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Abstract In past decades, molybdenum (Mo) has demonstrated the potential to replace tungsten (W) in designing lighter nickel-based single crystal superalloys with enhanced creep resistance. In this research, three groups of nickel-based single crystal superalloys are designed and prepared by tuning the Mo:W ratio. The experimental observations show that the primary and secondary dendrite arm spacings are both independent on Mo:W ratio, but the γ/γ′ eutectic volume fraction decreases as Mo:W ratio increases. The electron probe microanalysis reveals that Re, W and Co segregate to dendrite core regions, while Al, Ti, Cr, Mo and Ta to interdendritic regions. The microsegregation of Ta, W and Re are gradually relieved with increasing Mo:W ratio. Atom probe tomography results further indicate that Cr and Mo are depleted in γ/γ′ eutectics, leading to the enrichment of Cr and Mo at interdendritic regions away from γ/γ′ eutectics. Creep rupture results show that the rupture life at 1040 °C/145 MPa is improved as Mo:W ratio increases. [ABSTRACT FROM AUTHOR]

The research work explores the microstructure evolution and creeps rupture behavior of the shielded metal arc welded joint of reduced activation ferritic/martensitic P91 steel plate in the as-welded and different states of post weld heat treatment (PWHT). Two types of heat treatments were employed including (i) post weld heat treatment (PWHT) at 760 °C for 2 h and finally air cooled and (ii) re-austenitizing at 1040 °C for 60 min and air-cooled and tempered at 760 °C for 2 h, followed by air cooling (PWNT). The P91 steel plates were received in the cast and forged condition having fully tempered lath martensite with lath blocks, packet boundaries and prior austenite grain boundaries (PAGBs). In this research, microstructural evolution at fracture frontier of crept P91 weld sample, creep rupture life and effect of creep exposure time on microstructure evolution in the fine-grained heat affected zone (FGHAZ) were studied. The results show a dominating effect of PWNT treatment on fracture behavior and creep rupture life of the P91 welded joints. PWNT treatment results in negligible hardness variation across the transverse section of the weld joint. The creep rupture life of PWNT specimen was 594.895% higher as compared to that of PWHT specimen and 142.7% higher than that of the as-welded specimen for the similar condition of creep exposure (620 °C/150 MPa). In PWHT condition, the most common type IV cracking was observed. However, it was eliminated in PWNT specimens and fracture occurred form the base zone. The fracture frontier of crept PWNT specimen showed a higher amount of creep cavities that can be attributed to the formation of Laves phase. [ABSTRACT FROM AUTHOR]

This paper studied the creep rupture behavior of Hastelloy C276-BNi2 brazed joint by experimental. Based on a series of creep rupture tests at 600 °C under 110–250 MPa, a relation between the stress and rupture time was achieved to evaluate the creep life of brazed joint. The results show that all the brazed joints were fractured in brazed seam immediately after the second creep stage. The creep model, fracture behavior and failure mechanism are dependent on the level of applied stress. The creep behavior of the brazed joint should be depicted by two-regime Norton (2RN) creep model rather than single Norton model. The creep damage tolerance factor was used to identify the cause of creep damage. From low to high stress level, the failure mode is changed from intergranular brittle to transgranular ductile fracture due to the increases of damage tolerance factor with applied stress increases. [ABSTRACT FROM AUTHOR]

Creep rupture tests and tensile tests of Ti-22Al-25Nb alloy with bimodal size lamellar O phase microstructure were carried out at 650 °C and 700 °C. The fracture surface analyses indicate that the tensile fracture originated from the center of the cylinder sample while the creep rupture started at the surface. The different fracture mechanism of creep rupture samples is ascribed to the orthorhombic cases (O cases). It is found that the sub-surfaces of the creep rupture samples were enriched with the element oxygen. The interstitial oxygen, an alpha stabilizer for titanium alloys, promoted the transformation from B2 phase to O phase. Thus the sub-surfaces contained more acicular O phases than the substrates. The sub-surfaces with more O phase component are named as O cases. The dissolved interstitial oxygen and the added O phase component increased the strength but reduced the ductility and the toughness in the O cases. It was the incompatibility of the creep strains between the O cases and the substrates that made the creep rupture to originate at the surfaces. [ABSTRACT FROM AUTHOR]

