GB2163179A

GB2163179A - Aluminium/zirconia composite

Info

Publication number: GB2163179A
Application number: GB08420543A
Authority: GB
Inventors: Norman Tommis
Original assignee: AE PLC
Current assignee: AE PLC
Priority date: 1984-08-13
Filing date: 1984-08-13
Publication date: 1986-02-19
Also published as: JPS61106742A; GB2163179B; GB8420543D0; EP0178046B1; EP0178046A1; DE3569752D1; KR860001893A; US4624831A

Description

1

SPECIFICATION

Improvements in or relating to compositions of 55 matter and their manufacture The invention relates to a composition of matter and its manufacture.

According to afirstaspectof the invention, there is provided a composition of matter comprising alumi nium oran aluminium alloy, containing between 5% and 50% byvolume of zirconia.

Thezirconia is preferably present in.an amount from 10to 30% byvolume and most preferably20% byvolume.

Thezirconia may be incorporated in the aluminium oraluminium alloy in theform of fibres of zirconia.

In this case,the aspect ratio of thefibres isfrom 50 to 1000 and the diameterof thefibresfrom 2to 20 micrometers.

Thezirconiamay, however, be incorporated into the aluminium oraluminium alloy in theform of a powder.

The aluminium oraluminium alloy may bean aluminium alloy known as LM 13.

Alternatively, the aluminium or a] uminium alloy may be an aluminium alloy known as Lo-Ex.

The zirconia may, in any ofthe above cases, be partially stabilized by yttria andlor other rare earth metals or calcium oxide or magnesium oxides.

According to a second aspectof the invention, there is provided a method of manufacturing a composition of matter according to thefirst aspect of the invention, and comprising preparing molten aluminium or a molten aluminium alloy, then incor- porating thereinto zirconia in an amount of from 5% to 50% byvolume and then solidifying the matter so produced.

Wherethe zirconia is in theform of fibres, the method may comprise preparing a wad or mat of the zirconia fibres and then infiltrating the wad or mat with molten aluminium or aluminium alloy.

The aluminium or aluminium alloy is preferably infiltrated by a squeeze casting process.

The zirconia may, however, be in the form of a powder and in this case,the method may comprise incorporating the zirconia powder into the molten aluminium oraluminium alloy.

The incorporation is preferably ata temperature of 8000C.

The method may further comprise the step of heat treating the solidified matter.

Thefollowing is a more detailed description of

GB 2 163 179 A 1 some embodiments of the invention, by way of example, reference being made to the accompanying drawings, in which:- Figure 1 is a graph of the variation of tensile strength (in tons per square inch) againsttemperature (in'C)forthree materials: an aluminum alloy known as LM 13, LM 13 reinforced by 10% of zirconium oxide and LM 13 plus 20% of zirconium oxide, Figure 2 is a graph of elongation (in percent) against temperature (in'C) of the three materials of Figure 1, Figure 3 is a graph of compressive strength (intons persquare inch) againsttemperature (in'C) of the three materials of Figures 1 and 2, Figure4 is a graph of hardness (Brinell hardness test H132.40) againsttemperatue (in'C) of thethree three materials of Figures 1, 2 and 3, Figures 5to 13 are photomicrographs of an aluminium alloy known as LM 13 inctuding 20% by volume of zirconia, at a magnification of 200 and at temperatures of 2WC, 20WC, 30WC, 4009C, 50WC, 550-C, 60WC, 75WC and 95WC respectively.

A material is prepared in the following way:EXAMPLE 1:

Zirconiafibres, partly stabilized byyttria, and having an aspect ratio offrom 50to 1000 and a 80- diamaterfrom 2to20 micrometers are formed into a wad bycompaction.A binder may be included to hold the fibres together. The compaction issuch asto providea requiredvolume of zirconia in the finished material. This volume may befrom 5% to50% butis preferablyfrom 10to 30%, for example 20%.

Thewad or matisthen inserted into a closed die and a molten aluminium alloy is gravity fed intothe die.This aluminium alloy maybethatknown as Lo-Ex orthatin accordancewith BS.1490:1970:LM 13 and known as LM 13. The molten aluminium alloy may be solidified under a force of manytonnes by a method known as squeeze casting, to causethe molten aluminium alloyto penetrate fullythe wad or mat of fibres.

The material so produced is then solidified, heat treated by a solution treatment and aged. The thermal conductivity, coefficient of thermal expansion and density of the material prepared as described above with 20% by volume of zirconia fibres, and a comparison of such properties with the corresponding properties of the aluminium alloy by itself, grey cast iron and austenitic castiron are given in the following Tables 1, 11 and 111.

