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By time-of-flight (TOF) neutron diffraction experiments, the influence of segregation-induced microstructure bands of austenite (γ) and martensite (α′) phases on the partitioning of stress and strain between these phases was investigated. Initially, tensile specimens of a Co-added stainless steel were heat treated by quenching and partitioning (Q&P) processing. Tensile specimens were subsequently loaded at 350 °C parallel to the length of the bands within the apparent elastic limit of the phase mixture. Lattice parameters in both axial and transverse directions were simultaneously measured for both phases. The observation of a lattice expansion for the γ phase in the transverse direction indicated a constraint on the free transverse straining of γ arising from the banded microstructure. The lateral contraction of α′ imposed an interphase tensile microstress in the transverse direction of the γ phase. The multiaxial stress state developed in the γ phase resulted in a large deviation from the level of plastic strain expected for uniaxial loading of single phase γ. Since segregation-induced banded microstructures commonly occur in many engineering alloys, the analysis of stress and strain partitioning with the present Q&P steel can be used to interpret the observations made for further engineering alloys with two-phase microstructures. [ABSTRACT FROM AUTHOR]

Grain boundary structure and chemical composition have been shown to play important roles in plasticity, strength, creep, diffusivity, and conductivity of fine-grained metallic materials. Wetting of grain boundaries in metallic materials with nanoscale intergranular intermetallic compound films (NIICFs) is suggested to offer enhanced strength and ductility of alloys. In the current study, the NIICF wetting Cu-Zr micrograins of the matrix is observed in a Cu-5 at. pct Zr alloy produced by powder metallurgy. The underlying mechanism responsible for the formation of these NIICFs is discussed, and the effect of these films on the strength and strain-hardening capacity of the alloy is evaluated. [ABSTRACT FROM AUTHOR]

The Hall–Petch relation has long been used to relate the yield strength of a metal to its grain sizes in which the effectiveness of grain size strengthening in the metal is dictated by the Hall–Petch coefficient (slope). Therefore, understanding the microstructural dependence of the Hall–Petch slope would be very useful in designing new high-strength ultrafine grained (UFG) metallic materials. In this study, we investigated the microstructural factors affecting the Hall–Petch slope in UFG Al-Mg alloys with an average grain size range from 374 to 639 nm and different Mg contents of 0, 2.5, 5, and 7.5 at. pct. The rods prepared by extrusion of mechanically alloyed powder compacts were annealed for 5 hours at 380 °C, 420 °C, and 500 °C respectively followed by water quenching to produce the alloy samples in this study. The measured Hall–Petch slopes of the samples were found to increase with increasing Mg content and had higher values than those previously reported for Al(Mg) solid solutions with Mg concentrations comparable to the Mg contents in this study. Analysis of X-ray diffraction, transmission electron microscopy, and atom probe tomography experimental data as well as strengthening mechanisms demonstrates that the formation of nanoscale MgO dispersions plays a major role in the improved Hall–Petch slope observed in Al-Mg alloys. [ABSTRACT FROM AUTHOR]

Highlights • Amount of Mo 2 C precipitates is proportional to the amount of SiC in the initial powder mixture. • Mo 2 C precipitates readily dissolve into FLiNaK molten salt leaving behind empty voids. • The corrosion resistance of NiMo-SiC alloys is strongly dependent on the amount of SiC in the initial powder mixture. • The corrosion resistance of NiMo-SiC alloys with a low SiC content (<2 wt.%) is comparable to Hastelloy-N®. Abstract The corrosion performance of Ni-16%wt.Mo-X%wt.SiC (X = 0.5, 1.5, 2.0, 2.5 and 3.0) alloys prepared via mechanical alloying followed by consolidation using spark plasma sintering (SPS) from pure Ni, Mo and SiC powders is investigated. Corrosion testing at 650 °C/200 h in FLiNaK molten salt showed that increasing the volume fraction of SiC in the initial Ni-Mo-SiC powder mixture leads to formation of large amount of Mo 2 C precipitates, which readily dissolve into FLiNaK molten salt. Hence, only the corrosion resistance of NiMo-SiC alloys with a low SiC content (<2 wt.%) is comparable to that of Hastelloy-N® alloy. [ABSTRACT FROM AUTHOR]

This study aims to predict the creep response of Alloy 617 and assess the accuracy of three established creep damage models in predicting the creep time-to-failure ( t f ) and strain-to-failure ( ε f ) in the temperature range of 800–1000 °C. Idaho National Laboratory (INL) creep data were used to calibrate (1) Ductility Exhaustion (DE), (2) Stress-Modified Ductility Exhaustion (SMDE), and (3) Strain-Energy Density (SED) creep damage models using multiple linear regression (LR) and reverse damage (RD) approaches. In order to predict the creep response of Alloy 617 these creep damage models are then coupled with (secondary) creep strain model calibrated using Idaho National Laboratory (INL), Korean Atomic Energy Research Institute (KAERI), and Argonne National Laboratory (ANL) experimental data. Direct comparisons made between the investigated creep damage models revealed that the SED model with parameters calibrated through RD approach captures the creep response of Alloy 617 the most accurately and it thus produces the most accurate prediction of time-to-failure ( t f ) and strain-to-failure ( ε f ) across different temperature/stress (creep) conditions. However, it is also shown that none of the employed creep damage models are able to fully capture the material creep response at 1000 °C. This is attributed the strong oxidation of Alloy 617 at 1000 °C (tested in air) leading to the formation of a thick oxidation layer, which might affect the failure mechanism of the alloy at this temperature. • The most accurate prediction is achieved using Strain-Energy Density (SED) model. • Reverse damage approach yields more accurate results than linear regression approach. • No creep damage model was able to capture the creep behaviour at 1000 °C. [ABSTRACT FROM AUTHOR]

