GB1567850A

GB1567850A - Method for the manufacture of nickel or an alloy thereof

Info

Publication number: GB1567850A
Application number: GB30862/77A
Authority: GB
Original assignee: Commissariat a lEnergie Atomique CEA
Current assignee: Commissariat a lEnergie Atomique et aux Energies Alternatives CEA
Priority date: 1976-07-29
Filing date: 1977-07-22
Publication date: 1980-05-21
Also published as: DE2733277A1; FR2359665A1; FR2359665B1; JPS5352213A; SE7708663L

Description

(54) A METHOD FOR THE MANUFACTURE OF NICKEL OR AN ALLOY THEREOF (71) We, COMMISSARIAT A UNERGIE ATOMIQUE, a French company and state organisation, of 29, rue de la Federation, 75752, Paris Cedex 15, France, do hereby declare the invention, for which we pray that a patent may be granted to us, and the method by which it is to be performed, to be particularly described in and by the following statement: This invention relates to a method for manufacturing parts of nickel or nickel alloy by powder metallurgy and more precisely to a method for manufacturing nickel-base parts having good mechanical properties, especially under conditions of slow fatigue, this being achieved by obtaining a particular structure of the metal or alloy which constitutes said part.

This particular structure will be designated in the remainder of the description by the term "necklace structure": this corresponds to a heterogeneous structure of the material which constitutes the part and is essentially distinguished by the presence of large grains which are surrounded and bonded together by finely crystallized grains of smaller size.

This "necklace structure" is already known and has the reputation of endowing nickel or nickel alloy parts with good mechanical properties and especially very high resistance to oligocyclic fatigue between 550 and 650"C. In consequence, the development of processes for obtaining this structure has proved to be highly advantageous in many fields, especially for the fabrication of compressor discs.

Up to the present time, parts having the above-mentioned "necklace structure" have been obtained by subjecting billets formed of consolidated powders to thermomechanical treatments such as forging and then by shaping the powder which has thus been treated in order to obtain the part in the final form which exhibits this structure. These operations entail the need for costly and powerful devices such as isostatic presses or extrusion presses and this imposes a substantial increase in the cost of parts obtained.

This invention is precisely directed to a less costly method for manufacturing parts of nickel or of nickel alloy having the desired shape and the "necklace" structure by means of powder metallurgy techniques such as hot extrusion or sintering under pressure.

To this end, the method under consideration essentially consists in depositing a layer of a compound selected from the group comprising Ni3P and Ni3As on a powder of nickel or nickel alloy having a particle diameter of at least 100 u and in subjecting the powder which has thus been coated to sintering at a temperature within the range of 1100 to 1300"C under a pressure of at least 50 bar but preferably within the range of 150 to 1000 bar and during a maximum period of one hour which is preferably within the range of 10 minutes to one hour. The part thus obtained is then subjected to controlled cooling.

In accordance with the invention, the Ni3P or the Ni3As are preferably deposited in such a manner as to obtain a powder containing a proportion of 100 to 500 ppm of Ni3P or Ni3As.

The method as characterized in the foregoing primarily offers the advantage of ensuring the formation of the "necklace structure" aforesaid by sintering the powder under suitable conditions, with the result that no complementary operation is required for the fabrication of the part in its final form. The part can thus be obtained directly at the time of sintering by means of conventional and less costly devices.

In the practical application of this method, the dimension of the powder grains and the conditions of temperature, pressure and time-duration adopted for the sintering operation are very important parameters since they determine the formation of the "necklace structure".

In regard to the size of the powder grains, it is essential to ensure that these latter have a diameter of at least 100 CL and preferably within the range of 100 to 1000 tL It is also an advantage to ensure that the powder grains are of substantially uniform size.

