JPS6329001A - Ceramic turbo wheel - Google Patents

Abstract

PURPOSE:To improve the toughness and thereby reduce the breakage probability of a blade surface by forming a porous layer on the periphery of a blade made of ceramic in the turbin wheel of a turbo charger and impregnating the porous layer with metal. CONSTITUTION:In a turbin wheel of a turbo charger, the base metal 13 of a turbin wheel blade 11 is made of ceramic e.g. silicon nitride of 95-100% TD. In this case, a metal impregnated layer 12 is formed over the surface of the base metal 13. The metal impregnated layer 12 is composed of a porous layer 14 whose base material is silicon nitride and a metal layer 15 impregnated into the aperture of the porous layer 14. The porosity of the porous layer 14 is set at 50% or less. This enables the improved toughness and the reduced breakage probability of the blade 11 surface, and thereby the improved durability of the turbo charger.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a ceramic turbo wheel for a turbocharger installed in an internal combustion engine for supercharging intake air.

[Conventional technology]

In an internal combustion engine, a turbocharger is sometimes installed to improve output performance.The turbocharger uses exhaust gas from the internal combustion engine to drive a turbo wheel to operate a compressor, supercharging air to the internal combustion engine. do.

Because turbo wheels are exposed to exhaust gases, conventionally,
Previously, they were molded from metal with excellent heat resistance, but in recent years it has been proposed that they be molded from ceramic, which has excellent heat resistance and is lightweight. Now, iron powder, foreign matter, rust, oxide scale, etc. generated in the engine may be mixed into the exhaust gas. In this case, since the turbo wheel is rotating at high speed inside the turbine housing, if this iron powder collides with the blades of the turbo wheel, the blades may chip or crack, which may eventually lead to damage. . In order to prevent the occurrence of such chipping and cracking of blades, the present applicant has already filed patent application No. 60-140878.
No. 60-210808 and Japanese Patent Application No. 60-210808 proposed a configuration in which a metal coating is provided on the blade and a configuration in which a blade outer peripheral member made of a material having high fracture toughness is bonded to the outer peripheral portion of the blade.

[Problem that the invention seeks to solve]

The structure with such a metal coating film or blade outer circumferential member prevents the blade from chipping due to collision with iron powder, etc., and improves the durability of the turbo wheel. It was found that the durability of the turbo wheel was still insufficient, as there was a risk that the joints of the members would peel off.

[Means for solving problems]

The turbo wheel according to the present invention is characterized in that the blades include ceramic, a porous layer is formed on the outer periphery of the blade, and the porous layer is impregnated with metal.

. 〔Example〕 The present invention will be explained below with reference to illustrated embodiments.

FIG. 2 shows an overview of the turbo wheel 10. This turbo wheel 10 is made of silicon nitride (Si3
N4), and the surface of the blade 11 is coated with a metal impregnated layer 12 as shown in FIGS. 1(a) and 1(b), as described later.
is formed.

The molding process of the turbo wheel 10 will be explained.

The main component is silicon nitride powder with an average particle size of approximately 1 μm, and 4% by weight of yttrium oxide is added to this silicon nitride powder as a sintering aid.
and 4% by weight of spinel were added and dispersed uniformly,
After that, 17% by weight of thermoplastic resin etc. was added as an organic binder.
Mix the added ingredients to make a kneaded product. By injection molding this kneaded material into a predetermined mold, an injection molded article in the shape of a turbo wheel is obtained. This injection molded article is then placed in a degreasing device and subjected to degreasing treatment. That is, after introducing an inert gas into the degreasing device and replacing the inside of the device with the inert gas, the inside of the device is heated to 450° C. at a rate of 5° C./h to perform degreasing. Thereafter, this turbo wheel-shaped degreased body is placed in a firing furnace and fired at 1750° C. for 4 hours to obtain a sintered body.

Next, the above kneaded material was made into a slurry and coated on the surface of the sintered body, and re-sintered at 1500°C for 4 hours to form a porous layer with a thickness of about 40 μm and a porosity of about 30% on the surface. Form. The turbowheel is then immersed in a bath of molten chromium and pressure is applied to impregnate the porous layer with metal. This metal may be any metal having high toughness, such as nickel, cobalt, or a nickel alloy.

