Process for producing a layer

Abstract

A process for producing a layer or a body built up of layers. A process gas which has a pressure of >10 bar is accelerated in a convergent-divergent nozzle and a coating material which is formed by particles and is composed of Mo, W, an Mo-based alloy or a W-based alloy is injected into the process gas. The particles are at least partly present as aggregates and/or agglomerates. It is possible to produce dense layers and components in this way. We also describe layers and components having a microstructure with cold-deformed grains having a high aspect ratio.

Claims

1. A process for producing a layer or a body built up of layers, the process comprising: providing a coating material formed of particles selected from the group consisting of Mo, W, an Mo-based alloy, a W-based alloy, and an MoW alloy, wherein greater than 50% of all of the particles are present as aggregates and/or agglomerates; providing the aggregates and/or agglomerates with an average surface area, which is measured by BET, of greater than 0.05 m.sup.2/g, and wherein the aggregates and/or agglomerates have an average porosity, which is determined by quantitative image analysis, of greater than 10% by volume; providing a process gas at a pressure of greater than 10 bar; accelerating the process gas in a convergent-divergent nozzle and injecting the coating material into the process gas before, in or after the convergent-divergent nozzle; and depositing the coating material to form the layer or the body built up of layers.

2. A process for producing a layer or a body built up of layers, the process comprising: providing a coating material formed of particles selected from the group consisting of Mo, Wo, an Mo-based alloy, a W-based alloy, and an Mo-W alloy, wherein the particles are at least partly present as aggregates and/or agglomerates and wherein the particles at least partly have an average porosity, determined by quantitative image analysis, of >10% by volume; providing a process gas at a pressure of greater than 10 bar; accelerating the process gas in a convergent-divergent nozzle and injecting the coating material into the process gas before, in or after the convergent-divergent nozzle; and depositing the coating material to form the layer or the body built up of layers.

3. The process according to claim 1, which comprises providing the aggregates and/or agglomerates with an average nanohardness HIT 0.005/30/1/30 of 10 GPa.

4. The process according to claim 1, which comprises providing the coating material at least partly in granulate form.

5. The process according to claim 1, which comprises providing the coating material with spherical particles having an average porosity, which is determined by quantitative image analysis, of <10% by volume.

6. The process according to claim 1, wherein the coating material comprises hard material particles.

7. The process according to claim 1, wherein the coating material has a bimodal or multimodal particle size distribution.

8. The process according to claim 1, which comprises passing the process gas through a heater.

9. The process according to claim 7, wherein the heater has, at least in regions, a temperature of >800 C.

10. The process according to claim 1, which comprises providing the process gas with a nitrogen content of >50% by volume.

11. The process according to claim 1, which comprises providing the coating material with >80 at. % of at least one element selected from the group consisting of Mo and W.

12. The process according to claim 1, which comprises introducing thermal energy into the coating material before and/or during impingement on a substrate body or a previously produced layer.

13. The process according to claim 12, wherein the introducing step comprises injecting the thermal energy by way of electromagnetic waves and/or by way of induction.

14. The process according to claim 1, which comprises depositing the coating material on a substrate body to form an adhering layer having an average layer thickness of >10 m on impingement on the substrate body.

15. The process according to claim 1, which comprises producing a body made up of a multiplicity of layers.

Description

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWING

(1) The invention will be described below by means of examples.

(2) FIG. 1 and FIG. 2 show scanning electron micrographs of Mo particles according to the invention in a sieve fraction of 45/+20 m.

(3) FIG. 3 and FIG. 4 show scanning electron micrographs of Mo particles according to the invention in a sieve fraction of 20 m.

(4) FIG. 5 shows a scanning electron micrograph of W particles according to the invention in a sieve fraction of 45/+20 m.

(5) FIG. 6 shows a scanning electron micrograph of a CGS Mo layer according to the invention.

(6) FIG. 7 shows a scanning electron micrograph of a spherical W powder used for comparative purposes.

DESCRIPTION OF THE INVENTION

EXAMPLE 1

(7) MoO.sub.2 powder having a particle size measured by the Fisher method (FSSS) of 3 m was introduced into a stirred tank and mixed with such an amount of water that a slurry having a viscosity of about 3000 mPa.Math.s was formed. This slurry was sprayed in a spray granulation plant to give granules. These granules were reduced under hydrogen in a reduction step at 1100 C. to give Mo metal powder. The Mo powder produced in this way was sieved at 45 m and 20 m (sieve fractions of 45/+20 m) and 20 m. The sieve fraction of 45/+20 m is shown in FIGS. 1 and 2, and the sieve fraction of 20 m is shown in FIGS. 3 and 4. FIGS. 1 and 4 show that the particles have the typical appearance of aggregates or agglomerates. An attempt was now made to deagglomerate the powder by action of ultrasound (20 Hz, 600 W). However, since this was possible only to a small extent, most of the powder is, according to the definition given in the description, present as aggregate. The determination of the porosity was carried out by quantitative image analysis as described in detail in the description. Here, the porosity of ten particles was determined, with the average porosity value for the sieve fraction of 45/+20 m being about 40% by volume and that for the sieve fraction of 20 m being about 35% by volume. The BET surface area was determined in accordance with ISO 9277:1995 (instrument: Gemini 2317/model 2, degassing at 130 C./2 h under reduced pressure, adsorptive: nitrogen, volumetric evaluation by five-point determination) and for the sieve fraction of 45/+20 m was 0.16 m.sup.2/g and for the sieve fraction of 20 m was 0.19 m.sup.2/g. The particle sizes were determined by laser light scattering (in accordance with ISO13320 (2009)). The d.sub.50 values are shown in table 1. A powder polished section was then prepared and the average (average of ten measurements) nanohardness H.sub.IT 0.005/30/1/30 (measured in accordance with EN ISO 14577-1, 2002 version, Berkovich penetration body and evaluation method of Oliver and Pharr) was determined on the cross section. The average nanohardnesses are likewise summarized in Table 1.

