Neutron irradiation hardening and microstructure changes in Fe-Mn binary alloys

Irradiation hardening and microstructure changes in Fe-Mn binary alloys were investigated after neutron irradiation at 290 °C and up to 0.13 dpa. Significant irradiation hardening comparable to that of Fe-1 at.%Cu alloy was observed in Fe-1 at.%Mn alloy. Manganese increases the number density of dislocation loops, which contributed to the observed irradiation hardening. Manganese serves as a nucleus of the loop by trapping interstitial atoms and clusters, preventing 1D motion of the loops.     

The theory of phase stability under irradiation

Irradiation-alteration of phase stability is examined from the thermodynamic and kinetic viewpoints. It is shown first that the flux of irradiating particles cannot be treated as a thermodynamic variable, so that an irradiated system is inherently in a driven irreversible state. A typical breeder reactor cladding or fusion first wall irradiation is seen to insert huge (> 10⁷ J/mol) amounts of energy into the material; this energy has the potential to do large amounts of work, given the existence of a coupling mechanism. The various coupling mechanisms are reviewed, and estimates made of their effectiveness. Irradiation-induced solute segregation, disordering, and the chemical vacancy effect are shown able to give changes in stability of up to 10³ J/mol. By contrast, the excess vacancy concentration is unlikely to increase the free energy of the irradiated metal by as much as 1 J/mol. The various mechanisms have the potential to give different kinds of alterations of phase stability, i.e., shift phase boundaries, produce unknown phases, or enhance diffusion. These are discussed and the potentials and limitations of each mechanism are enumerated.     

双束同时辐照对低活性Fe-Cr-Mn(W,V)合金相稳定性影响

采用电子束 /He+ ion束同时复合辐照方式 ,研究了低活性Fe Cr Mn(W ,V)合金高温长时时效后组织稳定性 ,评价了He对辐照相稳定性影响。结果表明 ,单独电子辐照 ( 10a-1 )只引起相界面低密度空洞形成。而双束同时辐照对组织损伤具有协同效果 ,加剧相稳定性发生变化 ,如 :促进相间溶质原子扩散 ,导致析出相长大 ;新相的形成 ;发生结构无序化 ,促进析出相改性。从He原子与晶体辐照点缺陷与溶质原子相互作用和扩散等机制 ,讨论了辐照相稳定性发生变化的原因。     

Defect buildup and solute segregation in alloys under pulsed irradiation

The Johnson-Lam kinetic model, which is based on a combination of diffusion and chemical reaction rate equations, has been used to study the buildup of point defects and defect-solute complexes, and segregation of minor elements in alloys under pulsed irradiation. Concentrations of defects and solutes have been calculated for various defect-production rates, defect-solute binding energies and pulse durations, with Ni as the model material. Precipitation at the sink surface is taken into account when the solute concentration at the sink exceeds the solubility limit. For a fixed damage rate, the longer the pulse duration the smaller the number of cycles needed to achieve a cyclic state for defects and defect-solute complexes and quasi-steady state for solute segregation. In addition, for a fixed pulse duration, the higher the damage rate the fewer the cycles required to observe these states. The resultant solute segregation obtained under pulsed irradiation can be similar to, or different from segregation achieved during steady irradiation depending on whether the beam-off period is comparable to, or much longer than the pulse duration. The microstructures of the material can also be different from those formed by unpulsed bombardment due to cyclic production and annealing of mobile defects.     

Microstructural investigation of the stability under irradiation of oxide dispersion strengthened ferritic steels

Some fuel pin cladding made from a ferritic steel reinforced by titanium and yttrium oxides were irradiated in the French experimental reactor Phénix. Microstructural examination of this alloy indicates that oxides undergo dissolution under irradiation. This irradiation shows the influence of dose and, in a smaller part, of temperature. In order to better understand the mechanisms of dissolution, three ferritic steels reinforced by Y₂O₃ or MgO were irradiated with different charged particles. Inelastic interactions induced by 1 MeV He ion irradiation do not lead to any modification, neither in their chemical composition, nor in their spatial and size distribution. In contrast, isolated Frenkel pairs created by electron irradiation lead to significant oxide dissolution with a radius decrease proportional to the dose. Moreover, the comparison between irradiation with ions (displacements cascades) and electrons (Frenkel pairs only) shows the importance of free point defects in the dissolution phenomena.     

C60薄膜在快重离子辐照下的结构稳定性研究

用傅立叶变换红外光谱、X射线衍射谱、X射线光电子谱和拉曼散射技术分析了能量为GeV量级的S、Fe、Xe、和U离子,以及120keV的H离子在室温下辐照多层堆积C60薄膜的结构稳定性,即快重离子在C60薄膜中由高密度电子激发引起的效应,主要包括C60分子的聚合、分子结构的损伤、新的高温-高压相的形成和晶态向非晶态的转变.     

Formation of steady state size distribution of precipitates in alloys under cascade-producing irradiation

The effect of coherency loss on the development of precipitate size distribution under cascade-producing irradiation is considered. The nucleation of coherent precipitates, their growth followed by coherency loss and cascade-induced dissolution of large incoherent precipitates can occur simultaneously resulting in formation of a quasi-stationary size distribution of semicoherent precipitates. To describe this process we consider co-evolution of a mixed population of coherent, semicoherent and incoherent precipitates. Mathematically, the problem is formulated as a set of discrete rate equations of nucleation kinetics (the Master equation approach) which is also used for later stages of evolution. To solve the corresponding large set of equations (typically, more than 10⁵ equations) an efficient numerical method is developed. The simulation results obtained for material parameters and irradiation conditions typical for nuclear reactors show that the coherency loss affects considerably evolution of the precipitate population. Under certain irradiation conditions, both in solution-annealed alloys and in aged ones, the mean precipitate size and the number density during prolonged irradiation tend to steady state values, whereas the size distribution function of large precipitates narrows. The width of the quasi-stationary size distribution is controlled by cascade parameters. It was found that the asymptotic quasi-stationary state of the precipitate population may depend on initial state of the alloy.     

