GB2112021A

GB2112021A - Method of producing a powdered metal article having isotropic physical properties

Info

Publication number: GB2112021A
Application number: GB08227717A
Authority: GB
Inventors: Vladimir S Moxson
Original assignee: Imperial Clevite Inc
Current assignee: Clevite Industries Inc
Priority date: 1981-12-16
Filing date: 1982-09-29
Publication date: 1983-07-13
Also published as: KR840001868A; AU8886482A; FR2517998A1; BR8207309A; JPS58107402A; DE3242404A1

Abstract

A metallic article having essentially isotropic physical properties as made by powder rolling powdered metal particles to a degree sufficient to produce a self-supporting article having a green density which is at least 50 percent of its theoretical density; cold rerolling said self- supporting article without heating to a degree sufficient to cause said article to have a green density which is at least 90 percent of its theoretical density, with said cold rerolling being effect so as to reduce the thickness of said as originally rolled article a percentage equal to at least 90 percent of the initial theoretical reciprocal density (porosity); and sintering said rerolled article at a temperature sufficient to produce a homogeneous article which is characterized by having essentially isotropic physical properties. Litanium, titanium alloys, iron and iron alloys may be rolled.

Description

SPECIFICATION Method of forming a powdered metal article having isotropic physical properties BACKGROUND OF THE INVENTION The present invention relates to a means of forming a metallic article by novel powder metal techniques and to the article so-produced. More particularly, it concerns a method for producing a powder metal article having essentially isotropic physical properties by first powder rolling metal particles to produce a self-supporting structure which has a green density of at least 50 percent of theoretical, further cold rerolling such a soformed structure without further heating to a degree sufficient to produce a structure having a green density which is at least 90 percent of theoretical, and then sintering the resultant article.

Dense powdered metal strip and wrought strip are conventionally used for structural applications.

However, while such strip products are widely used, in some applications certain undesirable problems are encountered in that the physical properties of such strips are generaliy an isotropic.

Accordingly, it is the principal object of the present invention to provide a means for producing a powdered metal article which is characterized by having essentially isotropic physical properties.

Other object of the invention will become apparent to those skilled in the art from a reading of the following specification and claims.

SUMMARY OF THE INVENTION In one aspect, the present invention concerns a method of producing a metallic article having essentially isotropic physical properties from powdered metal particles which method comprises providing a plurality of powdered metal particles having the desired chemical composition; powder rolling a desired amount of said powdered metal particles to a degree sufficient to produce a self-supporting article having a green density which is at least 50 percent of its theoretical density; cold rerolling said self-supporting article without heating to a degree sufficient to cause said article to have a green density which is at least 90 percent of its theoretical density, with said cold rerolling being effected so as to reduce the thickness of said as originally rolled article a percentage equal to at least 90 percent of the initial theoretical reciprocal density (porosity); and sintering said rerolled article at a temperature sufficient to produce a homogeneous article which is characterized by having essentially isotropic physical properties.

In another aspect, the instant invention concerns a metallic article having essentially isotropic physical properties which is produced by a process which comprises providing a plurality of powdered metal particles having the desired chemical composition; powder rolling a desired amount of said powdered metal particles to a degree sufficient to produce a self-supporting article having a green density which is at least 50 percent of its theoretical density; cold rerolling said self-supporting article without additional heating to a degree sufficient to cause said article to have a green density which is at least 90 percent of its theoretical density, with said cold rerolling being effected so as to reduce the thickness of said as originally rolled article a percentage equal to at least 90 percent of the initial theoretical reciprocal density (porosity); and sintering said rerolled article at a temperature sufficient to produce a homogeneous article which is characterized by having essentially isotropic physical properties.

DESCRIPTION OF THE PREFERRED PRACTICE OF THE INVENTION The present invention concerns a unique method of producing powdered metal articles having essentially isotropic physical properties. In this regard, "essentially isotropic physical properties" is intended to mean that the resultant article is not textured, i.e., that a given physical property measured in the longitudinal direction is quite similar to the same physical property measured in the transverse direction.

