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Ti2AlNb alloy holds large research significance as a lightweight material for high-temperature structural applications in the next generation of aero-engines. In this work, pre-alloyed Ti2AlNb powders were spark plasma sintered to fabricate the raw compact, which was then hot rolled at different phase fields to fabricate sheets. The high-temperature properties of the sheets were tested directly without the prior heat treatment. Results show that the Ti2AlNb sheets have good high-temperature strengths even without the heat treatment prior to testing. For the sheet rolled at the single B2 phase region, the maximum tensile strength was up to 931.4 MPa at 650 °C. The sheet mainly shows intergranular fracture mode due to the weak bonding at grain boundaries. The sheets rolled at the O + B2 phase region have low tensile strengths at different testing temperatures. For the sheet rolled at α2+O + B2 phase region, the tensile strength gains its maximum strength of 956.6 MPa at 650 °C, and the sheet shows transcrystalline fracture mode. The fracture mechanisms of the sheets rolled at different phase regions are analyzed in detail and proved by experiment. This work shows the potential of fabricating Ti2AlNb sheet by using the spark plasma sintered compact.

This work presents a data reduction procedure of the direct pulse heating technique with both contact and radiance temperature measurements. The technique is applied for the measurement of thermophysical properties of electroconductive solids over a wide temperature range, i.e., from room temperature up to about 2300°C. Absolute and radiance temperatures of a tested material are measured by thermocouple and radiation thermometer, respectively and these and other experimental data are then reduced to the values of specific heat, specific electrical resistivity, hemispherical total emissivity and normal spectral emissivity of the tested material. The related data reduction and corresponding uncertainty assessment for each property is described in detail. An example of uncertainty assessment is given for the recent measurement of specific heat, specific electrical resistivity, hemispherical total emissivity and normal spectral emissivity at 900 nm of molybdenum alloy TZM specimens. [ABSTRACT FROM AUTHOR]

A blend of only commercial powders, including Ni625, CoCrF75, and 316L, were used as the raw material for fabricating non-equiatomic CoCrFeNiMoxNby high entropy alloys (HEAs) through laser powder bed fusion (PBF-LB/M) via in situ alloying, instead of using pure elemental powders, thus reducing the raw materials cost. The rapid cooling inherent in the PBF-LB/M process facilitated the dissolution of Mo and Nb, resulting in a single FCC phase characterized by high relative densities. High-temperature tensile tests were conducted at room temperature, 700 °C, 800 °C, and 900 °C, revealing mechanical properties that surpassed those reported in existing HEA literature. The remarkable strength of the HEAs developed in this study primarily stemmed from the incorporation of Mo and Nb, leading to the precipitation of Mo and Nb-rich lave phases at elevated temperatures. While constraining elongation when confined to grain boundaries, these precipitates enhanced strength without compromising elongation when distributed throughout the matrix. This work is a feasibility study to explore the usage of commodity compositions from the market to develop HEAs using PBF-LB/M, which opens the possibility of using scraps to further the development of new materials. Consequently, this study presents a rapid and cost-effective approach for HEA development, improving efficiency and sidestepping the direct utilization of critical raw metals for sustainable manufacturing. Moreover, this work also underscores the outstanding mechanical performance of these HEAs at high temperatures, paving the way for the design of innovative alloys for future high-temperature applications. [ABSTRACT FROM AUTHOR]

Hot deformation of sintered cobalt during hot compression testing was investigated in the temperature range of 700–1000 °C and at strain rates ranging from 0.0005 to 0.1 s−1. Cobalt underwent considerable dynamic recrystallization (DRX) during hot deformation, with stress-strain flow curves exhibiting one or several peaks followed by significant flow softening and leading to a steady-state stress. Constitutive equations were used to derive the flow stress behaviour. A physically based model to describe the strain rate as a function of stress was suggested for temperatures ranging between 775 and 1000 °C. In this case, a creep exponent (n) of 5 indicated that the deformation mechanism was controlled by the glide and climb of dislocations. The activation energy coinciding with the one for self-diffusion of ferromagnetic cubic cobalt implied a diffusion-controlled mechanism and the presence of face-centered cubic (FCC) cobalt during deformation. Interestingly, the results at 700 °C could not be perfectly fitted to this model and exhibited a higher resistance to deformation. This revealed that the glide and climb deformation mode was close to the transition where glide mode was dominant, and thus mostly glide occurred at 700 °C, especially for the largest strain rates.

This paper presents experimental results on five thermophysical properties of the TZM alloy over a wide temperature range. Specific heat and specific electrical resistivity were measured from room temperature to 2200 °C and 2450 °C, re.spectively. normal spectral emissivity at 900 nm from 1150 °C to 2300 °C. hemispherical total emissivity from 1100 °C to 2450 °C and the coefficient of the linear thermal expansion from room temperature to 2000 °C. The specific heat. specific electrical resistivity and both emissivities were obtained by the direct pulse heating technique or pulse calorimetry, while the thermal expansion coefficient by the pushrod dilatometry. The specimens in the form of a thin rod were used, 200 mm in length and 3 inm in diameter in the first, while 25 min in length and 6 min in diameter in the second technique. The results are presented and compared with available literature data. [ABSTRACT FROM AUTHOR]

