High Temperature Mechanical Behavior Research Articles

Enhanced High-Temperature Mechanical Behavior of an in Situ TiAl Matrix Composite Reinforced With Alumina

A Ti-45Al-3Cr-2.5Nb alloy reinforced with in situ formed alumina has been produced by means of centrifugal casting by adding zirconium oxide in the crucible. The dispersion-strengthened alloy has been characterized to verify its microstructure and particle distribution. Mechanical tests carried out over the temperature range 850–950 °C highlighted that in situ formed alumina allows to increase the alloy yield stress by 21% at 850 °C and by 35% at 900 °C. Moreover, the in situ formed oxide particles produced an increase of the Young’s modulus of about 10% at 850 °C and of about 8% at 900 °C. Considering that the tested alloy has a density that is about a half of nickel superalloys, obtaining high specific mechanical properties over the temperature range 850–950 °C can boost its application in the production of turbine blades.Graphical abstract

An Al-5Fe-6Cr alloy with outstanding high temperature mechanical behavior by laser powder bed fusion

This research aims to study the laser powder bed fusion ( L -PBF) processability, the microstructure and the tensile mechanical properties of an AlFeCr alloy at a wide range of temperatures. With this goal, Al-5Fe-6Cr (wt%) pre-alloyed powder was produced by casting and gas atomization. The microstructure of the as-atomized powders and the as-built specimens was characterized via scanning electron microscopy, x-ray diffraction, and transmission electron microscopy. Following a parameter optimization study, dense as-built specimens with a high relative density of 99.8% and a Vickers hardness at room temperature of 192 HV were fabricated. In addition, the newly developed AlFeCr alloy exhibits yield strength values of 273 ± 5 MPa and 179 ± 3 MPa at 300ºC and 400ºC, respectively. The exceptional strength of this alloy at high temperature is attributed to the homogeneous precipitation during processing of large density of nanoscale icosahedral (i-phase) and intermetallic phases, which are endowed with high thermal stability. These values are significantly higher than those corresponding to the conventional wrought Al7075 aluminum alloy in the T6 condition and to all Al alloys manufactured by L -PBF to date. The current research sheds guidelines for the design of high strength aluminum alloys containing transition alloying elements that are suitable to be processed by L -PBF for high temperature structural applications in a cost effective way.

Effect of Boronizing on the High Temperature Mechanical Behavior of Inconel 625

Inconel 625 is a frequently used material specifically in the exhaust and piping components of gas turbine engines, because of its good corrosion resistance even at high temperatures. In this work, the effect of boronizing on the room and high temperature tensile behavior of Inconel 625 alloy was investigated. According to the room temperature tensile test results, yield strength (YS) and ultimate tensile strength (UTS) of the samples reduced after boronizing. This strength reduction may be attributed to the softening of the material throughout the boronizing process at a high temperature of 1100°C. On the other hand, ductility of the Inconel 625 samples decreased. At elevated temperature, the yield strength of the boronized sample significantly reduced because of the possible decomposition of boron particles throughout tensile straining at elevated temperatures. Consequently, the fracture morphology observations revealed that the main fracture mechanism of both coated and uncoated conditions at high temperature was ductile fracture represented by coarse and deep dimples.

Room and high-temperature mechanical behavior of reduced graphene oxide‑aluminum (RGO-Al) composite wire conductors – A micro-mechanical investigation

In this study, we present a micro-mechanical investigation of cold-drawn reduced graphene oxide (RGO) reinforced aluminum (Al) composite wires from 293 K up to 523 K. Room temperature micro-tensile, high-temperature (HT) micro-pillar compression, and HT nanoindentation tests revealed the superior mechanical properties of the composite compared to the unreinforced Al sample over the whole temperature range. Complementary thermal stability measurements and associated microstructural analysis proved that RGO effectively prohibited grain growth by grain boundary pinning. The RGO-Al composite wires are shown to be much stronger, heat-resistant, and easier to fabricate than conventional HT Al alloy-based conductors with adequate conductivity.

