DE4119705A1 - Ceramic composite body with metallic components - comprising wear resistant gas tight outer ceramic layer, inner structure of cement and intermediate layer - Google Patents

Abstract

A ceramic composite body (I) contg. metallic components comprises a gas-tight outer layer comprising wear resistance ceramic, an inner structure of cement mixt. comprising metallic and ceramic phases and an intermediate layer. The outer layer is connected to the inner structure forming a continual transition from outer layer to inner structure. Prodn. of (I) is also claimed. USE/ADVANTAGE - (I) is used as wear- and thermal shock-resistant parts in machine construction, esp. as turning cutting plate (claimed).

Description

The invention relates to a ceramic body with special strength and thermal shock resistance and its origin position and use.

Oxide ceramic, wear-stressed parts such. B. Inserts based on Al ₂ O ₃ often fail under the action of thermal shocks, ie less due to excessive wear or insufficient strength for stress. Constant heat changes as they occur with indexable inserts can lead to subcritical crack growth with subsequent breaking out of large parts (Maschinenmarkt 94 (1988), No. 7, 54-58). The main reason for this is the low thermal conductivity of Al ₂ O ₃ base ceramics; this applies in particular to ZrO ₂ -reinforced Al ₂ O ₃ ceramics, which are particularly suitable for machining steel due to their good mechanical properties and chemical stability. Some of these problems are solved by adding thermally conductive phases such as SiC (Ceramic Bulletin 67 (1988) 1016-19). The use of Al ₂ O ₃ layers on a thermal shock-resistant surface such as B. WC-Co brings improvements (Inter. J. High Tech Ceramics 3 (1987) 113-127). However, these advantages must be bought with disadvantages such as low thermal stability or high price. Such layers also tend to flake off due to different thermomechanical behavior. In any case, pure or ZrO ₂ -reinforced Al ₂ O ₃ with high thermal conductivity would be ideal for many applications.

The invention is therefore based on the object of a kerami to create the body, which is characterized by the combination of the Properties high strength, especially wear-resistant excels with high thermal shock resistance, but  is still not expensive to manufacture and an exterior layer that does not tend to flake off.

According to the invention, the problem is solved in principle by a composite ceramic body that is wear-resistant Outer layer and a heat-conducting interior with higher Has breaking resistance.

A ceramic composite body according to the invention containing metallic components is therefore characterized by a gastight outer layer made entirely of wear-resistant Ceramic consists and an internal structure of a cermet-like Mixture of metallic and ceramic phases, as well as one Intermediate layer, which the ceramic outer layer with the Internal structure connects and a continuous transition from forms the outer layer to the metal-containing inner structure.

The interior of the ceramic composite body of the invention consists predominantly of the components of the starting powder, ie in the preferred use of Al, Al ₂ O ₃ , ZrO ₂ and AlN from precisely these phases. Since both Al and AlN have a high thermal conductivity (approx. 150 W / mK compared to approx. 15 with ZrO ₂ -reinforced Al ₂ O ₃ ), a quick heat balance between the outer layer and the core zone leads to a better thermal shock process without the good surface properties of the pure oxide layer are impaired. Between the core and the outer layer there is a smooth transition between the originally used and the fully oxidized phases, which is referred to as the intermediate layer. The grain size of the ceramic grains formed from the metal phase is very small and is usually at or below 1 μm.

This composite body is produced by using a intimate mixture of Al and one or more of the elements and compounds Zr, Nb, Cr, Ta, Ti, Al₂O₃, ZrO₂, Nb₂O₅,  Cr₂O₃, AlN, ZrN, Si₃N₄, TaC, WC, NbC, ZrC, Cr₂C₃, SiC, TiC, B₄C, ZrB₂, AlB, TiB₂, NbB₂, TaB₂ manufactures, in particular by mechanical alloying, the mixture powder metallurgy forms and then the resulting green body under Formation of the gas-tight outer layer is heat-treated, whereby this heat treatment at least temporarily in the presence of Oxygen and rapid heating to a temperature between 800 ° C and 1700 ° C is carried out so long that metal phase is present and then optionally the formed bodies are hot isostatic at temperatures between 1400 and 1800 ° C in argon or nitrogen or a mixture is further compressed by argon and oxygen.

Al and Zr with Al ₂ O ₃ and further oxides, nitrides, carbides and borides of the above-mentioned metals are preferably mechanically alloyed with one another, formed into bodies and then heat-treated in such a way that their outer layer is reacted mainly with wear-resistant ceramic on ZrO ₂ based on reinforced Al ₂ O ₃ base, and the interior still contains large proportions of metallic and / or carbidic heat-conducting phases of the above-mentioned metals, preferably Al, Zr, AlN, ZrN or carbides.

