YTTRIA-COATED REFRACTORY METAL COMPONENT

Abstract

A component formed of a refractory metal has a surface that is at least partially coated with a layer of yttria. There is also described a method of manufacturing a coated component, and the application of Y.sub.2O.sub.3 as a release agent in high temperature applications.

Claims

1-12. (canceled)

13. A component consisting of a refractory metal and having a surface at least partially coated with a layer of yttrium oxide.

14. The component according to claim 13, wherein said refractory metal is a metal selected from the group consisting of titanium, zirconium, hafnium, vanadium, niobium, tantalum, chromium, molybdenum, tungsten, rhenium, and alloys of said metals.

15. The component according to claim 13, wherein said refractory metal consists of at least 70% by weight of molybdenum.

16. The component according to claim 13, comprising a component body formed as a bolt, a nut, a pin, a dowel pin, a washer, a bolt, a sheet, a clamp, a tube, a rod, or a U-shaped rail.

17. The component according to claim 13, being an assembly of welded and/or riveted individual parts.

18. The component according to claim 13, wherein the layer of Y.sub.2O.sub.3 layer has a thickness in a range from 10 ?m to 150 ?m.

19. The component according to claim 13, wherein the surface of the component is completely coated.

20. The component according to claim 13, wherein the surface of the component is only partially coated.

21. The component according to claim 13, wherein the layer of Y.sub.2O.sub.3 is a Y.sub.2O.sub.3 layer applied to the surface by slurry coating.

22. A component for a high-temperature application, comprising a layer of yttria forming a separating agent for the component for the high-temperature application.

23. A method of manufacturing a coated component, the method comprising the following steps: providing a component consisting of a refractory metal; and applying a layer of yttrium oxide to at least a portion of a surface of the component by slurry coating.

24. The method according to claim 23, which comprises providing an ethanol-based Y.sub.2O.sub.3 slurry and coating the component from the slurry.

Description

EXAMPLE 1: SCREW CONNECTION

[0032] TZM plate (molybdenum with a weight fraction of 0.5 Ti and 0.08 Zr as well as 0.01 to 0.04 C) 140?80?9 mm, 9 mm deep through bore milled with M6 thread

[0033] Molybdenum washer: 18?6, 4?1.5 mm

[0034] Molybdenum screw: M6?12 mm

[0035] Several screws were coated by slurry coating with a Y.sub.2O.sub.3 (according to the invention), ZrO.sub.2, TaC or ZrC suspension and then dried. The coatings had a thickness in the range of 50 to 70 ?m.

[0036] As indicated in the table below, several tests were conducted to evaluate the Y.sub.2O.sub.3 coating versus the comparative coatings under different conditions. For this purpose, three screws (S1 to S3) with washers were selected in each case and screwed into the plate at a tightening torque of 12 Nm. High temperature treatments were performed at temperatures (T (in ? C.)) ranging from 400? C. to 1400? C. and different atmospheres (A) (hydrogen (H), vacuum 10.sup.?6 mbar (V)) with a holding time of 2 h. The opening torque (L (in Nm)) was measured after the high temperature treatment and the threads were visually inspected for seizing (S) and, if applicable, breakage (B) of the screw was detected.

TABLE-US-00001 S1 S2 S3 Total Layer T A L S B L S B L S B L S B Y.sub.2O.sub.3 400 V 0 no no 0 no no 0 no no lower no no Slurry 1000 V 5 no no 5 no no 5 no no lower no no 1400 V 5 no no 5 no no 10 yes yes lower partly partly 1400 H <5 no no <5 no no <5 no no lower no no ZrO.sub.2 400 V 15 yes no 15 yes no 15 yes no similar yes no Slurry 1000 V 10 yes no 10 yes no 10 yes no similar yes no 1400 V 12 yes no 10 yes no 10 yes no similar yes no 1400 H 10 yes no 10 yes no 10 yes no similar yes no TaC 400 V 15 yes no 15 yes no 15 yes no similar yes no Slurry 1000 V 10 yes no 10 yes no 10 yes no similar yes no 1400 H 10 yes no 10 yes no 10 yes no similar yes no ZrC 400 V 10 no no 10 no no 10 no no similar no no Slurry 1000 V 5 yes no 5 yes no 5 yes no lower yes no 1400 H 10 yes no 10 yes no 10 yes no similar yes no

[0037] As can be seen from the above table, the ZrO.sub.2 and TaC coated screws already show seizing at low temperatures as of 400? C. and are therefore unsuitable for high-temperature applications. The ZrC-coated screws show seizing above 1000? C. and are therefore also unsuitable for high-temperature applications.

[0038] In contrast, with the Y.sub.2O.sub.3 coating according to the invention, no seizing of the screw connection occurs. Consequently, the coating can achieve the detachability of contacting refractory metal components. In addition, no cross-contamination between the components could be detected.

