Competitive oxidation behavior of Ni-based superalloy GH4738 at extreme temperature

A high thrust-to-weight ratio poses challenges to the high-temperature performance of Ni-based superalloys. The oxidation behavior of GH4738 at extreme temperatures has been investigated by isothermal and non-isothermal experiments. As a result of the competitive diffusion of alloying elements, the oxide scale included an outermost porous oxide layer (OOL), an inner relatively dense oxide layer (IOL), and an internal oxide zone (IOZ), depending on the temperature and time. A high temperature led to the formation of large voids at the IOL/IOZ interface. At 1200℃, the continuity of the Cr-rich oxide layer in the IOL was destroyed, and thus, spallation occurred. Extension of oxidation time contributed to the size of Al-rich oxide particles with the increase in the IOZ. Based on this finding,the oxidation kinetics of GH4738 was discussed, and the corresponding oxidation behavior at 900-1100℃ was predicted.

Porous high-entropy rare-earth phosphate(REPO_(4),RE=La,Sm,Eu,Ce,Pr and Gd)ceramics with excellent thermal insulation performance via pore structure tailoring

Thermal insulation materials play an increasingly important role in protecting mechanical parts functioning at high temperatures.In this study,a new porous high-entropy(La_(1/6)Ce_(1/6)Pr_(1/6)Sm_(1/6)Eu_(1/6)Gd_(1/6))PO_(4)(HE(6RE_(1/6))PO_(4))ceramics was prepared by combining the high-entropy method with the pore-forming agent method and the effect of different starch contents(0–60vol%)on this ceramic properties was systematically investigated.The results show that the porous HE(6RE_(1/6))PO_(4)ceramics with 60vol%starch exhibit the lowest thermal conductivity of 0.061 W·m^(-1)·K^(-1)at room temperature and good pore structure stability with a linear shrinkage of approximately1.67%.Moreover,the effect of large regular spherical pores(>10μm)on its thermal insulation performance was discussed,and an optimal thermal conductivity prediction model was screened.The superior properties of the prepared porous HE(6RE_(1/6))PO_(4)ceramics allow them to be promising insulation materials in the future.

Research Progress of Refractory High Entropy Alloys:A Review

Owing to superior comprehensive performance than conventional superalloys at high temperature,refractory high entropy alloy(RHEA)is becoming a promising candidate for the next generation high-temperature material.Herein,contemporary aspects of corresponding development of RHEAs are reviewed to discuss various factors affecting the organization structure and service performance.It mainly covers alloying system and strengthening mechanism,the preparation method,plastic deformation and the related mechanism,as well as microstructure control by heat treatment.Firstly,the alloy systems and strengthening mechanism are introduced.This is followed by different preparation methods and the comparison of strengths and shortcomings based on different RHEAs.Then,hot deformation behavior and plastic deformation under different loadings are analyzed.Based on this,the influence of heat treatment on microstructures prior to and after the deformation is further summarized.Finally,some important research areas to be carried out in future are pointed out.This review will give a deep understanding of the effects of different factors on the service performance and provide scientific guide in designing RHEAs with improved performance.

Synthesis of CA_(6)/AlON composite with enhanced slag resistance

Different amounts of AlON have been introduced in calcium hexaaluminate(CA_(6)) using two approaches, that is, one-step and twostep methods, to improve the slag resistance of CA_(6). A one-step method can directly sinter the mixtures combining Al_(2)O_(3), CaCO_(3), and Al in flowing nitrogen, in which AlON clusters are always formed because of the poor wettability of Al by Al_(2)O_(3), leading to the high porosity of CA_(6)/AlON composite. In a two-step method, CA_(6)and AlON are prepared separately and then mixed and sintered in flowing nitrogen. Compared with the sample prepared by the one-step method, CA_(6)and AlON in composite by the two-step method are more uniformly distributed,and the optimized amount of AlON added is 10wt%. The slag corrosion and penetration test shows that the CA_(6)/AlON composite using the two-step method exhibits superior slag corrosion protection. The promoted effect of AlON on slag penetration and corrosion resistance is also discussed.