In a special embodiment, the mechanical Alloy by using fine-grained (1 µm) powder of intermetallic phases Al₃Zr, AlZr or AlZr₃ entirely or partially avoided.

Powder metallurgical molding can be done by cold pressing, hot pressing or hot extrusion. Cold pressing can be carried out uniaxially or isostatically. It can be replaced by hot pressing or hot extrusion at temperatures between 300 and 550 ° C. This Warmfor mung a higher density of the unreacted state is achieved. When ZrO ₂ and especially metallic Zr were added, such higher densities (55 to <75% TD) proved to be favorable for the following O ₂ reactions. Green bodies which have only been cold-pressed are preferably sintered at temperatures between 400 and 550 ° C. in a vacuum or inert atmosphere before the reaction annealing, as a result of which strength and density increase without oxidation taking place.

After this first compression step, the samples in the subsequent reaction step are heated as quickly as possible (preferably approximately 8-15 K / min) to temperatures between 800, preferably 1400, and 1700 ° C. in air or in another oxygen-containing oxidizing atmosphere. Due to this rapid heating process, in which, however, tearing of the sample must be avoided, only the surface area of the samples is oxidized. This mainly forms Al ₂ O ₃ and ZrO ₂ . In addition, the outer layer becomes gas-tight due to the sufficiently high temperature, which on the one hand prevents a further oxidation reaction inside, but on the other hand also creates the conditions for hot isostatic post-compression (HIP). Since the powder mixtures contain not only Al ₂ O ₃ (and optionally ZrO ₂ ) but mainly Al and optionally Zr and their carbides, nitrides or borides, Al ₂ O ₃ and ZrO _{2 are also formed} as the corresponding oxidation products in the surface area. The thickness of the oxidized outer layer (edge area) depends

• 1) the volume fraction of ZrO ₂ or Zr in the starting mixture,
• 2) on the density of the unreacted or partially reacted preform (cold pressed and pre-sintered or only hot pressed),
• 3) the heating rate as well
• 4) the level of the sintering temperature in air.

A desired thickness of the outer layer and / or the intermediate layer can be adjusted accordingly Achieve factors easily, with few simple preliminary trials sufficient to determine appropriate values of these factors.  

The reaction step is preferably 15 to 90 minutes 1450 to 1650 ° C carried out.

The second step (reaction step) leads to a gas-tight surface, so that the body can be post-compressed isostatically at temperatures at which Al ₂ O ₃ and ZrO _{2 can be} deformed superplastically, namely at 1400 to 1800 ° C. It is important that the gas pressure (e.g. Ar, Ar + O ₂ or N ₂ ) is only fully applied at these temperatures, so that cracking and thus the flowing out of the liquid metal phase (mainly Al) of the internal structure is prevented. This danger exists with outer layer thicknesses of less than ∼1 mm.

According to the invention, samples which were pressed in a steel die at 200 MPa to form green bodies with the dimensions 13 × 13 × 8 mm and partially cold-isostatically post-densified at 800 MPa, as described in the following examples, were heat-treated. Hot-pressed cylinder samples with a diameter of 10 mm and a height of 8 mm were similarly processed further. They were then subjected to a comparative thermal shock test in which the bodies were first heated to 1000 ° C in air and then quenched in water or silicone oil at 25 ° C. Afterwards, a fully cracked sample (they were annealed in air for 4 h at 1000 ° C) and a commercial indexable insert made of Al ₂ O ₃ with approx. 8 vol.% ZrO ₂ (field mill SN 80) showed a high crack density (approx 50 areas separated by cracks per cm ² ) on the surface, while in the case of samples treated according to the invention, the crack density decreased considerably in the case of water quenching (approximately 10 to 15 areas per cm ² ) and no longer occurred at all in the case of silicone oil quenching. This can only be explained by the improved thermal conductivity of the interior and an increased K _{I c} value (due to the metal content).

The wear resistance of the composite body according to the invention is comparable to that of the conventional indexable inserts. Particularly good wear resistance is obtained if the elastic modulus of the interior containing metal is high due to the proportions of AlN, ZrN, ZrC and / or ZrB ₂ and a supporting effect is thus exerted. It is thus ensured that, for example, indexable inserts, which were produced by the method according to the invention, no longer have the known temperature shock sensitivity of Al ₂ O ₃ -based cutting ceramics.