TABLE 1

COMPARISON OF THERMAL CONDUCTIVITIES (20-200'C) (CALSISO.CMICMISEC) (WIMK) LM 13 Alloy 0.40 140 LM 13 + 20% Zirconia Fibres 0.22 63 GreyCastiron 0.13 37 Austenitic Cast Iron 0.11 31 The drawing(s) originally filed was (were) informal and the print here reproduced is taken from a later filed formal copy. The claims were filed later than the filing date within the period prescribed by Rule 25(1) of the Patents Rules 1982.

2 GB 2 163 179 A 2 TABLE 11 COMPARISON OF COEFFICIENTS OF THERMAL EXPANSIONS (X 10-61OC) 20-1000C 20-2000C 20-300'C LM 13Alloy 19.0 19.520.0 LM L3 + 20% Zirconia 14.0 16.0 17.7 GreyCastiron - 11.0 11.7 12.2 Austenitic Cast Iron 19.0 19.0 19.0 TABLE Ill COMPARISON OF DENSITIES (GIVIS/CC) LM13Alloy LM L3 + 20% Zirconia Fibres GreyCastiron Austenitic Cast Iron 2.70 3.42 7.2 7.6 - The effect of thezirconia contenton the coefficient of expansion of a material prepared as described above is given in Table IV. The percentage figures of zirconia are by volume.

TABLE W

EFFECT OF ZIRCONIA CONTENT ON COEFFICIENT OF THERMAL EXPANSION (X 10-6PC) 20-1000C 20-2000C 20-3000C LM13+10%Zirconia 16.7 16.7 17.7 LIVI13+20%Zirconia 14.0 16.0 17.7 LM 13 + 25% Zirconia 13.5 13.7 17.0 Referring nexttothe drawings, Figures 1, 2,3 and 4 showthe variation with temperature of, respectively, tensile strength, elongation, compression and hard ness forthree materials; the aluminium alloy used in Example 1,the aluminium alloyincluding 10% of zirconia fibres prepared as described above with referenceto Example 1 and the aluminium alloy including 20% of zirconia fibres prepared as de scribed abovewith referenceto Example 1.Tensile strength testswere performed on a specimen of diameter 0.178 inches gauge,with a length five times the diameter and after soaking the specimen for a 100 - hours atthetesttemperature. The elongation tests were performed on a similarspecimen and after similar heatsoaking. Thecompression tests showthe 80 0.1 % compression stress on a specimen 0.375 inches in diameter arid 0.375 inches long, aftersoaking the specimen atthe test temperature for 100 hours. The hardness testwasa Brine[] hardness test H132.40 on the ends of the specimens used forthetensile strength tests.

ltwill be seen from these tables and from the Figures that the thermal conductivity& a material prepared as described above in Example 1 is much lessthan thatof the aluminium alloy itself and approaches thethermal conductivity ofgrey cast iron and austenitic cast iron. From Table 11, it can be seen thatthe coefficient of thermal expansion of this material issimilarly reduced in comparison with that of the aluminium-alloy Itself and, once again, - approachestha values of this propertyfor grey cast iron and austenitic cast iron. The density of such a material is somewhat higherthan the density of the aluminium alloy itself but is still substantially less than that of grey cast iron and austenitic cast iron.

Table IVshowsthata reduction in the coefficientof thermal expansion of the material can be obtained by increasing the percentage of zirconia butthatthe effect is less marked asthetemperature range is 40"broadened.

Figure 1 shows that although thetensile strength of materials prepared as described above are less than the strength of the aW minium a] loy itself at temperatures below about 20WC, above such temperatures these materials show a significant increse in tensile strength. Figure 2 shows that materials prepared as described above have, above 20WC, very substantially reduced elongation in comparison with the aluminium alloVitself and that, indeed,the elongation of the material prepared as described above with 20% - by volume of zirconia remains substantially constant even attemperaturesof 6000Cand above. - Figure.3 shows thatthe compressIve strength of materials prepared as described above is substantial- lythe same as the compressive strength of the aluminium alloy itself attemperatures below 20WC butthat above such temperatures there is a substantial increase in compressive strength. Fina lly, Figure4 showsthatthe hardness of materials prepared as described above is substantially greaterthan that of the alloy attemperatures above-500'C. Indeed, both specimens prepared asdescribed above exhibitthe property of an increase in hardness above about 60WC, rightupto temperatures of 10OWC,in contrast with the melting of the aluminium alloy itself at about 540C. This property is particularly marked in the material prepared as described above and including 20% byvolume of zirconia.