Effect of heat treatment temperature of the glaze lager on the structure and the formaldehyde removal performance of an interior wall tile

With the improvement of people’s living standards,a large number of petroleum products,daily necessities and decorations that can produce volatile organic compounds are used in decoration,which seriously affects the indoor air quality.Interior decoration materials have become a research hotspot in recent years.The purpose of this paper is to develop a kind of interior wall material with good indoor formaldehyde removal effect,easily using,and low cost.In this paper,combining different heat treatment temperatures of the glaze layer,tourmaline/diatomite-based interior wall tiles were prepared by ultrafine grinding,solid sintering,and low temperature calcination.The glaze layer under different heat treatment temperatures was characterized by thermogravimetric-differential thermal analysis,X-ray diffraction,and scanning electron microscope.The influences of heat treatment temperature on the microscopic morphology and structure of the glaze layer were analyzed.Taking formaldehyde as the target degradation product,the effects of tourmaline/diatomite-based interior wall tiles on the removal of formaldehyde under different heat treatment temperatures of the glaze layer were investigated.The results showed that with the increase in heat treatment temperature,the original pores of diatomite decreased,the specific surface area decreased,and the structure of tourmaline changed.At 850℃,the surface structure of the material was slightly damaged,the strength was increased,and the removal effect of formaldehyde was better.In a 1 m^(3) environmental chamber,the formaldehyde removal rate reached 73.6%in 300 min.When the temperature was increased to 950℃ and above,diatomite and the structure of tourmaline were destroyed,and the ability of the material to adsorb and degrade formaldehyde decreased.

PVDF/6H-SiC composite fiber films with enhanced piezoelectric performance by interfacial engineering for diversified applications

Piezoelectric silicon carbide(SiC)has been quite attractive due to its superior chemical and physical properties as well as wide potential applications.However,the inherent brittleness and unsatisfactory piezoelectric response of piezoelectric semiconductors remain the major obstacles to their diversified applications.Here,flexible multifunctional PVDF/6H-SiC composite fiber films are fabricated and utilized to assemble both piezoelectric nanogenerators(PENGs)and stress/temperature/light sensors.The open cir-cuit voltage(V_(oc))and the density of short circuit current(I_(sc))of the PENG based on the PVDF/5 wt%6H-SiC composite fiber films reach 28.94 V and 0.24μA cm^(-2),showing a significant improvement of 240%and 300%compared with that based on the pure PVDF films.The effect of 6H-SiC nanoparticles(NPs)on inducing interfacial polarization and stress concentration in composite fiber films is proved by first-principles calculation and finite element analysis.The stress/temperature/light sensors based on the composite fiber film also show high sensitivity to the corresponding stimuli.This study shows that the PVDF/6H-SiC composite fiber film is a promising candidate for assembling high-performance energy harvesters and diverse sensors.

Textured CsPbI_(3) nanorods composite fibers for stable high output piezoelectric energy harvester

The utilization of piezoelectric nanogenerator(PENG)based on halide perovskite materials has demonstrated significant promise for energy harvesting applications.However,the challenge of synthesizing halide perovskite materials with both high output performance and stability using a straightforward process persists as a substantial obstacle.Herein,we present the fabrication of CsPbI_(3) nanorods(NRs)exhibiting highly uniform orientation within polyvinylidene fluoride(PVDF)fibers through a simple texture engineering approach,marking the instance of enhancing PENG performance in this manner.The resultant composite fibers showcase a short-circuit current density(I_(sc))of 0.78μAcm^(-2) and an open-circuit voltage(V_(oc)) of 81V,representing a 2.5 fold increase compared to the previously reported highest value achieved without the electric poling process.This outstanding output performance is ascribed to the orientation of CsPbI_(3) NRs facilitated by texture engineering and dipole poling via the self-polarization effect.Additionally,the PENG exhibits exceptional thermal and water stability,rendering it suitable for deployment in diverse and challenging environmental conditions.Our findings underscore the significant potential of textured CsPbI_(3) NRs composite fibers for powering low-power consumer electronics,including commercial LEDs and electronic watches.

Xenotime-type high-entropy(Dy_(1/7)Ho_(1/7)Er_(1/7)Tm_(1/7)Yb_(1/7)Lu_(1/7)Y_(1/7))PO_(4):A promising thermal/environmental barrier coating material for SiCf/SiC ceramic matrix composites

