DE1558715C - Alloys with a martensitic transition - Google Patents

Description

and third position elements are practically arbitrary in the aforementioned wide temperature range is selectable.

Preferred compositions of the alloy according to the invention are set out in the subclaims marked.

In the following the invention is illustrated more schematically by means of hand Drawings of exemplary embodiments explained in more detail. It shows

F i g. 1 is a graph of the temperature range ( ⁰ C) in which the peculiar martensitic transition of the TiNi alloy occurs as a function of the atomic percent (and the weight percent) Ni,

F i g. 2 shows a graph in which, for the ternary alloys TiNIaCo ₁ -S and TiCOzFe ₁ -Z, the logarithm of the temperature (° Kelvin) at which the peculiar martensitic transition takes place was plotted as a function of the concentration of "free" electrons, and '■ ·;':

3 shows a graph in which, for the alloys TiNiZCo ₁ -:,; and TiCOzFe ₁ -Z the critical temperatures (° K) at which the peculiar martensitic transition occurs are plotted as a function of the concentration of the "free" electrons.

The term “critical temperature” used in the following refers to the temperature at which the alloy in question exhibits a martensitic (diffusion-free) transition. The TiNi alloy with near stoichiometric amounts of titanium and nickel and the related alloys of the present invention exhibit unusual and overt deformation and temperature dependent properties. TiNi alloys show e.g. B. a mechanical memory at the critical temperature of the alloy, that is, the alloys can be deformed below the critical temperature and then by heating to or slightly above the critical temperature, return completely to their original shape, which was before the deformation. The TiNi alloys with almost stoichiometric amounts of titanium and nickel are able to convert thermal energy directly and very effectively into mechanical energy. The nearly stoichiometric composition TiNi alloys have at the critical temperature _latent: heat of about 6cal / g.

Furthermore, the acoustic damping and elasticity properties and the other mechanical properties (in particular the yield point) change drastically within the temperature range ^ in which the critical temperatures are. The critical temperatures at which the changes in the atomic structure take place change greatly with small changes in the alloy composition. The known alloys show a temperature maximum of 439 ° K (166 ° C) for TiNi alloys with exactly stoichiometric composition and fall to below 273 ⁰ K (0 ° C) for TiNi alloys having slightly enriched nickel content, such as F i g. 1 shows.

While this temperature range of the martensitic transition is impressively and favorably at normal mean temperatures, even extremely small amounts of excess nickel in the binary alloy cause the formation of a second phase, namely a TiNi ₃ phase. A very small amount of the second phase of TiNi ₃ can be tolerated as well as the normal non-metallic impurities Ti ₄ Ni ₂ O, Ti ^ Ni ₂ N, TiC, etc., but these insoluble impurities tend to show the effectiveness of the TiNi alloy with the behavior described above.

The task of creating alloys which show the peculiar properties of the TiNi alloy with a nearly stoichiometric composition at any desired temperature within the range from absolute zero (O ⁰ K) up to temperatures above 439 ^{0 K (166 ° C),} is solved according to the invention by careful and well-considered addition of further elements according to the table, whereby the salient properties of the TiNi alloy are not reduced in their effectiveness.
When looking at the table, a few emerge

basic structural similarities. These similarities exist primarily with regard to the ratio of the * atomic radii, with regard to the valence electrons the corresponding metallic elements, with regard to the crystal structures and with regard to of the electron concentrations of their intermetallic Links. In this table the first, second and third long periods of the periodic System of elements. taken into account.

Information about the elements and the intermetallic compounds built up from them

Atom-
radius
: (A); . Elements of the first Valence-
Electrons long period of the periodic table Crystal structure -.- - ■ ■ '■ Kntiscne
Transitional '
temperature
( ⁰ K) element .1.45+ Ratio of
Atomic radii *) 4th Educated
connection I ■ Electrons
concentration
'e / atom ' Ti ". ' . ■ ■ - ... "■ Complex f '. "■ 1.24 :: 8th «Ο = 9Ä . : '■ , <4. . Fe ■ ._ "': -: v; 1.17 TiFe fl.uft = 2.98 A . 6.0 Complex 1.25+ 9 flo = 9Ä 35 Co 1.16 "TiCo Complex 6.5 1.25- 10 fl ₀ = 9 A 439 ' Ni 1.16 TiNi a, ub = 2.98 A 7.0

