FR2560087A1 - BORE NITRIDE SURFACE ATOMIZATION ADJUSTMENT - Google Patents

Abstract

A BODY OF MELTED MATERIAL HAVING A HIGH MELTING POINT IS ATOMIZED TO PRODUCE A SIGNIFICANT PERCENTAGE OF FINE PARTICLES BY DIRECTING THE BODY IN THE FORM OF CURRENT TO PUT IT INTO A ZONE OF ATOMIZATION AND BY DIRECTING 22 A CURRENT OF ATOMIZING GAS IN THE PREVIOUS CURRENT SO AS TO ATOMIZE AND DISPERSATE IT. WHEN THE MATERIAL IS ATOMIZED IN THE MELT STATE, ORIFICE 22 FROM WHICH THE GAS EXITS IS LOCATED IN A LOCATION EXTREMELY CLOSE TO THE SURFACE OF THE CURRENT TO BE ATOMIZED. APPLICATION TO THE MANUFACTURING OF POWDERS.

Description

The present invention relates generally

  the manufacture of powders from a liquid melt

  by atomization and solidification. More particularly,

  it relates to a process for the preparation of tempered materials

  high temperature in finely divided form by atomization

  fluid, an apparatus in which such a process is carried out

cut and the product thus obtained.

  By way of example, the present invention can be applied to the manufacture of powders from masses

fuses of superalloys.

  There is a well-established need for a means

  economical way of making super-thermal powders

  bindings. Powders of this type can be used in the production of super alloy articles by making use of

  powder metallurgy techniques. Industrial needs

  trials present for such powders are expanding and this expansion will continue as the demand for

  Superalloys is getting bigger and bigger.

  Currently, only about 3% of the industrially manufactured powder has a diameter of less than 10 microns and the cost of such a powder is therefore

very high.

  An important element of the cost price of

  The fine, spray-prepared and used in industrial applications is the cost of the gas used in the atomization. Currently, the cost of the gas increases with the percentage of fine powder desired to be obtained in an atomized sample. In addition, as we seek to obtain finer and finer powders, the amount of gas per unit mass of powder produced increases. The gases consumed in the manufacture of the powder, in particular the inert gases

such as argon, are expensive.

  There is currently a growing industrial demand for finer powders. Therefore, it is necessary to develop techniques and devices

  gas atomization which increases the efficiency of

  the conversion of a molten alloy into powder, and to save the gas consumed in the production of powder in a desired size range, in particular

  in case this beach becomes smaller and smaller.

  The manufacture of fine powders is influenced by the surface tension of the melt from which the fine powder originates. For melts having a high surface tension, the manufacture of a fine powder is more difficult and requires more gas and energy. The typical current yield of industrial manufacture of a fine powder having an average diameter of less than 37 micrometers obtained from molten metals having high surface tensions is of the order of 25 to 40%

in weight.

  Fine powders of certain metals are used

  having a diameter of less than 37 micrometres in the pulverulent

  low pressure plasmas. In the preparation of powders of this type by the industrial processes currently available, a percentage of powder as high

  60-75% should be discarded because the powder is

  mensionnée. This requires selective removal of the only fine powder and the disposal of the oversized powder has the effect of increasing the cost

usable powder.

  Fine powders also find uses

  in the field, changes and growth

  fast, accelerated solidification materials. In general

  the higher the percentage of fine powder that can be

  If a process or apparatus is large, the process

  or the device proves useful in the technology of

accelerated development.

  It is known that the solidification rate of a melt particle having relatively small dimensions in a convective environment such as a moving fluid or mass of fluid is approximately

  proportional to the inverse of the square of the diameter of the

  ticule. The following expression therefore applies to

That relation.

o Tp D2 tp o

  T is the cooling rate of the

P ticle and,

D is the diameter of the particle.

  Therefore, if the average particle diameter value of the composition is reduced by half, the cooling rate then increases by a factor of about 4. If the average diameter is again reduced by half, the overall cooling rate is 16 times

bigger.

  It is desirable to manufacture powders having

  small particles for some applications

  especially for those where cooling speed is

  the particle plays an important role in the ob-

  retention of properties. For example, there is a need -4-

  for rapidly solidifying powders having

  less than 37 micrometres and, in particular, for the production of powders of this kind with economic means. In addition, for some applications it is also important to have particles whose size spectrum is narrow. Therefore, if it is desired to have particles having a diameter of 100 micrometers

  for certain applications, a method allowing

  most of the particles in the 80-120 micro-

  meters will have a significant advantage for many applications of these particles compared to, for example,

  a process in which the majority of particles are

  taken in the range 60-140 micrometers. There is also a

  important economic advantage to be able to manufacture

  of average known or predictable particle size and a predictable range of

  particles. The present invention makes it possible to improve the

  study in the manufacture of powders of this type on the scale

industrial.

  If 100 micron particles are made with a first process from a given molten liquid metal for a particular application, and

  then learns to produce particles with a

  average of 50 micrometers, this second method will

  much faster cooling and solidification

  particles formed from the same metal in the molten state. The present invention teaches a method which

  makes it possible to form smaller particles with

  higher percentages from melts, among others, from a liquid metal in the molten state. In this new process a much faster rate of solidification of these particles is obtained, partly because the particles produced are themselves smaller on average and also because the manufacture can be repeated.

  and is reproducible on an industrial scale.

