DE2362650C3 - Process for improving the deformability of atomized powders - Google Patents

Description

20th

The invention relates to a method for improving the thermoformability of atomized powders made of wrought alloys, especially superalloys.

The known superalloys must be used as a material for heat-resistant parts, for example Gas turbine parts, have high creep resistance and creep rupture strength. This requires again a high hardness with correspondingly poor hot formability, so that superalloys often not thermoformed and can only be used as a cast material.

In order to meet the aforementioned difficulties, it is known in the manufacture of superalloys of a manufactured according to the Sprühveri'fahren Powder running out. This leads to some improvement in the hot formability, but it works Cost of the very fine and homogeneous microstructure. The powder can be thermoformed, for example by hot isostatic pressing, if necessary with subsequent hot deformation, to form kneaded products to process. A further improvement resulted from a combined mechanical and thermally treating the compact; however, this requires compliance with very strict procedural conditions in advance. *

The lack of deformability of the superalloys is particularly important when making large parts, such as For example, turbine disks with a diameter of up to 1.5 m, a major disadvantage. The invention is therefore the object of a method for producing a superalloy with sufficient To create hot formability. The solution to this problem is based on the finding that the deformability of pre-alloyed atomizing powders is deformed by deforming the powder particles can improve, in which the powder particles are given internal tensions.

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

It is known that the hardness of an alloy decreases with increasing temperature. With pre-alloyed powders it is customary to reduce the hardness of the compact after pressing to at least 99% of the theoretical density to eat.

The diagram in the drawing shows the change in hardness as a function of temperature. Curve A relates to an atomized powder, the particles of which have internal stresses according to the invention, and curve B to an atomised powder without internal stresses in the powder particles When the powder particles are deformed, the hardness decreases more rapidly with increasing temperature than in the case of powder B, the hardness of which decreases significantly more slowly from the point of intersection TY ₀

(ATM) ¹ A H ₀ ,

where AT corresponds to the temperature difference between the two curves at ¹ A H ₀ and TM the absolute melting temperature resulting from the diagram in the drawing

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 _{0 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 hot deformability is possible of at least 1%, preferably of at least 2% or even better of at least 5%, gives Im In individual cases, the level of internal tension required depends on the nature of the powder.

The internal stresses can be applied to the particles of an atomized powder by high energy dry milling according to the procedure described in German Offenlegungsschrift 1909 781 will. This process consists in making the alloy by grinding powders of the alloy components in which the powder particles repeatedly welded together and crushed again until the powder reaches its saturation hardness achieved In the context of the process according to the invention, however, dry high-energy milling is used only to give the particles of a pre-alloyed atomizing powder the necessary internal stresses to grant without the saturation hardness must or should be reached. In high-energy milling should the grinding tools, for example grinding balls made of steel, nickel or tungsten carbide, kinetically im State of strong relative movement to be maintained, at least at a given time 50 to 75% of the balls are in a non-contact state. In this way the acceleration forces ensure a repeated collision of the bullets. Spex- and stirring arm mills, such as Szegvari mills, as well as vibratory and planetary ball mills. Usual Ku-

Test temperature CQ

Gel mills require, on the other hand, even if they use the table Π

able to raise the required energy, im

generally too long a grinding time.

Of decisive importance is the species the mill, but the internal tension imparted to the powder particles. A Szegvari ball mill with through hardened 8 mm balls made of AISIE steel 52100 with 0.95 to 1.10% carbon, 0.25 to 0.45% Manganese, not more than 0.025% sulfur, 0.2G to 0.35% Silicon and 1.3 to 1.60% chromium, the remainder being iron preferably with an argon atmosphere containing 10% methane, taking into account the results the conditions resulting from Table I operated below; of course others are also suitable Milling atmospheres such as nitrogen and nitrogen / oxygen atmospheres.

Table I.

Compact hardness (R _A ) ground unground

RT

538 649 760 871 982 74.5
73.2
72.4
71.0
63.2
37.2

78.5
76.2
74.1
69.8
14.4
too low

Fas- By Impeller Bullet/ sensational knife speed Powder- ver age Volume- to like relationship

0)

(m)

(Rpm)

Grinding time

(H)

3.8 2.74 300 until 400 5-50: 1 1 until 10 15.2 3.96 200 until 300 5-50: 1 1 until 10 37.9 4.88 125 until 250 5-50: 1 1 until 10 379 10.97 50 until 150 5-50: 1 1 until W.

20th

25th

30th

The particle size of the powder can be very different and be up to at least 1000 μm, although the particle size under the aforementioned process conditions is initially preferably 20 to 350 μΐη is

The invention is illustrated below with the aid of exemplary embodiments explained in more detail:

example 1

An atomized powder made from the alloy IN-100 with 15% cobalt, 10% chromium, 5.5% aluminum, 4.75% titanium, 3% molybdenum, 0.02% carbon, 0.15% Boron and 0.06% zirconium, the balance nickel and a particle size below 43 μm was ten hours in a 3.8-1 agitator ball mill in flowing Ground nitrogen at an impeller speed of 350 rpm. The mill contained 16.8 kg of full hardened Balls made of AISIE 52100 steel with a diameter of 8 mm; the volume ratio Spheres / powder was 17: 1.