Studying the Effect of High Temperature on the Content of Glass and Brick Waste Binders after Alkaline Activation

The high-temperature mechanical behaviour of a glass and brick waste alkaline to synthesize geopolymer mortar was studied. The mortar in question contained 100% glass powder GWP and 90% of a blend of brick waste GBWP, brick waste BWP and a solid activator (10 mol concentration of NaOH mixed with glass water (Na2SiO3). The material was tested during exposure to high temperatures to establish its density, weight loss, compressive strength, accessible porosity in water, expansion of pastes, XRD and TG-DSC analysis using an innovative methodology to notch the hydrated geopolymers paste specimens after exposed to five maximum temperatures, 100℃, 200℃, 400℃, 600℃ and 800℃ without any imposed load during the heating. The results were found that GBWP gave better values in compressive strength, reaching 38.3 MPa at 100℃ and other proportional values at 400℃, 600℃ respectively compared with GWP. As for the density, the high temperature contributed to its decrease, which caused the presence of high porosity at 800℃. On the other hand, the high temperature helped to improve the mechanical and physical behavior of BWP, where the resistance reached 24.91 MPa at 200℃. In addition, for the microstructure and different particles related to the interactions were identified through the XRD and TG-DSC analysis procedure, in order to know the highest temperatures that allow changing the structure and properties of this type of alternative binders.

Metal-like peak stress behavior of yttrium-doped BaCeO3 ceramic

The high-temperature mechanical behavior of polycrystalline 5 at% yttrium-doped barium cerate with submicronic grain size (d = 0.5 µm) has been studied in compression between 1200 and 1300 °C at different initial strain rates. The true stress – strain curves display an initial peak stress followed by a softening stage and then by an extended steady-state stage; the magnitude of the peak stress is strongly dependent on strain rate and temperature. These characteristics are very similar to those found in metals and metallic alloys that exhibit dynamic recrystallization during creep at elevated temperatures. Microstructural observations by scanning and transmission electron microscopy have shown that the grain structure is progressively refined with increasing strain due to the strong interaction between dislocations and pre-existing twin boundaries, originated by the various crystal transformations that occur upon cooling from the sintering temperature. The empirical equations used in metals to describe the relationship between strain rate, peak stress, and peak strain are also valid in the present ceramic material.

High-temperature mechanical behavior of ultra-coarse cemented carbide with grain strengthening

Ultra-coarse grained cemented carbides are often used under conditions of concurrently applied stress and high temperature. Improvement of high-temperature mechanical performance of ultra-coarse grained cemented carbides is highly desirable but still a big challenge. In this study, it is proposed that the high-temperature compression strength of ultra-coarse cemented carbides can be enhanced by modulating hard matrix grains by activated TaC nanoparticles, through solid solution strengthening of Ta atoms. Based on the designed experiments and microstructural characterizations combined with finite element simulations, the grain morphology, stress distribution and dislocation configuration were studied in detail for ultra-coarse grained cemented carbides. The mechanisms of Ta dissolving in WC crystal and strengthening ultra-coarse grains through interaction with dislocations were disclosed from the atomic scale. This study opens a new perspective to modulate hard phases of cemented carbides for improving their high-temperature performance, which will be applicable to a variety of cermet and ceramic-based composite materials.

Strength and rupture geometry of un-irradiated C26M FeCrAl under LOCA burst testing conditions

Ferritic iron-chromium-aluminum (FeCrAl) alloys are an accident tolerant fuel candidate to replace the incumbent Zr-based claddings. Nuclear grade FeCrAl alloys are marked by superior high temperature mechanical behavior and exceptional steam oxidation resistance , both of which increase safety margins during accident scenarios. In the present study, the loss of coolant accident (LOCA) burst behaviors of three un-irradiated commercially fabricated cladding materials in a simulated LOCA environment were compared: (1) T35Y2, a 1 st generation nuclear grade FeCrAl, (2) C26M, a 2 nd generation nuclear grade FeCrAl, and (3) Zircaloy-2. Both FeCrAl alloys showed improved mechanical strength and steam oxidation resistance compared to Zircaloy-2. C26M claddings burst at significantly higher temperatures for all tested engineering hoop stresses , had limited ballooning, and demonstrated preferential fuel retention behavior in terms of burst opening area and length. High temperature tensile data for C26M is also presented. For both un-irradiated FeCrAl alloys, it was found that a distinct “threshold” burst stress signified the transition between small and large openings. Higher threshold hoop stresses were associated with higher uniaxial strength for the FeCrAl alloys, indicating that tensile data, rather than creep data, could be useful for predicting rupture size and assessing fuel dispersal concerns.