A blend of only commercial powders, including Ni625, CoCrF75, and 316L, were used as the raw material for fabricating non-equiatomic CoCrFeNiMoxNby high entropy alloys (HEAs) through laser powder bed fusion (PBF-LB/M) via in situ alloying, instead of using pure elemental powders, thus reducing the raw materials cost. The rapid cooling inherent in the PBF-LB/M process facilitated the dissolution of Mo and Nb, resulting in a single FCC phase characterized by high relative densities. High-temperature tensile tests were conducted at room temperature, 700 °C, 800 °C, and 900 °C, revealing mechanical properties that surpassed those reported in existing HEA literature. The remarkable strength of the HEAs developed in this study primarily stemmed from the incorporation of Mo and Nb, leading to the precipitation of Mo and Nb-rich lave phases at elevated temperatures. While constraining elongation when confined to grain boundaries, these precipitates enhanced strength without compromising elongation when distributed throughout the matrix. This work is a feasibility study to explore the usage of commodity compositions from the market to develop HEAs using PBF-LB/M, which opens the possibility of using scraps to further the development of new materials. Consequently, this study presents a rapid and cost-effective approach for HEA development, improving efficiency and sidestepping the direct utilization of critical raw metals for sustainable manufacturing. Moreover, this work also underscores the outstanding mechanical performance of these HEAs at high temperatures, paving the way for the design of innovative alloys for future high-temperature applications.

Purpose: This paper presents a review concerning the analytical and inverse methods of small punch creep test (SPCT) in order to evaluate the mechanical property of component material at elevated temperature. Design/methodology/approach: In this work, the effects of temperature, specimen size and shape on material properties are mainly discussed using the finite element (FE) method. The analytical approaches including membrane stretching, empirical or semi-empirical solutions that are currently used for data interpretation have been presented. Findings: The state-of-the-art research progress on the inverse method, such as non-linear optimization program and neutral network, is critically reviewed. The capabilities of the inverse technique, the uniqueness of the solution and future development are discussed. Originality/value: The state-of-the-art research progress on the inverse method such as non-linear optimization program and neutral network is critically reviewed. The capabilities of the inverse technique, the uniqueness of the solution and future development are discussed. [ABSTRACT FROM AUTHOR]

Previous studies on the modification of fast-growing wood have extensively examined the effects of density and lignin content on the strength and high-temperature properties of modified wood. However, a comprehensive quantitative analysis of their effects on high-temperature performance remains insufficient. To address this knowledge gap, we applied alkali treatment and compression densification to fast-growing poplar, resulting in modified specimens with varying densities and lignin levels. The quantitative effects of density and lignin content on high-temperature properties were meticulously evaluated. Chemical changes were analyzed using Fourier transform infrared spectroscopy (FT-IR), while the mechanical and high-temperature properties were comprehensively assessed. Delignification was found to be positively correlated with treatment duration, with hemicellulose degradation also detected via FT-IR analysis. Significant enhancements were recorded in flexural strength, tensile strength, and modulus of elasticity, accompanied by improvements in ductility ratio and compressive strength. The modified poplar wood exhibited increased thermal stability at elevated temperatures. Furthermore, density and lignin content were identified as significant factors affecting high-temperature performance, establishing minimum density thresholds for various lignin contents in modified poplar wood to ensure optimal performance. This study enhances to the understanding of the intricate relationships among wood properties, modification techniques, and high-temperature performance. • Enhance performance of fast-growing wood for sustainable construction • Strengthen and increase ductility of modified specimens • Optimal alignment of equivalent lignin content with activation energy • Establish minimum density for varying lignin contents [ABSTRACT FROM AUTHOR]

Hot deformation of five microstructurally different sintered WC-Co cemented carbides during hot compression testing was investigated in the temperature range of 700–1000 °C and at strain rates ranging from 0.0005 to 0.1 s−1. The stress-strain flow curves of the studied materials exhibited a peak followed by a fast drop in stress or sudden failure. A higher peak stress was achieved by decreasing the testing temperature, increasing the strain rate or lowering the amount of binder content. Constitutive equations were used to develop a useful physically based model describing the mechanical resistance of cemented carbides as a function of three different stress terms, representing stresses carried by the binder phase, accommodated by the carbide phase and associated with the interaction between the metallic and ceramic phases. The first term was modelled after the hot deformation of Co and was very small. The second one revealed an activation energy of Q = 585 kJ/mol, identified as that of W pipe diffusion in WC, and was barely dependent on the temperature and strain rate. Finally, the third stress contribution provided valuable insight on the role of the carbide skeleton in cemented carbides, proving the major effect of the microstructural arrangement in the deformation resistance. All the testing conditions were included in the model, with only a few extreme data points having to be excluded. Outcomes of the model were further supported by a thorough EBSD characterization. [Display omitted] • Hot deformation behaviour of cemented carbides is studied over a wide range of temperatures and strain rates. • A constitutive equation is developed for describing a physical-based model for the mechanical resistance of WC-Co. • W pipe diffusion in the WC grains is responsible for the plastic deformation of the ceramic phase. • In the binder, plastic deformation is controlled by self-diffusion. • The interaction term highlights the role of the microstructural arrangement on the deformation resistance. • EBSD proved that WC and binder suffer plastic deformation, which is affected by the interaction between all the interfaces. [ABSTRACT FROM AUTHOR]

