Microstructural Design and Control of Silicon Nitride Ceramics

MRS Bulletin ◽  
1995 ◽  
Vol 20 (2) ◽  
pp. 38-41 ◽  
Author(s):  
Mamoru Mitomo ◽  
Naoto Hirosaki ◽  
Hideki Hirotsuru
Keyword(s):  
Mechanical Properties ◽  
Grain Size ◽  
Phase Transformation ◽  
Silicon Nitride ◽  
Grain Growth ◽  
Processing Parameters ◽  
Microstructural Development ◽  
Nitride Ceramics ◽  
Microstructural Design ◽  
And Control

The improvement of mechanical properties by microstructural control has been one of the main topics of interest in the development of silicon nitride ceramics. Toughening, by developing an in situ composite or self-reinforced microstructure, has attracted particular attention.Microstructural design is a key factor in the optimization of processing parameters. The microstructures of sintered materials are composed of silicon nitride grains and grain boundaries, which can be either crystalline, amorphous, or partially crystalline, depending on the composition, amount of sintering additives, and processing parameters. Silicon nitride ceramics have been fabricated with an addition of metal oxides and rare-earth oxides that form a liquid phase during sintering and accelerate grain boundary diffusion. The effect of composition of the glassy phase on the mechanical properties of ceramics is presented by Becher et al. and Hoffmann elsewhere in this issue. This article focuses specifically on the design and control of grain size.As it is well recognized, many processing parameters affect grain growth behavior and the resulting microstructure. During sintering, the α- to β-phase transformation leads to a self-reinforcing microstructure on account of the anisotropic grain growth of the stable hexagonal β- Si3N4 phase. Therefore, α-rich powders are widely used for starting materials. Phase transformation accelerates anisotropic grain growth, resulting in an increase in the fracture toughness of Si3N4 ceramics. Kang and Han discuss the effect of phase transformation on nucleation and grain growth in an article in this issue. The effect of the grain-size distribution on microstructural development is described in this article, based on studies conducted mostly with β-Si3N4 powders.

Fabrication of Nanocrystalline Dense Silicon Nitride Ceramics

2012 ◽  
Vol 715-716 ◽  
pp. 738-738
Author(s):  
Hai Doo Kim ◽  
Seong Hyeon Hong
Keyword(s):  
Grain Size ◽  
Silicon Nitride ◽  
Grain Growth ◽  
Oxygen Content ◽  
High Surface ◽  
Full Density ◽  
Microstructural Development ◽  
Nitride Powder ◽  
Nitride Ceramics ◽  
Silicon Nitride Powder

Since the properties of the bulk ceramics are dependent on the grain size the ceramic materials with nanoscale grain size is of interest. Sintering of nanosized powder compacts to full density with minimum grain growth is a difficult task to achieve due to its high surface energy. Two step sintering methode was developed to enhance densification with minimum grain growth for silicon nitride ceramics with liquid phase. Starting with nano-sized silicon nitride powder two step sintering methode gives rise to a very fine-grained b-Si3N4 matrix with large agglomerated Si2N2O grains due to its high surface oxygen content. Addition of Y2O3 shifts the composition point to a primary phase field with no Si2N2O, gives rise to b-Si3N4 with nano scale grain size and near full density. Carbothermal reduction method was employed to reduce the oxygen content in nano-sized silicon nitride powder to give nanocrystalline dense silicon nitride ceramics without Si2N2O formation. Use of SPS was effective to suppress the grain growth and to give near full density. Microstructural development and mechanical properties will be reported.

