Void-swelling in 20% cold-worked FV548 austenitic stainless steel irradiated with 22 MeV C2+ ions or 46.5 MeV Ni6+ ions

A study has been made of the void-swelling behaviour of 20% cold-worked FV548 steel irradiated with 22 MeV C²⁺ or 46.5 MeV Ni⁶⁺ ions in the Harwell Variable Energy Cyclotron after room-temperature pre-injection with 10 ppm helium. The dose dependence of void-swelling under 46.5 MeV Ni⁶⁺ irradiation at 500 and 600°C, and the temperature dependence of void-swelling of specimens irradiated with 22 MeV C²⁺ ions in the range 500–650°C have been established. In addition the temperature dependence of void-swelling in specimens aged for 1000 h at 650° C before irradiation has also been studied. Subsidiary annealing experiments have demonstrated the high recovery resistance of the 20% cold-worked structure in FV548, compared with types 316 and 321 steels.The void-swelling behaviour is interpreted in terms of the balance between the dislocation and NbC point defect sink strengths and the observed resistance to recovery of the cold-worked structure in FV548.     

Effect of helium preinjection and prior thermomechanical treatment on the microstructure of type 316 SS

Samples of 316 SS were preinjected with 15 appm helium either hot (650°C) or cold (room temperature) and irradiated with 3 MeV Ni⁺ ions to a dose level of 25 dpa at 625°C in order to test the validity of helium preinjection as a means of simulation of transmutant helium production. Results for preinjected and single-ion irradiated samples were compared to samples irradiated at 625°C to a 25 dpa dose level with 3 MeV Ni⁺ and simultaneously injected with helium at a rate of 15 appm He/dpa (dual-ion irradiated samples). Preinjected samples exhibited bimodal cavity size distributions. Preinjected samples of solution annealed or solution annealed and aged material showed lower swelling than dual-ion irradiated samples. However, He preinjected 20% cold worked samples showed greater swelling than dual-ion irradiated samples.     

The void-swelling behaviour of solution-treated FV548 stainless steel irradiated with 22 MeV C2+ and 46.5 MeV Ni6+ ions and the influence of heat-treatment

A study has been made of the void-swelling behaviour of 1150°C solution-treated FV548 steel irradiated with 22 MeV C²⁺ and 46.5 MeV Ni⁶⁺ ions in the Harwell Variable Energy Cyclotron (VEC) after pre-injection with 10 ppm helium. The temperature dependence of void-swelling in the range 400–700°C, and the dose dependence of void-swelling at 600°C, have been established. In addition, the effects of ageing at 650°C, solution-treatment at 1300°C, and irradiation without helium pre-injection, on the void-swelling at 600°C have been investigated.Differences between void-swelling values obtained using C²⁺ ions, Ni⁶⁺ ions, and previously reported values obtained from 1 MeV electron irradiation of 1150°C solution-treated FV548 steel are discussed, as are the marked differences between the void-swelling behaviour reported here for VEC-irradiated FV548 steel and the established behaviour of type 316 steel irradiated under the same conditions. Finally, the present results are compared with the published data on reactor-irradiated solution-treated FV548 steel.     

The temperature dependence of nickel-ion damage in nickel

The temperature dependence of void and dislocation structures was studied in high-purity nickel irradiated with 2.8 MeV ⁵⁸Ni⁺ ions to a displacement density of 13 displacements per atom (dpa) at a displacement rate of $\text{7 × 10}{}^{\mathrm{?2}}\text{dpa/sec}$ over the temperature range 325 to 625°C. Dislocation loops, with no significant concentrations of voids, were observed in specimens irradiated at 475°C and below. Specimens irradiated between 525 and 725°C contained both voids and dislocations. The maximum swelling was measured as 1.2% at 625°C. Analysis of the data by theoretical models for void nucleation and growth indicated that the swelling in the present experiment was principally limited by void growth at low temperatures and by void nucleation at high temperatures. The data were also compared with previously reported neutron and nickel-ion irradiation results.     

Precipitation and void-swelling in nickel-manganese austenitic stainless steels

The precipitation and void-swelling characteristics of austenitic stainless steels in which nickel is partially replaced by manganese have been investigated. Alloy compositions were chosen on the basis of manganese being half as effective as nickel in stabilizing austenite, and steels with “nickel equivalent” contents of 25–37% were examined. The steels were irradiated with 46 MeV Ni⁶⁺ ions to 60 dpa at 625°C and also aged for 1000 h at 600°C. The high-Mn alloys (20–30% Mn) were very susceptible to the formation of intermetallic phases during thermal ageing but less so in the shorter-duration irradiation experiment. Irradiation promoted the formation of Ni- and Si-rich phases—the suicide G phase (in which Mn can replace Ti) and in one instance M₆C. The Cr-rich carbide M₂₃C₆ formed in both the aged and irradiated steels. Among the high-Mn alloys, void-swelling decreased with increasing Ni and (Ni+Mn) contents, although a 25Ni-1Mn steel showed no swelling at 625°C.     

