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The mechanical performance of a Ni–Mo–Cr (GH3535) alloy weldment, produced using a matching filler metal, was assessed and compared to the surrounding parent metal. Ambient-temperature mechanical characterisation included hardness testing, small punch testing and uniaxial tensile testing, while a crystal plasticity finite element model was used to assess the impact of crystallographic texture on the mechanical properties. Despite the similar chemical composition, the weld metal exhibited superior strength and ductility to that of the parent metal. The higher strength was primarily attributed to the high dislocation density in the weld metal imbued by the welding-induced thermo-mechanical loading. In contrast, the ductility difference was attributed to M6C carbide stringers in the parent metal that initiated fracture at lower strains when compared to the weld metal, with the latter containing finer, well-dispersed M6C carbides.

This study aims to assess the accuracy of various modelling methodologies in predicting creep-fatigue damage (dcf) and cycles-to-crack-initiation (Ni) of Alloy 617 at 850 °C and 950 °C. In the decoupled methodologies, four creep damage models were employed: (i) the time fraction (TF), (ii) ductility exhaustion (DE), (iii) stress-modified ductility exhaustion (SMDE), and (iv) strain-energy density (SED), to capture the creep damage (dc) contribution to the overall creep-fatigue damage (dcf), while fatigue damage (df) contribution was always calculated using the simple “average” approach. Furthermore, we employed Holmström's integrated ϕ model, which combines the dcf into a single parameter without a need of separate assessment of creep damage (dc) and fatigue damage (df). The results show that there is no significant difference between the integrated ϕ model and decoupled creep-fatigue methodologies when the creep damage models are calibrated to creep-fatigue (CF) data. However, it is shown that the accuracy of the creep-fatigue damage (dcf) predictions using the decoupled approach gets significantly worse when the creep damage models are calibrated against independent creep-rupture (CR) data. It is further shown that when using DE, SMDE, SED creep damage models, the dcf predictions are arranged by strain range, suggesting that these models are better at capturing strain range variations rather than temperature changes. Based on the obtained results it is recommended that any of the employed creep damage models are all suitable for coupling with the “average” fatigue damage model when capturing the creep-fatigue behaviour of Alloy 617, as long as the employed creep damage model is calibrated directly to the experimental creep-fatigue (CF) data.

Laser additive manufacturing of bulk metallic glass (BMG) provides an effective bypassing of the critical casting thickness constraints that limit the size of components that can be produced; however, open questions remain regarding the resulting mechanical properties. In this work, a Zr-based BMG known as AMZ4 with composition Zr59.3Cu28.8Nb1.5Al10.4 was printed using a laser powder bed fusion (LPBF) technique. Micro X-ray computed tomography results together with electron microscopy imaging revealed porous processing defects in LPBF produced AMZ4 that led to a loss in tensile strength. Fatigue crack growth studies revealed a fatigue threshold, ΔKth., of ∼1.33 MPa√m and a Paris law exponent of m = 1.14, which are relatively low values for metallic materials. A KIC fracture toughness of 24−29 MPa√m was found for the LPBF BMG samples, which is much lower than the KQ of 97−138 MPa√m and KJIC of 158−253 MPa√m measured for the cast alloy with the same composition. The lower fracture toughness of the laser processed AMZ4 was attributed to ∼7.5× higher dissolved oxygen in the structure when compared to the cast AMZ4. Despite the higher level of oxygen, the formation of oxide nanocrystals was not observed by transmission electron microscopy. Oxygen induced toughness loss was confirmed by dissolving elevated concentrations of oxygen into cast AMZ4 rods, which led to a reduction in bending ductility and changes in the short-range order of the glass structure, as revealed by synchrotron X-ray diffraction.

© 2019 The molten salt corrosion performance of a Ni–Mo–Cr (GH3535) alloy weldment, produced using matching filler metal, was assessed. Corrosion testing was performed in FLiNaK molten salt at 750 °C for 500 h. Present results reveal that, despite a similar chemical composition, the weld metal has somewhat superior corrosion resistance to the parent metal. The difference is primarily attributed to the significantly lower density of high-angle grain boundaries (HAGBs) in the weld metal. Results further suggest that large M6C carbides present in the parent metal may contribute to corrosion attack of the alloy matrix via galvanic corrosion.

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.