  The obtaining of small particles is interesting in terms of rapid cooling and

  benefits that result from the rapid cooling of cer-

  Some materials in the molten state. In this way we can ob-

  to maintain new amorphous and related properties. The

  The present invention allows the manufacture of powder constituents.

  killed particles with small dimensions with the

  fast cooling so allowed.

  Powder metallurgy technology currently requires fine and ultrafine particles and particles ranging in diameter from 10 to 37 micrometers. The new process of this

  The invention allows the manufacture of particles having a di-

  average meter between 10 micrometers and 37 micrometers.

  Obtaining particles having this small diameter may be important for the consolidation of the material by conventional powder metallurgy, since it has been observed that a powder having small particles may allow a higher sintering rate. In addition, it can play an important role in the consolidation of the material having small particles with a material having particles of larger dimensions in the case where this consolidation is desirable on the

  based on a higher packing density.

  Current trends in metal-

  The powder industry is of great interest for fine metal powders, ie for powders having a diameter of less than 37 micrometers, as well as for ultrafine powders, in particular for powders having a diameter of less than 10 micrometers. High surface tension in a molten material makes it more difficult

  the formation of particles of smaller dimensions.

  Conventional apparatus for the manufacture of atomized powder from molten metals gives products whose characteristics depend on the processes of the invention.

  preparation and materials that have spectra of

  relatively large particles. Spectra of

  large width of the particle dimensions are

  shown in Figure 3 by the curves A, B, C and D. The examination of

  these curves show that particles everywhere have dimensions

  from less than 10 microns to more than 100 micro-

  meters. The percentage of particles of a fine powder,

  that is, less than 37 micrometers in diameter,

  Bricked by conventional technology is in the range of about 0 to 40%, and the percentage of the powder

  ultrafine, that is to say with a diameter of less than 10 micro-

  meters, obtained with this technology is in the range from rC O to 3%. Because of the small percentage of the small particle powder that is formed in such products, the cost of manufacturing ultrafine powder may be excessive, as high as hundreds, or even

  thousands, of dollars per kilogram.

  The curves in Figure 3, and more particularly

  curve E, show that the size range of

  particles obtained with the processes of the present invention.

  when they are used in the manufacturing process of

  fine powders is significantly better than

  existing conventional assignments. The data on which Curves A, B, C, and D in Figure 3 are based are from an article by A. Lawly entitled "Atomization of Specialty Powder" (Atomization of Specialty).

  Alloy Powders), published in the January 1981 issue of

nal Of Metals.

  The data of the article of the Journal Of Metals, as well as those which made it possible to build the curves A, B, C and D, concern a powder formed from masses

  fuses of superalloys. The data that made it possible

  parte curve E are also data relating to the preparation of a powder from a melt of 7 superalloys so that the two sets of curves

are quite comparable.

  It is known that there are great differences in the ease of preparation of a powder from different families of alloys. Figure 3 gives typical distributions of

  particles of powders in the case of powders of super-

  bindings produced by different atomization technologies.

  Curve A relates to atomized powder with argon, curves B, C and D relate to powders produced by the rotary electrode method,

  rapid solidification, and vacuum atomization, respectively

tively.

  The area or hatched strip delimited by the

  besides E and F, indicates the range of distributions of

  of powder obtained using the present invention.

  in the manufacture of fine powders.

  It is readily apparent from the various curves of FIG. 3 that the powder prepared according to the process of the present invention, and using its apparatus, has a range of particle size and cumulative particle size, which is much smaller than the ranges obtained with conventional methods, particularly in the small size range of about 60 micrometers and

less.

  The hatched area of the graph between lines B and F is an envelope showing the part of this graph where powdered products can be produced in

  using the technical processes of this invention.

  in the case of the production of fine powders.

  According to this graph, it appears that the process of the present invention allows the formation of powders having between 10 and 37% of particles of 10 microns and less and that of powders having between 40 and 70% cumulative

  particles less than 37 micrometers.

  - 8 - With the methods and apparatus of this

  It is possible to manufacture a fine powder with a yield of

  higher than that obtained with the other procedures

  The practice of the present invention results in more efficient energy transfers between the atomizing gas and the liquid metal to be atomized. One way of implementing this better manufacture of fine powders is to bring closer to a closeness never reached so far.

  flow of the melt and the nozzle of the atomizing gas

  tion. This close proximity of the gas nozzle and the melt flow orifice is referred to herein as the "close coupling". The advantages of the principle of close coupling have been recognized in the literature as will be explained hereinafter; however, no invention has so far permitted the use of this principle with high temperature materials. This is due, at least in part, to the problem of the accumulation of the high temperature solidified melt on the nozzle of the

  atomization gas and other parts of the

atomization.

  An important problem associated with gas atomization nozzles and processes of the prior art has been the solidification of small dots and globules of the alloy.

  atomized at high temperature on the surfaces of the nozzle.

  The resulting accumulation on the nozzle was sometimes the cause of the cessation of the atomization process. This cessation originates from the closure of the melt discharge hole or, at least in part, is due to the fact that the atomizing gases can not strike directly.

  with a high energy the current leaving liquid metal.

  In the most severe cases, this accumulation of solid deposit at the tip of the nozzle caused its separation from the nozzle. This sometimes results in contamination of the powder formed with the material from the nozzle or - 9

  of the melt discharge system.

