JPH0832594B2 - Silicon nitride ceramics design support system - Google Patents

Description

TECHNICAL FIELD The present invention relates to a silicon nitride ceramics design support device. More specifically, the present invention relates to a silicon nitride ceramics design support device capable of efficiently selecting the sintering aid and predicting the strength of the produced ceramics at room temperature and high temperature.

(Prior Art) Conventionally, silicon nitride ceramics have been attracting attention as having high strength and high hardness.
Application to machine parts such as engine parts, machine parts for metal cutting or machining, and precision machine parts has been studied. Such silicon nitride-based ceramics are usually manufactured by adding metal oxide to a silicon nitride powder as a sintering aid, shaping it into a predetermined shape, and then heating and sintering it in nitrogen.

(Problems to be Solved by the Invention) However, conventionally, it is not always sufficient to select an oxide effective as a sintering aid involved in the production of silicon nitride-based ceramics or an index or a guideline about the strength of the obtained ceramics. Instead, in general, the actual situation is to improve the characteristics of ceramics based on the results of trial and error through experiments.

Therefore, there has been a serious problem that development of silicon nitride ceramics requires a great deal of time and labor. In addition, since the data obtained during development is not accumulated as the basis for the design of silicon nitride ceramics, there is a problem that such data is not always utilized in the design of new ceramics. .

The present invention has been made in view of the above circumstances, solves the drawbacks of the conventional silicon nitride ceramics development, selects the sintering aid and the strength of the produced ceramics at room temperature and high temperature. It is an object of the present invention to provide a new silicon nitride ceramics design support device that enables prediction of

(Means for Solving the Problems) As a solution to the above problems, the present invention provides an input means for selecting and inputting a metal element containing silicon and an oxide formed of the metal element, and the metal element. Storage with data including electronegativity, ionic and covalent radii, free energies of formation of nitrides and oxides of these metals, sublimation and thermal dissociation temperatures, and melting points of silica-metal oxide systems; A calculation unit for performing a thermodynamic calculation for the reaction between silicon nitride and the metal oxide and a calculation of the strength of the ceramics to be generated, and a calculation result calculated by the calculation unit for storing data and / or data stored in the storage unit. Or a display that includes a comparison means that compares with the set value that is the basis for inference, and an inference result about the possibility of forming silicon nitride ceramics and the strength of the resulting ceramics. The present invention provides a silicon nitride ceramics design support device characterized by comprising:

In the present invention, a metal oxide effective as a sintering aid for silicon nitride is stable at a sintering temperature of a metal oxide. A liquid phase formation temperature (T ₀ ) of a silica-metal oxide system which coexists stably with silicon nitride. Attention is paid to the three characteristics that the temperature is below the sintering temperature (T).

The stable condition is that the sublimation temperature and the thermal dissociation temperature are higher than the sintering temperature. In the case of a substance that undergoes thermal dissociation, the free energy of formation of the metal oxide at the sintering temperature is positive.

The silicon nitride and the metal oxide have the following <1> formula or <
When the reaction represented by the formula 2> occurs, silicon nitride and metal oxide do not coexist stably.

Si ₃ N ₄ + M _a O _b → 3SiO ₂ + M _c N _d … <1> Si ₃ N ₄ + M _a O _b → 3SiO + M _c N _d + eN ₂ … <2> In the right side of <1> and <2> If the value obtained by subtracting the sum of the free energy of formation of the substance on the left side from the sum of the free energy of formation of the substance of 0 is 0 or more than the set value that is the standard of inference, the reaction does not proceed, as shown in The silicon nitride and the metal oxide coexist.

The sintering aid reacts with the silica layer on the surface of the silicon nitride powder to generate a liquid phase, and the sintering proceeds by diffusing the substance in the liquid phase. Therefore, in order to obtain ceramics, the condition that a liquid phase exists at the sintering temperature must be satisfied.

By the way, if a metal oxide effective as a sintering aid is used, silicon nitride ceramics should be obtained. However, the room temperature strength of the sintering aid is that the sintering aid remains at the grain boundaries or forms a solid solution in the grains. It depends on what you do. Strength (σ _f , MPa)
Is (K _1c : fracture toughness, c: defect size).

When the sintering aid dissolves in the grains, the fracture proceeds through the grains. The fracture toughness (K _1c ) at this time is approximately
It is 3.0 MPa · m ^1/2 .

