Superior Creep Research Articles

Effect of microstructure and temperature on the bulk and small-scale deformation behavior of 2nd and 3rd generation advanced intermetallic TiAl alloys

Advanced intermetallic TiAl alloys have attracted considerable attention as a high-temperature structural material in aerospace and automobile sectors owing to their low density, elevated temperature strength, superior creep, and oxidation resistance. The present study is focused on assessing the effect of alloy composition, heat treatment and microstructural variation on the bulk and small-scale deformation behavior of commercial grade 2nd generation and newly developed 3rd generation TiAl alloys at 25 °C (298 K), 300 °C (573 K), and 500 °C (773 K). Twinning is noted to be the dominant deformation mechanism irrespective of the temperature. The highest yield strength and hardness are noted for the as-cast 3rd generation TiAl alloy owing to the finer microstructure and compositional variation. Heat treatment however modifies the TiAl microstructure significantly resulting to unique bilamellar-biglobular (BLBG) microstructure, devoid of the brittle β0 phase. Consequently, nano twins- and micro twins-induced enhanced deformability is noted for such microstructure, as compared to the as-cast counterparts. Interestingly, an anomalous increase in strength with an increase in temperature is observed for the studied alloys owing to the presence of high-density twins and Kear-Wilsdorf locks. Most importantly, a temperature dependant hardness anomaly is noted in the TiAl alloys that opens new avenues for further research in nanoscale deformation. This piece of research potentially strengthens the understanding of the role of constituent phases and temperature in the deformation behavior of complex TiAl alloys. Twin-induced deformation mechanism noted for the novel BLBG microstructure, can also be valid for different generations of TiAl alloys to achieve enhanced deformability that paves the way for the development of next-generation material.

Length effect of crosslinkers on the mechanical properties and dimensional stability of vitrimer elastomers with inhomogeneous networks

Inhomogeneous network construction is a useful strategy to solve the trade-off between mechanical strength and creep in vitrimer rubbers. But it is still lack of tools to tune the mechanical properties and network dynamics of this new system. In this paper, uneven distribution of functional groups was realized by sequential coordination polymerization of myrcene and isoprene and epoxidation. The following epoxidation and curing generated VMI-x samples with inhomogeneous network. Polyisoprene was used to prepare control samples called VPI-x with homogeneous network. Different lengths of dicarboxylic acid crosslinkers (SA = succinic acid, HA = heptanedioic acid, DA = decanedioic acid) were used to probe their effects on dynamic behaviors, mechanical properties and recyclability. Morphological test and nanomechanical mapping confirmed the inhomogeneous feature of VMI-x samples. For both inhomogeneous and homogeneous samples, SA and DA crosslinkers brought higher tensile strength and modulus, earlier SIC phenomenon and higher orientation percentage of amorphous molecular chains than those of HA, which are ascribed to extra permanent cross-linking existing in SA samples and transition entanglements existing in DA samples. However, the constrain effect of SA crosslinker is too strong in inhomogeneous network to sacrifice the extensibility, which is much smaller than those of HA and DA. SA and DA samples also present restricted segmental motion and superior creep resistant properties compared to HA samples according to the results of broadband dielectric spectroscopy and DMA test. Differently, at high temperature above 130 °C, the stress relaxation, topology freezing transition temperature (Tv) and recycling efficiency of strength are dominated by the crosslinker length monotonically, probably due to the disentanglement of DA crosslinkers. Compared to homogeneous network, inhomogeneous ones showed obvious enhanced mechanical properties, lower hysteresis, quicker segmental relaxation, lower creep and quicker network relaxation. This work demonstrates that crosslinker lengths could tune the vast aspects of vitrimer elastomers and is a non-negligible factor to determine their properties, especially for those with inhomogeneous networks.