This study provides an empirical analysis of the spalling phenomena and mechanical properties of ultrahigh-performance concrete (UHPC) after exposure to high temperatures. The main purpose of this research was to elucidate the use of polypropylene fibres (PPFs) as an effective method to mitigate UHPC samples' propensity to explosive spalling while evaluating changes in their mechanical properties after being exposed to different thermal conditions. The effect of the PPFs dose, heating rate and pre-drying conditions of the spalling phenomenon was systematically examined. Adding up to 2 kg/m3 of PPFs (PP2.0 samples) positively reduced spalling events, with no significant variation in the compressive strength recorded at room temperature (145 MPa to 155 MPa). The incorporation of 2 kg/m3 PPFs proved an effective measure against spalling but resulted in loss of workability. However, the combination of 0.5 kg/m3 PPFs with pre-drying at 80ºC for 3 days was also a feasible strategy to mitigate spalling. The PP2.0 samples, which did not undergo spalling no matter what the heating rate or drying cycle was, were selected to investigate their mechanical behaviour when exposed to temperatures of 200ºC, 400ºC, 600ºC, 800ºC and 1000ºC. For each temperature, compressive strength tests were run in hot-tested, air-dried (natural) and water-cooled (forced) samples. The developed UHPC concrete samples' compressive strength remained relatively stable at up to 400ºC and progressively reduced with higher temperatures, with the best results obtained during air cooling. • Polypropylene fibers (PPF) effectively reduced spalling in UHPC. • Steel fibers alone were insufficient to prevent spalling. • No spalling occurred with 2 kg/m3 PPF or 0.5 kg/m3 PPF plus accelerated drying. • Strength reduction of UHPC with rising temperatures. • Best post-fire compressive strength in the air-cooled UHPC. [ABSTRACT FROM AUTHOR]

Magnesium potassium phosphate cement (MKPC) is extensively employed in patching materials and fireproof coatings owing to its outstanding properties. This study employs a blend of fly ash and silica fume to substitute a portion of the cementitious materials, aiming to enhance the performance of MKPC under high-temperature conditions. The relative proportions of fly ash and silica fume were considered. MKPC was subjected to cubic compression and three-point flexural tests. Additionally, the phase and microstructure of MKPC were also characterized using XRD and SEM. The compressive strength, flexural strength, visual appearance, and mass loss of MKPC specimens were evaluated before and after exposure to various high temperatures. Following exposure to elevated temperatures, MKPC specimens without fly ash and silica fume doping showed a significant decrease in strength. Conversely, specimens doped with 15 % or 10 % silica fume exhibited the most remarkable strength enhancement. The dehydration of K-struvite at elevated temperatures was the primary reason for the mass loss and strength reduction of MKPC. Silica fume and fly ash can facilitate the sintering of phases and amorphous particles derived from K-struvite decomposition, leading to the formation of ceramic-like structures. Notably, the contribution of silica fume to the sintering effect exceeds that of fly ash. Therefore, blending fly ash and silica fume proves to be an effective approach to enhancing the high-temperature resistance of MKPC. [Display omitted] • The influence of the relative content of fly ash and silica fume on the high-temperature performance of MKPC was examined. • Fly ash and silica fume significantly enhanced the mechanical properties of MKPC after exposure to high temperatures. • Fly ash and silica fume did not influence the hydration products of MKPC before and after exposure to high temperatures. • Notably, silica fume contributes more to the sintering effect compared to fly ash. [ABSTRACT FROM AUTHOR]

Continuous ceramic fiber‐reinforced ceramic composite materials are targeted for high temperature thermostructural components in aerospace. Advanced joining and integration technologies are enabling for the fabrication of large and complex shaped ceramic matrix composite components. Silicon rich refractory eutectic phase compositions in silicon‐chromium (Si‐18 at% Cr), silicon‐titanium (Si‐16 at% Ti), and silicon‐hafnium (Si‐8.5 at% Hf) systems were investigated for joining studies. The Si‐8.5 at% Hf system was down‐selected and further evaluated for joining silicon carbide fiber bonded composite (SA‐Tyrannohex) and additional fiber‐reinforced composite materials. Microstructural analysis of polished cross‐sections using optical microscopy and scanning electron microscopy (SEM) with energy dispersive spectroscopy (EDS) was used to evaluate the joint quality and determine the composition of the reaction formed phases. Joints along the full length of the paired substrates were observed to be well adhered, uniform, and free of gaps and pores. Single lap offset testing conducted at room temperature, 750°C, and 1200°C showed very good strengths when the fibers in the SA‐Tyrannohex material were perpendicular to the joint interface. However, when the fibers were orientated parallel to the joining plane, failures were premature due to the low interlaminar strength of the SA‐Tyrannohex material and occurred away from the joint interface. [ABSTRACT FROM AUTHOR]

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Phenylethynyl-terminated polyimide resin/carbon fiber composites become ideal structure materials for aerospace vehicle because of excellent mechanical properties and high-temperature thermal stability. However, the curing temperature of the polyimide resin/carbon fiber composite was higher than 370 °C, which caused much thermal stress that would inevitably deteriorate the performance of the composite and restrict its application. In this paper, a compound catalyst of isopropyl peroxide and cobalt naphthenate was used to catalyze the cross-linking reaction of phenylethynyl-terminated polyimide resin and decrease the curing temperature of the polyimide/carbon fiber composite. The result showed that the phenylethynyl characteristic absorption peak at cm−1 was still existed in the polyimide resin without catalyst and disappeared for the catalystic polyimide resin when curing temperature was 300 °C, in which the spectrum was the same as that of the polyimide resin cured at 370 °C without catalyst. The inter-laminar shear strength and flexure strength of the catalytic polyimide/carbon fiber composite were 96.8 MPa and 2080.0 MPa, there were increases of 28.8% and 23.8% compared to that of the composite without catalyst cured 370 °C. All these results demonstrate that the compound catalyst of radical initiator and coordination catalyst could efficiently decrease the curing temperature of phenylethynyl terminated polyimide resin and increase the mechanical properties of the polyimide resin/carbon fiber composite. [ABSTRACT FROM AUTHOR]

