High-temperature Behavior Research Articles

Effect of the elevated temperature on the wear behavior of Laser Metal Deposition IN718 repairs

IN718, a nickel-based superalloy popular in aerospace, has good high-temperature mechanics/corrosion resistance. Laser Metal Deposition (LMD) repairs using IN718 are extensively explored, yet few studies delve into their tribological aspects. This research examines post-treated IN718 coatings, mimicking rapid repairs, investigating their high-temperature tribological behavior. Samples underwent tribological tests at diverse loads and temperatures. Results show the scanning strategy does not impact the wear behavior. At elevated temperatures, a glaze layer forms in the contact zone, impacting lubrication and surface protection based on its uniformity. Despite its advantageous lubricating ability, at 400°C and 50 N force, the oxidized debris layer lacks mechanical stability. IN718 LMD repairs manifest enhanced high-temperature wear resistance compared to ambient conditions, attributed to the glaze layer.

High temperature and short-term oxidation behavior of a TiBw/TA15 network composite in an air environment at 950 °C

The oxidation behavior of materials used in aerospace is crucial for their service life, and short-term oxidation behavior is an essential means to reveal the oxidation mechanism. The high temperature and short-term oxidation behavior of the TiBw/TA15 network composite in an air environment at 950 °C for 5 min, 15 min, 30 min, and 60 min was investigated. The experimental result indicates that the composite shows a slight mass change over the whole test times. The all-oxide scale mainly contains two-layer. From the top to the bottom of the oxide scale, an Al2O3 layer and a TiO2 layer existed, which increased with the oxidation time. The oxidation mechanism of the initial oxidation behavior of the network composite has been established, which is crucial for promoting its application in high-temperature service environments.

Experimental nuclear quadrupole resonance and computational study of the structurally refined topological semimetal TaSb2

The local electric field gradients and magnetic dynamics of TaSb2 have been studied using Sb121, Sb123, and Ta181 nuclear quadrupole resonance (NQR) with density functional theory (DFT) calculations using XRD-determined crystal structures. By measuring all structurally expected 13 NQR lines, the nuclear quadrupole coupling constant (νQ) and asymmetric parameter (η) for Ta, Sb(1), and Sb(2) sites were obtained. These values are all in good agreement with the presented DFT calculations. Principal axes of the electric field gradients was determined for a single-crystal sample by measuring the angular dependencies of NMR frequency under a weak magnetic field. The unusual temperature dependence of η(T) of Sb(2) hints at the suppressed thermal expansion along the a axis. Spin-lattice relaxation rate (1/T1T) measurements reveal an activated-type behavior and an upturn below 30 K. Neither the low-temperature upturn nor the high-temperature activation-type behaviors are reproduced by the calculated 1/T1T based on the calculated density of states (DOS). On the other hand, the agreement between the calculated DOS and specific heat measurements indicates that the band renormalization is small. This fact indicates that TaSb2 deviates from the simple semimetal scenario, and magnetic excitations are not captured by Fermi liquid theory. Published by the American Physical Society 2024

High temperature decomposition and age hardening of single-phase wurtzite Ti1−xAlxN thin films grown by cathodic arc deposition

Wurtzite TmAlN (Tm=transition metal) themselves are of interest as semiconductors with tunable band gap, insulating motifs to superconductors, and piezoelectric crystals. Characterization of wurtzite TmAlN is challenging because of the difficulty to synthesize them as single-phase solid solution and such thermodynamic, elastic properties, and high temperature behavior of wurtzite Ti1−xAlxN is unknown. Here, we investigated the high temperature decomposition behavior of wurtzite Ti1−xAlxN films using experimental methods combined with first-principles calculations. We have developed a method to grow single-phase metastable wurtzite Ti1−xAlxN (x=0.65, 0.75, 085, and 0.95) solid-solution films by cathodic arc deposition using low duty-cycle pulsed substrate-bias voltage. We report the full elasticity tensor for wurtzite Ti1−xAlxN as a function of Al content and predict a phase diagram including a miscibility gap and spinodals for both cubic and wurtzite Ti1−xAlxN. Complementary high-resolution scanning transmission electron microscopy and chemical mapping demonstrate decomposition of the films after high temperature annealing (950∘C), which resulted in nanoscale chemical compositional modulations containing Ti-rich and Al-rich regions with coherent or semicoherent interfaces. This spinodal decomposition of the wurtzite film causes age hardening of 1–2 GPa. Published by the American Physical Society 2024

Correction: High-Temperature Oxidation and Hot Corrosion Behaviors and Mechanism of One Typical Aero-Engine Material 0Cr18Ni9 by One Novel Superhydrophobic and Oleophobic Ultrafine Dry Powder Extinguishing Agent

