Classifications

• • C—CHEMISTRY; METALLURGY
  • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
  • C22C—ALLOYS
  • C22C1/00—Making non-ferrous alloys
  • C22C1/04—Making non-ferrous alloys by powder metallurgy
  • C22C1/045—Alloys based on refractory metals
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B22—CASTING; POWDER METALLURGY
  • B22F—WORKING METALLIC POWDER; MANUFACTURE OF ARTICLES FROM METALLIC POWDER; MAKING METALLIC POWDER; APPARATUS OR DEVICES SPECIALLY ADAPTED FOR METALLIC POWDER
  • B22F3/00—Manufacture of workpieces or articles from metallic powder characterised by the manner of compacting or sintering; Apparatus specially adapted therefor ; Presses and furnaces
  • B22F3/10—Sintering only
• • C—CHEMISTRY; METALLURGY
  • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
  • C22C—ALLOYS
  • C22C27/00—Alloys based on rhenium or a refractory metal not mentioned in groups C22C14/00 or C22C16/00
  • C22C27/04—Alloys based on tungsten or molybdenum
• • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
  • F27—FURNACES; KILNS; OVENS; RETORTS
  • F27D—DETAILS OR ACCESSORIES OF FURNACES, KILNS, OVENS, OR RETORTS, IN SO FAR AS THEY ARE OF KINDS OCCURRING IN MORE THAN ONE KIND OF FURNACE
  • F27D1/00—Casings; Linings; Walls; Roofs
  • F27D1/0003—Linings or walls
  • F27D1/0006—Linings or walls formed from bricks or layers with a particular composition or specific characteristics
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B22—CASTING; POWDER METALLURGY
  • B22F—WORKING METALLIC POWDER; MANUFACTURE OF ARTICLES FROM METALLIC POWDER; MAKING METALLIC POWDER; APPARATUS OR DEVICES SPECIALLY ADAPTED FOR METALLIC POWDER
  • B22F2998/00—Supplementary information concerning processes or compositions relating to powder metallurgy
  • B22F2998/10—Processes characterised by the sequence of their steps
• • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
  • F27—FURNACES; KILNS; OVENS; RETORTS
  • F27B—FURNACES, KILNS, OVENS, OR RETORTS IN GENERAL; OPEN SINTERING OR LIKE APPARATUS
  • F27B14/00—Crucible or pot furnaces
  • F27B14/08—Details peculiar to crucible or pot furnaces
  • F27B14/10—Crucibles