Detailed investigations have been performed to examine the creep deformation behavior and microstructural evolution of modified 9Cr-1Mo steel which is widely used in high temperature power plant component. The creep data were analysed in terms of the temperature compensated power law and Monkman-Grant relation. The creep activation energy of Grade 91 steel was determined with 543±30 kJ/mol without threshold stress compensation, while after correcting the threshold stress; the activation energy is decreased to 303±15 kJ/mol. This value is close to the activation energy of creep in α-Fe. The calculated threshold stress showed a strong dependence on temperature. The creep behavior of the steel was described by the modified Bird-Mukherjee-Dorn relation. The rate controlling creep deformation mechanism was identified as the edge dislocation climb with stress exponent of n=5. Further, the value of creep damage tolerance factor (λ) and stress exponent was used to identify the cause of creep damage, showed significant difference in the high and low stress regimes. The fracture surface morphology of the ruptured specimens was studied by scanning electron microscopy to further elucidate the failure mechanisms. Whereas deformed microstructure was examined by transmission electron microscopy. The significant decrease in creep strength in the alloy has been attributed to microstructural degradation associated with precipitates and dislocation substructure. [ABSTRACT FROM AUTHOR]

Creep rupture behavior of fusion welded Grade 91 steel was studied in the temperature range of 600 – 700 °C and at stresses of 50–200 MPa. The creep data were analyzed in terms of the Monkman-Grant relation and Larson-Miller parameter. The creep damage tolerance factor was used to identify the origin of creep damage. The creep damage was identified as the void growth in combination with microstructural degradation. The fracture surface morphology of the ruptured specimens was studied by scanning electron microscopy and deformed microstructure examined by transmission electron microscopy, to further elucidate the rupture mechanisms. [ABSTRACT FROM AUTHOR]

The creep rupture behavior and microstructure changes of a new type of 10% Cr martensitic heat-resistant steel (MHRS) welded joints during short-term creep at 130–250 MPa and 650 °C were investigated. The results showed that type IV cracking took place in the fine-grained heat affected zone (FGHAZ). Creep cavities mainly formed at the intersection points of prior austenite grain (PAG) boundaries. M 23 C 6 carbides coarsened significantly, coarse Laves phases formed next to M 23 C 6 along the PAG boundaries and acted as the nucleation sites for creep cavities. It was considered that the high-density of PAG intersection points of FGHAZ in per unit area, combined with the coarsening of M 23 C 6 precipitates and the formation of Laves phases on PAG boundaries caused the formation of type IV cracking. [ABSTRACT FROM AUTHOR]

To estimate the service life of the reactor internals made of 2.25Cr–1Mo steel in the high temperature gas-cooled reactor pebble-bed module demonstration plant, creep rupture test was performed on the simulated post weld heat treated steel at 773 K over a range of stress levels 300–200 MPa. It has been shown that the rupture time is 126–5532 h, correspondingly. Then, the service life under stress of 161.2 MPa at 648 K was calculated to be so long as 210,374,853 h (≈24,015 years). Four types of carbides M 3 C, M 2 C, M 7 C 3 and M 23 C 6 existed in both the steel plate and the post-rupture specimens. As the rupture time increases, the weight percentages of M 23 C 6 and M 2 C that are stable in thermodynamics in the post-rupture specimens increase while those of metastable M 3 C and M 7 C 3 decrease on the whole. During the long term creep exposure, the deformation promotes the precipitation of M 3 C, M 2 C and M 23 C 6 , according to the experimental results with the deformed and undeformed parts of the post-rupture specimens, but its influence on the weight percentage of M 7 C 3 seems rather complicated. [ABSTRACT FROM AUTHOR]