EXAMPLE 2

(8) Mo-1.2% by mass HfC metal powder having an FSSS (particle size determined by means of Fisher Subsieve Sizer) of 2 m was processed by spray granulation to give granules, with the individual granules having a virtually ideal spherical shape. Polyvinylamine dissolved in water was used as binder for this purpose. The binder was removed thermally at 1100 C. in a hydrogen atmosphere. The heat treatment in hydrogen also led to sinter bridge formation by surface diffusion, but without densification by grain boundary diffusion occurring. The spherical shape was not altered by the heat treatment. The determination of the porosity was carried out by quantitative image analysis as described in detail in the description. Here, the porosity of ten granules was determined, with the average porosity value being about 57% by volume. The particle sizes were determined by laser light scattering (in accordance with ISO13320 (2009)). The d.sub.50 is reported in Table 1.

EXAMPLE 3

(9) Mo-30% by mass W metal powder (not prealloyed) having an FSSS (particle size determined by means of Fisher Subsieve Sizer) of 2.5 m was processed to give granules and characterized in a manner analogous to Example 2. The binder was removed at 1100 C. The average porosity was about 59% by volume. The d.sub.50 is reported in Table 1.

EXAMPLE 4

(10) W blue oxide (WO.sub.3-x) having a particle size determined by the Fisher method (FSSS) of 7 m was reduced under hydrogen at 850 C. in a single-stage reduction process. The W powder produced in this way was sieved at 45/+20 m. FIG. 5 shows that the particles have the typical appearance of aggregates or agglomerates. An attempt was made to deagglomerate the powder by action of ultrasound (20 Hz, 600 W). However, since this was possible to only a small extent, most of the powder is, according to the definition given in the description, present as aggregate. The determination of the porosity was carried out by quantitative image analysis as described in detail in the description. Here, the porosity of ten particles was determined, with the average porosity being about 45% by volume. The BET surface area was determined in accordance with ISO 9277:1995 (instrument: Gemini 2317/model 2, degassing at 130 C./2 h under reduced pressure, adsorptive: nitrogen, volumetric evaluation by five-point determination) and was 0.14 m.sup.2/g. The particle sizes were determined by laser light scattering (in accordance with ISO13320 (2009)). The d.sub.50 is reported in Table 1. A powder polished section was subsequently prepared and the average (average of ten measurements) nanohardness H.sub.IT 0.005/30/1/30 (measured in accordance with EN ISO 14577-1, 2002 version, Berkovich penetration body and evaluation process of Oliver and Pharr) was determined on the cross section. This is likewise reported in Table 1.

(11) TABLE-US-00001 TABLE 1 Mo powder Mo powder Mo-1.2% by W powder Sieve Sieve mass HfC/Mo- Sieve fraction 45/+20 fraction 20 30% by mass fraction 45/+20 m (as per m (as per W powder (as per m (as per Example 1) Example 1) Examples 2, 3) Example 4) d.sub.50 particle size (m) 13 11 26/22 14 Nanohardness H.sub.IT 3.0 3.2 6.1 0.005/30/1/30 (GPa)

EXAMPLE 5

(12) Mo powder having the sieve fractions of 45/+20 m and 20 m as per Example 1, Mo-1.2% by mass HfC granules as per Example 2, Mo-30% by mass W granules as per Example 3 and W powder of the sieve fraction 20 m as per Example 4 were sprayed by cold gas spraying (CGS). A ground tube made of the steel 1.4521 (X 2 CrMoTi 18-2) was used as substrate, with the diameter being 30 mm and the length being 165 mm. The tubes were cleaned by means of alcohol before coating, clamped in a rotatable holder and coated at the free end. A circumferential layer was produced on the rotating substrate. The cold gas spraying process was carried out using nitrogen (86 m.sup.3/h). The process gas pressure was 49 bar. The process gas was heated in a heater which had a temperature of 1100 C. and was arranged in the spray gun. The process gas/powder mixture was conveyed through a Laval nozzle and sprayed perpendicularly to the substrate surface at a spraying distance of 40 mm. The axial advance of the spray gun was 0.75 mm/s and the speed of rotation of the substrate was 650 rpm. The powder was supplied by means of a perforator disk from a powder container which was under a pressure of 50 bar.

(13) In further experiments, the temperature of the heater was reduced to 700 C. and 800 C. or increased to 1200 C.

(14) Layers could be deposited at all temperatures using all powders. However, at 700 C., isolated layer defects such as detachment between individual grains were observed, so that these layers are suitable only for relatively undemanding conditions. At 800, 1100 and 1200 C., dense layers which adhered well and had average layer thicknesses of >10 m and the typical appearance (see, for example, FIG. 6 for Mo 45 m/+20 m/heater temperature 1100 C.) of CGS layers could be produced. The deposited layers had cold-deformed Mo or W grains. The average grain aspect ratio GAR (grain length divided by grain width) was determined by means of quantitative metallography and was in the range from 2 to >5. The average nanohardness H.sub.IT 0.005/30/1/30 was about 5 GPa in the case of Mo (powder as per Example 1) and about 9 GPa in the case of W (powder as per Example 4). At the heater temperature of 1200 C., it was possible to produce not only layers having a thickness of 150 m and above but also shaped bodies having a volume of about 500 cm.sup.3 using all powders.

(15) For comparison, a noninventive spherical, dense W powder (see FIG. 7) having a d.sub.50 particle size of 28 pm was also sprayed at 1100 C. No buildup of a layer occurred here.