DE2411324A1 - Process for the production of dispersion strengthened kneading nickel - Google Patents

Description

Dipl.-Ing. H. Sauerland · Cr.-lng. R, König · Dipl.-Ing. K. Bengen Patent Attorneys - Aoaa Düsseldorf 3D · Cecilienallee 7B · Telephone 432732

-

March 8, 1974 29 216 K

Henry Wiggin & Company Limited, Holmer Road, Hereford .

HR.4 9FL, UK

"Method of making dispersion-strengthened

Kneading nickel "

Addition to patent application P 22 31 012.9

The invention relates to a method for producing dispersion-strengthened kneaded nickel, in which a powder mixture with 0.07 to 0.1% magnesium and a refractory oxide with a lower free enthalpy than magnesium oxide at sintering temperature, the remainder being essentially nickel at at least 1175 ^° C. Protective gas sintered, the refractory oxide is completely reduced and at least part of the magnesium is oxidized and the sintering is then thermoformed, according to patent application P 22 31 012.9.

Commercially pure wrought nickel has high toughness, ductility, corrosion resistance and weldability; It is therefore used as a material for machines in food production, apparatus in the chemical industry, Parts of electrical and electronic equipment, in space travel and rocket technology, for corrosion-resistant Containers and tubes, rocket propulsion housings, and ultrasonic equipment used. Nevertheless owns The nickel also has disadvantageous properties such as in the case of flat material such as

fu 409845/0957

Sheet metal or band the appearance of Lüders ¹ shear lines or bands, "which are surface defects caused by local flow" during bending. A further disadvantage is the risk of undesirable grain growth during high-temperature annealing, as well as a strength that is too low for some applications.

According to the method of the earlier patent application, the above-mentioned disadvantages are largely "eliminated" and to produce a nickel with improved strength at room temperature and elevated temperatures Annealing is not subject to grain growth, is weldable and, as sheet metal or strip, has no Lüdersian lines.

A disadvantage of the method according to the earlier patent application, however, is that although a considerable Improvement in strength compared to commercially available pure nickel results, but at the same time the electrical Properties are impaired, so that the dispersion-strengthened kneading nickel everywhere cannot be used where a low electrical resistance is important.

Experiments have now shown that it with the method according to the earlier patent application succeeds in a dispersion strengthened nickel with high Establish strength and good electrical properties when the carbon content is reduced and in particular, the nickel is carbon-free.

The invention therefore consists in a method for producing dispersion-strengthened kneading nickel, in which a powder mixture with 0 to 0.196 carbon,

409845/0357

Ms 0.07 0.156 Magnesium and a Feuerfestoxyd whose free enthalpy reducing sintered by magnesium vapor at the sintering temperature allows the sintering das'während and is completely reduced and at least a portion of the magnesium oxidizes, balance nickel under protective gas at ⁰ C and mindestens.1175 the sintered body is then thermoformed.

The nickel powder should be very fine-grained and preferably have an average particle size of at most 7 μm. own. Carbonyl nickel powder with an average particle size of 4 to 7 / Wm is therefore particularly suitable. Carbon is optionally added to the mixture as a fine powder, for example with a particle size below 43 ytfm and preferably coated with nickel by the carnonyl process. If optimal electrical conductivity is important, the powder or the dispersion-hardened nickel, on the other hand, should be completely carbon-free »

The mixture must contain magnesium in order to reduce the refractory oxide, for example aluminum oxide. Preferably elemental magnesium powder is added to the mixture. On the other hand, however, it can also be a powdery Magnesium alloy, for example a nickel-magnesium alloy with 10 to 20% can be used, although the reaction rate is then lower and higher temperatures are required to achieve the To vaporize magnesium.

