GB2243617A - High strength amorphous alloy - Google Patents

Abstract

A high strength amorphous alloy which comprises an amorphous matrix phase comprising a predominant metal element, at least one first additional element selected from the rare earth elements, and at least one second additional element selected from elements other than rare earth elements, with homogeneously dispersed in said amorphous phase a crystalline phase comprising said predominant metal element and said first and second additional elements with said first and second additional elements in supersaturated solid solution, wherein the content of said predominant metal element in said crystalline phase is in the range of at least 85 atom percent to at most 99.8 atom percent, and wherein in said crystalline phase the rare earth element ratio CR, where CR = a / a + b and a is the atom percent content of said first additional element and b is the atom percent content of said second additional element, is no more than 0.5. <IMAGE>

Description

-:1, _ It::, -2. - _1 1 HIGH STRENGTH AMORPHOUS ALLOY

The field of the present invention is high strength amorphous alloys, and more particularly, improvements of high strength amorphous alloys comprising an amorphous phase containing a predominant metal element, a first additive element consisting of rare earth element(s), and a second additive element consisting of element(s) other than rare earth elements.

There are various conventionally known amorphous aluminium alloys of this type, such as described in Japanese Patent Application Laid-open No. 47831/89. Any of such amorphous alloys are aimed at the formation of a single phase in order to promote an increase in strength.

However, the prior art amorphous alloys suffer from a problem that if a crystalline phase is partially incorporated due to conditions of production when the intent is to form a single amorphous phase as in the prior art amorphous alloy, the resulting entire alloy may be reduced in strength and toughness due to the appearance of such crystalline phase.

1 k 2 It is an object of the present invention to provide an amorphous alloy of the type described above, wherein the crystalline phase incorporated in the matrix consisting of an amorphous phase, the content of a predominant metal element in the crystalline phase and the ratio value (which depends upon a relationship with the content of a second additive element) of a rare earth element are controlled, thereby preventing a reduction in strength of the entire alloy and permitting the strength to be increased more than that of an amorphous single-phase alloy.

To achieve the above object, according to the preferred embodiment of the present invention, there is provided an amorphous alloy comprising an amorphous matrix-forming phase comprising a predominant metal element, at least one first additional element selected from the rare earth elements, and at least one second additional element selected from elements other than rare earth elementsiwith homogeneously dispersed in said amorphous phase a crystalline phase comprising said predominant metal element and said first and second additional elements with said first and second additional elements in supersaturated solid solution, wherein the content of said predominant metal element in said crystalline phase is in the range of at least 85 atom percent to at most 99.8 atom percent, and wherein in said crystalline phase the rare earth element ratio C R, where CR = a / a + b 1 3 and a is the atom percent content of said first additional element and b is the atom percent content of said second additional element, is no more than 0.5.

If the content of the predominant metal element in the crystalline phase dispersed in the amorphous matrix phase and the rare earth element ratio are controlled in the above manner, it is possible to further increase the strength of the entire amorphous alloy and to improve the hot plastic workability of such alloy.

However, if the content of the predominant metal element is less than 85 atom %; compounds are liable to be produced in the crystalline phase in production of the amorphous alloy, and any such compound is liable to appear alone, resulting in an embrittlement of the entire resulting amorphous alloy. On the other hand, if the content exceeds 99.8 atom %S it is difficult to provide a mixture of an amorphous phase and a crystalline phase at a normal cooling rate. If the cooling rate is significantly increased, the mass productivity is considerably detracted. Moreover, there is also a problem of a degraded heat resistance of the amorphous alloy itself. The term "predominant metal element" used herein refers to Al and Mg in the preferred embodiment.

A rare earth element is an element required for achieving the noncrystallization, i.e, formation of an amorphous phase, but if the rare earth element is incorporated in a content more than a specified content into a crystal lattice of the 4 predominant metal element forming the crystalline phase, the lattice constant of the crystal lattice is increased, resulting in an embrittlement of the amorphous alloy.

Therefore, the ratio of the rare earth element in the crystalline phase is set at 0.5 or less. By setting the ratio value in this manner, it is possible to provide a lattice constant of the crystal lattice approximating that of a pure predominant metal element.

