DE2261644C3 - Isostatic hot pressing process for the production of dense sintered products - Google Patents

Description

The container and its contents are then cooled down

The invention relates to an isostatic and the glass container is separated from the pressed body.

Hot pressing process for the production of dense sintering The known isostatic processes have the

products and especially objects made of ceramics, disadvantage that the powder to be compacted in a

where such from piezoelectric, ferroelectric 45 separated, is brought to be evacuated,

or ferromagnetic ceramic as well as more transparent that after the hot isostatic pressing from the pressing

Ceramic must be separated from a special body for optical purposes.

Are interested. The invention includes a method in which

For certain applications of such sintering these process steps are omitted and thus the

products require non-porous materials. Does not have the disadvantage mentioned to 50. The technical

these applications include B. transparent ferro- wall when performing the invention

electrical or paraelectric ceramics for electro-process is significantly less than with the

optical purposes, piezoelectric ceramics for known processes.

Surface acoustic wave filters, ferromagnetic ceramics The known methods (i.e. without

for magnetic heads and for microwave applications, 55 pressure application) have produced sintered bodies

and transparent ceramics for lamp envelopes. still a residual porosity, which is generally

So must z. B, namely for the applications of and in particular for certain applications as

z. B. lithium zinc ferrites of the formula proves disadvantageous.

(Li Fe) Zn Fe O ^ ' ^e invention now further includes a method

o, s 0.6 lx 2 4 H _{6o to ers e} ii _un g t _of sintered bodies without significant

where χ varies from 0.2 to 0.7, in the microwave residual porosity.

area for circulators and phase shifters in hollow Further disadvantages of the known methods (NTC thermistors The porosity of the ferrites can be very low, because the pressing process) are sometimes that not or Demagnetizing fields of the pores the desired only difficult objects arbitrarily complicated Disrupt the homogeneity of the magnetic field in the ferrite. 65 form are to be produced.

In the application of ferrites as a material for the invention now also includes a method

Magnetic heads for magnetic recording and which do not have this disadvantage.

Reproduction it has been found that the When using the usual sintering process for

Manufacture of ceramic objects, i.e. by sintering without the application of pressure, become objects obtained whose density is 90 to 99% of the theoretical density.

The method according to the invention is also suitable for the further densification of sintered bodies made from Ceramic and metal (cermet) consist.

The invention relates to a hot isostatic pressing process for producing a sealed Sintered product made of ceramic or made of ceramic and metal, in which a sintered product with closed Porosity made of ceramic or of ceramic and metal at the sintering temperature directly and on all sides Is exposed to gas pressure.

Such a process is described in US Pat. No. 3,562,371. In this known method, gas pressures of at least 700 kg / cm ^a (= 700 atm) are used.

If such high pressures are used, a special type of apparatus must be used, including in connection with the safety to be taken into account. This disadvantage arises in particular from the fact that the apparatus is used at high temperature. In the (single) exemplary embodiment described in the cited patent, a temperature of 165O ⁰ C is used.

In the method according to the invention significantly lower gas pressures are used, so that the mentioned disadvantage does not occur.

It has been found that closed porosity sintered products can be produced by hot isostatic pressing further compressed using a much lower gas pressure than in the known method can be, if in the crystals from which a polycrystalline sintered product subjected to the treatment, Lattice defects are present.

The invention now relates to a method for densifying a polycrystalline sintered body with closed porosity, in which this body is directly inert on all sides at the sintering temperature Gas is exposed to increased pressure, and is characterized in that a polycrystalline sintered body, lattice defects appear in its crystals, an inert gas with a pressure of 25 to 300 kg / cm * is exposed.

The production of polycrystalline sintered bodies, in the crystals of which lattice defects occur, can be carried out by per se known methods take place.

The lattice defects can be caused by vacancies in the crystal lattice (cation or anion vacancies) Interstitial ions, through deviations from stoichiometry, through piatical deformation or through Combination of two or more of these causes may be brought about.

The lattice errors can e.g. B. can be achieved by incorporating foreign ions (doping), their valence differs from the valency that usually takes the place of these ions.

They can be obtained by sintering or post-heating in such an atmosphere is that at the temperature used, the sintered body absorbs or releases oxygen. Also can they are obtained in certain cases by an excess of one of the constituents.