Partial quantities of the powder were filled into cans made of soft steel both before and after the grinding. 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 ⁰ C, compressed in a continuous press against an anvil, and cooled under vermiculite After remove of the cans, the Rockwell hardness of the compacts was determined at different temperatures, wherein ereaben the apparent from the following Table II Values .

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

The hot formability was found to be that described above Way to 6%.

Example 2

A further batch of the atomized powder was prepared according to Example 1, ground, were being taken prior to and after grinding subsets and hot-pressed in the aforementioned manner at 1066 ⁰ C. Samples of the pressed bodies were examined at 982 ° C and an elongation of 0.0025 to 0.625 per minute. The results for the samples from the milled powder were a flow resistance of 33.6 to 77 N / mm ² , an elongation at break of 144% and a constriction of 99%.

In contrast, the samples made from the unground powder had a flow resistance of 59.8 to 110 N / mm ² , an elongation of 10% and a necking of 4.5%. Further samples were annealed for four hours at 1149 ° C, oil quenched, annealed twenty-four hours at 649 ⁰ C, cooled in air for eight hours at 760 ⁰ C cured and cooled again in the air and at 732 ° C under a load of 690 N / mm ² examined. This resulted in a standing time of 22.5 hours for the sample from the ground powder

so and for the sample from the unground powder a standing time of only two hours.

Example 3

55 Two further batches of the above-mentioned atomized powder with a particle size of 43 to 246 μm were placed in an airtight M-cm ball hole with a rotational speed of 80 rpm in the presence of fully hardened 9.5 mm balls made of AISIE 52100 steel for five and fifty hours, respectively Balls / powder volume ratio of 10: 1 ground. Furthermore, two batches of powder with a particle size of less than 43 μm were ground for one or three hours in a ball mill according to Example 1. Each of the four batches was hot-pressed and examined in the manner described in connection with Example 2, with the results from the following table

Belle III resulted in apparent data. The data in Table III also contain the test results of the. unground powder and the ten-hour milled powder according to Table I and from the literature hardness values derived from a conventional IN-100 cast alloy.

Table III Starting Rockwell hardness R _A 50 h Agitator mill 3 h 10 h As-cast state powder Ball mill 75.8 77.2 78.5 temperature 73.8 1 h 76.0 76.2 74.5 5h 73.2 76.4 74.0 74.1 69.5 (C) 73.2 74.8 71.5 74.4 69.4 69.8 68.2 RT Tl A
I i, T 73.9 55.7 74.1 33.0 14.4 68.2 593 71.0 73.8 *) 70.0 *) *) 67.8 649 63.2 71.3 47.2 65.0 760 37.2 61.7 *) 58.5 871 27.4 982

Hot formability (%) 1.2
*) Too small for the measurement.

3.5

4.3

5.7

The data in Table III show that grinding the powder for only one hour in a stirring arm ball mill leads to significantly better deformability at temperatures above 76O ⁰ C than five hours of dry ball milling. The deformability is a little better than that of a powder ball-milled for fifty hours. 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 unground Powders according to Example 2 are at least partly due to the much finer particles or the Due to the dislocation structure of the particles with internal stresses. The deformation of the powder particles grinding also leads to a finely dispersed distribution of the brittle phases. When pressing an untreated atomizing powder, however, difficulties arise because of the surface phases the powder particles.

Pressed bodies made from atomized powders ground according to the invention also have a completely different one Structure as an untreated powder, especially when it is a powder made of always carbon Superalloys. In the untreated In this state, there are usually relatively large carbides with a size over 1 μπα as incoherent Structural component whose atomic structure has no relationship to the basic structure surrounding them. With compacts from according to the invention Process treated powders, on the other hand, the carbides are mostly finely dispersed semi-coherent particles. This difference in the carbide structure is due to the severe deformation of the powder particles during grinding, which leads to a comminution and redistribution of the carbides During the subsequent heating to the hot pressing temperature, the fine carbides go into solution and are deposited again at temperatures at 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. On the other hand, the particles of an untreated atomizing powder contain non-comminuted Carbides that are relatively stable and maintain their compact size.

At the higher temperatures of hot pressing there is a certain loosening of the compact carbides instead of. However, the higher temperatures also increase the atomic mobility at the same time, so that the dissolved carbides precipitate again on cooling at the grain boundaries or other surfaces.

