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Ion bombardment damage in a modified Fe-9Cr-1Mo steel

Description: A normalized-and-tempered Fe-9Cr-1Mo steel, with small Nb and V additions, was bombarded with 4-MeV iron ions to 100 dpa at 400, 450, 500, 550, and 600/sup 0/C. Major damage feature was dislocation tangles which coarsened with increasing bombardment temperature. Sparse cavities were heterogeneously distributed at 500 and 550/sup 0/C. Incorporation of helium and deuterium simultaneously in the bombardments at rates of 10 and 45 appM/dpa, respectively, introduced very high concentrations of small cavities at all temperatures, many of them on grain boundaries. These cavities were shown to be promoted by helium. A small fraction of the matrix cavities exhibited bias-driven growth at 500 and 550/sup 0/C, with swelling <0.4%. This is a very narrow temperature range for bias-driven swelling. It is about 125/sup 0/C higher than the peak swelling temperature found in neutron irradiations, which is compatible with the higher damage rate used in the ion bombardments. High concentrations of subgrain boundaries and dislocations resulting from the heat treatment, and unbalanced cavity and dislocation sink strengths in the damage structures contribute to the swelling resistance. Such resistance may not be permanent. High densities of bubbles on grain boundaries indicate a need for helium embrittlement tests.
Date: January 1, 1984
Creator: Farrell, K. & Lee, E.H.
Partner: UNT Libraries Government Documents Department

Swelling suppression in phosphorous-modified Fe-Cr-Ni alloys during neutron irradiation

Description: Phosphorous-containing austenitic alloys in the solution annealed condition were irradiated at 745--760/degree/K. The alloys were variations on Fe--13Cr--15Ni--0.05P with respective additions of 0.8 Si, 0.2 Ti, or 0.8 Si /plus/ 0.2 Ti; also included were low (0.01) and zero P compositions (all values in wt. %). The reference ternary and the two phosphorous-only variations contained little precipitation and numerous voids and swelled rapidly, while the three variants containing P with Si and/or Ti showed little or no void formation and profuse phosphide precipitation. Results indicate that phosphorous in solution alone does not have a major influence on void swelling, whereas fine-scale phosphide precipitation is quite effective at eliminating void formation. The principal mechanism restricting swelling is the effect of the dense precipitate microstructure. These precipitates foster profuse cavity nucleation which in turn dilutes the helium atoms (and more time) in order for individual cavities to surpass their critical size and number of gas atoms necessary for subsequent growth as voids. This mechanism for swelling suppression was not found to be particularly sensitive to moderate variations in either the dislocation or cavity densities; the mechanism is strongest at elevated temperature where the critical quantities are large and is less effective at lower temperatures where the critical quantities are small. 19 refs., 10 figs., 3 tabs.
Date: January 1, 1988
Creator: Lee, E.H. & Packan, N.H.
Partner: UNT Libraries Government Documents Department

Radiation damage and phase instability in irradiated stainless steel

Description: A 316 stainless steel, LS1A, with greater than nominal levels of silicon and titanium has been developed which exhibits high resistance to swelling under ion irradiation. The origin of this swelling resistance and the roles of silicon and titanium have been investigated in the current study.
Date: January 1, 1983
Creator: Kenik, E.A. & Lee, E.H.
Partner: UNT Libraries Government Documents Department

Effects of thermomechanical treatment on phase stability and swelling in alloy D9

Description: Improvement in the swelling of AISI 316 may be achieved through adjustments to levels of Ni, Cr, Mo, Ti, and Si. Effort is concerned with optimizing the composition range for greater phase stability and improving alloy homogeneity. Irradiation response to variations in thermomechanical treatment (TMT) was studied. Swelling peak is suppressed by TMT which produces a high dislocation density or by increasing the solution treatment temperature to 1200/sup 0/C. (FS)
Date: January 1, 1979
Creator: Lee, E.H. & Rowcliffe, A.F.
Partner: UNT Libraries Government Documents Department

