scholarly journals Densification of Ceramic Matrix Composite Preforms by Si2N2O Formed by Reaction of Si with SiO2 under High Nitrogen Pressure. Part 2: Materials Properties

2021 ◽  
Vol 5 (7) ◽  
pp. 179
Author(s):  
Brice Taillet ◽  
René Pailler ◽  
Francis Teyssandier
Keyword(s):  
Elastic Modulus ◽  
Yield Strength ◽  
Room Temperature ◽  
Outer Part ◽  
Ceramic Matrix Composites ◽  
Ceramic Matrix ◽  
Nitrogen Pressure ◽  
High Nitrogen ◽  
Yield Strain ◽  
High Nitrogen Pressure

Ceramic matrix composites (CMCs) have been prepared and optimized as already described in part I of this paper. The fibrous preform made of Hi-Nicalon S fibers was densified by a matrix composed of Si2N2O prepared inside the CMC by reacting a mixture of Si and SiO2 under high nitrogen pressure. This part describes the oxidation resistance and mechanical properties of the optimized CMC. The CMC submitted to oxidation in wet oxygen at 1400 °C for 170 h exhibited an oxidation gradient from the surface to almost the center of the sample. In the outer part of the sample, Si2N2O, Si3N4 and SiC were oxidized into silica in the cristobalite-crystallized form. The matrix microstructure looks similar to the original one at the center of the sample, while at the surface large pores are observed and the fiber/matrix interphase is consumed by oxidation. The elastic modulus and the hardness measured at room temperature by nano-indentation are, respectively, 100 and 8 GPa. The elastic modulus measured at room temperature by tensile tests ranges from 150 to 160 GPa and the ultimate yield strength from 320 to 390 MPa, which corresponds to a yield strain of about 0.6%. The yield strength identified by acoustic emission is about 40 MPa.

scholarly journals Densification of Ceramic Matrix Composite Preforms by Si2N2O Formed by Reaction of Si with SiO2 under High Nitrogen Pressure. Part 1: Materials Synthesis

2021 ◽  
Vol 5 (7) ◽  
pp. 178
Author(s):  
Brice Taillet ◽  
René Pailler ◽  
Francis Teyssandier
Keyword(s):  
Heating Rate ◽  
Ceramic Matrix Composite ◽  
Ceramic Matrix Composites ◽  
Ceramic Matrix ◽  
Nitrogen Pressure ◽  
Major Influence ◽  
High Nitrogen ◽  
Joule Effect ◽  
The Matrix ◽  
High Nitrogen Pressure

Ceramic matrix composites (CMCs) have been designed and developed for extreme operating environments. The aim of the present study is to look for a rapid densification process providing a high level of material performance. The fibrous preform was made of Hi-Nicalon S fibers woven in a 3D interlock weave. The matrix was composed of Si2N2O prepared inside the CMCs by reacting a mixture of Si and SiO2 under high nitrogen pressure (1 to 3 MPa). Silica was either impregnated by slurry or obtained by oxidation of silicon grains inside the preform. The synthesis reaction was initiated by heating the impregnated preform by means of a carbon resistor submitted to Joule effect. Composition, homogeneity and porosity of the formed matrix were studied and interpreted as a function of the experimental parameters (nitrogen pressure, heating rate of the preform) as well as the recorded thermal history of the process. The present results show that the matrix formation is almost completed in less than one minute. Melting of silicon has a major influence on the process. Competition was observed between the formation of Si3N4 and Si2N2O, which could be mainly controlled by the heating rate of the preform and the nitrogen partial pressure.

Chemically activated combustion synthesis of AlON under high nitrogen pressure

2021 ◽  
Vol 232 ◽  
pp. 111560
Author(s):  
Tigran G. Akopdzhanyan ◽  
Sergey I. Rupasov ◽  
Stepan Vorotilo
Keyword(s):  
Combustion Synthesis ◽  
Nitrogen Pressure ◽  
High Nitrogen ◽  
High Nitrogen Pressure

The influence of erbium on the physical properties of GaN crystals grown from N solution in Ga at high nitrogen pressure