We propose a novel strengthening strategy that involves the introduction of a high-entropy nanoscale phase (HENP) and semicoherent refractory nanoparticle into the A2 matrix of an as-cast equimolar HfMoNbTaTi refractory high-entropy alloy (RHEA). Based on the design concept of low difference in elemental melting points, equiaxed grains with slight segregation were obtained. The HENP was characterized as a disordered near-coherent structure with a composition significantly similar to the matrix that differed from traditional coherent intermetallics. The heterogeneous nucleation was attributed to the aggregation of the largest Hf atoms and interstitial complexes in the locally distorted matrix. Moreover, the refractory nanoparticle was inferred to be hafnium nitride, possessing high thermal stability and establishing a semicoherent interface with the matrix. Notably, the interface was lined with a Ti film of one or two atomic layers. Furthermore, owing to the high melting point and precipitation strengthening, a highest yield strength (851 MPa) was obtained at 1200 °C compared with those reported cast RHEAs. At room temperature, a high yield strength (1713 MPa) was revealed mainly due to the combined effect of solid-solution strengthening and precipitation strengthening. The present study provides a new pathway for the future design of HEAs.

The effects of aging treatment on the high temperature mechanical behavior of laser-welded Mg-Gd-Y alloy were systematically studied. The microstructure and high temperature tensile properties of as-welded and aging-treated joints were analyzed. The microhardness of the weakest part of the heat affected zone was improved by 41% due to the precipitation of large amount of β′ and the ultimate tensile strengths at room temperature and 300 °C was increased by 11 and 8% by aging treatment. The elevated temperature tensile properties of two types of joints decreased slightly from room temperature to 250 °C, then plummeted at 300 °C. The failure mechanism of aging-treated joints was the originating and propagation of cracks at the interior of Mg24(Gd,Y)5 by the local stress concentration when the temperature was lower than 250 °C, whereas the failure mechanism at 300 °C was the deformation of ultrafine grains and unstable Mg24(Gd,Y)5. [ABSTRACT FROM AUTHOR]

High alloyed Si ferritic ductile irons can offer potential benefits because they combine high strength, ductility at room temperature, and low oxidation rate at high temperature. However, there is one known drawback and that is these cast irons have limited performance during thermal cycling due to a significant drop of ductility at warm temperatures. This decrease in ductility has been linked to poisoning ferrite grain boundaries by Mg. Therefore, thermodynamic simulations were used to identify altering additions which were able to meditate this negative effect by forming intermetallic phases with Mg. To verify thermodynamic predictions, three alloys were cast including a base and two high Si ductile irons with additions of P and Sb. High-temperature performance of these alloys was experimentally verified including tensile properties at warm temperatures (350–550 °C), oxidation in air at temperatures (700–800 °C), and thermal cycling between 300 and 800 °C. SEM and TEM analyses confirmed that the studied additions reacted with Mg forming different compounds which could prevent poisoning ferrite grain boundaries and improve high-temperature performance of high Si ductile iron. [ABSTRACT FROM AUTHOR]

• Ablation of C/C composites was investigated in a nitrogen plasma environment with a high heat flux of ∼25 MW/m2. • The linear ablation rate of C/C composites is 0.114 mm/s, which is close to the value in the solid rocket motor with a pressure of ∼15.2 MPa. • Ablation of C/C composites is mainly controlled by the thermal chemical ablation and mechanical breakage, and sublimation of carbon. • The calculated results show that C n (g) (n = 1–3), CN(g), C 2 N(g), and C 2 N 2 (g) may be the major reaction products consuming carbon. Ablation of carbon/carbon (C/C) composites was investigated in a nitrogen plasma torch with a heat flux of ∼25 MW/m2. The reaction products of carbon in C/C composites and nitrogen plasma jet were calculated based on the principle of free energy minimum. The calculated results show that the thermal chemical ablation and sublimation of carbon occur and C n (g) (n = 1–3), CN(g), C 2 N(g) and C 2 N 2 (g) may be the major reaction products consuming carbon. Ablation is apt to begin at the interfaces, especially the fibre-matrix interface and interfaces inside the matrix. Ablation of C/C composites is mainly controlled by the thermal chemical ablation, sublimation of carbon, and mechanical breakage. The formation of needle-shaped fibres and shell-shaped matrices is attributed to both the thermal chemical ablation and sublimation of carbon, while carbon fragments and fractured fibres or matrices result from the mechanical breakage. [ABSTRACT FROM AUTHOR]

In this study, the effect of coir fiber reinforcement on the mechanical properties of vulcanized natural rubber composite has been studied. An attempt has been made to predict the effect on tensile strength, maximum load, and elongation at break (%) of coir fiber-reinforced vulcanized natural rubber composites under cold, heat, and water aging tests. The natural rubber was vulcanized at 150°C. The fibers were soaked in a 5% solution of NaOH for 48 h at room temperature. At different temperatures, cold, heat, and water aging resistance tests were conducted to understand the behavior of the composite under different environment. The properties recorded after aging tests were compared with initial properties to investigate the effect of fiber reinforcement. The results revealed that the samples containing coir fiber showed better performance after each aging test. The specimens showed the highest properties in case of water aging resistance.

