US2082126A - Method of manufacturing porous metallic bodies - Google Patents

Description

' 1; .lie powders.

Patented June 1, 1937 METHOD. OF MANUFAc'runmG ronous METALLIC nonms nuaou Schulz,"Stuttgart, Germany a I no Drawing. Application June 14, 1934, Serial No. 730,677. In Germany June 15, 1933 12 Claims. (CI. 75-22) This methodrefers' to manufacturing porous metallic bodies of every kind. There are already known numerous proceedings of manufacturing rcus metallic bodies all of which were found- 5 ed on the idea to obtain, with relatively low temperatures, a'sintering as rapid and easy as possible, in order to maintain in the thus composed materials a greatest possible porosity; it has been ascertained, however, that such materials, made according to the proceedings known up to this day-suffer important shrinking and consequently condensation under prolonged heat treatment. The opinion-existed that a great volume of pores wasonly obtainable with easily sintering metal- A proceeding has for instance become known, in which the initial .product is a metallic powder obtained by the sintering together of metals obtained from carbonyls, because just such tiny particles sinter together par-' ticularlyveasily and quickly in consequence of their condition of. surface. Contrary to the above mentioned proceedings any metallic powder is chosen according to the present methodi however, its composition; mustbe, either through different 'conditions or through previous treatment of different duration of the separate, under certain circumstances completely homogeneous ingredients, that the ingredient, forming, as it were,a rigid frame or skeleton, shows, during the heat process, which causes the sintering, no, or at the utmost insignificant, appearances of shrinking. Y

According to the present invention the small method.

skeleton particles are obtained by the following As initial material there is generally a highly active, exceedingly fine metallic powder, susceptible to sintering, which may be obtained byprecipitation or by reduction from oxide powder.

. 40 This metallic powder is exposed to a suitably long heat-treatmenn in absence of oxygen or in presence of reducing gases, as for instance hydrogen.

The temperature and the duration of the first sintering are chosen such as to form a coherent but easily crumbling mass cake. This mass cake subjected in further successive steps in the same' manner to an analogous heat treatment, whereby the separate little grains always bake together and form anew a friable mass cake. With these separate processes of heat treatment the single 5 small grains condense more and more intheir' inner structure; In each mechanical trituration taking place after each sintering the mass cakes sinteredtogether. crumble essentially again into the small particles obtained after the first .sin- 10 by the following example of copper obtained from' oxide. Black, finely divided copper oxide arranged in. a loose mass is reduced in a hydrogen atmosphere at a comparatively low temperature. In order to maintain this low temperature, it is necessary when large amounts of copper oxide areused, to add an inert gas, for instance, nitrogen, to the hydrogen atmosphere, in an amount up to The mass obtained after the reduction is ground and is then passed through a sieve. The uniform granulated material thus obtained may be. de-

scribed as an active material, since it sinters and since its volume is reduced during the sintering process.

In order to obtain the other component whichis necessary for the production of porous bodies in accordance with the present invention, it is possible either to subject these active particles to a further treatment or to use a different material 35 which is obtained in exactly the same way as the active granulated substance by a reduction of copper oxide,- and which is passed through a sieve. The following procedure may be used:-

Copper granules which have been reduced at a comparatively low temperature and then comminuted and passed through a sieve, are arranged in a loose heap and are heated for four hours in a hydrogen atmosphere. A black, adhe'rent mass is formed which is then very care- 45 fully. comminuted, not so much by grinding as by' As used throughout this specification, the term non-shrinkable particles or skeleton particles is used to describe a substance, the density of which can be increased only with great difiiculty by a diminutionpf its volume; this term has no reference to the expansion and contraction of a substance caused by variations in temperature.

An essential point of this proceeding is further, the possibility of soldering together, respectively of sintering together massive metallic objects with the porous metallic body. To this purpose essentially longer heat treatments and such of generally higher temperatures are necessary, than those employed for instance in the manufacture of metallic bodies of carbonyl: metal-powder. The shrinking which always takes place with a similar treatment, hitherto was an unsurmountable obstacle for the manufacture of porous compound-metal-bodies by sintering. By mixing the ingredients which form the no more shrinking scaffold with finer ingredients which eventually are subject also to a greater shrinking, it is possible, to choose and to determine beforehand the porosity and size of pores within certain limits in a quite determined way.

If porous metallic bodies, obtained at a com paratively low temperature and in a comparatively short time from specially quick-sintering metallic powder, are subjected in the practice to a heat treatment of longer duration, as a rule a considerable shrinking takes place, whereby at the same time, the size of the pores decreases, and destroying cracks appear on generally the Whole porous body.

'To the contrary, if a change takes place at all, the change of porosity of the bodies made according to this new method, moves just in the contrary sense, viz. in thedirection of greater porosity, the outer volume remaining unchanged.

On account of the stability of volume of the metallic bodies prepared according to this proceeding, any granulous or powdered ingredients may be added to the initial powder or mixture of powder, for instance oxides, mineral sub.- stances or the like without any detrimental influence to the' good mechanical qualities of the originatedporous metallic bodies.