Oxidation-creep interactions for an Hf-doped Ni-based superalloy with different wall thickness at 760 °C

Stress rupture tests of an Hf-containing Ni-based superalloy with different wall thicknesses were carried out at 760 °C/691 Mpa using the RD-100 electronic machine. At the fracture edge, electron backscatter diffraction (EBSD) analysis showed that recrystallization (RS) occurred, and the width of RS increased with increasing sample thickness. The RS induced the intergranular corrosion cracking and accelerated the failure of the sample. At the interior of the substrate, voids were preferentially nucleated at the site of the Hf(Ta)C carbides, and the thinner sample suffered lighter creep damage than the thicker sample. Consequently, the thinner sample had a superior creep life.

Recent progress in the microstructurally based creep modelling of Ni-based alloy 617

ABSTRACT Solid solution strengthened (SSS) Ni-based superalloys, such as A617, show superior creep resistance at 700°C. Established for many years in land- and aero-based gas turbines, these materials are increasingly being considered for use in high-temperature thermal power plants. Apart from SSS, the creep strength in A617 stems from γ’ and carbide precipitates. In this work, a microstructurally based creep model for A617 is presented. Mobile dislocations in the model interact with fine grain-interior precipitates, and grain boundaries act as dislocation sources/sinks. The model is capable of simulating creep curves and time-to-rupture (TTR) diagrams based on the evolution of mobile dislocations. At lower stresses, the accuracy of modelled TTR can be improved by adding diffusion creep to dislocation creep. The simulated evolution of dislocation densities is realistic compared to the literature data. The reduction of area of ruptured samples was included in a damage factor, enabling the consideration of creep ductility.

Mechanisms for high creep resistance in alumina forming austenitic (AFA) alloys

Castable alumina forming austenitic (AFA) alloys have demonstrated superior creep life and oxidation resistance at temperatures exceeding 800⁰C. Despite the success in the applicability of these alloys in extreme environments, there is a limited understanding of the deformation modes and the influence of each alloying element guiding the alloy design strategies that could further enhance the creep strength of these AFA alloys, particularly at temperatures at and above 900⁰C. In this study, we reveal the mechanism underpinning the superior creep performance of castable AFA alloys that involves suppressing primary carbide formation through minor compositional modification. This approach results in a three-fold increase in creep strength at 900⁰C and 50 MPa. By employing integrated characterization techniques, we analyzed the microstructures of two AFA alloys, both before and after the creep process. We discovered that the suppression of primary carbides permits the in-situ clustering of now-available interstitial elements such as C, Si, and O during high-temperature creep. This improved solid solution strengthening and reduced stacking fault energy of the alloy. Moreover, it also enabled controlled secondary carbide formation during testing, further improving the creep resistance. These findings underline the important interplay between alloy composition, microstructure, and creep properties, and offer a promising design strategy for developing economical high-temperature Fe-based alloys suitable for advanced applications.

Unveiling High Performance Solder Alloys for Automotive Applications

Vehicle electrification and advances in autonomous driving technologies are creating unique opportunities and challenges in the automotive electronics assembly industry. The ever-increasing demand of reliability at higher temperatures and longer service life, especially for automotive electronics, is leading to the evolution of high reliability solder alloy design in the electronics assembly industry. The combination of harsh operating conditions, increasing power densities, and miniaturization has added to the complexity of assembly designs in the automotive electronics market for which traditional surface mount solders are no longer applicable. Thermo-mechanical reliability of solder alloys under harsh operating conditions has been a primary factor for defining suitability and selection of solder alloy for next generation designs. A next generation high reliability alloy for automotive electronics is introduced herein. The microstructure of this novel alloy consists of a well-distributed eutectic phase and finely distributed precipitates of intermetallic compounds which contributes towards solid solution strengthening as well as precipitation strengthening. It is shown that a high-temperature superior creep strength improvement of more than 100% over existing high reliability alloys is achieved at temperatures of 150°C. This and other mechanical properties of the bulk alloy are then correlated to performance with thermal cycling testing under extreme conditions. The novel alloy showed significantly higher thermal cycling performance, exhibiting more than 40% increase in the characteristic life over other existing high-reliability alloys while maintaining traditional surface mount target reflow temperatures. Considering these results, this new class of alloys has the capability to meet the increasingly challenging reliability requirements of automotive electronics.