In the case of the sintering operation, the time-duration, the temperature and the pressure applied at the time of sintering are chosen from the ranges indicated in the foregoing, these values being adjusted with respect to each other and as a function of the size of the powder grains. The result thereby achieved is that the liquid phase formed at the sintering temperature by the Ni3P or the Ni3As which is initially deposited on the surface of the powder is prevented from diffusing to any appreciable extent within the mass of the powder grains during the sintering operation. The choice of these parameters thus makes it possible to localize the diffusion of Ni3P or of Ni3As along the periphery of the powder grains and to prevent this liquid phase from reaching the center of the grains which accordingly remains intact during the sintering operation.

After sintering, a structure corresponding to the "necklace structure" is obtained since the center of each initial unconverted powder grain is surrounded by a border of finely crystallized grains obtained during the sintering process.

In order to carry out said sintering process it is also an advantage to ensure that heating of the powder to the sintering temperature takes place as rapidly as possible, especially within the temperature range comprised between 880"C and the sintering temperature, namely from the time of appearance of the liquid phase formed by Ni3P or Ni3As in order to prevent substantial diffusion of said liquid phase while heating is in progress.

The powder is preferably heated in such a manner as to ensure that the temperature of this latter increases by 1000"C per hour, at least within the temperature range comprised between 880"C and the sintering temperature.

In an alternative embodiment of the method according to the invention, the part which exhibits said "necklace structure" is obtained by hot extrusion of a nickel or nickel alloy powder having a particle diameter of at least 100 ,u, said powder being coated with a layer of a compound chosen from the group comprising Ni3P and Ni3As.

A more complete understanding of the invention will be obtained from the following examples which are given without any limitation being implied, reference being made to the accompanying drawing which illustrates the "necklace structure" of a part obtained by means of the method according to the invention.

These examples relate to the fabrication of parts of nickel superalloy marketed by the Inco Company under the trade mark IN100.

Example 1 This alloy is in the form of a powder having a mean grain size within the range of 100 to 300 ,u.

In the method according to the invention, a thin layer of Ni3P is deposited on the nickel powder by chemical process in order to obtain a nickel powder which contains 300 ppm of Ni3P. This deposit is obtained in a conventional manner by immersing the nickel superalloy powder with continuous agitation in an aqueous bath containing nickel chloride (NiCl2 . 6H20) sodium acetate, sodium hypophosphite (reducing agent) and hypophosphorous acid.

The deposition of Ni3P is performed at a temperature within the range of 30"C to 50"C while maintaining the bath at a pH value of 6 by adding sodium hypophosphite when the pH of the bath decreases to a value of 4.

The powder which has just been coated is then introduced into a furnace for sintering under pressure and in vacuo.

With a view to carrying out the sintering operation, the powder is heated in order to attain the sintering temperature of 1200"C as rapidly as possible, whereupon the sintering operation is carried out at this temperature under a pressure of 300 bar for a period of 10 minutes. The mechanical properties of the part obtained are as follows: -the elastic limit at 0.2% is 90 hectobar, -the load at fracture is 135 hectobar, -the elongation at fracture is 16 to 20%total.

Example 2 The nickel alloy is in the form of a powder in which the mean particle size is within the range of 100 to 300 ,a. As in Example 1, a layer of Ni3P is deposited on said alloy powder by chemical process in order to obtain a proportion of Ni3P of the order of 300 ppm.

Sintering of the coated powder is then carried out under a pressure of 600 bar at a temperature of 1200"C for a period of 10 minutes.

As in Example 1, the powder is heated in order to attain the sintering temperature as rapidly as possible.

Example 3 The alloy is in the form of a powder having a mean particle size of 300 to 600 ,u. A thin layer of Ni3P is deposited on the alloy powder by chemical process as in Example 1 in order to obtain a proportion of 300 ppm of Ni3P. The powder is then sintered in a furnace for sintering under pressure and in vacuo at a temperature of 1210 C, under a pressure of 350 bar and for a period of 10 minutes Example 4 The starting material consists of an alloy powder having a mean particle size within the range of 100 to 300 . A thin layer of Ni3P is deposited on the powder by chemical process as in Example 1 in order to obtain a proportion of 300 ppm of Ni3P and the powder which has thus been coated is sintered in a furnace for sintering under pressure and in vacuo at a temperature of 12200C, under a pressure of 150 bar and for a period of 10 minutes.