Definitions

• isostatic compression processes are also used, combining for example cold isostatic compression with hot isostatic compression and then heat treatment at medium temperature.
• cold isostatic compression with hot isostatic compression and then heat treatment at medium temperature.
• tungsten can be activated by adding elements such as nickel, cobalt, palladium, even iron and platinum.
• These activating elements are generally mixed in the form of metallic powder with tungsten powder, but can also be introduced in the form of oxides or deco salts which can be placed at low temperature in tungsten powder or tungsten oxide O 3 before co-reduction. under hydrogen.
• Many publications describe the effects of these activators added in weight proportions varying from 0.15 to 4, or even 5%, to the tungsten powder.
• this magnification of the tungsten grains becomes very important as soon as the relative density of 92% is obtained with the coarse powder and 97% with the fine powder.
• the different structural states and densities of previously described materials may be sufficient for applications where specific properties of the sintered product are not expected.
• these materials require, when it is technically feasible, costly additional operations of working and then machining of the solid tungsten blank to modify these structural states which have too large grain sizes and porosities and not uniformly distributed within these materials making them unsuitable for this use.
• the object of the invention is to define a sintered material based on tungsten capable of satisfying a set of severe physicochemical characteristics and therefore having a structure with fine grains and very low porosities uniformly distributed, essential for achieving in particular tungsten sintered parts of more or less complex shape or of thin thickness.
• Another object of the invention is a process for the direct production of said sintered material with the properties and shape required under the best economic conditions of production, in particular by avoiding additional operations of wrought and machining in most cases. if an accuracy of more or less 0.5 mm is not sought, but also by implementing sintering conditions at a sufficiently low temperature (T ⁇ 1600 ° C.) to allow the use of the industrial means conventionally used for example for the manufacture of tungsten alloys with liquid phase sintering
• the subject of the invention is therefore a sintered material tungsten base, of relative average density greater than 93% and of hardness HV0.3> 400, characterized in that it comprises:
• tungsten having a purity greater than 99.9% - an additive consisting of nickel and / or cobalt powder in a percentage by mass less than or equal to 0.08%,
• the percentage by mass of cobalt is less than 0.08% and the percentage by mass of nickel equal to zero, and the size of the tungsten grains of equiaxed form is between 2 and 6 ⁇ m, with porosities uniformly distributed and with an elementary volume of less than 4 ⁇ m for more than 95% of the grain population.
• the percentage by mass of nickel is less than 0.08% and the percentage by mass of cobalt equal to zero, and the size of the tungsten grains of equiaxed form is less than 28 ⁇ m, with uniformly distributed porosities and of volume elementary less than 4 ⁇ m for more than 95% of the grain population.
• the subject of the invention is also a method of manufacturing a sintered material based on tungsten, characterized in that it comprises the following steps: a) selection of a tungsten powder of purity greater than 99.9% and Fisher average diameter between 0.1 and 0.8 ⁇ m, b) mixing of this powder with an organic compression binder added in the weight proportion less than or equal to 0.4%, c) addition to the mixture of a sintering activator chosen from the group consisting of nickel, cobalt, nickel oxide, or a mixture of these, in the proportion by weight of the metallic part equal to or less than 0.08% of the mass of tungsten and production of the pulverulent material, d) shaping of the material by compression between
• the sintering is carried out in the absence of an activator by direct illumination of the material at a level temperature between 1,500 and 1,600 ° C, with a holding time between 30 minutes and 3 hours.
• the sintering is carried out in the presence of activator by direct illumination at a level temperature between 1150 and 1500 ° C, with a holding time between 10 and 90 minutes.
• the sintering is carried out in the presence of activator by indirect lighting at a level temperature between 1,500 and 1,600 ° C, with a holding time between 15 to 30 minutes.
• a particular application of the tungsten-based sintered material according to the invention lies in the manufacture of products of complex shape or with a thin wall.
• tungsten-based sintered material obtained according to one of the invention resides in the manufacture of components such as refractory crucibles.
• the great compressibility of submicron powders allows the almost direct shaping of products of complex shape or of thin thickness which can also be sintered at temperatures not exceeding 1600 ° C instead of 2000 ° C, even 2400 ° C of the prior art, taking into account a significant activation of the submicron powder linked to its very high specific surface.
• FIGS. 5 to 14 are representative micrographs of structures of sintered materials based on tungsten powder prepared according to the invention.
• tungsten crucibles of thickness varying from 1 to 15 mm for heights between 40 and 200 mm and diameters included between 20 and 80 mm.
• the main physicochemical characteristics of four examples of tungsten powder with different particle sizes have been collected in table 1: 4 to 5 ⁇ m powder A; 2 to 3 ⁇ m powder B; 0.5 to 0.8 ⁇ m powder C and 0.1 to 0.4 ⁇ m powder D.
• the powders A and B are powders conventionally used in the technical sector, while the powders C and D are powders selected from the part of the invention.
• the fine C or ultra-fine D submicron powders are distinguished from the powders A and B generally used in the prior art by a weaker granulometric spreading of non-friable agglomerates (measured by laser diffraction), by greater compressibility. according to Heckel's law and above all by greater sinterability measured by the percentage of relative shrinkage after isothermal maintenance of 1 hour under dry hydrogen. In fact, it is found with submicron powders shrinkages 2 to 5 times greater than 1100 ° C. than those obtained with the powders of the prior art at 1500 ° C.
• Impurities (ppm): C ⁇ 5, S ⁇ 5, Na ⁇ 30, K ⁇ 5, Ni ⁇ 10,
• Example 2 Dispersoid: 0.8% Sintering temperature 2,200 ° C (level) Sintering time: 4 hours Density: 17.6
• Example 3 Dispersoid: 1.6% Sintering temperature 2 200 ° C (level) Sintering time: 4 hours Density: 17.8
• the tungsten powder may be according to the invention added by successive dilutions of a sinter activator in very small proportion ( ⁇ 800 ppm) such as iron, palladium, but preferably nickel and / or cobalt.
• a sinter activator in very small proportion ( ⁇ 800 ppm) such as iron, palladium, but preferably nickel and / or cobalt.
• This sintering activator is generally in the form of a metal powder whose diameter
• the supply of activator can also be carried out by mixing the tungsten powder or tungsten oxide W0 3 with the activator itself in the form of powdery oxide (NiO, CoO) or in the form of a salt in an aqueous medium (Ni (N0 3 ) 2 , Co (N0 3 ) 2 ,
• the material is sintered under relatively dry hydrogen at average temperature rise rates ranging from 1 to
• the heating by direct illumination of the material to be sintered can preferably be carried out at bearing temperatures of between 1,500 and 1,600 ° C. for holding times varying from 30 minutes. at 3 o'clock. These bearing temperatures and these holding times can be further significantly reduced (between 1,500 and 1,150 ° C for holding times between 10 and 90 minutes) with activated tungsten powders.
• a crucible is prepared having the following characteristics: Diameter 20 to 80 mm, Height 40 to 200 mm, Thickness 1 to 15 mm. The following results are obtained: Density: maximum 18.25 minimum 18.04 average 18.15 relative 94% Grain size: maximum 6 ⁇ m, minimum 2 ⁇ m, average 4 ⁇ m, Porosity (volume): ⁇ 4 ⁇ m 3 99%,
• a crucible is prepared having the following characteristics: Diameter 20 to 80 mm, Height 40 to 200 mm, Thickness 1 to 15 mm. The following results are obtained: Density: maximum 18.1 minimum 17.9 average 18 relative 93.3% Grain size: maximum 6 ⁇ m, minimum 2 ⁇ m, average 4 ⁇ m,
• HV30 370.
• the above results show according to Example 4 that a first series of 8 crucibles sintered at 1500 ° C for 3 hours has exactly the same structure as a second series of 8 crucibles sintered at 1500 ° C for 30 minutes with a low density dispersion in both cases, a homogeneous distribution of 3 porosities of the order of 1 ⁇ m (volume ⁇ 4 ⁇ m).
• the third and fourth series of crucibles according to Example 5 made from the same tungsten powder, but in the presence of 0.15% by mass of binder and then sintered respectively at 1,500 ° C for 3 hours and 1,550 ° C for 30 minutes, also show structural characteristics very similar to those of the previous series.
• the tungsten grain sizes do not exceed 6 ⁇ m.
• the Gx500 micrograph of the sintered material at 1500 ° C. without attack, according to example 4, shown in FIG. 5 shows a low density dispersion and a homogeneous distribution of the porosities of size of the order of 1 ⁇ m (volume ⁇ 4 um 3 ) for 99% of the population. Note an absence of porosities from 5 to 20 ⁇ m.
• the Gx500 micrograph of the material sintered at 1500 ° C. after etching, according to Example 5, shown in FIG. 8 shows that the size of the tungsten grains is homogeneous from 4 to 6 ⁇ m, and does not exceed 6 ⁇ m.
• FIG. 9 shows the structure of this tungsten material obtained according to Example 6, without attack, having a distribution of the porosity of homogeneous size and an absence of porosities from 5 to 20 ⁇ m.
• Figure 10 shows grain sizes varying from 20 to 30 ⁇ m after attack.
• the sintering with indirect lighting (screening by a protective layer of alumina) of the crucibles produced from powder activated by 660 ppm of Ni and in the absence of a binder according to Example 8, requires increasing the temperatures at 1500 ° C-1550 ° C, even 1600 ° C, for holding times of 15 to 30 minutes if one wishes to achieve the desired structural characteristics, in particular in density (> 98%) and in hardness (> 400 HV0.3) with a homogeneous distribution of porosities 95% of which are made up of pores of the order
• Activator 660 ppm of active Ni, from NiO.
• Activator 660 ppm of active Ni, from NiO.
• a crucible is prepared having the following characteristics:
• Activator 660 ppm of Ni A crucible is prepared having the following characteristics:
• a crucible is prepared having the following characteristics: Diameter 20 to 80 mm,
• a crucible is prepared having the following characteristics: Diameter 20 to 80 mm,
• Grain size average 15 ⁇ m
• EXAMPLE 14 Activated Tungsten Powder 0.7 ⁇ m Sintering bearing temperature: 1,500 ° C. Sintering time: 90 min. Direct lighting Binder none Activator: 330 ppm Ni and 330 ppm Co.
• Example 16 Activated tungsten powder C of 0.7 ⁇ m Sintering temperature: 1,500 ° C. Sintering time: 90 min Direct illumination
• the Cobalt activator alone requires the implementation of the most severe sintering cycle 1,500 ° C. for 90 minutes to obtain a relative density greater than 93% while maintaining grain sizes and
• the nature of the activator with equal weight proportion has an incontestable impact on the sintering conditions which must therefore be adapted to obtain the desired structure for the material, it is not the same for the grain size of the powder.
• the high purity tungsten material according to the invention makes it possible to obtain an excellent compromise between the characteristics of density, hardness, toughness, and consequently to overcome '' costly complementary operations of wrought and machining. Furthermore, its production process by almost direct final shaping and sintering at temperatures not exceeding 1600 ° C. and therefore allowing the use of conventional industrial means, also contributes to significantly lowering its production cost.
• This tungsten-based material finds its best application in the manufacture of refractory products of complex shape or with a thin wall (0.4 to 15 mm) such as refractory crucibles.

