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The cast coarse-grained polycrystalline Alloy 247 is investigated, which is typically used in the rear turbine blades of land-based gas turbines. High rotational speeds up to 10,000 rpm in combination with high temperatures induce creep deformation. Additionally, gas turbine blades are subjected to high-frequency cyclic stresses. This complex loading state requires the investigation of the interaction of creep damage and high-cycle fatigue (HCF). Therefore, HCF tests with a stress ratio of Rσ = −1 were carried out on as-received and pre-crept specimens. In comparison, an HCF test series with high mean stresses (Rσ = 0.5) was conducted to consider the superposition of creep and fatigue. Since nickel-base alloys exhibit a pronounced elastic anisotropy, the grain orientations were considered in the damage analysis. The results show that creep-induced grain boundary damage is a dominant structural parameter for the HCF behaviour of Alloy 247 in both, sequential and superpositioned creep-fatigue loading. [ABSTRACT FROM AUTHOR]

A study of the mechanical properties of Ti64 alloy through Small Punch Test is presented in this paper. The method and the validity of the correlation coefficients developed for nuclear steels are first verified on wrought alloy and then applied to additive manufactured material. The yield strength values obtained agree with the literature and domains of negative strain rate sensitivity could be highlighted for the microstructure resulting from additive manufacturing. The creep tests carried out showed good agreement between the present results and those reported in the literature on usual creep representations. This allows to validate the models used and to extend the small punch methods to the case of titanium alloys. The results are used for comparing the mechanical behaviour of additive manufactured Ti64 alloy to that of wrought alloys. [ABSTRACT FROM AUTHOR]

The effects of Re/Re on the element distribution and creep performance of nickel-based single crystal alloy by using atom probe tomography (APT) and creeping property testing has been studied. Results show that the elements Re, Ru, W, Mo, Cr, and Co are the former of γ phase; the elements are distributed in γ and γ' phases of two alloys according to various ratios. Some of the Ru atoms in Re-containing alloy make more Al, Ta atoms are dissolved in γ matrix and make more Mo, W, and Re atoms dissolving in γ' phase, which increases the alloying degree of γ", γ phases to enhance the strength and creep resistance of alloy. Particularly, the Re and W atoms dissolved in γ" phase are excluded, during creep, for the enrichmrnt in γ phase near the interface to form their peak content; the lattice distortion coming from the enriched Re and W atoms restrains dislocations gliding to delay the γ' phase from being sheared. The deformed mechanisms of alloy in the later stage of creep are the dislocations gliding in γ phase and shearing γ' phase. Wherein, the dislocations of shearing γ' phase are both glided on {111} planes and cross-glided from {111} to {001} planes to form the KW locks, the ones that restrain the gliding and cross-gliding of dislocations for improving the creep resistance of alloy. While the interaction of the Ru with Re and W atoms make some Reand W atoms reserved in the γ′ phase to delay the diffusion of other elements, which prevents the KW locks from being released, to keep the good resistance of alloy. [ABSTRACT FROM AUTHOR]

The γ/γ' microstructure is a key factor for the mechanical performance of nickel-based single crystal superalloys. Experimental results have shown that the size and shape of the γ' precipitates are not uniform and follow certain probability distributions. In order to study the effect of the microstructure on the mechanical behavior of the superalloys, a method is proposed to reproduce its initial microstructure with the distribution function of its γ′ particle size. The effect of different microstructures on the creep behavior at different locations of a real blade is predicted to demonstrate the application of the method. It can be found from the simulation results that the mechanical behavior of the blade is related to not only the thickness of the blade wall but also the position in the blade. [ABSTRACT FROM AUTHOR]

Additive manufacturing of alloys has gained attention by industry as it provides economical production of complex-configuration engine parts with fewer joining steps and greater geometric freedom. The creep behaviour of additively manufactured (AM) Inconel 625 and 718 at 650 and 800 °C was compared with that of the wrought alloy after 24 hour and long-term tests up to about one year. Inconel 718 is precipitation strengthened while 625 is solid-solution strengthened. It was discovered that the creep strength of the 625 and 718 produced by additively manufacturing is essentially identical than that of the wrought alloy. Complications occur, however, with a marked loss of ductility in the AM alloys. Fatigue and impact toughness were adversely affected as well. The basis for these degradations was particularly investigated. [ABSTRACT FROM AUTHOR]

