Room Temperature Creep Behavior Research Articles

Room temperature creep behavior of a single crystal nickel-based alloys

The deformation characteristics of a single-crystal nickel-based alloy containing Re during creep at room temperature were studied by means of creep property tests, microstructure observations and contrast analysis of the dislocation configuration. The results show that during the deformation of the alloy at room temperature, the original cubic γ′ phase transforms into a rhombus shape along the direction of maximum shearing stress, and its deformation feature is that the dislocation slips in the matrix and shears the γ′ phase. The <110> superdislocation shear into the γ′ phase can cross slip from the {111} plane to the {100} plane, forming a K-W lock, and can also be decomposed at the {111} plane. The dislocation configurations of (1/2)<110> partial dislocation plus antiphase boundary (APB) and (1/3)<112> partial dislocation plus SISF can effectively inhibit the slip and cross-slip of the dislocation and improve the deformation resistance of the alloy. At the later stage of creep, under the action of shear stress, the initial slip system is activated first to distort the γ and γ′ phases, and then the secondary slip system is activated and shears the primary slip system, resulting in a large stress concentration at the delivery point and the initiation of cracks in this area. With the alternating activation of the primary slip system and secondary slip system during creep, the initiation and expansion of cracks continue. Damage and fracture mechanisms occur in alloys during room temperature creep.

Effect of recrystallization on aging embrittlement and high temperature creep properties of AFA steel

As a kind of typical precipitate strengthened steel, alumina-forming austenitic (AFA) stainless steels usually suffer obvious aging embrittlement issue. Recrystallization treatment was performed by cold rolling followed with heat treatment at 1080 ℃ for a Fe-25Ni-15Cr-3.5Al based AFA steel to evaluate the effect of recrystallization on aging embrittlement. The materials before and after recrystallization were aged at 700 ℃ for 120 h to evaluate the effect of recrystallization on precipitation behavior. After recrystallization, the average grain size decreased and the density of grain boundaries increased obviously. The size of precipitates along grain boundaries was smaller and more uniform after recrystallization, and the precipitation of Cr rich phase was inhibited. Room temperature tensile test, Charpy impact, and creep behavior at high temperature of samples with different treatment states were measured and compared. The aging embrittlement of AFA steel was alleviated obviously after recrystallization. The creep resistant was also improved for sample treated by recrystallization and aging. The relevant mechanisms were discussed.

Microstructural effects on the ambient temperature indentation creep behavior of metastable β Ti-5Al-5V-5Mo-3Cr alloy

Ti-5553 alloy is considered as a potential candidate for heavy structural components such as landing gears in aerospace industries, that operate particularly at room temperature. For achieving the targeted performance, microstructural modification and corresponding improvement in mechanical properties, particularly room temperature creep behavior of Ti-5553 alloy is of significant concern. In this regard, an optimized thermomechanical processing (TMP) schedule is employed to tailor the microstructure of as-cast Ti-5553 alloy. Typical bimodal microstructure containing both α and β phases is noted to evolve upon TMPing, as compared to its as-cast counterpart, having sole β phase. The size and volume fraction of αp are noted to be 0.85 ± 0.39 µm and 11.7 ± 0.5%, respectively. Such pronounced variation in the microstructural features is expected to alter the localized mechanical properties significantly. To assess that, room temperature small-scale creep behavior of as-cast and TMPed Ti-5553 alloys is investigated using nanoindentation technique. The effect of maximum load on different creep parameters are analyzed and correlated with the corresponding microstructures. It is noted that at any particular applied load level, creep deformation of TMPed Ti-5553 alloy is ∼ 20–64% lower than that for the as-cast one. This is reflected in significant reduction in the minimum creep strain rate from 10−4 s−1 for as-cast to 10−5 s−1 for TMPed Ti-5553 alloy. Dislocation creep mechanism is found to be active for both the alloys since creep exponent for both the as-cast and TMPed Ti-5553 alloys exceed the value of 2. Discontinuous semi-circular micro-shear bands are noted to form around the indents for the as-cast Ti5553 alloy. The kernel average misorientation map for this alloy reveals a lower degree of misorientation and a more homogeneous distribution of plastic strain. In contrary, the TMPed Ti-5553 alloy exhibits higher misorientation around the indent impression, thereby indicating towards the restriction of dislocation movement against α/β laths and hence positively influencing the creep behavior. Overall, the study highlights the important role of TMP in enhancing the creep resistance of Ti-5553 alloy for industrial applications.