In the case of samples that are produced by hot pressing or hot extrusion already has a high density in the unreacted or partially reacted state can have a HIP post-compression after the annealing and sintering treatment can also be dispensed with.

The following examples illustrate the invention.

example 1

150 g of a powder mixture of 50 vol .-% Al (Alcan 105), 150 vol .-% Al ₂ O ₃ (CT 3000 Alcoa), 15 vol .-% ZrO ₂ (Tosoh TZ2Y) and 20 vol .-% AlN ( Alcan) were mechanically alloyed in an attritor with 3Y-TZP grinding balls (2 to 5 mm) in ethanol for 6 h and then dried in air. The dried powder mixture was pressed uniaxially in a die into platelets with the dimensions 13 × 13 × 10 mm with a pressure of 200 MPa. The compacts were sintered for 2 hours at a temperature of 550 ° C. in vacuum and then at 1550 ° C. in air for 30 minutes. The air sintering was heated at a rate of 10 K / min. An approximately 1 mm thick gas-tight oxide layer (Al ₂ O ₃ + ZrO ₂ ) then formed, the interior of the sample still consisting of the starting components. The platelets were then hot isostatically densified at a temperature of 1650 ° C. for 30 min and an N ₂ pressure of 180 MPa.

The platelets then had an approximately 1 mm thick oxide layer (ZrO ₂ -reinforced Al ₂ O ₃ ) and consisted of approximately 20% by volume AlN, approximately 40% by volume Al ₂ O _3, approximately 25 vol.% Al and approx. 15 vol.% ZrO ₂ . A smooth transition between the different volumes of the phases was found between the edge zone and the interior.

When quenched in 20 ° C cold water at 1000 ° C, the platelets treated in this way contained only a few cracks compared to platelets which had reacted completely and were produced with the same starting powder mixture (in this case, vacuum annealing was dispensed with, instead the platelets became Oxidized in air at 1000 ° C for 1 h). This proves the positive influence of the high thermal conductivity inside the Al / AlN-containing samples on the thermal shock resistance. Conventional ZrO ₂ -reinforced Al ₂ O ₃ inserts (SN 80 from Feldmühle, Plochingen) also showed significantly more cracks with the same water quenching.

Example 2

The procedure was as in Example 1, except in one case instead of 35% AlN by volume

• a) 20 vol .-% AlN and 15 vol .-% TiC and in another case
• b) 20% by volume of AlN and 15% by volume of TiB _{2 are} added.

After the complete annealing and HIP cycle, Al-titanate was found in the surface layer as well as TiC in case a) and TiB ₂ in case b). In both cases, the thermal shock test from Example 1 showed a higher crack density on the surface of the samples than when only AlN (Example 1) was used. However, the crack density was still lower than in the fully reacted sample from Example 1. However, the cracks remained in the transition zone. The core zone of the TiC-containing sample had a K _{I c} value of 8.5 MPa / m (crack length method) and a surface area of 3.2 MPa / m.

Example 3

150 g of a powder mixture of 45% by volume Al, 25% by volume Al ₂ O ₃ , 4% by volume ZrO ₂ , 15% by volume AlN (all qualities as in Example 1), 1% by volume Y ₂ O ₃ (Alfa Prod.) And 9 vol.% ZrC (HC Starck) were attrited for 8 hours as in Example 1, only in acetone, dried, and pressed into platelets. The platelets were then post-densified isostatically at 800 MPa, after which they had a green density of 74% TD. Then they were annealed in forming gas at 550 ° C for 4 h and then sintered in air at 1500 ° C for 1 h (heating rate 10 K / min). The platelets treated in this way showed an approximately 0.5 mm thick, dense, pure oxide skin. They were then post-compressed hot isostatically at 1400 ° C in an Ar-1% O ₂ gas mixture for 1 h. The edge zone made of ZrO ₂ -containing Al ₂ O ₃ thereby increased to approx. 3 mm; the core zone continued to consist of the starting substances. However, the edge zone showed a few cracks, through which a small amount of liquid Al leaked out, where it reacted to Al ₂ O ₃ . After the thermal shock treatment from Example 1, the number of cracks did not increase.

Example 4

The procedure was as in Example 3, except that 9% by volume of ZrB ₂ (HC Starck) was used instead of ZrC. In addition, instead of the oxidizing HIP post-compression from Example 3, as in Example 1, post-isostatic hot compression was carried out. The samples then had an approximately 2.5 mm thick oxide layer made of Al ₂ O ₃ and tetragonal ZrO ₂ , while the core zone consisted of the starting substances. The K _{I c} value of the surface was 5.2 MPa / m, that of the inside was 7.6 MPa / m. Quenching 1000 ° C in 25 ° C silicone oil did not cause cracking.

