High Temperature Mechanical Properties Research Articles

High temperature tensile properties and deformation behavior of CoCrFeNiW0.2 high entropy alloy

High entropy alloys (HEAs) have been a new-type of structural materials, which show good performance in various extreme conditions. In the present study, we systematically investigated the high temperature deformation behavior of as-cast CoCrFeNiW0.2 HEA under different temperatures from 298 to 1173 K and various strain rate of 1 × 10−4 s−1 to 5 × 10−3 s−1. An obvious temperature dependence of yield strength can be found with a remarkable decrease from 362 MPa at 298 K to 119 MPa at 1173 K. The normal Portevin–Le Chatelier (PLC) effect was presented in the intermediate temperature range of 673 K to 1073 K, the serrated flow transformed in the sequence of A → A + B → A + C → B + C → C with the increasing temperature, which is caused by dynamic strain aging (DSA). W atoms played an important role in the interaction between solute atoms and dislocations. Fractography analysis suggests the failure mode transition from transgranular fracture to intergranular fracture. Electron backscatter diffraction (EBSD) demonstrates that the high temperature deformation mechanism of the HEA is dominated by dynamic recovery (DRV). Additionally, transmission electron microscopy (TEM) was performed to observe the dislocation configurations and the interaction between dislocations and μ phase precipitates at various temperatures, and these results further identify the high temperature deformation mechanism. To summarize, this study indicates the proposed HEA has excellent high temperature mechanical properties and a wide range of potential applications in many fields.

Boron and Nitrogen Doping in Fused Silica Ceramics: Structural, High-Temperature Mechanical and Long-Term Ablation Resistance Properties of Si-B-O-N Ceramics

Boron and Nitrogen Doping in Fused Silica Ceramics: Structural, High-Temperature Mechanical and Long-Term Ablation Resistance Properties of Si-B-O-N Ceramics

High-temperature mechanical properties and microstructure of 2.5D C/C–SiC composites applied for the brake disc of high-speed train

This paper uses chemical vapor infiltration method to prepare 2.5D C/C-SiC composites, and conducts various tests to reveal its high-temperature mechanical properties and failure mechanism. The results show that the test temperature significantly affects the mechanical properties. As the test temperature increased from room temperature to 800 °C, the tensile strength of the 2.5D C/C-SiC composite dropped from 127.67 ± 20.87 MPa to 94.74 ± 28.15 MPa, and the performance dropped by 25.79 %. The compressive strength dropped from 326.92±17.37 MPa to 192.31 ± 29.15 MPa, resulting in a performance decrease of 41.18 %. The bending strength dropped from 355.74 ± 40.80 MPa to 235.88 ± 23.52 MPa, and the performance dropped by 33.69 %; the interlaminar shear strength dropped from 9.77 ± 2.79 MPa to 7.80 ± 3.26 MPa, and the performance dropped by 20.16 %. High-temperature oxidation will lead to interface degradation, destroy the composite matrix and carbon fiber structure, change the interface bonding strength, and ultimately lead to a decline in composite performance.

Effect of deep cryogenic treatment on improving the high-temperature impact resistance of Al–Zn–Mg–Cu alloy

The aging Al–Zn–Mg–Cu alloy exhibits a significant decrease in performance after undergoing thermal shock. In order to improve the resistance of this type of alloy to thermal shocks, the influence of deep cryogenic treatment (DCT) on the high temperature mechanical properties and microstructure of thermal shocked Al–Zn–Mg–Cu alloy is investigated in this paper. It was found that the mechanical properties of Al–Zn–Mg–Cu alloys decrease significantly with the increase of electric heating temperature. The deep cryogenic treatment reduced the grain size of Al–Zn–Mg–Cu alloy, increased the density of the precipitates, and also inhibited the coarsening of the precipitates. Therefore, the deep cryogenic treatment can slow down the weakening effect of Al–Zn–Mg–Cu alloy at high temperatures.

Effects of normalizing and tempering temperature on the bainite microstructure and properties of low alloy fire-resistant steel bars

Abstract Different combinations of normalizing and tempering were carried out to optimize the microstructure and enhance the high-temperature mechanical properties of HRB400FR fire-resistant steel bars. The results showed that with the increasing of the tempering temperature from 400 to 600°C, the steel bar’s hardness decreases linearly, mainly due to the formation of quasi-polygon ferrite and granular bainite. Besides, the reduced width and the dissolution of the lath bainite also undermine the performance of the tempered steel bars. The highest Vickers hardness of 380 HV is achieved when the steel is normalized at 950°C and then tempered at 400°C, mainly due to precipitation strengthening and bainite strengthening. The hardness of the test steel tempered at 600°C gives the lowest value, only 230 HV since the least amount of bainite is obtained. When the tempering temperature reaches 650°C, the hardness rises to 260 HV due to the formation of the lath bainite. The emergence of needle bainite generally reduces the matrix grain size, and the appearance of lath martensite refines the precipitated carbides.