In practice, various metal and metal alloy particles may be utilized either alone or in combination. The main requirement being that the powdered metal particles utilized are capable of being powder rolled to produce a self-supporting article having a green density which is at least 50 percent of its theoretical density, then cold rolled without additional heating to a green density which is at leat 90 percent of theoretical density (with the cold rerolling being effected so as to reduce the thickness of said as originally rolled article a percentage equal to at least 90 percent of the initial theoretical reciprocal density), and subsequently sintered at a temperature sufficient to produce a homogeneous article which is characterized by having essentially isotropic physical properties.

In the instant invention it is critical that the strip being processed be green rerolled to essentially the gauge at which it is to be used. That is, the gauge of the strip after green rerolling is the finished gauge of the strip with the exception of the possible employment of minor sizing operations or the like. This requirement is needed to provide the desired isotropic properties in the strip.

In the preferred practice of the invention the powder metal utilized is selected from the group consisting of titanium, titanium alloys (such as alloys of aluminum and vanadium), iron and iron alloys (such as alloys or iron and silicon).

The particle size of the powdered metal is not critical, except it must be such that it will render the powdered metal capable of being rolled and cold rerolled as described herein.

The apparatus utilized in the practice of the instant invention is not critical and for the sake of brevity will not be described in detail herein.

Likewise, the article produced by the subject invention can be sintered by any conventional means. Accordingly, sintering techniques used in the practice of the invention will not be discussed herein in great detail.

The following are examples of powder metal articles produced according to both the prior art and the technique of the present invention.

EXAMPLE 1 A titanium base powder mixture consisting of 90%-1 00% mesh titanium powder and 10%-80 mesh 60% aluminum40% vanadium V.S.M. master alloy was prepared by blending the foregoing powders together at room temperature in a conventional blending apparatus. The mixture obtained was then cold rolled using one pass directly to a 0.025" green strip. The density of green strip was approximately 6364% of theoretical. One portion of this graven strip was then heated for 4 hours at 1900OF while another portion was heated under similar conditions at 23000F. The density of the strip sintered at 1900OF was 7476% of theoretical.The density of the strip sintered at 23000F was 8384% of theoretical. Strip of this low density is typically not suited for structural applications.

EXAMPLE 2 The procedure for Example 1 was repeated, except the powder roiled strip was green rerolled to 100% green density. One portion of this green strip was then heated for 4 hours at 19000 F preferrably in vacuum while another portion was heated under similar conditions at 23000 F. The density of the strip sintered at 1 9000 F was over 90% of theoretical. The density of the strip sintered at 23000F was over 94% of theoretical.

Strips of this density can be used for some structural applications and exhibit isotropic microstructures.

EXAMPLE 3 In another instance, one hundred (100) parts 60% AI-40% Va of fine master alloy having a median particle size of 2-1 5 microns were mixed at room temperature with 900 parts of titanium powder having a particle size of -100 mesh. A conventional type of blender was employed. The mixture obtained was then rolled directly to 0.080" green strips in a single pass. This green strip was then heated for 4 hours at 23000F. The resulting sintered strip exhibited a green density which was 9698% of theoretical density.

However, it had an undesirable course micorstructure and poor ductility. As sintered strip was further densified by cold rerolling and resintering but the tensile ductility of the strip was not improved. Upon physical examination the strip was observed to have anisotropic microstructure.

EXAMPLE 4 The procedure of Example 3 was repeated yielding a green strip having a 0.025-0.027" thickness. This strip was cold rerolled to a thickness of 0.018-0.020" and then heated for 4 hours at 1850OF in vacuum. Surface cracks observed in as rolled strip were healed during green rerolling. The as sintered density was over 99% of theoretical and the microstucture was a highly desirable fine equiaxeal one. This is shown in the following table.

TABLE A Material of Elong. Reduction of Example 5 (%) Area (%) Average for specimens tested in transverse direction 8.6 1 5.4 Average for the same specimens tested in longitudinal direction 8.9 15.08 EXAMPLE 5 Example 4 was repeated with the addition of a further rolling after sintering to 0.016" thickness and a subsequent anneal for 2 hours at 1550OF.

