scholarly journals Bulk high-entropy nitrides and carbonitrides

2020 ◽  
Vol 10 (1) ◽  
Author(s):  
Olivia F. Dippo ◽  
Neda Mesgarzadeh ◽  
Tyler J. Harrington ◽  
Grant D. Schrader ◽  
Kenneth S. Vecchio
Keyword(s):  
Mechanical Properties ◽  
High Temperature ◽  
Configurational Entropy ◽  
Temperature Stability ◽  
High Hardness ◽  
Valence Electron Concentration ◽  
High Temperature Stability ◽  
High Entropy ◽  
Rule Of Mixtures ◽  
Traditional Ceramics

AbstractHigh-entropy ceramics have potential to improve the mechanical properties and high-temperature stability over traditional ceramics, and high entropy nitrides and carbonitrides (HENs and HECNs) are particularly attractive for high temperature and high hardness applications. The synthesis of 5 bulk HENs and 4 bulk HECNs forming single-phase materials is reported herein among 11 samples prepared. The hardness of HENs and HECNs increased by an average of 22% and 39%, respectively, over the rule-of-mixtures average of their monocarbide and mononitride precursors. Similarly, elastic modulus values increased by an average of 17% in nitrides and 31% in carbonitrides over their rule-of-mixtures values. The enhancement in mechanical properties is tied to an increase in the configurational entropy and a decrease in the valence electron concentration, providing parameters for tuning mechanical properties of high-entropy ceramics.

The Influence of Degree of Polymerization on Precursor-Derived Si-B-C-N Ceramics

2010 ◽  
Vol 650 ◽  
pp. 355-360
Author(s):  
Xiang Geng ◽  
X. Huang ◽  
Ya Jing Li ◽  
Song Li ◽  
Xiao Bin Shi
Keyword(s):  
High Temperature ◽  
Solid State ◽  
Amorphous Materials ◽  
Chemical Properties ◽  
Temperature Stability ◽  
High Hardness ◽  
Nitrogen Atmosphere ◽  
Degree Of Polymerization ◽  
Pyrolysis Process ◽  
High Temperature Stability

Precursor derived Si-B-C-N ceramic is a kind of amorphous materials with high hardness, low density, durability at extremely high temperature. The materials show a great potential to be used in the field of the Thermal Protective System (TPS). The physical states and chemical properties of the amorphous materials greatly depend on the starting materials. The effect of degree of polymerization (DP) of the precursor on the pyrolysis process and the characteristics of the amorphous Si-B-C-N materials are studied. The SiBCN-based preceramic polymer synthesized by dichloromethylvinylsilane, ammonia and BH3•SMe2. Dichloromethylvinylsilane reacted with ammonia and BH3•SMe2 in toluene or tetrahydrofuran (THF) as solvent in the presence of catalytic amounts of pyridine. The polymeric precursors were cured at low temperature to obtain solid-state precursors. Pyrolysis process of the solid-state precursors under various temperatures and carried out in nitrogen atmosphere. The results showed that DP of the precursor influences the pyrolysis process and the high temperature stability of the Si-B-C-N amorphous ceramics.

The Research on Hard Cutting the Powder Metallurgy Valve Seat

2016 ◽  
Vol 693 ◽  
pp. 1177-1181
Author(s):  
Ning Ding ◽  
Hai Dong Yang ◽  
Xiao Jun Niu ◽  
Hong Yun Chen
Keyword(s):  
Surface Roughness ◽  
Wear Resistance ◽  
High Temperature ◽  
Powder Metallurgy ◽  
Temperature Stability ◽  
High Hardness ◽  
Dimensional Accuracy ◽  
High Temperature Stability ◽  
Valve Seat ◽  
Hard Cutting

Powder metallurgy valve seat is an important part for engine; the material has excellent properties such as the wear-resistance of high temperature, corrosion proof and high temperature stability etc. But because of its high hardness, porous nature and contains many microscopic characteristics of the hard particles and the like, common tools cut these parts wear out quickly. And the valve seat requires higher dimensional accuracy and surface roughness, so these bring a lot of difficulties to cut these parts. Because of Polycrystalline Cubic Boron Nitride (hereafter referred to as PCBN) cutting tool has such advantages as high hardness; wear resistance; minimum surface roughness, so it has a great advantage on hard cutting the powder metallurgy valve seat. By hard cutting the powder metallurgy valve seat experiments, to research on the wear form and the cutting parameters impact on the cutting force.