On the other hand, when the sintering aid remains at the grain boundary, the fracture proceeds at the grain boundary. The fracture toughness (K _1c ) in this case corresponds to the shape of the particles and is calculated by an approximate expression. Since the defect size (c) depends on the manufacturing method, it can be introduced as a set value by designating the manufacturing method. It is also possible to input estimated values for the fracture toughness (K _1c ) and the defect size (c).

By the way, the solid solution metal is a substitutional solid solution at the silicon position of silicon nitride. Therefore, by comparing with the electronegativity, ionic radius and covalent bond radius of the metal element, it is determined whether or not the sintering aid is solid-solved in the grain.

The set value that serves as the basis for inference in the contrasting process is the most probable value from the experimental data on conventional silicon nitride ceramics. For example, <1 above
> And <2> reference values for preventing reaction, relational expression between fracture toughness (K _1c ) and particle shape, relation between manufacturing method and defect size (c), and solid solution metal Electronegativity, range of ionic radius and covalent radius are included. If such a set value is not obtained in the conventional experimental data, a more probable estimated value can be set as the set value in the inference process.

High temperature strength is further estimated from the judgment of solid solubility. The high-temperature strength greatly differs depending on whether or not the sintering aid dissolves in the grains. When it forms a solid solution in the grains, the fracture behavior is similar to that at room temperature even at high temperature, and therefore the fracture toughness (K _1c ) and the defect size (c) do not depend on temperature. However, if it does not form a solid solution in the grains and remains at the grain boundaries, the strength at high temperatures decreases. The temperature at which the decrease in strength starts and the degree of decrease are calculated from the relational expression. In this relational expression, it is assumed that the strength is 0 at the melting point of the silica-metal oxide system, and the temperature at which the decrease in strength starts is 1/2 and 2/3 of the melting point. It is defined that the strength linearly decreases from this temperature and becomes zero at the melting point of the silica-metal oxide system.

(Operation) In the silicon nitride ceramics design support device of the present invention, it is possible to generate silicon nitride ceramics from the thermodynamic calculation of the reaction system containing silicon nitride and the calculation result using the relational expression regarding strength. And the strength of ceramics can be inferred, and the inference can be simulated interactively. The guideline for developing silicon nitride ceramics can be obtained.

(Embodiment) An embodiment will be described below with reference to the drawings, and the silicon nitride ceramics design support device of the present invention will be described in more detail.

FIG. 1 is a block diagram illustrating the configuration of a silicon nitride ceramics design support device of the present invention.

In the device of the present invention, the input means (1), the conversion section (2), the storage section (3), the calculation section (4), the contrast means (5).
And the display section (6). Storage unit (3)
Include electronegativity of metal elements including silicon, ionic and covalent radii, free energies of formation of nitrides and oxides of these metals, sublimation and thermal dissociation temperatures, and silica-metal oxide systems. It has various data including melting points.

FIG. 2 is a screen view showing an example in which a part of the data in the storage unit (3) is displayed on the display unit (6) when the sintering temperature is 2000 k.

In this example, the valence of each metal element, the sintering temperature 2000
The free energies of formation of metal nitrides and oxides at k (kcal / mol), melting points (° C), and sublimability are shown. Such data is stored in the storage unit (3) and can be displayed on the display unit (6) as required. These data signals are transmitted to the calculation unit (4) and the contrast means (5) via the conversion unit (2). The display on the display unit (6) is of an interactive type, as will be described later. Examples of the input means (1) include a keyboard and a mouse.

FIG. 3 is a flow chart illustrating an inference process in the device of the present invention.

As illustrated in FIG. 3, in the silicon nitride-based ceramics design support apparatus of the present invention, the input means (1) selects and inputs the metal element containing silicon and the oxide made of the metal element. Then, first, the stability of the oxide at the sintering temperature and the stability with respect to silicon nitride is inferred. The stability check at the sintering temperature is performed by determining whether the sublimation temperature and the thermal dissociation temperature are higher than the sintering temperature, as described above. Also,
To check the stability with silicon nitride, the thermodynamic calculation based on the above formula <1> or <2> is performed by the calculation unit (4), and the stability is compared with the set value which is the standard of inference set in advance. Done by. The determination of such stability is performed by the control means (5). If it is determined to be stable, the fact is displayed on the display unit (6), and the process can proceed to the next step. On the other hand, when it is inferred that it is unstable, the fact is displayed on the display unit (6) and it is suggested whether the oxide should be selected again. The types of metal oxides that can be selected are, in the device of the present invention,
It is possible to use one or more kinds, and it is possible to make an inference when two or more kinds of sintering aids are used.