Void Swelling of Solution-Annealed Type 316 Stainless Steel under Long Time Proton Irradiation

Solution-annealed type 316 stainless steel was irradiated by 150 keV proton to a dose of about 6 dpa at the irradiation temperature ranging 450–700°C. To examine the effect of aging during irradiation, the present proton irradiation was carried out for about 25 h at a low dose rate of 7×10–^?5dpa/s. The specimens without He preinjection showed much smaller void swelling than those preinjected with He to the content of 10 at.ppm. Similarly to the case of neutron irradiations, the void swelling in the He preinjected specimens showed the temperature dependence with double peaks, and the peak swelling temperatures were about 550 and 650°C. In these specimens with He preinjection. void number density decreased and average void diameter increased with the increase of irradiation temperature in the range of 450–600°C, but these trends were reversed between 600 and 650°C. The volume of the grain boudary M₂₃C6 precipitates increased with the increase of irradiation temperature from 600 to 700°C, and it was concluded that the decrease of soluble carbon due to the precipitation of M₂₃C6 caused the second swelling peak at 650°C.     

Interstitial loop nucleation and growth in solution-treated type 316 stainless steel irradiated to low doses with 22 MeV C2+ and 46.5 MeV Ni6+ ions

The nucleation and growth of interstitial dislocation loops have been studied in solution-treated type 316 austenitic steel irradiated to low doses in the Harwell Variable Energy Cyclotron. Specimens have been irradiated with 46.5 MeV Ni⁶⁺ ions and 22 MeV C²⁺ ions, after room temperature pre-injection with 10 ppm helium and without helium pre-injection, at temperatures in the range 300–600°C. The effects of these irradiation variables on the interstitial loop populations produced are discussed. At low doses, where loop intersection is rare and dislocation network formation is minimal, the number of interstitial atoms stored in loops can give an indication of the swelling rate in circumstances where voids remain submicroscopic. It is shown that extrapolation of the low-dose swelling rates indicated by interstitial loop populations gives reasonable fit with experimentally determined high-dose void swelling values.     

Nickel-ion bombardment of annealed and cold-worked type 316 stainless steel

Bombardment with high doses of 5 MeV nickel ions has produced swellings as high as 90% and 60%, respectively, in annealed and 20% cold-rolled Type 316 steels. The steels contained 15 ppm of cyclotron-injected helium. Swellings were determined by both transmission electron microscopy and by a step-height method that measures the total swelling integrated along the ion path. The swelling in annealed Type 316 has a pronounced peak in the vicinity of 625°C, which is about 155°C higher than the peak swelling temperature in-reactor. The magnitudes of the swelling, void densities and void sizes produced in annealed Type 316 by nickel ions and in-reactor at the respective peak swelling temperatures are similar and it is concluded that the nickel ion bombardments provide an acceptable simulation of in-reactor behavior. Using the high dose ion results to guide extrapolation of presently available EBR-II data to higher fluences leads to the prediction that the swelling of annealed Type 316 steel at the peak swelling temperature will reach 40% at $\text{2 × 10}{}^{\mathrm{p23}}\text{n/cm}{}^2\text{(E > 0.1 MeV)}$ in EBR-II core, and 70% at $\text{3 × 10}{}^{23}\text{n/cm}{}^2$. These fluences in EBR-II correspond to 155 and 230 dpa respectively. Twenty percent reduction by cold-rolling reduces the ion produced swelling by 35% at 625°C and by 50% at 575°C.     

The irradiation creep of nickel and AISI 321 stainless steel during 4 MeV proton bombardment

An apparatus has been developed to study the creep of thin metal specimens under tensile stress during bombardment by 4 MeV protons from the Harwell Van de Graaff Accelerator. The specimen is held in a helium atmosphere and the proton beam reaches it through a thin metal window at the end of the accelerator beam line. The proton beam passes through the thin (25 μm) specimen, losing ~1.5 MeV in the process (most of which contributes to heating the specimen) and creating almost uniform radiation damage at the rate of $\text{(1–10) × 10}{}^{\mathrm{?7}}$ displacements per atom per second (dpa s^?1). The specimen temperature is monitored by infra-red pyrometry and controlled to ± 0.2°C by additional DC heating via the infra-red pyrometer output to compensate for ion beam fluctuations. The irradiation creep strain of the specimen is continuously measured with a sensitivity of $\text{5 × 10}{}^{\mathrm{?6}}$ by a linear variable differential transformer. Irradiation times up to about 100h with reasonable beam stability are possible. Results are presented of the irradiation creep behaviour of pure Ni and both solution treated and cold-worked AISI 321 stainless steel bombarded in the temperature range 400–600°C under tensile stresses in the range 20–250 MPa.     