This strip revealed a non-uniform tensile ductility in the transverse and longitudinal directions, as shown below.

TABLE B Longitudinal Direction Elong. Reduction of Sample l.D. (%) Area (%) Average for specimens tested in transverse direction 7.16 9.46 Average for the same specimens tested in longitudinal direction 4.4 5.2 The foregoing examples are intended to illustrate the benefits of the practice of the instant invention but are not intended to limit the reasonable scope thereof. As before noted, the instant invention is ideally suited for use in forming powdered metal sheet or strip material which exhibits isotropic physical properties from such metals and alloys as pure titanium, titaniumaluminum-vanadium alloys, iron and iron-silicon alloys.

An additional benefit derived from the practice of the subject invention is that it makes it possible to produce a dense, sintered powder metal article at lower than normal sintering temperatures. In this regard, via the practice of the instant invention it is possible to achieve a dense, sintered, homogeneous article or structure by sintering at a temperature which is approximately 70 percent or less of the melting point of the metal or major constituent of the alloy being processed.

Another advantage of this low temperature sintering is the fine microstructure which is produced which yields a better combination of the mechanical properties.

While there have been described what are at present considered to be the preferred embodiments of this invention, it will be obvious to those skilled in the art that various changes and modifications may be made therein without departing from the invention, and it is, therefore, intended in the appended claims to cover all such changes and modifications as fall within the true spirit and scope of the invention.

Claims

1. A method of prnduci'ng a metallic article having essentially isotropic physical properties from powdered metal particles which comprises: (a) providing a plurality of powdered metal particles having the desired chemical composition; (b) powder rolling a desired amount of said powdered metal particles to a degree sufficient to produce a self-supporting article having a green density which is at least 50 percent of its theoretical density; (c) cold rerolling said self-supporting article without heating to a degree sufficient to cause said article to have a green density which is at least 90 percent of theoretical density, with said cold rerolling being effected so as to reduce the thickness of said as originally rolled article a percentage equal to at least 90 percent of the initial theoretical reciprocal density (porosity); and (d) sintering said rerolled article at a temperature sufficient to produce a homogeneous article which is characterized by having essentially isotropic physical properties.

2. The method of claim 1 wherein said powdered metal particles are fashioned from at least one material selected from the group consisting of titanium, titanium alloys, iron and iron alloys.

3. The method of claim 1 wherein said powdered metal particles are fashioned from a mixture of titanium particles and aluminiumvanadium alloy particles.

4. The method of claim 2 wherein said iron alloy particles are fashioned from an alloy of iron and silicon.

5. The method of claim 1 wherein said sintering is effected at a temperature which is 70 percent or less than the melting point of the major component of said powdered metal particles.

6. A sintered powdered metal article having essentially isotropic physical properties produced by the process which comprises: (a) providing a plurality of powdered metal particles having the desired chemical composition; (b) powder rolling a desired amount of said powdered metal particles to a degree sufficient to produce a self-supporting article having a green density which is at least 50 percent of its theoretical density; (c) cold rerolling said self-supporting article without heating to a degree sufficient to cause said article to have a green density which is at least 90 percent of theoretical density, with said cold rerolling being effected so as to reduce the thickness of said as originally rolled article a percentage equal to at least 90 percent of the initial theoretical reciprocal density (porosity); and (d) sintering said rerolled article at a temperature sufficient to produce a homogeneous article which is characterized by having essentially isotropic physical properties.

7. The article of claim 6, wherein said powdered metal particles are fashioned from at least one material selected from the group consisting of titanium, titanium alloys, iron and iron alloys.

8. The article of claim 6 wherein said powdered metal particles are fashioned from a mixture of titanium particles and aluminium-vanadium alloy particles.

9. The article of claim 6 wherein said iron alloy particles are fashioned from an alloy of iron and silicon.

10. The article of claim 6 wherein said sintering is effected at a temperature which is 70 percent or less than the melting point of the major component of said powdered metal particles.