Assessing the Long-Term Creep Behaviour of Hydrothermally Treated Japanese Cedar Wood Using the Short-Term Accelerated Stepped Isostress Method.

In this study, short-term accelerated creep tests were conducted using the stepped isostress method (SSM) to investigate the impact of hydrothermal treatment on the long-term creep behaviour of Japanese cedar wood and to determine optimal hydrothermal treatment conditions. The results showed that SSM can effectively predict the creep behaviour of hydrothermally treated wood. Among the treatment conditions tested, Japanese cedar wood treated hydrothermally at 180 °C for 4 h exhibited higher flexural strength retention (91%) and moisture excluding efficiency (MEE) (44%) and demonstrated superior creep resistance compared to untreated wood. When subjected to a 30% average breaking load (ABL) over 20 years, the specimen's creep compliance, instantaneous creep compliance, b value, activation volume, and improvement in creep resistance (ICR) were 0.17 GPa-1, 0.139 GPa-1, 0.15, 1.619 nm3, and 4%, respectively. The results indicate that subjecting Japanese cedar wood to hydrothermal treatment at 180 °C for 4 h has a negligible effect on its flexural properties but results in significant improvements in both dimensional stability and creep resistance.

The influence of processing methods on creep of wrought and additively manufactured CrCoNi multi-principal element alloys

The influence of vacuum arc melting and mechanical processing (wrought) versus additive manufacturing (AM) on the creep behavior of multi-principal element alloys (MPEA) is investigated in this study. Annealed wrought and hot isostatically pressed (HIP) AM CrCoNi were creep tested under constant tensile stress of 40 to 200 MPa at temperatures of 1023 to 1173 K. Stress exponents of 4.5 ± 0.2 and 5.9 ± 0.1 and activation energies ranging from 240 to 259 and 320 to 331 kJ/mol were found for wrought and AM CrCoNi, respectively. The results indicate that the AM material exhibits superior creep resistance and inferior creep ductility compared to the wrought alloy. This difference is attributed to the AM material having a higher percentage of Cr-rich oxides, a smaller total low angle grain boundary (LAGB) length on a percentage basis, and a greater total twin boundary (TB) length on a percentage basis. The AM and wrought materials have similar grain sizes; however, the smaller LAGB length and greater TB length in the AM material reduce slip transmission on the other side of the boundaries and contribute to strength. The dislocation structures of the AM and wrought materials consist of individual curved dislocations with dislocation multijunctions and jogs, which is similar to the arrangements previously observed in CrMnFeCoNi.

A Calibration Approach for Accelerated Creep Testing for Electron Beam Melted Ti-6Al-4V Using the Wilshire–Cano–Stewart Model

Abstract This study outlines a model calibration approach for an accelerated creep test called the dynamic negative stepped test (DNST) to enable the rapid screening of creep-resistant materials. In DNST, stress is stepped decreased based on the attainment of a sufficient minimum-creep-strain-rate (MCSR) at each stress level. Steps are repeated, torturing the material, until rupture occurs. The DNST is advantageous as a screening test for new alloys. Alloys and heats with superior creep resistance will be able to survive longer and with greater ductility than those with poor creep resistance. The calibration of a constitutive model to DNST data furnishes predictions of the conventional creep response being between 65 h and 6685 h from the relatively short (<130 h) DNST Data. In this study, DNSTs are performed on electron beam melted (EBM) Ti-6Al-4V at 650 °C with stepping through 150, 75, 60, and 50 MPa. Six build orientations are tested including 0 deg, 30 deg, 45 deg, 60 deg, 90 deg, and V (vertical) direction. The Wilshire–Cano–Stewart (WCS) model is employed to calibrate the experimental data. A systematic calibration approach is adopted. Each step is calibrated numerically. A unique set of minimum-creep-strain-rate (MCSR) and stress-rupture (SR) related material constants, i.e., the Wilshire and Sinh constants are obtained for each build direction. A nonhomogenous objective function is used to numerically optimize the strain trajectory and damage trajectory constants. To find the best-fit curve, the strain trajectory constants, and damage trajectory constants are numerically refined for each step. The WCS model shows a near-perfect prediction of the DNST data. Based on the calibrated constants, conventional creep curves are generated in order to determine which build orientations are likely to exhibit poor, moderate, and superior creep resistance. Predictions of MCSR and SR curves over a wide stress range are estimated outside the experimental range to investigate the extrapolation pedigree of the approach. This will allow the material designers to have more confidence in DNST-generated test data for predicting long-term creep response and structural lifetime.