I claim:

1. The method of manufacturing porous metallic bodies,.which comprises mixing a metallic powder consisting of particles of a comparatively large size with a powder consisting of particles of the same metal of a comparatively small size, the first-mentioned particles being substantially less compressible than the second-mentioned particles and sintering the mixture in the absence of oxygen and pressure at a temperature which is lower than the melting point of said metal.

2. The method of manufacturing porous metallic 'bodies, which comprises mixing a powderv consisting of particles of a metallic alloy of a comparatively large size with a powder consisting of particles of the same metallic alloy of a comparatively small size, the first-mentioned particles being substantially less compressible than the second mentioned particles and sintering the mixture in the absence'of oxygen and pressure at a temperature which is lower than the melting point of said metallic alloy.

3. The method of manufacturing porous metallic bodies, which comprises mixing a powder consisting of particles of a metallic alloy of a comparatively large size with a powder consisting of particles of a: metal of a comparatively 'small size, the first-mentioned particles being compressible than the first-mentioned particles,

and sintering this mixture in the absence of oxygen and pressure at a temperature which is lower than the melting points of said metallic powders.

5. The method of manufacturing porous metallic bodies, which comprises reducing a metal compound in a reducing atmosphere at a low temperature obtained by diluting the reducing gas by an inert gas to produce a metallic powder consisting of particles of a comparatively small size, mixing said metallic powder with a metallic tively large size which are substantially less compressible than the first-mentioned particles, and

sintering this mixture in the absence of oxygen and pressure at a temperature which is lower than the melting points of said metallic powders.

6. The method of manufacturing porous metallic bodies, which comprises'reducing a mixture of metallic compounds, each of which comprises at least one of the components of a metallic alloy,

powder consisting of particles of a comparain a reducing atmosphere at a low temperature to produce a powder consisting ofparticles of a metallic alloy of a comparatively small size, mixing said powder with a powder consisting of metallic particles of a comparatively large size which are substantially less compressible thanthe first-mentioned particles, and sintering this mixture in the absence of oxygen and pressure at a temperature which is lower than the melting points of said powders.

7. The method of manufacturing porous metallic bodies, which comprises sintering a finely divided loose metallic powder in a reducing atmosphere at a temperature which is considerably lower than the melting point of said metallic powder, whereby said powder forms a cake, comminuting said cake to provide a metallic powder having particles of a comparatively large predetermined size, subjecting the powder thus obtained a number of times to a sintering procws resulting in the formation of a cake and a subsequent oomminuting of this cake until a metallic powder is produced, which consists of particles of a comparatively large size, mixing the lastmentioned powder with a powder consisting of metallic particles of a comparativelysmall size, the first-mentioned particles being substantially lesscompressible than the second-mentioned particles and sintering the mixture in the absence of oxygen and pressure at a temperature which .is lower than the melting points of the powder, whereby said powder forms a cake, com- 1| minuting said cake to provide a metallic powder 4 and then reducing the surfaces of some or the body. so

last-mentioned particles, whereby particles oi a comparatively small size are produced which are mixed with the particles of a comparatively large size, and sintering the resultantvmixture in a reducing atmosphere at a temperature which is lower than the particles.

9. The method 'of manufacturing porous me tallic bodies, whichcomprises mixing a metallic powder consisting of particles of a comparatively large size with a powder consisting of metallic particles of a comparatively small size the ilrstmentioned particles being substantially less compressible than the second-mentioned particles, immersing a metallic body into said mixture, and sintering the mixture along with the metallic body in the absence of oxygen and pressure at a temperature which is lower than the melting points at said metallic powders and said metallic 10. The method tallic bodies, which comprises mixing a metallic powder consisting of particlesoi. a comparatively large size with a powder consisting of metallic particles of a comparatively small size, the firstmentioned particles being substantially less com pressible than the second-mentioned particles, mechanically 'roughening some oi the surfaces of a metallic body, immersing said metallic body-into said mixture, said mixturebeing in contact with theroughened surfaces or said body. and sintermelting points of the metallic of manufacturing porous me-f points ing the mixture along with the metallic body in the absence or oxygen and pressure at a temperature which is lower than the melting points of said metallic powders and said metallic body.

ll..The method of'manufacturing porousrnetallic bodies, which comprises mixing a metallic powder consisting of particles of a comparatively large size with a powder consisting of metallic particles of a comparatively small size, the firstmentioned particles being substantially less'compressible than the second-mentioned particles; subjecting some of the surfaces of a metallic body to an oxydation and a subsequent reduction,

whereby said surfaces are roughened, immersing said metallic body into said mixture, said mixture being in contact with the roughened surfaces of said body, and sintering the mixture along with the metallic body in. the absence of oxygen and pressure at a temperature which is lower than the melting points of said metallic powders and said metallic body.

12. The method of manuiacturing porous metallic bodies, which comprises mixing a metallic powder consisting of particles of a comparatively large size with a powder consisting of metallic particles of a comparatively small size, the thatmentioned particles being substantially less comm'e'sslble than the second-mentioned particles. subjecting-some of the surfaces oi a metallic body to an oxydation to roughen the same, im-

' mersing said metallic body into said mixture, said mosphere and in the absence of pressure at a temperature which is lower than the melting RUD'.

of said metallic powders and said metallic