Annealing usually softens Al–Mg based alloys due to grain coarsening. This work shows that annealing induces strengthening in bulk ultrafine-grained Al and Al-(2.5, 5 and 7.5) at.% Mg samples fabricated by mechanical alloying and rapid powder extrusion. Experimental investigation of the microstructure of the annealed samples reveals that the annealing promotes in-situ formation of nanoscale dispersoids which strongly suppresses grain growth and recrystallization. The in-situ formed nanodispersoids warrant high thermal stability of the ultrafine-grained matrix microstructure and improve the strength of the as-extruded samples while maintaining their good ductility. The present findings offer an exciting pathway in developing thermally stable ultrafine-grained Al–Mg based alloys with a notable combination of high strength and good ductility. [ABSTRACT FROM AUTHOR]

The irradiation damage behavior was studied in the nano-grained Ni–Mo–Cr alloy (nano-grained GH3535), which was irradiated by He ion to various dose. The evolution of defects and hardness changes are characterized by transmission electron microscopy and nanoindentation to explore the irradiation tolerance of the nano-grained GH3535 and the coarse-grained GH3535 (annealed GH3535), where the later was chosen as reference material to make comparison with nano-grained GH3535. The results show that though both the average size and number density of He bubbles increase with an increase in the irradiation dose, the smaller volume fraction is found in the nano-grained GH3535 compared with the coarse-grained GH3535 under the same irradiation condition. This indicates that the nano-grained GH3535 possess better irradiation swelling resistance than the coarse-grained GH3535. However, the increase in the hardness of the nano-grained GH3535 is more significant than in the coarse-grained GH3535 under the same irradiation dose. This suggests stronger irradiation-induced hardening of the nano-grained alloy comparing to coarse-grained alloy, due to the impeding effect caused by grain boundaries decorated with He bubbles. This study provides insight into the design of irradiation-tolerant nickel-based alloys for nuclear industry applications. [ABSTRACT FROM AUTHOR]

A new Powder-bed Arc Additive Manufacturing (PAAM) processing which includes on-line remelting of deposited material has been developed for the manufacturing of high entropy alloys (HEAs) based on an existing AlCoCrFeNi 2.1 pseudo-eutectic system. The remelting process is typically applied in the arc melting process to improve the homogeneity of prepared material. We investigated the microstructure and mechanical properties of produced AlCoCrFeNi 2.1 HEA after applying a remelting process (1, 3, and 6 times) on each deposited layer. The results show the formation of the pseudo-eutectic microstructure, which consists of relatively large columnar grains of the dominant FCC phase (~90 wt%) and fine dendritic grains of the minor BCC phase (~10 wt%). The applied layer-remelting process shows negligible effects on the phase fractions and their compositions, however, it significantly degraded the tensile strength and ductility of prepared alloys. Particularly, the ductility of the alloy reduced dramatically from about 27% after one time layer-remelting to only about 3% after 3 times layer-remelting. This is rationalised by the significant localisation of thermally induced plasticity caused by repeated remelting of deposited material. We also show that this thermally induced plasticity leads to an increased amount of local misorientation in both constitute phases, which suggests an increased amount of stored dislocations in the microstructure. Despite the potentially strain hardening due to this accumulation of the thermally induced plasticity, the appreciable growth and constrained dendritic morphology of BCC grains that developed after remelting play a prevailing role on the materials strength, which limit the interfacial strengthening of the eutectic microstructure and consequently result in the loss of the tensile strength. The obtained results will assist in the further development and microstructure optimisation of novel HEAs using powder-based additive manufacturing processes. [ABSTRACT FROM AUTHOR]

High strength has always been pursued in binary Al–Mg and 5xxx series Al alloys. However, these alloys usually provide medium strength due to lack of multiple strengthening methods. Here, this study reports on multiple strengthening effects existing in a binary ultrafine-grained (UFG) Al-7.5at.%Mg alloy prepared by mechanical alloying and hot extrusion. Different strengthening mechanisms, in particular, dispersoid strengthening and stacking fault strengthening, are analyzed and evaluated in terms of their respective contribution to the 511 MPa yield strength of the alloy. The strengthening analysis proves that the concurrent generation of nanoscale dispersoids and stacking faults (SFs) can be used as a new microstructural design in developing novel Al–Mg-based alloys with higher strength and enhanced ductility. [ABSTRACT FROM AUTHOR]