Deformation behavior, microstructure evolution, and rupture mechanism of the novel G115 steel welded joint during creep

To promote the wide application of the G115 steel in ultra-supercritical (USC) power plants, creep deformation, microstructure evolution and rupture mechanism of the G115 welded joint were systematically investigated. The fabricated G115 welded joint exhibits superior creep strength to the P92 or MARBN steels. The deformation behaviors are analyzed by the Norton's power law, proving that the deformation mechanism is closely associated with the stress levels. During short-term creep under higher stress, the weld metal (WM) and heat-affected zone (HAZ) exhibit outstanding microstructure stability, and the rupture occurs within the base metal (BM) due to the lath fracture. While, during long-term creep under lower stress, the brittle Type IV cracking occurs within the inter-critical heat-affected zone (ICHAZ) or fine-grained heat-affected zone (FGHAZ) due to the formed micro-voids along boundaries, obviously deteriorating the creep strength. The weld strength reduction factors are calculated under different stresses, and prove that synergistic action of back stress and dislocation motion can enhance the creep resistance of the G115 welded joint. Additionally, the allowable service stress of G115 weldments should be designed according to the creep strength of the welded joints under expected performance life.

Microstructural and mechanical properties of precipitation-strengthened Al-Mg-Zr-Sc-Er-Y-Si alloys

We study the precipitation behavior of two L12-strengthened alloys with Mg and Y additions: ultralow-Sc, Si-free, Al-1Mg-0.09Zr-0.007Sc-0.006Er-0.02Y-0.01Si, and low-Sc, Si-added, Al-1Mg-0.09Zr-0.013Sc-0.006Er-0.02Y-0.08Si (at.%), and their ambient temperature strength and high-temperature creep resistance. Scanning transmission electron microscopy analyses reveal that β-Mg2Si precipitates or their precursors (β’, β’’) form in the Si-added alloy at ∼ 200°C, which act as preferential nucleation sites for the L12-nanoprecipitates and cause partial depletion of Si solute atoms, which decelerates L12 precipitation-kinetics, resulting in a microhardness peak at the same isochronal temperature, 475°C, in both alloys. Atom-probe tomography analyses reveal that the L12-nanoprecipitates in both alloys exhibit Sc/Er/Y-rich cores and Zr-rich shells, as well as Mg segregation at the interfacial regions. The L12-nanoprecipitates in the Si-added alloy has a smaller Sc/Er/Y and higher Zr and Si concentrations. The Si-free alloy exhibits superior creep properties at 300°C, due to a larger lattice parameter mismatch of the L12-nanoprecipitates with the Al(f.c.c.) matrix provided by higher Sc/Er/Y concentrations. Both alloys exhibit slower L12 nanoprecipitation-kinetics, extremely high coarsening resistance, and similar high-temperature creep resistance compared to a recently developed Mg/Y-free low-Sc, Al-0.08Zr-0.014Sc-0.008Er-0.09Si (at.%) alloy. The extremely high coarsening resistance of the Si-added alloy is attributed to the smaller Si concentration in the Al(f.c.c.) matrix. Silicon is scavenged by the β-Mg2Si precipitates, thermodynamically stable at < 475°C, which is then not available in the matrix to accelerate the coarsening of the L12-nanoprecipitates.

