JPS6295461A - Reliability guarantee testing method for high-temperature long-life strength of ceramic parts - Google Patents

Abstract

PURPOSE:To secure the reliability of the high-temperature long-life strength of a ceramic component without any nondestructive inspection by taking a guarantee test which utilizes a static fatigue limit at in-use test and the defect size dependency of low-temperature, short-time strength. CONSTITUTION:When a guarantee test of the root part 2 of the ceramic component 1 is taken, a temperature raising means 3 heats the ceramic components 1 uniformly up to 800 deg.C where this material has almost no static fatigue. A solenoid valve 5 is opened and pressurized water is blown to the root part 2 from a porous nozzle 6. The stress reaches 405MPa while the solenoid valve 5 is left open, but when the solenoid valve 5 is closed when the stress reaches 330MPa slightly higher than 320MPa, the stress decreases speedily. If no breaking sound is detected by an acoustic emission sensor 9 in the process of this guarantee test, the component is acceptable and when a sound is detected, the component is defective.

Description

[Detailed Description of the Invention] [Field of Application of the Invention] The present invention relates to a reliability assurance test method for high-temperature long-life strength of ceramic parts, and is particularly suitable for preventing high-temperature static fatigue fracture during operation. Regarding.

[Background of the invention]

Regarding the reliability assurance test method for high-temperature long-life strength for conventional ceramic parts, see Mechanical Properties of Ceramics (1972), Volume 96--edited by the Ceramics Association Editorial Committee Course Subcommittee.
It is described in the section "Material fracture and fracture mechanics" on page 99. This method assumes that the growth rate V of a static fatigue crack depends on the stress intensity factor K, and that V increases according to the power east as K increases, and that the load of the guarantee test is determined by operating stress conditions such as an overspeed test. A common method was to make the conditions harsher.

[Purpose of the invention]

The purpose of the present invention is to provide a simple and reliable test method for high-temperature long-life strength of ceramic components, based on the following new findings regarding the behavior of static fatigue cracks.

[Summary of the invention]

High temperature static fatigue failure of ceramic parts occurs from contained defects. Therefore, we added various defects to silicon nitride and
A static fatigue test was conducted at 0°C. The results are shown in Figure #1. In any of the defects, the static fatigue strength decreases with increasing time up to 103 to 10' seconds, but does not decrease beyond that, indicating the static fatigue limit. It was not previously clear that ceramics had this static fatigue limit.

Figure 2 shows the propagation behavior of a Vickers indentation crack with a diameter of 700 μrr during the static fatigue process at too high a temperature. 'I? The results are shown below. When the initial stress intensity factor was 4 and 0 MPa JM, it rapidly progressed to fracture, but when it was lower than that, 3 and 0
In the case of MP*5, the propagation speed was initially reduced and then increased again, leading to fracture. KI is 2.4MPaJ”
In the case of ';'r, the rate of progress decreased to a eulogy and reached a stagnation.

When K1 is further lowered, the size of the crack that reaches stasis becomes smaller, but in all cases, the crack grows a little and then stagnates. As a crack propagates, the stress intensity factor I expressed as =fn5] (f: crack shape correction coefficient) increases, but if the crack propagation rate slows down or stops, the crack propagation rate This means that J depends on the stress intensity factor and is not 7. At this time, the behavior of J is the same in air and vacuum1),
The same was true for surface defects and internal defects. Therefore, this crack deceleration phenomenon is thought to be due to self-evaporation at the newly generated highly active crack tip due to propagation, which produced a healing effect.

FIG. 3 shows the relationship between the initial defect size and static fatigue limit seen from the experimental results shown in FIG. 1. The defect size is expressed as an equivalent crack size ae, which is the equivalent half length of a crack in an infinite plate. The equivalent crack size ae is the stress intensity factor of the defect and the stress σ
It is determined from the relationship ae = (K/σ)z/π, and for a scratch with depth a, ae = 1.258a, and for a surface semicircular defect with diameter, ae '' 0, 25 D. Figure 3 also shows the brittle fracture strength at room temperature and 1000°C, which are almost equal, and the fracture toughness value Krc for large cracks is approximately 4.3 MPar.The static fatigue limit is also similar to the brittle fracture strength. For defects with an initial equivalent crack size ae of approximately 200 μm or less, the smaller the defect, the smaller the critical stress intensity factor Ks.
pyth decreases, indicating that linear fracture mechanics using stress intensity factors is no longer effective. KS with large crack
F, th is about 2.7 MPa and KIC's 63
%, but for micro defects with an equivalent crack size as of approximately 10 μm, the decrease is as large as 47%.

FIG. 4 shows the results of static fatigue tests conducted at various temperatures on silicon nitride having an indentation crack with a diameter of 700 μm. A static fatigue limit exists at all temperatures. Figure 5 shows the initial equivalent crack dimensions ae obtained for two types of sialon, silicon nitride and silicon carbide, and the temperature at 1000°C.
This shows the relationship between static fatigue limits at Although the strength differs depending on the material, they all have similar defect size dependence.