Mechanism of swelling suppression in phosphorous-modified Fe-Ni-Cr alloys

Description: Five simple alloys were ion irradiated at 948/sup 0/K in an experiment designed to investigate the mechanism of swelling suppression associated with phosphorous additions. One of the alloys was the simple ternary Fe-15Ni-13Cr, another had 0.05% P added and the other three had further additions of the phosphide precipitate-forming elements Ti and/or Si. Ion irradiations were carried out with heavy ions only (Ni or Fe) or with heavy ions followed by dual heavy ions and helium. The ternary with and without P swelled readily early in dose with or without helium. The other three alloys only showed swelling in the presence of helium and exhibited a long delay in dose prior to the onset of swelling. These displayed fine distributions of Fe/sub 2/P type phosphide precipitates enhanced by irradiation. The phosphide particles gave rise to very high concentrations of stable helium filled cavities at the precipitate matrix interfaces. The results were analyzed in terms of the theory of cavity swelling. The accumulation of the critical number of gas atoms in an individual cavity is required in the theory for point defect driven swelling to begin. It is concluded that the primary mechanism leading to swelling suppression is therefore the dilution of injected helium over a very large number of cavities. It is suggested that this mechanism may offer a key for alloy design for swelling resistance in high helium environments.
Date: January 1, 1986
Creator: Lee, E.H. & Mansur, L.K.
Partner: UNT Libraries Government Documents Department

Influence of injected helium on the phase instability of ion-irradiated stainless steel

Description: The influence of helium injection on phase instability under ion irradiation was studied for two modified 316 stainless steel alloys. Helium is required to nucleate voids in both alloys, though both exhibit phase instability without helium. The injected helium promotes associated growth of voids with precipitates. At low simultaneous helium injection rates 0 to 4 appm He/1 dpa), little or no effect on the precipitation process occurs. As the injection rate increases to 20 appm He/dpa, an increase in precipitate density and a decrease in precipitate size is observed. This result is in contrast to the observation that cold preinjected helium strongly suppresses the phase instability and swelling. The influence of helium on the phase instability is interpreted in terms of its effect on loop nucleation, which in turn influences the subsequent evolution of the damage microstructure.
Date: January 1, 1980
Creator: Kenik, E.A. & Lee, E.H.
Partner: UNT Libraries Government Documents Department

Multiple sectioning and perforation techniques for TEM sub-surface studies. [4 MeV Ni/sup +2/ ions]

Description: Techniques for preparing multiple electron transparent regions at several depth levels below the surface of a metal disk specimen are described. These techniques are relatively rapid and find application in many areas involving surface studies. Examples are shown of multiple thin areas produced at intervals of approximately 200 nm below the original surface of a stainless steel bombarded with 4 MeV Ni/sup +2/ ions for void swelling studies.
Date: January 1, 1978
Creator: Lee, E.H. & Rowcliffe, A.F.
Partner: UNT Libraries Government Documents Department

Effects of Si and Ti on the phase stability and swelling behavior of AISI 316 stainless steel. [Neutron and heavy ion irradiations]

Description: Swelling behavior of neutron irradiated stainless steels is influenced by solute segregation and preciptation phenomena. The extent to which in-reactor swelling behavior may be simulated by heavy ion irradiation depends upon the extent to which in-reactor phase changes are reproduced; this question is addressed by comparing the precipitation behavior under neutron irradiation with behavior during 4 MeV Ni ion irradiation for AISI 316 stainless steel and a related stainless steel containing additions of titanium and silicon. The results are discussed qualitatively in terms of the effects of damage rate on solute segregation and the effects of displacement cascades on the dissolution of particles. It is shown that the partitioning of elements into various phases during irradiation is not a sufficient condition for the initiation of swelling in stainless steels modified with silicon and titanium. It is also necessary for helium to be generated simultaneously with the breakdown of the matrix into various phases; it is believed that helium trapping at the growing particle-matrix interface is responsible for the observed physical association between voids and precipitates.
Date: January 1, 1978
Creator: Lee, E.H.; Rowcliffe, A.F. & Kenik, E.A.
Partner: UNT Libraries Government Documents Department

Effects of pulsed dual-ion irradiation on phase transformations and microstructure in Ti-modified austenitic alloy

Description: The influence of pulsed 4 MeV Ni ion bombardment, with and without simultaneous helium injection, has been explored in a low swelling, Ti-modified austenitic stainless steel. Irradiations were carried out to 70 dpa at 950/sup 0/K; the pulsing frequencies were either 60 s on/off or 1 s on/off. Compared to continuous irradiation, pulsing caused a decrease in the interstitial loop diameter at 1 dpa, although at higher doses the overall dislocation density was not affected. Pulsing and helium both promoted the stability of MC precipitates and retarded the subsequent G phase formation; in some cases G-phase was suppressed and eta phase formed instead. Small bubble-like cavities were observed to grow into large voids after steady dual beam irradiation to 70 dpa. However, this conversion was suppressed by pulse irradiation to 70 dpa and furthermore the sizes of the small cavities were somewhat reduced. The results are explained in terms of current mechanistic understanding of mean point defect kinetics and the evolution of microstructure and microcomposition during irradiation with superimposed annealing periods.
Date: January 5, 1983
Creator: Lee, E.H.; Packan, N.H. & Mansur, L.K.
Partner: UNT Libraries Government Documents Department