Creep behavior of titanium alloy used in deep-sea pressure shell considering tensile/compressive asymmetry: Experiments and numerical modeling

Titanium alloy pressure shell of deep-sea submersible suffers from room-temperature creep problem, which can affect the safety of the structure. There is currently a lack of research on the tensile/compressive asymmetry of the creep response of titanium alloy structures at room temperature. In this paper, room-temperature creep behavior and mechanism of titanium alloy were investigated by creep test of twisting of titanium alloy square plate. Taking cylindrical pressure shell with geometrical imperfection and multi-sphere pressure shell as examples, the creep mechanical behavior of titanium alloy pressure shells under complex stress states were investigated by numerical simulation. It is found that only under tensile stress can slip bands move across phase boundaries, resulting in tensile/compressive asymmetry in creep behavior. The proposed DTC model can accurately describe the room-temperature creep behavior of titanium alloy structures. For cylindrical pressure shell with geometrical imperfection, creep deformation results in a 121 % increase in the magnitude of geometrical imperfection. The results obtained with the tensile model towards the conservative side. For multi-sphere pressure shell, the evolution of physical quantities cannot be accurately described without considering the tensile/compressive asymmetry in creep properties. The range of relative error when using traditional models is between 5% and 33%.

Creep crack tip opening displacement (CCTOD) of X80 pipeline steel at room temperature

The room temperature creep behavior of X80 pipeline steel has attracted increasing attention because it is considered to be the main cause of time-delayed failure in pipeline steel. The crack tip opening displacement (CTOD) is a general criterion to characterize the time-delayed failure and assessment safety of pipeline steel. However, there are few methods to demonstrate crack behavior of the pipeline steel caused by room temperature creep. Based on the traditional CTOD theoretical model, a modified creep crack tip opening displacement (CCTOD) theoretical model is presented to calculate the CCTOD from the crack mouth opening displacement (CMOD). The room temperature creep experiment with a single edge notched beam subjected to three-point bending creep load for 36 h at room temperature is performed to know more about the CCTOD of X80 pipeline steel. Based on a power-law time delayed relationship among creep strain, stress and time fitted from experiment results of tensile creep tests, the finite element model is also established to evaluation the CCTOD of pipeline steel at room temperature. It is found that there is about 10% CTOD increment caused by room temperature creep added to that of the traditional elastic and plastic CTOD which indicates that room temperature creep is also further blunted the crack tip of X80 pipeline steel. Meanwhile, The results will provide an approach for failure evaluation and an integrity guideline for X80 pipeline steel.

Prediction of nanoindentation creep behavior of tungsten-containing high entropy alloys using artificial neural network trained with Levenberg–Marquardt algorithm

This paper describes the synthesis of tungsten-containing high-entropy alloys (HEAs). The synthesis method involves a powder metallurgy process, and spark plasma sintering (SPS) is used to compact the powder. XRD and SEM analyses of synthesized HEAs showed that the main phases formed were body-centered and face-centered cubic phases, and a sigma phase was also observed after sintering at 900 ℃. Furthermore, nanoindentation showed that the introduction of tungsten in HEA resulted in high hardness and elastic modulus, which ranged from 8.31 to 13.57 GPa and 197.21–209.43 GPa respectively. The indentation creep behavior was ascertained at room temperature. The HEAs exhibited a significant benchmark after the addition of a specific amount of W for further investigation because of their lower creep rate. Experimental creep displacement data were used for modeling by artificial neural networks (ANNs) in which the training has been performed by the Levenberg–Marquardt algorithm. The experimental creep displacement data and the ANN model predictions have an excellent agreement. The ANN model is reliable and can accurately forecast the room temperature creep behavior of HEAs. HEAs are promising candidates for use in elevated and wear-resistance applications, owing to their unique combination of high hardness and high creep resistance.