With such a configuration, a relatively soft crystalline phase is dispersed in an amorphous phase having a higher hardness. Therefore, it is believed that the toughness of the entire amorphous alloy is improved, because the crystalline phase absorbs the strain in an interface between the crystalline phase and the amorphous phase.

Preferred embodiments of the invention will now be described further by way of example and with reference to the accompanying drawingsi-in which:

Fig.1 is a schematic view of an apparatus for producing an amorphous alloy; Fig.2 is a diagram of an X-ray diffraction pattern for an amorphous single-phase aluminium (Al) alloy; Fig.3 is a diagram of an X-ray diffraction pattern for an amorphous Al alloy containing a crystalline phase having a content of 9% by volume; 1.

Fig.4 is a diagram of an X-ray diffraction pattern for an amorphous Al alloy containing a crystalline phase having a content of 29% by volume; Fig.5 is a diagram of an X-ray diffraction pattern for an amorphous Al alloy containing a crystalline phase having a content of 37% by volume; Fig.6 is a graph illustrating a relationship between the content of a crystalline phase in an amorphops Al alloy and the tensile strength; Fig.7 is a graph illustrating a relationship between the Y ratio value CR and the lattice constant; Fig-8 is a graph illustrating a relationship between the Y ratio value Cand the tensile strength; Fig.9 is a graph illustrating a relationship between the Y ratio value CR and the Young's modulus; Fig.10 is a graph illustrating a relationship between the Y content and the lattice constant; Fig.11 is a thermocurve of differential thermal analysis for an amorphous single-phase Al alloy; Fig.12 is a thermocurve of differential thermal analysis for an amorphous Al alloy containing a crystalline phase having a content of 26% by volume; and Fig.13 is a thermocurve of differential thermal analysis for an amorphous Al alloy containing a crystalline phase having a content of 37% by volume.

6 1 Fig.1 schematically illustrates an amorphous alloy producing apparatus using a single-roller process. The apparatus comprises a cooling roller 1 made of pure copper and adapted to be rotated in a clockwise direction as viewed in Fig.1, a quartz nozzle 2 fixedly mounted above the cooling roller 1 with its outlet being in proximity to an outer peripheral surface of the cooling roller 1, and a high frequency heating coil 3 disposed to surround a lower end of the nozzle 2. The cooling roller 1 has a diameter set at 200 mm, and the nozzle 2 has a bore diameter set at 0.3 mm at the outlet. The gap between the outlet and the outer peripheral surface of the cooling roller 1 is set at 0.3 mm.

In producing an amorphous Al. alloy as an amorphous alloy, a molten alloy M containing aluminium as the predominant metal element, a first additional element selected from rare earth elements-, and a second addittonal element selected from elements other than rare earth elements is extruded from the outlet of the nozzle 2 onto the outer peripheral surface of the cooling roller 1 under a pressure of argon gas (for example, 0.4 kg/cm2), and spread on the outer peripheral surface of the roller 1 from between the nozzle 2 and the cooling roller I as the cooling roller 1 is rotated. Thus, it is drawn into a thin ribbon form, while at the same time being quenched, thereby providing an amorphous Al alloy.

In this case, if the rotational speed of the cooling roller 1 is reduced below a speed that forms an amorphous single-phase Al alloy (i.e., an alloy having a volume fraction 7 of an amorphous phase of 100%), thereby providing a reduced cooling rate for the molten alloy, a crystalline phase is produced in the molten metal.

The use of such a procedure provides a high strength amorphous Al alloy comprising an amorphous phase containing a predominant metal element and first and second additive elements and forming a matrix, and a fine crystalline phase containing the predominant metal element and the first and second additive elements and dispersed homogeneously in the amorphous phase with the first and second additive elements formed into a supersaturated solid-solution.

The content of Al as the predominant metal element in the crystalline phase is set in a range of at least 85% by atom to at most 99.8% by atom. If the Al content is less than 85% by atom.,- compounds (such as A13Y, A13Ni, AlNimYn, etc.) are liable to be produced in the crystalline phase in the production of the amorphous Al alloy, and any such compound is liable to appear alone, resulting in an embrittlement of the entire amorphous Al alloy. On the other hand, if the Al content exceeds 99.8% by atom, it is difficult to provide a mixture of an amorphous phase and a crystalline phase at a normal cooling rate. If the cooling rate is significantly increased, the mass productivity is considerably affected'. Moreover, the heat resistance of the resulting amorphous Al alloy itself is degraded.