Example material or 5 The starting material consists of a nickel alloy powder having a mean particle size within the range of 100 to 300 . A thin layer of Ni3P is deposited on the nickel alloy powder by chemical process as in Example 1 in order to obtain a proportion of 400 ppm of Ni3P. The coated powder is then sintered in a furnace for sintering under pressure and in vacuo at a temperature of 1210 C, under a pressure of 350 bar and for a period of 10 minutes.

The parts obtained in Examples 1 to 5 have a "necklace structure" which is similar to that shown in the single accompanying figure, in which there are shown large grains of nickel alloy surrounded by finely crystallized grains.

Example material or 6 The starting material consists of a nickel alloy powder having a mean particle size within the range of 100 to 300 . A thin layer of Ni3P is deposited on the powder by chemical process as in Example 1 in order to obtain a proportion of 300 ppm of Ni3P. This powder is introduced into a mild steel container which is closed in vacuo and for subsequent hot extrusion under a pressure of 100 kg/mm2. The container is previously heated to 800"C for 45 minutes, then to 10000C for 15 minutes and then introduced into an extrusion press in which the cross-section ratio is 4, the extrusion die being preheated to a temperature of 300"C. The part thus obtained exhibits a "necklace structure".

It should simply be noted that the use of a hot extrusion technique results in a structure in which the large nickel grains surrounded by a border of finely crystallized grains have a slightly elongated shape.

It can thus be noted that the method in accordance with the invention makes it possible to obtain parts which are endowed with good mechanical properties, which exhibit the "necklace structure", and which contain between 100 and 500 ppm of phosphorus.

WHAT WE CLAIM IS: 1. A method for manufacturing parts of nickel or nickel alloy having a "necklace structure" as hereinbefore defined, wherein said method consists in depositing a layer of a compound having the formula Ni3P or Ni3As on a powder of nickel or nickel alloy having a particle diameter of at least 100 CL and in subjecting the powder which has just been coated to sintering at a temperature within the range of 1100 to 13000C under a pressure of at least 50 bar during a maximum period of one hour.

2. A method according to claim 1, wherein the powder of nickel or nickel alloy has a particle diameter within the range of 100 to 1000 ,u.

3. A method according to claim 1, or claim 2 wherein a layer of Ni3P or of Ni3As is deposited on said nickel or nickel alloy powder in such a manner as to obtain a powder containing a proportion of 100 to 500 ppm of Ni3P or Ni3As.

4. A method according to any one of claims 1 to 3, wherein the time-duration of said sintering operation is within the range of 10 minutes to one hour.

5. A method according to any one of claims 1 to 4, wherein the pressure is within the range of 150 to 1000 bar.

6. A method according to claim 1, wherein heating of said powder is carried out for the purpose of sintering in order to attain said sintering temperature as rapidly as possible.

7. A method according to claim 6, wherein said heating is carried out in such a manner as to increase the temperature of said powder by approximately 1000"C per hour, at least between 880"C and said sintering temperature.

8. A method for manufacturing parts of nickel or nickel alloy having a "necklace structure", as herein before defined, wherein said method consists in depositing a layer of a compound of the formula Ni3P or Ni3As on a nickel or nickel alloy powder having a particle diameter of at least 100 ji and subjecting the coated powder to hot extrusion.

9. A method according to claim 1 for manufacturing parts of nickel or nickel alloy having a "necklace structure", substantially as herein before described with reference to the examples.

