Search

Abstract: The paper presents irradiation creep data for V–4Cr–4Ti irradiated to 3.7dpa at 425 and 600°C in the HFIR-17J experiment. Creep deformation was characterized by measuring diametral changes of pressurized creep tubes before and after irradiation. It was found that the creep strain rate of the US Heat 832665 of V–4Cr–4Ti exhibited a linear relationship with stress up to ∼180MPa at 425°C with a creep coefficient of 2.50×10−6 MPa−1 dpa−1. A linear relationship between creep rate and applied stress was observed below ∼110MPa at 600°C with a creep coefficient of 5.41×10−6 MPa−1 dpa−1; non-linear creep behavior was observed above ∼110MPa, and it may not be fully accounted by invoking thermal creep. The bilinear creep behavior observed in the same alloy irradiated in BR-10 was not observed in this study. [Copyright &y& Elsevier]

Abstract: The stress relaxation behavior of 14YWT and ODS-Eurofer97 was examined within the framework of an internal-variable theory of inelastic deformation. Stress versus strain rate curves obtained by stress relaxation tests for 14YWT were described well by the equations for grain-matrix deformation while those of ODS-Eurofer97 were fitted with the combined curves of grain matrix deformation and grain boundary sliding. The sudden drop of total elongation of 14YWT was discussed in light of fracture surface observations. Grain boundary decohesion at 900°C was identified. [Copyright &y& Elsevier]

Ferritic alloys containing a high density of nanoscale clusters of Y–Ti–O exhibit superior creep strength and potential for high resistance to radiation damage. Small angle neutron scattering (SANS) was used to characterize the sequence-of-events and the necessary ingredients for the formation of nanoclusters (NCs) during processing, as well as their thermal stability during high temperature aging. Mechanical alloying (MA) dissolves Y2O3 in the master alloy Fe–Cr–W powders. A large population of 1–2 nm NCs precipitate during subsequent high temperature consolidation. The NC sizes increase and their volume fractions and number densities decrease with increasing the consolidation temperature. Both Ti and Y are necessary for NC formation at higher temperatures. The NCs in MA957 are stable during aging at 1150 °C for times up to 243 h, but systematically coarsen at 1200 °C. The NCs coarsen rapidly and become unstable at higher aging temperatures. Variations in the alloy hardness are consistent with differences in the NC sizes and number densities. [Copyright &y& Elsevier]

A new larger heat of a 14YWT nanostructured ferritic alloy (NFA), FCRD NFA-1, was synthesized by ball milling FeO and argon atomized Fe-14Cr-3W-0.4Ti-0.2Y (wt%) powders, followed by hot extrusion, annealing and cross rolling to produce an ≈10 mm-thick plate. NFA-1 contains a bimodal size distribution of pancake-shaped, mostly very fine scale, grains. The as-processed plate also contains a large population of microcracks running parallel to its broad surfaces. The small grains and large concentration of Y–Ti–O nano-oxides (NOs) result in high strength up to 800 °C. The uniform and total elongations range from ≈1–8%, and ≈10–24%, respectively. The strength decreases more rapidly above ≈400 °C and deformation transitions to largely viscoplastic creep by ≈600 °C. While the local fracture mechanism is generally ductile-dimple microvoid nucleation, growth and coalescence, perhaps the most notable feature of tensile deformation behavior of NFA-1 is the occurrence of periodic delamination, manifested as fissures on the fracture surfaces. [ABSTRACT FROM AUTHOR]

Considerable progress has been made toward development of vanadium alloys for fusion. Much of the recent research has focused on vanadium alloys containing 4–5% Cr and 4–5% Ti, but a number of alternative compositions and processing routes have been explored in an effort to achieve improved performance. The goal of this paper is to review significant new results and to highlight critical issues that remain for future research. Progress in understanding the influence of interstitial impurities on microstructural evolution in both thermal and radiation environments are covered. The current state of knowledge of hardening and embrittlement of vanadium alloys in response to neutron irradiation is reviewed. Atomic-scale computer simulations to elucidate fundamental irradiation damage mechanisms are presented. The thermal and irradiation creep behavior of V–4Cr–4Ti is summarized along with an overview of the effects of He on tensile properties. [Copyright &y& Elsevier]