TD-NICKEL

Alloy Digest ◽  
1965 ◽  
Vol 14 (7) ◽  
Keyword(s):  
Mechanical Properties ◽  
Fracture Toughness ◽  
Corrosion Resistance ◽  
High Temperature ◽  
Melting Point ◽  
Physical Properties ◽  
Temperature Stability ◽  
Heat Treating ◽  
High Temperature Stability ◽  
Temperature Performance

Abstract TD-NICKEL is a dispersion hardened nickel alloy offering high-temperature stability and useful mechanical properties virtually to the melting point of the base metal. It is easy to fabricate. It is capable of operating for long periods of time at high temperatures without degradation of mechanical properties. This datasheet provides information on composition, physical properties, and tensile properties as well as fracture toughness and fatigue. It also includes information on high temperature performance and corrosion resistance as well as forming, heat treating, machining, and joining. Filing Code: Ni-103. Producer or source: E. I. DuPont de Nemours & Company Inc..

Processing, mechanical properties and oxidation behavior of TaC and HfC composites containing 15 vol% TaSi2 or MoSi2

2009 ◽  
Vol 24 (6) ◽  
pp. 2056-2065 ◽  
Author(s):  
Diletta Sciti ◽  
Laura Silvestroni ◽  
Stefano Guicciardi ◽  
Daniele Dalle Fabbriche ◽  
Alida Bellosi
Keyword(s):  
Mechanical Properties ◽  
Fracture Toughness ◽  
High Temperature ◽  
Mechanical Strength ◽  
Hot Pressing ◽  
Room Temperature ◽  
Oxidation Behavior ◽  
Temperature Stability ◽  
High Temperature Stability ◽  
Better Than

Fully dense HfC and TaC-based composites containing 15 vol% TaSi2 or MoSi2 were produced by hot pressing at 1750–1900 °C. TaSi2 enhanced the sinterability of the composites and nearly fully dense materials were obtained at lower temperatures than in the case of MoSi2-containing ones. The TaC-based composites performed better than HfC composites at room temperature, showing values of mechanical strength up to 900 MPa and a fracture toughness of 4.7 MPa·m1/2. However, preliminary oxidation tests carried out in air at 1600 °C revealed that HfC-based composites have a superior high temperature stability compared to TaC-based materials.

Fundamental Core Effects in Transition Metal High-Entropy Alloys: “High-Entropy” and “Sluggish Diffusion” Effects

2021 ◽  
Vol 29 ◽  
pp. 75-93
Author(s):  
Abhishek Mehta ◽  
Yong Ho Sohn
Keyword(s):  
High Temperature ◽  
Temperature Stability ◽  
High Temperature Strength ◽  
High Entropy Alloys ◽  
High Temperature Stability ◽  
High Entropy ◽  
Diffusion Effects ◽  
Initial Work ◽  
Entropy Effect ◽  
Sluggish Diffusion

High entropy alloys (HEAs) are equimolar multi-principal-element alloys (MPEAs) that are different from traditional solvent-based multicomponent alloys based on the concept of alloy design. Based on initial work by Yeh and co-workers, HEAs were postulated to exhibit four “core” effects: high entropy, sluggish diffusion, lattice distortion, and cocktail effect. Out of these four proposed core effects, “high entropy” and “sluggish diffusion” effects were most debated in the literature as these core effects directly affect the thermodynamic and kinetic understanding of HEAs. The initial work on HEAs by several researchers utilized these effects to indirectly support the experimentally observed “unique” properties, without independent investigation of these core effects. The presumed implications of these core effects resulted in justification or generalization of properties to all HEAs, e.g., all HEAs should exhibit high temperature stability based on high entropy effect, high temperature strength owing to limited grain growth, good diffusion barrier application due to sluggish diffusion kinetics, etc. However, many recent studies have challenged these core effects, and suggested that not all HEAs were observed to exhibit these core effects.