Effects of Sintering Additives on the Microstructure and Mechanical Properties of Silicon Nitride Ceramics by GPS

2010 ◽  
Vol 105-106 ◽  
pp. 27-30 ◽  
Author(s):  
Wei Ru Zhang ◽  
Feng Sun ◽  
Ting Yan Tian ◽  
Xiang Hong Teng ◽  
Min Chao Ru ◽  
...  
Keyword(s):  
Mechanical Properties ◽  
Fracture Toughness ◽  
Phase Transformation ◽  
Silicon Nitride ◽  
Porous Silicon ◽  
Flexural Strength ◽  
Relative Density ◽  
Sintering Additives ◽  
Microstructure And Mechanical Properties ◽  
Nitride Ceramics

Silicon nitride ceramics were prepared by gas pressure sintering (GPS) with different sintering additives, including La2O3, Sm2O3 and Al2O3. Effect of sintering additives on the phase-transformation, microstructure and mechanical properties of porous silicon nitride ceramics was investigated. The results show that the reaction of sintering additives each other and with SiO2 had key effects on the phase-transformation, grain growing and grain boundaries. With 9MPa N2 atmosphere pressure, holding 1h at 1850°C, adding 10wt% one of the La2O3, Sm2O3, Al2O3, porous silicon nitride was prepared and the relative density was 78%, 72%, 85% respectively. The flexural strength was less than 500MPa, and the fracture toughness was less than 4.8MPam1/2. Dropping compounds sintering additives, such as La2O3+Al2O3, Sm2O3+Al2O3 effectively improves the sintering and mechanical properties. The relative density was 99.2% and 98.7% with 10wt% compounds sintering additives. The grain ratio of length to diameter was up to 1:8. The flexural strength was more than 900MPa, and the fracture toughness was more than 8.9MPam1/2.

scholarly journals Influence of MXene (Ti3C2) Phase Addition on the Microstructure and Mechanical Properties of Silicon Nitride Ceramics

Materials ◽  
2020 ◽  
Vol 13 (22) ◽  
pp. 5221
Author(s):  
Jaroslaw Wozniak ◽  
Mateusz Petrus ◽  
Tomasz Cygan ◽  
Artur Lachowski ◽  
Bogusława Adamczyk-Cieślak ◽  
...  
Keyword(s):  
Mechanical Properties ◽  
Fracture Toughness ◽  
Phase Transformation ◽  
Silicon Nitride ◽  
Powder Processing ◽  
Sintering Process ◽  
Microstructure And Mechanical Properties ◽  
Plasma Sintering ◽  
Nitride Ceramics ◽  
Spark Plasma

This paper discusses the influence of Ti3C2 (MXene) addition on silicon nitride and its impact on the microstructure and mechanical properties of the latter. Composites were prepared through powder processing and sintered using the spark plasma sintering (SPS) technic. Relative density, hardness and fracture toughness, were analyzed. The highest fracture toughness at 5.3 MPa·m1/2 and the highest hardness at HV5 2217 were achieved for 0.7 and 2 wt.% Ti3C2, respectively. Moreover, the formation of the Si2N2O phase was observed as a result of both the MXene addition and the preservation of the α-Si3N4→β-Si3N4 phase transformation during the sintering process.

scholarly journals Structural evaluation and mechanical properties of AZ31/SiC nano-composite produced by friction stir welding process at various welding speeds

2017 ◽  
Vol 233 (5) ◽  
pp. 831-841 ◽  
Author(s):  
A Abdollahzadeh ◽  
A Shokuhfar ◽  
H Omidvar ◽  
JM Cabrera ◽  
A Solonin ◽  
...  
Keyword(s):  
Mechanical Properties ◽  
Grain Size ◽  
Friction Stir Welding ◽  
Grain Growth ◽  
Welding Process ◽  
Processing Parameters ◽  
Nano Particles ◽  
Homogeneous Distribution ◽  
Friction Stir ◽  
The Matrix

A metal matrix composite made of AZ31 containing SiC nano-particles was successfully produced by friction stir welding (FSW), and the effect of processing parameters such as rotational and transversal speeds on the microstructure (grain size) and mechanical properties (tensile and hardness tests) were investigated. Prior to friction stir welding, nano-sized SiC particles were incorporated into the joint line and then different rotational (600, 800 and 1000 r/min) and transversal speeds (25, 75, 125 and 175 mm/min) were tested. The results indicated that the grain size of the matrix and SiC nano-particles are two key parameters controlling different characteristics of the developed composite. Both parameters, in turns, are dependent on the heat generated during the FSW process. The increase of rotational speed and decrease of transversal speed result in high amount of heat and homogeneous distribution of SiC nano-particles. The former leads to grain growth and decrease of strength and hardness, while the latter causes grain refinement and increases of strength and hardness. Accordingly, the heat input has opposite effects on matrix grain growth and homogeneous distribution of particles. Therefore, optimum values of rotational and transversal speeds were found (800 r/min and 75 mm/min) to produce the best microstructure and mechanical properties.

