at 1050°C. Both TEM and SAS revealed that the voids in the center of the grains did not coarsen during annealing, and the average size remained at ~400 A up to the temperature of complete annealing (1050°C). Such behavior has been predicted for voids that are partially gas-filled, and annealing studies at 1050 and 1150°C did indeed reveal gas bubbles at the recrystallized grain boundaries. Microhardness measurements were also made on the samples after various anneals, and a good correlation was found between the hardness increase, ΔH, and the quantity (Nd)12, where N is the number of voids/cm3 and d is their diameter. More specifically, ΔH = 6 μb(Nd)12, where μ is the shear modulus and b is the burgers vector.

14 MeV Neutron damage in molybdenum

Abstract The radiation damage in molybdenum produced by 14 MeV neutrons has been compared with that produced by fission reactor neutrons. The increased damage level from 14 MeV neutrons compared to fission neutrons as measured by lattice parameter and microstructural changes is much greater than predicted from displaced atom calculations. The damage level measured by electrical resistance changes nearly agrees with the displaced atom calculations. The results are interpreted in terms of an increase in the ratio of clustered defects to free defects after 14 MeV neutron irradiation compared to fission reactor irradiations.

Physical characterization of molybdenum single crystals for irradiation experiments

Abstract Highly perfect molybdenum single crystals were prepared by repeated zone refining and subsequent annealing. Crystalline perfection was characterized by X-ray diffraction topography, integrated diffracted intensity, precision lattice parameter, X-ray profile, and electron microscopy. These measurements were repeated after exposure to high energy neutrons, and were supplemented by precision measurements of dimensional changes. The observed changes in these properties are explained in terms of irradiation-induced point defects. During a 40°C irradiation, interstitial defects migrate and form stable clusters which grow in size with increasing exposure. Vacancies are less mobile, and persist as isolated defects or very small clusters.

Effect of He on the swelling/microstructure produced in Mo by ion bombardment

Abstract Pure molybdenum has been bombarded simultaneously with heavy ions and helium in a dual beam accelerator facility to simulate the helium generation and displacement damage expected in a fusion reactor first wall. Compared to the damage produced by the heavy ions (7 MeV Ta +++ ) alone, simultaneous helium injection results in a high void density that continues to increase with dose. The results suggest continuous void nucleation due to the helium. The swelling during dual beam irradiations is essentially independent of dose at high dose levels. At high doses >40dpa, the helium has little effect on the absolute magnitude of the swelling which is approximately 0.5% with or without helium. Comparisons are made to extrapolated swelling data from fission neutron irradiation studies.

Refractory-metal stabilized amorphous stainless steel

Concurrent heavy ion irradiation during annealing lowered the normal crystallization temperature and altered the type of crystallization reaction in an amorphous 304 stainless steel containing 14 at% tungsten. The crystallization temperature was lower by approximately 150 K during irradation and only a fine grained χ phase was formed during irradiation compared to the dual structure of b c c + χ phase formed in the absence of irradiation. The decrease in the crystallization temperature was attributed to radiation enhanced diffusion and the preferential formation of the χ phase was attributed to localized rearrangement of the amorphous structure due to displacement spikes.

Superconductivity Critical Current Densities in Ti–V Alloys

Specimens of Ti‐20% V alloy were heat treated to a β‐solid‐solution condition and then aged for several fixed times and temperatures below the β transus. X‐ray and electron diffraction were used to determine the composition and distribution of the metallurgical phases produced by the aging treatments. These data were correlated with measurements of the superconducting transition temperature and critical current density. In order for these materials to carry resonable supercurrent densities at 4.2°K, it is necessary that the matrix be rich enough in V for the transition temperature to be greater than 4.2°K and that there be present an array of flux‐pinning sites. It was found that aging temperatures of 400°, 500°, or 600°C were required to insure the first condition. The flux pinners produced were ω particles in the case of the 400°C treatment and α precipitates in the case of the 500° and 600°C treatments. In many specimens, the superconducting‐to‐normal transition at a given value of applied field was sp...