Physical principles of ion-beam processing of polymeric materials and applications

Description: Irradiation of polymeric materials with energetic ions in the range of several hundreds of keV to several MeV causes drastic changes in physical, chemical, and mechanical properties. Studies indicate that irradiation produces many active radicals which then react with each other, transforming spaghetti-like tangled polymer chains into a highly cross-linked network structure. Analysis of experimental data shows that the most important parameter for cross-linking is the deposited energy density along the ion track, often expressed in terms of linear energy transfer (LET) in units of eV/nm. High LET produces a high number of free radicals over many neighboring molecular chains and thereby facilitates cross-linking. On the other hand, under low LET conditions, radicals are produced so sparsely that cross-linking efficiency decreases. Moreover, the deposited energy in the chain often leads to chain scission when there are no radicals in the neighboring chains for crosslinking. This paper reviews the current understanding of cross-linking mechanisms in terms of nuclear and electronic stopping and their impact on materials` properties.
Date: November 1, 1998
Creator: Lee, E.H.
Partner: UNT Libraries Government Documents Department

Precipitation and cavity formation in austenitic stainless steels during irradiation

Description: Microstructural evolution in austenitic stainless steels subjected to displacement damage at high temperature is strongly influenced by the interactions between helium atoms and second phase particles. Cavity nucleation occurs by the trapping of helium at partially coherent particle-matrix interfaces. The recent precipitate point defect collector theory describes the more rapid growth of precipitate-attached cavities compared to matrix cavities where the precipitate-matrix interface collects point defects to augment the normal point deflect flux to the cavitry. Data are presented which support these ideas. It is shown that during nickel ion irradiation of a titanium-modified stainless steel at 675/sup 0/C the rate of injection of helium has a strong effect on the total swelling and also on the nature and distribution of precipitate phases.
Date: January 1, 1981
Creator: Lee, E.H.; Rowcliffe, A.F. & Mansur, L.K.
Partner: UNT Libraries Government Documents Department

Mechanisms affecting swelling in alloys with precipitates

Description: In alloys under irradiation many mechanisms exist that couple phase instability to cavity swelling. These are compounded with the more familiar mechanisms associated with point defect behavior and the evolution of microstructure. The mechanisms may be classified according to three modes of operation. Some affect cavity swelling directly by cavity-precipitate particle association, others operate indirectly by precipitate-induced changes in sinks other than cavities and finally there are mechanisms that are mediated by precipitate-induced changes in the host matrix. The physics of one mechanism of each type is developed in detail and the results compared where possible to experimental measurements. In particular, we develop the theory necessary to treat the effects on swelling of precipitation-induced changes in overall sink density; precipitation-induced changes in point defect trapping by solute depletion and creation of precipitate particle-matrix interfacial trap sites.
Date: January 1, 1980
Creator: Mansur, L.K.; Haynes, M.R. & Lee, E.H.
Partner: UNT Libraries Government Documents Department

Structure and composition of phases occurring in austenitic stainless steels in thermal and irradiation environments

Description: Transmission electron diffraction techniques coupled with quantitative x-ray energy dispersive spectroscopy have been used to characterize the phases which develop in austenitic stainless steels during exposure to thermal and to irradiation environments. In AISI 316 and Ti-modified stainless steels some thirteen phases have been identified and characterized in terms of their crystal structure and chemical composition. Irradiation does not produce any completely new phases. However, as a result of radiation-induced segregation principally of Ni and Si, and of enhanced diffusion rates, several major changes in phase relationships occur during irradiation. Firstly, phases characteristic of remote regions of the phase diagram appear unexpectedly and dissolve during postirradiation annealing (radiation-induced phases). Secondly, some phases develop with their compositions significantly altered by the incorporation of Ni or Si (radiation-modified phases).
Date: January 1, 1980
Creator: Lee, E.H.; Maziasz, P.J. & Rowcliffe, A.F.
Partner: UNT Libraries Government Documents Department

Spatial variation in void volume during charged particle bombardment: the effects of injected interstitials

