DE2362650A1 - PROCESS FOR THE POWDER METALLURGICAL PRODUCTION OF PARTS FROM A WEDGE ALLOY - Google Patents

Description

International Nickel Limited, Thames House, Millbank, London . S. ¥. 1, UK

"Process for the powder metallurgy manufacture of parts

made of a wrought alloy "

The known superalloys must be used as a material for heat-resistant parts, such as gas turbine parts, have a high creep resistance and creep strength. This in turn requires a high level of hardness with a correspondingly high level of hardness poor hot formability, so that superalloys are often not hot worked and only used as a cast material can be «,

In order to overcome the aforementioned difficulties, it is known in the manufacture of superalloys from one to one powder produced by spraying. This leads to a certain improvement in the hot formability, However, this is at the expense of the very fine and homogeneous microstructure. The powder can optionally be mixed by hot molding, for example by hot isostatic pressing subsequent hot forming to produce kneaded products ,, A further improvement resulted from a combined mechanical and thermal treatment of the compact; this

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however, requires compliance with very strict procedural conditions in advance.

The lack of deformability of the superalloys is particularly evident when making large parts such as Turbine disks up to 1.5 in diameter are now a major disadvantage. The invention is therefore the object based on creating a method for producing a superalloy with sufficient hot formability. The solution to this problem is based on the finding that the deformability of pre-alloyed atomizing powder can be improved by deforming the powder particles, in which internal stresses are imparted to the powder particles.

If the powder particles have internal stresses before pressing, their hot deformability increases or becomes Deformation resistance at the temperature of hot working decreased. The better hot deformability allows the powder to be hot-pressed at lower temperatures and / or pressures, to produce larger parts for a given capacity and to achieve high dimensional accuracy, with the good Deformability is also retained in subsequent processes.

It is known that the hardness of an alloy decreases with increasing temperature. In the case of pre-alloyed powders, it is common to to measure the hardness of the pressed body after pressing to at least 99 # of the theoretical density «

The diagram in the drawing shows the change in Hardness as a function of temperature. Thereby refers

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curve A to an atomized powder, its particles according to the invention have internal stresses, and the. Curve B on an atomized powder with no internal stresses the powder particles. ' The curve shows that despite the higher hardness of the powder from the particles with inner Stress at room temperature or during the deformation of the powder particles the hardness with increasing temperature decreases more rapidly than in the case of powder B, the hardness of which decreases much more slowly from the point of intersection H on. A measure of the improvement in hot deformability due to the internal stresses of the powder particles results from the equation

T / TM) _{i / 2}

¹ O '

where ^ T is the result of the diagram in the drawing Temperature difference between the two curves at 1/2 H_ and TM corresponds to the absolute melting temperature.

If the internal stresses mentioned do not lead to an increase in hardness, because a hardening phase is also destroyed at the same time, then the value H _Q must be replaced by the hardness of the two reference powders at room temperature.

The internal tension of the powder particles should be adjusted in such a way that the result is a hot deformability of at least 1%, preferably of at least 2% or, even better, of at least 5%. In individual cases, the level of internal stress required depends on the nature of the powder.

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The internal stresses can affect the particles of an atomized powder by dry high-energy grinding according to that in the German Offenlegungsschrift 1 909 781 procedure described. This process consists in making an alloy by grinding of powders of the alloy components, in which the powder particles are repeatedly welded together and crushed again until the powder reaches its saturation hardness. In the context of the invention Process, the dry high-energy grinding is only used to the particles of a pre-alloyed To give atomizing powder the necessary internal stresses without reaching the saturation hardness must or should be. With high-energy grinding, the grinding tools, for example grinding balls, should be made of Steel, nickel or tungsten carbide, can be kept kinetically in a state of strong relative movement in which at least 50 to 7556 of the Ball are in a non-contact state. In this way, the acceleration forces ensure a repeated Collision of bullets. Spex and agitating arm mills such as Szegvari mills are suitable for high-energy milling Vibratory and planetary ball mills. Conventional ball mills, on the other hand, require even if they have the necessary Ability to apply energy, generally too long a grinding time.

What is of decisive importance is not the type of mill, but the internal tension imparted to the powder particles. A Szegvari ball mill with hardened 8 mm balls from the steel AISI E 52 100 is preferably with a

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10% methane containing argon atmosphere taking into account the conditions resulting from the following table I operated, of course Other grinding atmospheres, such as nitrogen and nitrogen / oxygen atmospheres, are also suitable.

Table I.