scholarly journals The formation and stability of bulk amorphous and high entropy alloys

2021 ◽  
Vol 4 (1) ◽  
pp. 51-57
Author(s):  
Attila Szabó ◽  
Krisztián Bán ◽  
József Hlinka ◽  
Judit Pásztor ◽  
Antal Lovas
Keyword(s):  
Amorphous Alloys ◽  
Configurational Entropy ◽  
Temperature Stability ◽  
High Entropy Alloy ◽  
Alloy Formation ◽  
High Entropy Alloys ◽  
High Temperature Stability ◽  
High Entropy ◽  
Phase Stabilization ◽  
Fcc Phase

Abstract Two kinds of phase stabilization mechanism are discussed and compared: the first is characteristic of the formation of bulk amorphous alloys, in which the high supercooling ability of multicomponent liquids is responsible for the glassy phase stabilization. Here the hindered nucleation of crystalline phases is the center phenomenon. The origin of this hindering is the slowing atomic mobility in the supercooling melt. In contrast the melt supercooling is negligible during the high entropy alloy formation. It is believed that stability of the crystalline single fcc phase is the consequence of the characteristic of high configurational entropy at high temperatures. However, the significance of this entropy-dominated stabilization is overestimated in several references. It has been concluded that transition metal contraction (arising from the d electron participation in the overall bonding state) does also contribute to the high temperature stability of fcc single phase in the high entropy alloys.

Investigation on Microstructure, Wave Absorbing Properties and High Temperature Stability for (Mg0.2Ni0.2Co0.2Cu0.2Zn0.2)O High-entropy Ceramics

2021 ◽  
Author(s):  
Shen Bao ◽  
Yongqiang Chen ◽  
Fei yue Hu ◽  
Xiao han Wang ◽  
B.B. Fan ◽  
...  
Keyword(s):  
High Temperature ◽  
Temperature Stability ◽  
High Temperature Stability ◽  
Promising Candidate ◽  
High Entropy ◽  
Microwave Absorbing Properties ◽  
Interface Defects ◽  
Conventional Sintering ◽  
Salt Phase ◽  
Sintering Method

Abstract In this work, high entropy (Mg0.2Ni0.2Co0.2Cu0.2Zn0.2)O ceramics were fabricated with three different precursors by conventional sintering method. SEM and XRD analyses revealed the microstructure is related to the precursors while the phase composition is independent with the precursors. Compared with S1 and S2 samples, the S3 samples show well distributed small pores located inside the grain or at the grain boundary. While all the samples exhibit a single rock salt phase. The RL values could reach to -30.5 dB (S3) at 6.8 GHz under the thickness of 4.0 mm, the excellent microwave absorbing properties stem from the bonding interface defects, the micro-pores and many grain boundaries. The (Mg0.2Ni0.2Co0.2Cu0.2Zn0.2)O ceramics keep stable under 1200 oC for S3. The results demonstrate that (Mg0.2Ni0.2Co0.2Cu0.2Zn0.2)O ceramics may be a promising candidate for microwave absorption materials at high temperature.

Revolutionary High-entropy Zr-Y-Yb-Ta-Nb-O Oxides for Next Generation Thermal Barrier Coating Applications

2021 ◽  
Author(s):  
Yao Yao ◽  
Fan Yang ◽  
Xiaofeng Zhao ◽  
Ping Xiao
Keyword(s):  
High Temperature ◽  
Coefficient Of Thermal Expansion ◽  
Temperature Stability ◽  
Thermal Barrier ◽  
Next Generation ◽  
Transformation Toughening ◽  
High Temperature Stability ◽  
High Entropy ◽  
Barrier Coating ◽  
Phase Transformation Toughening