Description: Experimental observations of the void volume at several depths along the range of 4 MeV Ni ions in 316 stainless steel are reported. The specimens were first preconditioned by neutron irradiation at temperatures of 450 and 584/sup 0/C to fluences of approximately 8 x 10/sup 26/ n/m/sup -2/. The void volume after ion bombardment to 60 dpa at the peak damage depth is significantly lower at the peak damage depth than in the region between that and the free surface. The ratio of the step height to void volume at the depth of peak energy deposition between regions masked from and exposed to the beam is strongly dependent on bombardment temperature. The reduction of void volume near the peak damage depth is larger for the 584/sup 0/C than for the 450/sup 0/C preconditioned material. These observations are consistent with recent theoretical results which account for the injection of the bombarding ions as self-interstitials. The theory necessary to understand the effect is developed.
Date: January 1, 1979
Creator: Lee, E.H.; Mansur, L.K. & Yoo, M.H.
Partner: UNT Libraries Government Documents Department

Effect of phosphorus on the swelling and precipitation behavior of austenitic stainless steels during irradiation

Description: It has been observed that increasing the volume fraction of the needle-shaped iron phosphide phase in austenitic stainless steels tends to inhibit void swelling during neutron irradiation. An earlier analysis showed that this effect could not be accounted for in terms of enhanced point defect recombination at particle-matrix interfaces. The behavior of the iron phosphide phase has been further examined using dual ion beam irradiations. It was found that the particle-matrix interface serves as a site for the nucleation of a very fine dispersion of helium bubbles. It is thought that since a high number density of cavities lowers the number of helium atoms per cavity, the irradiation time for the cavities to accumulate the critical number of gas atoms for bias-driven growth is correspondingly increased. Although the phosphide phase nucleates rapidly, it eventually undergoes dissolution if either the G or Laves phase develops with increasing dose.
Date: January 1, 1983
Creator: Lee, E.H.; Mansur, L.K. & Rowcliffe, A.F.
Partner: UNT Libraries Government Documents Department

Rapidly solidified long-range-ordered alloys. [(Fe, Co, Ni)/sub 3/V]

Description: The influence of rapid solidification processing on the microstructure of long-range-ordered alloys in the (Fe, Co, Ni)/sub 3/ V system has been studied by transmission electron microscopy. The main microstructural feature of the as-quenched alloys was a fine cell structure (approx. 300 nm diameter) decorated with carbide particles. This structure was maintained aftr annealing treatments which develop the ordered crystal structure. Other features of the microstructures both before and after annealing are presented and discussed. 6 figures.
Date: January 1, 1981
Creator: Lee, E.H.; Koch, C.C. & Liu, C.T.
Partner: UNT Libraries Government Documents Department

Effects of pulsed and/or dual ion irradiation on microstructural evolution in a Ti and Si modified austenitic alloy

Description: The influence of pulsed 4 MeV Ni-ion bombardment, with and without simultaneous helium injection, at 958 K and damage levels from 1 to 50 dpa has been studied in a low swelling, Ti- and Si- modified austenitic stainless steel. Compared to continuous irradiation, pulsing caused an increase in the number density of interstitial loops formed during irradiation. Helium also increased the nucleation of interstitial loops. The main precipitates formed were a large number of small TiC particles uniformly distributed in the matrix, and a small number of relatively large eta and G precipitates. These course precipitates were somewhat larger in the pulsed specimens. Pulsing appeared to produce no significant change in swelling compared to continuous irradiation. However, for one specimen irradiated to 54 dpa, pulsing concurrent with substantial temperature fluctuations caused by beam heating may have been responsible for a larger swelling compared to continuous irradiation.
Date: January 1, 1983
Creator: Hishinuma, A.; Packan, N.H.; Lee, E.H. & Mansur, L.K.
Partner: UNT Libraries Government Documents Department

Control of helium effects in irradiated materials based on theory and experiment

Description: Helium produced in materials by (n,..cap alpha..) transmutation reactions during neutron irradiations or subjected in ion bombardment experiments causes substantial changes in the response to displacement damage. In particular, swelling, phase transformations and embrittlement are strongly affected. Present understanding of the mechanisms underlying these effects is reviewed. Key theoretical relationships describing helium effects on swelling and helium diffusion are described. Experimental data in the areas of helium effects on swelling and precipitation is reviewed with emphasis on critical experiments that have been designed and evaluated in conjunction with theory. Confirmed principles for alloy design to control irradiation performance are described.
Date: January 1, 1986
Creator: Mansur, L.K.; Lee, E.H.; Maziasz, P.J. & Rowcliffe, A.F.
Partner: UNT Libraries Government Documents Department