  In a conventional apparatus, the problem of the accumulation of solidified material at high temperature on the gas nozzle or on the orifice of the metal in the molten state is solved by maintaining the nozzle at a relatively remote distance.

  of the atomization zone, as will be explained more fully

below.

  The problems of the progressive increase of

  numerous small dots and solid melt globules

  depended on the atomization nozzle is most critical for

  melts at very high temperatures and in particular

  bind for molten metals that exhibit temperatures

high melting point.

  There is a big difference between the practices that can be used with low temperature materials

  for the formation of fog by

  gases on liquid currents and the phenomenon occurring at high temperatures. In general, in the

  formation of fogs at low temperature, it is possible to use

  be materials that are liquid at room temperature

  and those that become so at temperatures up to about 300 C. The atomization of materials at these low temperatures and in particular materials that are liquid at room temperature is not affected by the occlusion of the nozzle of solidified metal spray with the importance encountered when using high temperature fused metals or other

  high temperature. The accumulation of material at low tempera-

  The temperature on an atomization nozzle does not lead to the destruction of the elements of the nozzle itself. Moreover, at low temperatures, there is much less reaction and interaction between the atomized metal and the tube of

  supply of melt or materials from other parts

  of the atomization nozzle. A metal melt supply tube can be used to atomize the

- 10 -

  materials at a temperature of 300 C or less, but ceramic supply systems must be used at high

  temperatures of 1000 C, 1500 C, and 20000 C, and more.

  Another difference is that the thermal gradient in the wall of a melt supply tube between this melt and the atomizing gas increases with the temperature of the melt to be atomized. For an atomization system with a constant geometry, it takes a

  gaseous flow rate when the heat of the mass

  due is higher because of the greater amount of heat to extract. A larger amount of gas per unit volume of the atomized melt may result in a greater tendency for spurting and bubbling of the melt into the apparatus. In the case where the melt is very hot, with a temperature

  on the order of 1000 C or more, a droplet can become

  instantly change and adhere to a surface with

  lower temperature. At elevated temperatures, materials

  They are chemically more active and can form stronger bonds to the surfaces they are in contact with than the melted materials at lower temperatures.

  Although we do not wish to be bound by the

  the representation or description given here,

  it is thought useful to highlight the nature and character of the present invention to

  general description of the atomization mechanisms of which he

  are discussed and which have been described in the prior art and provide a graphical representation of the phenomenon occurring with the atomization of the prior art. In this

  Indeed, reference is made to Figure 4 which is a representation

  schematic representation of a phenomenon of atomisation of the art

  which is implied to have occurred during

  that the methods of the prior art are used. In the figure, the position of two gas orifices is represented.

- 11 -

  and 32 with respect to a melt stream 34 as

  this is conventional in the prior art. More specific-

  the nozzles 30 and 32 of the gas jet are spaced from the melt stream and also form a certain angle between them so that the gas jets are directed on the

  melt stream at a significant distance from the

  ges. This figure is somewhat schematic and we

  will assume that the nozzles 30 and 32 could actually be a single annular nozzle surrounding the melt supply apparatus and could be powered from

  from a conventional gas chamber. The supply apparatus

  The melt 36 is also shown schematically. In the prior art, the phenomenon is known that an inverted hollow cone is formed in the melt stream during its descent to the region where the junction of currents from the respective nozzles 30 and 32 occurs. Junction 38 is the one where the two axes, or directions, of the two gaseous currents could be cut if there were no interference between them. However, they act on the flow of the melt during its descent and part of this action is reflected by the formation of the inverted hollow cone, shown

  in the figure by the reference 40.

  The following phenomenon occurring in the process

  The classic atomization is the bursting of the cone wall in ligaments or globules of melt. This phenomenon occurs in the area shown in the figure by the

reference 42.

  The following phenomenon occurring in the atomisa-

  tional dislocation is the dislocation or atomisation of

  in droplets. This is shown in the figure as generally occurring in the area below which there is ligament formation. The individual droplets or particles are shown as being

- 12 -

  formed of droplets or larger globules.

  According to this schematic representation, the atomisa-

  tion is a multi-phenomenon, multi-

  stages, of which the first phenomenon is the formation of the inverted cone; the second phenomenon is the bursting of the wall

  cone in ligaments, and the third phenomenon dislocates

droplet ligaments.

  With regard to the formation of droplets,

  sees from this description that this is a phenomenon

  in the sense that a very high percentage of

  telettes is formed by bursting ligaments or globules.

  The most advanced work on the atomization of liquid metals with remote coupling found in

  The technical literature is entitled: "The Disintegration

  Liquid Lead Streams by Nitrogen Jets

  Flow of Lead Liquid Currents by Nitrogen Jets) by J. B. See, J. Rankle and T. B. King, Met. Trans. 4 (1973) p.

  2669-2673, this document describing the phenomena of atomisa-

  on the basis of studies carried out with the help of

fast graphing.

  What is distinct and new in the process of the present invention is the greatly reduced formation of

  secondary particles and the very high degree of

  main direct action of particles immediately from the melt and without the need to go through a second step of subdivision of the melt,

  as schematically illustrated in Figure 4 and de-

previously written.

