Effect of Grain Boundary Composition on High-Temperature Mechanical Properties of Hot-Pressed Silicon Carbide Sintered with Yttria

2007 ◽  
pp. 139-145
Author(s):  
Donna Hermanutz ◽  
Hagen Klemm
Keyword(s):  
Mechanical Properties ◽  
Silicon Carbide ◽  
High Temperature ◽  
Grain Boundary ◽  
Boundary Composition ◽  
High Temperature Mechanical Properties

Study on the Heat–Treatment Reinforcement of Aluminum Nitride–Silicon Carbide Composites

1993 ◽  
Vol 327 ◽  
Author(s):  
Li Ningfang ◽  
Zhang Hongquan ◽  
Wang Guomei
Keyword(s):  
Mechanical Properties ◽  
Heat Treatment ◽  
Silicon Carbide ◽  
Phase Composition ◽  
High Temperature ◽  
Grain Boundary ◽  
Aluminum Nitride ◽  
Phase Structure ◽  
Glass Phase ◽  
Boundary Phase

AbstractThe effects of heat – treatment on the mechanical properties of AIN – SiC whisker composites with Y2O3 and SiO2 additives has been studied. When the sample containing 10 wt% Y2O3 +SiO2 (Y2O3/SiO2= 1/0. 66) was treated at 1300°C in air for 140 hours the strength of compositqs was raised from 481 MPa to 784 MPa.The phase composition, microstructure and grain boundary phase structure have been characterized by combining XRD, SEM, TEM/EDXA and HREM techniques. The reinforcement mechanism of the composites results from crystallization of the glass phase in the grain boundary at the high temperature oxidizing atmosphere to form the crossing structure of 2Hδ Sialon fibrous phase and SiC whisker.

Solid State Sintering of SiC-Ceramics

2009 ◽  
Vol 624 ◽  
pp. 71-89 ◽  
Author(s):  
Koushik Biswas
Keyword(s):  
Mechanical Properties ◽  
Silicon Carbide ◽  
High Temperature ◽  
Solid State ◽  
Grain Boundary ◽  
Hot Pressing ◽  
Amorphous Film ◽  
Structure Property ◽  
Secondary Phases ◽  
Sintering Aid

The most interesting feature in silicon carbide is the structure-property relation where the formation of different types of microstructure due to different structural modifications (polytypism) and grain-boundary/interfacial phase chemistry dictate the final properties of the monoliths. Since synthesis of SiC in last century, several methods such as hot pressing with a sintering aid (B, C), pressureless sintering with a sintering aid (B, C, Al) and reaction bonded (Si-SiC) were used to fabricate dense SiC. A newer method of fast sintering (spark plasma sintering) using pulsed current is also employed to consolidate nano/submicron size SiC with or without additives. The solid state sintered SiC materials have fine-grained equiaxed microstructure (grain size 1 to 4 µm) with thin layer of intergranular phases (amorphous film), exhibit moderate high-temperature creep and oxidation resistance, fracture toughness (3 to 4 MPam1/2) and have highly flaw-sensitive strength at room temperature. The high temperature mechanical properties are highly influenced by the presence of free C, Al and B + C containing grain-boundary phases. Moreover, during prolong processing, abnormal grain growth occurs resulting in anisotropic -SiC phase formation. The Si-SiC materials are poor candidates for high-temperature applications due to the limit set by the melting point of silicon, and the limitations of hot pressing (HPSiC) as a densification technique are well known. SPSed SiC without sintering additive revealed inferior mechanical properties attributed to poor bonding between adjacent grains. In the present survey, an overview of the new developments in silicon carbide processing and properties will be presented together with the information on structure-properties correlationship. Information on the structure of the grain-boundary/secondary phases and interfaces until now was not comprehensively analyzed.