Abstract We report a revolutionary ceramic material with exceptional high temperature stability and superior thermo-mechanical properties for next generation thermal barrier coatings (TBCs) for aeroengines. The multicomponent oxides (Zr1 − 4xYxYbxTaxNbxO2) designed via a high entropy concept could exhibit a double tetragonal phase. The optimized composition breaks the limitation of intrinsic brittleness in previously reported TBC candidate materials and shows a superior toughness up to ~ 4.59 MPa m1/2 due to ferroelastic and phase transformation toughening mechanisms. It also shows a remarkable high temperature stability at 1600 ºC, which is almost 400 ºC higher than the state-of-the-art yttria stabilized zirconia TBC material. In addition, it also exhibits a significantly lower thermal conductivity (~ 1.37 W∙m− 1∙K− 1 at 900 ºC) and a higher coefficient of thermal expansion (~ 11.3 × 10− 6 K− 1 at 1000 ºC), as well as excellent corrosion resistance to molten silicate (~ 2.9 µm/h at 1300 ºC). This work provides a new approach to design ceramics by extending the high-entropy concept to both medium-entropy and high-entropy compositions searching for multifunctional properties.

scholarly journals Effects of a Reactive Phosphorus–Sulfur Containing Flame-Retardant Monomer on the Flame Retardancy and Thermal and Mechanical Properties of Unsaturated Polyester Resin

Polymers ◽  
2020 ◽  
Vol 12 (7) ◽  
pp. 1441 ◽  
Author(s):  
Kang Dai ◽  
Zhenzhen Deng ◽  
Guyue Liu ◽  
Yutong Wu ◽  
Wenbin Xu ◽  
...  
Keyword(s):  
Mechanical Properties ◽  
Fourier Transform ◽  
High Temperature ◽  
Polyester Resin ◽  
Unsaturated Polyester ◽  
Temperature Stability ◽  
Thermal And Mechanical Properties ◽  
High Temperature Stability ◽  
Reactive Phosphorus ◽  
Sulfur Containing

A novel reactive phosphorus and sulfur-containing monomer (bis(acryloxyethyldiphenylphosphate)sulfone, BADPS) was synthesized to enhance the comprehensive performance of unsaturated polyester resin (UPR), and corresponding flame-retardant unsaturated polyester resins (FR-UPRs) with various amounts of BADPS were prepared by radical bulk polymerization. The flame retardancy and thermal and mechanical properties of the UPR samples were investigated by limiting oxygen index (LOI) measurements, cone calorimetry, differential scanning calorimetry (DSC), a thermogravimetric analysis (TGA), and a tension test. The results showed that the introduction of BADPS remarkably enhanced the flame resistance and high-temperature stability, as well as the tensile performance of UPR. Scanning electron microscopy (SEM), Fourier transform infrared (FTIR), and Raman spectroscopy studies revealed that BADPS can efficaciously promote the formation of UPR char residue with an improved microstructure and increased graphitization degree, which enhancedthe high-temperature stability and char yield of UPR. Additionally, a thermogravimetry-Fourier transform infrared (TG-FTIR) analysis corroborated that the evolution of combustible volatiles from UPR decomposition was substantially restrained by the incorporation of BADPS, which is beneficial for the suppression of fire hazards in UPR.

REYNOLDS 390 and A390

Alloy Digest ◽  
1971 ◽  
Vol 20 (8) ◽  
Keyword(s):  
Mechanical Properties ◽  
Wear Resistance ◽  
Corrosion Resistance ◽  
High Temperature ◽  
Physical Properties ◽  
High Hardness ◽  
Heat Treating ◽  
Silicon Alloys ◽  
Aluminum Silicon Alloys ◽  
Temperature Performance

Abstract REYNOLDS 390 and A390 are hypereutectic aluminum-silicon alloys having excellent wear resistance coupled with good mechanical properties, high hardness, and low coefficients of expansion. This datasheet provides information on composition, physical properties, hardness, elasticity, and tensile properties as well as fatigue. It also includes information on high temperature performance and corrosion resistance as well as casting, heat treating, and machining. Filing Code: Al-203. Producer or source: Reynolds Metals Company.

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