Dose-rate dependence of swelling and damage in ion-irradiated nickel

The results of an irradiation experiment using 46 MeV Ni⁶⁺ ions from the Variable-Energy Cyclotron facility in Harwell are presented. The dose rate was varied, at a constant total dose, by a factor of 20 and the damage produced examined in the peak region of damage and at smaller depths. The temperature range 450–700°C was investigated. It was found that the temperature dependence of swelling varies with both the dose rate and the dose.     

Nickel ion bombardment of type 304 stainless steel: Comparison with fast reactor swelling data

Annealed Type 304 stainless steel containing 15 atomic ppm of helium has been bombarded with 5 MeV nickel ions at 525°C to 700°C. A pronounced swelling peak occurs at 625°C, compared to a swelling peak temperature of about 475°C in reactor. TEM measurements of void swelling at 625°C as a function of ion dose show a swelling of almost 40% at 124 dpa without evidence of saturation. Measurements of gross swelling of the ion-bombarded material by a new step-height method provide information that is in good agreement with TEM data, and can be extended to larger swellings. The step-height results indicate a swelling of over 90% at 290 dpa at 625°C. The ion-produced swelling agrees well with in-reactor data when the two are compared at the respective peak swelling temperatures, and the void concentrations and average void diameters are comparable for the two cases. The high ion dose results are used to guide extrapolation of reactor data to higher fluences, leading to the following predictions for swellings at the peak swelling temperature in reactor: 18% swelling at $\text{1× 10}{}^{23}\text{n/cm}{}^2$ (fast), 50% at $\text{2 × 10}{}^{23}$, and 80% at $\text{3 × 10}{}^{23}$.     

Swelling of type-316 stainless steel at high fluences in EBR-II

A test to measure swelling induced by fast neutron irradiation in unstressed specimens of type-316 stainless steel has completed irradiation in the EBR-II reactor. Results are reported and discussed which describe the swelling as a function of neutron fluence, temperature of irradiation and extent of cold work in the alloy. Density determinations showed swellings of up to 15% $\text{ΔV}\text{V}{}_{\mathrm{f}}$ for 20% cold worked type-316 stainless steel at a neutron fluence level of 1.4 × 10²³n/cm², E > 0.1 MeV (70 dpa). The peak swelling temperature range was 550°C–600°C regardless of the extent of cold working. Increasing the cold work level reduced the swelling and tended to broaden the swelling temperature peak. Transmission electron microscopy (TEM) investigations showed that cold working had reduced the average void sizes compared to those observed in the solution annealed material.     

Ferrite formation in neutron-irradiated austenitic stainless steel

Magnetic measurements were carried out on type 316, 321 and three modified heats of 316 austenitic stainless steels that had been irradiated to high fluences (1 ? 8 × 10²²n/cm², E > 0.1 MeV) in EBR-II at temperatures ranging from 450–700°C. Most of the specimens showed increases of magnetization after exposure to the reactor environment that can be attributed to formation of numerous small ferrite particles. The amount of ferrite formed during irradiation is a function of alloy composition as well as irradiation temperature and fluence. Specimens with low molybdenum concentrations had a greater ferrite content than specimens with the normal molybdenum content of type 316 stainless steel. A modified heat of type 316 with 0.23 wt% Ti had lower levels of ferrite under given irradiation conditions than the other heats. Some particles with diffraction patterns corresponding to the ferrite phase were found in an irradiated type 321 stainless specimen, but none were observed in the type 316 stainless specimens.     

Dose and Temperature Dependence of Void Swelling in Electron Irradiated Stainless Steel

In a high voltage electron microscope, solution treated Type 316 stainless steel was electron-irradiated at temperatures in the range of 370–630°C to a dose of about 30 dpa. The swelling (ΔV/V) induced by the irradiation beyond about 5 dpa is well described by an empirical equation, ΔV/V=A(dpa) ⁿ , under constant void and dislocation densities. With increasing irradiation temperature, the fluence exponent n increases and the pre-exponent term A decreases. At 550°C irradiation, the fluence exponent takes the value of 1.5 due to the diffusion-limited void growth. The value of n larger than 1.5 at higher temperature (>550°C) is attributable to the surface reaction-limited void growth. The smaller value of n for the low temperature (?500°C) irradiation appears to arise from the dislocation assisted vacancy diffusion. The peak swelling temperature of the specimen irradiated to 30 dpa is about 570°C, which shifts to a higher temperature with increase in electron dose.     