It has been found that ceramic materials have static fatigue limits that depend on defect size and temperature. Therefore, in order to guarantee the reliability of the long-life strength of ceramic parts that are subjected to tensile loads for long periods of time in high-temperature ranges, it is necessary to set the allowable defect size of the fatigue limit corresponding to the stress that occurs in each part of the part during use. It is preferable to obtain the defects as shown in Fig. 6 and manage them by non-destructive inspection such as ultrasonic flaw detection or radiographic inspection so that the defect size contained in each place is below the allowable defect size. However, in the case of silicon nitride used at 1000°C, the generated stress is 180M as shown in Figure 6.
Pa is as small as 35 μm, and it is difficult to reliably detect it by non-destructive testing.

As shown in FIG. 6, the present invention enables high-temperature testing of ceramic parts without nondestructive testing by performing a guarantee test that utilizes the static fatigue limit of the operating temperature and the defect size dependence of low-temperature short-term strength. This ensures long-life strength and reliability. In other words, for ceramic parts that are subjected to tensile loads for long periods in high temperature ranges where static fatigue strength is lower than short-time strength at low temperatures, the relationship between defect size and low-temperature short-term strength in the material and defect size Determine in advance the relationship between the static fatigue limit and the static fatigue limit at the operating temperature.

From the defect size of the static fatigue limit corresponding to the stress generated locally in the part at the operating temperature, find the low temperature short-time strength corresponding to the defect size, and generate a tensile stress higher than this strength in the local area at low temperature. It is something that makes you If no fracture occurs in this guarantee test, there is no defect larger than the allowable defect size of the fatigue limit in that local area, and it can be guaranteed that static fatigue failure will not occur from that part even after long-term use.

[Embodiments of the invention]

Hereinafter, one embodiment of the present invention will be described with reference to FIGS. 6 to 8. The ceramic component 1 is a implantable rotor blade of a gas turbine for power generation made of silicon nitride, and the root part 2 attached to the dovetail on the combustion gas inflow side is subjected to a centrifugal force of 180 MPa at an operating temperature of 1000°C. Stress acts for a long time. The temperature raising means 3 consists of a plurality of condensing infrared radiation heaters, and raises the temperature of the entire ceramic component 1. Local cooling means 4
Pressurized water is introduced through a solenoid valve 5, and is sprayed onto the surface of the root portion 2 through a porous nozzle 6. The destruction detection means 7 includes a waveguide 8 made of heat-resistant ceramic that contacts the ceramic component 1, an acoustic emission sensor 9 attached to the tip thereof, and a signal amplifier 10 thereof that removes cooling noise and detects only high-frequency destruction noise. This detects the occurrence of breakage within the ceramic component 1. The temperature difference measuring means 11 calculates the difference between the average temperature of the ceramic component and the temperature of the surface of the root portion 2 by two microfocus infrared thermometers 12.13 and the measured values of these thermometers 12.13. and a controller 14 that closes the solenoid valve 5 of the local cooling means 4 when the difference reaches a set value.

With the above configuration, a reliability guarantee test method for the root portion 2 of the ceramic component 1 will be described below. The relationship between defect size and low-temperature short-time strength in silicon nitride, and the relationship between defect size and 1000
The relationship between static fatigue limits at °C is as shown in Figures 3 and 6. 180 MP at 1000℃ for root part 2
Stress a occurs for a long period of time.

From FIG. 6, the equivalent crack size a8 of the static fatigue limit at 1000° C. corresponding to this state is 35 μm, and the corresponding low-temperature short-time strength is 320 MPa.

When the root portion 2 of this ceramic component 1 is cooled, the tensile stress σ generated at the root portion is obtained by the following equation.

Here, E is the longitudinal elastic modulus and is 310G P for this material.
a and α are linear expansion coefficients of 2.6×10-8/ for this material.
'C1ν is Poisson's ratio and is 0.28 for this material.

8T is the difference between the average temperature of the part 1 and the surface temperature of the root part 2, and β is the shape factor, which is obtained as 0.85 from the thermal stress analysis results for this state. Therefore, in order to generate a tensile stress of 320 MPa in the root portion 2, the temperature difference ΔT needs to be 430°C.

In order to carry out the 'C guarantee test on the root part 2 of the ceramic part 1, each device is arranged as shown in Fig. 7, and the temperature raising means 3 is used to ensure that this material hardly causes any static fatigue phenomenon. The ceramic component 1 is uniformly heated to a temperature of 800°C. Next, the solenoid valve 5 is opened and the porous nozzle 6 sprays pressurized water onto the root portion 2. FIG. 8 shows a thermometer 12. ．．
13 shows a change in stress in the root portion 2 over time calculated by the controller 14 from the measured values in FIG. When the solenoid valve 5 remains open, the stress reaches 405 MPa. The stress is 330 MPa, which is slightly higher than the above 320 MPa.
When the solenoid valve 5 is closed at the point a, the stress rapidly decreases. During this guarantee test, if no sound is detected by the acoustic emission sensor 9, the test is passed; if any sound is detected, the test is failed.