Characterization of grain boundary phases in Si3N4 sintered using Y-Si-Al-O-N additives

1990 ◽  
Vol 48 (4) ◽  
pp. 1070-1071
Author(s):  
C. Koehler ◽  
G. Thomas
Keyword(s):  
Mechanical Properties ◽  
High Temperature ◽  
Silicon Nitride ◽  
Grain Boundary ◽  
Grain Boundaries ◽  
Elevated Temperatures ◽  
Secondary Phases ◽  
Amorphous Phases ◽  
High Temperature Mechanical Properties

The usefulness of silicon nitride as a high temperature ceramic can be limited by the presence of amorphous phases at the grain boundaries. Dense silicon nitride ceramics are produced using pressureless sintering of Si3N4 with Y-Si-Al-O-N additives. When these additives are left as a glassy phase at the grain boundaries and triple grain junctions, the mechanical properties at elevated temperatures are weakened due to these low viscous glasses. Post-sintering heat treatments and close compositional control can be effective in transforming the glass into crystalline phases at the grain boundaries thereby increasing the refractoriness.To optimize high temperature mechanical properties, processing must be controlled not only to fully crystallize the grain boundaries but also to avoid certain unstable secondary phases whose oxidation leads to large molar volume changes which causes possible cracking. Transmisssion electron microscopy and x-ray microanalysis (EDS) are significant methods to characterize the amorphous grain boundary pockets and to identify the crystalline grain boundary phases.

scholarly journals High-Temperature Mechanical Properties of 4.5%Al δ-TRIP Steel

2019 ◽  
Vol 9 (23) ◽  
pp. 5094
Author(s):  
Dayu Chen ◽  
Heng Cui ◽  
Rudong Wang
Keyword(s):  
Mechanical Properties ◽  
Phase Transformation ◽  
High Temperature ◽  
Grain Boundary ◽  
Trip Steel ◽  
Scanning Calorimetry ◽  
The Third ◽  
High Temperature Mechanical Properties ◽  
Brittle Zone ◽  
Austenite Grain Boundary

The high-temperature mechanical properties of a 4.5% Al-containing δ-transformation-induced plasticity (TRIP) steel were studied by using the Gleeble 3500 thermomechanical simulator. The zero ductility temperature (ZDT) and the zero strength temperature (ZST) were measured, and the brittle zones were divided. The phase transformation zone was determined by differential scanning calorimetry (DSC). The temperature of the phase transformation and the proportion of the phase were calculated by the Thermo-Calc software. The ZDT and the ZST of the 4.5% Al-containing δ-TRIP steel are 1355 and 1405 °C, respectively. The first brittle zone and the third brittle zone of the steel are 1300–1350 °C and 800–975 °C, respectively. The reason for the embrittlement of the third brittle zone of the 4.5% Al-containing δ-TRIP steel is that the α-ferrite formed at the austenite grain boundary causes the sample to crack along the grain boundary under stress. The ductility of the 4.5% Al-containing δ-TRIP steel decreases first and then increases with the increase of the α-ferrite. When the proportion of the α-ferrite reaches 37%, the reduction of area (RA) of the 4.5% Al-containing δ-TRIP steel is reduced to 44%. The 4.5% Al-containing δ-TRIP steel has good resistance to the high-temperature cracking.

TEM Studies of Grain Boundary Films in Si3N4 Ceramics

1991 ◽  
Vol 49 ◽  
pp. 930-931
Author(s):  
H.-J. Kleebe ◽  
J.S. Vetrano ◽  
J. Bruley ◽  
M. Rühle
Keyword(s):  
Mechanical Properties ◽  
High Temperature ◽  
Silicon Nitride ◽  
Hot Isostatic Pressing ◽  
Amorphous Film ◽  
Liquid Phase Sintering ◽  
Second Phase ◽  
High Temperature Mechanical Properties ◽  
Triple Points ◽  
Boundary Films

It is expected that silicon nitride based ceramics will be used as high-temperature structural components. Though much progress has been made in both processing techniques and microstructural control, the mechanical properties required have not yet been achieved. It is thought that the high-temperature mechanical properties of Si3N4 are limited largely by the secondary glassy phases present at triple points. These are due to various oxide additives used to promote liquid-phase sintering. Therefore, many attempts have been performed to crystallize these second phase glassy pockets in order to improve high temperature properties. In addition to the glassy or crystallized second phases at triple points a thin amorphous film exists at two-grain junctions. This thin film is found even in silicon nitride formed by hot isostatic pressing (HIPing) without additives. It has been proposed by Clarke that an amorphous film can exist at two-grain junctions with an equilibrium thickness.

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