Chromium-containing powder or granulated powder

Abstract

A powder or powder granulate includes a chromium content >80 Ma %, which contains 2 to 20 Ma % iron, optionally up to 5 Ma % dopant, and optionally up to 2 Ma % oxygen, wherein the chromium-containing particles at least partially have pores. The powder displays significantly improved compression behavior and allows the production of sintered components having a very homogeneous distribution of the alloy elements.

Claims

1. A powder or powder granulate, comprising: a chromium content >80 Ma %; 2 to 20 Ma % iron; optionally up to 5 Ma % dopant; optionally up to 2 Ma % oxygen; iron-rich regions having an iron content >60 Ma %; and chromium-rich regions having a chromium content >95 Ma % and forming chromium-containing particles at least partially having pores, said chromium-containing particles having a mean porosity determined by quantitative image analysis of >20 Vol %.

2. The powder or powder granulate according to claim 1, wherein said chromium-containing particles are at least partially classified as porous according to the classification according to p. 472 of Vol. 7 of the ASM handbook of 2007.

3. The powder or powder granulate according to claim 1, wherein said chromium-containing particles have a particle size d.sub.50>20 m measured by laser diffractometry and a surface area >0.05 m.sup.2/g measured by BET.

4. The powder or powder granulate according to claim 1, wherein said pores are at least regionally open-pored and cross-linked.

5. The powder or powder granulate according to claim 1, which further comprises 0.005 to 5 Ma % of at least one dopant selected from the group consisting of scandium, yttrium, lanthanides, titanium, zirconium and hafnium.

6. The powder or powder granulate according to claim 1, which further comprises 0.002 to 2 Ma % oxygen.

7. The powder or powder granulate according to claim 1, wherein said iron-rich regions are at least partially provided as iron-containing particles.

8. The powder or powder granulate according to claim 1, wherein said iron-rich regions are provided at least in one form selected from the group consisting of unbound/elementary iron and iron oxide.

9. The powder or powder granulate according to claim 1, wherein said iron-rich regions are at least partially intercalated in said pores of said chromium-containing particles.

10. The powder or powder granulate according to claim 1, wherein said iron-rich regions are connected to said chromium-containing particles at least partially by a diffusion connection.

11. The powder or powder granulate according to claim 1, wherein said dopant is provided at least partially as an oxide in the form of particles.

12. The powder or powder granulate according to claim 1, wherein said dopant is provided at least in one form selected from the group consisting of intercalated in said chromium-containing particles and deposited on a surface of said chromium-containing particles.

13. The powder or powder granulate according to claim 1, wherein said chromium-rich regions have a nanohardness .sub.HIT 0.005/5/1/5 according to EN ISO 14577-1 of 4 GPa.

14. The powder or powder granulate according to claim 1, which further comprises a particle size/granulate size d.sub.50 of the powder or powder granulate measured by laser diffractometry of 10 m<d.sub.50<800 m.

15. A component, comprising: a powder or powder granulate according to claim 1.

16. A method for the powder-metallurgy production of a component, the method comprising the following steps: providing a chromium content >80 Ma %; providing 2 to 20 Ma % iron; providing optionally up to 5 Ma % dopant; providing optionally up to 2 Ma % oxygen; providing iron-rich regions having an iron content >60 Ma %; and providing chromium-rich regions having a chromium content >95 Ma % and forming chromium-containing particles at least partially having pores, the chromium-containing particles having a mean porosity determined by quantitative image analysis of >20 Vol %.

17. A method for producing a powder or powder granulate, the method comprising the following steps: reducing at least one chromium-containing compound selected from the group consisting of oxides and hydroxides in at least partial chronological presence of a carbon source and hydrogen at 1100 to 1550 C. to produce a powder or powder granulate having: a chromium content >80 Ma %; 2 to 20 Ma % iron; optionally up to 5 Ma % dopant; optionally up to 2 Ma % oxygen; iron-rich regions having an iron content >60 Ma %; and chromium-rich regions having a chromium content >95 Ma % and forming chromium-containing particles at least partially having pores, the chromium-containing particles having a mean porosity determined by quantitative image analysis of >20 Vol %.

18. The method according to claim 17, which further comprises admixing the dopant to the chromium-containing compound before the reducing step.

19. The method according to claim 17, which further comprises after the reducing step adding an iron-containing powder having an iron content >60 Ma %.

20. The method according to claim 19, which further comprises annealing the powder or powder granulate at a temperature T with 400 C. <T<1200 C. after the step of adding the iron-containing powder.

21. The method according to claim 17, which further comprises granulating the chromium-containing compound alone or optionally jointly with the dopant.

Description

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWING

(1) The invention will be explained in greater detail hereafter on the basis of examples.