2000 ◽  
Vol 18 (1-6) ◽  
pp. 35-39
Author(s):  
H. Teisseyre ◽  
T. J. Ochalski ◽  
P. Perlin ◽  
T. Suski ◽  
M. Leszczynski ◽  
...  
Keyword(s):  
Physical Properties ◽  
Nitrogen Pressure ◽  
High Nitrogen ◽  
High Nitrogen Pressure

Fatigue Behavior of Cement Asphalt Emulsion Mortar

2016 ◽  
Vol 847 ◽  
pp. 25-30 ◽  
Author(s):  
Dong Mei Tian ◽  
Jian Yin
Keyword(s):  
Elastic Modulus ◽  
Yield Strength ◽  
High Speed ◽  
Room Temperature ◽  
Fatigue Behavior ◽  
Permanent Deformation ◽  
Negative Temperature ◽  
Fatigue Tests ◽  
Asphalt Emulsion ◽  
Slab Track

As one of the key components of non-ballast slab track in high speed railway, cement asphalt emulsion mortar (CAM) has low compressive strength and low elastic modulus. This makes CAM possible to be served as supporting, height-adjusting, vibration-dissipating and deformation-fitting sandwich-layer between pre-stress slab and concrete roadbed. To study the fatigue behavior of the CAM, fatigue tests were conducted at room temperature and negative temperature, respectively. The permanent strain, elastic modulus and yield strength of fatigue-tested specimens were compared to the reference one. The results showed that the small permanent deformation lead to very little displacement differences among the slab track system. Secondly, the elastic modulus and yield strength of fatigue test specimens were both higher than that of reference one. Because the fatigue process might strengthen the CAM by compacting micro-cracks. Additionally, arising from the temperature sensitivity of asphalt, viscosity behavior of asphalt mortar at room temperature is changed to brittleness behavior at negative temperature.

Dynamic Mechanical Properties of 2D-C/SiC and 2D-SiC/SiC

2019 ◽  
Vol 956 ◽  
pp. 244-252
Author(s):  
Xiao Ju Gao ◽  
Chao Li ◽  
Hasigaowa ◽  
Zhi Peng Li ◽  
Yu Guang Bao ◽  
...  
Keyword(s):  
Strain Rate ◽  
Room Temperature ◽  
Ceramic Matrix Composites ◽  
Rate Sensitivity ◽  
Ceramic Matrix ◽  
Dynamic Mechanical Properties ◽  
Matrix Composites ◽  
Fiber Reinforced ◽  
Mechanical Behaviors ◽  
Sic Composites

The quasi-static and dynamic compressive mechanical behaviors of two kinds of fiber reinforced SiC-matrix composites including 2D-C/SiC and 2D-SiC/SiC were investigated. Their compressive behaviors of materials at room temperature and strain rate from 10-4 to 104 /s were studied. The fracture surfaces and damage morphology were observed by scanning electron microscopy (SEM). The results showed that the dynamic failure strengths of the two kinds of fiber reinforced SiC-matrix composites obey the Weibull distribution. The Weibull modulus of the two materials were 13.70 (2D-C/SiC) and 5.66 (2D-SiC/SiC), respectively. It was found that the two kinds of fiber reinforced ceramic matrix composites presented a transition from brittle to tough with the decrease of strain rate. The 2D-SiC/SiC materials demonstrated a more HYPERLINK "http://dict.cnki.net/dict_result.aspx?searchword=%e6%98%be%e8%91%97%e7%9a%84&tjType=sentence&style=&t=remarkable"significant strain rate sensitivity and smoother fracture surface compared to the 2D-C/SiC composites, implying that the former composites present brittle features. This was because the SiC/SiC composites possessed high bonding strength in interface of fiber/fiber and fiber/matrix is very strong.

Ageing Effect on Mechanical Properties of Machined Nanostructures

2013 ◽  
Vol 683 ◽  
pp. 145-149
Author(s):  
Xing Lei Hu ◽  
Ya Zhou Sun ◽  
Ying Chun Liang ◽  
Jia Xuan Chen
Keyword(s):  
Mechanical Properties ◽  
Elastic Modulus ◽  
Yield Strength ◽  
Md Simulation ◽  
Fracture Strain ◽  
Machining Process ◽  
Ageing Process ◽  
Yield Strain ◽  
Before And After ◽  
Mc Simulation