Abstract: The microstructural evolution and mechanical properties of S31042 heat-resistant steel after crept at 923K were systematically investigated. Results show that secondary NbCrN and M23C6 are the predominant precipitates during creep. Long-term creep results in the precipitation of a small amount of σ phase and a few Cr3Ni2SiX. Secondary NbCrN is the most important strengthening precipitate of S31042 steel. At least 75% of the precipitation hardening results from secondary NbCrN. Furthermore, secondary NbCrN is the main factor to affect the variation of hardness of S31042 steel during creep. The dramatic degradation of plasticity is mainly caused by the precipitation of M23C6 at the grain boundaries. Chain-like M23C6, cuboids M23C6 and undissolved NbCrN are also harmful to the creep plasticity of S31042 steel. [Copyright &y& Elsevier]

A multiple-heat set of tensile and creep-rupture data generated from a single laboratory was used to establish and evaluate predictive equations for the average creep-limited lifetime of an aged wrought Haynes 282 alloy using two different time- and temperature-compensated parametric models (those of Larson and Miller and Wilshire et al.). The range of temperatures and stresses used to produce the creep-rupture data used in the analyses revealed that two distinct regimes, above and below the proportional limit, were necessary for more accurate predictions of creep lifetimes over the range of conditions studied. Furthermore, a 2x difference in grain size amongst the three heats revealed a breakdown in the relationship between ultimate tensile strength and creep-rupture time, thus impacting the predictive ability of the Wilshire model. Lifetime predictions based on the formulations from the respective models were compared to other available Haynes 282 datasets and found to reasonably replicate the experimental trends established in other studies. [ABSTRACT FROM AUTHOR]

Abstract: Traditional creep lifing techniques based on power law equations have shown themselves to be extremely limited, particularly in the prediction of long term data based only on short term experiments. More recently, alternative approaches such as the Wilshire equations and hyperbolic tangent methods have been proposed which offer a new insight into the field, with the Wilshire equations in particular showing promise in predicting long term behaviour based on short term results. The aerospace industry however has different requirements to the power generation industry where the Wilshire equations have been thoroughly tested. The current work seeks to investigate the ability of these methods to extrapolate across temperatures and in the case of the Wilshire equations offer a capability to accurately describe the time to specific strains during creep deformation. [Copyright &y& Elsevier]

Abstract: The present paper highlights the effect of Na2SO4 and NaCl salt mixture on creep rupture properties of Nimonic-263 alloy at 800 and 850°C. Results revealed that for short duration tests, the rupture life is not much affected by the corrosive action of the salt mixture at both the temperatures. Whereas for long term creep tests, salt mixture affects the creep rupture properties of the material catastrophically. Minimum creep rate increases marginally for salt deposited sample compared to the bare alloy. Fractographic features of the ruptured salt deposited and bare samples have been discussed. [Copyright &y& Elsevier]

Abstract: Grade 91 steel is considered a potential structural material for advanced nuclear reactors. The creep deformation behavior of Grade 91 steel was studied in the temperature range of 600–700°C and at stresses of 35–350MPa. The data were analyzed in terms of Monkman-Grant relation and Larson–Miller parameter. Creep damage tolerance factor and stress exponent were used to identify the cause of creep damage. The fracture surface morphology of the ruptured specimens was studied by scanning electron microscopy to elucidate the failure mechanisms. Fracture mechanism map for Grade 91 steel was developed based on the available material parameters and experimental observations. [Copyright &y& Elsevier]

Abstract: The creep rupture behavior of semi-solid cast 7075-T6 Al alloy produced by the Gas Induced Semi-Solid (GISS) process was investigated and compared to that of commercial 7075-T651 Al alloy. The semi-solid cast 7075-T6 Al alloy displayed lower minimum creep rate and longer creep rupture time than the commercial 7075-T651 Al alloy. On the basis of their stress exponent, n, values of 6.3, dislocation creep was seemingly the predominant mechanism controlling the creep deformation of both alloys. The creep rupture time of the semi-solid cast 7075-T6 Al alloy was distinctly longer than that of the commercial 7075-T651 Al alloy at stress regimes of 120–140MPa. This difference was attributed to the lower precipitate coarsening and higher precipitate density in the semi-solid cast alloy. Creep cavities predominately controlled the creep rupture of the semi-solid cast 7075-T6 Al alloy despite the appearance of precipitate coarsening. The commercial 7075-T651 Al alloy creep rupture behavior was controlled by the combination of rapid precipitate coarsening and creep cavities. However, de-cohesion between insoluble particles and the matrix is evidently accelerated with increasing stress to 180MPa, leading to cavity propagation and resulting in the convergence of creep rupture time in the semi-solid cast 7075-T6 Al alloy to that of the commercial 7075-T651 Al alloy. [Copyright &y& Elsevier]