Effect of Nd on Microstructure and High-Temperature Mechanical Properties of As-cast Mg–Y–Nd–Zn–Zr Alloy

Effect of Nd on Microstructure and High-Temperature Mechanical Properties of As-cast Mg–Y–Nd–Zn–Zr Alloy

Simultaneous enhancement of elevated temperature strength and ductility in additive-manufactured nickel-based superalloy via doping Y2O3 nanoparticles

In this work, we coated a layer of Y2O3 particles in Hastelloy X (HX) nickel-based superalloy powder by in situ chemical method and combined with laser powder bed fusion (LPBF) technology to develop a high-performance Y2O3-doping alloy, designated as Y-HX. The results show that the doping of Y2O3 particles prevents crack formation during the printing process and reduces solute segregation at cell and grain boundaries by increasing the viscosity of the molten pool. The doping of Y2O3 particles to the printed Y-HX alloy enhances grain boundary characteristics, transforming coarse sheet-like carbides into finely dispersed granular carbides at the boundaries during subsequent heat treatment. Additionally, doping with Y2O3 particles increases the recrystallization activation energy of the Y-HX alloy from 149.4 to 278.8 kJ mol–1. At 750 °C, the Y-HX alloy exhibits an ultimate tensile strength of 619 ± 2 MPa and an elongation of 52 % ± 2 %, along with an ultimate tensile strength of 325 ± 3 MPa and an elongation of 47 % ± 2 % at 900 °C. Our work provides a promising way to develop additive-manufactured superalloys with exceptional thermal stability and remarkable high-temperature mechanical properties.

Enabling multi-stage high-temperature strength evolution prediction of ceramizable composites using a novel multi-field coupled model

Strength varies significantly under high-temperature environment, due to the inherent thermomechanical behavior of the ceramizable material and its coupling with possible chemical reactions. The complexity amplifies for composite materials, considering their multi-phase and multi-scale features, and more importantly, their complicated chemical reactions under high-temperature service conditions. This study proposes an innovative multi-field coupling theory framework for predicting the multi-stage evolution behavior of high-temperature mechanical properties of a ceramizable composite, through incorporating an extended chemical kinetics method, coupled deformation, mass diffusion and heat conduction. The developed model enables direct coupling and simultaneous solving of physical, chemical and thermal variables. It captures well the degradation of mechanical properties for the initial stage and the increase of strength for the later stage, along with the increasing of temperature. The validated model also enables well prediction of time-dependent mechanical properties at high service temperature, with an average error of 8.67% against experimental measured results. The developed method can serve as a general method for the prediction of high-temperature mechanical property of thermal protection composites and structures.

High-temperature dynamic failure behavior and compressive mechanical properties of alumina porous ceramic with various pore sizes

The dynamic compressive mechanical properties of alumina porous ceramic with various average pore sizes are tested at strain rates and temperatures ranging from 0.01 s−1 to 2900 s−1 and 20 °C to 850 °C, respectively. The corresponding 3d Voronoi models are employed to simulate the meso‑characteristics of cells and failure characteristics of alumina porous ceramic in multiscale. The failure in macroscale of quasi-static compression is fragmentation, and that of dynamic compression is comminution. But in mesoscale, the failure, both of quasi-static and dynamic compression, is the fracture of cell walls. Its dynamic strength increases with the increase of strain rate, but decreases with the increase of temperature and average pore size. The increase in temperature and average pore size leads to a decrease in its strain rate sensitivity. Its Young's modulus is not sensitive to the strain rate, but increases with the decrease of average pore size, and decrease with the increase of temperature, which is presented as a temperature and average pore size dependent function. The strain rate and temperature effects are also presented by average pore size dependent functions, respectively. A constitutive model is proposed based on them. It shows that the constitutive model fits well with the experimental results.