Quantitative estimation of coarsening behavior of L12 domains in Ni–Al–V alloys by a first-principles calculation

Ni–Al–V based alloys possess superior creep resistance at higher temperatures because of the sluggish interdiffusion of constituent elements within the L12-Ni3(Al, V) matrix. In this study, intrinsic diffusion coefficients of Ni, Al and V in quasi-binary Ni3Al1-xVx (x = 0, 0.125, 0.25, 0.5) were quantified based on a first-principles calculation for elucidating the effect of V concentration on the coarsening behavior of L12 domains. From the results of the estimated formation energies, migration energies and activation energies, it was found that intrinsic diffusion coefficients of Ni and Al are decreased by the addition of V, while intrinsic diffusion coefficient of V remains two or three orders of magnitude smaller than them. Such a suppressed diffusion of Ni and Al by V addition well explains the experimentally obtained lower coarsening rates of L12 domains in Ni3Al0.58V0.42 and Ni3Al0.48V0.52 alloys.

The relative effect of boron and nitrogen concentrations on microstructure and creep resistance of weld simulated heat-affected zones of modified 9Cr-1Mo steel

To comprehend the combined impact of B and N concentrations on modified 9Cr-1Mo steel's heat affected zone (HAZ) creep resistance, five different steels with varying B (0-100 ppm) and N (20-500 ppm) concentrations were subjected to two types of weld thermal cycles (WTC), namely coarse-grained HAZ simulation and inter-critical HAZ simulation with peak temperatures of 1175 °C and 850 °C, respectively. Prior to and after creep testing (at 650 °C, 120 MPa stress), the microstructures and precipitates in the WTC simulated samples were studied using optical and electron microscopy, electron backscattered diffraction, and auger electron spectroscopy techniques. As expected, simulated HAZs of high B-containing steels (70-100 ppm B) showed superior creep resistance compared to low B steels (0-25 ppm B) due to the B stabilizing effect of M23C6 precipitates (primarily (Fe,Cr)23(B,C)6) though the rupture time for the simulated HAZs are lower than that of the base metals tested at the same test temperatures and stress levels. An interesting finding is that, despite the fact that 70 ppm B steel (with 108 ppm N) demonstrated the best creep resistance in normalized and tempered condition, 100 ppm B steel (with just 20 ppm N) obtained the best creep resistance of simulated HAZ. Large difference in the rupture lives between simulated ICHAZ and simulated CGHAZ specimens reveals the effect of triaxility in reducing the rupture lives in simulated CGHAZ specimens. This is also applicable to actual weld joints.

Superior tensile creep behavior of a novel oxide dispersion strengthened CrCoNi multi-principal element alloy

The creep behavior of an additively manufactured (AM) yttrium oxide dispersion strengthened (ODS) CrCoNi multi-principal element alloy (MPEA) is investigated in this study. Tests were conducted over a constant tensile stress range of 40–200 MPa and a temperature range of 973–1173 K. A stress exponent of 6.5 ± 0.1 and activation energies in the range of 335–367 kJ/mol were measured. Compared to its non-ODS counterpart and its parent alloy (CrMnFeCoNi), AM ODS CrCoNi has superior creep resistance at all tested stresses and temperatures. The mechanism contributing to the excellent creep resistance of AM ODS CrCoNi is attributed to the interaction of mixed character dislocations with oxide particles. The creep ductility of AM ODS CrCoNi is higher than its non-ODS counterpart due to a large percentage of low angle grain boundaries associated with its columnar grain structure. It was also found that creep ductility is significantly greater at the highest applied stress of 200 MPa compared to lower stresses. The steady state dislocation structure of AM ODS CrCoNi consists of long arrays of dislocations, which is different from that observed in non-ODS CrCoNi which consists of individual curved dislocations.