Furthertests have indicated thatthe material prepared as described above and including 20% of zirconia may be able to withstand temperatures of 1350'Cto 1400'Cwithoutthe aluminium alloy melting out. Although the reasons forthis are notfully understood atthe presenttime,it is believed thatthis may be due to a solid state reaction between the aluminium a] loy and the zirconia fibres which appears to commence attemperatures of about 55WC to 600'C and may betime related. In this regard, reference-is made to Fig ures 5to 12 which are photo micrographs, ata magnification of 200,.of specimens of materials prepared as described above and including 20% byvolume of zirconia, attemperatures of 20', 2000,300% 4000,5000,5500C, 6000,750', and 95WC respectively. Initial indications arethatthe reaction leadsto the growth of alumina zirconate.

An alternative way of producing the material will now be described. EXAMPLE2:

An aluminium alloy in accordance with BS1 490:1970.LM 13, known as LM 12 is pre pared in a molten state at800'C. Azirconia powderist-hen stirred into the molten LM 13 aluminium alloy in a quantityto give a required volume proportion which may be between 5-and 50% by volu me but is preferably between 10 and 30% by volume, for example 20%. This produces a reaction between the zirconia and the aluminium alloywhich forms a pasty material which can be shaped by press forging.

The materials described above with references to

Claims

Examples 1 and 2 can have properties which can find many industrial uses. For example, they mayform blades for gas turbine engines or pistons for internal combustion engines. 5 CLAIMS

1. A composition of matter comprising aluminium oran aluminium alloy containing between 5% and 50% by volume of zirconia.

2. A composition according to claim 1, wherein the amount of zirconia is from 10% to 30% by volume, preferably 20% by volume.

Printed in the United Kingdom for Her Majesty's Stationery Office, 8818935, 2186 18996. Published at the Patent Office, 25 Southampton Buildings, London WC2A lAY, from which copies may be obtained.

2. A composition according to claim 1 or claim 2, wherein the zirconia is present in an amount from 10% to 30% by volume, preferably 20% by volume.

3. A composition according to claim 1 or claim 2, wherein the zirconia is incorporated into the aluminium or aluminium alloy in the form of fibres of zirconia.

4. A composition according to claim 3, wherein theraspect ratio of the fibres if from 50to 1000 and wherein the diameter of the fibres.is from 2 to 20 micrometers.

5. A composition according to claim 1 or claim 2, wherein the zirconia is incorporated into the aluminium or aluminium alloy in the farm of a powder.

6. A composition according to anyone of claims 1 to 5,wherein the aluminium or aluminium alloy is an aluminium alloy known as LM 13.

7. A composition according to anyone of claims 1 to 5, wherein the aluminium or aluminium alloy is an aluminium alloy known as Lo-Ex.

8. A composition according to anyone of claims 1 to 7, wherein the zirconia is partially stabilized by yttria andlor another rare earth element or calcium oxide or magnesium oxide.

9. A composition of matter substantially as hereinbefore described with reference to Example 1 and the accompanying drawings orto Example 2.

10. A method of manufacturing a composition of matteras claimed in anyone claims 1 to 9 and comprising preparing molten aluminium or an aluminium alloy and then incorporating thereinto zirconia in an amountof from 5% to 50% byvolume and then solidifying the matter so produced.

11. A method according to claim 10, wherein the zirconia is in the form of fibres, the method comprising preparing a wad or mat of the zirconia fibres and then infiltrating the wad or mat with molten aluminium or aluminium alloy.

12. A method according to claim 11, wherein the aluminium or aluminium alloy is infiltrated by a squeeze casting process.

13. A method according to claim 10, wherein the zirconia is in the form of a powder, the method comprising incorporating the zirconia powder into the molten aluminium or aluminium alloy.

14. A method according to claim 13, wherein the incorporation is at a temperature of 800T.

15. A method according to anyone of claims 10to 14 and further comprising heattreating the solidified matter.

16. A method of manufacturing a composition of matterasclaimed in anyone of claims 1 to 9 and substantially as hereinbefore described with referenceto Example 1 and the Figures orto Example 2.

New ortextually amended claims have been filed as follows:- GB 2 163 179 A 3 CLAIMS 1. A composition of matter comprising aluminium or an aluminium alloy into which has been incorporated between 5% and 50% byvolume of 70 zirconia.