Elements of the second long period of the periodic table

element atom
radius
(A) Ratio of
Atomic radii *) Valence-
Electrons Educated
connection Crystal structure, Electrons
concentration
e / atom Critical
Transition
temperature
CK) Zr
Ru
Rh
Pd 1.59
1.32
1.35
1.37 1.20
1.18
1.16 4th
8th
9
10 ZrRu
ZrRh
ZrPd Complex
a ₀ = 9.6 A
a _SU b = 3.2 A
Complex
σ ₀ = 9.6 A
a _S ub - 3.2 A
Complex
α ₀ = 9.6 A
a _S ub = 3.2 A 6.0
6.5
7.0 40
653
1000

Elements of the third long period of the periodic table

element atom
radius
(A) Ratio of
Atomic radii *) Valence-'
Electrons Educated
connection Crystal structure Electrons
concentration
e / atom Critical
Transition
temperature
( ⁰ K) Hf
Os
Ir
Pt 1.56
1.33
1.35
1.39 1.17
. 1.16
1.12 4th
8th
9
10 HfOs
HfIr
HfPt Complex
a ₀ = 9.6 A
a _S ub = 3.2 A
Complex
a ₀ = 9.6 A
asub = 3.2 A
Complex
O ₀ = 9.6 A
asub = 3.2 A 6.0
6.5
7.0

*) Ratio of the atomic radius of Ti, Zr, Hf to the atomic radius of Fe, Co, Ni or Rh, Ru, Pd or Os, Ir, Pt.

If one plots the natural logarithm of the transition temperatures (critical temperatures) of the compounds of the first long period, TiNi, TiCo and TiFe and also those of the intermediate ternary alloys, ie TiNIzCo ₁ -Z and TiCOzFe ₁ -Z as a function of the "free" electron concentration , one obtains the in FIG. 2 linear and smooth curve shown. From this graph, which applies to the alloys formed from the elements of the first long period in the correct proportions, it follows immediately that progressively lower temperatures can be achieved by replacing nickel with cobalt (TiNi ₁ Co ₁ -I), this exchange happening atom by atom. This replacement of Ni by Co in no way changes the titanium content of the ternary alloys of this series.

All ternary phases TiNIzCo ₁ -! and TiCo _x Fe ₁ -Z, which are formed by replacing Ni with Co and replacing Co with Fe, show crystal structures which are similar to the underlying binary TiNi compound. The crystal structure of TiNi was determined by X-ray diffraction experiments on both thin crystals and powdered crystals, and the occurrence of a martensitic transition (without a first-order crystallographic transformation) was confirmed. If one observes that the / aiii of the free halves, which are contributed to their alloys by Ti, Fe, Co and Ni, are 4, 8, 9 and 10 (the number of electrons outside the closed shells), then it results if the critical temperature is plotted as a function of the free electron concentration in these alloys (number of free electrons per atom), the smooth curve shown in FIG. This curve indicates that the martensitic transition observed in TiNi is not restricted to this compound, but also occurs in the binary compounds of TiCo and TiFe and in the above-described ternary combinations of these elements according to the invention.

In the case of the ternary alloys according to the invention, which are formed by titanium and selectively varied nickel, cobalt and iron, it is possible to achieve any desired critical temperature from almost zero degrees Kelvin up to 439 ° K. Selected ternary combinations of the elements Ti, Ni, Co were _{alloyed in the ratio TiNIzCo 1} -S and processed into test specimens. These ternary systems show practically all the same apparent and peculiar properties as the TiNi alloy (critical temperature 439 ° K), but at a lower temperature, which in turn depends on the amount of cobalt which has been introduced in place of nickel. "

Looking further at the table becomes clearly that the intermetallic compounds

ZrRu, ZrRh and ZrPd should behave similarly. This structural behavior should also be expected from the compounds HfOs, HfIr and HfPt of the third long line of the periodic table. Experiments have shown that the compounds of the last two series also have critical temperatures, and that they also show the same peculiar behavior that was already observed with the TiFe-TiCo-TiNi series. Furthermore, ternary substitution products, e.g. B. ZrPdaRhj-2; and HfPUIr ₁ -S etc. are possible, which have essentially medium critical temperatures. As the table shows, the compounds of Zr and Hf and their intermediate ternary alloys according to the invention show higher critical temperatures for the atomic structure transformation that occurs. Practically "has reached so that the critical temperature has been extended over a range extending from about the absolute zero ⁽⁰ K O) to addition to almost 100O ⁰ K (717 ° C).