The rare earth elements include those of atomic numbers 21, 39 and 57-71 and typical examples of the rare earth elements that may be used as the first additional elements include Y, Lai Ce, Sm, Nd, and mixtures thereof such as Md (Misch metal - a mixture of a rare earth of the cerium group, containing for example 40-50% Ce and 20-40% lanthanum),and the content thereof is 8 preferably in the range from at least 0.1 atom % to at most 4k atom If the content of the rare earth element is too low it is impossible tQ provide a mixture of amorphous and crystalline phases. On the other hand, if the content is too high, - the resulting crystalline phase is embrittled and as a result, the amorphous Al alloy itself is brittle.

Examples of the second additional elements that may be used include other metals such as NiS Fe and Co and mixtures thereof.

The content of these is preferably at most 10 atom If the content of the second additional element is too high then compounds are liable to appear in the resulting crystalline phase, and the amorphous phase forming ability for the entire alloy is reduced from a interrelation with the content of the rare earth element. The lower limit f or the content of the second additional element is preferably 5 atom%. Too low a content of the second additional element can result in undesirable conditions during production.

It is preferable that the contents of the predominant metal element and the first and second additional elements in the amorphous matrix phase are greater than in the crystalline phase. If this relationship of the contents is reversed, compounds are liable to appear in the crystalline phase, causing the embrittlement of the entire alloy. Thus the crystalline phase preferably forms 540%, specially 15-25%, b volume of the amorphous alloy.

9 Using the above-described procedure with varied rotational speeds of the cooling roller 1, amorphous Al alloy specimens A to D having A1.9y5N'6 (wherein numeric values represent % by atom, which is true with each of the alloy specimens) were produced, and the relationship between the rotational speed of the cooling roller 1 and the content of the crystalline phase was examined, thereby providing results given in Table below. The crystal structure of the crystalline phase was of a fcc (a face-centered cubic structure) due to Al, and the average diameter of the crystalline phase was in a range of at least 300 A to at most 8oo A.

Amorphous Rotational speed of Content of crystalline AI allov coolincr roller (rDm) Phase R by volume) A 4,000 0 B 3,000 9 c 2, 000 29 D 1,500 37 Figs.2 to 5 illustrate diagrams of X-ray diffraction patterns of the amorphous Al alloys A to D, respectively. The anticathode of the X-ray tube used for measurement was of Cu, and Ka ray was used.

The amorphous Al alloy A is an amorphous single-phase Al alloy because of a more rapid cooling speed, and a halopattern having no steep peak and peculiar to the amorphous phase can be seen in Fig.2.

The amorphous alloy B was produced at a cooling rate 1,000 rpm lower than when the alloy A was produced, and in the amorphous alloy B, a peak pi has appeared as a result of the appearance of a slight crystalline phase, as shown in Fig.3. This peak pl corresponds to a (111) plane of the fcc.

The amorphous Al alloy C wa s produced at a cooling rate half of when the alloy A was produced, and about 30% of the entire amorphous Al alloy was a crystalline phase. Hence, a higher peak pl and lower peaks p2 to p4 have appeared as a result of the appearance of a crystalline phase, as shown in Fig.4. Among these peaks p2 to p4, the peak p2 corresponds to a (200) plane of the fcc; the'peak p3 corresponds to a (220) plane of the fcc, and the peak p4 corresponds to a (311) plane of the fcc.

The amorphous Al alloy D was produced at a cooling rate lower than when the alloy C was produced, and about 40% of the entire amorphous Al alloy was a crystalline phase. Therefore, higher peaks pi and p2 and lower peaks p3 and p4 have appeared as a result of the appearance of a crystalline phase, as shown in Fig.5.