It should also be mentioned that a paper in "Ceramic Abstracts", April 1969, p. 160, c, can be found that when using high pressures pores through a

Make diffusion disappear. This process obviously depends on the pore size. From the The report shows that the lattice defects only arise through the use of high pressures. This Work is therefore not the teaching that the hot isostatic pressing of presintered Material with closed pores the lattice defects are a prerequisite for having a very large Density can hold ei even when using relatively low pressures.

In the examples below, lattice errors are achieved in a number of ways, namely:

In the case of lead titanate zirconate by incorporating lanthanum (Examples I, II, III, VI and VII) or by incorporation of iron (Example IV); for the Mn-Zn ferrite mentioned below (Example X) and the Ni-Zn ferrite (Example XI) by an excess of oxide of a divalent metal; in the case of the aluminum oxide mentioned below by adding magnesium oxide;

in the case of barium titanate by an excess of titanium.

The method according to the invention serves for the further compression of ceramic or ceramic and Metal composite sintered bodies, which can be produced by known methods and the pores in the body have no direct connection to the body surfaces, d. H. Sintered bodies that have a so-called closed porosity. This is with the after the usual Sintered bodies made of ceramic or made of ceramic and metal with a sintering process Density of over 90% of the theoretical density is the case for practically all pores. For such sintered bodies the method according to the invention can therefore be used with good success.

In the known isostatic hot press sintering process, the material to be sintered is placed in a container, the z. B. made of glass or rubber (see DT-OS 14 49 403) is brought, the container is closed and evacuated. Then the container with its contents is heated to sintering temperature and the container is a exposed to hydrostatic pressure.

In the method according to the invention, the sintered body to be further compacted is not combined into one Brought to a separate container, but (at sintering temperature) directly exposed to a gas pressure.

This means a particular advantage of the method according to the invention: by using the With gas pressure on all sides, sintered bodies of any shape can be further compressed.

In general, an inert gas is used as the working gas. In some cases a gas mixture is used wherein a component is not to be considered inert. This is e.g. B. the case when further Compaction of z. B. ferrite bodies a certain oxygen partial pressure is required to achieve the desired Maintain the oxygen content of the ferrite.

Inert gases that can be used are, for example, noble gases such as argon; further is z. B. nitrogen is a suitable gas.

In the context of the invention, an inert gas is considered to be a gas that is released while the method is being carried out leaves the chemical composition of the sintered body unaffected.

It has been found that when using the

The method according to the invention still has a considerable valve (for the inlet of the working gas), 10 a mano further compression at such temperatures instead of meter and 11 a gas outlet valve, which are lower than the temperatures. It has been found that the purity of which nor a sintering with the usual working gases (e.g. nitrogen or argon) no special sintering process takes place and so the requirements of 5, sintering objects do not exert any external pressure. The term sintering temperature in the sense of the same results. For this purpose, methods according to the invention were therefore used, which, according to the customary sintering process, also the temperatures, wherein according to the application, are produced. These bodies were further densified in accordance with the method according to the present invention. Objects subject to the procedure were held for example. E. in the usual way by sintering in and in which, according to the usual method, O ₈ atmosphere for 4 hours at 1250 ° C samples without the application of external pressure no sintering or no significant sintering would take place with the composition. _{ph T} rr ₇ sn

It is assumed that the further 15 ™ o.8875La ₀ . ₀₇₅ (l W ^ ₅ ) U ₈

seal of the method according to the invention under- produced. These samples had a density of

sintered bodies caused renewed sintering instead of 7.68 ± 0.01 g / cm *. The theoretical density should

takes place, even in cases where the temperature, depending on the vacancy distribution, is between 7.79 and

at which the process is carried out is lower than 7.82 g / cm '. The samples became prismatic

than the usual sintering temperature. It is further an- ao body with the approximate dimensions of

taken that this is made possible in that 16 χ 5 X 5 mm formed.

the pressure applied promotes sintering and ins- After hot isostatic pressing according to the invention

special in that in the inventive method at 1250 ° C. in 200 atm N ₂ as the working gas, the density was

drive the exertion of the pressure in isostatic up to 7.78 g / cm 'and with hot isostatic pressing

looks to be considered ideal. In the known as according to the invention with 200 atm of argon as the working gas

isostatic method, on the other hand, in which the to be increased to 7.81 g / cm *.

sealing body is in a container, on In F i g. 2 is the increase in density D - appropriately

the isostatic pressure is exerted, it will give as a percentage of the theoretical density - at

isostatic exertion of pressure on the application of the method according to the invention to be compacted in

Body can only be approximately fulfilled. 30 Dependence of the Nj working gas pressure P in atmo- The pores of the spheres with the invention using the example of two different ceramics

drive further to be compacted sintered bodies can be shown

be filled with various gases. In curve 1, the density increase for a BaTiO ₃ -

It can be assumed that the piezoelectric kera sample with an initial density of 98.1% of the

mix sintered bodies with perovskite structure, which after 35 theoretical density at a working temperature of

usual method shown by sintering in an acidic 125O ⁰ C and a duration of 1 hour.