High-temperature tribological properties of (TiZrNbMoTa)N and (TiZrNbMoTa)CN ceramic coatings

As dry-cutting tool coatings, high-entropy ceramics (HECs) exhibit excellent hardness, toughness, and wear resistance properties. However, the hardening mechanism of HEC coatings and their mechanical and frictional properties under high-temperature conditions have not been studied. In this study, we successfully prepared (TiZrNbMoTa)N high-entropy nitride (HEN) and (TiZrNbMoTa)CN high-entropy carbon nitride (HECN) coatings using reactive magnetron sputtering technology. The strengthening mechanism and thermodynamic properties of HEN and HECN coatings were systematically studied using the Debye-Grüneisen quasi-harmonic approximation model combined with density functional theory (DFT) calculations. At room temperature (RT, 25 °C) and high temperature (HT, 500 °C), the microhardness of HECN is 62 % and 56 % higher than that of HEN, respectively. Especially at RT, the microhardness of HECN reaches 46.37 GPa. Through in-situ XRD, in-situ nanoindentation, and high-temperature friction and wear analysis, we conducted in-depth research on the phase stability, high-temperature mechanical properties, and high-temperature tribological properties of HECs coatings in high-temperature. XRD test results show that HEN and HECN coatings exhibit a single-phase FCC structure and maintain good stability under HT. DFT calculation results show that the M − C bond in HECN is stronger than the M − N bond in HEN, which is why the HECN coating is harder. At HT, the wear rate of HECN coating is only reduced by 10 % compared with HEN coating. Different from RT, under high-temperature conditions, the primary wear mechanism of the coating is oxidative wear. The coating's red hardness and friction coefficient (COF) have a limited impact on the coating's high-temperature anti-wear performance. This research provides a theory and technical basis for designing and preparing protective coatings with high hardness and low friction coefficient.

Component regulation and high-entropy engineering for enhanced antioxidant and high-temperature mechanical properties of protective films

Transition metal nitrides (TMNs) have gained widespread application in protecting structural components due to their high strength and hardness. However, TMNs still have the challenge of structural instability and mechanical deterioration caused by oxidation under harsh high temperature conditions. Herein, we present a strategy combining component regulation with high-entropy engineering to develop an advanced high-temperature Al-containing high-entropy nitrides (HENs) material. To prevent the phase decomposition of AlN within the (NbMoTaWAl)N, theoretical simulations were employed to determine a critical atomic percent of 25.0% Al for maintaining the stability of the high-entropy structure. Ensuing experimental synthesis creates three NbMoTaWAlN films with varying Al content: a high-entropy film with 0.0% Al (HEN), a high-entropy film with 21.2% Al (HEN-Al), and an amorphous transition metal nitride film with 30.2% Al (a-TMN-Al), validating key high-entropy engineering benchmarks. It is found that the unique HEN-Al film exhibits excellent oxidation resistance and high-temperature hardness, attributed to the uniform distribution of Al atoms in the robust high-entropy structure, which creates conditions for forming a dense and continuous Al2O3 barrier layer, effectively hindering the diffusion of oxygen into the film interior. This study provides new insights to develop a new generation of high-temperature protective materials.

Anodic Dissolution Characteristics of GH4169 Alloy in NaNO3 Solutions by Roll-Print Mask Electrochemical Machining Using the Linear Cathode.

GH4169 alloy/Inconel 718 is extensively utilized in aerospace manufacturing due to its excellent high temperature mechanical properties. Micro-structuring on the workpiece surface can enhance its properties further. Through-mask electrochemical micromachining (TMEMM) is a promising and potential processing method for nickel-based superalloys. It can effectively solve the problem that traditional processing methods are difficult to achieve large-scale, high-precision and efficiency processing of surface micro-structure. This study explores the feasibility of electrochemical machining (ECM) for GH4169 using roll-print mask electrochemical machining with a linear cathode. Electrochemical dissolution characteristics of GH4169 alloy were analyzed in various electrolyte solutions and concentrations. Key parameters including cathode sizes, applied voltage and corrosion time were studied in the roll-print mask electrochemical machining. A qualitative model for micro-pit formation on GH4169 was established. Optimal parameters were determined through experiments: 300 μm mask hole and cathode size, 10 wt% NaNO3 electrolyte, 12 V voltage, 6 s corrosion time. The results demonstrate that the micro-pits with a diameter of 402.3 μm, depth of 92.8 μm and etch factor (EF) of 1.81 show an excellent profile and localization.

