Effect of Grain Size on the Irradiation Response of Grade 91 Steel Subjected to Fe Ion Irradiation at 300 °C

Irradiation using Fe ion at 300 °C up to 100 dpa was carried out on three variants of Grade 91 (G91) steel samples with different grain size ranges: fine-grained (FG, with blocky grains of a few micrometers long and a few hundred nanometers wide), ultrafine-grained (UFG, grain size of ~ 400 nm) and nanocrystalline (NC, lath grains of ~ 200 nm long and ~ 80 nm wide). Electron microscopy investigations indicate that NC G91 exhibit higher resistance to irradiation-induced defect formation than FG and UFG G91. In addition, nano-indentation studies reveal that irradiation-induced hardening is significantly lower in NC G91 than that in FG and UFG G91. Effective mitigation of irradiation damage was achieved in NC G91 steel in the current irradiation condition. Graphical abstract: [Figure not available: see full text.

Comparison of the Thermal Stability in Equal-Channel-Angular-Pressed and High-Pressure-Torsion-Processed Fe–21Cr–5Al Alloy

Nanostructured Steels Are Expected to Have Enhanced Irradiation Tolerance and Improved Strength. However, They Suffer from Poor Microstructural Stability at Elevated Temperatures. in This Study, Fe–21Cr–5Al–0.026C (Wt%) Kanthal D (KD) Alloy Belonging to a Class of (FeCrAl) Alloys Considered for Accident-Tolerant Fuel Cladding in Light-Water Reactors is Nanostructured using Two Severe Plastic Deformation Techniques of Equal-Channel Angular Pressing (ECAP) and High-Pressure Torsion (HPT), and their Thermal Stability between 500–700 °C is Studied and Compared. ECAP KD is Found to Be Thermally Stable Up to 500 °C, Whereas HPT KD is Unstable at 500 °C. Microstructural Characterization Reveals that ECAP KD Undergoes Recovery at 550 °C and Recrystallization above 600 °C, While HPT KD Shows Continuous Grain Growth after Annealing above 500 °C. Enhanced Thermal Stability of ECAP KD is from Significant Fraction (\u3e50%) of Low-Angle Grain Boundaries (GBs) (Misorientation Angle 2–15°) Stabilizing the Microstructure Due to their Low Mobility. Small Grain Sizes, a High Fraction (\u3e80%) of High-Angle GBs (Misorientation Angle \u3e15°) and Accordingly a Large Amount of Stored GB Energy, serve as the Driving Force for HPT KD to Undergo Grain Growth Instead of Recrystallization Driven by Excess Stored Strain Energy

Strength and fatigue of an ultrafine-grained Al-Cu-Mg alloy

The dependence of strength and fatigue on microstructure of the Al-Cu-Mg alloy has been investigated. Various microstructures of the alloy were produced: the one with a coarse-grained (CG) structure after T6 heat treatment; the one with a homogeneous ultrafine-grained (UFG) structure and the one with a bimodal (mixed) structure, both processed by equal-channel angular pressing (ECAP). The mean grain size and morphology of precipitates were studied by transmission electron microscopy. The ultimate tensile strength and the fatigue endurance limit were determined using the tensile and fatigue tests of standard specimens. It is established that the formation of a homogeneous UFG structure and of a bimodal (mixed) structure alloy contributes to a significant increase in microhardness by 16% and 60%, and an increase of the ultimate tensile strength by 20 and 52%, respectively, as compared to the samples subjected to T6 heat treatment. Fatigue tests show that the alloy with a bimodal (mixed) structure has the highest fatigue endurance limit, 45% higher than in the sample subjected to T6 heat treatment. In contrast, the formation of a homogeneous UFG structure enables increasing the fatigue endurance limit by 15% only