Substance atmosphere are produced, such. B. those from samples 2 and 3 consist of Lead zirconate titanate, the pores filled with oxygen _{PK T.} fr-, ₇ _ _Λη

are. Since in such materials at the sintering _tempe- ^ b 018876 La ₀₁₀₇₆ (I i _0i4 , £ r _{0. M} ) O _s

temperature, the O ₂ diffusion is large, can be assumed 40 with an initial density of 98.2% of that when carrying out the theoretical density according to the invention. For curve 2, the working process was the oxygen through the material hinaus- temperature HOO ⁰ C for curve 3 1150 ⁰ C. The Verdiffundiert, seal time was for Prob; 2 and 3 respectively

However, it has been shown to be successful for 0.5 hours.

Rich implementation of the process according to the invention. It can be seen from these examples that pressures

rens, it is not necessary that the gas, which is between 100 and 200 atm for optimal compression

Pores of the sintered body to be further compacted care: n. A further increase in the working gas

finds, through the material of the body, diffusion pressure beyond 200 atm is for the invention

can date. Process not harmful, but should not have any significant

In both cases, sintered bodies can have the same advantages with regard to further densification Dimensions are compacted. It is believed that ceramics bring. Working gas pressures above 200 atm

in those cases in which this is useful in the pores, if the sintering temperature is not

the gas cannot diffuse out, the gas can be increased sufficiently,

in the pores when the pore volume is reduced. 2 can be seen, set noticeable

With the exception of the pressure of the working gas, grain seals at pressures of 25 or 50 atm

is primed. a comparison of curves 2 and 3 in FIG. 2 gehl

The method according to the invention is shown on the basis of the fact that the lower pressures lead to a noticeable

gender exemplary embodiments explained in more detail: the higher the sintering temperature, the higher the sintering temperature

In Fig. 1 i.rt is the rature leading to the invention. Therefore bet on a further increase Tests used apparatus schematically again - the sintering temperature already noticeable densities

given. 1 means a water-cooled working gas pressure of 10 atm.

cylindrical steel car, designed for a maxi. Tables 1 and 2 show some results mi

painting pressure of 200 atm, 2 the thermal insulation, 3 a sintered body made of ferroelectrisdien perovskhischei

resistance-heated furnace, 4 the materials to be compacted of the compositions mentioned below

ceramic body, 5 clamps (a total of 14 65 which when using nitrogen or argon al

all around), 6 the gasket, 7 a thermocouple to get the working gas. The sintered body wasei

Temperature control of the furnace 3, 8 insulated thermo in the usual way by sintering in oxygen atmosphere

element and heating supply lines, 9 a gas inlet sphere made.

7 8

Table 1 Working gas N,

ABCDE FGH

I 200 0.5 1220 7.57 7.68 1.45 7.64-7.69

II 200 0.67 1170 7.63 7.72 1.18 7.71-7.74 III 200 0.5 1250 7.68 7.79 1.43 7.79-7.82 IV 200 5 1250 7.95 8.01 0.75 8.0 V 200 2 1250 5.87 6.00 2.21 6.02 Table 2 Working gas Aigon A. B. C. D. E. F. G H VI 200 0.5 1220 7.57 7.67 1.32 7.64-7.69 VII 200 0.5 1250 7.67 7.81 1.83 7.79-7.82

Thereby means A: Sample number. B: pressure in atm. C: time in hours. D: temperature in degrees Celsius.

E: starting density in g / cm ³ \ _o ... . _do . ₄ ·. nt

_ _, * *. . , t determined with hydrostatic balance.

F: final density in g / cm ^s J ' ^K

G: density increase in percent. H: Theoretical density.

