High Temperature Creep Damage Research Articles

The influence of grain boundary character distribution on the high-temperature creep behavior and damage mechanism of Inconel 718

Thermomechanical processing as the main method of grain boundary engineering (GBE), can modulate the grain boundary character distribution (GBCD) in turn affects the mechanical properties and stability of alloys at high temperature. In this study, the microstructural evolution and creep behaviour of different GBCD alloys were investigated during the creep process at 660 °C and 690 MPa, and the effect of GBCD on high temperature creep behaviour and associated damage mechanism were analyzed from the viewpoints of grain size, recrystallisation and dislocation motion. The findings indicate that the larger grain size prolongs the steady-state creep duration, which is beneficial to the increase of creep life. During the creep process, the coherent twin boundary is susceptible to transformation into non-coherent twin boundary, resulting in the loss of its difficult-to-migrate properties and increased susceptibility to becoming recrystallisation nucleation sites. Furthermore, the formation of twins is conducive to the stimulation of dynamic recrystallisation. Discontinuous dynamic recrystallisation, characterised by the nucleation and growth of grains, occurs concurrently with continuous dynamic recrystallisation with strain gradients and orientations. The combined effect of these processes is grain boundary slip and restricted dislocation migration, which in turn alter the creep properties of the alloy.

Effect of alloying elements on coexisting phases and microstructure of M174 heat-resistant aluminum alloy

Abstract This article mainly focuses on high-power density diesel engine piston alloys, with the main component system being M174 heat-resistant aluminum alloy. On this basis, the main heat-resistant alloying elements Cu, Ni, and Fe were optimized and designed. This article is based on Thermo-Calc thermodynamic software, and comprehensively calculates and analyzes the multi-component alloy equilibrium phase diagram and Scheil non-equilibrium solidification of Al-(4-6)Cu-(1.5-3)Ni-(0.7-1.1Fe)-12.5Si-0.85Mg (mt.%) heat-resistant aluminum alloy system. Through the orthogonal experimental method of alloy composition, the phase distribution and microstructure composition of different alloy compositions are obtained. Research has found that Fe-rich phases such as Al5FeSi and Al9FeNi, as well as Ni-rich phases such as A13CuNi, A17Cu4Ni, and Al3Ni, are the main heat-resistant phases of the alloy in the temperature range of 350°C-420°C, providing important support for the high-temperature mechanical properties and creep damage resistance of piston aluminum alloy. At the same time, this article further studies the solidification history and microstructure precipitation of alloys. Fe-rich heat-resistant phases such as Al5FeSi and Al9FeNi have a higher solidification sequence. As primary and secondary phases, it is easy to generate coarse solidified structures. The organizational content is sensitive to the alloy composition. A13CuNi and A17Cu4Ni mainly precipitate in a multi-component eutectic structure, with layered and petal-shaped morphologies. The research results of this article have important theoretical significance and application value for the optimization design of high-power density piston aluminum alloy composition and the coordinated control of multi-phase structure.

In situ monitoring of high-temperature creep damage in CrMoV high-strength structural steel using acoustic emission

The accurate detection and evaluation of creep damage in structural steel is essential for ensuring the safety and reliability of high-temperature structures. In this work, the in situ monitoring and identification of high-temperature creep damage in CrMoV high-strength steel under different stress levels was conducted using the acoustic emission (AE) technique. A denoising procedure was proposed and applied to raw AE signals to reduce the noise unrelated to the growth of creep damage. To characterize the creep damage both qualitatively and quantitatively, multiple AE features were extracted from the creep-related signals, including peak amplitude, count, and information entropy. The results showed that a sudden increase in multiple cumulative parameters accompanied by high-entropy and high-count AE signals can accurately identify the transition from the secondary to the tertiary stage and can offer an early warning of the final rupture. In the log-log scale, the quantitative relationship between the AE rate and the minimum creep rate was found to be linear. Additionally, the substantial plastic deformation, and the nucleation, growth and coalescence of creep cavities were the dominating source mechanisms contributing to the generation of numerous high-count and high-entropy AE signals in the tertiary creep stage. Findings from this work will offer an approach for in situ monitoring and evaluation of the state of creep damage of high-temperature structures based on AE.