Fig.6 illustrates a relationship between the content of a crystalline phase in each of three amorphous Al alloys and the tensile strength. In Fig.6, a line x1 corresponds to the above-described Al,9y,K'6 alloy; a line x2 corresponds to an Al,,Y2Nij, alloy, and a line x3 corresponds to an Al,,y6N'4 alloy.

As apparent from Fig.6, in each alloy, the strength is increased as the content of the crystalline phase is increased, as compared with an amorphous single-phase (the z 1 content of a crystalline phase = 0). Therefore, the content of the crystalline phase is preferred to be in a range of at least 5% by volume to at most 40% by volume.

In this case, in the Al,9Y5 Ni 6 and Al88Y2NijO alloys indicated by the lines x1 and x. 2, an embrittlement begins-at near a crystalline phase content of 40% by volume. on the other hand, in the Al9Oy6N'4 alloy indicated by the line x3, an eibrittlement begins at near a crystalline phase content of 20% by volume, and hence, this alloy is compositionally not included in the present invention.

The average diameter of the crystalline phase is preferably in a range of at least 300 A to at most 800 A.

If the average diameter is too low the meaning of the appearance of the crystalline phase is lost. If the average is too high the stabilization of the crystalline -phase is not provided and a homogeneous dispersion is impossible, resulting in a redu ctpd strength of the entire amorphous Al alloy.

The rare earth element is an element required for achieving a noncrystallization or formation of an amorphous phase, but if a rare earth element in an amount more than a specified amount is incorporated in a crystal lattice (fcc) of Al forming a crystalline phase, the lattice constant (a = 4.05 A) of the crystal lattice is increased, resulting in a embrittlement of the amorphous alloy, because the rare earth element has a relative large atomic radius (e.g., Y has a radius of 1.8 A).

12 T he ratio CR of the rare earth element component L in the crystalline phase is def ined above as being CR a / a + b and as having a value of 0.5 or less.

By setting the ratio -- CR of the rare earth element component in the crystalline phase in the above manner, it is possible to provide a lattice constant of the crystal lattice approximating that of pure Al.

Such a configuration results in a relatively soft crystalline phase dispersed in an amorphous phase having a higher hardness. Therefore, it is believed that the entire amorphous alloy has an improved toughness, because the crystalline phase absorbs the strain in an interface between the crystalline phase and the amorphous phase.

Figs.7 to 9 illustrate relationships between the ratio value CR (a / a + b, wherein a represents a Y content and b represents a Ni content) of Y in an Al-Y-Ni based amorphous alloy having a crystalline phase content of 20% by volume and the lattice constant of a crystal lattice in a crystalline phase, the tensile strength and the Young's modulus, respectively.

As is apparent from Fig.7, by setting the ratio c of Y at no greater than 0.5, it is possible to provide a lattice constant approximating that (4.05 A) of pure Al.

R In addition, as apparent from Figs-8 and 9, the tensile strength an( the Young's modulus can be maintained at high values, respectively, by setting the ratio CR of Y at no greater than 0.5.

A relation, a 5 b, is established from the above-described relation, a /(a + b):5 0.5. This means that the content of an expensive rare earth element such as Y, La, Ce, etc., can be reduced, which is effective for reducing the cost of an amorphous A1 alloy.

Fig.10 illustrates the relationship between the Y content and the lattice constant of a crystal lattice in a crystalline phase in each of Alloo-xyx based amorphous alloy (indicated by a line yl) and an Alga-jxNi2 based amorphous alloy (indicated by a line y2) when the contents of the crystalline phase are set in a range of 5 to 40 by volume.

It can be seen from the lines yl and y2 in Fig.10 that the lattice constant is substantially constant if the Y content is equal to or less than 2% by atom, but the lattice constant is increased if the Y content exceeds 2% by atomic weight.

Therefore, in the A195jxNi2 based amorphous alloy, the Y content is preferably in a range cú at least 0. 5 atom % to at most 2 atom % in order to ensure the required strength.is achieved.

Figs.11 to 13 illustrate differential thermal analysis thermocurves for three A1.9Y,N'6 alloys which are amorphous Al alloys. Fig.11 corresponds to the alloy having a single amorphous phase; Fig.12 corresponds to the alloy having a 4 14 crystalline phase content of 26% by volume, and Fig.13 corresponds to L, the alloy having a crystalline phase content of 37% by volume.