These letters apply to Tables 1 to 4. The composition of the samples was as follows: I and VI: Pb ₀ . ₇ , La ₀ . ₁ «(Tio« Zr _{0. E5} ) O _i . II: Pb ₀₁₈ S ₅ La ₀₁ Ii ^ o ₁ MZr ₀₁ W) O ₃ . III and VII: Pb ₀₁₈₈₇₆ I ^ ₀₇₅ (Ti ₀₁₈₆ Zr ₀₁₈₆ ) O ₈ . IV: PbCri ₀ , ₄ Zr ₀ ,, V, «Fe ₀ . _0ie O ₈ .

V: Ba ,. ₀ Ti _li00S O ₈ .

It can be seen from both tables - compare the values in columns F and H - that when using the process according to the invention, the theoretical density is practically reached.

For comparison, a was _{sintered after the usual atmosphere and N s} had a

drive by sintering in a nitrogen atmosphere from a density of 7.55 g / cm ^s . According to the invention

Piezoelectric, perovskite material together 50 isostatic hot pressing with 200 atm N ₈ as working

mixed sintered body with the gas according to the invention for 2 hours at 1170 ⁰ C, the increased

Process with 200 atin N ₂ as the working gas increased density, as can be seen from Table 3, to 7.73 g / cm *.

seals samples of the composition In this case it is assumed that the nitrogen

". t rr; 7V λγ » rnciA diffuses ^{out of} the pores, but under

rDe.eMLaiwUio.w ^ o.eju, _{55 strong} reduction in pore volume up to the

which is compressed in the usual way at 1170 ⁰ C working gas pressure for 4 hours.

Table 3

ABCDEFGH

Vin 200 2 1170 7.55 7.73 2.38 7.71-7.74

In addition to materials with a perovskite structure, 05 yttrium iron garnet (composition YjFe ₈ O ₁₁ )

z. B. the following other compounds with the as a characteristic representative of the compounds

hot isostatic pressing process according to the invention with garnet structure (results see column IX in

compacted to almost complete density: Table 4).

ίο

Mn-Zn ferrite (composition: 52.6 percent by weight of the compounds with a spinel structure

percent Fe ₂ O ₃ , 24.5 percent by weight MnO, (results see columns X and XI in table 4).

22.9 percent by weight ZnO) and aluminum oxide Al ₂ O ₃ (results see column XI

Ni-Zn ferrite (composition 49.7 weight- in Table 4). To make this body wa;

percent Fe ₈ O ₃ , 18.1 weight percent NiO, 32.2 5 aluminum oxide powder, which is 0.3 weight percent

Percent by weight ZnO) as a characteristic magnesium oxide contained, used.

Table 4

DEFGH

IX 200 4th 1300 4.82 5.16 7.0 5.17 X 200 4.5 1200 4.94 5.10 3.24 5.12 XI 200 4th 1200 5.31 5.33 0.38 5.33 XII 200 22nd 1300 3.93 3.98 1.27 3.99

It has been shown that the elimination of the residual seal by the method according to the invention at porosity in hot isostatic pressing according to the various gas pressures as a function of the sintering invention checked by light microscopic microsection duration ..

Can confirm examinations. Thus, according to the The lattice defects in the crystals of the polycrystalline

Usual procedures sintered samples to the polished linen sintered body are due to the excess Grinding brought about the residual porosity clearly recognizable in the form of titanium.

darker holes. If the same sample is subjected to the isostatic hot pressing process according to the invention, the sintering temperature was always 130O ⁰ C. at 25, 50 and 150 atm. Add as gas. These findings were made on all subjects - nitrogen was used, samples were examined. 30 The results are shown in FIG. 3 shown.

The samples I, H, III, VI, VII, VIII and XII of the above vertical ginks) are the specific gravity and

Tables showed after hot isostatic pressing vertically (right) the density in percent is theoretic of the invention in contrast to previously high table density (= 100%) specified. Transparency. A sample showed the horizontal is the pressing time (in hours loga-

Setting II with a thickness of 0.7 mm at 0.6 μm 35 rithmic scale) indicated. From this figure it can be seen that already at

less than 20%. a pressure of 25 atm (curve 25 atm)

There are examples in the art of materials that can achieve substantial compression in a good 10 hours, Due to their properties in principle especially at a gas pressure of 50 atm it takes about 5 hours are suitable for certain applications, the 40 of which almost reaches the theoretical density (curve practical use, however, fails because 50 atm) while using a gas pressure one with the known method of this Ma- of 150 atm this was the case in about 1 hour materials for such applications do not meet the requirements (curve 150 atm), th body with sufficient density can produce. The mean grain size in the compacted bodies

