GB2182876A

GB2182876A - Alloy strip production

Info

Publication number: GB2182876A
Application number: GB08625716A
Authority: GB
Inventors: Dr Brian Cantor; Katherine Ianthe Moore
Original assignee: UK Atomic Energy Authority
Current assignee: UK Atomic Energy Authority
Priority date: 1985-11-14
Filing date: 1986-10-28
Publication date: 1987-05-28
Also published as: GB8625716D0

Abstract

Binary alloys in which the component elements do not exhibit complete mutual solubility in the liquid form (e.g. Al-Pb) are made into strip. A particular alloy is melted to a temperature where a single liquid phase only is present and rapidly solidified at a rate greater than 10<4> DEG K/s (e.g. 10<5> - 10<6> DEG K/s) to give the strip. For example, a jet of the molten liquid may be caused to impinge upon a cool moving surface (e.g. a rotating wheel) so that solidified alloy in the form of strip is ejected therefrom. The strip has a fine, uniform dispersion of one component of the alloy in the other which, in the case of Al-Pb, may make it useful as a bearing material. In an example, the particle size range quoted is 0.15nm to 8nm. Other binary alloys to which the invention may be applied are Cu-Pb and Cu-In.

Description

SPECIFICATION Alloy strip production This invention relates to the production of binary alloy strip by rapid solidification.

A number of binary alloy systems are known in whichthecomponentelementsdo notexhibitcom- plete mutual solubility in the liquid form. Thus, the composition against temperature phase diagram of such systems is 'dome' shaped, alloys at compositions and temperatures within the 'dome' consisting oftwo liquid phases. There is usually a con siderable difference in the specific gravities of the respective phases and, in such cases, separation into two liquid layers in the manner of oil and water occurs. Such systems also exhibit a monotectic changewherein,when cooled from a liquid composition and temperature within the 'dome', they reach the so-called 'monotectic temperature' and are transformed into a second liquid of a differentcomposition and a solid.

The above-described phenomena mean that such binary alloys (referred to as 'binary alloys of the kind described') cannot normally be melted and cast without occurrence of liquid segregation and nonuniform distribution inthefinal solid. Thus, commercially important binary alloys ofthe kind described (such as Al-Pb) have hitherto been made by complicated routes in order to achieve a fine, uniform dispersion of one phase (e.g. Pb) in the other phase (e.g. Al). For example, Al-Pb alloy stripfor use as an automotive engine bearing material has been made by inert gas atomising ofthealloyfollowed bydirect forming into strip (ex Imperial-Clevite), and it has additionally been proposed to carry out solidification in space to prevent gravity segregation.

J. Japan Inst. Metals, Vol 46, No.6(1982), pp., 645651 describes a way of overcoming the g ravity seg re- gation problem, namely by cooling single liquid phase Al-2 to 8 mass % Pb alloys at from 70to 1 000 K/s. This, however, is stated to give coarse particles of Pb, i.e. of size 1 Am (1000 nm) orgreater, which is not holly desirableforcertain applications ofthealloy.

The present invention relates to a simple route for preparing strip of binary alloys of the kind described having fine particles in uniform distribution. Th us, the invention provides a method of making strip of a binary alloy ofthe kind described by melting the alloy to a temperature where a single liquid phase only is present and rapidly solidifying the molten alloy at a rate greater than 1 040K/s under conditions to give strip of the alloy comprising a uniform dispersion offine particles.

The rapid solidification may be effected by methods known in the art,forexample by causing a jet ofthe molten alloy to impinge upon a cool mov ing surface sothatsolidified alloy in theform of strip is ejected therefrom. Preferably, the rapid solidification is carried out at a rate in the range of 1 050kits to 1 060K/s.

It should be noted that the molten alloy used in the invention is of such a composition and temperature that it is situated outside of the 'dome' in the above mentioned phase diagram, i.e. complete miscibility obtains. It appears that the cooling rate in the present invention is so rapid as to prevent gravity segregation and build up of large particles as the alloy passes through the region of the phase diagram within the dome.

Thus, it has been found that strip may be produced where one component of the alloy is in very fine dispersion in the other component. For example, strip of Al-Pb may be produced where the Pb is dispersed in the Al in a particle size oflessthan 100 nm. In specific cases said particle size is considerably less than 100 nm and may be less than 10 nm. Notall of the particles will necessarily be of substantially the same size as indicated in the example herein.

The presence of a fine, uniform dispersion of Pb in Al is very desirable when using the strip in a bearing where the Pb acts as a lubricating phase.

Other examples of binary alloys to which the invention is applicable are Cu-Pb and Cu-In. The composition ofthe alloys may be varied within wide limits in the practice of the invention subject, of course, to practical requirements and operating constraints.

The binary alloys used in the invention may contain incidental impurities and may contain small quantities of additional ingredients, for example as processing aids orto improve properties in some respect.

One way of carrying outthe invention will now be described by way of example only.

Example A mixture of Al and Pb in the proportions by weight of 95 % Al and 5 % Pb was induction melted in an argon atm osphere to give an Al-5Pb alloy.

The resulting alloy in solid form was placed in a quartz nozzle (1 mm diameter) suitable for melt spinning.Thealloywas melted a temperature of about 1 0000C (measured by an optical pyrometer) using an induction coil.

The molten alloy was forced out of the knozzle by means of a blast of argon and onto a rotating copper wheel (Sin diameter) at ambient temperature. The molten alloy was thereby cooled at a rate of 105 105- 105 K/sto give a continuoustapewhichwasflung from the rotating wheel as it was formed.

The tape, which had a thickness of 40 to 80 lim, was examined by transmission electron microscopy and found to have a uniform distribution of Pb particies in an Al matrix. The majority of the particles were of the same size though there were some smallerparticles and some larger; thesize rangewas from 0.15 nmto8 nm.