  To prevent droplets at such a high temperature from adhering to the portion of the apparatus that is cooled by the gas supply mechanism, the prior art high temperature atomizing apparatus provides

  the gas from one or more nozzles which are relatively

  distant from the surface of the current struck by the jets

gaseous.

- 13 -

  When the nozzle is spaced from the atomization zone

  There is an appreciable reduction in the energy of the gas during its movement between the nozzle providing it and the point of impact with the liquid metal to be atomized. There are significant losses of diffusion and entrainment as the gas travels the distance between the nozzle and the stream from the melt. It has been estimated that the loss

  more than 90% of the initial energy to

  some embodiments of commonly used molten metal atomization equipment. As a result,

  processes using gas jets located at a

  The distance of a current or a mass of molten material to be atomized does not use the gas economically.

  because it takes a lot of gas to make up for the loss of energy

  occurring in the gaseous stream before there is

  contact with the stream of molten metal.

  Such a remote coupling of a current of a

  melt and atomizing gas supply orifices

  This is illustrated in U.S. Patent Nos. 4,272,463; 3,588,951; 3,428,718; 3,646,176: 4,080,126; 4,191,516 and 3,340,338, although not described in terms of

remote coupling.

  It is known in the prior art to use nozzles made of metal and even of plastic material

  gas jet is very close to the tube or

  liquid. For example, the atomization of a liquid at room temperature can be carried out without solidification and serious accumulation of liquid on the nozzle. Some

  paint spray nozzles, for example, corres-

lay with this type of construction.

  In the book titled "The Production of Metal

* Powders by Atomisation "(The manufacture of metal powders

  by atomization) by John Keith Beddow and published by

  Hayden Publishers, see page 45 for various

  nozzle designs for the manufacture of a metal

- 14 -

  powder from a metal stream in the molten state. Such atomization involves gas atomization at high temperature. The Beddow nozzles are annular in that they have a central orifice for the development and supply of a liquid metal stream. The gas is

  provided by an annular nozzle which surrounds the central orifice

  tral. Beddow's nozzles are similar

  superficial with that shown in Figure 1 of the pre-

  description. The problem of accumulation on

  Annular nozzles such as those described in Beddow's work are developed immediately below the figures on page 45 in the following form: "An important problem raised by the annular 1S nozzles is that of" build-up "on the body of the metal nozzle, this is due to

  molten metal spurting on the part

  top of the nozzle, especially near the perimeter at the bottom. There is solidification of the metal that has sprung up, accumulation of more

  liquid metal and, at a later stage of the process,

  the air jet causes inflammation of the metal

  hot having accumulated. This is how the opera-

  It may well be possible for a nozzle block to lose a nozzle block relatively easily. "Thus, although such a nozzle design is known, one skilled in the art has not been able in the prior art to solve the problem presented by Beddow of gas atomization of materials at high temperature and

especially metals.

  It is found in the United States of America patents

  other sources of information on the shape of the nozzles

  intended for use in atomizing technology

  tion. U.S. Patent No. 2,997,245 describes a method of atomizing a liquid metal into

- 15 -

  using what is called "shock waves".

  In U.S. Patent No. 3,988,084, a schemappermettant is disclosed for generating a thin metal current on a hollow inverted cone and for intercepting this current by an annular gas jet. In this scheme, the atomizing gas stream is directed against only one side of the molten metal cone, that is, against the outside of the cone, and no gas is directed against the other side of the cone. molten metal, i.e. the inner surface of the cne. In the practice of certain embodiments of the present invention, the atomizing gas is directed against all surfaces of the melt stream. The inverted cone of US Pat. No. 3,988,084 resembles the inverted cone formed during conventional gas atomization with remote coupling of a downward liquid metal stream, described above, in that the gas only acts on one side of the veil of the liquid metal at the lower edge of the inverted cone. The veil spreads on the inverted cone to its edge and the gas sweeps

  the metal between the edge and the hollow cone converge.

  The present inventor has prepared a thesis entitled "The Production and Consolidation of Amorphous Metal Powder".

  amorphous metal) and supported this thesis before the Depart-

  Department of Mechanical Engineering at Northeastern University, Boston, Massachusetts, September 1980. The thesis describes the use of an annular gas nozzle with a ceramic and / or graphite metal feed tube. In

  this thesis presents improvements in the

  forming a powder having a high proportion of finer powder by atomizing a metal in the melt with

an annular jet of gas.

The present invention aims to:

  to make a fine metallic powder directly

  from the liquid state and without having to use a

  secondary process such as change, if not subdi-

- 16 -

  vision, of material initially formed into a ribbon or sheet or strip of similar solid-state material, making powder from a melt with a substantially higher percentage of finer particles,

  directly make powder with di-

  more uniform particle sizes, making powder by more efficient atomization by a gas,

  provide a method and apparatus for a manufacturer

  more efficient cation of a powder having the desired particle size by gas atomization, making powder from melts at high temperatures, at low cost, making useful articles in powder from alloys which can not be transformed into useful articles when conventional techniques are used, allow the manufacture of powder by fast solidification techniques for the formation of manufactured articles, produce a new and distinct powder from a gaseous atomized melt and to do it in an economical way, to provide a nozzle and a process of atomization which is self-cleaning; provide a nozzle that has a long service life; provide a nozzle that can be reused;

  provide a nozzle that is not subject to

  and the attack on liquid metals like this is

  the case of the nozzles of the prior art.

  provide a method of limiting the pile

  melt on an atomizing device, provide a process that allows the use of

  Continuous long-term atomization apparatus.