The effects of in-situ synthesis columnar mullite and pore structure on the hot modulus of rupture (HMOR), thermal shock resistance and corrosion resistance of corundum castables have been investigated in this paper. When 2% nano silica was added, the pore diameters of castables could be decreased to 15 nm (at 110 °C), 1 μm (1100 °C) and 6 μm (1500 °C), respectively. The corresponding reducing magnitude of pore size is 98.5%, 83.3% and 33.3%. The HMOR of castables fired at 1500 °C increased by 110% to 3.64 MPa. Furthermore, after three thermal shock cycles, the residual strength ratio of castables increased from 5.2% to 15.3%. A large amount of cross-distributed columnar mullite was formed between nano silica and α-Al 2 O 3 by the two-dimensional nucleation mechanism, which remarkably enhanced the high temperature properties. The penetration index reduced from 30.86% to 19.88%, suggesting that smaller pore size and higher viscosity had a great influence to the penetration process. [ABSTRACT FROM AUTHOR]

In the context of cast alloy development for high temperature applications, high entropy superalloys (HESA) have exhibited superior cost specific tensile strength than that of superalloys such as CM247LC. Compositions of HESA are distinctively different from those of cast superalloys with higher contents of Fe and Ti, making HESA cheaper and lighter. Comparing to superalloys, although HESA has adopted the template of FCC-structured (γ) matrix and coherent L1 2 -structured (γ′) precipitates, γ′ is enriched with solutes with higher intrinsic strength, rendering positive lattice misfit, and the high entropy γ matrix may have attributed to a good combination of strength and ductility. Image, graphical abstract [ABSTRACT FROM AUTHOR]

• Ductile-to-brittle transition was revealed by small punch and miniature tensile tests. • Miniature tensile tests demonstrated high consistency and repeatability. • An inverse method developed to determine the temperature-dependent mechanical properties. • Finite element modelling was carried out to predict damage evolution and fracture. Small punch tensile (SPT) tests have been carried out for a CoNiCrAlY coating at room temperature (RT), 500°C and 700°C. Highly re-producible results have been obtained for SPT at 700°C while the formation of early cracking at lower temperatures tends to compromise the repeatability of the tests. An alternative novel miniature specimen testing method has been developed and used for the miniature tensile tests of the CoNiCrAlY coating in the same temperature range. Good agreements have been achieved between the SPT and miniature tensile testing results regarding the ductile to brittle transition temperature (DBTT). Excellent repeatability has been achieved over the full range of the temperature for the miniature tensile tests. An inverse approach has been developed and used to extract the mechanical properties of the material from the miniature tensile tests, using a temperature-dependent Johnson-Cook model. Finite element (FE) modelling of the SPT tests, including damage evolution, has been carried out using the extracted material properties to give comparable predictions of the SPT testing results, such as the load-displacement curves and the approximate locations of the fracture failures. [ABSTRACT FROM AUTHOR]

This study investigated the effects of yttrium addition (0wt%–0.5wt%) on the purification, microsegregation and mechanical properties of K417 cast superalloy. The results showed that the addition of Y could significantly reduce the content of oxygen. Purified K417 superalloy with 4∼7ppm O content was obtained after adding a moderate amount of Y. With the increasing Y addition, the segregation degrees of alloying elements (Ti, V and Mo) dropped as a whole, γ′ phase was refined, and the size and volume fraction of γ/γ′ eutectic increased. The decrease in the degree of Ti segregation and the solid solution of Y in carbide periodicity changed the morphology of carbide. When the Y addition increased from 0wt% to 0.1 wt%, the decrease of O content, the refinement of γ′ phase and the formation of rod carbides increased the high temperature tensile strength of the alloy. When the Y addition increased from 0.2wt% to 0.5 wt%, the production of large-size Y-rich phase reduced the mechanical properties of the alloy. The plasticity of the alloy rised and then decreased with increasing Y addition. The appropriate amount of Y addition was about 0.01wt% to 0.05wt%. • The addition of Y hindered the segregation of alloying elements. • High purity K417 alloy with oxygen and nitrogen content of 5ppm was obtained. • Yttrium addition caused the carbide shape to exhibit periodic change in the shape of a block and a rod. • The formation of rod-shaped carbide promoted the improvement of high temperature tensile strength. [ABSTRACT FROM AUTHOR]

Abstract A novel high entropy alloy with the composition of CoFeNi 2 V 0.5 Mo 0.2 , shows unusual strain hardening ability and an excellent combination of ductility and strength. Especially at 873 K, the elongation can reach 189.2%, almost three times that of the common high temperature alloys. Microstructural characterization suggests a coexistence of planar slip and cross slip. The resistance of planar slip serves to strengthen the alloy, while the cross slip effectively relieves strain concentration, substantially contributing to the uniform elongation. Also, the interaction of planar slip and cross slip will lead to the formation of two kinds of dislocation loops. Graphical abstract Unlabelled Image [ABSTRACT FROM AUTHOR]