Evaluation of external tubular configurations for a high-temperature chloride molten salt solar receiver operating above 700 °C

Next-generation concentrating solar power (CSP) tower technologies target operating temperatures exceeding 700 °C to increase the thermal-to-electric conversion efficiency. Molten chloride salts are one possible alternative to current commercial molten nitrate salts to enable the higher operating temperature. This paper analyzes the predicted optical, thermal-fluids, and structural performance of traditional external tubular solar receiver configurations applied with a chloride salt heat transfer fluid (HTF) and inlet/outlet temperatures of 500 °C/735 °C, and considers sensitivity analysis and optimization relative to receiver sizing, tube sizing, number of panels, flow circuit configurations, and solar flux concentration under constraints on internal velocity, pressure drop, wall thickness, and required creep-fatigue lifetime. The high temperature conditions increase the significance of inelastic deformation mechanisms such as creep relative to that expected in commercial 565 °C nitrate salt designs. High-temperature creep and creep-fatigue damage in the metal alloy tubes are the key factors that limit allowable solar flux concentration and achievable receiver thermal efficiency at the near-800 °C wall temperature conditions. For a traditional external cylindrical receiver configuration, the design parameters and conditions capable of satisfying all constraints produced, at best, a design point receiver efficiency of 78.2%, or 80.5% when excluding receiver intercept efficiency. Variation in the optimal receiver performance relative to uncertainty in the binding maximum velocity, minimum wall thickness, and minimum lifetime constraints is presented.

A combined fugacity and multi-axial ductility damage approach in predicting high temperature hydrogen attack in a reactor inlet nozzle

High temperature hydrogen attack (HTHA) and creep damage and cracking are time-dependent phenomena which can occur at relatively low temperatures (300–500 °C) in low alloy steel components used in petroleum refinery and petrochemical plant. The present study combines a novel multiaxial ductility creep model with a sub-grain level fugacity partial pressure strain-based failure criterion due to a build-up of methane gas to predict progressive damage accumulation and HTTA degradation in an aging nozzle component. Finite element (FE) simulations using appropriate subroutines for the coupled approach allow progressive failure predictions combining HTHA and creep deformation in a C-0.5Mo steel inlet nozzle which had seen 80,000 h operation. A sensitivity study has been carried out to quantify the effects of different operating temperatures, failure strains, hydrogen concentration and pressure and material hydrogen diffusivity on the levels of damage in the nozzle over its lifetime. The predictions accurately bound the measured damage observed in the nozzle component and highlight the sensitivity of the model with respect to the input variables.

Nanosized-Precipitate Behavior of Ferritic 11Cr Heat-Resistance Steel Subjected to High Temperature Creep Damage.

The nanosized-precipitate behavior of ferritic 11Cr heat-resistance steel subjected to high temperature creep damage was investigated. The ferritic 11Cr4W3Co steel has been prepared by vacuum induction melting process. The microstructure shows significant changes in precipitate size and precipitate number. With increasing aging time, the size of the precipitates clearly grew following the Ostwald ripening. The coarsening rate of Laves (Fe₂W) phase is much faster than that of other precipitates such as Cr23C6 and NbC carbides.

Experimental Study on High Temperature Creep Damage of 1Cr5Mo Steel Based on Magnetic Parameters

Aiming at the evaluation of creep damage at elevated temperature of ferromagnetic materials in engineering application, the hysteresis loop measurement technology was adopted to study the creep damage behaviour of 1Cr5Mo steel. The creep testing at 600°C/90MPa of 1Cr5Mo steel were carried out to prepare specimens with various degrees of creep damage. The variation of magnetic parameter including coercivity (HC) and remanence (Br) with creep damage was analyzed. The microstructure evolution of 1Cr5Mo steel with different degrees of creep damage was observed by optical microscope. The results show that the coercivity and remanence show certain regularity with creep damage at elevated temperature. Moreover, the regularity is repeatable which indicates that the measurement technology based on magnetic parameters can be used for the evaluation of high temperature creep damage.