High-temperature mechanical properties and deformation behavior of carbides reinforced TiNbTaZrHf composite

Refractory high entropy alloys (RHEAs) have broad prospects in the field of high-temperature structural materials because of their outstanding mechanical properties at high temperatures. In this work, a novel TiNbTaZrHf based composite was fabricated by powder metallurgy in-situ method. By introducing carbides, the TiNbTaZrHf based composite exhibits an ultra-high yield strength of 2620 MPa at room temperature. Meanwhile, the composite still maintains a high strength of 508 MPa at 1000 °C. The significant strength improvement can be attributed to the load-bearing effect caused by the dispersed carbides with high volume fraction, while the intergranular fracture of carbides is responsible for the plastic instability. When the temperature rises to 1200 °C, the yield strength decreases significantly. The weakening of load-bearing effect and the activation of grain boundary sliding are the main reason for the strength reduction, while interfacial debonding between the matrix and carbides becomes the main failure behavior.

Study on high-temperature deformation mechanical behavior and dynamic recrystallization kinetics model of Ti-47.5Al-2.5V-1.0Cr-0.2Zr alloy

The high-temperature deformation mechanical behavior and dynamic recrystallization(DRX) kinetics model of Ti-47.5Al-2.5 V-1.0Cr-0.2Zr alloy were studied by thermal compression tests on a Gleeble thermal simulator. The influences of deformation heat and friction on rheologic stress were calculated and corrected. The results show that the rheologic stress corrected by friction is less than the experimental stress value. This shows that the existence of interface friction has a negative effect on stress. The influence of deformation heat on the stress is significant at lower temperatures and higher strain rates. The stress-strain curve shows the peak stress at low strain, and then descends with increasing of strain. Based on the curve of the work hardening rate versus stress (dσ⁄dε versus σ) the characteristic strain of the alloy was determined, containing the critical strain of DRX and peak strain, and the expression between the critical stress of DRX, the peak stress and the Z parameters was established. To describe the variation law of the DRX volume fraction, DRX kinetics were examined. The Avrami index values of the alloy were all less than 2 within the parameters of this experiment. The smaller Avrami index of this alloy indicates that the recrystallization rate is lower than that of ordinary alloy. The fraction of DRX rises with increasing of strain. That is, the higher the thermal deformation strain is, the higher the external input energy and the greater the degree of DRX. At the same strain rate, the peak value of the DRX growth rate increases with the increasing of temperature, which reflects the effect of the thermal activation energy on the DRX dynamics.

Effects of Aging Treatment on The High-Temperature Mechanical Behavior of Laser-Welded High-Strength Mg-Gd-Y Alloy

Effects of Aging Treatment on The High-Temperature Mechanical Behavior of Laser-Welded High-Strength Mg-Gd-Y Alloy

Timely and atomic-resolved high-temperature mechanical investigation of ductile fracture and atomistic mechanisms of tungsten

Revealing the atomistic mechanisms for the high-temperature mechanical behavior of materials is important for optimizing their properties for service at high-temperatures and their thermomechanical processing. However, due to materials microstructure’s dynamic recovery and the absence of available in situ techniques, the high-temperature deformation behavior and atomistic mechanisms of materials are difficult to evaluate. Here, we report the development of a microelectromechanical systems-based thermomechanical testing apparatus that enables mechanical testing at temperatures reaching 1556 K inside a transmission electron microscope for in situ investigation with atomic-resolution. With this unique technique, we first uncovered that tungsten fractures at 973 K in a ductile manner via a strain-induced multi-step body-centered cubic (BCC)-to-face-centered cubic (FCC) transformation and dislocation activities within the strain-induced FCC phase. Both events reduce the stress concentration at the crack tip and retard crack propagation. Our research provides an approach for timely and atomic-resolved high-temperature mechanical investigation of materials at high-temperatures.

Microstructural Investigation and High Temperature Mechanical Behavior of AXE622 Cast Mg Alloy

The microstructure and high temperature properties of the AXE622 Mg alloy were investigated after the conventional and semisolid casting processes. The tensile test was conducted at room temperature, and 473 K. Impression creep test was performed at a temperature range of 423–498 K under the stress range of 450–600 MPa. The microstructure of the conventional and semisolid alloys contains α-Mg dendrites, the eutectic phase, secondary phases including (Mg–Al)2Ca, eutectic Mg17Al12, and Al11RE3. During semisolid processing, coarse dendrites of the α-Mg became fine, globular, and Rosetta shape. The average length of the secondary phases in the semisolid alloy decreased from 4.21 to 2 μm and the average grain size of the α-Mg reduced from 113 to 96 μm. Semisolid processing caused a significant improvement in the tensile and creep resistance of the AXE622 Mg alloy. The stress exponent for creep was calculated in the range 5.6–7.7 for the conventional alloy and in the range 10.3–11 for the semisolid alloy. The activation energy for conventional and semisolid alloy was determined as 71.4 kJ/mol and 78.3 kJ/mol, respectively. It was concluded that the dominant creep mechanism in the conventional alloy was the grain boundary diffusion-controlled dislocation climb, while in the semisolid alloy was the power-law breakdown.