1. A method of making strip of a binary alloy of the kind described by melting the alloy to a temperature where a single liquid phase only is present and rapidly solidifying the molten alloy at a rate gma- terthan 1 040K/s under conditions to give strip ofthto alloy comprising a uniform dispersion offine particles.

2. A method according to claim 1 wherein the

**WARNING** end of DESC field may overlap start of CLMS **.

Claims

**WARNING** start of CLMS field may overlap end of DESC **. SPECIFICATION Alloy strip production This invention relates to the production of binary alloy strip by rapid solidification. A number of binary alloy systems are known in whichthecomponentelementsdo notexhibitcom- plete mutual solubility in the liquid form. Thus, the composition against temperature phase diagram of such systems is 'dome' shaped, alloys at compositions and temperatures within the 'dome' consisting oftwo liquid phases. There is usually a con siderable difference in the specific gravities of the respective phases and, in such cases, separation into two liquid layers in the manner of oil and water occurs. Such systems also exhibit a monotectic changewherein,when cooled from a liquid composition and temperature within the 'dome', they reach the so-called 'monotectic temperature' and are transformed into a second liquid of a differentcomposition and a solid. The above-described phenomena mean that such binary alloys (referred to as 'binary alloys of the kind described') cannot normally be melted and cast without occurrence of liquid segregation and nonuniform distribution inthefinal solid. Thus, commercially important binary alloys ofthe kind described (such as Al-Pb) have hitherto been made by complicated routes in order to achieve a fine, uniform dispersion of one phase (e.g. Pb) in the other phase (e.g. Al). For example, Al-Pb alloy stripfor use as an automotive engine bearing material has been made by inert gas atomising ofthealloyfollowed bydirect forming into strip (ex Imperial-Clevite), and it has additionally been proposed to carry out solidification in space to prevent gravity segregation. J. Japan Inst. Metals, Vol 46, No.6(1982), pp., 645651 describes a way of overcoming the g ravity seg re- gation problem, namely by cooling single liquid phase Al-2 to 8 mass % Pb alloys at from 70to 1 000 K/s. This, however, is stated to give coarse particles of Pb, i.e. of size 1 Am (1000 nm) orgreater, which is not holly desirableforcertain applications ofthealloy. The present invention relates to a simple route for preparing strip of binary alloys of the kind described having fine particles in uniform distribution. Th us, the invention provides a method of making strip of a binary alloy ofthe kind described by melting the alloy to a temperature where a single liquid phase only is present and rapidly solidifying the molten alloy at a rate greater than 1 040K/s under conditions to give strip of the alloy comprising a uniform dispersion offine particles. The rapid solidification may be effected by methods known in the art,forexample by causing a jet ofthe molten alloy to impinge upon a cool mov ing surface sothatsolidified alloy in theform of strip is ejected therefrom. Preferably, the rapid solidification is carried out at a rate in the range of 1 050kits to 1 060K/s. It should be noted that the molten alloy used in the invention is of such a composition and temperature that it is situated outside of the 'dome' in the above mentioned phase diagram, i.e. complete miscibility obtains. It appears that the cooling rate in the present invention is so rapid as to prevent gravity segregation and build up of large particles as the alloy passes through the region of the phase diagram within the dome. Thus, it has been found that strip may be produced where one component of the alloy is in very fine dispersion in the other component. For example, strip of Al-Pb may be produced where the Pb is dispersed in the Al in a particle size oflessthan 100 nm. In specific cases said particle size is considerably less than 100 nm and may be less than 10 nm. Notall of the particles will necessarily be of substantially the same size as indicated in the example herein. The presence of a fine, uniform dispersion of Pb in Al is very desirable when using the strip in a bearing where the Pb acts as a lubricating phase. Other examples of binary alloys to which the invention is applicable are Cu-Pb and Cu-In. The composition ofthe alloys may be varied within wide limits in the practice of the invention subject, of course, to practical requirements and operating constraints. The binary alloys used in the invention may contain incidental impurities and may contain small quantities of additional ingredients, for example as processing aids orto improve properties in some respect. One way of carrying outthe invention will now be described by way of example only. Example A mixture of Al and Pb in the proportions by weight of 95 % Al and 5 % Pb was induction melted in an argon atm osphere to give an Al-5Pb alloy. The resulting alloy in solid form was placed in a quartz nozzle (1 mm diameter) suitable for melt spinning.Thealloywas melted a temperature of about 1 0000C (measured by an optical pyrometer) using an induction coil. The molten alloy was forced out of the knozzle by means of a blast of argon and onto a rotating copper wheel (Sin diameter) at ambient temperature. The molten alloy was thereby cooled at a rate of 105 105- 105 K/sto give a continuoustapewhichwasflung from the rotating wheel as it was formed. The tape, which had a thickness of 40 to 80 lim, was examined by transmission electron microscopy and found to have a uniform distribution of Pb particies in an Al matrix. The majority of the particles were of the same size though there were some smallerparticles and some larger; thesize rangewas from 0.15 nmto8 nm. CLAIMS

2. A method according to claim 1 wherein the molten alloy is rapidly solidified at a rate in the range of 1050KIsto 1060K/s.

3. Amethod according to claim 1 orclaim2 wherein the molten alloy is rapidly solidified by causing a jetthereofto impinge upon a cool moving surface so that solidified alloy in the form of strip is ejected therefrom.

4. A method according to any of the preceding claims wherein the alloy is a AI-Pb alloy and the strip produced comprises a uniform dispersion offine particles of Pb in Al.

5. Amethod of making strip su bstantial Iy as des- cribed herein with reference to the example.