Strength and fatigue of an ultrafine-grained Al-Cu-Mg alloy

The dependence of strength and fatigue on microstructure of the Al-Cu-Mg alloy has been investigated. Various microstructures of the alloy were produced: the one with a coarse-grained (CG) structure after T6 heat treatment; the one with a homogeneous ultrafine-grained (UFG) structure and the one with a bimodal (mixed) structure, both processed by equal-channel angular pressing (ECAP). The mean grain size and morphology of precipitates were studied by transmission electron microscopy. The ultimate tensile strength and the fatigue endurance limit were determined using the tensile and fatigue tests of standard specimens. It is established that the formation of a homogeneous UFG structure and of a bimodal (mixed) structure alloy contributes to a significant increase in microhardness by 16% and 60%, and an increase of the ultimate tensile strength by 20 and 52%, respectively, as compared to the samples subjected to T6 heat treatment. Fatigue tests show that the alloy with a bimodal (mixed) structure has the highest fatigue endurance limit, 45% higher than in the sample subjected to T6 heat treatment. In contrast, the formation of a homogeneous UFG structure enables increasing the fatigue endurance limit by 15% only

Effects of the Tempering and High-Pressure Torsion Temperatures Onmicrostructure of Ferritic/Martensitic Steel Grade 91

Grade 91 (9Cr-1Mo) steel was subjected to various heat treatments and then to high-pressure torsion (HPT) at different temperatures. Its microstructure was studied using transmission electron microscopy (TEM) and X-ray diffraction (XRD). Effects of the tempering temperature and the HPT temperature on the microstructural features and microhardness in the ultrafine-grained (UFG) Grade 91 steel were researched. The study of the UFG structure formation takes into account two different microstructures observed: before HPT in both samples containing martensite and in fully ferritic samples

High-Pressure Torsion Assisted Segregation and Precipitation in a Fe-18Cr-8Ni Austenitic Stainless Steel

During irradiation or high-temperature aging, stainless steel can develop precipitates, significantly affecting mechanical properties. In this study atom probe tomography (APT) was used to study grain boundary segregation and secondary phases in a purely austenitic SS304 (a Fe-18Cr-8Ni steel) processed by high-pressure torsion (HPT) at 300 °C. Ni, Mn, Si enriched phase was observed at grain boundaries, and Cu nanoprecipitates were observed along and near phase/grain boundaries. Precipitation is facilitated by deformation assisted segregation along grain boundaries with a mechanism similar to vacancy diffusion in irradiated steels

Nanostructure and related mechanical properties of an Al-Mg-Si alloy processed by severe plastic deformation

Microstructural features and mechanical properties of an Al-Mg-Si alloy processed by high-pressure torsion have been investigated using transmission electron microscopy, X-ray diffraction, three-dimensional atom probe, tensile tests and microhardness measurements. It is shown that HPT processing of the Al-Mg-Si alloy leads to a much stronger grain size refinement than of pure aluminium (down to 100 nm). Moreover, massive segregation of alloying elements along grain boundaries is observed. This nanostructure exhibits a yield stress even two times higher than that after a standard T6 heat treatment of the coarse grained allo

Evolution of Microstructure and Texture during Annealing in a High-Pressure Torsion Processed Fe-9Cr Alloy

The microstructure and texture of a Grade 91 (Fe-9Cr)alloy, which were subjected to high-pressure torsion (HPT)and annealing at 600 °C, were investigated. The HPT significantly refined the grain size, and generated typical body-centered cubic (bcc)torsion textures, including J{110} \u3c 211\u3e , D{112} \u3c 111 \u3e and E{011} \u3c 111 \u3e. During annealing, grains grew, and J became the most important texture component. Grains orientated in J showed increased number density and larger average grain sizes in the annealed microstructure. The dominance of J can be explained based on the stored energy and grain boundary characteristics of the J grains

Nanostructure and related mechanical properties of an Al-Mg-Si alloy processed by severe plastic deformation

Microstructural features and mechanical properties of an Al-Mg-Si alloy processed by high-pressure torsion have been investigated using transmission electron microscopy, X-ray diffraction, three-dimensional atom probe, tensile tests and microhardness measurements. It is shown that HPT processing of the Al-Mg-Si alloy leads to a much stronger grain size refinement than of pure aluminium (down to 100 nm). Moreover, massive segregation of alloying elements along grain boundaries is observed. This nanostructure exhibits a yield stress even two times higher than that after a standard T6 heat treatment of the coarse grained allo