Microstructural Development of Electrical Steels under Si and Al Diffusion

2006 ◽  
Vol 258-260 ◽  
pp. 39-45
Author(s):  
José Barros ◽  
Yvan Houbaert
Keyword(s):  
Grain Size ◽  
Phase Transformation ◽  
Grain Growth ◽  
Alpha Phase ◽  
Microstructural Development ◽  
Diffusion Annealing ◽  
Electrical Steels ◽  
Common Features ◽  
Columnar Grain ◽  
Size And Morphology

The effect of Si and Al diffusion from a coating in the microstructure of electrical steels have been investigated for three different processing routes. In general the final texture is not affected by the diffusion of Si or Al from the coating whereas the grain size and mor- phology can be affected if the silicon content of the substrate is low enough to allow phase transformation. The gamma to alpha phase transformation caused by the diffusion of Si and Al determines the grain size and morphology resulting in columnar grain growth. The evolu- tion of the microstructures during the diffusion annealing for the production of high Si steels shows some common features with the microstructure evolution during the grain growth in conventional low silicon (Si < 3 wt.%) electrical steels.

Principles of Microstructural Design in Two-Phase Systems

2007 ◽  
Vol 558-559 ◽  
pp. 827-834 ◽  
Author(s):  
Suk Joong L. Kang ◽  
Yang Il Jung ◽  
Kyoung Seok Moon
Keyword(s):  
Growth Rate ◽  
Grain Growth ◽  
Driving Force ◽  
Driving Forces ◽  
Interface Reaction ◽  
Processing Parameters ◽  
Microstructural Development ◽  
Two Phase ◽  
Interface Mobility ◽  
Microstructural Design

When a polycrystal is in chemical equilibrium, the microstructure evolves as a result of grain growth under the capillary driving force arising from the interface curvature. As the growth rate of an individual grain is the product of the interface mobility and the driving force, the growth of the grain can be controlled by changing these two parameters. According to crystal growth theories, the growth of a crystal with a rough interface is governed by diffusion and its interface mobility is constant. In-contrast, the growth of a crystal with faceted interfaces is governed by the interface reaction and diffusion for driving forces below and above a critical value, respectively. As the growth rate is nonlinear for the regime of interface reaction control, the grain growth is nonstationary with annealing time. Calculations reveal that the types of nonstationary growth behavior including pseudo-normal, abnormal, and stationary are governed by the relative value of the maximum driving force, gmax, to the critical driving force for appreciable growth, gc. Recent experimental observations showing the effects of critical processing parameters on microstructural development also support the theoretical prediction. The principles of microstructural design are deduced in terms of the coupling effects of gmax and gc.

The Milling Time Effect on Sintering Kinetics of Silicon Nitride Based Composites

2009 ◽  
Vol 409 ◽  
pp. 369-372
Author(s):  
Orsolya Koszor ◽  
Csaba Balázsi
Keyword(s):  
Mechanical Properties ◽  
Grain Size ◽  
Phase Transformation ◽  
Silicon Nitride ◽  
Milling Time ◽  
Nitrogen Pressure ◽  
Nitride Phase ◽  
Sintering Kinetics ◽  
Kinetics Of ◽  
Low Nitrogen

We have investigated the influence of the milling time on the structure and mechanical properties of the nanocomposite, as well as the effect of grain size on the sintering kinetics (α to β silicon nitride phase transformation). As we observed, by increasing the milling time the mechanical properties of the ceramics may be improved. The reason of this improvement is partly due to the α-Si3N4 to β-Si3N4 transformation facilitated by the smaller grain size, on the other hand it is due to the better dispersion of the carbon nanotubes. The X-ray measurements confirmed that in the case of samples milled for 5 hours, even when sintered at 1700°C, low nitrogen pressure (2MPa) and without holding time, a faster phase transformation occurs, resulting in improved mechanical properties.

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