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• Chemical & Material Sciences (AREA)
• Engineering & Computer Science (AREA)
• Mechanical Engineering (AREA)
• Materials Engineering (AREA)
• Metallurgy (AREA)
• Organic Chemistry (AREA)
• Manufacturing & Machinery (AREA)
• General Engineering & Computer Science (AREA)
• Powder Metallurgy (AREA)
• Inorganic Compounds Of Heavy Metals (AREA)
• Ceramic Products (AREA)
• Compositions Of Oxide Ceramics (AREA)

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Citations (4)

• 1999
  • 1999-06-25 FR FR9908186A patent/FR2795430B1/fr not_active Expired - Fee Related
• 2000
  • 2000-06-15 WO PCT/FR2000/001656 patent/WO2001000892A1/fr active IP Right Grant
  • 2000-06-15 CA CA002377773A patent/CA2377773A1/fr not_active Abandoned
  • 2000-06-15 AU AU65748/00A patent/AU6574800A/en not_active Abandoned
  • 2000-06-15 IL IL14719200A patent/IL147192A0/xx unknown
  • 2000-06-15 EP EP00953219A patent/EP1206585B1/de not_active Expired - Lifetime
  • 2000-06-15 DE DE60002476T patent/DE60002476T2/de not_active Expired - Lifetime
  • 2000-06-15 AT AT00953219T patent/ATE239100T1/de not_active IP Right Cessation

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