(2) FIG. 1 shows typically classified powder shapes

(3) FIG. 2 shows a scanning electron microscope picture of a Cr.sub.2O.sub.3/carbon black powder granulate

(4) FIG. 3 shows a scanning electron microscope picture of a powder granulate according to FIG. 2 in the reduced state

(5) FIG. 4 shows a scanning electron microscope picture of the powder granulate according to FIG. 3 with greater enlargement

(6) FIG. 5 shows a scanning electron microscope picture of the surface of a chromium particle with Y.sub.2O.sub.3 particles according to example 2 (1.2 g Y.sub.2O.sub.3 addition)

(7) FIG. 6 shows a scanning electron microscope picture of the surface of a chromium particle with Y.sub.2O.sub.3 particles according to example 2 (5.95 g Y.sub.2O.sub.3 addition)

(8) FIG. 7 shows a scanning electron microscope picture of the surface of a chromium particle with Y.sub.2O.sub.3 particles according to example 3 (Y(NO.sub.3).sub.3.6H.sub.2O) concentration in relation to 100 ml H.sub.2O.sub.deionized: 4.5 g)

(9) FIG. 8 shows a scanning electron microscope picture of the surface of a chromium particle with Y.sub.2O.sub.3 particles according to example 3 (Y(NO.sub.3).sub.3.6H.sub.2O) concentration in relation to 100 ml H.sub.2O.sub.deionized: 20.2 g)

(10) FIG. 9 shows a scanning electron microscope picture of the surface of a chromium particle with Y.sub.2O.sub.3 particles according to example 3 (Y(NO.sub.3).sub.3.6H.sub.2O) concentration in relation to 100 ml H.sub.2O.sub.deionized: 40.3 g)

(11) FIG. 10 shows a scanning electron microscope picture (secondary electron contrast) of a chromium particle according to example 1 with admixed/alloyed iron particles

(12) FIG. 11 shows a scanning electron microscope picture (backscattered electron contrast) of a chromium particle according to example 1 with admixed and alloyed iron particles

(13) FIG. 12 shows a scanning electron microscope picture (in transverse microsection) of a chromium particle with pores which are partially filled with Fe.sub.2O.sub.3 according to example 5

(14) FIG. 13 shows a scanning electron microscope picture of a chromium particle with alloyed iron particles according to example 6

(15) FIG. 14 shows a scanning electron microscope picture with greater enlargement of a powder according to FIG. 13

(16) FIG. 15 shows the relative density of green bodies produced from CFY powder (prior art) and AS-113 powder (according to the invention)

(17) FIG. 16 shows the iron distribution (measured by means of EDX Line Scan) of sintered samples produced from CFY powder (prior art, identified as standard) and AS-113 powder (according to the invention)

(18) FIGS. 17a,b,d,c show scanning electron microscope pictures of powder according to the invention with analysis frames for the quantitative image analysis

DESCRIPTION OF THE INVENTION

Example 1

(19) Cr.sub.2O.sub.3 powder with pigment quality of the type Lanxess Bayoxide CGN-R was mixed in a diffusion mixer with carbon black powder of the type Thermax Ultra Pure N 908 from Cancarb. The carbon content of the mixture was 18.64 Ma %. By adding water and 1.7 Ma % paraffin wax, a slurry was produced. This slurry was processed in a laboratory spray tower to form granulate (see FIG. 2). The granulate thus produced was screened out with 45 to 160 m. The granulate was then heated at a heating speed of 10 K/min to 800 C. and then heated at a heating speed of 2 K/min to 1050 C. The heating was performed under the effect of H.sub.2, wherein the H.sub.2 pressure was set so that in the temperature range from 800 C. to 1050 C., the CH.sub.4 partial pressure measured by mass spectrometry was >15 mbar. The total pressure was approximately 1.1 bar in this case. The reaction mixture was then heated at a heating speed of 10 K/min to 1450 C. The holding time at 1450 C. was 5 h. Heating from 1050 C. to 1450 C. and holding at 1450 C. were performed with the supply of dry hydrogen with a dewpoint <40 C., wherein the pressure was approximately 1 bar. The furnace cooling was also performed under H.sub.2 with a dewpoint <40 C. The granulate thus reduced externally had the shape and the dimensions of the spray-granulated granulate (FIG. 3), but internally had a network of pores as shown in FIG. 4. According to the ASM classification for the powder shape, the granulate corresponds to the classification porous. The porosity was carried out by means of quantitative image analysis as explained in greater detail in the description, wherein circles (see FIG. 17a) and rectangles (see 17b) were used as measurement frames. The porosity of 10 particles was determined, wherein the values were between 74 Vol % and 76 Vol %. The mean porosity was 75.3 Vol %. The BET surface area was determined according to ISO 9277:1995 (device: Gemini 2317/Type2, degassing at 130 C./2 h in vacuum, adsorptive: nitrogen, volumetric analysis via five-point determination) and was 0.10 m.sup.2/g. The particle size d.sub.50 determined by means of laser diffractometry (according to ISO13320 (2009)) was 120 m. In the further procedure, a powder microsection was produced and, in the transverse microsection on chromium-rich regions, the mean (mean value from 10 measurements) nanohardness .sub.HIT 0.005/5/1/5 (measured according to EN ISO 14577-1, edition 2002, Berkovich penetration body and analysis method according to Oliver and Pharr) was determined. The nanohardness .sub.HIT 0.005/5/1/5 was 2.9 GPa.