Thermal stability of dislocation structure and its effect on creep property in austenitic 316L stainless steel manufactured by directed energy deposition

The objective of this study is to investigate the thermal stability of dislocation structure and its effect on the creep behaviour of laser-directed energy deposited 316L stainless steel (L-DED-316L SS). Post-processing heat treatments at temperatures ranging from 300 to 1200 °C were performed on the as-deposited DED samples. The microstructural changes induced by the heat treatment were correlated to the corresponding variations of the room temperature tensile properties and creep behaviour at 650 °C/225 MPa. Results show that dislocations produced during DED process tend to distribute uniformly, with only a few localized fine dislocation cells (average cell size of ∼0.4 μm) being detected. At 600 °C, the remaining dislocations rearrange and organize into a coarse dislocation cell structure with an average cell size of ∼1.6 μm, leading to a slight decrease in yield strength, while the creep performance is not obviously affected. At 800 °C, the annihilation of dislocations and destruction of dislocation cell structure, as well as elemental diffusion contribute to a significant drop in yield strength and creep rupture time with a noticeable increase in steady creep rate. Further increasing heat treatment temperature above 1000 °C removes the dislocation cell structure and elemental segregation on cell walls, which results in a continuous increase in steady creep rate. The present work demonstrates that the presence of chemical micro-segregation is crucial for the stabilization of dislocation cells structure and the resulted creep performance of the heat-treated L-DED samples.

Effect of Uniaxial Pre-strain on Room Temperature Tensile and Creep Behavior of Aluminum Alloy AA2219-T87 for Propellant Tanks of Satellite Launch Vehicles

Effect of Uniaxial Pre-strain on Room Temperature Tensile and Creep Behavior of Aluminum Alloy AA2219-T87 for Propellant Tanks of Satellite Launch Vehicles

Room temperature creep behavior of Ti–Nb–Mo–Sn based shape memory alloy for biomedical application

Room temperature creep behavior of Ti–Nb–Mo–Sn based shape memory alloy for biomedical application

Room temperature creep behaviors of base metal and welding materials for X80 pipeline steel

The room temperature creep behavior of X80 pipeline has attracted increasing attention because it is considered to be a reasonable cause of failure in pipeline steel. In order to investigate the influence of loading stress, loading rate and creep-fatigue interaction on the room temperature creep, three types of room temperature creep experiments of base metal and welding specimens were carried out when loading stress changes from 0.85 σs to 1.05 σs (σs is the yield strength of material) and loading rates changes from 0.63 kN/min to 1.23 kN/min. The results of experiments show that the room temperature creep of X80 pipeline steel strongly depends on the loading stress and loading rate, but no creep was measured when loading stress is lower than 0.85σs. One hour fatigue load has no effect on the creep, and the second creep strain is much smaller than the first creep strain. The room temperature creep and dislocation creep mechanisms of the base metal and welding zones are revealed. In addition, the nonlinear creep expression of primary and second stages related to loading stress at room temperature are obtained to evaluate the base metal and welding specimens based on Norton power function theory. The results obtained from the study will provide a reference to the research of room temperature creep of the X80 pipeline steel and corresponding welding zone.

Creep anisotropy characteristics and microstructural crystallography of marine engineering titanium alloy Ti6321 plate at room temperature

The anisotropy of the mechanical properties of high-performance titanium-alloy plates has always been a key challenge in the fabrication of alloy plates and the application of components in service. In this work, the room-temperature creep behavior and microstructural crystallography of Ti6321 alloy plates along the rolling direction (RD), 45°, and transverse direction (TD) have been thoroughly investigated and discussed. The study demonstrates that the plates exhibit significantly different room-temperature creep characteristics along the three sampling directions. Among them, the creep strain along the 45° direction was the largest, whereas the creep strain along the TD was the smallest. Such anisotropic deformation was associated with the global Schmid factor variation caused by the T-type microtexture. Both the basal and prismatic slips occur easily along 45°, whereas it was hard to activate along the TD. In addition, the basal and prismatic slips were the main contributors to creep deformation, which also showed strong crystallographic orientation dependence. Among them, the basal slip was found to be more easily activated than prismatic slip, especially in the high Schmid factor range. The study also discusses the potential influence of elastic anisotropy on the activation of basal slip.

