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

Definitions

• the invention relates to a shape memory alloy with A s temperatures above 100 ° C for repeated applications, which contains no noble metals.
• NiTi shape memory alloys are known to have excellent properties. With an almost stoichiometric composition, they are characterized by a particularly high amount of reversible deformation in the one-way and two-way effect, by high tensile strength and ductility and by very good corrosion resistance. In addition, these shape memory alloys have an excellent stability of the effect size against thermal cycles. In addition, they can be heated relatively far above the temperature A f (temperature at the end of the austenite formation) without harmful irreversible structural changes occurring, which reduce the size of the shape memory effect or inadvertently shift the transformation temperature.
• a f temperature at the end of the austenite formation
• the A s temperature (temperature at the start of austenite formation) should be relatively high, for example at temperatures above 100 ° C. However, the maximum A s temperatures that can be achieved with NiTi shape memory alloys for repeated applications are below 100 ° C. In the following there will be considered as coming A s temperature that A s temperature indicated that appears after several thermal cycles.
• a shape memory alloy based on Ni-Ti is known from FR-A-2 389 990 (for example according to Table I), which may contain up to 30% by weight of Zr and up to 5% of Zr in addition to Cu. -% contains. With the composition mentioned here, however, this Zr fraction only makes up about 3.5 at%.
• the invention has for its object to propose a shape memory alloy based on NiTi, which has good values for the two-way effect, elongation at break, overheatability and reversible deformation at an A s temperature of more than 100 ° C.
• the object is achieved by a shape memory alloy with A s temperatures above 100 ° C., which consists of 41.5 to 54 at.% Ni, 24 to 42.5 at.% Ti, 14 to 22 at.% Zr and 0 to 8.5 at% Cu; Within the framework of the teaching according to the invention, Zr can be replaced by Hf.
• the shape memory alloys in question are obtained in a known manner from suitable starting melts or master alloys by remelting in a vacuum induction furnace under an argon atmosphere in graphite crucibles; the starting melts or master alloys are composed such that a reaction with the graphite crucible is largely suppressed. Contrary to expectations, it was found that shape memory alloys in the composition range mentioned have shape memory properties with significantly higher transition temperatures than binary NiTi shape memory alloys.
• the shape memory alloys are ductile and can be deformed at room temperature, provided that their composition has a single-phase structure.
• a composition formula Ni 1-x TiZr x is given for a memory alloy with the alloy components nickel, titanium and zircon, whose x value can be between 0 and 0.21.
• shape memory alloys with advantageous properties can also be designed in such a way that they range from 24 to 34 at.% Ti and 16 to 22 at.% Zr or Hf (claim 2) or 24 to 30 at% of Ti and 20 to 22 at% of Zr or Hf (claim 3).
• the A s temperature is above 120 ° C, with a Zr content of 20 at% above 145 ° C.
• the shape memory alloy according to claim 1 can advantageously be further developed in that the (Ni + Cu) content 47 to 50 at.% (Claim 4) or 48 to 49.5 at.% (Claim 5) or 48, 5 to 49 at% (claim 6).
• the Zr or Hf content can be modified in such a way that it can contain up to 19 at% (claim 7) or up to 18 at% (Claim 8).
• a shape memory alloy with particularly favorable properties can be produced by dimensioning the composition ranges in the manner described by claims 1, 6 and 8.
• Such a shape memory alloy therefore has the following composition: 48.5 to 49 at.% Ni; 24 to 42.5 at% Ti and 14 to 18 at% Zr or Hf.
• Tables 1 and 2 below list, by way of example, primarily shape memory alloys of the claimed composition with their A s temperatures.
• Table 2 also shows an example of a binary NiTi shape memory alloy whose A s temperature is expected to be below 100 ° C.
• the exemplary embodiments in Tables 1 and 2 show that the A s temperatures increase with increasing Zr content: with more than 16 at.% Zr, the A s temperature is above 120 ° C., with more than 20 at. -% Zr higher than 150 ° C.
• the size of the shape memory effect ie the extent of the reversible deformation, is another important feature. Since the shape memory effect decreases with increasing Zr content, the shape memory alloys given in the tables only have Zr contents in the order of 20 at%, taking into account the opposite tendency of the properties.
• Master alloys of the claimed composition are produced in the button port and remelted in the vacuum induction furnace under argon atmosphere in graphite crucibles to cylindrical samples.
• the transition temperatures A s and A f given in the tables were determined calorimetrically on the samples in the as-cast state after several thermal cycles.

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• Chemical & Material Sciences (AREA)
• Physics & Mathematics (AREA)
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• Crystallography & Structural Chemistry (AREA)
• Engineering & Computer Science (AREA)
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• Mechanical Engineering (AREA)
• Metallurgy (AREA)
• Organic Chemistry (AREA)
• Powder Metallurgy (AREA)
• Manufacture And Refinement Of Metals (AREA)
• Continuous Casting (AREA)

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• 1990
  • 1990-02-27 DE DE4006076A patent/DE4006076C1/de not_active Expired - Lifetime
  • 1990-07-21 DE DE9090114034T patent/DE59002023D1/de not_active Expired - Fee Related
  • 1990-07-21 EP EP90114034A patent/EP0419789B1/de not_active Expired - Lifetime
  • 1990-07-24 US US07/557,629 patent/US5108523A/en not_active Expired - Fee Related
  • 1990-08-10 JP JP2210555A patent/JPH0372046A/ja active Pending

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