Unexpected creep behavior in a rejuvenated metallic glass

Rejuvenation, bringing metallic glasses (MGs) to the younger and higher energy states, provides an alternative avenue to explore the interplay between the property and microstructures of MGs. In this study, the creep behavior of the Zr69.5Cu12Ni11Al7.5 MGs was experimentally examined by controlling the energy state in terms of structural rejuvenation and thermal annealing. It is found that compared to the as-cast counterpart, the annealed MG at a lower energy state exhibits a higher hardness, a smaller displacement, and a lower creep rate due to the decreased free volume and the inhibited activation of the shear transformation zone. Conversely, the rejuvenated MG at a high energy state displays lower hardness and increased free volume content, yet it demonstrates superior creep resistance compared to its as-cast counterpart, which deviates from conventional understanding. This unexpected phenomenon occurs as the initial high-content free volume annihilates during creep, and strain hardening takes precedence over strain softening as the prevailing process during creep deformation, leading to a superior creep performance in extremely rejuvenated MGs.

Creep anisotropy reduction and improvement via post-heat treatment in yttrium-added Hastelloy-X fabricated by laser powder bed fusion

The development of laser powder bed fusion (LPBF) has made it possible to produce complex three-dimensional components for high-temperature applications. The LPBF process needs to be refined to address several key factors, such as high-temperature elongation, microstructure heterogeneity, and mechanical anisotropy. Hastelloy-X Ni-based superalloy was used to illustrate these issues in this study. First, 0.046 wt.% of yttrium (Y) was added to Hastelloy-X (HX-y) to prevent grain boundary embrittlement. The second step involves two kinds of post-heat treatments; i) at 850 °C for 2 h (DA) for carbides and ii) solution heat treatment at 1240 °C for 8 h upon aging at 850 °C for 2 h (HTA). The creep properties of the samples were compared at 900 °C/ 80 MPa to understand the effect of Y addition and post heat treatments. The HX-y specimen was strengthened by solid solution and dispersion of Y-rich oxides, together with stabilization of oxygen-based contamination at the grain boundaries. The DA and HTA HX-y specimens had better creep properties than the HX specimens. The HX-y specimen showed superior creep properties to the HX specimen due to the presence of carbides M6C and Cr23C6 inside grains and at grain boundaries. However, carbides remained stable even at high temperatures within grains and at grain boundaries. Nevertheless, the HTA HX-y specimen exhibited superior isotropic creep properties. As a result of grain boundary pinning, serrated grain boundaries prevented grain boundary sliding. In contrast, HX specimens exhibited poor creep properties. This study confirmed that the optimal addition of Y together with the optimization of post-heat treatment drastically enhances the creep properties of materials fabricated by the LPBF process.

Effect of prior heat treatment on the microstructure evolution and creep resistance of ZK60 Mg alloy under tensile creep loading along normal direction

Tensile creep tests were performed along the normal direction on the as-solutioned (AS) and as-aged (AA) samples of a commercial ZK60 alloy in this work. The results showed that the AA sample obtained a stronger 0.2% proof stress but a poorer creep resistance in comparison to the AS sample. It was revealed that the creep deformation in the AS sample was attributed to basal slip and twinning while the creep behavior of the AA sample was controlled by basal slip, pyramidal <c+a> slip and twinning. Besides, the reasons for the poorer creep resistance of the AA sample were unveiled. Pyramidal dislocations towards various moving directions were found to accelerate the creep deformation, and basal dislocations kinking at twin boundaries were found to induce heavy stress concentration. Furthermore, massive dynamic precipitates including β1′ and β2′ types were formed in the AS sample during the creep exposure, contributing to the superior creep resistance. But in the AA sample, plentiful β1′ and β2′ phases generated during the prior peak-ageing treatment, dissolved into the matrix fast and only β1′ phases re-precipitated during the creep process. With the decreased area fractions of precipitates, the age-hardening effect slacked off and failed in enhancing the creep resistance.