Rare-earth phosphates(REPO4)are regarded as one of the promising thermal/environmental barrier coating(T/EBC)materials for SiCf/SiC ceramic matrix composites(SiC-CMCs)owing to their excellent resistance to water vapor and CaO–MgO–Al_(2)O_(3)–SiO_(2)(CMAS).Nevertheless,a relatively high thermal conductivity(κ)of the REPO_(4) becomes the bottleneck for their practical applications.In this work,novel xenotime-type high-entropy(Dy_(1/7)Ho_(1/7)Er_(1/7)Tm_(1/7)Yb_(1/7)Lu_(1/7)Y_(1/7))PO4(HE(7RE_(1/7))PO_(4))has been designed and synthesized for the first time to solve this issue.HE(7RE_(1/7))PO_(4) with a homogeneous rare-earth element distribution exhibits high thermal stability up to 1750℃and good chemical compatibility with SiO_(2) up to 1400℃.In addition,the thermal expansion coefficient(TEC)of HE(7RE_(1/7))PO_(4)(5.96×10^(−6)℃^(−1) from room temperature(RT)to 900℃)is close to that of the SiC-CMCs.What is more,the thermal conductivities of HE(7RE_(1/7))PO_(4)(from 4.38 W·m^(−1)·K^(−1) at 100℃to 2.25 W·m^(−1)·K^(−1) at 1300℃)are significantly decreased compared to those of single-component REPO4 with the minimum value ranging from 9.90 to 4.76 W·m^(−1)·K^(−1).These results suggest that HE(7RE_(1/7))PO_(4) has the potential to be applied as the T/EBC materials for the SiC-CMCs in the future.

In situ reduced MXene/AuNPs composite toward enhanced charging/discharging and specific capacitance

In this work,gold nanoparticles(AuNPs)decorated Ti_(3)C_(2)T_(x) nanosheets(MXene/AuNPs composite)are fabricated through a self-reduction reaction of Ti_(3)C_(2)T_(x) nanosheets with HAuCl_(4) aqueous solution.The obtained composite is characterized as AuNPs with the diameter of about 23 nm uniformly dispersing on nanosheets without aggregation.The composite(MXene decorated on 4.8 wt% AuNPs)is further employed to construct supercapacitor for the first time with a higher specific capacitance of 278 F·g^(-1) at 5 mV·s^(-1) than that of pure Ti_(3)C_(2)T_(x) and 95% of cyclic stability after 10,000 cycles.Furthermore,MXene/AuNPs composite symmetric supercapacitor with filter paper as separator and H_(2)SO_(4) as electrolyte,is assembled.The supercapacitor exhibits a high volumetric energy density of 8.82 Wh·L^(-1) at a power density of 264.6 W·L^(-1) and ultrafast-charging/discharging performance.It exhibits as a promising candidate applied in integrated and flexible supercapacitors.

Maximizing the mechanical performance of Ti_(3)AlC_(2)-based MAX phases with aid of machine learning

Mechanical properties consisting of the bulk modulus,shear modulus,Young’s modulus,Poisson’s ratio,etc.,are key factors in determining the practical applications of MAX phases.These mechanical properties are mainly dependent on the strength of M–X and M–A bonds.In this study,a novel strategy based on the crystal graph convolution neural network(CGCNN)model has been successfully employed to tune these mechanical properties of Ti_(3)AlC_(2)-based MAX phases via the A-site substitution(Ti_(3)(Al1-xAx)C_(2)).The structure–property correlation between the A-site substitution and mechanical properties of Ti_(3)(Al1-xAx)C_(2)is established.The results show that the thermodynamic stability of Ti_(3)(Al1-xAx)C_(2)is enhanced with substitutions A=Ga,Si,Sn,Ge,Te,As,or Sb.The stiffness of Ti_(3)AlC_(2)increases with the substitution concentration of Si or As increasing,and the higher thermal shock resistance is closely associated with the substitution of Sn or Te.In addition,the plasticity of Ti_(3)AlC_(2)can be greatly improved when As,Sn,or Ge is used as a substitution.The findings and understandings demonstrated herein can provide universal guidance for the individual synthesis of high-performance MAX phases for various applications.

Effect of Sn doping concentration on the oxidation of Al-containing MAX phase(Ti_(3)AlC_(2))combining simulation with experiment

Sn doping is usually adopted to prepare Ti_(3)AlC_(2)in mass production because it can reduce the synthesis temperature while increasing the phase purity.However,excessive Sn doping usually deteriorates the oxidation resistance of Ti_(3)AlC_(2).Therefore,an appropriate Sn doping concentration is a vital issue.In this work,the effect of Sn doping concentration on the oxidation behavior of Ti_(3)AlC_(2)was systematically investigated by combining theoretical calculations and experimental methods.Density function theory calculations suggest that the oxygen adsorption mechanisms for the(001)surface of Ti_(3)AlC_(2)with and without Sn doping are similar,and Ti-O bonds are always preferentially formed.The molecular dynamics simulation further indicates that Al atoms have a faster diffusion rate during the oxidation process.Therefore,a continuous Al_(2)O_(3)layer can form rapidly at high temperature.Nevertheless,when the Sn doping concentration exceeds 10 mol%,the continuity of the Al_(2)O_(3)layer is destroyed,thereby impairing the oxidation resistance of Ti_(3)AlC_(2).Furthermore,oxidation experiments verify the above results.The oxidation mechanisms of Ti3AlC2 with different Sn doping concentrations are also proposed.