Abstract: The influence of nitrogen on the creep behaviour of 316L(N) SS has been studied at nitrogen levels of 0.07, 0.11, 0.14 and 0.22wt.%. Creep tests were carried out at 923K at stress levels of 140, 175, 200 and 225MPa with rupture life up to 16,000h. Creep rupture strength was found to increase substantially with increase in nitrogen content; rupture life increased almost 10 times by increasing nitrogen content from 0.07wt.% to 0.22wt.%. Steady state creep rate decreased significantly with increasing nitrogen content. The extent of internal creep damage and surface creep damage decreased remarkably with increasing nitrogen content, resulting in increased creep rupture strength. Solid solution strengthening, increase in Young''s modulus, decrease in stacking fault energy and matrix precipitation of carbonitrides have contributed to the increase in creep strength with increasing nitrogen content. [Copyright &y& Elsevier]

Abstract: A stochastic model for the creep damage evolution and associated scatter in austenitic stainless steel has been developed in terms of a discontinuous Markov process. The magnitude of damage has been described in the form of a probability distribution function whose evolution in time characterizes the nondeterministic nature of the damage accumulation process. The long-term creep behavior on samples obtained from different locations of a thick walled SS304 LN steel pipe are studied under an identical stress and temperature condition so as to observe the scatter in creep deformation and failure data. Also the occurrences of damage and its accumulation due to creep deformation were evaluated through microstructural assessment using light optical microscope and scanning electron microscope. The validity of the model has been established by repeat data of SS304 LN steel and 316 stainless steel . [Copyright &y& Elsevier]

Abstract: The present study investigates creep in three TiAl-base intermetallic alloys, Ti–48Al–2Cr–2Nb–1B, Ti–46Al–7Nb–0.6Cr–0.2Ni–0.1Si and Ti–46Al–2W–0.5Si–0.7B (all at.%), in the range of rupture times up to 25000h. Creep behaviour of the individual alloys at 1023K is assessed and compared and reasons for creep strength variations are discussed. Results suggest that dislocation processes contribute to the creep strain accumulation even at creep rates as low as 7×10−10 s−1. Finally the applicability of Monkman–Grant-type relationships is critically analyzed. It is shown that these relationships stem from a general functional identity that is valid for any continuous creep curve. The role of the creep curve shape factor S is highlighted. [Copyright &y& Elsevier]

Abstract: Clarification of creep damage mechanism and establishment of remaining life assessment methods of boiler pipings of P91 steel with weldment are important subjects to maintain reliable operation of thermal power plants. In order to characterize the creep damage of a P91 steel weldment and to discuss creep rupture life prediction methods, uniaxial creep tests on a P91 steel cross weld and internal pressure creep tests on a longitudinal welded tube specimen were conducted. Three-dimensional finite-element creep analysis of the longitudinal welded tube specimen was conducted to identify stress and creep strain distribution within the specimen. Creep rupture time of the weld joints was reduced significantly from that of the base metal due to Type IV failure. It was found from an examination of creep damage in interrupted cross weld specimens that creep voids have already initiated around 20% creep damage, and that the number of voids inside the specimens was larger than those at the surface of the specimens. Creep analysis results indicated that triaxial tensile stress yielded at mid-thickness in the heat affected zone (HAZ) of the tube specimen due to differences of creep deformation properties of the base metal, the HAZ and the weld metal. It was suggested that triaxial stress states caused acceleration of creep damage evolution in the HAZ resulting in internal failure of the tube specimens. Rupture life of the longitudinal welded tube specimen under internal pressure creep is predicted from the circumferential steady-state creep strain rate at the HAZ obtained from creep analysis using a three-materials finite-element model of the tube specimen. [Copyright &y& Elsevier]