Effect of strain rate and temperature on dynamic compressive behavior of HfBeTiZrCuNi high entropy bulk metallic glass

This study investigated the high-temperature dynamic mechanical properties of Hf-based high entropy bulk metallic glass (HE-BMG). Uniaxial dynamic compressive tests of Hf-based HE-BMG were conducted at elevated temperatures (from 298 to 800 K) under a high strain rate (from 1000 to 5000 s−1) by a split Hopkinson pressure bar (SHPB) device with a high-temperature system, and the failed specimens were analyzed in terms of microstructures and fracture modes. The dynamic test results show that the maximum compressive stress and the total strain decrease with increasing strain rate and temperature, exhibiting significant strain rate and temperature sensitivity. Three different fracture modes were observed with increasing strain rates, while heating the temperature could promote the transition process of the fracture modes. When the adiabatic or heating temperature reaches above the crystallization temperature, the embrittlement caused by metallic glass crystallization makes the fracture mode change. The mechanical behavior of Hf-based HE-BMG at high temperatures and high strain rates could be attributed to the combination of adiabatic heating and embrittlement.

Selective laser melting of a novel Al-Si-Fe-Mn-Ni alloy with superior mechanical properties at both room and elevated temperatures: Influence of processing parameters and heat treatment

In this study, a novel heat-resistant Al-Si-Fe-Mn-Ni alloy suitable for selective laser melting technique was developed. By optimizing the process parameters, as-built alloy with few defects and superior mechanical properties was manufactured at a laser power of 350 W and a scanning speed of 1300 mm/s, with horizontal and vertical ultimate tensile strengths of 589 and 529 MPa, respectively. Conventional annealing, solid solution and T6 treatments were conducted to investigate the effect of post heat treatments on the microstructure and mechanical properties. Owing to the low diffusion capacity of Fe, Mn and Ni elements, the alloys show excellent high-temperature stability. The initial eutectic structure is retained after annealing, with few changes in the morphology of the precipitated phases. During solution treatment, the AlSi eutectic breaks up to form diffusely distributed Si particles, and Fe, Mn-rich intermetallic compounds as well as AlFeNi phases gradually precipitate out, which further occurs in T6 state. Due to its high-temperature resistance, the alloy developed in this study exhibits better high-temperature mechanical properties than conventional commercial AlSi10Mg alloys, showing higher strength in high-temperature tensile experiments from 150 °C to 300 °C.

Regulating the concentration of silica sol to prepare high thermal insulation ceramic nanofiber aerogel composites

Abstract Ceramic aerogels can maintain excellent thermal insulation performance under extreme conditions due to their outstanding pore structure and specific surface area. However, the current application of ceramic aerogels is limited by their brittleness, easy collapse of the structure under external forces, and insufficient mechanical properties. In this study, ceramic nanofiber aerogels prepared by PEO as a polymer were used as building blocks, and silica sol was selected as a high-temperature binder. Through the sol impregnation-atmospheric pressure drying method and calcination treatment, we obtained ceramic nanofiber composites with excellent performance. It is found that when the impregnation concentration is 0.4wt%, the thermal conductivity at room temperature is as low as 27 m W·m-1·K-1, the cold surface temperature at 800°C is as low as 255°C, the tensile strength at 20% tensile strain is as high as 400 kPa, and the compressive strength at 80% compressive strain is as high as 32 kPa. Compared with the traditional ceramic fiber aerogel material, the material exhibits excellent high-temperature insulation performance and mechanical properties, which greatly broadens the application scene of ceramic aerogel.

Towards post-curing parameters optimization of phthalonitrile composites through the synergy of experiment and machine learning

Phthalonitrile composites are highly anticipated in fields such as aerospace, marine, and electronics due to their exceptional heat resistance, excellent high-temperature mechanical properties, and outstanding processability. The conversion of nitrile functional groups to macrocyclic structures during post-curing is essential for performance enhancement. However, the influence of post-curing conditions on the mechanical properties of phthalonitrile composites is complicated, and the underlying mechanism remains unclear. In this study, an experimental and machine learning synergic strategy was employed to optimize the post-curing parameters of the phthalonitrile composites, including temperature, time, and pressure. Through mechanical experiments conducted at both room temperature and 400 °C, scanning electron microscope, and dynamic mechanical analysis, the underlying mechanism of the influence of post-curing parameters on the composite mechanical properties was revealed. The enhancement of the polymerization degree brought about by post-curing is the decisive factor for high-temperature performance, while the room-temperature properties are a tradeoff between the polymerization degree improvement and the defect proliferation. The genetic algorithm-optimized backpropagation (GA-BP) neural network was trained for the efficient and accurate prediction of the optimal post-curing parameters. The tendency of mechanical properties with the post-curing parameters predicted by machine learning is consistent with the mechanism revealed by experiments.