- 17 -

  Other objects will appear in part and will be

  partly underlined in the following description.

  In one of their general aspects, the objects of the present invention can be achieved by providing a melt supply tube so as to deliver the mass directly to an atomization zone, providing

  the atomizing gas to the zone from at least one ori-

  gas located in a place immediately close to the zone, and realizing in boron nitride the surfaces of

  the apparatus subject to splashing from the area.

  The following description refers to the appended figures

  which respectively show: Figure 1, a vertical sectional view of a type of gas atomization nozzle suitable for use in the practice of the present invention; Figure 2, a detail of the atomization tip of Figure 1, illustrating certain dimensions A and B; Figure 3 is a graph of some parameters relating to particle size distribution of the cumulative fraction of particles in powder samples prepared by different methods;

  Figure 4 is a schematic illustration of a phenomenon

  atomization leads of the prior art.

  In connection with Figure 1, there is shown

  vertically cutting an embodiment of an atomization nozzle

  10 according to the present invention. In the practice of the present invention, it is also possible to use numerous variants of atomization nozzles, these being described

  otherwise in this specification.

  The nozzle 10 has a ceramic inner liner 12 having an upper end 14 into which the liquid metal to be atomized is introduced, and a lower end 16 of o can output the metal to be atomized as a downflow. The lower end

  has a lower tip 17 having an outer surface

- 18 -

  upper 18 in the form of inverted truncated cone. The metal to

  the molten state coming out of the tube 12 at the end 16 is

  gas jet from an annular orifice of the nozzle 10. The annular gas jet is made of a gas from a chamber 20 and

  passing through an opening 22 formed between an integral surface

  chamfered top 24 and the inverted cone-shaped surface or chamfered surface 18 of the metal feeding tube 12. The annular orifice 22 serving for the exit of the jets

  of gas, may have surfaces having a

  braked so as to generally correspond to the chamfered surface 18 of the coating 12. Therefore, the aperture 22 may be defined by the chamfered outer surface 18 of the coating 12, the corresponding chamfered surface 26 of the lower portion of the annular gas chamber 20

  and the opposite and facing surface 24 of a plate 32 con-

  locating the lower closure of the chamber 20. The lower surface 18 of the coating 11 forms an edge of a small

  19. The other edge of the flat 19 is formed by the opening

  the output of the melt, also provided in

the coating 12.

  After introduction of a gas at high pressure into a pipe 30 from a source not shown, it enters the annular chamber 20 and leaves the annular orifice 22 to strike the current of

  molten metal descending into the tube 12 and leaving the end

  16 of the coating 12 to the tip 17.

  The outlet surface 24 may be formed in the conventional manner on the inner edge of the chamber closure plate 32. The plate 32 may comprise external threads so as to allow its screwing into the lower edge 36 threaded internally of the side wall 34 of the chamber. Raising and lowering the plate 32 obtained by screwing its inner edge more or less in the chamber 20 has the effect of moving the surface 24

- 19 -

  relative to the surEace 18 and therefore to open or close the annular orifice 22 and to raise this orifice

  relative to the lower tip 17 of the supply tube 12

melt.

  The housing 34 of the chamber has an annular upper portion 38 having an inner rim 40 in one piece with it. An annular cone 42, which may be made of ceramic material or metal, and which constitutes a

  part of the tube 12 for guiding the melt, is sup-

  carried on the flange 40 by a collar 44. The shape of the outer surface 26 of the cone 42 plays an important role in

  the formation of the inner annular surface of the chamber

  wherein the outer surface 26 of the cone 42 can be aligned with the outer conical lower end surface 18 of the tube 12 so that the two surfaces form a conical surface.

  continues that gas runs from the chamber 20 when

  it is discharged through the annular orifice 22.

  As shown in the figure, the tube 12 com-

  carries the lower tip 17 and its outer lower surface 18 has the same profile as the surface

  inside 26 of the annular cone 42. The tube also comprises

  an intermediate rim 46 which makes it possible to determine accurately its vertical positioning and to adjust it with respect to the entire nozzle 10 and the surface

conical 26.

  An annular upper ring 48 has a one-piece inner boss 50 which rests on the flange 46 to hold the tube and conical portions of the

  device following a precise alignment.

  The means for holding the assembled nozzle in the apparatus in which the molten metal is atomized is

  conventional and is not part of the present invention.

  The configuration and shape of the gas orifice for practicing the present invention are not

- 20 -

  limited to the shape shown in Figure 1. For some applications, it is preferred a nozzle having the shape of a nozzle called Laval to adjust the expansion of the released gas

through the orifice 22 of FIG.

  In addition, it is not essential that the jet

  ring of gas is formed only by an annular orifice

  although this type of orifice is preferred. On the contrary, the annular jet can be created with a circle of individually powered tubular nozzles, each directed towards the surface of the melt. The gas from such a circle can form a single annular jet because all the gas streams leaving the individual nozzles converge at or near the surface of the melt.

this surface.

  On the other hand, the angle at which gas is directed from an orifice to the surface of the melt stream is not limited to that shown in the figure. While some angles are preferred for

  certain combinations of nozzles and melts

  being atomized, we know that we can obtain atomization

  tion with incident angles between a fraction of a degree and 90 C. It has been found that the atomization performed with a nozzle having the shape of Figure 1 and at an angle

  incidence of 22 is particularly effective in

  powders with a higher concentration

  than that obtained with the processes of the prior art.