The latter is in certain cases also 45 was about 2 μπι.

causes the shape of the desired polycrystalline sintered body to be the same is so complicated that after composition, which was made in the usual way, a conventional sintering process but for a significantly longer time than usual on the body was not maintained at sintering temperature, or only with great effort, was used according to the use a known isostatic hot pressing 50 drive treated according to the invention. In a sintering process can be compressed, with the temperature of 1300 ° C and a gas pressure of sealing body in a tight 200 atm (nitrogen) body on all sides was no sealing after 10 hours Container must be brought. seal received. The mean grain size of the

In this context one could very many pers was about 100 μπι. It is believed that examples mention such. B. Magnetic heads made of fer- 55 with continued sintering (in the usual way) rituals, transformer cores made of ferrites, thin disc a recrystallization with strong grain growth chen with holes, tubular bodies made of Al ₂ O, and that this was originally for Lamp envelopes. pores located at the grain boundaries (intergranular

In addition to the advantages of the inven- tive pores already mentioned) due to the strong grain growth in the according to the process, 60 grains (crystals) have been obtained with this process (intragranular pores), Achievable greater dimensional accuracy is also mentioned worthwhile advantage. Pores, but intragranular pores do not

Removable for polycrystalline sintered bodies made of barium. This could explain why in the case of the coarse titanate, the composition of which can be given by the formula crystalline sintered body, no compaction Ba, ₀ Tij «» Ο, represented, the 65 was.

For this purpose 2 sheets of drawings

Claims (6)

Wear resistance of the heads due to the presence of patent claims: pores is particularly unfavorably affected. The arrival 1. Method of densifying a polycrystalline entity of pores is not only a disadvantage in relation to it linen sintered body with closed porosity, in terms of wear resistance, but also in terms of in which this body at the sintering temperature 5 the production of the magnetic heads, in which one medirekt and mechanical processing with an inert gas on all sides in the form of sawing, milling, Pressure is exposed, thereby marked grinding and polishing takes place. Especially with draws that a polycrystalline sintered body, machining with a saw or a chisel Lattice defects in the crystals of which can occur due to the presence of pores in the material inert gas with a pressure of 25 to 300 kg / cm * io crystallites are torn off. is exposed. It soute ^ ^ar ^ ¹¹ »that * ^ur <" ^ε mentioned users 2. The method according to claim 1, characterized in that fertilize the presence of pore-free ferrites draws that a polycrystalline sintered body is of paramount importance. whose crystals lattice defects occur, a The invention now aims to provide a method for inert gas with a pressure of 50 to 200 kg / cm ² 15 Production of practically pore-free sintered bodies is exposed and preferably from 100 to and in particular from such bodies made of ferrites, 200 kg / cm *. to accomplish. 3. The method according to claim 1 or 2, characterized in that one has already tried in various ways characterized in that, as the sintered sinter to be compacted, sintered bodies are produced with few pores. This is how in body a sintered body is used, which from ao "Philips Technische Rundschau", 29, pp. 25 to 33 (1968) Ceramic or cermet. a (non-isostatic) continuous hot pressing 4. The method according to claim 3, characterized in the described method for the production of ferrites, shows that the sintered body to be compacted is one which is sought after, body less Sintered body is used to manufacture from a porosity. Material of the group, which includes: ceramics, as Next are processes for the production of an iso- the crystals of which have a perovskite structure, known as a statically hot-pressed object. Both Ceramic, whose crystals have a spinel structure known process, is a container with the powder and ceramic ferrite. filled from which the item can be made 5. The method according to claim 4, characterized thereby; then the container is evacuated and marked, that closed as a sintered body to be compressed, a 30 table, then to high temperature Sintered body is used, which is made of ceramic heated, during which the container is deformed and the powder Ferrite exists, while a gas is compressed and sintered as an inert gas. such an oxygen content is used, So in the DT-AS 19 01 766 a method for that the oxygen content of the ferrite remains unchanged. Manufacture of isostatically hot-pressed objects remains. 35 of powder of metals or of inorganic ones 6. Formed sintered body, which is described by a non-metallic compounds, wherein move to one or more of the preceding glass containers with the powder under negative pressure going claims has been condensed. filled, then hermetically sealed and under pressure is heated to a temperature at which the container 40 soft and the powder is compacted and sintered.