Aluminum oxide is preferably suitable as the refractory oxide, although other refractory oxides with corresponding ones are also suitable free enthalpy, for example nickel, cobalt, iron, copper, manganese, tungsten or

409845/0957

Titanium oxide come into question. The content of refractory oxide should be adjusted so that at least 10% of the magnesium is oxidized during sintering. Preferably the mixture contains 0.01 Ms 0.06% aluminum oxide with a particle size of preferably at most 0.10 / * m, for example 0.01 Ms 0.03 / Mm.

Before sintering, the powder mixture can be pressed, for example hydrostatically compressed with a pressing pressure of Ms 20.7 hb, in order to produce a sufficiently green-strength pressed body with a theoretical density of at least 65% _s ", for example an apparent density of 5.8 g / cm compact is then a stream of hydrogen, Amoniakspaltgas or another inert gas having at least 10%, preferably at least 30% hydrogen and a dew point of not more than -51 ⁰ C sintered other hand, the powder mixture can, however, be sintered without previous pressing. This can be done in such a way that the powder is poured into a mold coated with a release agent and the mold is sealed with sand to prevent the ingress of combustion gases from the sintering furnace. The protective gas is supplied to the mold via a gas inlet and leaves it through the sand layer Sintering temperature at least 1175 ° C and dab ei are sufficiently far above the evaporation temperature of the magnesium to ensure that the magnesium evaporates during sintering.

The sintered body can by hot extrusion or hot rolling into a blank, a rod or a Tube deformed and processed in the usual way into sheet metal, rods, wire or tubes. Given the relatively high sintering temperature achieved

409845/0957

the apparent density of the sintered body is generally at least 95%.

Although the reaction mechanism during the sintering of the powder mixture could not yet be fully clarified, it can be assumed that the magnesium vapor is in the interstices penetrates between the solid nickel particles and the refractory oxide with simultaneous formation of Magnesium oxide reduced. The sintering atmosphere can be slight Amounts of oxygen, for example from the nickel powder or the atmosphere, are also contained reacts with the magnesium. The free enthalpy of magnesium oxide at the sintering temperature of, for example 1175 to 14OO ° C must in any case be greater than the free enthalpy of the refractory oxide, for example aluminum oxide at the sintering temperature.

Regardless of the not yet fully understood reaction mechanism If possible, the sintered body should not be discrete from the initial refractory oxide Particles contain more. Instead, the sintered body should, for example, in the case of aluminum oxide only contain metallic aluminum, the amount of which corresponds to the original proportion of aluminum oxide and that is dissolved in the nickel structure.

If the powder mixture contains enough magnesium, this is partly dissolved in the nickel after sintering and is partly in the form of fine-grain magnesium oxide with a particle size of less than 0.1 / Wm. During an investigation with a microprobe with an image sharpness of 5 am It was found that zones rich in magnesium are distributed over the entire cross section, although the resolving power the microprobe was insufficient to single out

409845/0957

Detect oxide particles. The examination also showed that there were no agglomerations the dispersoid particles had come. In addition, the extremely fine subdivision of the Dispersoid particles in sintered nickel, which are just taking into account the low alloy additions must be the cause of the high strength. Finally, a microscopic examination also revealed it up to 200 times magnification a remarkably pure Structure.

The nickel produced by the process according to the invention preferably contains 0 to 0.196 carbon, 0.004 to 0.03%, preferably 0.006 to 0.025%. Aluminum and 0.08 to 0.1% magnesium, the remainder with the exception of oxygen. Nickel is only in bound form as magnesium oxide and makes 0.1 to 0.25 vol-96. The amount of the metallic magnesium may be carried for 20 hours annealing a thin 0.127 mm thick sheet into oxygen- and hydrogen-containing, saturated at room temperature with water vapor atmosphere at 1092 ⁰ C to determine, since the magnesium metal diffuses to the plate surface and is oxidized there. The magnesium oxide produced in this way can be removed by pickling, so that the magnesium determined by subsequent chemical analysis is only the magnesium of the magnesium oxide, as this cannot diffuse. In general, the nickel contains 40 to 70%, for example 50%, of the magnesium in metallic form.