Hydrogen retention in ion irradiated steels

Description: In the future 1--5 MW Spallation Neutron Source, target radiation damage will be accompanied by high levels of hydrogen and helium transmutation products. The authors have recently carried out investigations using simultaneous Fe/He,H multiple-ion implantations into 316 LN stainless steel between 50 and 350 C to simulate the type of radiation damage expected in spallation neutron sources. Hydrogen and helium were injected at appropriate energy and rate, while displacement damage was introduced by nuclear stopping of 3.5 MeV Fe{sup +}, 1 {micro}m below the surface. Nanoindentation measurements showed a cumulative increase in hardness as a result of hydrogen and helium injection over and above the hardness increase due to the displacement damage alone. TEM investigation indicated the presence of small bubbles of the injected gases in the irradiated area. In the current experiment, the retention of hydrogen in irradiated steel was studied in order to better understand its contribution to the observed hardening. To achieve this, the deuterium isotope ({sup 2}H) was injected in place of natural hydrogen ({sup 1}H) during the implantation. Trapped deuterium was then profiled, at room temperature, using the high cross-section nuclear resonance reaction with {sup 3}He. Results showed a surprisingly high concentration of deuterium to be retained in the irradiated steel at low temperature, especially in the presence of helium. There is indication that hydrogen retention at spallation neutron source relevant target temperatures may reach as high as 10%.
Date: November 1, 1998
Creator: Hunn, J.D.; Lewis, M.B. & Lee, E.H.
Partner: UNT Libraries Government Documents Department

Hardness enhancement and crosslinking mechanisms in polystyrene irradiated with high energy ion-beams

Description: Surface hardness values several times larger than steel were produced using high energy ion beams at several hundred keV to MeV. High LET is important for crosslinking. Crosslinking is studied by analyzing hardness variations in response to irradiation parameter such as ion species, energy, and fluence. Effective crosslinking radii at hardness saturation are derived base on experimental data for 350 keV H{sup +} and 1 MeV Ar{sup +} irradiation of polystyrene. Saturation value for surface hardness is about 20 GPa.
Date: December 31, 1996
Creator: Lee, E.H.; Rao, G.R. & Mansur, L.K.
Partner: UNT Libraries Government Documents Department

Depth-independent hardness improvements in ion irradiated polystyrene

Description: Polystyrene (PS) was irradiated with 2 MeV He{sup +} ions to a fluence of 3.3 {times} 10{sup 9} ions/m{sup 2}. A cross-section of the irradiated layer was subjected to hardness measurements across the section using a nanoindentation technique. Results showed that hardness increased as a function of irradiation depth and showed a maximum value of 12 GPa at a depth of approximately 6.5 {mu}m, for a total ion penetration range of 9 {mu}m, as compared to a hardness of 0.45 GPa for unirradiated PS. The hardness variation with depth followed the trend for Linear Energy Transfer (LET) for ionization from the energetic ions to substrate atoms. This investigation showed for the first time how hardness varies as a function of depth for ion-irradiated polymers; this variation approximately follows the ionization LET profile, suggesting that cross-linking in the polymers could be proportional to ionization.
Date: December 31, 1994
Creator: Rao, G.R.; Riester, L. & Lee, E.H.
Partner: UNT Libraries Government Documents Department

Effects of rapidly pulsed ion bombardment on microstructure and phase stability in a Ti-modified stainless steel

Description: A low-swelling Ti-modified austenitic stainless steel has been bombarded with pulsed 4 MeV Ni/sup + +/ and in some cases simultaneously with 0.2 to 0.4 MeV He/sup +/ ion beams at 948/sup 0/K over a dose range from 1 to 70 dpa. The interruption periods studied were 60, 1, 10/sup -3/, or 10/sup -5/ s on time with equal off time. At 1 dpa, pulsed irradiation caused interstitial dislocation loops (and subsequent MC precipitates) to be more refined with decreasing pulse periods down to the realm of the vacancy lifetime (10/sup -1/ to 10/sup -3/ s); still faster pulsing at 10/sup -5/ s yielded little difference from steady irradiation. At higher doses, 40 to 70 dpa, pulsing reduced the amount of radiation-induced G phase. Long pulse periods promoted the thermally-stable MC phase, while shorter periods like 10/sup -3/ s aided M/sub 6/C and M/sub 23/C/sub 6/ development. In helium-implanted material bubbles were present for all pulsing conditions but bias-driven voids only developed in continuously-irradiated specimens. The results are interpreted with regard to the inherent fluctuations in point defect concentrations that result from cascade formation.
Date: January 1, 1985
Creator: Lee, E.H.; Packan, N.H.; Lewis, M.B. & Mansur, L.K.
Partner: UNT Libraries Government Documents Department