Twinning-Induced Abnormal Strain Rate Sensitivity and Indentation Creep Behavior in Nanocrystalline Mg Alloy.

Nanocrystalline materials exhibit many unique physical and chemical properties with respect to their coarse-grained counterparts due to the high volume fraction of grain boundaries. Research interests on nanocrystalline materials around the world have been lasting over the past decades. In this study, we explored the room temperature strain rate sensitivity and creep behavior of the nanocrystalline Mg–Gd–Y–Zr alloy by using a nanoindentation technique. Results showed that the hardness and creep displacements of the nanocrystalline Mg–Gd–Y–Zr alloy decreased with increasing loading strain rate. That is, the nanocrystalline Mg–Gd–Y–Zr alloy showed negative strain rate sensitivity and its creep behavior also exhibited negative rate dependence. It was revealed that the enhanced twinning activities at higher loading strain rates resulted in reduced hardness and creep displacements. The dominant creep mechanism of the nanocrystalline Mg–Gd–Y–Zr alloy is discussed based on a work-of-indentation theory in this paper.

Indentation behavior of creep-feed grinding induced gradient microstructures in single crystal nickel-based superalloy

The gradient microstructures of surface layer in single crystal nickel-based superalloy were produced by creep-feed grinding. The mechanical properties (i.e., hardness, elastic modulus) and room-temperature (RT) creep behavior of such structures were evaluated using a nano-indentation technique. Results show that the gradient structures along depth from ground surface consisted of nanograins, submicron grains and lamellar-shape structures, and dislocation structures. Furthermore, it was found that the hardness and elastic modulus of gradient structures were higher by 8–10% than that of bulk material on average. However, the regions containing nanograins showed a remarkable increase in creep depth compared to bulk material, implying that the creep behavior of ground layer was changed unfavorably. The obtained stress exponents of gradient structures suggested that dislocation activities were the main mechanism for indentation creep deformation.

Multi-scale indentation creep behavior in Fe-based amorphous/nanocrystalline coating at room temperature

This work reports first ever investigation on multi-scale room temperature creep behavior of Fe-based amorphous/ nanocrystalline coatings, synthesized via plasma spraying at varying plasma power. Micro- and nano-indentation testing at different loading scales was carried out to reveal the combined effect of microstructural heterogeneities viz. porosity and constituent phases, as well as the individual contribution of amorphous and crystalline phases on the creep behavior of the coatings. Microindentation creep tests revealed higher creep resistance for the coating deposited at elevated power, ascribed to lower porosity and higher degree of crystallinity. Nanoindentation creep tests showed that mixed (amorphous and intermetallic) phase possessed lower creep displacement and retardation spectra compared to fully amorphous one, indicating better creep resistance. The present work provides valuable insight into the effect of microstructural features on the creep deformation behavior of amorphous-nanocrystalline coatings.

Room temperature creep behavior of nanocrystalline Gd2Zr2O7 ceramic with grain size below 10 nm

Creep behavior at room temperature was firstly observed in nanocrystalline Gd2Zr2O7 ceramic (NC-GZO) having an average grain size about 7.8 nm. The creep strain rate sensitivity of NC-GZO was calculated, and many dislocations can be observed in the strained region. The mechanism causing this room temperature creep behavior was associated with the dislocations slipping which most likely occurs though grain boundaries sliding.

On the Room-Temperature Creep Behavior and Its Correlation with Length Scale of a LiTaO3 Single Crystal by Spherical Nanoindentation.

Relying on nanoindentation technology, the room-temperature creep behavior of a LiTaO3 single crystal in the typical orientation (012), i.e., Y-42° plane was investigated. Three kinds of spherical tips with the radii of 0.76, 2.95 and 9.8 μm were respectively applied to detect nanoindentation length scale effect on creep deformation at both elastic and plastic regions. Superficially, both creep displacement and rate were nearly linearly increased with increasing holding depth and independent of tip size, which could be ascribed to the simultaneously enlarged holding strain and deformation volume beneath the indenter. At a similar holding strain, creep deformation, i.e., creep strain and strain rate were more pronounced under smaller spherical tips. Strain rate sensitivities of creep flows under different spherical tips and holding strains were also estimated. The potential room-temperature creep mechanism of LiTaO3 under high shear compression stress was discussed.