Phase stability under irradiation — a review of theory and experiment

A critical review of the current state of the theories for phase stability under irradiation is presented. Starting from the primary damage structure a formalism is presented which is used to describe radiation enhanced diffusion, precipitate dissolution, metastable precipitate sequences and phase diagram modification under irradiation. In the case of precipitate dissolution it is shown that current theory has been misinterpreted, and an alternative steady state analysis is presented which shows that the particle distribution depends on the pre-existing distribution or on new nucleation. Current theories for phase diagram modification under irradiation are critically reviewed and extended to cover the effect of radiation-induced disordering and amorphization. For the former case a calculated phase diagram (Ti-Ru) is presented as modified by irradiation.     

Recombination mechanism of point defect loss to coherent precipitates in alloys under irradiation

A new mechanism of defect loss by enhanced recombination inside coherent precipitates in alloys under irradiation is described. The mechanism is examined quantitatively to find the microstructural parameters responsible for resistance to dimensional instability. The proposed model explains why radiation properties of Zr–Nb alloys depend on density of fine-grained precipitates of β_Nb-phase.     

Kr ion irradiation study of the depleted-uranium alloys

Fuel development for the reduced enrichment research and test reactor (RERTR) program is tasked with the development of new low enrichment uranium nuclear fuels that can be employed to replace existing high enrichment uranium fuels currently used in some research reactors throughout the world. For dispersion type fuels, radiation stability of the fuel-cladding interaction product has a strong impact on fuel performance. Three depleted-uranium alloys are cast for the radiation stability studies of the fuel-cladding interaction product using Kr ion irradiation to investigate radiation damage from fission products. SEM analysis indicates the presence of the phases of interest: U(Al, Si)₃, (U, Mo)(Al, Si)₃, UMo₂Al₂₀, U₆Mo₄Al₄₃ and UAl₄. Irradiations of TEM disc samples were conducted with 500 keV Kr ions at 200 °C to ion doses up to 2.5 × 10¹⁹ ions/m² (∼10 dpa) with an Kr ion flux of 10¹⁶ ions/m²/s (∼4.0 × 10⁻³ dpa/s). Microstructural evolution of the phases relevant to fuel-cladding interaction products was investigated using transmission electron microscopy.     

Modification of the precipitate interface under irradiation and its effect on the stability of precipitates

Ni-alloys containing coherent γ'-précipitates of different lattice mismatch and an A1-Mg-Si alloy with semicoherent β' -precipitates were irradiated with self-ions of 25 0 keV energy. The microstructural changes as a function of irradiation dose, ranging from 2 to 398 dpa, and temperature, ranging from 323 to 998 K, were followed by transmission electron microscopy. It was found that irrespective of the initial interface, the alloy chemistry or the irradiation condition, the precipitate interface is considerably modified under irradiation. Further, the interfacial dislocations, evolved either during preaging or irradiation, obstructed the dissolution, and their loss marked the beginning of rapid dissolution starting from the surface of precipitates. Based on these observations, a hypothesis is proposed to account for the interfacial modification and to explain the stabilizing effect of the interfacial dislocations during the radiation-induced dissolution.     

Neutron irradiation of dilute aluminium alloys

Aluminium alloys containing up to 0.4% silicon and 0.1% indium were irradiated at various doses up to 10²¹ n/cm² (E > 0.1 MeV) at pile temperature. Indium was found to enhance and silicon to suppress the nucleation of voids. The reasons for this are discussed in terms of possible nucleation processes. The changes in 0.2% proof stress were correlated with the change in microstructure.     

Radiation stability of ZrN under 2.6 MeV proton irradiation

Zirconium nitride is a promising alternative material for the use as an inert matrix for transuranic fuel, but the knowledge of the radiation tolerance of ZrN is very limited. We have studied the radiation stability of ZrN using a 2.6 MeV proton beam at 800 °C. The irradiated microstructure and hardening were investigated and compared with annealed samples. A high density of nano-sized defects was observed in samples irradiated to doses of 0.35 and 0.75 dpa. Some defects were identified as vacancy-type pyramidal dislocation loops using lattice resolution imaging and Fourier-filter image processing. A very slight lattice expansion was noted for the sample with a dose of 0.75 dpa. Hardening effects were found for samples irradiated to both 0.35 and 0.75 dpa using Knoop indentation.     

Assessment of irradiation temperature stability of the first irradiation test rig in the HTTR

The High Temperature Engineering Test Reactor (HTTR) can provide very large irradiation spaces at high temperatures for various irradiation tests. The first irradiation test rig for the HTTR, the I–I type irradiation equipment, was developed for an in-pile creep test on a stainless steel with large standard size specimens. The equipment uses the ambient high temperature of the core for the irradiation temperature control. The target irradiation temperatures are 550 and 600 °C with the target temperature deviation of ±3 °C. In this study, the specimen temperature stability at the irradiation test was assessed by both analytical and experimental approaches. The irradiation temperature changes at transient conditions were analyzed by a finite element method (FEM) code and the temperature controllability of the equipment was examined by a mockup test. The controllability was evaluated with the measured temperature transient data at the core graphite components in the Rise-to-Power tests of the HTTR. The result indicates that the temperature control method of the I–I type irradiation equipment is effective to keep the irradiation temperature stable in the irradiation test.