Properties Of Silicon Nitride Ceramics Research Articles

High temperature creep behaviour of [formula omitted] ceramics

The improvement in high temperature mechanical properties of silicon nitride ceramics has been explored by fabrication of a β′-Si 3N 4 α-YSiAlON ceramic densified, without additives and without HIP treatment, by sintering of a mixture of α-Si 3N 4 and α- YSiAlON powders under a nitrogen pressure of 5 MPa. The high temperature creep behaviour was investigated in the ranges 100–400 MPa and 1280–1400 ° C by compressive tests. The creep performances were very impressive. The activation energy (Q = 770 kJ/mol) and the stress exponent ( n = 1) are consistent with a deformation mechanism resulting from grain boundary sliding accommodated by volume diffusion. Microstructure was not affected by the deformation conditions, in particular no cavity formation was observed after creep at 1400 °C and 300 MPa. This behaviour is related to the probable absence of a thick boundary film which may result from crystallization during cooling of small glass pockets and from internal stresses caused by the volume change of crystallizing pockets.

Relationship between microstructure and mechanical properties of silicon nitride ceramics

Abstract

Particulate silicon nitride-based composites

In an attempt to optimize the structure and properties of silicon nitride ceramics, a variety of novel processing techniques and materials compositions have evolved over the last 15 years. Among the most important, was the development of various silicon nitride-based composites. A review of particulate, silicon nitride-based composites other than whisker- or platelets-reinforced, is presented. Materials based on silicon nitride and SiAlONs, with additions of carbides, nitrides and borides of transition metals are described. Special emphasis is placed on TiN- and TiC-containing ceramics. The manufacture of composites by hot pressing, reaction sintering, pressureless and gas-pressure sintering is discussed. The data on properties, including conductivity, density, Young's modulus, strength, fracture toughness, hardness, thermal expansion, wear, creep and oxidation resistance are presented. Analysis of actual and potential uses of the selected composites demonstrates that the particulate composites are very promising as tool, structural and electronic materials.

Tribological properties of silicon nitride ceramics coated with molybdenum films under boundary lubrication

The tribological behaviour of Si 3N 4 ceramics, with and without molybdenum films deposited by means of ion beam mixing (IBM), was investigated on a reciprocating friction tester under boundary lubrication. Paraffin oil containing 3 wt.% tricresyl phosphate (TCP), sulfide olefin (SO), chlorinated paraffin (CP) and zinc dialkyldithiophosphate (ZDDP) additives were used to lubricate the ceramics. SEM, EPMA and XPS were used to examine the rubbed surfaces. It was found that concurrent use of the IBM modification and additives reduced the friction of the tribosystem and wear of blocks, and in particular reduced the wear volume of blocks by a factor of 30 with SO lubrication. The wear mechanism and synergistic effects are discussed.

Effect of Powder Surface Modifications on the Properties of Silicon Nitride Ceramics

The effect of surface oxygen concentration of silicon nitride powders on the properties of resulting ceramics was studied. A high‐purity silicon nitride powder was treated physically and chemically to modify its surface oxygen content. The resulting powders were hot‐pressed into dense ceramics using 6 wt% yttria as a sintering aid. Strength and oxidation resistance of these ceramics were measured and correlated with the powder and ceramic compositions as well as the resulting intergranular phases. Results show that the phases developed in yttria‐containing silicon nitride ceramics vary with slight changes in the initial powder oxygen content, as predicted, and that strength can be correlated to initial oxygen concentration. The mechanical strength vs oxygen content curve has a definite maximum; i.e., there is a small oxygen concentration range at which optimum ceramic strength is realized. Best results are obtained when the oxygen content is increased by thermal oxidation; other techniques such as chemical oxidation or addition of silica are not as effective, particularly in attaining high strength at elevated temperatures.

Development of High Performance Silicon Nitride Ceramics and their Applications

ABSTRACTProgress in sintering process and improvement of mechanical properties of silicon nitride ceramics are reviewed. Emphases are placed on contributions of advanced sintering techniques and better understanding of sintering additives and microstructure-properties relations. Current applications as engine components and cutting tools are described, and future prospect is considered.

常圧焼結窒化珪素の高温破壊強度特性と統一的評価法

For the purpose to clarify the temperature dependence above 1000°C of fracture strength properties of silicon nitride ceramics, which are expected to apply to a gas turbine from the viewpoint of high resistances to heat, corrosion and wear as well as light weight, fast-fracture, cyclic fatigue and static fatigue tests were carried out in 3-point bending at 1000°C, 1100°C, 1200°C and 1300°C.On the basis of the unified estimation method, which is proposed here for the evaluation of ceramic strength property, the temperature dependence of fracture strength of sintered Si3N4 was investigated in the temperature range from 1000°C to 1300°C. The results obtained are summarized as follows;(1) The normalized fracture strength data, which were measured by three kinds of high temperature tests, can be commonly expressed by a formula with two statistical parameters (m, σ0), the crack growth property parameter, n, and the activation energy, Q*.(2) The value of n, which is the index in the formula of crack growth rate, decreases with elevating temperature. It becomes more than twice compared with the value below 1000°C.(3) The temperature-dependence of fracture strength can be expressed well in Arrhenius plots.(4) The strength follows the Weibull distribution with two parameters. So, both fracture strength and fracture life at an arbitrary temperature, Tθ, within 1000°C-1300°C, can be probabilistically estimated, if the effective volume, Veff, and the effective hold time, teff, are given.

Some features of the strength properties of silicon nitride ceramics at high temperatures

Some features of the strength properties of silicon nitride ceramics at high temperatures