Correction: High-Temperature Oxidation and Hot Corrosion Behaviors and Mechanism of One Typical Aero-Engine Material 0Cr18Ni9 by One Novel Superhydrophobic and Oleophobic Ultrafine Dry Powder Extinguishing Agent

Creep in a nanocrystalline VNbMoTaW refractory high-entropy alloy

Refractory high-entropy alloys (RHEAs) are considered to be a promising candidate for elevated temperature applications. Nanocrystalline (NC) RHEAs are supposed to exhibit many different high-temperature mechanical behaviors in comparison with their coarse-grained (CG) and ultrafine-grained (UFG) counterparts. However, the creep behaviors of NC RHEAs, which must be well evaluated for high-temperature applications, are largely unknown because it is difficult to produce bulk quantities of NC RHEAs for creep tests. In the present work, an equiatomic bulk NC VNbMoTaW RHEA with an average grain size of 67 ± 17 nm was synthesized by mechanical alloying (MA) and the subsequent high-pressure/high-temperature sintering. The creep tests were performed on bulk specimens by compression at high temperatures (973 and 1073 K) under different stresses (70–1100 MPa). The creep resistance of the bulk NC VNbMoTaW is slightly lower than that of the bulk CG VNbMoTaW, but much higher than that of previously reported CG and UFG HEAs. The derived activation volume, stress exponent, and activation energy of bulk NC VNbMoTaW indicate that the creep deformation is dominated by grain boundary diffusion. The creep deformation is controlled by the diffusion of Mo and Nb elements, which have the two slowest grain boundary diffusivities among the five alloying elements. The present work provides a fundamental understanding of the creep behavior and deformation mechanism of NC RHEAs, which should help design advanced creep-resistant RHEAs.

Influence of Ru on high-temperature creep rupture properties and oxidation behavior of Ni-based single-crystal superalloys

The present study investigates the microstructure, high-temperature creep rupture properties and oxidation resistance of three fourth-generation single-crystal Ni-based superalloys containing 0, 3.5 and 7 wt% of Ru. The addition of Ru changes the partitioning behavior of the alloying elements, decreases γ' size and increases the γ/γ' lattice misfit. The creep resistance keeps increasing as Ru content rises up 7 wt% under 1100 °C/140 MPa. However, it was discovered that 7 wt% Ru alloy has inferior creep resistance compared with the 3.5 wt% Ru one under 1150 °C/140 MPa, although no TCP precipitation was observed in this 7 wt% Ru-containing alloy. It was revealed that 7 wt% Ru-addition caused significant γ' dissolution and induced the generation of creep cavities, which may account for the anomaly. Furthermore, the increase in Ru content up to 7 wt% keeps degrading the oxidation resistance of the superalloys by facilitating the formation of pores and cracks within the oxide scales, which also accelerate scale spallation. This work suggests that excess Ru addition may adversely affect both the mechanical properties and the oxidation resistance of the fourth-generation Ni-based superalloys.

Initial Vacancy-Dependent High-Temperature Creep Behavior of Nanocrystalline Ni by Molecular Dynamics Simulation

Nanocrystalline metals possessing excellent mechanical strength have great potential to replace traditional metal materials as structural materials, but their poor resistance to creep deformation seriously restricts their engineering applications at high temperatures. The high-temperature creep behavior of nanocrystalline Ni with different volume fractions of initial vacancies ranging from 0% to 10% was studied systematically by molecular dynamics simulation in this study. The results showed that the steady-state creep displacement first increased and then decreased with increasing initial vacancy concentration, reaching the maximum when the initial vacancy concentration was 6%. The microstructural characteristics, such as quantity increment and distribution of the vacancies, the number and types of dislocations, and shear strain distribution during creeping, were analyzed in detail. The deformation-induced vacancies formed at the grain boundary (GB) in the initial creep stage, and their variation trend with the initial vacancy concentration was consistent with that of the creep displacement, indicating that the initial vacancy-dependent high-temperature creep behavior of nanocrystalline Ni was mainly determined by the rapidly increasing number of vacancies at the GB in the initial creep stage. Afterwards, the deformation-induced, vacancy-assisted 1/6{112} Shockley partial dislocation activities dominated the creep deformation of nanocrystalline Ni in the steady-state creep stage. The results can provide theoretical support for expanding the application of nanocrystalline metals from the perspective of crystal defect engineering.