  For many metals that are atomized, obtaining

  of a droplet or particle solidifying faster-

  will lead to an improvement of certain properties

  compared to a slower cooling particle.

  As has been emphasized in the context of this

  description, the rapid rate of solidification increases when

  that the diameter of the particles decreases. Thus, a finer powder involves obtaining larger solidification rates and not just a finer powder per se. A

- 21 -

  finer powder in itself presents other advantages vis-à-

screws classical materials.

  With regard to the achievement of solidi-

  One of the most common observations is a large decrease in the segregation of the components of an alloy from which the particle is formed. For example, as a result of this decrease in segregation, the point of the incipient fusion of the alloy can be raised. We can raise the point of the nascent fusion for the essential reason

  that the process of the present invention permits a nucleation

  uniformity, which essentially means that the solidarity

  will occur virtually instantaneously, so that the solidified front will move rapidly

  the liquid material of the droplet without any segregation

  occur. The net effect of the above is a homogeneous structure. By obtaining a homogeneous structure, the difference between the liquidus temperature of the alloy and its solidus temperature is reduced and finally these two temperatures are close to one another. The resulting benefit is that finally the nascent melting point is the solidus temperature. The melting temperature of

  fine particles of this type increase and moreover the temperature

  The potential operating temperature of the alloy is high. With a powder prepared in this manner and in accordance with the present invention, successful consolidation with improved properties can be achieved.

  thanks to the existing consolidation techniques.

  If one tries to consolidate an amorphous, fine powder, rapidly solidified using the types of techniques used in the past, one passes above the transition temperature, the material crystallizes. Thus, one can not consolidate the material and keep the amorphous structure for most amorphous alloys. Some amorphous alloys have been consolidated, but in the case of the remaining superalloys

- 22 -

  crystalline in the rapidly solidified form, they have been consolidated and some improvement in the properties or beneficial properties in the material has been observed.

  consolidated and in particular in solid-state

Quickly attached.

  Take the case of a sample of a very powdery

  finely divided; even if the effects of

  cooling are eliminated, simply because they are

  particle size, since each particle has its origin in the melt which is supposed to be homogeneous, and allowing segregation to occur, if we have a very small particle, we will observe a potentially less significant segregation that in a very large particle simply by the definition of

  material that is able to segregate.

  Second, with respect to the advantages of small particles, it has been shown in the literature that smaller metal particles tend to sinter earlier at lower temperatures and in shorter times than particles. of

  large powders. There is a driving force

  larger for the sintering process itself. This presents an economic advantage; Thirdly, one of the problems associated with powder metallurgy is the contamination of the powder by foreign bodies. These foreign bodies mix with the powder, then tighten in the room and finally

  represent a potential site of failure in the room.

  If a very fine powder is available, the conviction

  rante is that the powder can be sieved and the large foreign bodies removed so that by having a finer powder a final sample can be prepared which will have virtually smaller defects than in the case where a

coarser powder.

  Continuing consideration of other benefits

- 23 -

  fine powders, in the case where it is possible to

  to obtain them at economic conditions in the

  according to the process of the present invention, by

  spheres of 10 micrometers to spheres of 100 micrometers, the tamping factor is the same. Therefore, it is desirable to have another set of even smaller spheres to fill these voids. But there will again be gaps between small spheres and large spheres, so we would like to have another set of smaller spheres to essentially fill the voids

smaller in size.

  A relatively new field originating from rapid solidification is the development of new series of alloys. Because of the slower solidification rates of conventional materials, the components of the alloy separate either as fragile internal metal compounds or as long-grain boundaries. Such materials have properties that are in some respects inferior to those of fast-curing materials. Due to the fast solidification, some of these solute materials can be maintained in solution and act as reinforcing agents and as a result, new alloy compositions are now being sought through the fast solidification channel. These same alloys, when manufactured by conventional methods, may have to

  to be rejected because they are brittle. However, we have now

  found that these alloys have useful properties

  if they are solidified quickly. This phenomenon varies from one

  alloy system to another, a speed of solidification

  to another. Finally, consolidation techniques

  have an effect on whether or not the material can be used. An important feature of this

- 24 -

  invention is that it allows the formation of a powder to

  from a melt with a high efficiency of use

  gas. The improvement thus obtained is quite surprising in that the finely divided powder has a higher percentage of fine particles and

  would reasonably be thought that in order to obtain a subdivision

  Such a fine fraction would require a much larger gas flow. With a much larger gas flow, there would naturally be a decrease in the efficiency of gas utilization; however, it was by surprise that we found that

  the use of the processes of this description

  actually reduced the gas used when

  brick the very fine particles in the higher percentages obtainable with the present invention by

compared to classical processes.

  In general, it is advantageous to have

  powders having fine particles of a relative diameter

  uniformly or of a diameter within a smaller range. Indeed, particles of more uniform diameter

  will have a history of cooling itself more

  form. A more uniform cooling history is

  translated by particles with metallurgical properties

more uniform.

