Classifications

• • C—CHEMISTRY; METALLURGY
  • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
  • C22F—CHANGING THE PHYSICAL STRUCTURE OF NON-FERROUS METALS AND NON-FERROUS ALLOYS
  • C22F1/00—Changing the physical structure of non-ferrous metals or alloys by heat treatment or by hot or cold working
  • C22F1/006—Resulting in heat recoverable alloys with a memory effect
• • 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
  • C22C1/0425—Copper-based alloys

Definitions

• the invention is based on a method for producing a memory alloy according to the preamble of claim 1.
• Memory alloys based on the Cu / Al / Ni system are known and have been described in various publications (e.g. U.S. Patent No. 3,783,037). Such memory alloys, which belong to the general type with the ⁇ high-temperature phase, are generally produced by melt metallurgy.
• the invention has for its object to provide a manufacturing method for memory alloys based on copper, aluminum and nickel, which leads to dense, compact bodies with good mechanical properties and at the same time to exactly reproducible values of the transition temperature and other variables related to the memory effect.
• the essence of the new process is not to start from elementary powders or from a starting powder corresponding to the final alloy, but to use a mixture of pre-alloyed powders and specially composed powder mixtures. This allows the required ductility to be optimally adapted to the processing process with extensive freedom in terms of composition.
• the grain size of the crystallite of the finished body can largely be predetermined. Grain growth is not to be feared. Coherent oxide skins that prevent homogenization and impair mechanical properties are avoided. If a certain small percentage is present, the metal oxides are present in finely divided form as dispersoids and have a beneficial effect on the mechanical properties of the end product, preventing grain growth.
• the following sample was mixed in a tumble mixer for 10 min: 240 g of this powder mixture were filled into a rubber tube with an inner diameter of 20 mm and pressed isostatically at a pressure of 8000 bar to a cylinder with a diameter of 18 mm and a height of 220 mm.
• the green compact was reduced and presintered in a hydrogen stream at a temperature of 950 ° C. for 1 h and then sintered in a stream of argon at a temperature of 950 ° C. for 19 h.
• the raw sintered body was turned to a diameter of 17 mm and introduced into a soft-annealed copper tube with an outer diameter of 20 mm and completely encapsulated by covering the ends with plugs and soldering under an argon atmosphere.
• thermomechanical processing consisted of round hammering at 950 ° C, with the diameter of the rod being 18 mm in the first round hammering stitch and every subsequent one Stitch was reduced by 2 mm each.
• the procedure was such that 2 thermomechanical operations were followed by homogenization annealing.
• the rod hammered down to 8 mm in diameter was finally subjected to a final annealing in a stream of argon for 15 minutes at a temperature of 950 ° C. and immediately quenched in water.
• the test showed a density of 99.5 - 99.8% of the theoretical value for the workpiece.
• thermomechanical machining / homogenization can be continued for as long as required until the final shape of the workpiece is reached. When the theoretical density is reached, further homogenization is generally no longer necessary.
• Example I The powders given in Example I were weighed out as follows and mixed in a tumble mixer for 15 minutes: 240 g of this powder mixture were filled into a soft annealed copper tube with an inner diameter of 18 mm and a wall thickness of 2 mm and completely encapsulated by covering the ends and soldering under an argon atmosphere. The tube and powder were then isostatically pressed at a pressure of 10,000 bar, and the compact was reduced and presintered in a hydrogen / nitrogen stream at a temperature of 750 ° C. for 2 h and then in a stream of argon at a temperature of 800 ° C. for 25 h sintered.
• the workpiece was then alternately subjected to 2 round hammer operations and a homogenization anneal at 900 ° C each, similar to Example I.
• the rod hammered down to 6 mm was subjected to a final annealing at 1000 ° C. for 10 minutes in a stream of argon and quenched in water.
• the density was 99.5% of the theoretical value.
• Example I The powders given in Example I were weighed out as follows and mixed in a tumble mixer for 12 minutes: 240 g of this powder mixture were filled into a soft annealed tombac tube with an inner diameter of 20 mm and a wall thickness of 1.6 mm and completely encapsulated by covering the ends and soldering under an argon atmosphere. The tube and powder were then isostatically pressed at a pressure of 12,000 bar and the compact was reduced and presintered in a hydrogen stream at a temperature of 850 ° C. for 1 Y2 h and then sintered in a stream of argon at a temperature of 820 ° C. for 22 h.
• the workpiece was then reduced in 2 round hammer passes at a temperature of 900 C to 18 or 16 mm in diameter and homogenized in a stream of argon at 920 ° C for 1 h. This was followed by two round hammer stitches at 900 ° C, so that the rod finally had a diameter of 13 mm.
• the rod was rolled down in several successive hot rolling operations, each with 20-25% reduction in cross section, to form a strip 1.5 mm thick and 20 mm wide. After a final annealing at 950 ° C. for 12 minutes, the strip was quenched in water. The density of the finished tape was 99.7%.