Room temperature nanoindentation creep of nitrocarburised AISI 4140 steel

ABSTRACTRoom temperature indentation creep behaviour of different regions of nitrocarburised AISI 4140 steel is investigated by employing the nanoindentation creep testing method in the present study. A structure consisting of a compound layer, a diffusion layer and a substrate is observed in the nitrocarburised AISI 4140 steel. The stress exponents are calculated from the loading curve produced by nanoindentation during the holding time. The results indicate that with the increase in distance from the material surface, the obtained stress exponent decrease. From the compound layer to the diffusion layer to the substrate, the stress exponent decreases rapidly first, and then decreases gradually revealing a deeper test point that yields a lower creep resistance. The correlations between the room temperature creep behaviour and the corresponding microstructure of nitrocarburising surface are discussed.

Room-Temperature Creep Behavior and Activation Volume of Dislocation Nucleation in a LiTaO3 Single Crystal by Nanoindentation.

The crystal orientation effect on mechanical heterogeneity of LiTaO3 single crystals is well known, whilst the time-dependent plastic behavior, i.e., creep is still short of understanding. Relying on nanoindentation technology, we systematically studied room-temperature creep flows at various holding depths (100 nm to 1100 nm) in three typical orientations namely the X-112°, Y-36° and Y-42° planes. Creep resistance was much stronger in the X-112° plane than the others. In the meanwhile, creep features were similar in the Y-36° and Y-42° planes. The orientation effect on creep deformation was consistent with that on hardness. The nanoindentation length scale played an important role in creep deformation that creep strains were gradually decreased with the holding depth in all the planes. Based on strain rate sensitivity and yield stress, the activation volumes of dislocation nucleation were computed at various nanoindentation depths. The activation volumes ranged from 5 Å3 to 23 Å3 for the Y-36° and Y-42° planes, indicating that a point-like defect could be the source of plastic initiation. In the X-112° plane, the activation volume was between 6 Å3 and 83 Å3. Cooperative migration of several atoms could also be the mechanism of dislocation activation at deep nanoindentation.

Indentation strain rate sensitivity of ball-milled spark-plasma sintered Cu-C metal matrix composite

Bulk ultrafine grained metal matrix composites (MMC) have attracted much attention of many researchers due to their potential in terms of excellent mechanical properties for engineering applications, such as high strength, which can be two or more times of that of their coarse grained counterpart. Bulk ultrafine grained Cu-3wt.%C MMC samples were produced by Ball-Milling (BM) followed by Spark Plasma Sintering (SPS), at a temperature of 900 °C. The Cu-C MMC was compacted progressively by repeating the BM + SPS procedure without changing the weight ratio between Cu and graphite. The room temperature creep behavior, and the strain rate sensitivity (SRS) were inspected by using nanoindentation measurements. Strain rate ranged 0.0025-to-0.5 s−1, and the contact dwelling times ranged 5-to-300 s. A secondary steady-state regime was reached starting from a dwelling time of 120 s irrespective of the strain rate and Cu-C compaction level. A negative trend of the SRS exponent with Cu-C compaction was obtained, with creep stress exponent as high as 28. These results were discussed according to the microstructure features that differentiated the Cu-3wt.%C MMC obtained by the progressive BM + SPS compaction levels.

Alloying effect on the room temperature creep characteristics of a Ti-Zr-Be bulk metallic glass

The effect of alloying elements (e.g. Fe, Al, and Ni) on the room temperature creep behavior of a lightweight Ti41Zr25Be34 bulk metallic glass (BMG) was investigated via nanoindentation tests. The generalized Kelvin model was adopted to describe the creep curves. The strain rate sensitivity m has been derived as a measure of the creep resistance. The compliance spectrum and retardation spectrum were also derived. The results show that the creep resistance of Ti41Zr25Be34 alloy can be obviously improved with the addition of alloying elements, and the most effective element is found to be Al. The mechanism for enhancing the creep resistance was discussed in terms of the scale variation of the shear transformation zone induced by alloying.