Development of failure evaluation method for BWR Lower head in severe accident; high temperature creep test and creep damage model

Development of failure evaluation method for BWR Lower head in severe accident; high temperature creep test and creep damage model

Preparation of Oxide Dispersion Strengthened Fe by Co-Precipitation

Oxide dispersion strengthened (ODS) materials have received extensive attention due to their excellent resistance to high temperature creep, fatigue, corrosion and radiation damage. In this paper, the ODS iron powder is prepared by co-precipitation. The oxide dispersion strengthened iron was prepared by spark plasma sintering (SPS) from the ODS iron powder. The microstructure and mechanical properties of the materials were investigated by Scanning Electron Microscope and micro-electronic universal tester. The results reveal the Al2O3 dispersion of ODS iron powder by co-precipitation is uniform and the mechanical properties are excellent.

In-Situ Microtomographic Characterization of Single-Cavity Growth During High-Temperature Creep of Leaded Brass

Synchrotron microtomography was used for in-situ characterization of high-temperature creep damage in leaded brass. Applying image registration to subsequent tomographic reconstructions, the volumetric growth rate of single cavities with equivalent radii between 2 and 4.3 μm was assessed. We conclude from the volume dependence of the growth rates that both the viscous flow and grain boundary (GB) diffusion mechanisms influence void growth. We show that void growth in leaded brass is retarded by negative stress triaxiality, which develops in the matrix during heating the specimen to the deformation temperature.

A coupled damage model for creep

Alloy steels of type 9Cr1Mo are being developed worldwide for the boiler and turbine components of supercritical and ultra supercritical thermal power plants and for the pressure vessel of fast breeder reactors. These steels exhibit very complex high temperature creep cavitation processes with coupled influences of creep strain, material softening and ageing etc. A new viscoplastic model considering both deformation and damage evolution has been developed in this work to predict high temperature creep deformation and damage of a 9Cr1Mo steel. Smooth tensile specimens have been analysed using this new model and the evolution of creep damage has been predicted. The results have been compared with those of experiment from literature. From the initial results, it is observed that this approach is very promising to carry out design and fitness-for-purpose of service of actual plant components.

Verification of 3-D parallel CDM software for the analysis of creep failure in the HAZ region of Cr–Mo–V crosswelds

The finite element-based Continuum Damage Mechanics (CDM) software DAMAGE XXX has been developed: to model high-temperature creep damage initiation, evolution and crack growth in 3-D engineering components; and, to run on parallel computer architectures. The driver has been to achieve computational speed through computer parallelism. The development and verification of the software have been carried out using uni-axial crosswelded testpieces in which the plane of symmetry of the V-weld preparation is orthogonal to the tensile loading axis. The welds were manufactured using 0.5Cr–0.5Mo–0.25V ferritic parent steel, and a matching 2.25Cr–1Mo ferritic steel weld filler metal. The Heat Affected Zones (HAZ) of welds were assumed to be divided into three sub-regions: Coarse grained-HAZ (CG-HAZ); Refined grained-HAZ (R-HAZ); and, the inter-critical HAZ regions (Type IV-HAZ). Constitutive equations and associated parameters are summarised for weld, CG-HAZ, R-HAZ, Type IV-HAZ, and parent materials, at 575, 590, and 600 °C. These are used to make finite element-based predictions of crossweld testpiece lifetimes and failure modes using the newly developed 3-D parallel computer software, and independent 2-D serial software, at an average minimum cross-section stress of 69.5 MPa. Crossweld testpiece analyses, done using the newly developed 3-D parallel software, have been verified using independent results of 2-D serial software; and, of laboratory experiments.

