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The thermally activated dislocation motion due to plastic deformation in Inconel 690 has been carried out by performing tensile tests in air and in environmental hydrogen using the strain relaxation technique. The results show that the variation of - δ (Δ A/b 2 ) or ln( V H / V Air ) with ε p depends on the nickel content in the alloy and the microstructure, and generally increases with increasing Ni% for low value of ε p (tensile test). The maximum increase in the rate change was observed for the austenized and aged microstructure. On the other hand, fatigue crack propagation rate ( da / dN ) has been measured in the same environments. An attempt has been carried out to correlate the rate change - δ (Δ A/b 2 ) or ln( V H / V Air ) with the variation of ( da / dN ) H against ( da / dN ) Air (the variation of Ω ) and has shown that for the austenized and aged microstructure, Ω is higher than those for stress relieved or only aged at 700 °C. These results are similar to those obtained by the thermal activation parameter – δ (∆ A / b 2 ) or the ratio ln( V H / V Air ). The maximum values of – δ (∆ A / b 2 ) and Ω are obtained when the density of precipitates on the grain boundaries is higher than that in the matrix. In this case, intergranular fractures with fin slip lines features on the grain surfaces were observed. Finally, in the presence of environmental hydrogen, about the fatigue crack propagation rate, two relationships were established and expressed as: 1) in stages I and II: ( Δε p /2) = Θ Δ K + Γ and 2) only in stage II: ( da / dN ) II = c II ( Δε p / 2) λ , where λ ≈ m = 2, the power factor in Paris' law. [ABSTRACT FROM AUTHOR]

Microstructure and mechanical performance of the welded joints of UNS N10003 alloy have been investigated in this work. Primary precipitates in base metal and eutectic precipitates in Heat Affected Zone (HAZ) and weld metal have been characterized and identified as M 6 C type. The hardness value of HAZ (Eutectic zone) is significantly higher than the rest of joint, including weld and base metal. Tensile tests suggested the welded joints possess a very stable mechanical performance at elevated temperature from 650 °C to 725 °C. Moreover all the tensile samples were fractured in base metal, indicating that the eutectic carbides have no adverse effects on the short-time mechanical performance of joint. The fine carbides, acting as dispersion strengthening in weld metal, are main contribution to enhance the hardness and strength of weld. The good mechanical performance of HAZ is ascribed to the presence of eutectic carbides and twins. [ABSTRACT FROM AUTHOR]

This study investigated the creep deformation properties of GH3535, a Ni–Mo–Cr corrosion resistant structural alloy being considered for use in future Gen IV molten salt nuclear reactors (MSR) operating at around 700 °C. Creep testing of the alloy was conducted at 650–750 °C under applied stresses between 85–380 MPa. From the creep rupture results the long term creep strain and rupture life of the alloy were estimated by applying the Dorn Shepard and Larson Miller time-temperature parameters and the alloy's allowable ASME design stresses at the MSR's operating temperature were evaluated. The material's microstructural degradation at creep rupture was characterised using scanning electron microscopy (SEM), electron backscatter diffraction (EBSD) and transmission electron microscopy (TEM). The microstructural study revealed that the material failure was due to wedge cracking at triple grain boundary points and cavitation at coarse secondary grain boundary precipitates, nucleated and grown during high temperature exposure, leading to intergranular crack propagation. EBSD local misorientation maps clearly show that the root cause of cavitation and crack propagation was due to large strain localisation at the grain boundaries and triple points instigated by grain boundary sliding during creep deformation. This caused the grain boundary decohesion and subsequent material failure. [ABSTRACT FROM AUTHOR]

Ni-based alloy Haynes 230 is of interest for high temperature applications (e.g. Intermediate Heat eXchanger (IHX)) because of its high temperature strength and oxidation resistance. In this work, the temperature dependence of the tensile behavior of the alloy and the strain rate effect was studied by tensile tests in the temperature range of 25–950°C, at strain rates of 10−3 s−1, 10−4 s−1, and 10−5 s−1. The tensile strength decreased with increasing temperature regardless of the strain rate. The total elongation at rupture fluctuated more with temperature. The alloy showed an abnormal variation of the yield stress with increasing temperature i.e. the yield strength decreased slightly with temperature up to about 600°C and then increased between 600 and 850°C followed by a rapid decrease. This Yield Stress Anomaly (YSA) was however absent at the slowest strain rate of 10−5 s−1. SEM and TEM characterization was performed on fractured specimens to determine the predominant deformation mechanisms accounting for the observed Yield Stress Anomaly. Also, serrations were observed in the stress–strain curves at temperatures above 300°C, the shape and amplitude of which depended on temperature and strain rate. The analysis of the stress–strain curves coupled with the microstructure investigation of the fractured samples showed that two different deformation mechanisms occur depending on the temperature and strain rate. The saw-tooth type serrations at intermediate temperatures and higher strain rates were associated with dynamic strain aging whereas the oscillations with a sinusoidal shape were associated with dynamic recrystallization at temperatures higher than 800°C and slower strain rates. [ABSTRACT FROM AUTHOR]

A composite coating with TiC particles of various shapes and sizes embedded in nickel based alloy has been in situ synthesized by laser melting a precursor mixture of nickel based alloy powder, graphite and titanium powders. The experiment result showed that the coating epitaxially grew from the substrate with excellent bonding between the coating and the carbon steel substrate. The coating is uniform, continuous and free of pores and cracks, and about 0.6 mm thick. The microstructure of the coating is mainly composed of γ-Ni dendrite, a small amount of interdendritic (γ-Ni+M23C6) eutectic, and dispersed TiC particles. The volume fraction of TiC particles and the microhardness gradually increased from the bottom to the top of the coating layer. [Copyright &y& Elsevier]