Example 2

(20) 1627.2 g Cr.sub.2O.sub.3 powder (pigment quality Lanxess Bayoxide CGN-R), 372.8 g carbon black (Thermax Ultra Pure N 908 from Cancarb), 1.2 g Y.sub.2O.sub.3 with a particle size d.sub.50 measured by laser diffractometry of 0.9 m were ground in an attritor for 3 hours with the addition of 1.5 L isopropanol. The mill balls were made in this case from stabilized Y.sub.2O.sub.3. The ball to powder ratio was 6:1. The slurry thus produced was dried in vacuum and heated at a heating speed of 10 K/min to 800 C. and then heated at a heating speed of 2 K/min to 1050 C. The heating was performed under the effect of H.sub.2, wherein the H.sub.2 pressure was set so that in the temperature range from 800 C. to 1050 C., the CH.sub.4 partial pressure measured by mass spectrometry was >15 mbar. The total pressure was approximately 1 bar in this case. The reaction mixture was then heated at a heating speed of 10 K/min to 1450 C. The holding time at 1450 C. was 4.5 h. Heating from 1050 C. to 1450 C. and holding at 1450 C. were performed with the supply of dry hydrogen with a dewpoint <40 C., wherein the pressure was approximately 1 bar. The furnace cooling was also performed under H.sub.2 with a dewpoint <40 C. The sinter cake was then broken into a powder. In the same manner, powders were manufactured which, instead of 1.2 g Y.sub.2O.sub.3, contained 1.2 g TiO.sub.2 with a particle size of 0.5 m, 1.2 g ZrO.sub.2 with a particle size of 1.2 m, or 1.2 g HfO.sub.2 with a particle size of 1.9 m, respectively. The powders thus produced have a porous structure and the powder shape corresponds to the classification porous according to the ASM classification. FIG. 5 shows an example of the particle surface for the variant doped with Y.sub.2O.sub.3. Fine particles having a mean particle diameter <1 m are recognizable on the surface of the chromium-containing porous particles. These particles are distributed uniformly on the surface. The variants doped with TiO.sub.2, HfO.sub.2, and ZrO.sub.2 also display a fine and uniform distribution of the dopants. The chemical analysis for the variant doped with Y.sub.2O.sub.3 resulted in 291 g/g carbon, 1320 g/g oxygen, and 1128 g/g yttrium, the remainder chromium and typical contaminants. The porosity of the variant doped with Y.sub.2O.sub.3 was carried out by means of quantitative image analysis, as explained in greater detail in the description, wherein circles (see FIG. 17c) and rectangles (see 17d) were used as measurement frames. The porosity of 10 particles was determined, wherein the values were between 61 Vol % and 75 Vol %. The mean porosity was 67.1 Vol %.

(21) In a further variant, 5.95 g Y.sub.2O.sub.3 were added instead of 1.2 g. The further manufacturing was performed as described above. According to FIG. 6, the chromium particles are again highly porous. Finely distributed Y.sub.2O.sub.3 particles having a mean particle size of <1.5 m are recognizable on the surface. The result of the chemical analysis provided 288 g/g carbon, 2076 g/g oxygen, and 4049 g/g yttrium.