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

409845/0957

Of two 10 kg batches, one contained 0.0896 metallic magnesium with a particle size below 43 μm and .0.12% aluminum oxide powder with an average particle size of 0.03 / 6 / m, the remainder carbonyl nickel powder with a Particle size from 4 to 7 / µm and about 0.054% iron, 0.003% carbon and 0.062% oxygen. This mixture was used to make a sample 1, while from the other batch, which differed from the aforementioned batch only in that it an additional 0.16% carbon in the form of nickel-plated particles with a particle size below 43 // m and 25% carbon contained, a sample C was prepared according to the method of the earlier patent application.

Both batches were mixed in a 7.5 liter mixer for 20 minutes. The mixtures were then pressed hydrostatically at a pressure of 20.7 hb into rods 230 mm long and 100 mm in diameter. The bars were then sintered for eight hours at 1200 ⁰ C and each forged one half at 1175 ⁰ C to a square bar having a side length of 19 mm, which then again to 1175 ° C is heated and forged to a wire having a diameter of 19 mm became.

The other half of each rod was forged into a 9.5 mm thick and 51 mm wide strip, which was subsequently heated and rolled out at 1175 ° C. to a thickness of 4.75 mm. Both strips were annealed for one hour at 980 ^° C. and cold-rolled to a thickness of 1.42 mm. The rods were annealed for 30 minutes at 980 ° C and the strips for three minutes at 1025 ° C «

In Tables I to VI below, the technological properties of sample 1 are those of

409845/0957

Sample C according to the earlier patent application as well as commercially available pure, unannealed nickel N with a nickel content of 99.97% and less than 0.02% carbon or a conventional wrought nickel W in the annealed state with 0.08% carbon, 0.18% manganese, 0.2% iron and 0.18% silicon, compared.

The data in Table I relate to the annealed bars, those in Table II relate to the cold-rolled and annealed strips, while Table III is based on tests with strips which are cold-rolled with a cross-section reduction of at least 50% and then with the exception of nickel N three minutes were annealed at 1023 ° C, while the nickel N was annealed for three minutes at 760 ⁰ C. The data in Table IV indicate the mechanical properties of the annealed bars at 649 ⁰ C and 871 ⁰ C again, while it is in the data of Table V to the determined at 649 ⁰ C the mechanical properties of the annealed strips and Table VI the electrical Shows resistance at room temperature with a deviation of + 6%.

Tensile strength
speed
(hbar) Tabel I. Constriction
(%) sample 54.6
39.4
34.5 Stretch limit
(hbar) strain
(%) 65.6
83.9 C.
1
N 17.6
14.7
11.0 45
55
50

409845/0957

Table II

sample

Tensile strength (hbar)

Yield point (hbar)

strain

C.
1
¥

57.4 41.5 34.5

19.2 12.1 11.0

44.5 44.7 50

sample Tabel 11.2 871 ⁰ C 5.6 III IV strain Constriction 0 C. 7.0 5.7 9 1 ASTM grain size 31.0 37, ¥ 8.0 44.0 41, 2 N 8.0 3 6.5 38 33, Tensile strength
speed
(hbar) Tabel 7.0 24 20, sample Stretch limit
(hbar} 20.2 649 ° C C. 17.0 1 7.3 C. 7.4 1

409845/0957

Tensile strength
speed
(hbar) Table V strain
(96) - sample 18.1
16.1 Stretch limit
(hbar) 39.5
41.5 C.
1 8.0
• 6.1 Table VI el. ¥ resistance
(// ohm-cm) sample 10.3
⁷ ' ⁵
9.47
7.48 C.
1
¥
N

The data in the above tables show that the prepared by the process according to the invention, sample containing practically no carbon .1 better strength at room temperature than commercially available pure nickel and also has comparatively good electrical properties. Furthermore is shown both on the carbon-free sample 1 and on the carbon-containing comparative sample C. According to Table III, the effect of the dispersoid which determines the grain size and which is mentioned in the earlier patent application. With regard to the grain size, the pure nickel becomes crystalline at low temperatures.