The increase in the hot deformability of an atomized powder by the method according to the invention allows the use of a wide variety of shaping processes. This includes vacuum hot pressing, Forging, rolling, hot isostatic pressing at lower temperatures than usual common as well as hot extrusion. In this way, small turbine disks can be closed Die forged with tool stamps, resulting in completely pore-free disks, which are immediately can be heat treated and machined. When manufacturing large turbine disks, a preliminary

cross-rolled in this way or forged in a closed die to almost the final shape and size. The low material loss of the expensive super alloys with minimal machining is a particular advantage. Of course, the deformation must take place at temperatures above the temperature of H _1.

The method according to the invention can be carried out with the most varied of pre-alloyed powders, in particular made of superalloys and other alloys that are difficult to deform. These include nickel superalloys with up to 60%, for example 1 to 25%, chromium, up to 30%, 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. Koball superalloys and the alloy are also suitable IN-738 with 0.17% carbon, 8.5% cobalt, 16% Chromium, 1.75% molybdenum, 2.6% tungsten, 1.75% tantalum, 0.9% niobium, 3.4% aluminum, 3.4% titanium, 0.01% boron and 0.10% zirconium, the remainder nickel and IN-792 with 12.7% chromium, 9% cobalt, 2% molybdenum, 3.9% each Tungsten and tantalum, 3.2% aluminum, 4.2% titanium, 0.21% carbon, 0.1% zirconium and 0.02% boron, Remainder nickel and Rene 41 with 0.09% carbon, 19% chromium, 11% cobalt, 1.5% aluminum, 3.1% Titanium, 10% molybdenum, up to 5% iron and 0.007% boron, balance nickel, or Rene 95 with 0.15% carbon, 14% chromium, 8% cobalt, 3.5% aluminum, 2.5% titanium, 3.5% each of molybdenum, tungsten and niobium, 0.01% boron and 0.05% zirconium, the balance nickel.

The alloys Inconel 718 with 0.04% carbon, 18.6% chromium, 0.4% aluminum, 3.1% molybdenum, 5% niobium and 18.5% iron, the remainder nickel, Waspaloy with 0.07 are also suitable % Carbon, 19.5% chromium, 13.5% cobalt, 1.4% aluminum, 3% titanium, 4.3% molybdenum, 2% iron, 0.006% boron and 0.07% zirconium, the remainder nickel, astroloy with 0.06% carbon, 15% chromium and cobalt each, 4.4% aluminum, 3.5% titanium, 5.25% molybdenum and 0.03% boron, the remainder nickel, Mar-M 200 with 0.15% carbon , 9% chromium, 10% cobalt, 5% aluminum, 2% titanium, 12.5% tungsten, 1% niobium, 0.015% boron and 0.05% zirconium, balance nickel, or Mar-M 246 with 0.15% Carbon, 9% chromium, 10% cobalt, 5.5% aluminum, 1.5% titanium, 2.5% molybdenum, 10% tungsten, 1.5% tantalum, 0.015% boron and 0.05% zirconium, the remainder nickel .
Also available as pre-alloyed powder are Nimocasl 713 with 0.12% carbon, 12.5% chromium, 6.1% aluminum, 0.8% titanium, 4.2% molybdenum, 2.2% niobium, 0.012% boron and 0, 1% zirconium, balance nickel, UdimetSOO with up to 0.15% carbon, 17.5% chromium, 16.5%

ίο cobalt, each 2.9% aluminum and titanium, 4% molybdenum, up to 4% iron and up to 0.01% boron, remainder nickel, Udimet700 with a maximum of 0.15% carbon, 15 Chromium, 17% cobalt, 4.3% aluminum, 3.4% titanium, 5.3% molybdenum, at most 4% iron and at most 0.05% boron, balance nickel, and A-286 with 0.05% carbon, 15% chromium, 26% nickel, 1.25% molybdenum, 2.2% titanium, 0.2% aluminum, 0.03% boron and 0.3% vanadium, the remainder iron, in question. Finally, are suitable also titanium alloys and the refractory alloys SU-16 with 11% tungsten, 3% molybdenum, 2% Hafnium and 0.08% carbon, balance niobium, TZM with 0.025% carbon, 0.48% titanium and 0.09% zirconium, Remainder molybdenum, as well as Zircaloy for example with 1.5% tin, 0.12% iron, 0.1% chromium and 0.05% Nickel, balance zirconium, or with a maximum of 0.05% carbon, 0.25% tin and 0.25% iron, balance zirconium, and dispersion strengthened alloys with up to 10 volume percent and more of a dispersoid, such as yttrium oxide, thorium oxide or lanthanum oxide.

1 sheet of drawings

Claims (3)

Patent claims: L Process to improve the deformability of the bath of atomizing powders made from kneaded alloys, in particular superalloys, characterized that the powder particles are initially cold deformed and thus with internal stresses be provided. 2. The method according to claim 1, characterized in that that the powder particles are cold deformed in a stirring arm mill. 3. Use of the atomizing powder pretreated according to claim 1 or 2 for production of turbine disks.