Mild fabrication of SiC/C nanosheets with prolonged cycling stability as supercapacitor

A facile and mild route to synthesize C-coated SiC nanosheets(SiC/C NSs)via wet-chemical etching in hydrofluoric acid(HF)at 60°C for 48 h using carbon aluminum silicate(Al_(4)SiC_(4))as raw materials is reported for the first time.HF molecule leads to the breaking of C-Al bonds in Al_(4)SiC_(4),which eventually results in the formation of two-dimensional SiC nanosheets.A carbon layer with a thickness of approximately 1.5 nm is formed on the surface of SiC nanosheets due to the excess carbon.The prepared SiC/C NSs possess a smooth and rectangular sheet with a mean 150 nm in width,500 nm in length and10 nm in thickness,respectively.The crystallographic characterization indicates that 3C-SiC and 2H-SiC coexist and the parallel plane relationship of 3C/2H-SiC heterojunction is(111)_(3C-SiC)//(001)_(2H-SiC).Due to the formed 3C-SiC/2H-SiC heterojunction and graphitic carbon,the fabricated electrode based on SiC/C NSs exhibits prolonged cycling stability and high specific areal capacitance as a promising supercapacitor candidate.It remains 91.2%retention even after 20,000 cycles and 734μF/cm^(2)at a scan rate of 10 m V/s.

New design concept for stableα-silicon nitride based on the initial oxidation evolution at the atomic and molecular levels

As the dominated composition of Si_(3)N_(4)ceramics,α-silicon nitride(α-Si_(3)N_(4))can satisfy the strength and fracture toughness demand in the applications.However,α-Si_(3)N_(4)is oxygen-sensitive at high temperatures,which limits its high-temperature performance.To improve the oxidation resistance ofα-Si_(3)N_(4)ceramics,it is necessary to shed light on the oxidation mechanism.Herein,the initial oxidation ofα-Si_(3)N_(4)was systematically studied at the atomic and molecular levels.The density functional theory(DFT)calculation denotes that the(001)surface ofα-Si_(3)N_(4)has the best stability at both room temperature and high temperature.Besides,the oxidation process of theα-Si_(3)N_(4)(001)surface consists of O adsorption and N desorption,and the consequent formation of nitrogen-vacancy(VN)is the key step for further oxidation.Moreover,the molecular dynamics(MD)simulation indicates that the oxidation rate ofα-Si_(3)N_(4)(100)surface is slower than that ofα-Si_(3)N_(4)(001)surface due to the lower N concentration at the outermost layer.Therefore,the oxidation resistance ofα-Si_(3)N_(4)can be improved by regulating the(100)surface as the dominant exposure surface.In addition,reducing the concentration of N on the final exposed surface ofα-Si_(3)N_(4)by mean of constructing the homojunction of the Si-terminal(100)surface and other N-containing surfaces(such as(001)surface)should be also a feasible approach.

Bifunctional hierarchical NiCoP@FeNi LDH nanosheet array electrocatalyst for industrial-scale high-current-density water splitting

Aiming to design and prepare non-noble metal electrocatalysts for hydrogen production at high current density(HCD),NiCoP@FeNi LDH hierarchical nanosheets were deposited on nickel foam progressively us-ing a hydrothermal-phosphorization-electrodeposition process.For hydrogen evolution reaction(HER)and oxygen evolution reaction(OER),NiCoP@FeNi LDH/NF requires only 195 and 230 mV overpotentials to reach 1000 mA cm−2,respectively.For overall water splitting,only 1.70 V is required at 1000 mA cm−2.This is the largest value for non-noble metal-based electrocatalysts reported so far at HCD.The hierarchi-cal structure exhibits good electron transport capability and the porous-macroporous structure enhances the gas release rate,resulting in enhanced hydrogen production at HCD.Especially,the synergistic effect of NiCoP and FeNi LDH contributes to the adsorption-desorption equilibrium of intermediate radicals dur-ing the reaction process and ultimately enhances the catalytic activity.This work provides useful direction for industrial-scale hydrogen production applications at HCD.