Abstract In-situ synthesized titanium borides reinforced Ti-6Al-4V composites with a tailored reinforcement architecture were successfully prepared by hot isostatic pressing (HIP) starting from a TiB 2 /Ti-6Al-4V powder system. The microstructure of the composite samples was investigated using X-ray diffraction (XRD) technique and scanning electron microscopy (SEM), and the mechanical properties were evaluated through room and high temperature tensile testing. It is found that during HIP the additive particles TiB 2 have totally transformed into TiB needles, which tend to decorate at prior particle boundaries of the consolidated powder particles to form a network structure. With increasing TiB 2 addition from 3 wt.% to 8 wt.%, the microstructural feature of the TiB network structure experiences the variations of discontinuous TiB reinforcement → quasi-continuous TiB reinforcement → continuous TiB reinforcement. The room temperature tensile properties of the composites are improved with increasing addition of TiB 2 from 3 wt.% to 5 wt.%, but the tensile strength of the sample with 8 wt.% TiB 2 drastically decreases. As to the high temperature properties, the titanium boride reinforced Ti-6Al-4V alloy composites can be an increased maximum service temperature by over 200 °C while retaining the same tensile strength accompanied with a suitable elongation. The strengthening mechanism is mainly attributed to the load-bearing transformation, grain refinement and dispersion strengthening. [ABSTRACT FROM AUTHOR]

Abstract Y 2 O 3 is mainly applied as a dispersoid in Ni-based oxide dispersion strengthened (ODS) alloys. The added Y 2 O 3 reacts with Ti and Al at a temperature above 1150 ℃ to form a complex oxide such as Y-Ti-O or Y-Al-O complex oxide. However, previous studies have shown that Y-Al-O complex oxide has relatively coarser particles than Y-Ti-O complex oxide. In this study, Ti was first added to form Y-Ti-O complex oxide, which has relatively fine particles. Subsequently, Al was added to inhibit the formation of Y-Al-O complex oxide, thus improving the high-temperature mechanical properties of ODS alloys. Ni-based ODS alloy powders with composition Ni-15Cr-xTi-1.1Y 2 O 3 (without aluminum) were mechanically alloyed using a planetary mill. Thereafter, the mechanically alloyed powders were heat treated to form a complex oxide of Y-Ti-O. A second mechanical alloying was performed by adding 4.5 wt% Al to the heat treated powders. The products obtained after the second alloying were sintered by spark plasma sintering. The phase of the sintered specimens were analyzed using X-ray diffraction, their microstructures were analyzed by transmission electron microscopy and the size distribution of oxide particles was confirmed by image analysis. Moreover, the high-temperature mechanical properties of each composition were analyzed using a hot hardness tester. [ABSTRACT FROM AUTHOR]

Abstract In this paper, high temperature creep and frictional wear behaviors of WCu pseudo-alloys were investigated using scanning electron microscopy, X-ray diffraction and X-ray fluorescence. Results showed that the Cu binder phase was uniformly distributed around the W skeleton in the WCu alloys. The W80Cu20 alloys exhibited a good creep resistance. The creep life of the WCu alloys was gradually reduced with a decrease in W content of the alloy. Copper tungstate (CuWO 4) was formed during the high-temperature friction and wear processes, and was found to be beneficial to improve the wear resistance of the WCu alloys. An increase in the content of Cu was found to be helpful to enhance the cohesiveness of W-Cu phases, improve the deformability of W, restrain the formation of WO 3 , and promote the formation of CuWO 4. In addition, the friction coefficient was decreased with an increase in both the Cu content and applied load. Therefore, W70Cu30 alloys demonstrated a better high temperature wear resistance than W80Cu20 alloys. The worn surface of the WCu alloys exhibited pits, furrow, micro-sized pores, fatigue cracks and wear debris. Wear mechanisms of the WCu alloys were identified to be a combination of adhesive wear, abrasive wear, oxidation wear, fatigue wear and evaporation of copper. [ABSTRACT FROM AUTHOR]

The Al-6.7Zn-2.6Mg-2.0Cu-0.1Zr alloy is modified by Sm for the purpose of improving its mechanical properties at high temperatures. According to the results, the as-cast structure can be refined through 0.3% Sm modification treatment, and finer precipitates can be obtained after aging. In the meantime, with the addition of Sm, a new high melting point Al _10 Cu _7 Sm _2 phase is formed, the initial decomposition temperature of the alloy is raised, and the thermal stability is enhanced. As indicated by the tensile test results at room temperature and high temperatures, the strength of the modified sample was improved compared with the unmodified alloy. According to fracture surface analysis, ductile fracture conforms to the fracture characteristic exhibited by the modified alloy at room temperature and high temperatures. The improvement on high temperature strength of the modified alloy is attributed largely to a combination of grain refinement, precipitation strengthening and heat resistant phase to grain boundary pinning.