Modelling high temperature creep flow, damage and fracture behaviour of 9Cr1Mo–NbV steel weldments

The present study aims at predicting creep flow and damage behaviour of welded components made of 9Cr1Mo–NbV steels. A creep model coupling several creep deformation and damage mechanisms was separately fitted to experimental data for the base metal, the weld metal and the heat affected zone. The model was then used in a three-material finite element simulation of the weldment for various kinds of creep specimen geometry. The influence of the heterogeneity in creep properties and of the cross-weld specimen geometry on the creep response could be particularly explored.

Modelling high temperature creep flow, damage and fracture behaviour of 9Cr1Mo–NbV steel weldments

Modelling high temperature creep flow, damage and fracture behaviour of 9Cr1Mo–NbV steel weldments

A three dimensional view of high temperature creep damage

A three dimensional view of creep voids in a hydrogen reformer tube is presented. By separating and reconstructing various microstructural features present, the proper representation of creep voids in 3D can be fully studied. Useful measurements of parameters such as void volume, void-to-void distance, and grain boundary angles were obtained. The data presented here represent the initial collection of creep void information for use in various creep void nucleation and growth models. Additional data are currently being collected for material subjected to different service conditions.

A three dimensional view of high temperature creep damage

A three dimensional view of high temperature creep damage

Failure analysis of furnace radiant tubes exposed to excessive temperature

Radiant tubes of an ethane pyrolysis furnace at a petrochemical plant failed after a fraction of service life. The tubes developed longitudinal cracks that in extreme cases penetrated the entire tube thickness. The tubes were manufactured from HP 45 heat-resistant steel casting. Scanning electron microscopy and energy dispersive X-ray spectroscopy were used to characterize the microstructure and chemical composition of the tube samples. Microhardness testing was used to evaluate the mechanical strength while structural analysis was conducted in an X-ray diffractometer. The experimental results showed that the mode of tube failure was a combination of high temperature carburization attack and creep damage leading to intergranular cracking. The cause of failure was overheating likely during decoking operations. Better control of furnace temperature was recommended in order to avoid overheating. However, if the furnace temperature exceeds 900 °C during operation, alloy replacement must be considered. In this case, steel casting material more resistant to carburization and creep damage such as the HP + W grade was suggested as an alternative.

High temperature creep flow and damage properties of 9Cr1MoNbV steels: Base metal and weldment

High temperature creep flow and damage properties of 9Cr1MoNbV steel and weldment are investigated in the present study. First, an experimental database is built to compare both creep flow and damage properties of the base metal and the weldment. Metallurgical investigations before and after creep tests revealed that the microstructural state is responsible for the lower creep strength in the weldment. A simple analysis based on the description of the steady-state creep stage and on use of empirical lifetime prediction relationships is performed. It allows to predict the weldment creep lifetime without performing an extensive number of experiments.

Creep failure model of a tempered martensitic stainless steel integrating multiple deformation and damage mechanisms

A new model considering both deformation and damage evolution under multiple viscoplastic mechanisms is used to represent high temperature creep deformation and damage of a martensitic stainless steel in a wide range of load levels. First, an experimental database is built to characterise both creep flow and damage behaviour using tests on various kinds of specimens. The parameters of the model are fitted to the results and to literature data for long term creep exposure. An attempt is made to use the model to predict creep time to failure up to 105 h.

High Temperature Creep Flow and Damage Properties of the Weakest Area of 9Cr1Mo-NbV Martensitic Steel Weldments

In the present study, creep flow and damage behaviour of modified P91 steel weldments are investigated. Premature creep failure of weldments (with respect to base metal) occurs in the intercritical heat affected zone (ICHAZ). This microstructure is reproduced by thermal simulation applied to blanks cut from the base metal. Metallurgical investigations of what happens during the welding cycle show that the weakest part of the heat affected zone is heated slightly below complete austenitisation, with little (if any) carbide dissolution. During the post-weld heat treatment, extensive recovery is allowed by carbide coarsening. The intrinsic creep behaviour of the resulting microstructure is experimentally determined under controlled constraint conditions. The welding cycle strongly decreases the creep strength by increasing the creep strain rate, but not necessarily by decreasing the ductility, at least for lifetimes up to 3 500 h.