With the same thermal shock treatment on conventional SN 80 indexable inserts showed numerous cracks, however, their density is not as high as that of water was horror.

Example 5

The procedure was as in Example 1, except that 20% by volume AlB ₂ (HC Starck) was used instead of AlN. In addition, as in Example 3, the platelets were isostatically densified at 800 MPa. After the annealing and HIP treatment, the samples had an approx. 1 mm thick edge zone. Quenching as in Example 4 also did not result in cracking.

Example 6

The powder mixture from Example 1 was mechanically alloyed with 10 g of metallic zirconium powder (Alfa Products) for 4 hours in ethanol. The procedure was then as in Example 1, except that the platelets were isostatically compressed again at a pressure of 800 MPa. These platelets were then heated to 550 ° C. in forming gas at 1 K / min and held for 6 hours. The sample was then heated to 1550 ° C. in air at 15 K / min and held for 20 min. The HIP post-compression was carried out in Ar at 1750 ° C for 30 min. The ZrO ₂ -reinforced edge zone was approx. 2.5 MPa / m thick, the transition area was approx. 1 mm and the rounded core zone was only approx. 2.5 mm in diameter. However, the oil quenching from example 4 did not lead to any cracking.

Example 7

The powder from Example 6 became platelet as in Example 6 Chen pressed, which then in air at 1 K / min were heated to 600 ° C. and held for 20 min. Not this one  HIP post-compacted samples showed after thermal shock action from Example 4 also no cracks.

Example 8

150 g of a powder mixture of 50 vol.% Al, 5 vol.% Zr, 1 vol.% Y ₂ O ₃ , 10 vol.% Cr (Ventron Chemie) and 24 vol.% Al ₂ O ₃ ( Ceralox HPA 05) were attrited and dried as in Example 1. The powder was then hot pressed at 300 ° C. in a die to form cylinders 10 mm in diameter and 6 mm in height of 100 MPa for 10 minutes. The green density was then <95% TD. The samples were then heated to 1550 ° C. in air at 5 K / min and held at this temperature for 30 min and then HIP-post-compressed as in Example 1. An approx. 1.5 mm edge zone was completely oxidized, while an approx. 3 min core zone still contained approx. 30 vol.% Of a metallic mixture of Al, Cr and Zr. For comparison, the same samples were annealed in air at 1550 ° C for 4 h and thus completely oxidized. The oil quenching from Example 4 led to complete destruction, while the samples with the partially oxidized interior contained only a few cracks.

Example 9

10 g of a powder mixture of 40 vol.% Al, 10 vol.% ZrO ₂ , 5 vol.% ZrN (HC Starck) and 15 vol.% Al ₂ O ₃ (Ceralox HPA 05) and 30 vol. % AlN (Alcan) were attrited and dried as in Example 1. The powder was then hot-pressed at 400 ° C. in air in a steel die to form cylinders as in Example 8. The green density was then <90% TD. The cylinders were then heated to 1600 ° C. in air at 15 K / min and held for 30 min and then post-compressed as in Example 6 HIP. The samples, which contained an approximately 3 mm large unreacted core zone, showed no crack formation at all after the oil quenching from Example 4.

Example 10

The hot pressed samples from Example 9 were at 5 K / min Heated to 1550 ° C and held there for 4 hours. This not HIP- post-compacted samples only showed after oil quenching few cracks.

Example 11

The powder from Example 9 was pressed as in Example 1 and heat treated. Even with these samples, after the Oil quenching no cracks are observed.

Claims (20)