Effect of homogenization and solution treatments time on the elevated-temperature mechanical behavior of Inconel 718 fabricated by laser powder bed fusion

In the present study, the effect of homogenization and solution treatment times on the elevated-temperature (650 °C) mechanical properties and the fracture mechanisms of Inconel 718 (IN718) superalloy fabricated by laser powder bed fusion (LPBF) was investigated. Homogenization times between 1 and 7 h at 1080 °C were used, while solution treatments at 980 °C were performed in the range from 15 to 60 min. The as-printed condition showed the lowest strength but the highest elongation to failure at 650 °C, compared to the heat-treated conditions. After heat treatments, the strength of the IN718 alloy increased by 20.3–31% in relation to the as-printed condition, depending on the treatment time, whereas the ductility decreased significantly, by 67.4–80%. Among the heat treatment conditions, the 1 h homogenized conditions at 1080 °C (HSA1 and HSA2) exhibited the highest strength and ductility due to the combined effects of the precipitation hardening and sub-structural changes. Further increases in the homogenization time to 4 and 7 h led to a decrease in the strength and significant ductility loss of the LPBF IN718 due to the considerable annihilation of the dislocation tangles and a greater precipitation of coarse MC carbide particles. Furthermore, it was found that the solution treatment duration had a crucial influence on the mechanical properties at 650 °C due to the increase in the grain boundary strength through the pinning effect of the intergranular δ-phase. In addition, the fracture mechanism of the LPBF IN718 was found to be dependent on the heat treatment time. Finally, this investigation provides a map that summarizes the effect of homogenization and solution treatment times on the high-temperature mechanical behavior of LPBF IN718 by relating it to the corresponding microstructural evolution. This effort strives to assist in tailoring the mechanical properties of LPBF IN718 based on the design requirements for some specific applications.

High-Temperature Mechanical Behaviors of SiO2-Based Ceramic Core for Directional Solidification of Turbine Blades.

The high-temperature mechanical behaviors of SiO2-based ceramic cores for the directional solidification of turbine hollow blades were investigated. Isothermal uniaxial compression tests of ceramic core samples were conducted on a Gleeble-1500D mechanical simulator with an innovative auxiliary thermal system. The stress–strain results and macro- and micro- structures of SiO2-based ceramic cores were investigated experimentally. The microstructures were characterized by the scanning electron microscope (SEM). Based on the experimental data, a nonlinear constitutive model for high temperature compressive damage was established. The statistical results of Weibull moduli show that the stability of hot deformation increases with the increase of temperature. The fracture type of the SiO2-based core samples is brittle fracture, but when the temperature exceeds 1400 °C, the mechanical behavior exhibits thermo-viscoelastic and viscoplastic property. Under high-temperature (>1400 °C) and stress conditions, the strength of the ceramic core is weakened owing to the viscous slip of SiO2, which is initially melted at the temperature of 1400 °C. The comparison results between the predictions of nonlinear model and experimental values indicate that the model is applicable.

High-temperature mechanical behavior of proton-conducting yttrium-doped barium zirconate perovskite

The high-temperature mechanical properties of yttrium doped barium zirconate obtained by two different routes are reported in this work. Polycrystals with composition BaZr0.85Y0.15O2.925 have been fabricated from nanopowders synthesized by a modified EDTA-citrate complexing method and conventionally sintered at 1600 °C for 24 h. The material exhibits a single cubic perovskite phase, with a homogeneous, dense and fine-grained microstructure consisting of equiaxed grains with an average size of 0.2 μm. Mechanical tests were carried out in compression between 1100 and 1325 °C in air at constant initial strain rate and at constant load. As the temperature increases and/or the strain rate decreases, a gradual transition from brittle-to-ductile behavior was found. In the brittle regime, the fracture is governed by an intergranular failure mode. In the ductile region, grain boundary sliding is the main deformation mechanism, characterized by a stress exponent of 2 and an activation energy of 570 kJ/mol.