Example 3

(22) 1632.6 g Cr.sub.2O.sub.3 (pigment quality Lanxess Bayoxide CGN-R) were mixed with 367.4 g carbon black in a diffusion mixer. During the mixing operation, an aqueous yttrium nitrate (Y(NO.sub.3).sub.3.6H.sub.2O) solution was added by means of spray technology. In this case, three different batches were produced, which differed in the (Y(NO.sub.3).sub.3.6H.sub.2O) concentration. This concentration, in relation to 100 mL of deionized water in each case, was 4.5 g, 20.2 g, and 40.3 g, respectively. The mixtures thus produced were dried in a vacuum furnace and heated at a heating speed of 10 K/min to 800 C. and then heated at a heating speed of 2 K/min to 1050 C. The heating was performed under the effect of H.sub.2, wherein the H.sub.2 pressure was set so that in the temperature range from 800 C. to 1050 C., the CH.sub.4 partial pressure measured by mass spectrometry was >15 mbar. The total pressure was approximately 1 bar in this case. The reaction mixture was then heated at a heating speed of 10 K/min to 1450 C. The holding time at 1450 C. was 7 h. Heating from 1050 C. to 1450 C. and holding at 1450 C. were performed with the supply of dry hydrogen with a dewpoint <40 C., wherein the pressure was approximately 1 bar. The furnace cooling was also performed under H.sub.2 with a dewpoint <40 C. Chromium particles were again obtained, which are to be classified according to the ASM classification as porous. The respective particle surfaces are shown in FIGS. 7, 8, and 9. In all three cases, the mean Y.sub.2O.sub.3 particle size was <1 m. Furthermore, it is recognizable that the particles were provided very uniformly distributed. The BET surface area was 0.10 m.sup.2/g (4.5 g addition), 0.14 m.sup.2/g (20.2 g addition), and 0.18 m.sup.2/g (40.3 g addition) and the particle size d.sub.50 determined by laser diffractometry was approximately 130 m for all three variants. In the further procedure, a powder microsection was produced and in the transverse microsection on chromium-rich regions, the mean (mean value of 10 measurements) nanohardness .sub.HIT 0.005/5/1/5 was determined. The nanohardness .sub.HIT 0.005/5/1/5 was 3.0 GPa (4.5 g addition), 3.0 GPa (20.2 g addition), and 3.1 GPa (40.3 g addition).

Example 4

(23) Powders, produced according to examples 1 to 3, were mixed in a diffusion mixer with 2, 5, or 10 Ma % iron powder, respectively (particle size d.sub.50 measured by laser diffractometry approximately 8 m). The mixtures thus produced were annealed in a furnace under hydrogen atmosphere at 1000 C./30 min. Due to the use of the porous chromium powder, the mixing, and the diffusion annealing, it is possible, on the one hand, to partially introduce the iron particles into the pores of the chromium particles, and, on the other hand, to fix them by the annealing by means of a diffusion bond (so-called alloy powder). As an example (chromium powder according to example 1), powder thus produced is shown in FIGS. 10 and 11.

Example 5

(24) Powder, produced according to examples 1 to 3, was mixed with Fe.sub.2O.sub.3 powder (particle size measured according to Fisher of 0.17 m). The chromium to iron ratio in Ma % was 95 to 5. The fine Fe.sub.2O.sub.3 particles could again penetrate into the pores of the porous chromium particles (FIG. 12), whereby a very homogeneous distribution of Fe.sub.2O.sub.3 in chromium occurred. The powder mixture was reduced at a temperature of 600 C./4 h in H.sub.2O (reduction of the Fe.sub.2O.sub.3 to iron). In addition, the heat treatment caused the reduced iron particles to adhere via a diffusion bond on the surface of the chromium particles (alloy powder). FIGS. 13 and 14 show the chromium-containing particles with alloyed iron particles at different enlargements.

Example 6

(25) A CrFeY powder (identification CFY), produced according to EP 1 268 868 (A1), having an iron content of 5 Ma %, a Y.sub.2O.sub.3 content of 0.11 Ma %, a grain size d.sub.50 of 132 m, and a BET surface area of 0.03 m.sup.2/g was mixed with 0.6 Ma % compression wax and compressed to form bending samples having the dimensions 31.5 mm12.7 mm6 mm using a compression pressure of 550 MPa or 850 MPa. A CrY.sub.2O.sub.3 powder with 0.11 Ma % Y.sub.2O.sub.3 was produced as described in example 2. Fe.sub.2O.sub.3 powder was added to this powder, wherein the chromium:iron Ma % ratio was 95:5. The powder was subsequently reduced at 600 C./4 h. The fraction screened out with 45 to 250 m was mixed with 0.6 Ma % compression wax. From this powder (identification: AS-113), bending samples having the dimensions 31.5 mm12.7 mm6 mm were also compressed at 550 MPa or 850 MPa. The green strength was determined according to ASTM B 312-09 by means of a three-point bending test. A significant improvement of the green strength was achieved using the powder according to the invention (see FIG. 15).

Example 7

(26) The bending samples compressed at 550 MPa according to example 6 were subjected to a sintering in H.sub.2 atmosphere at 1450 C./180 min. The iron concentration was determined by means of EDX over a distance of 2000 m. As shown in FIG. 16 (CFYprior art, AS-113according to the invention), the iron distribution using the powder AS-113 according to the invention is much more homogeneous and uniform than in the case of the powder CFY of the prior art.

KEY TO THE FIGURES

(27) FIGS. 2-14, 17 Hochsp. high voltage Vergrerung enlargement Arbeitsabstand working distance FIG. 15 Grnfestigkeit green strength Pressdruck compression pressure FIG. 16 Fe-Gehalt iron content Entfernung distance Erfindung invention