The crystallization temperature Tx of the amorphous single-phase Al alloy shown in Fig.11 is 89C, but tends to be gradually raised as the crystalline phase content is increased. For this reason, the crystallization temperature Tx of the amorphous Al alloy shown in Fig.12 is raised to 99C, and the crystallization temperature Tx of the amorphous Al alloy shown in Fig.13 is raised to 109C.

In addition, from a comparison of the calorific values after the heating temperature exceeds the crystallization temperature Tx, i.e., the heights of the peaks, it can be seen that the height of the peak for the amorphous single phase Al alloy of Fig.11 is highest, and the height of the peak is reduced with increasing of the crystalline phase content. This means that the amount of the crystalline phase produced by crystallization is smaller.

Thus, when a material is formed from an amorphous Al alloy having a thermal characteristic as shown in Figs.12 and 13 and such material is subjected to a hot plastic working, e.g., a hot extrusion, the thermal control for the material is relatively easy.

It should be noted that a crystalline phase appears even when an amorphous single-phase Al alloy is subjected to a thermal treatment, but the crystalline phase in this case is coalesced because of an increased rate of growth of crystalline particles. In addition, the strength and toughness 4 are reduced as compared with those of the amorphous. Al alloy accordingto the present invention, because the dispersion is heterogeneous and moreover, a segregation of the crystalline phase is produced. It will be understood that amorphous Mg alloys containing Mg as a predominant metal element rather than Al are also included in the scope of the present invention.

It will also be appreciated that in a further aspect the present invention also provides a process for the preparation of the new alloys, the process comprising extruding a molten mixture of said predominant metal element and said first and second additional elements through extrusion means and onto a cooling surface which is moving relative to said extrusion means.

4,k 16

Claims (9)

1. An amorphous alloy comprising an amorphous matrix-forming phase comprising a predominant metal element, at least one first additional element selected from the rare earth elements,, and at least one second additional element selected from elements other than rare earth elements, with homogeneously dispersed in said amorphous phase a crystalline phase comprising said predominant metal element and said first and second additional elements with said first and second additional elements in supersaturated solid solutioni wherein the content of said predominant metal element in said crystalling- phase is in the range of at least 85 atom percent to at most 99.8 atom percent, and wherein in said crystalline phase the rare earth element ratio C R, where C R a / a + b and a is the atom percent content of said first additional element and b is the atom percent content of said second additional element-; is no more than 0.5.

2. An alloy as claimed inclaim 1, wherein said first additional element is selected from Y Lai Ce, Sm, Nd and Md (Misch metal) and is present in a content of from at least 0.1% by atom to at most 5% by atom.

3. An alloy as claimed in either of claims'l and 2 wherein said second additional element is selected from Ni, Fe and Co and is present in a content of no greater than 10% by atom.

4. An alloy according to any one of the preceding claims wherein said crystalline phase is present in a range of from at least 5% by volume to at most 40% by volume.

4 17

5. An alloy according to any one of the preceding claims wherein the average diameter of the crystals in said crystalline phase is in the rahge of from at least 300 A to at most 800 AO.

6. An alloy as claimed in any one of the preceding claims wherein said predominant metal element is selected from aluminium and magnesium.

7. An alloy as claimed in any one of the preceding claims wherein said predominant metal element is aluminium, said first additional element is yttrium and said second additional element is nickel.

8. A process for the production of an alloy as claimed in any of the preceding claimsi said process comprising extruding a molten mixture of said predominant metal element and said first and second additional elements through extrusion means and onto a cooling surface which is moving relative to said extrusion means.

9. High strength crystalline phase containing amorphous alloys substantially as herein disclosed and containing rare earth and non rare earth additives in a relative atom ratio of less than 1:1.

Published 1991 at 7be Patent Office. Concept House. Cardiff Road, Newport, Gwent NP9 I RH. Further copies may be obtained ftm Sales Branch, Unit 6. Nine Mile Point, Cwuifelinfach, Cross Keys, NewporL NP I 7HZ. Printed by Multiplex techniques ltd, St Mary Cray, Kent.