FIGS. 1(a) and 1(b) show enlarged cross sections of the blade 11. FIG. wing 1
1 is composed of a base material 13 made of silicon nitride with a TD of 95 to 100% and a metal impregnated layer 12 formed on the surface of the base material 13. The metal impregnated layer 12 consists of a porous layer 14 whose main component is silicon nitride, and a metal layer 15 impregnated into the space of the porous layer 14.

Other embodiments of the invention include the following.

That is, the degreased body obtained in the middle of the manufacturing process in the above example was coated with a slurry-like mixed powder product (2% by weight of aluminum oxide, 2% by weight of indium oxide) having worse sinterability than the degreased body, and A porous layer having a thickness of about 60 .mu.m and a porosity of 20% was formed on the surface by sintering at .degree. C. for 4 hours, and then impregnated with metal in the same manner as in the above embodiment.

In this way, multiple turbo wheels were manufactured with various porous layer thicknesses, and the relationship between the porous layer thickness, moment of inertia, and acceleration performance was investigated through experiments.

The results are shown in FIGS. 3 and 4. As is clear from these figures, when the porous layer thickness exceeds 60 μm,
It can be seen that the moment of inertia increases and the acceleration performance deteriorates accordingly. Therefore, when applying a porous layer to the entire surface, it is desirable that the layer thickness be 60 μm or less.

In addition, as described above, a plurality of products with different porous layer thicknesses were manufactured and a durability test was conducted. This test was conducted as follows. In other words, one with a porous layer of different thickness and one without a porous layer were prepared, each was attached to an engine, and the exhaust gas was used to speed it up to 180,000 rpm.
I ran the test with the revs up to . At this time, 2 vertically and 2 horizontally
The test was carried out for 20 minutes at 180,000 rpI11 while supplying metal pieces of dragon, thickness 0, 2* for 10 minutes at a rate of 6 pieces per minute.

The results are shown in FIG. As is clear from Figure 5,
If no porous layer was provided, all of the products would be damaged, but if the porous layer thickness was 5 μm or more, the damage rate would be significantly reduced.
It can be seen that when the thickness is 10 μm or more, there is no damage at all.

As described above, in each of the embodiments, a porous layer is formed on the surface of the turbo wheel and this layer is impregnated with metal, so the bonding strength of this metal to the base material 13 is large, and the metal layer is formed on the base material 13. There is no risk of it peeling off.

Note that when the porosity of the porous layer is greater than 50%,
This is not preferable because the bonding force between the porous layer and the base material 13 becomes weak.

Further, the material of the porous layer is preferably one having a coefficient of thermal expansion close to that of the base material, and may be, for example, an oxide such as aluminum oxide.

Furthermore, the porous layer may be provided over the entire turbowheel, the entire surface of the blade, or only a portion of the blade.

(Effects of the Invention) As described above, according to the present invention, the toughness of the blade surface of the turbo wheel is improved, the probability of breakage is reduced, and the durability of the turbocharger can be improved. The metal layer is less likely to peel off from the base material than when a coating film or mold outer peripheral member is provided, so the amount of metal required is smaller than when a metal coating film is provided. It is possible to further reduce the weight of the turbocharger, thereby increasing the responsiveness of the turbocharger and improving the acceleration performance of the vehicle.

[Brief explanation of the drawing]

Figure 1 (a) is an enlarged sectional view showing the vicinity of the surface of the blade of the turbo wheel, Figure 1 (b) is a further enlarged sectional view of Figure 1 (a), and Figure 2 shows the turbo wheel. Front view, Figure 3 is a graph showing the relationship between porous layer thickness and moment of inertia, Figure 4 is a graph showing the relationship between porous layer thickness and θ ~ 400 m acceleration, Figure 5 is a graph showing the relationship between porous layer thickness and ceramic It is a graph showing the relationship between the failure probability of manufactured turbo wheels. 11... Wing, 14... Porous layer, 15
···metal.

Claims (1)

[Claims] 1. A turbo wheel for a turbocharger that supercharges air to the internal combustion engine by driving a turbine with the exhaust gas of the internal combustion engine, the turbo wheel comprising: A ceramic turbo wheel characterized by forming a porous layer on the outer periphery of the wheel and impregnating the porous layer with metal. 2. The ceramic turbo wheel according to claim 1, wherein the porous layer has a porosity of 50% or less.