Synthesis and mechanical and elevated temperature tribological properties of a novel high-entropy (TiVNbMoW)C 4.375 with carbon stoichiometry deviation

High-entropy carbides are a nascent group of ceramics that are promising for high-temperature applications due to the combination of good stability, high hardness (<i>H</i>), high strength, and superior creep resistance that they display. Due to high melting points and low lattice diffusion coefficients, however, the high-entropy carbides are usually difficult to consolidate to a nearly full density. To cope with this challenge, herein, binary carbides including TiC, V₈C₇, NbC, Mo₂C, and WC with different carbon stoichiometry were used to prepare dense high-entropy (TiVNbMoW)C_4.375, and the influence of carbon vacancy on formation ability and mechanical properties of carbon-deficient high-entropy (TiVNbMoW)C_4.375 were investigated. Intriguingly, although the starting binary carbides have different crystal structures and carbon stoichiometry, the as-prepared high-entropy material showed a rock-salt structure with a relatively high density (98.1%) and good mechanical properties with hardness of 19.4±0.4 GPa and fracture toughness (<i>K</i>_IC) of 4.02 MPa·m^1/2. More importantly, the high-entropy (TiVNbMoW)C_4.375 exhibited low coefficient of friction (COF) at room temperature (RT) and 800 ℃. Wear rate (<i>W</i>) gradually increased with the temperature rising, which were attributed to the formation of low-hardness oxidation films at high temperatures to aggravate wear. At 800 ℃, lubricating films formed from sufficient oxidation products of V₂O₅ and MoO₃ effectively improved tribological behavior of the high-entropy (TiVNbMoW)C_4.375. Wear mechanisms were mainly abrasive wear resulting from grain pullout and brittle fracture as well as oxidation wear generated from high-temperature reactions. These results are useful as valuable guidance and reference to the synthesis of high-entropy ceramics (HECs) for sliding parts under high-temperature serving conditions.

Design and Investigation of a Fiber Bragg Grating Tilt Sensor With Vibration Damping

Fiber Bragg grating (FBG) sensors play an increasingly important role in structural health monitoring, and tilt sensors are one of the most commonly used among them. Traditional FBG tilt sensors are easily affected by external vibration, and to overcome such a problem, this work proposes a novel FBG tilt sensor with a vibration damping feature. Based on the classical equal strength beam structure, a vibration-isolating spring is used as the vibration-damping connection between the beam and the mass block, while a damping fluid is filled inside the sensor housing as the vibration-damping material. After elaborating on the details of sensor structural design and measurement theory, five sensors were set up for relevant performance tests, and the controlled experiments were carried out for the FBG sensors with and without the vibration isolation springs. Meanwhile, for sensors with vibration isolation springs, the viscosity of filled damping fluid was also varied in the experiments, to better reveal its influence on the sensor performance. The experimental results show that the proposed sensors have a high sensitivity of 112.743 pm/° within a range of ±15° and also have superior creep resistance as well as good temperature compensation capability. From controlled experiments, it is evident that the proposed sensor with a vibration damping structure offers better vibration stability and monitoring accuracy and can be effectively adapted to safety monitoring tasks in different engineering applications by simply adjusting the viscosity of filled damping fluid.

Effects of individual and combined additions of transition elements (Zr, Ti and V) on the microstructure stability and elevated-temperature properties of Al–Cu 224 cast alloys

The effects of individual and combined additions of transition elements (TEs) Zr, Ti, and V on the microstructure evolution and elevated-temperature mechanical and creep properties of Al–Cu 224 cast alloys were investigated. All alloys had a mixed precipitate microstructure of θʺ- and θʹ-Al2Cu after T7 heat treatment. During the thermal exposure at 300 °C, θʺ transferred into θʹ as the predominant strengthening phase. The coarsening resistance of θʹ during the thermal exposure and further creep deformation was greatly improved by the addition of TEs. Individually, Zr addition demonstrated the best efficiency in stabilizing θʹ, while the combination of Zr + V and Ti + Zr + V achieved the highest efficiency. The addition of TEs generally improved the yield strength (YS) at 300 °C, and the ZrV and TiZrV alloys achieved the highest YS. A close correlation between the YS and the distribution and thermal stability of θʹ was observed. The creep resistance at elevated temperatures was affected by the thermal stability of θʹ and grain size. Zr-containing alloys (ZrV, Zr, and TiZrV) exhibit superior creep resistance. In terms of comprehensive properties, the combined addition of TiZrV alloy exhibited the best elevated-temperature performance.