Classifications

• • C—CHEMISTRY; METALLURGY
  • C04—CEMENTS; CONCRETE; ARTIFICIAL STONE; CERAMICS; REFRACTORIES
  • C04B—LIME, MAGNESIA; SLAG; CEMENTS; COMPOSITIONS THEREOF, e.g. MORTARS, CONCRETE OR LIKE BUILDING MATERIALS; ARTIFICIAL STONE; CERAMICS; REFRACTORIES; TREATMENT OF NATURAL STONE
  • C04B35/00—Shaped ceramic products characterised by their composition; Ceramics compositions; Processing powders of inorganic compounds preparatory to the manufacturing of ceramic products
  • C04B35/622—Forming processes; Processing powders of inorganic compounds preparatory to the manufacturing of ceramic products
  • C04B35/64—Burning or sintering processes
  • C04B35/645—Pressure sintering
• • 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
  • B22F3/12—Both compacting and sintering
  • B22F3/14—Both compacting and sintering simultaneously
  • B22F3/15—Hot isostatic pressing
• • 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
  • C22C1/05—Mixtures of metal powder with non-metallic powder
  • C22C1/051—Making hard metals based on borides, carbides, nitrides, oxides or silicides; Preparation of the powder mixture used as the starting material therefor

Definitions

• the present invention relates to a method for densifying previously sintered parts of powdered metals, ceramics and the like.
• the powdered material is first intermixed with a fugitive binder which holds the part in the desired shape after cold pressing.
• a fugitive bonder or "wax” consists of a paraffin, polyetheleneglycol or a metal containing a hydrocarbon.
• the cold pressed part is conventionally known as a preform.
• the preforms are then subjected to a presintering step in which the preforms are slowly heated thus vaporizing the fugitive binder and the vaporized binder is removed . from the part by a wash gas, vacuum pumping or other means. Following the presintering step, the parts retain their shape despite the absence of the fugitive binder.
• the parts are then subjected to a sintering operation in which the parts are raised to their liquid phase temperature which not only densifies the parts but also further releases any residual contaminants contained within the parts. These contaminants are removed from the part during the sintering operation by vacuum pumping or by flowing a wash gas, such as hydrogen, across the parts. Following the sintering of the parts, the parts are sufficiently dense and hard for many applications. For applications requiring still further densification, greater strength of the sintered part or better internal integrity, these properties of the part can be improved by subjecting the part to hot isostatic pressing or "HIP" procesing.
• HIP hot isostatic pressing
• the parts are elevated to their liquid phase temperature and subjected to pressures in excess of 5, ⁇ psi and typically in excess of 1 ⁇ , ⁇ psi, for a period of 6 ⁇ to 9 ⁇ minutes.
• the primary advantsge of HIP processing is to eliminate virtually all porosity within the part as well as greatly minimizing larger randomly spaced holes, slits or factures which may be present in the part provided such holes, slits or fractures are not open to the surface.
• a primary disadvantage of HIP processing is that, due to the high temperatures and high pressures used during the HIP processing, the previously known HIP equipment is exteremly massive in construction and expensive to produce and acquire. Furthermore, the long cycle time for the HIP processing limits the production volume of HIP equipment and greatly increases the per part cost of the parts which are HIP treated.
• the present invention provides a method for densifying previously sintered parts which overcomes all of the above mentioned disadvantages of HIP processing.
• the method of the present invention comprises placing previously sintered parts within a pressurizable chamber.
• the parts may be either vacuum or hydrogen sintered and, similarly, may be cooled following the sintering step.
• the parts are then heated to their liquid phase temperature.
• the liquid phase temperature will vary, of course, depending upon the part material. Typically, however, the liquid phase temperature is in the ange of 1,3 ⁇ degrees Celsius to 1,6 ⁇ degrees celsius.
• the pressure vessel With the parts at their liquid phase temperature, the pressure vessel is pressurized with an inert gas, such as argon, to a range of 5 ⁇ -2, ⁇ psi.
• the parts are maintained within the pressure vessell at their liquid phase temperature and subjet to a pressure or 5 ⁇ -2, ⁇ psi for a relatively short period of time, typically 3 ⁇ -6 ⁇ minutes, and then removed from the furnace chamber.
• the pressure vessel can be heated first and then pressurized, pressurized first and then heated or simultaneously pressurized and heated.
• the method of the present invention substantially eliminates all porosity within the parts as well as closing larger randomly spaced holes, slits or practures in the part in a manner comparable to and, in many cases, superior to HIP processing.
• porosity and flow closures could be effected at pressures in the range of 5 ⁇ psi-2 ⁇ psi.
• FIGS. 1-14 are all microphotographs of the cross section of parts illustrating the present invention. Detailed Description of a Preferred Embodiment of the Present Invention
• the method of the present invention is designed to further densify previously sintered parts constructed from powdered metal, ceramics, or the like.