A novel high-Cr CoNi-based superalloy with superior high-temperature microstructural stability, oxidation resistance and mechanical properties

A novel high-Cr CoNi-based superalloy with superior high-temperature microstructural stability, oxidation resistance and mechanical properties

Microstructure, high temperature mechanical properties and sliding wear behavior of (NiCrW)1-x(Al2O3)x

(NiCrW)1-x(Al2O3)x composites with different nano-Al2O3 ratios (x = 0, 1, 2.5, 5 wt %) were prepared using powder metallurgy techniques. The influence of the Al2O3 content on the microstructure, phase composition, high-temperature mechanical properties, and wide-temperature-range friction and wear performance of the composites was investigated. The corresponding high-temperature strengthening and wear-resistance mechanisms were also investigated. The results indicated that as the alumina content increased, the tensile and compressive strengths of the composites decreased at room temperature (RT). However, at high temperatures (800 °C), the opposite trend was observed. Notably, the composite with 5 wt % Al2O3 exhibits the highest tensile strength (189.20 MPa) and compressive strength (446.61 MPa) at 800 °C. The addition of alumina had a relatively minor impact on the friction coefficient of the composites but significantly affected the wear rate. Specifically, the composite with 5 wt % Al2O3 demonstrates optimal friction and wear performance at high temperatures. This enhancement was primarily attributed to the reinforcement of the mechanical properties of the matrix material owing to the addition of alumina. Additionally, the formation of a friction glaze layer rich in Cr2O3 and NiO oxides on the worn surface contributed to improved wear resistance. This study is important for understanding the performance and applications of metallic materials.

Insights into hardening and strengthening in ultrafine Ti(C, N)-based cermets

Ultrafine Ti(C, N)-based cermets are vacuum-sintered by refining the particle size of raw materials and tailoring the WC/TaC ratio to achieve the improvements in comprehensive mechanical properties and cutting performance. The hardness, flexural strength and tool lifespan of ultrafine Ti(C, N)-based cermets are substantially higher than those of submicron Ti(C, N)-based cermets with the same composition because of the refined grains and the improved distributions of both metal phases and residual stress. The hardness attenuation behavior and strengthening mechanism in Ti(C, N)-based cermets at different test temperatures have been proposed. At 400 ℃, the hardness attenuation of Ti(C, N)-based cermets depends mainly upon the softening of metal phases. However, at 800 ℃, the hardness attenuation of Ti(C, N)-based cermets is mainly related to the reduced bearing capacity of hard ceramic phases and interfacial sliding. The addition of refractory TaC is beneficial for the improvement of high-temperature mechanical properties and the tool lifespan, attributed to the strengthening of the ceramic framework by tantalum atoms.

Study of high temperature mechanical properties and damage behavior of Ni-YSZ anode/SrO–MgO–SiO2 glass-ceramic sealant/430 s.s. interconnect system in solid oxide fuel cells (SOFC)

In the sealing system of Ni-YSZ anode/SrO–MgO–SiO2 glass-ceramic sealant/430 s s. interconnect, the phase transformation and mechanical properties of interfaces are studied after operating 0 h, 100 h, and 1800 h at 750 °C. The results show that the interface fracture appears in the glass/anode and glass/interconnect interfaces after operating at 1800 h. The interface mechanical parameters within different operation times are collected to investigate the effects of crystallization, penetration, and high temperature mechanical properties on the interlayer stress and structure damage. The Sr2MgSi2O7 crystal phase increases the glass modulus from 104.5 GPa to 129.8 GPa with a runtime from 0 h to 1800 h. The modulus of the Ni-YSZ interface also increases from 82.4 GPa to 128.3 GPa with the glass penetration process. The 430 s s. modulus is reduced by 13 % at 750 °C after 1800 h to reach 191.1 GPa. The established anode/glass/interconnect interlayer stress model accurately calculates the compressive stress at the glass/anode side interface and glass/interconnect side interface, with values reaching −755.2 MPa and −587.1 MPa, respectively. The crystallization zone of the SrO–MgO–SiO2 glass-side interface near Ni-YSZ and 430 s s. become the stress damage sensitive zones and break under interlayer stress.