Microstructure-Property Relationship and Embrittlement Mechanism of HR3C Steel with High-Temperature Service of 65000 h

HR3C steel, an austenitic helat-resistant steels, due to its good strength, high temperature behaviour and cost effectiveness, which lead to the extensive use in ultra-supercritical boilers. In order to study the microstructure characteristics and embrittlement mechanism of superheater tube of 660 MW thermal power boiler, the microstructure and chemical composition as well as the mechanical performance of HR3C steel pipe after service were tested. The results showed that HR3C steel, after approximately 65,000 hours of service, exhibited a continuous sheet-like distribution of M23C6 phasealong the grain boundaries, accompanied by needle-like or strip-like M23C6 phase growing into the grain boundaries, as well as the presence of Z phase (NbCrN) and σ-equivalent precipitation phase along the periphery of the grain boundaries. Following service, the hardness of HR3C steel experienced a slight increase, the tensile strength remained relatively unchanged, and the yield strength exhibited an increase of approximately 15%. However, the elongation after fracture significantly decreased, resulting in a decrease in plasticity decreased by 64% to 73% compared to its original state. HR3C steel displayed notable embrittlement after 65,000 hours of service at 650 °C, with a 96% reduction in impact toughness. The precipitation of M23C6 and σ phase were identified as the primary causes of embrittlement in HR3C steel.

High-temperature deformation behaviour and processing map of near eutectic Al–Co–Cr–Fe–Ni alloy

The high-temperature deformation behaviour of near-eutectic high entropy alloy was studied at 800–1100 °C and 0.01–10 s−1. The microstructure of the as-cast alloy depicted a proeutectic L12 phase and epitaxially grown eutectic colonies of lamellar L12 and B2. Deformation temperature and strain rate played vital roles in defining the precipitation and deformation behaviour of the alloy. The lower-temperature deformed samples were characterized by extensive deformation twinning and strain accumulation. In contrast, high-temperature deformation led to uniform deformation with dynamic recrystallization, recovery, B2 lamellar fragmentation and B2 precipitation. The microstructure of the deformed samples corresponded well with the processing maps developed via dynamic materials model. The processing zones for the alloy were identified to be 800–950 °C and 10−2 – 10−1.25 s−1 as well as 925–1100 °C and 10−2 – 10−0.5 s−1. The critical material flow parameters displayed a complex relationship with temperature, strain rate and strain. In the studied temperature and strain rate regime, the critical strain rate was determined to be 0.1s−1. At strain rates above and below this value, the critical strain for recrystallization was higher. Within the studied temperature and strain rate regime, the near eutectic alloy displayed superior compressive strength and wider thermos-mechanical processing region than its eutectic counterpart.

Microstructure and high-temperature oxidation behavior of Al2O3/Cr composite coating on Inconel 718 alloy

In this paper, Al2O3/Cr composite coatings were prepared on the surface of Inconel 718 alloy by cathodic liquid plasma electrolytic deposition (CLPED) and double-glow plasma surface alloying (DGPSA) processes. The microstructure and high-temperature oxidation behavior of Al2O3/Cr composite coating were investigated. The results showed that the Al2O3 interlayer surface was fully covered with Cr coating. The interface between the Al2O3 layer and the Cr metal layer presents a mechanical interlock effect, which can absorb the deformation caused by thermal expansion, thereby reducing the adverse effects of thermal stress. The surface roughness of the Al2O3 coatings decreased after depositing Cr coating. The oxidation weight gain of the Al2O3/Cr composite coatings were significantly lower than that of the substrate, indicating that the Al2O3/Cr composite coatings improved the high-temperature oxidation resistance of Inconel 718 alloy. The oxidation weight gain of the Al2O3/Cr composite coatings at different frequencies were similar, while the Al2O3/Cr composite coating at 400 Hz was lowest. During the high-temperature oxidation process, the Al2O3 interlayer can effectively inhibit the external diffusion of Ni, Fe and other elements in the matrix, which helps to prevent the cracking of the outer oxide film, thereby reducing the oxidation rate.

High-temperature oxidation behaviors and mechanical properties of TiAlCrMnHEAs during heat treatment

A series of TiAlCrMn high entropy alloys (HEAs) with variable atomic ratios of Al, Cr, and Mn were prepared using vacuum melting. High-temperature oxidation behaviors and mechanical properties were investigated before and after heat treatment. The oxidation mass gain rate is declined dramatically with increasing Al, Cr, and Mn element contents. Enhanced oxidation resistance is attributed to a continuously dense (Al,Cr)-rich oxidation layer, which can hinder the inter-diffusion of O and alloying elements. Furthermore, microhardness increases monotonously with increasing Al, Cr, and Mn element contents of the alloys before and after heat treatment. Grain coarsening can result in lower microhardness, but precipitation strengthening contributes to higher hardness of the alloys with high alloying element contents. Meanwhile, deformation-induced strengthening also contributes to higher compressive strength. The value after heat treatment at 500 °C is lower than that of as-cast samples while an increased value occurs after heat treatment at 900 °C accompanied by sacrificing the malleability.