Abstract: Lifetime models for both creep and thermo-mechanical fatigue are presented for P23 steel. The models are the result of the joint European RFCS project ALoAS. The creep model, developed for robust creep strain modeling, here adjusted to describe the strain response of the ALoAS data, i.e. P23 pipe material fabricated by TenarisDalmine and plate material heat fabricated by Industeel. The creep modeling range covers 550–660°C in temperature and 80–180MPa in stress. The thermo-mechanical fatigue model is adjusted to the acquired data on thick walled P23 pipe material fabricated by TenarisDalmine. The load range covers 20–625°C and up to 16,000 cycles to failure. A good description of the data has been achieved for both creep and fatigue models. [Copyright &y& Elsevier]

Abstract: Three modified Cr steels were investigated for the types, sizes and volume fractions of precipitates. It is shown that precipitation of V in the form of fine M2X-particles provides high short-term creep resistance, but causes relatively fast degradation of creep resistance due to Ostwald ripening. In the later stages, precipitation of Z-phase and related phenomena accelerate the degradation. [Copyright &y& Elsevier]

Abstract: The biaxial creep damage of type 304 stainless steel is studied at 973K. Biaxial tension creep tests were carried out using cruciform specimens under the principal stress ratio (λ) of 0≦ λ ≦1, where the principal stress ratio is the ratio of y-directional principal stress to x-directional stress in the gage part of the specimen (λ = σ y /σ x ). Creep rupture times under biaxial stress conditions were shorter than those in uniaxial conditions at the same von Mises equivalent stress. Earlier void nucleation and faster void growth were observed in creep tests at larger principal stress ratio tests. Creep rupture times in biaxial stress states were discussed in relation to the void observations. [Copyright &y& Elsevier]

Abstract: (TiB+La2O3)/Ti composite was synthesized in a consumable vacuum arc remelting furnace by a novel in situ technique based on the reaction between Ti, LaB6, and oxygen in the raw materials. The phases were identified by X-ray diffraction. The microstructures were examined by means of optical microscopy and scanning electron microscopy. TiB whiskers and nano-sized La2O3 spherical particles were distributed uniformly in the matrix. Creep rupture properties of the composite were tested at 873, 923 and 973K. The results showed the creep rupture life of the composite increased significantly at elevated temperature while keeping good plasticity. The creep rupture life even exceeded the best elevated titanium alloy IMI 834. The improvement of creep rupture life and plasticity were mainly attributed to undertaking load by TiB whiskers, dispersion strengthening by nano-sized La2O3 particles and decrease of the oxygen content in the matrix by the addition of the LaB6. [Copyright &y& Elsevier]

Abstract: The creep data obtained in the previous work on Fe–34.5 Mn–9.2 Al–1.8 Si–0.95C (wt.%) steel are analysed according to traditional parameterization methodologies which consider the pattern of the iso-stress lines variation in the coordinates axis (t, time; T, temperature) log(t r ) versus T and log(t r ) versus 1/T. The better performance was achieved with the Manson–Succop method, followed by the Larson–Miller and Orr–Sherby–Dorn techniques. Results are compared with the scarce creep data available in literature for this material. It is suggested that the creep strength of Fe–Mn–Al alloys may be improved considerably by development of systematic work on the effect of chemical composition and thermo-mechanical treatments in their creep behaviour. [Copyright &y& Elsevier]