The fracture toughness of a nearly lamellar Ti-45Al-8Nb-0.2W-0.2B-0.1Y alloy and a fully lamellar Ti-45Al-7Nb-0.2W-0.2Hf-0.3B-0.15 C alloy at 750℃ was investigated by prefabricating a fatigue crack in the compact tension(CT) specimen,and the corresponding fracture morphologies were observed by optical microscopy and scanning electron microscopy. It is found that the fracture toughness of the nearly lamellar high Nb-containing Ti Al alloy is 19.54 MPa·m1/2 at 750℃,obviously lower than the value of 31.58 MPa·m1/2 for the fully lamellar alloy. The maximum cyclic load at which the fatigue crack initiates in the nearly lamellar alloy is noticeably less than that in the fully lamellar alloy. Fracture images show that for the nearly lamellar alloy,cracks initiate mainly in equiaxed γ grains and propagate in different ways,intergranularly or transgranularly in γ grains or lamellar colonies. But for the fully lamellar alloy,cracks initiate mainly at lamellar interfaces perpendicular to the load direction and propagate in both interlamellar and translamellar ways,in accompanying with secondary crack initiation.

A new single crystal high entropy alloy is developed and produced using Bridgman directional-solidification and seed-crystal method. The microstructure exhibits the directional dendrite morphology and is mainly composed of the FCC matrix and the L1 _2 ordered precipitates. Its high-temperature yield strengths are far higher than those of the first-generation single crystal superalloys, and close to those of the second- generation ones. The solid-solution strengthening effect from the high content of W and Mo, as well as the precipitation strengthening effect from the combined addition of Al, Ti, Ta, and Nb, should be responsible for the excellent high-temperature strength of the investigated alloy.

The high-temperature mechanical properties of Al-TRIP steel with 0.16% C,1.49% Mn and 1.35% Al,which is applied to automobiles,were investigated by using a Gleeble 3500 machine. The phase transition temperature interval was measured by differential scanning calorimetry(DSC). The fractographs and microstructures near the tensile fracture of the steel at different tensile temperatures were analyzed by means of a scanning electron microscope and an optical microscope. The zero ductility temperature(ZDT) and the zero strength temperature(ZST) of the steel were measured to be 1425℃ and 1430℃,respectively. The brittleness temperature interval Ⅰ is from 1400℃ to the melting point,and the brittleness temperature interval Ⅲ is from 800℃ to 925℃.Ferrite precipitation from austenite grain boundaries is the main cause of the presence of the brittleness temperature interval Ⅲ. With specimens cooling from 975℃ to 700℃,the proportion of ferrite increases continuously,while the reduction of area(ψ) decreases firstly and then increases. When the proportion of ferrite reaches to 8.1%(at 850℃),the value of ψ decreases to 28.9%; but when being stretched at 800℃,the proportion of ferrite is greater than 16.7%,and the value of ψ is more than 38.5%. A small number of Al N particles precipitate in the steel at 1275.6℃. These Al N particles are coarse,but they have no influence on the ductility of the steel.

MAX phases represent a gruop of alloys which is also defined as multilayered alloys because of their crystal shape specifictiy that started to be used in the late 1960's. MAX phase alloys are usually sorted like this. Mn+1AXn n:1,2,3; M: Transition metals (Like Ti, Zr, Hf, V, Mo, Ta ) : A: A group metals (Like Al, Si, In, Ge, Ga, Sn, Pb ) and X: C (carbide) and/ or N (nitride) . MAX phase alloy are stable at high temparature and they have transcendent thermo physical properties. They have high hardness and chemical resistance so they make them interesting in aviation, thermal energy component and cutting tools sectors. In the high temperature executions, they are prefered because they have high thermal shock resistance, high creep lifetime , high oxidation resistance and thermal fatigue endurance. Layered crystal shape put together both metallic and seramic characteristics. Chemical stoichiometry and crystal shape modify material properties.MAX phase alloys can buusedas bulk, powder and coating forms.MAX phase alloys are expensive due to their superior specificties in trading executions as a patented product. In this study we tried to introduce MAX phase multi layered alloys. Ti3SiC2 MAX phase alloy with reference to the MAX phase alloys as compared to other compositional structures, technological properties were examined and potential applications are discussed [1-11].

Carbon fiber-reinforced composites with matrices containing ultra-high temperature ceramics show excellent potential as high ablation-resistant materials. In this study, two non-oxide nanostructures, ZrB2 nanofibers and SiC nanoparticles, as reinforcement phases were utilized to develop the carbon/phenolic-ZrB2-SiC (C/Ph-ZS) nanocomposite for the first time. Thermogravimetry analysis illustrated that the residue yield of C/Ph composite at high temperatures was increased by the introduction of above-mentioned nanostructure ceramics. The addition of 7 wt% of ZrB2/SiC nanoadditives homogeneously in a C/Ph composite resulted in an enhancement of the room temperature thermal diffusivity, from 0.00622 to 0.00728 cm2/s. The incorporation of 4–7 wt% of ZrB2/SiC nanofillers in C/Ph composites leads to a reinforced material with about 73% increasing of Shore D hardness. The modified thermal behavior of prepared nanocomposites was examined using oxyacetylene torch at 2500℃ for 160 s. It suggested that the C/Ph-ZS7% nanocomposites with lower density may drastically contribute to meliorate the thermal insulation and ablative properties. The linear ablation rates of C/Ph composites were decreased after adding 7 wt% ZrB2/SiC nanofillers by 18%. The formation of a dense and uniform SiO2 and ZrO2 layer on the ablated surface of C/Ph-ZS nanocomposites could function as an effective oxygen barrier which greatly reduced the ablation rates of the nanocomposites because of the evaporation at elevated temperature, which absorbs heat from the flame and reduces the erosive attack to C/Ph. The ablated C/Ph-ZS nanocomposite with complicated cross-section structure displayed four dense oxidized, porous surface, transient and matrix regions. [ABSTRACT FROM AUTHOR]