EXAMPLE 2: PRODUCTION AND EVALUATION OF COATED RELEASE SHEETS

[0039] Various products were tested and evaluated as possible release agents for stack annealing of sheets. For this purpose, the different release agents were applied between the sheets. The sprays or suspensions were applied on one side of 1 mm thick molybdenum sheets (area about 40?20 mm). The applied layers had a thickness between 50 and 70 ?m. 25 sheets were annealed in a stack at 1900? C. for one hour in a hydrogen atmosphere.

[0040] The evaluation results are summarized below:

[0041] ZrO.sub.2 slurry via corrosion lab (ISTO) as pump spray: separation only possible with tools; slurry baked onto sheets; unsuitable.

[0042] Al.sub.2O.sub.3 solid via corrosion lab (ISTO), ceramics, 99.7% purity: separation only possible with tool; ceramics partly with edge marks from sheets; unsuitable.

Boron Nitride Spray (Spray Henze HeBoCoat 21E):

[0043] Sheets separable after annealing, but a 10-20 ?m thick molybdenum boride layer forms during annealing; unsuitable.

ZrO.sub.2 Spray (Spray from ZYP Coatings Inc. 98% ZrO.sub.2, 0.7% MgO, 1.2% SiO.sub.2):

[0044] The sheets are separable after annealing, but the spray layer is mainly loose on the sheet. Contamination of the plant due to flaking of the ZrO.sub.2 spray layer; unsuitable.

ZrO.sub.2 Solid 80 ?m Ceramic from CeramTec 3YSZ:

[0045] The solid sticks to the sheet and the sheets can only be separated with resistance; the solid is very difficult to remove and in some cases cannot be removed completely; unsuitable.

[0046] ZrO.sub.2 Solid 300 ?m Ceramic from CeramTec 5YSZ:

[0047] The solid sticks to the sheet and the sheets can only be separated with resistance. The solid is very difficult to remove and in some cases cannot be removed completely, and a an imprint of the solid appears on the opposite side; unsuitable.

ZrO.sub.2 Suspension from Sindlhauser Materials Type Zr-W-37:

[0048] The suspension shows poor wetting of the sheets in the brush application process. After annealing, the sheets are strongly stuck together in the sandwich and the coating cannot be removed from the coated sheets. In some cases, residues of the coating are found on uncoated sheet sides; unsuitable.

Y.sub.2O.sub.3 Suspension from Sindlhauser Materials Type Y-E-32:

[0049] The suspension shows good wetting of the sheets in the brush application process. The sheets can be separated well after annealing. There are no residues of the coating on the uncoated sheet sides. Additional microsection analysis showed that there is no surface diffusion into the sheet; suitable.

[0050] As can be seen from the above evaluation, some products are not suitable as release agents in high temperature service. Although ZrO.sub.2 spray and boron nitride spray are able to maintain sheet releasability, contamination of plants or products occurs because the flaking of the ZrO.sub.2 spray layer after high-temperature use requires special cleaning in sintering plants, and boron nitride spray borates the annealed material at the surface. In addition, the use of sprays is only suitable to a limited extent in a production environment with series production.

[0051] To the contrary, the use of a layer applied by means of Y.sub.2O.sub.3 suspension allows easy separation of Mo sheets annealed at 1900? C. The layer does not flake off the surface of the annealed material. The layer does not flake off the sheets and there is no diffusion of the layer into the surface of the sheets. Therefore, Y.sub.2O.sub.3 is excellent as a release agent in high temperature applications.

[0052] In another series of experiments, 1 mm molybdenum sheets (area 265 mm?265 mm) were coated on both sides with a Y.sub.2O.sub.3 suspension and used for several stacking anneals 1850? C. for 6 h in a hydrogen atmosphere as separator sheets between molybdenum charging sheets (each paired side by side; 2 mm?130 mm?260 mm). For stacking, a Mo Y.sub.2O.sub.3 separator plate was followed by two charging plates placed side by side, followed by a separator plate, and so on. The charging plate layers were rotated alternately by 90? to form a cross-layer structure. The stacks comprised between 20 and 25 charging plate layers. The separator sheets were still operational after 13 applications.

[0053] Due to the Y.sub.2O.sub.3 layer, sintering of the charging sheets does not occur. The stacked plates could also be separated again without problems after annealing. The Y.sub.2O.sub.3 layer adheres stably to the separator plates even after several applications. After heat treatment, the sheets can always be easily separated from each other. Moreover, no negative effects on the base material and the sintering furnace due to contamination were observed. It can be seen that Mo carrier plates with a thin Y.sub.2O.sub.3 layer on both sides are very well suited for high-temperature treatments of charging sheets. In particular, the multiple usability of such Y.sub.2O.sub.3-coated molybdenum separator plates results in a considerable economic and ecological advantage and over tungsten fines.