  In addition, small particles are generally faster cooling particles

  as indicated in the equation contained in the introduction

  the present application. In the case where a powder has a wide range of particle size and is processed using powder metallurgy techniques, there is a limit to the desirable properties that can be imparted to a composition and this limit is related to the composition and properties of large particles of the powder used in the composition. Large particles will constitute a point or points potentially weak, to which will correspond weak

- 25 -

  nascent melting point values or other properties.

  In general, the smaller the particle diameter, the smaller the average particle diameter, the smaller the particle size of the powder of an ingredient used to form a solid object,

  the more likely it is that the product will have some

  certain combinations of desirable properties in solid objects prepared from the powder. Ideally,

  if all the particles formed had exactly one di-

  micrometers, their thermal history would be essentially the same and the objects formed from these particles would have characteristic properties of

  particles of uniform diameter of which they are formed.

  It would, of course, be desirable to have larger particle bodies which would have solidified rapidly at speeds that are passable with smaller particle bodies. However, because of the internal segregation of metallurgical ingredients,

  producing inside a large particle body

  the solidification of large bodies and as there is a limit to the rate at which heat can be extracted

  large bodies of particles to obtain such solidity

  However, the formation of these large bodies of particles from a molten metal during powder production by conventional atomization techniques has a limitation as to the character of the powder which can be

  made by classical techniques as well as a limitation

  tion as to the uses that can be made of such a powder in the production of large bodies by the metallurgy of powders. The use of powder metallurgy techniques is currently the main route through which higher quality products are obtained by using a rapidly solidified powder. The present invention makes it possible to improve the formation of both these small particles and these large bodies with the

- 26 -

  highly desirable combination of properties of rapidly solidifying metals. In addition, the formed articles have a more uniform set of properties because of the more uniform diameter of the particles of the powder of which they are made.

  One of the unique features of the technology

  made possible by the present invention is that it

  allows for closer control of a number of

  meters of a powdered product produced by atomization

  according to the teachings of the present description.

  For example, it has been found that it is possible to modify the somewhat random distribution of diameters

  of particles found in pulverulent products.

  slow ones obtained from the processes of the prior art of

  in order to achieve a greater concentration of

selected value.

  Secondly, for selected particle sizes, it is possible to produce a larger quantity of particles of these dimensions in a given batch regardless of the particle diameter that has been selected. If, for example, we have chosen a

  particle diameter of 10 microns as the primary size

  product for a powder, the control of the variables in the present invention will make it possible to focus on

  the manufacture of particles of this selected size.

  Alternatively, if particles of 50 micro-

  meters or 100 micrometers as the desired diameter of the

  Therefore, the process parameters can be modified in accordance with the teachings of the present invention to obtain products which have a higher concentration.

  particulate matter in the range of

  born. When using the methods of the prior art, it is possible to manufacture a wide range of particle sizes in any batch or in a single batch.

- 27 -

  manufacturing series. However, the economic advantage

  of in the possibility of making a particle diameter with a relatively small standard deviation compared to a

  product having a particle size selected or pre-

  selected. Therefore, the present invention allows the production of economically valuable powders during a given manufacturing run involving the consumption of a certain amount of energy.

and materials.

  A secondary advantage of powder manufacture according to the present invention is that not only

  this allows the manufacture of a powder with a rela-

  However, thanks to this low dispersion, the particles will have a selected microstructure. Consequently, he

  possible, thanks to the teachings of the present invention.

  tion, to form particles having a relative diameter

  large size and low dispersion of dimensions for a given sample. Larger particles, as they will have cooled down more slowly, will have a coarser crystalline structure than those with

cooled faster.

  However, alternatively, by choosing the conditions

  manufacturing processes for which the size of the

  ticles is finer, it is possible to produce a

  amorphous powder because the smaller particles get cooler

  more quickly as explained above and

  also because there is very little dispersion of

  around the preselected size for the sample

in production.

In a preferred embodiment, an atomization zone is formed at the junction zone of the molten metal stream and the annular stream of the gas.

  atomising out of the annular opening 22 at the end.

  lower mite of the gas supply chamber 28. By

- 28 -

  therefore, the tube 12 guiding the melt provides the flow of liquid metal through the throat

  from the gas nozzle to the atomization zone. A characteristic

  The present invention is the presence of a gas nozzle body which cooperates with a shaped end of a melt guide tube to form a gas nozzle providing an annular gas jet which cooperates with with the shaped outlet end of the tube

guiding the melt.

  In other words, the presence of shaped ends forming and cooperating together at the bottom of the melt guide tube is one aspect of the present invention as will be explained more fully hereinafter. According to this explanation, this is one of the many independent acting phenomena used to obtain the superior atomization of

various melts.

  The proximity of the gas orifice and the orifice of the melt allows the surface of the guide tube to

  the melt to form part of the annular orifice

  In this way, the gas jet is exhausted from the gas chamber on the shaped end of the melt guide tube. This action

  the jet of gas on and against the lower end of the melt guide tube was found to be

  effective in leading to a large extent

  solidifying or solidifying metal which otherwise would tend to form or settle and accumulate on the lower end of the melt guide tube. It is not known if such particles do not actually accumulate on the lower end of the tube and it is known that such adhesion occurred in the nozzles

  atomization of the prior art as discussed above.

  in connection with the reference to Beddow's work.

  However, as a result of the measures taken in the practice of

- 29 -

  the present invention, the adhesion of these liquid particles

  or solidified is reduced and the flushing gas has the ability either to avoid the deposition of these particles, or to cause their removal when they have deposited or accumulated on the lower end of the supply tube

of the melt.