Expanded perlite/A356 aluminium syntactic foams (P-MSF) were produced via a counter-gravity infiltration process. The quasi-static compressive properties of these foams were investigated at 25, 125, 250, 375, and 500 °C and compared with those of the matrix material, tested at the same conditions. Young's modulus, offset yield stress, plateau stress and energy absorption was evaluated for all samples. The improved ductility of the foams at higher temperatures results in more uniform deformation and smoother stress-strain curves. At the same time, the mechanical strength and the energy absorption of the foams and the matrix material decrease. The results indicate that the high temperature mechanical properties of the foams are controlled by two counter-acting mechanisms, i.e. the softening of the matrix material and the improved ductility of the foam. [ABSTRACT FROM AUTHOR]

The use of fiber reinforced polymer (FRP) bars in reinforced concrete members enhances corrosion resistance when compared to traditional steel reinforcing bars. Although there is ample research available on the behavior of FRP bars and concrete members reinforced with FRP bars under elevated temperatures (due to fire), there is little published information available on their post-fire residual load capacity. This paper reports residual tensile strength, modulus of elasticity, and bond strength (to concrete) of glass fiber reinforced polymer (GFRP) bars after exposure to elevated temperatures of up to 400 °C and subsequent cooling to an ambient temperature. The results showed that the residual strength generally decreases with increasing temperature exposure. However, as much as 83% of the original tensile strength and 27% of the original bond strength was retained after the specimens were heated to 400 °C and then cooled to ambient temperature. The residual bond strength is a critical parameter in post-fire strength assessments of GFRP-reinforced concrete members. [ABSTRACT FROM AUTHOR]

Highly porous nano-SiC is fabricated by partial sintering and decarburizing process using SiC nano-powders as starting materials and graphite flakes as pore forming agents. The prepared porous nano-SiC ceramics possess multiple pore structures, including well-distributed meso-pores in the skeleton and interconnected flakelike micro-pores. The samples prepared at 1800 °C have relatively low thermal conductivities of 5.61 ∼ 0.25 W m −1 K −1 with porosities of 55.5–76.1%. While the samples sintered at 1500 °C with porosities between 54.0% to 76.3% show very low thermal conductivities of 0.74 ∼ 0.14 W m −1 K −1 , which is attributed to the integrated nano-scale phonon-scattering mechanisms and duplex pore structures. Porous nano-SiC ceramics also show good retention of elastic stiffness up to 1350 °C and low thermal conductivity at 1400 °C. Our results shed light on porous nano-SiC as a promising thermal insulator used in extreme thermal and chemical environments. [ABSTRACT FROM AUTHOR]

This study presents a one-pot preparation of gradient porous high emissivity coatings on ceramic fibrous insulations. MoSi 2 -SiO 2 -SiOC coatings have been prepared on mullite fibrous substrates with polysiloxane-derived SiOC glass as low-temperature adhesive, SiO 2 as high-temperature ceramic aggregate, MoSi 2 as emission agent and polydimethylsiloxane (PDMS) as pore former by slurry-spraying, drying and sintering. Scanning electron microscopy shows the MoSi 2 -SiO 2 -SiOC coating gradually changes from a porous structure into a dense structure with obviously decreasing porosity from substrate to surface. The pore size and porosity of the bonding-layer increase with the PDMS content and the density of the surface-layer increases with the sintering temperature suggesting the gradient porous structure is formed by two-steps of “low-temperature decomposition pore-forming” and “high-temperature sintering pore-sealing” during sintering. Firstly, the pores come into formation after decomposition of PDMS and the organic-to-inorganic transformation of the SiOC glass at lower temperature (<1000 °C). Secondly, the formed pores are partly sealed accompanied by carbothermal reduction of the SiOC glass and carburization reaction of the MoSi 2 at higher temperature (>1400 °C). The gradient MoSi 2 -SiO 2 -SiOC coating increases the bonding strength between the coating and substrate up to 0.6 MPa, which is nearly twice as high as that of dense MoSi 2 -SiO 2 coating. The MoSi 2 -SiO 2 -SiOC coating exhibits high spectral emissivity (0.90 at 700 °C), excellent thermal shock resistance (90 cycles without cracking at 25–1500 °C) and oxidation resistance up to 1500 °C, all of which can meet requirements of high temperature application. [ABSTRACT FROM AUTHOR]

AlO-CrO/NiCoCrAlYTa coatings were prepared via atmosphere plasma spraying (APS). The microstructure and phase composition of the coatings were analyzed by X-ray diffraction (XRD), scanning electron microscopy (SEM), laser confocal scanning microscopy (LSCM), and transmission electron microscopy (TEM). The dry frictional wear behavior of the coatings at 500°C in static air was investigated and compared with that of 0Cr25Ni20 steel. The results show that the coatings comprise the slatted layers of oxide phases, unmelted particles, and pores. The hot abrasive resistance of the coatings is enhanced compared to that of 0Cr25Ni20, and their mass loss is approximately one-fifteenth that of 0Cr25Ni20 steel. The main wear failure mechanisms of the coatings are abrasive wear, fatigue wear, and adhesive wear. [ABSTRACT FROM AUTHOR]