Abstract: Microstructural changes in boiler tubes during prolong operation at high temperature and pressure decrease load bearing capacity limiting their useful lives. When the load bearing capacity falls below a critical level depending on operating parameters and tube geometry, failure occurs. In order to avoid such failures mainly from the view point of economy and safety, this paper describes some basic principles behind remaining life assessment of service exposed components and also a few case studies related to failure of a reheater tube of 1.25Cr–0.5Mo steel, a carbon steel tube and final superheater tubes of 2.25Cr–1Mo steel and remaining creep life assessment of service exposed but unfailed platen superheater and reheater tubes of 2.25Cr–1Mo steel. Sticking of fly ash particles causing reduction in effective tube wall thickness is responsible for failure of reheater tubes. Decarburised metal containing intergranular cracks at the inner surface of the carbon steel tube exhibiting a brittle window fracture is an indicative of hydrogen embrittlement responsible for this failure. In contrast, final superheater tube showed that the failure took place due to short-term overheating. The influence of prolong service revealed that unfailed reheater tubes exhibit higher tensile properties than that of platen superheater tubes. In contrast both the tubes at 50MPa meet the minimum creep rupture properties when compared with NRIM data. The remaining creep life of platen superheater tube as estimated at 50MPa and 570°C (1058°F) is more than 10 years and that of reheater tube at 50MPa and 580°C (1076°F) is 9 years. [Copyright &y& Elsevier]

The creep rupture mechanisms of IN617 were systematically investigated by establishing the relationship between microstructural characteristics and creep performance, including rupture time, percentage elongation, microhardness, and minimum creep rate. The Wilshire equation was employed to extrapolate long-term creep life by normalizing the stress, σ , using the ultimate tensile strength, σ TS. The results indicated that at temperatures ≤950 °C, when σ / σ YS values were >0.2 (σ YS = yield strength), the creep rupture mechanism involved the sliding and migration of recrystallized grain boundaries, leading to matrix softening and necking fractures. When applied stresses ranged from 0.12 σ TS to 0.2 σ YS , creep voids along the grain boundaries became a pronounced feature, implying the rupture mechanism of the weakening of the grain boundaries without sufficient secondary-phase pinning. At a low stress level (σ / σ TS < 0.12), creep ruptures were governed by a composite mechanism of microstructural degradation and internal oxidization, which was reflected in the brittle fractures caused by the connection of cracks along carbide networks and internal oxidized voids. A temperature–stress–rupture mechanism map was constructed by combining a comparison and summary from the literature. The Wilshire extrapolation curve described the creep rupture times well with temperatures and stresses, and the turning point of the curve suggested that microstructural degradation and internal oxidization increased the minimum creep rates and accelerated creep rupture. [ABSTRACT FROM AUTHOR]

This research study aims at investigating the influence of partial solution treatment and the subsequent cooling strategy on the microstructure and mechanical properties of an as-cast Co–Cr–W superalloy. Three different cooling scenarios were employed to explore the effect of cooling rate on the carbide reprecipitation potential from the \solid solution formed during the heat treatment. The partial dissolution/breakdown of the continuous network of the Cr-rich M 7 C 3 carbides during the partial solution treatment cycle along with their transformation to M 23 C 6 carbides and formation of secondary carbides during the cooling stage were taken into account to discuss the obtained hardness values, and high-temperature creep results. Regardless of the applied cooling rate, the secondary carbides were formed during the cooling stage, and the heat-treated samples showed almost the same microstructure and mechanical properties, which eliminates the need for the aging cycle. This can alleviate the concerns associated with the heat treatment of the large-size X-40 industrial components since the gradient in the cooling rate after the heat treatment cycle would not lead to non-uniform parts. From the hardness and creep viewpoints, all of the samples could meet the minimum requirements of the X-40 superalloy. Mechanical properties suggest that the applied partial solution treatment cycle can be considered as a suitable candidate for high-temperature applications of X-40 superalloy. [ABSTRACT FROM AUTHOR]