Capacity diameter impeller ball / powder grinding time capacity this swift volume

speed ratio

(1) (m) (rpm) (h)

3. 8th 2.74 300-400 5 - 50: 1 1 - 10 15th 2 3.96 200-300 It 1 - 10 37. 9 4.88 125-200 tf 1 - 10 379 10.97 50-150 It 1 - 10

The particle size of the powder can be very different and be up to at least 1000 i # n, although the Particle size under the aforementioned process conditions is initially preferably 20 to 350 Zi ^ m.

The invention is explained in more detail below on the basis of exemplary embodiments:

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example 1

An atomized powder made from the alloy IN-1OO with 15% cobalt, 10% chromium, 5.5% aluminum, 4.75% titanium, 3% molybdenum, 0.02% carbon, 0.15% boron and 0.06% zirconium The remainder of nickel and a particle size below 43 / ^ / m was ground for ten hours in a 3.8 l stirring arm ball mill in flowing nitrogen at an impeller speed of 350 rpm. The mill contained 16.8 kg of hardened balls made of AISI E 52 100 steel with a diameter of 8 mm; the spheres / powder volume ratio was 17: 1.

Aliquots of the powder were placed in soft steel cans both before and after milling. After evacuation, the cans with the powder were ^{heated to 316 °} C. in a vacuum and sealed pressure-tight. The cans were then each heated to 1038 ° C., compressed against an anvil in an extruder and cooled under vermiculite. After the bushings had been removed, the hardness of the pressed bodies was determined at different temperatures, the values shown in Table II below resulting.

Table II

Test temperature press body hardness (R- _A )

( ⁰ C) unground ground

RT 74.5 78.5

538 73.2 76.2

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Table II continued

649 760 871 982

72.4 74.1 71.0 69o8 63 ο 2 14.4 37.2 too low

The data in Table II clearly show the remarkable decrease in hardness of the ground powder at temperatures from 760 ⁰ C as a result of internal stresses of the powder. At 871 ⁰ C the hardness is already below the very low value of 14.4 R ^ and at 982 ° C it is already lower than the Rockwell A scale. In contrast, the non-ground powder still has a hardness of 37.2 _RA and at 982 ⁰ C.

The hot deformability was found to be 6% in the manner described above.

Example 2

Another batch of the atomizing powder according to Example 1

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was ground, with partial amounts removed before and after the grinding and hot-pressed in the manner mentioned at 1066 C. became. Samples of the pressed bodies were examined at 982 ° C and an elongation of 0.0025 to 0.625 per minute « This resulted in a flow resistance of 33.6 to 77 N / mm for the samples from the ground powder, an elongation at break of 144% and a necking of 99%. In contrast, the samples made from the unground powder had a flow resistance of 59.8 to 110 N / mm, an elongation of 10% and a necking of 4.5%. Further samples were annealed for four hours at 1149 ° C, quenched in oil, Annealed for twenty-four hours at 649 ° C, cooled in air, cured for eight hours at 760 ° C and cooled again in air and at 732 C under a load of 690 N / mm. This resulted for the sample from the ground Powder a standing time of 22.5 hours and for the sample made from the unground powder a standing time of only two Hours.

Example 3

Two further batches of the aforementioned atomizing powder with a particle size of 43 to 246μ / πι were five and fifty hours in an airtight 14 cm ball mill at a speed of 80 rpm in the presence of fully hardened 9.5 mm balls made of the steel AISI E ^ 2. 100 milled at a volume ratio of balls / powder of 10: 1. Furthermore, two powder batches with a particle size below 43 / ^ - m were ground for one or three hours in a ball mill according to Example 1,

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_ 9 -

Each of the four batches was related to the; Example 2 described manner hot-pressed and examined, the audible from the following Table III apparent data. The data in Table III also includes the test results of the unground Powder and the powder milled for ten hours according to Table I, as well as hardness values from the literature for a customary IN-100 cast alloy.

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Table III

O CD OO

ver Rockwell hardness 50 h 1 h ^R A 10 H Cast condition 74.5 Ball mill 75.8 76.4 Agitator mill 78. 5 73.2 5 h 73.8 74.4 3 h 76. 2 69.5 72.4 74.8 73.2 74.1 77.2 74. 1 68.2 Temperature output coil 71.0 73.9 71.5 70.0 76.0 69. 8th 68.2 door
( ⁰ C) 63.2 73.8 55.7 47.2 74.0 14th 4th 67.8 R.T. 37.2 71.3 • X- 69 "4 # · 65.0 593 Hot deformability.it (%) 61.7 3.5 4.3 33.0 6th 58.5 649 27.4 ■ * 760 1.2 5.7 871 982

* Too small for the measurement

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The data of Table III show that only one hour grinding the powder in a paddle-ball mill performs as a five-hour dry ball-milling, "The deformability is still slightly better to significantly improved ductility at temperatures above 760 ⁰ C than that of a fifty hours of ball-milled powder. This improvement in deformability is a result of the internal stresses in the powder particles. In contrast, the hardness of the cast alloy remains practically unchanged over the entire temperature range.