High temperature mechanical behaviour of Mg–6Zn–1Y alloy with 1 wt.% calcium addition: Reinforcing effect due to I-(Mg3Zn6Y1) and Mg6Zn3Ca2 phases

The influence of small calcium additions on the high-temperature mechanical behaviour in an extruded Mg–6Zn–1Y (wt.%) alloy reinforced by the I-phase has been investigated. Calcium promotes the formation of the intermetallic Mg 6 Zn 3 Ca 2 phase instead of I-phase, which results in a noticeable improvement of the yield strength and ultimate tensile strength of the alloy above 100 °C. The strength of the alloys was analysed taking into account the contribution due to the grain size, the crystallographic texture and the volume fraction and nature of second phase particles. In situ synchrotron radiation diffraction experiments have been used to evaluate the load partitioning between the magnesium matrix and the second phase particles (I- and Mg 6 Zn 3 Ca 2 phases) in both alloys. The load transfer from the magnesium matrix towards the Mg 6 Zn 3 Ca 2 phase is markedly more effective than that for the I-phase over the entire temperature range, especially at 200 °C, temperature at which the reinforcement effect of the I-phase is null.

Room and high temperature mechanical behavior of Ti–Al–Nb–Mo alloy reinforced with Ti2AlN ceramic particles

In order to improve the room and high temperature mechanical properties of Ti46Al4Nb1Mo alloy, Ti46Al4Nb1Mo-xN (x = 0, 0.4%, 0.8%, 1.2%, 1.6%, atomic percent, hereafter in at.%) alloys were prepared by adding TiN powders. Results showed that when the N addition was more than 0.8%, the grain morphology changed from columnar dendrites to equiaxed grains due to the formation of Ti2AlN particles, and the equiaxed grain size decreased with further increasing of the N addition. With 1.6% N addition, the compressive strength increased by 16.8% at room temperature, which was due to the collective strengthening effect of lamellae refinement and Ti2AlN particles. While lamellae refinement and Ti2AlN particles had opposite effects and competed with each other at high temperature, strengthening by Ti2AlN particles had the dominant effect on improving the peak stress of the Ti46Al4Nb1Mo-1.6 N alloy, which increased by 21.8% and 24.1% at 900 °C and 1000 °C, respectively. In addition, compared with the fracture microstructure at room temperature, the deformed microstructure showed that the load transfer effect of Ti2AlN particles was more effective at high temperature, which was due to micro-damages in the Ti2AlN particles and the absence of cracks along irregular Ti2AlN particles.

High-temperature mechanical behavior of boron nitride nanosheets/fused silica composites

Boron nitride nanosheets (BNNSs) with relatively low dielectric constant and excellent mechanical strength were employed for fabrication of BNNSs/fused silica (FS) composites. High-temperature mechanical behavior and microstructural evolution of the composites were investigated. The addition of BNNSs can improve the mechanical properties of FS efficiently, and the reinforcement from BNNSs can be preserved during the high temperature service. The flexural strength of BNNSs/FS composites exhibited anomalous gains at certain high temperature range, which can be explained by the softening of FS matrix, the heal of defect tips, and the reinforcement from BNNSs.

On the Analysis of High-Temperature Mechanical Properties and Dry Sliding Tribological Behavior of Ultra-Fine Grained Boron Carbide-Reinforced Al5083-Based Trimodal Composites

Numerous research studies have been done on ultra-fine grained (UFG) aluminum and aluminum-based composites materials due to their higher tensile strength in comparison with coarse-grained (CG) bulks. However, the relationship between the mechanical behavior and dry sliding wear performance of ultra-fine grained Al5083-based boron carbide-reinforced trimodal composite bulks at room and high temperatures have been neglected. Furthermore, the effect of temperature rise on these properties seems critical since these materials have been used in several working and operating conditions. In the present paper, it is intended to study the impact of temperature rise on the mechanical behavior and wear resistance of ultra-fine grained Al5083-5wt%B4C trimodal composite bulks. Results revealed that increasing the temperature to 200 °C, did not have any significant effect on the hardness and strength of the Al5083-5wt%B4C bulk. However, significant changes occurred in the hardness and wear resistance of the composite samples by adding Al5083 coarse grains. In this case, severe plastic deformation and surface damage occurred in the Al5083-5wt%B4C-50%CG sample and the wear rate reached 9.7 × 10–7(mm3/m–N).