An Investigation into Microstructure Evolution and High-temperature Deformation Behavior during the Instability of In-service Welding

It is of great significance to reveal deformation behavior coupling with both the high-temperature effect and microstructure for the in-service welding instability zone. In the present paper, microstructure evolution and high-temperature deformation behavior at the representative temperatures 900 °C and 1100 °C inside the in-service welding instability zone were investigated based on the in-situ high-temperature laser scanning confocal microscope (LSCM). The results indicated that a sufficient condition of carbide precipitation is to hold it at 900 °C for a certain time. However, the phenomenon of carbide precipitation failed to be presented during continuous heating to 1150 °C. Although the slip and twining deformation occurred inside austenite grain, the fracture mechanism gave priority to intergranular cracking, which could be ascribed to the carbides with higher hardness and the grain boundary weakening caused by the temperature effect.

Crystal structure, microhardness and thermal expansion of ternary TaIr2B2 boride

The ternary TaIr2B2 boride was prepared by the reaction between iridium and TaB2 powders. It was shown that a choice in favor of any crystal structure of TaIr2B2 boride using only X-ray powder diffraction analysis and single-crystal XRD is rather difficult to make. The DFT calculations were carried out to predict the energetically preferred crystal structure of TaIr2B2. The 11B solid-state NMR spectrum of TaIr2B2 was recorded for the first time. A combination of diffraction and spectroscopic methods, as well as theoretical calculations, allowed us to make clear choice in favor of the triclinic space group P-1 for the crystal structure of TaIr2B2. The Vickers microhardness value for TaIr2B2 was found to be 17.9 ± 2.3 GPa, and the ternary TaIr2B2 boride can be considered a hard material. Therefore, the family of hard ternary boride phases got a new member. The coefficients of thermal expansion of TaIr2B2 measured by in situ high-temperature XRD analysis are independent of temperature along the a and b axes, but the CTE along the c axis deviates noticeably at elevated temperatures. The findings for the new ternary TaIr2B2 boride are of interest for the rational design of complex structural materials containing Ta–Ir–B-based components and prediction of their high-temperature behavior. Further research into this ternary boride as well as other iridium-containing ternary borides will provide a tool to solve the problems faced by high-temperature materials science.

Hot processing map and high temperature deformation behaviour of TB17 Ti alloy

The thermal compression experiments of TB17 titanium alloy under different thermal deformation process parameters were carried out using a thermal simulation compressor. The high-temperature plastic flow behaviour of the alloy was studied. It was found that with the decrease of the deforming temperature and the increase of the strain rate, the flow stress increased, and the discontinuous yield phenomenon occurred in hot deformation. The larger the strain rate, the more obvious the discontinuous yield phenomenon. The thermal activation energy Q decreased with the increase of strain, and the average value of activation energy Q is 209.54 KJ / mol. The constitutive equation of high-temperature plastic flow of TB17 titanium alloy was established. The predicted values of this equation are in good agreement with the experimental values. The average error is 3.987 %, and the correlation coefficient is 0.9972, which has high accuracy. Based on the Prasad criterion, the hot processing map of TB17 titanium alloy was constructed. It was found that the flow instability zone was mainly concentrated in the high strain rate region. The flow instability zone was determined to be 795 °C ~ 895 °C, 0.046s-1 ~ 1s-1, and the stable deformation zone was mainly located in the region with high temperature and low strain rate. The optimum processing parameter range is 860 °C ~ 895 °C, 0.001 s-1 ~ 0.025 s-1.

High-temperature Oxidation Behavior of In-situ Reaction/Hot Pressing Synthesized Ti 2 AlC-20TiB2 at 1000~1300 ℃ in air

High-temperature Oxidation Behavior of In-situ Reaction/Hot Pressing Synthesized Ti 2 AlC-20TiB2 at 1000~1300 ℃ in air

High-Temperature Oxidation Behaviour of High Entropy Alloys

High-temperature operation, such as in gas turbine engines, is typically limited by the ability of materials to withstand extreme operating conditions. The need for a combination of high-temperature strength and oxidation resistance, as well as microstructural stability, has led to the continued use of nickel-based superalloys as materials for turbine blades, the most critical component in aero gas turbine engines. Due to their limited melting points, materials beyond superalloys are needed to meet increasing fuel efficiency requirements. High entropy alloys have recently been considered as candidates for materials to replace nickel-based superalloys. This paper discusses the microstructures and high-temperature oxidation behavior of Al0.75CoCrCuFeNi high entropy alloy at 900, 1000, and 1100°C. It was found that the oxidation rate constants for Al0.75CoCrCuFeNi oxidized at 900, 1000, and 1100°C are 3.84 x 10-10, 5.99 x 10-10, and 8.97 x 10-10 (mg/cm2.s), respectively, with an activation energy for oxidation of 66.58 kJ/mol.