• Example I The powders given in Example I were weighed out as follows and mixed in a tumble mixer for 10 min. 250 g of this powder mixture were filled into a rubber tube with an inner diameter of 35 mm and pressed isostatically at a pressure of 12,000 bar to a cylinder with a diameter of 31 mm and a height of 80 mm. The green compact was reduced in a hydrogen stream at a temperature of 920 ° C. for 1 h and presintered and then sintered in a stream of argon at a temperature of 950 ° C. for 20 h. The raw sintered body was turned to a diameter of 30 mm, inserted in the recipient of an extrusion press and pressed at a temperature of 780 ° C.
• the reduction ratio (decrease in cross-section) was 11: 1.
• the rod was then homogenized at a temperature of 920 ° C. for 30 minutes and then pulled down in 2 passes on a warming bench at a temperature of 750 ° C. to an edge length of 6 mm. After the final one Annealing at 900 ° C for 15 min in a stream of argon, the rod was quenched in water. The density of the finished rod was 99.8% of the theoretical value.
• Example 1 The powders given in Example 1 were weighed out as follows and mixed in a tumble mixer for 15 minutes: 1000 g of this powder mixture were filled into a plastic tube with an inner diameter of 66 mm and pressed isostatically at a pressure of 12,000 bar into a cylinder with a diameter of 60 mm and a height of 80 mm.
• the green compact was reduced in a hydrogen / nitrogen stream at a temperature of 880 ° C. for 1 h and presintered and then sintered in a stream of argon at a temperature of 930 ° C. for 25 h.
• the raw sintered body was turned to a diameter of 58 mm, in a soft-annealed box made of soft iron with an outer diameter of 64 mm was inserted and completely encapsulated by placing the lid and soldering in an argon atmosphere.
• the workpiece produced in this way was subjected to thermomechanical processing under a hot press, interrupted by homogenization annealing. By alternately upsetting and annealing at 900 ° C, the height of the cylinder was successively reduced to approx. 32 mm, whereby the material condensed to approx. 95% of the theoretical density and now the die. had a corresponding diameter of 70 mm. After an additional homogenization annealing at 950 ° C.
• the preformed circular plate with parallel flat end faces was turned into a forge with a reduced diameter.
• the 20 mm thick plate had a radial bead of 5 x 5 mm on the upper side and a central recess of 20 mm diameter and 5 mm axial depth on the lower side.
• the plate was quenched in water. The density was 99.2 - 99.5% of the theoretical value.
• the powder mixtures can be within the following limits:
• Isotatic pressing preferably requires pressures of at least 8000 bar.
• the reduction and presintering of the compact can expediently take place in the temperature range from 700 to 1000 ° C. for at least 30 minutes in a stream of hydrogen or hydrogen / nitrogen.
• the sintering of the compact must be carried out above the temperature of the eutectoid transformation, ie at a temperature of at least 700 ° C. for 10 hours in an argon flow to achieve the most homogeneous structure possible.
• thermomechanical processing which can consist of hot pressing, hot extrusion, hot forging, hot rolling, hot drawing and / or hot round hammering, should be carried out at temperatures between 700 and 1000 ° C, as well as the intermediate homogenization in the inert gas flow (intermediate annealing) at at least 700 ° C for at least 30 min.
• the final annealing in a stream of argon is carried out at temperatures between 700 and 1050 ° C ( ⁇ mixed crystal region) for 10 to 15 minutes and the workpiece is then immediately quenched in water.
• thermomechanical processing it is advisable to encapsulate the material beforehand in a ductile metallic shell that does not chemically react with it, which is removed mechanically or chemically at the end of the shaping as a surface layer in most applications.
• Soft-annealed metals and alloys such as copper, copper alloys and soft iron are particularly suitable as materials for the casing. Encapsulation can take place immediately before the thermomechanical processing, in that the sintered body undergoes a mechanical surface treatment beforehand by turning, milling, planing, etc., or the powder can be filled directly into a suitable tube, a can, etc., instead of into a rubber or plastic tube will.
• the powder metallurgical method according to the invention enables the production of workpieces from a memory alloy of the Cu / Al and Cu / Al / Ni type, which are produced in a conventional manner, ie by melt metallurgy Bodies have a fine-grained structure and optionally contain dispersoids in the form of finely divided oxide particles.
• the mechanical properties, in particular the elongation, notch toughness and the working capacity of such workpieces are significantly better than those of cast and / or hot-kneaded bodies. This opens up a further area of application for this type of alloy.

Landscapes

• Chemical & Material Sciences (AREA)
• Engineering & Computer Science (AREA)
• Materials Engineering (AREA)
• Mechanical Engineering (AREA)
• Metallurgy (AREA)
• Organic Chemistry (AREA)
• Physics & Mathematics (AREA)
• Thermal Sciences (AREA)
• Crystallography & Structural Chemistry (AREA)
• Powder Metallurgy (AREA)
• Heat Treatment Of Nonferrous Metals Or Alloys (AREA)

Priority Applications (4)

Applications Claiming Priority (1)

Publications (2)

Family

ID=8186966

Family Applications (1)

Country Status (4)

Cited By (3)

Families Citing this family (16)

Citations (5)

Family Cites Families (10)

• 1980
  • 1980-03-03 EP EP80200184A patent/EP0035601B1/fr not_active Expired
  • 1980-03-03 DE DE8080200184T patent/DE3065931D1/de not_active Expired
• 1981
  • 1981-03-02 JP JP2850481A patent/JPS56136942A/ja active Pending
  • 1981-03-02 US US06/239,626 patent/US4365996A/en not_active Expired - Fee Related

Patent Citations (5)

Also Published As

Similar Documents

Legal Events