Void Swelling in Electron Irradiated High Purity Fe-Cr-Ni Austenitic Alloys

High-purity Fe-Cr-Ni austenitic alloys corresponding to commercial Type-316 stainless steel and Hastelloy-X were used to investigate the void swelling mechanism of the austenitic steels. The alloys were irradiated with 1 MeV electrons in a high voltage electron microscope in the temperature range of 300~600°C to a total dose of about 30 dpa. Low void swelling in Ni-base alloy is attributed to both low void number density and small void size. Void embryos in Fe-base alloy are stabilized by strain field arised from Ni solute segregation around the void surface. The stabilization does not occur in Ni-base alloy, which results in extremely low void number density at high temperatures (>500°C). Higher void growth rates in Fe-base alloy than in Ni-base alloy are attributable to large climbing rate of dislocations produced during the irradiation.     

Évolution de la densité de dislocations dans des aciers austénitiques du type 316 L irradiés par des ions Ni+ de moyenne energie

Changes in dislocation density were examined in stainless steels of Type 316L on irradiation by 500 keV Ni⁺ ions. Over a wide temperature range (400–700°C) a high dislocation density was observed. This density was independent of the initial state of the material (hyperquenched or defomred) and of the dose, once this had attained the level of 10 dpa (equivalent to $\text{2 × 10}{}^{22}\text{n/cm}{}^2$ approximately). The dislocation density increased with instantaneous flux and decreased as the irradiation temperature rose. The irradiation-induced change of the mechanical properties of Type 316 stainless steels can be explained, at least partially, in terms of the rapid disappearance of the initial dislocation network in deformed material and the saturation of the dislocation density created by irradiation in hyperquenched or deformed material.     

Xe~+离子辐照诱导国产T91及316Ti钢微结构变化研究

对国产T91及316Ti钢进行室温下200keV的Xe~+离子辐照,使用X射线衍射(XRD)、透射电镜(TEM)等检测方法研究不同损伤剂量下辐照对材料相的稳定性和微观结构变化的影响。研究结果表明:T91钢辐照后未发生明显相变,而316Ti发生了γ(FCC)→α(BCC)的马氏体相变,且随辐照损伤剂量的增加,α相含量增加,相变的主要驱动力为辐照离子在辐照层的聚集从而产生的剪切应力;T91钢中的M_(23)C_6颗粒随辐照损伤剂量的增加,非晶化越来越明显,主要是由于辐照粒子的轰击削弱了M_(23)C_6颗粒晶格的稳定性,晶格塌陷成为非晶状态;316Ti钢在较低辐照损伤剂量(4.6dpa)下出现黑斑结构,而在高辐照损伤剂量(37.1dpa)下黑斑结构进一步聚集形成位错环。     

The effect of dose rate on the response of austenitic stainless steels to neutron radiation

Depending on reactor design and component location, austenitic stainless steels may experience significantly different irradiation dose rates in the same reactor. Understanding the effect of dose rate on radiation performance is important to predicting component lifetime. This study examined the effect of dose rate on swelling, grain boundary segregation, and tensile properties in austenitic stainless steels through the examination of components retrieved from the Experimental Breeder Reactor-II (EBR-II) following its shutdown. Annealed 304 stainless steel, stress-relieved 304 stainless steel, 12% cold-worked 316 stainless steel, and 20% cold-worked 316 stainless steel were irradiated over a dose range of 1–56 dpa at temperatures from 371 to 440 °C and dose rates from 0.5 to 5.8 × 10⁻⁷ dpa/s. Density and tensile properties were measured for 304 and 316 stainless steel. Changes in grain boundary composition were examined for 304 stainless steel. Swelling appears to increase at lower dose rates in both 304 and 316 stainless steel, although the effect was not always statistically significant. Grain boundary segregation also appears to increase at lower dose rate in 304 stainless steel. For the range of dose rates examined, no measurable dose rate effect on tensile properties was noted for any of the steels.     

Void swelling in a 9Cr ferritic/martensitic steel irradiated with energetic Ne-ions at elevated temperatures

In this work the void swelling behavior of a 9Cr ferritic/martensitic steel irradiated with energetic Ne-ions is studied. Specimens of Grade 92 steel (a 9%Cr ferritic/martensitic steel) were subjected to an irradiation of ²⁰Ne-ions (with 122 MeV) to successively increasing damage levels of 1, 5 and 10 dpa at a damage peak at 440 and 570 °C, respectively. And another specimen was irradiated at a temperature ramp condition (high flux condition) with the temperature increasing from 440 up to 630 °C during the irradiation. Cross-sectional microstructures were investigated with a transmission electron microscopy (TEM). A high concentration of cavities was observed in the peak damage region in the Grade 92 steel irradiated to 5 dpa, and higher doses. The concentration and mean size of the cavities showed a strong dependence on the dose and irradiation temperature. Enhanced growth of the cavities at the grain boundaries, especially at the grain boundary junctions, was observed. The void swelling behavior in similar 9Cr steels irradiated at different conditions are discussed by using a classic void formation theory.