Effects of size, geometry, and testing temperature on additively manufactured Ti-6Al-4V titanium alloy

This article presents a comprehensive study concerning size and geometry effect on the ambient and high-temperature mechanical behavior of additively manufactured laser powder bed fusion Ti-6Al-4V alloy. Key mechanical property metrics are presented, including strain hardening rate, yield strength, and Young’s modulus as a function of thickness and testing temperature (ambient, 250 °C, and 450 °C). The effect of specimen size on manufacturing-induced microstructural feature formation is demonstrated and discussed. A detailed analysis regarding Young’s modulus, yield strength, and strain hardening rate variation at elevated temperatures is also presented. Size effect and temperature-sensitive deformation mechanisms are linked to the underlying microstructural deformation mechanisms activated at respective temperatures. Counter-intuitively, this study determined that irrespective of the geometry, strain hardening rates increased as temperature increased. An in-depth microstructural examination is presented to explain the stated observation. The texture of Interrupted tensile test samples examined for ambient, 250 °C, and 450 °C post-yield was observed to be unchanged, indicating the strain hardening behavior was not texture dependent. Schmid factor analysis, coupled with experimental findings from previous work, was implemented to generate a hypothesis. This hypothesis suggests that the drop in critical resolved shear stress for basal and pyramidal slip systems, as temperature increases, paired with the high dislocation density of laser powder bed fusion Ti-6Al-4V, leads to dislocation entanglement and results in increased strain hardening at elevated temperatures.

Experimental investigation of mechanical and tribological properties of AA7065- B4C nano-composite

The present study used the stir casting technique to create hybrid composites employing aluminium AA 7065 alloy for the matrix and boron carbide reinforcements. In order to study the high-temperature tribological behaviour of aluminium boron carbide composites, the pin-on-disc method with pin heating setup was adopted. As a supplemental reinforcing material, fly ash particles were used due to their exceptional mechanical, metallurgical, and tribological properties. Microhardness testing, microstructure analysis, and tensile testing were all carried out. The wear rate of hybrid composites was studied on load, sliding velocity, and temperature. Mechanical properties and particle distribution were vastly improved during the testing phase. Although the ductility of hybrid composites was down, their tensile and compression strengths increased dramatically. The surface morphology of the pin was analyzed using a high-resolution scanning electron microscope. The impact of wear parameters on wear rate was analyzed using analysis of variance.

Exploring the interplay between thermo-oxidative degradation and asphalt aging in thermoplastic polyurethane-modified asphalt: Mechanisms, properties, and performance evolution

The aging behavior of thermoplastic polyurethane-modified asphalt (TPUMA) is intricate and the mechanisms of its thermal degradation are not well understood. This study examines the viscoelastic, chemical and morphological characteristics of thermoplastic polyurethane modified asphalt (TPUMA) under different aging conditions (RTFOT/PAV). The rheological master curve model of the S parameter was used to analyze the fitting effect on TPUMA, with SBS (styrene–butadiene–styrene) modified asphalt serving as the control group. The relationship between the phase angle plateau area and polymer aging degradation was elucidated. This study investigates the impact of polymer degradation on the high-temperature rheological behavior and medium-temperature fatigue properties of asphalt through temperature sweep, multiple stress creep recovery (MSCR), and linear amplitude sweep (LAS) tests. Fourier transform infrared spectrometer (FTIR) and confocal laser scanning microscopy (CLSM) are used to qualitatively and quantitatively analyze the chemical composition and morphological evolution of TPUMA during thermal-oxidative degradation. The findings suggest that TPUMA's performance changes in the aging environment is result from the dual coupling effect of polymer degradation and asphalt oxidative hardening. The closely arranged isocyanate (-NCO) and polar component molecular chains in asphalt slow down its oxidation speed, which enhances the aging and deformation resistance of TPUMA. The successful blending of TPU and asphalt was confirmed, and the degradation degree of the polymer was quantitatively characterized by the percentage of the degraded area. The results provide insights to better understand the interplay between TPU degradation and asphalt oxidation.