409845/0957

sated as Samples 1 and C, so it was annealed at low temperature. Nevertheless, the pure possessed Nickel is a not insignificantly coarser grain. At high temperatures, the process according to the invention should The alloy produced have properties similar to those of commercially available pure nickel.

The chemical analysis found for sample C 0.13% carbon, 0.076% magnesium and 0.007% aluminum; for sample 1 below 0.01% carbon, 0.073% magnesium and 0.007% aluminum, the remainder in both cases including nickel Oxygen. The magnesium activity was found to be 60.5% for sample C and 64.5% for sample 1.

Samples C and 1 were further examined to determine the nature of the dispersoid and the degree of conversion of the aluminum oxide and magnesium in the starting mixture. The results were determined by absorption spectrophotometry in order to obtain the most accurate data possible. In the experiments, the samples were transferred to a solution containing magnesium, magnesium oxide and aluminum, while the residue contained the oxidic aluminum, for example AlpO, and MgAl ₂ O ^, and the oxidic magnesium, for example MgO and MgAl ₂ O ^.

The tests showed that sample C was about 0.0001% oxidic aluminum and sample 1 contained approximately 0.0002% oxidic aluminum. As a result, the Sample 1 reduced about 97% of the initial oxidic aluminum to metallic aluminum while only about 3% of the oxidic aluminum was not reduced.

With regard to the magnesium content, it was found that in

409845/0957

samples 1 and C oxidized over 50% of the initial magnesium was. In addition, the absorption spectrophotometric analysis showed that for sample C only 0.0002% and in sample 1 only 0.0003% in a form other than magnesium or magnesium oxide, possibly as magnesium-aluminum oxide, templates. With regard to sample 1, this is less than 1% of the total magnesium oxide content, so that correspondingly 99% of the oxidic magnesium was present as magnesium oxide. Thus it can be seen that essentially all of the initial aluminum oxide, i.e. over 95% of both samples reduced to metallic aluminum and the dispersoid consisted essentially of magnesium oxide.

409 8 45/0957

Claims (9)

Henry ¥ iggin & Company Limited, Holmer Road, Hereford, HR4 9FL, Great Britain Patent claims: 1. Process for the production of dispersion-strengthened kneading nickel, in which a powder mixture with 0.07 to 0.190 magnesium and a refractory oxide with a lower free enthalpy than magnesium oxide at sintering temperature, the remainder essentially nickel is ^{sintered at at least 1175 0} C under protective gas, thereby the refractory oxide completely reduced and at least part of the magnesium is oxidized and the sintering is then thermoformed, according to patent application P 22 31 012.9, characterized in that the powder mixture contains a maximum of 0.1% carbon. 2. The method according to claim 1, characterized in that during sintering at least of magnesium are oxidized to magnesium oxide. 3. The method according to claim 1 or 2, characterized in that the powder mixture Contains aluminum oxide. 4 «, method according to claim 3, characterized in that that the powder mixture contains 0.01 to 0.06% aluminum oxide, 5. The method according to one or more of claims 1 to 4, characterized in that 409845/0957 that the powder mixture is compressed to a green density of at least 5.8 g / cm ^J. 6. The method according to one or more of claims 1 to 5, characterized in that that the sintering takes place under hydrogen. 7. The method according to one or more of claims 1 Ms 6, characterized that the mean particle size of the nickel powder is at most 7 μm ". 8. Wrought nickel produced by the method of claims 1 to 7, characterized by a magnesium content of 40 to 70%. 9. According to the method of claims 1 to 8 prepared Wrought nickel, consisting of 0 to 0.196 carbon, 0.006 to 0.025% aluminum, 0.008 to 0.1% magnesium and 0.1 to 0.25% by volume of oxygen in the magnesium oxide, the remainder being nickel. 409845/0957