10. A nickel of nickel alloy part whenever made by a method as claimed in any of the preceding claims.

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Claims

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

powder having a mean particle size within the range of 100 to 300 . A thin layer of Ni3P is deposited on the powder by chemical process as in Example 1 in order to obtain a proportion of 300 ppm of Ni3P and the powder which has thus been coated is sintered in a furnace for sintering under pressure and in vacuo at a temperature of 12200C, under a pressure of 150 bar and for a period of 10 minutes.

Example material or 5 The starting material consists of a nickel alloy powder having a mean particle size within the range of 100 to 300 . A thin layer of Ni3P is deposited on the nickel alloy powder by chemical process as in Example 1 in order to obtain a proportion of 400 ppm of Ni3P. The coated powder is then sintered in a furnace for sintering under pressure and in vacuo at a temperature of 1210 C, under a pressure of 350 bar and for a period of 10 minutes.

The parts obtained in Examples 1 to 5 have a "necklace structure" which is similar to that shown in the single accompanying figure, in which there are shown large grains of nickel alloy surrounded by finely crystallized grains.

Example material or 6 The starting material consists of a nickel alloy powder having a mean particle size within the range of 100 to 300 . A thin layer of Ni3P is deposited on the powder by chemical process as in Example 1 in order to obtain a proportion of 300 ppm of Ni3P. This powder is introduced into a mild steel container which is closed in vacuo and for subsequent hot extrusion under a pressure of 100 kg/mm2. The container is previously heated to 800"C for 45 minutes, then to 10000C for

15 minutes and then introduced into an extrusion press in which the cross-section ratio is 4, the extrusion die being preheated to a temperature of 300"C. The part thus obtained exhibits a "necklace structure".

It should simply be noted that the use of a hot extrusion technique results in a structure in which the large nickel grains surrounded by a border of finely crystallized grains have a slightly elongated shape.

It can thus be noted that the method in accordance with the invention makes it possible to obtain parts which are endowed with good mechanical properties, which exhibit the "necklace structure", and which contain between 100 and 500 ppm of phosphorus.

WHAT WE CLAIM IS: 1. A method for manufacturing parts of nickel or nickel alloy having a "necklace structure" as hereinbefore defined, wherein said method consists in depositing a layer of a compound having the formula Ni3P or Ni3As on a powder of nickel or nickel alloy having a particle diameter of at least 100 CL and in subjecting the powder which has just been coated to sintering at a temperature within the range of 1100 to 13000C under a pressure of at least 50 bar during a maximum period of one hour.
2. A method according to claim 1, wherein the powder of nickel or nickel alloy has a particle diameter within the range of 100 to 1000 ,u.
3. A method according to claim 1, or claim 2 wherein a layer of Ni3P or of Ni3As is deposited on said nickel or nickel alloy powder in such a manner as to obtain a powder containing a proportion of 100 to 500 ppm of Ni3P or Ni3As.
4. A method according to any one of claims 1 to 3, wherein the time-duration of said sintering operation is within the range of 10 minutes to one hour.
5. A method according to any one of claims 1 to 4, wherein the pressure is within the range of 150 to 1000 bar.
6. A method according to claim 1, wherein heating of said powder is carried out for the purpose of sintering in order to attain said sintering temperature as rapidly as possible.
7. A method according to claim 6, wherein said heating is carried out in such a manner as to increase the temperature of said powder by approximately 1000"C per hour, at least between 880"C and said sintering temperature.
8. A method for manufacturing parts of nickel or nickel alloy having a "necklace structure", as herein before defined, wherein said method consists in depositing a layer of a compound of the formula Ni3P or Ni3As on a nickel or nickel alloy powder having a particle diameter of at least 100 ji and subjecting the coated powder to hot extrusion.
9. A method according to claim 1 for manufacturing parts of nickel or nickel alloy having a "necklace structure", substantially as herein before described with reference to the examples.
10. A nickel of nickel alloy part whenever made by a method as claimed in any of the preceding claims.