The differences in flow resistance and ductility between the ground and the unground powder according to the example 2 are at least partly due to the much finer particles or the dislocation structure of the particles with internal Tensions attributed. The deformation of the powder particles during grinding also leads to a finely dispersed one Distribution of the brittle phases. On the other hand, difficulties arise when pressing an untreated atomizing powder because of the surface phases of the powder particles «,

Press bodies made from atomized powders ground according to the invention also have a completely different structure than untreated ones Powder, especially if it is a powder made from superalloys that always contain carbon. in the In the untreated state, there are usually relatively large carbides with a size of over 1 ^ m, which are more incoherent Structural component whose atomic structure has no relation to the basic structure surrounding it. For pressed bodies from On the other hand, powders treated by the process according to the invention are mostly in the form of finely dispersed carbides

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semi-coherent particles before »This difference in the carbide structure is due to the strong deformation of the powder particles during grinding, which leads to a comminution and redistribution of the carbides. At the next When heated to the hot-pressing temperature, the fine carbides dissolve and separate at temperatures again, in which the atomic mobility is relatively low and the chemical potential is high. This leads to the formation of a very fine, coherent carbide precipitate structure. The particles of an untreated In contrast, atomized powders contain uncomminuted carbides, which are relatively stable and theirs Maintain compact size.

At the higher temperatures of hot pressing takes place a certain loosening of the compact carbides takes place. However, the higher temperatures also increase the atomic temperature at the same time Mobility, so that the dissolved carbides are renewed when they cool down at the grain boundaries or other surfaces deposit.

The increase in the hot deformability of an atomized powder according to the method according to the invention allows it to be used the most diverse processes for molding or pressing. This includes press forging, vacuum hot pressing, forging, rolling, isostatic hot pressing at lower Temperatures than usual as well as hot extrusion. In this way, small turbine disks in the closed die with tool punches are press-forged, resulting in completely pore-free discs, which are immediately .heat treated and machined. At the start

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In the case of large turbine disks, a preform is cross-rolled or almost up to in a closed die Press-forged to the final shape and size. The low loss of material is of particular advantage of expensive superalloys with minimal machining. Of course, that has to be shaping and deforming take place at temperatures above the temperature of H.

The inventive method can be with the most varied pre-alloyed powders, especially from superalloys and other difficult to deform Perform alloys, These include nickel superalloys with up to 60%, for example 1 to 25 $ chromium, up to 30Ji, for example 5 to 25% cobalt, up to 10%, for example 1 to 9% aluminum, up to 8%, for example 1 to 7% titanium, individually or next to one another, and in particular with at least 4 or 5% aluminum and titanium, up to 30%, for example 1 to 8% molybdenum, up to 25%, for example 2 to 20% tungsten, up to 10% niobium, up to 10% tantalum, up to 7% zirconium, up to 0.5% boron, up to 5% hafnium, up to 2% vanadium, up to 6% copper, up to 5% manganese, up to 70% Iron and up to 4% silicon. Cobalt superalloys are also suitable and the alloys IN-738, IN-792, Rene and 95, the alloy 718, Waspaloy, Astroloy, the Mar-M alloys 200 and 246 ', alloys 713, 500, 700 and A-286. Finally, titanium alloys also come as well Refractory alloys SU-16, TZM and Zircaloy as well as dispersion strengthened Alloys with up to 10 percent by volume and more of a dispersoid such as yttrium oxide, thorium oxide or Lanthanum oxide.

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Claims (6)

Claims; 1. A method of making parts from wrought alloys by hot pressing atomizing powders thereby characterized in that the powder particles are first deformed and provided with internal stresses. 2. The method according to claim 1, characterized in that that the powder particles are brought to a hot deformability of at least 2% during deformation. 3. The method according to claim 2, characterized in that that the particles are brought to a hot deformability of at least 5% during deformation. 4. The method according to one or more of claims 1 to 3, characterized in that the Powder particles are shaped in a stirring arm mill. 5. The method according to one or more of claims 1 to 4, characterized in that particles a superalloy atomizing powder. 409826/0 819 6. The method according to one or more of claims 1 to 5, characterized in that from turn the deformed particles made of turbine disks. 40 9 8 26/0819 Blank page