Then, the control means (5) determines whether or not the liquid phase formation temperature of the silica-metal oxide system is equal to or lower than the sintering temperature. Here, when it is determined that there is no sinterability, it is possible to return to the oxide selection step as in the above. Also in this step, the inference result is displayed on the display unit (6).

When it is estimated that the oxide has sinterability, the solid solubility of the oxide can be subsequently checked. Input means (1)
The solid solubility is checked by contrasting the electronegativity, ionic radius and covalent radius of the metal element indicated in. In this step, if it is estimated that there is solid solubility, the process proceeds to the step of calculating the strength of the ceramics that will be generated next. When it is determined that there is no solid solubility, the process can be shifted to a process selection step for continuing inference, or similarly to the case where there is solid solubility, it can be forced to shift to a ceramic strength calculation step. Such a selection can be made in response to the interactive message displayed on the display unit (6).

The intensity calculation is performed by the calculation unit (4). The strength at room temperature and high temperature is calculated based on the calculation formula for strength. The calculation result is displayed on the display unit (6) as a correlation between temperature and intensity.

When all of the above inferences regarding the effectiveness of the metal oxide as a sintering aid have been completed, a message to that effect is displayed in the display section (6), and a process selection is made regarding the completion or continuation of the silicon nitride ceramics design. can do.

FIG. 4 and FIG. 5 are screen diagrams showing examples of a part of the inference result and the strength calculation result when yttria (Y ₂ O ₃ ) is used as the sintering aid.

As illustrated in FIG. 4, it is inferred that yttria (Y ₂ O ₃ ) is effective as a sintering aid. Further, FIG. 5 shows the strength (σ) from room temperature to high temperature when yttria (Y ₂ O ₃ ) is used as a sintering aid and sintered by hot pressing.
_f , MPa) is shown as a correlation diagram with temperature (k). The actually reported intensities are in the region between the solid line and the broken line illustrated in FIG. 5, confirming that the inference by the device of the present invention is valid.

In this way, the silicon nitride ceramics design support apparatus of the present invention selects a metal oxide effective as a sintering aid that can be used in the production of silicon nitride ceramics, and The strength can be predicted. The inference result can be used as a guideline or an index regarding the type of sintering aid, the manufacturing method, the material structure, etc. when manufacturing a ceramics sintered body having a predetermined strength or higher at a predetermined temperature.

Of course, the present invention is not limited to the above examples. Needless to say, various aspects are possible for details such as the type of data stored in the storage unit and the type of oxide to be instructed.

(Effects of the Invention) As described in detail above, according to the present invention, a guideline regarding the selection of the sintering aid and the strength of the ceramics produced can be easily and simply obtained. It is possible to efficiently design silicon nitride ceramics. The time and labor conventionally spent on the development of silicon nitride ceramics can be significantly reduced.

[Brief description of drawings]

FIG. 1 is a block diagram illustrating the configuration of a silicon nitride ceramics design support device of the present invention. FIG. 2 is a screen view showing an example in which a part of the data stored in the storage unit of the device of the present invention is displayed on the display unit. FIG. 3 is a flow chart illustrating an inference process in the device of the present invention. FIG. 4 and FIG. 5 each show an example of a part of the inference result and the strength calculation result when yttria (Y ₂ O ₃ ) using the apparatus of the present invention is used as a sintering aid. It is a screen figure. 1 ... Input means 2 ... Conversion section 3 ... Storage section 4 ... Calculation section 5 ... Comparison means 6 ... Display section

Claims (3)

[Claims] 1. Input means for selecting and inputting a metal element containing silicon and an oxide comprising the metal element, electronegativity, ionic radius and covalent bond radius of the metal element, and nitriding of those metals Memory having data including free energies of formation of oxides and oxides, sublimation and thermal dissociation temperatures, and melting points of silica-metal oxide systems, and thermodynamic calculations on the reaction of silicon nitride with the metal oxides. A calculation unit for calculating the strength of the ceramics to be generated, a comparison means for comparing the calculation result calculated by the calculation unit with the data stored in the storage unit and / or the set value serving as a reference for inference, and the silicon nitride A silicon nitride ceramics design support characterized by comprising a display section for displaying the inference result about the possibility of forming the ceramics and the strength of the generated ceramics. Supporting device. 2. The silicon nitride ceramics design support apparatus according to claim 1, wherein the control means determines the stability of the metal oxide and whether or not the metal oxide forms a solid solution with silicon nitride. 3. The silicon nitride ceramics design support apparatus according to claim 1, wherein the calculation unit calculates the strength of the ceramics in the temperature range from room temperature to the melting point of the silica-metal oxide system.