By performing solution treatment at various temperatures, creep property measurements, and microstructural observations, the influence of the solution temperature on the microstructure uniformity and high-temperature creep properties of the DZ125 nickel-based alloy were studied. The results showed that after the solution and aging treatment of the alloy under a relatively low temperature of 1230°C, microstructure inhomogeneities in the dendrite/inter-dendrite regions appeared, and the coarse g¢ phase and eutectic structure in the casted alloy were not removed. The processing and aging treatment of the alloy under a higher solution temperature of 1260°C caused the coarse g¢ phase and eutectic structure within the inter-dendritic area of the alloy to be eliminated, thus enabling the uniform distribution of the fine cubic g¢ phase with a high-volume fraction between the dendrite/inter-dendrite regions and the enhancement of the creep performance of the alloy. [ABSTRACT FROM AUTHOR]

The directionally solidified Ni-based superalloy DS200 + Hf is used in aero-engines and industrial gas turbines for the manufacturing of intermediate and low-pressure turbine blades. This material consists of ~<0 0 1> columnar grains oriented along the solidification direction and with random secondary orientations. In this study, the creep behaviour of the DS200 + Hf alloy has been investigated along longitudinal and transverse directions. The main objective was to investigate the durability of this alloy and the damage mechanisms for four different crystalline microstructures: DS200 + Hf composed of fine grains loaded longitudinally, the same alloy composed of coarse grains or fine grains, loaded transversally to the solidification direction and finally, the single crystal version, Mar-M200 + Hf, loaded along a <0 0 1> crystallographic orientation. Creep tests were performed from 750°C up to 1100°C. Under all conditions, a pronounced decrease in the strain to failure is observed for specimens loaded along the transverse direction compared to specimens tested along longitudinal direction or single crystals. Fracture surface observations revealed that the lower creep ductility along such a loading direction results from an intergranular failure mode. Furthermore, the creep life anisotropy significantly decreases when temperature increases. Additional creep experiments under vacuum at 900°C and experiments using single crystalline specimens far away from the <0 0 1> crystallographic orientation show a prominent damaging role of oxidation at very high temperature and a major contribution of the local crystallography at low temperatures. In addition, the grain size effect observed when testing in the transverse direction only results from the grain boundary oxidation. [ABSTRACT FROM AUTHOR]

The paper presents original results of standardized long- and short-term creep tests for P91 steel. A modified Garofalo creep equation is proposed which offers a good description of the three stages of creep. The proposed creep equation allows easy determination of all constants that represent the material's actual physical properties. All coefficients of this creep equation are determined using the Levenberg-Marquardt algorithm and they are presented in the paper. The proposed creep equation is a function of stress, which allows its implementation in numerical calculations. The paper shows the presented creep equation application for modelling the strain and stress state in a thick-walled pressure element installed in a power plant. [ABSTRACT FROM AUTHOR]

316L(N) stainless steel (SS) containing 0·02-0·03 wt-% carbon and 0·06-0·08 wt-% nitrogen is the principal material for the high temperature structural components of the prototype fast breeder reactor in India. In order to increase the economic competitiveness of sodium cooled fast reactors (SFRs), there is a strong desire to increase the design life from the current level of 40 years to at least 60 years for the future reactors. As a part of the efforts to develop materials with superior mechanical properties suitable for longer design life, the influence of nitrogen at concentrations higher than 0·07 wt-%, on the high temperature mechanical properties of type 316L(N) SS is being studied. Four heats of 316L(N) SS, containing 0·07, 0·11, 0·14 and 0·22 wt-% nitrogen have been evaluated extensively in terms of their tensile, creep, low cycle fatigue and creep fatigue interaction properties. Based on these studies, the nitrogen content has been optimised at 0·14 wt-%. This nitrogen enhanced grade of steel (NE316LN SS) was found to have significantly better tensile, creep, low cycle fatigue and creep-fatigue properties as compared to the PFBR grade of 316L(N) SS. This paper presents the influence of nitrogen on the creep deformation, damage and fracture behaviour of NE316LN SS. Design of high temperature SFR components is made on the basis of RCC-MR design code. The creep properties of NE316LN SS have been analysed in terms of the procedures for generation of the design code. Time-dependent design curves have been generated. [ABSTRACT FROM AUTHOR]

Evolution of γ′ precipitates during creep has been investigated over a wide range of temperatures from 760 to 1100 °C in a liquid metal cooling directionally solidified nickel-based superalloy. Cubic γ′ precipitates were found to remain in the specimens crept at low temperatures, while rafting and cellular-like precipitates remained at intermediate and high temperatures, respectively. [ABSTRACT FROM AUTHOR]