Both the yield point and the modulus of elasticity increase considerably above the critical temperature. To get out of the increased rigidity above To be able to benefit from the critical temperature, it is necessary to use the alloys which have critical temperatures that are below the working temperature range at a special application. This is particularly important in self-righting constructions

ίο for both hydraulic engineering and aerospace and Space purposes. In order to achieve that such structures erect themselves in every place, such as B. also in sea water, it is necessary to create self-righting alloys, which have critical temperatures that are well below the lower sea water temperature of about -2 ° C (27ΓΚ). In order to achieve a To ensure effective mechanical memory, etc., cobalt-substituted alloys (Ti

unusable.

1 sheet of drawings

209 652/176

Claims (5)

Patent claims: 1. Alloy with a martensitic transition at a desired temperature by-the composition ΛΪ xZjy-X, depending on the desired critical temperature in the range from 0 to 1000 ^° K, at which the martensitic transition takes place, X is an element of subgroup IV, namely Ti, Zr or Hf, ¹ and Y and Z are each an element of VIII . Subgroup, namely Fe, Co, Ni, Ru, Rh, Pd, Os, Ir or Pt, symbolizes and the alloy consists of about 50 atomic percent of an element symbolized by X and the remainder of the alloy consists of elements symbolized by Y and Z, where the elements X, Y, Z belong to the same period of the periodic table and 0 < χ < 1. 2. Alloy according to claim 1, characterized by the composition 3. Alloy according to claim 1, characterized by the composition 35 4. Alloy according to claim 1, characterized by the composition ZrRh ₂ Ru ₁ -J ₁ 5. Alloy according to claim 1, characterized by the composition 50 55 The present invention relates to alloys having a martensitic transition in a desired temperature. In the past, great efforts have been made ^y conclusions to a number of Legie- to develop which have the same peculiar characteristics as the stoichiometric TiNi alloy in which the components titanium and nickel are present in almost atomistic quantities and in the USA . Patent 3,174,851. This alloy is often referred to as "Nitinol". In particular, great efforts have been made to develop alloys which exhibit this exceptional martensitic transition at a desired temperature. Attempts to create a series of such alloys, each showing a martensitic transition at a different temperature, have so far met with little success. The reason for this is that until now there has been no clear understanding of the atomic structural transformation associated with the unusual mechanical and physical properties found in TiNi alloys. ' The alloys based on TiNi, especially those which are close to the stoichiometric TiNi composition are able to accomplish services of an unusual and previously unknown kind. These unusual properties, such as B. mechanical memory, acoustic damping, Energy conversion, etc., have opened up a whole new range of application possibilities. To the Time, these uses include self-righting airspace, space or Hydraulic components, machine bearings and machine equipment with low noise generation, prestressed Fastening elements and fastening or reinforcing elements, tools with saved Energy, energy converters, temperature actuated devices (switches, fire alarms, etc.), Clockworks and cooling devices are just a few of the possible applications. Almost stoichiometric TiNi alloys have the aforementioned properties, but they have the disadvantage that they are limited by a relatively narrow range of the critical temperature. With the discovery of further compounds with similar properties and their ternary intermediate alloys, the technical properties that originally only belonged to the TiNi alloy are now available over a wide range of the critical temperature. This applies in particular to combinations of the type TiNi ₁ Co ₁ -Z and TiCOzFe ₁ -Z. Since cobalt and iron are relatively cheap elements and are easily available for technical purposes, they are particularly suitable as additives for these alloy systems. The object of the present invention is to create alloys which, at a predetermined, a martensitic transition within a wide range of temperatures that can be selected show. This object is achieved by alloys of the composition XY ₁ Z ₁ -Z, wherein depending on the desired, lying in the range of O to 100O ⁰ K critical temperature at which the martensitic transition takes place, X is an element of the IV. Subgroups, namely Ti, Zr or Hf and Y and Z each symbolizes an element of the VIII. Subgroup, namely Fe, Co, Ni, Ru, Rh, Pd, Os, Ir or Pt and the alloys to about 50 atomic percent of an element symbolized by X and the remainder of the alloy consists of elements symbolized by Y and Z, where the elements X, Y, Z belong to the same period of the periodic table and O <each <1. The alloys according to the invention offer the advantage that the critical temperature at which the martensitic transition takes place by a partial or complete exchange of the second