• previously sintered parts mean parts that have been raised to liquid phase temperature regardless of whether the parts are cooled following sinter. It has been found through test results that the method used to sinter the parts, i.e., whether the parts were subjected to vacuum pumping or a wash gas during the sintering operation, has no observable effect on the parts following the treatment of the parts by the present method. Similarly, whether or not the sintered parts have been cooled following the sintering operation has no observable effect on the parts following treatment of the parts by the present method.
• the sintered parts are placed within a pressurizable chamber.
• the parts are then heated to the liquid phase temperature, i.e., the melting, point of the parts.
• the chamber is also pressurized with an inert gas, such as argon, to a pressure of 5 ⁇ -2, ⁇ psi.
• the parts are maintained at their liquid phase temperature and at a pressurization of 5 ⁇ -2, ⁇ psi for a relatively short period of time, typically 30-6 ⁇ minutes.
• the chamber is depressuri zed and the parts are removed.
• Test reulsts have established that the metjod of the present invention effectively eliminates substantially all prorsity within the sintered part as well as closing large holes or flaws that are present in the part following the sintering operation in a manner comparable and in many cases, superior to HIP processing.
• Example 2 The parts produced by the steps described in Example 1 were then subjected to the following steps : 1. Maintained at liquid phase temperature following sinter - 1415 degrees celsius.
• FIGS. 2 and 3 illustrate the complete closure of the large flaw at 75X and 15 ⁇ X magnification, respectively.
• FIGS. 4 and 5 illustrate complete closure of the large flaw at 75X and 15 ⁇ X magnification, respectively.
• FIGS. 7 and 8 show complete closure of the large flaw at 15 ⁇ X and 75X magnification, respectively.
• EXAMPLE 6 The parts from the lot of Example 1 were treated the same as Example 5 except that the parts were dewaxed in hydrogen atmosphere rather than vacuum dewaxed.
• FIGS. 9 and 1 ⁇ illustrate complete closure of the large flaw at 2 ⁇ X and 5 ⁇ X magnifiction, respectively.
• Example 1 The parts from the lot of Example 1 were treated in the same fashion as Example 2 except that the parts were cooled following sinter.
• FIGS. 11 and 12 show complete closure of the large flaw at 75X and 15 ⁇ X magnification, respectively.
• Example 2 The parts were processed in a manner identical to Example 1 except that 16% cobalt powder was used .
• FIGS. 13 and 14 illustrate complete closure of the flaws at 75X and 15 ⁇ X magnification, respectively. Test results have also shown that with 1 ⁇ % cobalt material, complete closure of the flaws is not possible at 5 ⁇ psi.
• the method of the present invention provides a substantial increase in the densification of a previously sintered part.
• the actual method employed in sintering the part has no observable effect on the densification or hole closure obtained by the practice of the present method.
• the densification and microstructural development of sintered parts obtainable by the method of the present invention are comparable or even superior to the corresponding densification and microstructure development obtainable from the previously known HIP process.
• the present invention is advantageous over the HIP process snce the present method employs comparatively much lower pressures than those used in the HIP process.
• the machinery and equipment necessary to practice the method of the present invention is much less massive and, theefore, much less expensive in construction than the corresponding machinery equipment necessary for the HIP process.
• a still further advantage of the method of the present invention is that the cycle time of the present method is much shorter than the corresponding cycle time of the HIP process. As such, a much greater volume of parts can be processed from a similarly sized furnace while practicing the present method than can be processed over the same tiem period with a similarly sized furnace using the HIP process.
• the method of the present invention pressurized the parts to a pressurization of between 5 ⁇ -2, ⁇ psi, preferably this pressure range is 5 ⁇ ,1, ⁇ psi and, still preferably, 5 ⁇ -3 ⁇ psi.
• this pressure range is 5 ⁇ ,1, ⁇ psi and, still preferably, 5 ⁇ -3 ⁇ psi.
• many types of metallurgical furnaces can be used to practice the method of the present invention, preferably, the metallurgical furnace described in my copending patent application entitled "Metalurgical Furnace” and filed on Marcy 22, 1982 and assigned Serial No.

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• Chemical & Material Sciences (AREA)
• Engineering & Computer Science (AREA)
• Manufacturing & Machinery (AREA)
• Ceramic Engineering (AREA)
• Materials Engineering (AREA)
• Organic Chemistry (AREA)
• Mechanical Engineering (AREA)
• Inorganic Chemistry (AREA)
• Structural Engineering (AREA)
• Metallurgy (AREA)
• Powder Metallurgy (AREA)

Applications Claiming Priority (1)

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• 1984
  • 1984-02-10 JP JP84500989A patent/JPS61501402A/ja active Pending
  • 1984-02-10 WO PCT/US1984/000191 patent/WO1985003464A1/fr not_active Application Discontinuation
  • 1984-02-10 EP EP19840900942 patent/EP0172164A4/fr not_active Withdrawn

Patent Citations (2)

Non-Patent Citations (1)

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