Tensile creep behavior of the Zr-2.5Nb alloy has been studied through tests under constant load (stress range ~ 137–371 MPa) between 275 and 375 °C. The minimum creep rate of the alloy is found to vary with applied stress and temperature following a power-law relation. The values of stress exponent (n) obtained in the range of 5.3–6.8 in the temperature interval of 300–375 °C; whereas it is calculated as 1.2 and 7.0 under low and high stresses, respectively at 275 °C. The apparent activation energy of creep (Q C) and stress exponent have been determined by analyzing the experimental data. The obtained Q C (~198.5 ± 10.7 kJ/mol) is found to be higher than the lattice self-diffusion activation energy of pure zirconium (113 kJ/mol). Using this value, stress exponent ~5.6 ± 0.23 is obtained by the temperature-compensated power law. Microstructural characterization by transmission electron microscopy (TEM) with energy dispersive spectroscopy (EDS) analysis has confirmed coarsening of β-(Nb, Zr) precipitates with compositional changes during creep. The dislocation-precipitate interaction as evidenced by TEM observations is considered to be the origin of threshold stress, which decreases with increasing temperature. Considering the threshold stress, true activation energy of creep (Q t) and true stress exponent (n t) are found as ~160.4 ± 6.9 kJ/mol and ~4.8 ± 0.22, respectively. Analysis of creep data has confirmed the role of dislocation climb as the rate-controlling mechanism, along with validity of Monkman-Grant and modified Monkman-Grant relations. Scanning electron microscopy (SEM) of creep fracture surfaces has revealed evidence for prominent ductile fracture. Further, the obtained creep damage tolerance factor value of 1.9, indicating the predominance for cavitation during creep. [ABSTRACT FROM AUTHOR]

The present study considers the effects of process parameters on the microstructural development and mechanical properties of SLM Inconel 718. A continuous scanning strategy was used in conjunction with changes in laser spot size to emphasize texture development in the samples; it was found that aligned laser scan vectors (continuous scans) enhanced the crystallographic and morphological texture that forms during solidification when compared to multi-directional scan vectors (island scans). Although room temperature tensile testing did not exhibit variation in material properties, creep rupture testing showed a significant difference in ductility and time to failure. As texture and preferred crystallographic orientation were increased parallel to the loading direction, an increase of 51% in creep elongation was observed for the continuous scanning strategy. This behavior is linked to differences in damage accumulation mechanisms in the microstructure based on grain boundary orientation and precipitation. Furthermore, comparison of the mechanical behavior of SLM and wrought materials showed that wrought had ~10% greater tensile yield strength at room temperature, while in creep rupture the increase in elongation was as high as 640%. The primary difference between SLM and wrought material contributing to this discrepancy was the difference in NbC distribution. Although small differences in mechanical behavior can be induced in SLM material through process parameter variation, the separation in properties when compared to a wrought product are more significant. • Laser focal shift and scanning strategy can enhance microstructural texture. • Microstructural texture persists through HIP and heat treatment. • SLM IN718 is shown to be environmentally sensitive due to NbC precipitation. • Wrought material displays superior high temperature ductility when compared to SLM. [ABSTRACT FROM AUTHOR]

In this study, creep rupture behaviors and rupture mechanism of dissimilar metal weld (DMW) between Inconel 617B and modified 9%Cr martensitic heat-resistant steel (hereinafter referred to 9Cr steel) with Inconel 617 filler metal were investigated. Creep tests were carried out at 600 °C and 620 °C in the stress range 130–240 MPa. Optical microscopy (OM), scanning electron microscopy (SEM), Electro-Probe Microanalyzer (EPMA) and micro-hardness test were used to examine the creep rupture behaviors and microstructure characteristics of the DMW. The results indicated that under different creep conditions, the rupture locations varied, including 9Cr base metal (BM), the intercritical heat affected zone (ICHAZ) of 9Cr steel, and the interface between weld metal (WM) and 9Cr steel. The rupture behavior occurring in the 9Cr BM was mainly controlled by plastic deformation, and the growth and coalescence of dimples eventually led to transgranular fracture. The rupture behavior occurring in the ICHAZ was caused by type IV crack due to matrix softening and lack of sufficient precipitates pinning the grain boundaries (GBs). The rupture behavior occurring at the interface was mainly related to the oxide notch forming at the interface. The formation and propagation of the oxide notch resulted in the interfacial failure. [ABSTRACT FROM AUTHOR]