Monte Carlo (MC) method and molecular dynamics (MD) are combined to analyze the influence of ageing on mechanical properties of machined nanostructures. Single crystal copper workpiece is first cut in MD simulation, and then the machined workpiece is used in MC simulation of ageing process, finally the tensile mechanical properties of machined nanostructures before and after ageing are investigated by MD simulation. The results show that machining process and ageing have obvious influence of tensile mechanical properties. After machining, the yield strength, yield strain, fracture strain and elastic modulus reduce by 36.02%, 28.86%, 20.79% and 7.16% respectively. However, the yield strength, yield strain and elastic modulus increase by 4.84%, 1.41% and 1.02% respectively, fracture strain reduce by 24.53% after ageing process. To research the ageing processes of machined nanostructures by MC simulation is both practical and meaningful.

Thermodynamics and Growth of GaN Single Crystals Under Pressure

1997 ◽  
Vol 499 ◽  
Author(s):  
S. Porowski ◽  
I. Grzegory ◽  
S. Krukowski
Keyword(s):  
Dislocation Density ◽  
Single Crystals ◽  
Experimental System ◽  
Nitrogen Pressure ◽  
Liquid Gallium ◽  
High Nitrogen ◽  
Substrate Quality ◽  
Homoepitaxial Growth ◽  
Device Structures ◽  
High Nitrogen Pressure

GaN is recently considered as the most important material for blue and ultraviolet optoelectronics. The device structures are usually grown on foreign substrates which results in high density of dislocations above 108cm−2. The application of high N2 pressure gives a unique possibility of growing of GaN single crystalline substrates which allows to lower dislocation density in epitaxial layers by 3–4 orders of magnitude.In this paper, the results of high nitrogen pressure study of properties of Al-N, Ga-N and In-N systems are presented. The results include the phase diagrams in large range of pressures and temperatures (up to 2 GPa and 2000K) and also growth of GaN single crystals from atomic nitrogen solution in liquid gallium. The kinetic limitations of dissolution of N2 in liquid Al, Ga and In will be discussed. It follows, that the best conditions for crystal growth at available pressures and temperatures can be achieved for GaN.The high nitrogen pressure experimental system equipped with multi-zone internal furnace was used for growth of high quality GaN crystals. At present both n-type and semi-insulating substrate quality GaN crystals with surface area up to 1cm2, with dislocation density below 105 cm-2 are routinely obtained and successfully used for homoepitaxy.Some results concerning homoepitaxial growth by the MOCVD and MBE methods are shortly reviewed. In particular, it is shown that perfectly matched (strain free) GaN layers can be deposited on the highly resistive GaN:Mg substrates.

High nitrogen pressure solution growth of GaN in multi feed-seed configuration

2012 ◽  
Vol 9 (3-4) ◽  
pp. 453-456 ◽  
Author(s):  
M. Bockowski ◽  
B. Lucznik ◽  
T. Sochacki ◽  
B. Sadovyi ◽  
G. Nowak ◽  
...  
Keyword(s):  
Nitrogen Pressure ◽  
Solution Growth ◽  
Pressure Solution ◽  
High Nitrogen ◽  
High Nitrogen Pressure

Tensile Behavior of 2.5D C/SiCN Composites

2012 ◽  
Vol 217-219 ◽  
pp. 67-70
Author(s):  
Yi Xia ◽  
Hong Fang Li
Keyword(s):  
Tensile Stress ◽  
Room Temperature ◽  
Ceramic Matrix Composites ◽  
Ceramic Matrix ◽  
Tensile Behavior ◽  
Matrix Composites ◽  
Stress Growth ◽  
C Fiber ◽  
Cracks Propagation ◽  
Thermal Stress Relaxation

Tensile behavior of C fiber reinforced amorphous SiCN ceramic matrix composites (C/SiCN ) were investigated by tensile machine. The microstructure morphologies were observed by scanning electron microscope. The results indicate that the tensile stress-strain curves of C/SiCN composites dispaly typical elastic deformation and cracks propagation stages. The 1500°C pre-sabilization treatment of C/SiCN in vacuum facilitates room temperature tensile stress growth. The higher treated temperature such as 1900°C is yet opposite. The reasons were attributed to thermal stress relaxation of C/SiCN after pre-stabilization treatment in vacuum.

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