1. Ceramic composite body containing metallic components, characterized by a gas-tight outer layer which consists entirely of wear-resistant ceramic and an inner structure made of a cermet-like mixture of metallic and ceramic phases, and an intermediate layer which connects the ceramic outer layer to the inner structure and forms a continuous transition from the outer layer to the metal-containing inner structure. 2. Composite body according to claim 1, characterized in that the outer layer consists of 50 to 100 vol .-% of feinkör nigem Al ₂ O ₃ and the rest of other ceramic phases embedded. 3. Composite body according to claim 2, characterized, that he as one other stored phase one or more of the following ceramic phases: Stabilized or unstabilized ZrO₂, Cr₂O₃, Nb₂O₅, SiC, TiC, NbC, ZrC, TaC, Cr₂C₃, WC, AlN, Si₃N₄, ZrN, TaN, B₄C, Cr₂B₅, Al₂B₂, TiB₂, ZrB₂, TaB₂. 4. Composite body according to claim 2 or 3, characterized, that the outer layer of oxides, carbides, nitrides or / and aluminum and zirconium borides. 5. Composite body according to one of claims 1 to 4, characterized, that the outer layer and the intermediate layer are independent  each have a thickness of 10 µm to 3 mm point. 6. Composite body according to one of the preceding claims, characterized, that its internal structure consists of a mixture of metallic and ceramic phases that still exist together setting of the green body corresponds. 7. Composite body according to one of claims 1 to 5, characterized, that its internal structure consists of a mixture of metallic and ceramic phases in heat treatment by partial reaction or conversion of the im Green body contained output phases is formed. 8. Composite body according to one of the preceding claims, marked by an internal structure of 5 to 60 vol.% Al, 0 to 30 vol.% Zr or / and Nb or / and Cr or / and Ta or / and Ti, each in metallic form, the rest of up to 40 vol .-% Al₂O₃ and 0 to 30 vol .-% of one or more of the following ceramic substances: ZrO₂, Nb₂O₅, Cr₂O₃, AlN, ZrN, Si₃N₄, TaC, WC, NbC, ZrC, Cr₂C₃, SiC, TiC, B₄C, ZrB₂, AlB, TiB₂, NbB₂, TaB₂. 9. Composite body according to claim 8, characterized in that its internal structure contains AlN, ZrN, ZrC or / and ZrB ₂ in an amount which gives a high modulus of elasticity. 10. Composite body according to one of the preceding claims, characterized, that the intermediate layer from the corresponding phases the outer layer and the inner structure.   11. Process for producing a composite body according to the Claims 1 to 10, characterized, that an intimate mixture of Al and an or several of the elements and connections Zr, Nb, Cr, Ta, Ti, Al₂O₃, ZrO₂, Nb₂O₅, Cr₂O₃, AlN, ZrN, Si₃N₄, TaC, WC, NbC, ZrC, Cr₂C₃, SiC, TiC, B₄C, ZrB₂, AlB, TiB₂, NbB₂, TaB₂ manufactures, especially by mechanical alloy Ren, the mixture forms powder metallurgically and the green bodies obtained thereafter with formation the gastight outer layer is heat-treated, this Heat treatment at least temporarily in the presence of Oxygen occurs and with rapid heating to one Temperature between 800 ° C and 1700 ° C only as long is led that still metallic phase in the internal structure is present and then optionally the one formed Body hot isostatic at temperatures between 1400 and 1800 ° C in argon or nitrogen or a mixture is further compressed by argon and oxygen. 12. The method according to claim 11, characterized, that the Al₂O₃ / ZrO₂ or Al / Zr share of the output mi at least partially through fine-particle (as 1st µm) powder from one or more of the intermetallic Phases Al₃Zr, AlZr and AlZr₃ is replaced. 13. The method according to claim 11 or 12, characterized in that one produces the mechanically alloyed mixture of the starting substances by attrition in a liquid organic medium with ZrO ₂ grinding media. 14. The method according to any one of claims 11 to 13, characterized in that one uses a starting mixture of Al, Al ₂ O ₃ , ZrO ₂ and AlN. 15. The method according to claim 14, characterized, that the mixture contains one or more of the components TiC, Contains TiB₂, Y₂O₃, ZrC, AlB₂, Zr, Cr or ZrN. 16. The method according to any one of claims 11 to 15, characterized, that the mechanically alloyed powder mixture at Temperatu Ren pressed between 200 and 500 ° C to the green body or is heat extruded and the green body on closing quickly to Tempe in an oxidizing atmosphere temperatures between 800 and 1700 ° C heated and annealed becomes. 17. The method according to any one of claims 11 to 15, characterized, that the green body first in a vacuum or in a non-oxidizing atmosphere at temperatures between Pre-sintered at 500 and 1400 ° C and then at Tempe temperatures between 800 and 1700 ° C in the presence of acid after-glowing. 18. The method according to claims 17 or 18, characterized, that the green body so quickly in an oxidizing atmosphere is heated that the outer layer is tight and completely is oxidized before the inside is completely oxidized becomes. 19. The method according to claim 18, characterized, that is heated with 8-15 K / min.   20. Use of a composite body according to one of the claims 1 to 10 as wear and thermal shock resistant part in Apparatus and mechanical engineering, especially as a turning point cutting plate.