  In the particular configuration represented in

  Figure 1, there is continuity, compliance and a

  between the shaped lower surface of the tube 18 of

  guiding the melt and the surrounding surface way-

  born 26 of the gas supply chamber 20. It will be understood that the annular jet of gas can, in fact, be obtained with

  a number of configurations and different

  Nières. However, the important feature that must be ensured in connection with the previously mentioned aspect in the form of a close coupling, is the presence of a jet

  ring of gas which is at least partly formed by the former

  formed lower trough of the melt guide tube and is close to the surface of this mass

molten.

  The main criteria for a melt guide tube material is that it must withstand the high temperature of the melt and withstand shocks

  thermal. It is desirable that the material be machined

  or sink it by giving it a regular surface of

  in order to avoid a mechanical connection with the

  cured, whether it is non-wetting with respect to the mass

  due, and that it has a low coefficient of thermal conductivity. Boron nitride meets all the above criteria. It has been found particularly suitable for forming a nozzle for gas atomization.

  metals having a high melting point.

  A melt supply tube similar to the tube 12 of FIG. 1 was made of boron nitride and

  found that he performed this function very well, in particular

  relate to the two main criteria set out above. The material was found to withstand molten metals at temperatures of 1350 ° C. and 1750 ° C. In addition, it was found that a boron nitride tube was extremely resistant to thermal shock when poured. a metal at a temperature of 1750 C in the tube, while there was circulation on its outer surface of a gas

  atomization at a temperature of about -200 ° C.

  boron tritium has a low heat transfer coefficient

  their compared to most metals.

  - boron nitride, sold commercially by the

  Union Carbide Corporation under the trade mark

  HBR, can be machined to take the form represented in

  Figure 1 and has smooth surfaces after machining.

  Another product, says HBC, also marketed

  by Union Carbide Corporation, may also be

  used to form the nozzle, although it has a breaking strength less than half that of the

HBR product.

  The boron nitride used in the manufacture of the melt supply tubes was apparently moderately wetted by the hot liquid metal, but this wetting was not so important as to prevent its satisfactory use as a supply tube. of melt and a surface component

  exposed to the atomization atmosphere of a metal.

  In this respect, boron nitride behaves

  very well. It resists the accumulation of molten metal

  at high temperature better than other materials tested.

  The present invention contemplates the formation of the surfaces of a boron nitride atomization nozzle so that they resist squirting accumulation, whether or not the nozzle complies with that of FIG.

  or it is done in some other way.

- 31 -

  For example, it is contemplated the realization of individual gas nozzles with surfaces of boron nitride of

  to inhibit the pile up. This is how we envision

  it is wise to form part 32 of FIG. 1 in boron nitride so as to avoid the adhesion of metallic stains.

  melted and the gradual accumulation of these tasks.

  In general, the use of boron nitride is contemplated for surfaces that are exposed to metal spurting during the gas atomization process, where these surfaces are prone to accumulations of solidified particles and where such accumulation interferes with flow

of the atomization process.

  The surface 18 of FIG. 1 corresponds to this type of surface for the reasons explained above. The gas from the annular nozzle can sweep away particles that may deposit on the surface because of the poor adhesion between the melt deposit and the

boron nitride surface.

  Surfaces such as Part 32 can be coated with boron nitride or boron nitride inserts to take advantage of

  non-adhesion in the event that other benefits

  thermal shock resistance and the like are not essential for the proper functioning of the

piece.

  It remains within the scope of the present invention to constitute entirely an annular orifice of inert ceramic material such as boron nitride. At the very least, the inert ceramic material such as boron nitride must either be provided, or at least deposited on the surface, where a solidified metal buildup will most likely occur. This part is the one that is closest to where the molten metal comes out. This is the chamfered surface 18 of the lower end 16 of the

guide tube of the melt.

- 32 -

Claims (8)

REVENOICATIONS   A process for producing a fine powder from a molten metal, characterized in that it comprises: providing a source of molten metal to be atomized;   the discharge of molten metal to a zone of atomization   via a melt supply tube (12), the portion of which is exposed to the atomization zone being substantially boron nitride; the routing of a stream of atomizing gas against the stream of molten metal in said zone   in order to atomize this metal in the molten state.   2. Method according to claim 1, characterized in that the surfaces exposed to the gushing of the metal to   the molten state are made of boron nitride.   3. Method according to claim 1, characterized in that the tube (12) of supply melt is in boron nitride.   4. Method according to claim 1, characterized in that the exposed surfaces of the source of the current of   Atomization gases are made of boron nitride.   High temperature atomization nozzle for the process according to claim 1, characterized in that   comprises a tube (12) for supplying molten mass in ni-   boron tritium; and in that it comprises a gas orifice (22) surrounding the tube.   6. Nozzle according to claim 1, characterized   in that the orifice is closely coupled to the furnace tube. melted mass.   7. Nozzle according to claim 5, characterized in that all the surfaces swept by the gas coming from - 33 -   of the gas orifice are made of boron nitride.   8. Atomization nozzle at high temperature, characterized in that it comprises a tube (12) for supplying   melt and a peripheral nozzle (22) for supplying   of gas, - the surface of the nozzle which is capable of receiving the melt being at least coated with nitride of boron.