In this example, a guarantee test is performed by applying thermal stress to a single implanted blade, so compared to when assembled into an actual aircraft and an overspeed test is performed, there is no possibility that excessive loads will be applied to other parts or the blade It is possible to prevent other parts from being damaged due to damage and imbalance.

Another embodiment of the invention is shown in FIG. Ceramic parts 1
is an integrated gas turbine rotor for automobiles also made of silicon nitride, and a large centrifugal stress is generated in the base portion 2 of the rotor.

When conducting warranty tests.

The ceramic component 1 is placed in a constant temperature furnace, and the root portion 2 is cooled by a small-diameter +p-hole nozzle 6. Since the temperature of the entire component 1 does not change, the temperature difference measuring means 11 is only a microfocus type infrared thermometer 13 that measures the temperature of the root portion 2. Further, the valve 5 of the local cooling means 4 is a manual valve, and the thermometer 13 is a manual valve.
Make adjustments while reading the value.

Another embodiment of the present invention, shown in FIG. 10, is directed to a base 2 of an exhaust gas turbocharger rotor for an automobile. The residence cooling means 4 is a container filled with cooling water,
A break detection means 7 is fixed to the container. This method utilizes the maximum stress as in the case of opening the solenoid valve shown in FIG. 8, and requires appropriate selection of the temperature of the cooling water and the temperature at which the ceramic component 1 is heated. In the case of this example, the water temperature was 50°C, and the heating temperature of the ceramic component 1 was 600°C. In addition, the inner diameter of the container is made small so that the thermal stress is reduced at the tip of the blade where the applied stress is small. Ceramic part 1 uses the residual heat after sintering to
A guarantee test was carried out by taking it out from the sintering furnace at 50° C. and suspending it in cooling water.

FIG. 11 shows an example of application to an extrusion die for high-temperature metals. During extrusion, tensile stress is generated in the inner circumference of the die, which is the ceramic component 1, due to internal pressure. In this embodiment, thermocouples 15 and 16 are installed on the inner and outer sides, and the inner thermocouple 15 is connected to the zero contact side of the temperature measurement section of the controller 14 so that the temperature difference can be directly read. It is. The coolant in this case is compressed air, which is sprayed from the large diameter portion of the die through the nozzle 6.

〔Effect of the invention〕

As explained above, according to the present invention, it is possible to test the reliability of high-temperature life strength of ceramic parts easily and reliably using 1 gN.

[Brief explanation of drawings]

Figures 1 to 11 are explanatory diagrams of the test method according to the present invention. Figure 1 is a diagram of the relationship between ceramic rupture time and stress, Figure 2 is a diagram of the relationship between ceramic load time and crack length, and Figure 2 is a diagram of the relationship between ceramic rupture time and stress. 3
The figure shows the relationship between the initial equivalent crack size, the scratch depth, the diameter of the surface semicircular defect, and stress, due to contingencies. Figure 4 shows the relationship between ceramic rupture time and initial stress intensity factor. Figure 5 shows the relationship between the initial Equivalent crack size. A diagram showing the relationship between the depth of a scratch, the diameter of a surface semicircular defect, and the static fatigue limit, FIG. 6 is a diagram showing the relationship between the equivalent crack size and stress in ceramic, and FIG. 7 is a perspective block diagram of an embodiment of the present invention. 8th
The figure is an explanatory diagram of the stress history, and FIG. 9 is a perspective block diagram of another embodiment of the present invention. FIG. 10 is an explanatory diagram of still another embodiment of the present invention, and FIG.
The figure is an explanatory diagram of still another embodiment of the present invention. DESCRIPTION OF SYMBOLS 1... Ceramic part, 2... Root part, 3... Temperature raising means, 4... Local cooling means, 5... Solenoid valve, 6...
... Nozzle, 7... Destruction detection means, 8... Waveguide rod,
9...Acoustic emission sensor, 1
1... Temperature difference measuring means, 12.13... Thermometer, 1
4...Controller.

Claims (1)

[Claims] 1. For ceramic parts that are subjected to tensile load for a long time in a high temperature range where the static fatigue strength is lower than the short-time strength at low temperatures, the defect size in the material and the short-time strength at low temperatures The relationship between the strength and the defect size and the static fatigue limit at the working temperature is determined in advance, and the defect size is determined based on the static fatigue limit defect size corresponding to the stress generated locally in the component at the working temperature. A reliability assurance test method for high-temperature long-life strength for ceramic parts, characterized by determining low-temperature short-time strength and generating a tensile stress higher than this strength locally at low temperature. 2. In the method according to claim 1, the heating means;
It has a local cooling means and a fracture detection means, and after raising the temperature of the ceramic component, locally cools it to generate the tensile stress in that part at a low temperature, and detects whether or not fracture has occurred at that point. A reliability assurance test method for high-temperature long-life strength for ceramic parts. 3. The method according to claim 2, which includes means for measuring a temperature difference between the local part and other parts of the part, and by controlling the operation of the local cooling means by the temperature difference measuring means, the tension is reduced. A reliability assurance test method for high-temperature long-life strength for ceramic parts, characterized by making the stress reach a set value.