GB2107742A

GB2107742A - Coating nickel containing alloys with titanium compounds

Info

Publication number: GB2107742A
Application number: GB08220189A
Authority: GB
Inventors: Dr August Muhlratzer; Edwin Erben
Original assignee: MAN Maschinenfabrik Augsburg Nuernberg AG
Current assignee: MAN AG
Priority date: 1981-08-07
Filing date: 1982-07-12
Publication date: 1983-05-05

Abstract

Nickeliferous alloys are coated with a titaniferous hard material layer by chemical vapour deposition. The alloy is pretreated by exposure to a gaseous phase with inert gas and/or hydrogen and a compound donating a non-metallic component, such as carbon or boron. In a subsequent stage deposition of the titaniferous hard material is effected preferably using TiCl4 together with a reaction gas. TiC, TiB2, TiCB or TiCN may be deposited using the appropriate gas.

Description

SPECIFICATION Method for coating nickeliferous alloys The invention relates to a method of coating nickeliferous materials particularly nickel-base alloys and highly nickeliferous steels.

Parts subject to high thermal and/or mechanical loads are normally made of hard, difficult to machine materials, such as tantalum or hard materials, such as carbides or similar materials. In order to economize on such costly materials and facilitate machining, said parts are occasionally machined from a less costly and less resistant material, and are then coated with a hard material. The required surface properties, such as resistance to wear and corrosion, are then governed by the hard material layer.

A combination of many uses is that of a core of a nickeliferous alloy with a titaniferous surface layer of a hard material.

Coating of nickel-base alloys and highly nickeliferous steels with titaniferous hard materials TiC, TiB2, TiC1~XBx or TiC,~xNx by chemical gaseous-phase deposition, however, often leads to the formation of the brittle intermetallic phase Ni3Ti. The inherently given intensive growth of the intermetallic phase on the surface of a part in contact with a titaniferous gas phase inhibits the formation of continuous layers of the titaniferous hard materials such as would be needed for wear resistance or protection from high-temperature frictional fusion. At best the layers obtained are heterogenous and consists of Ni3Ti with particles of the intended hard material imbedded therein. Such layers are rough and chip easily.Layers of this type are more particularly susceptible to the attack by gaseous injurious substances, because of the porosity inherent in their heterogeneous structure.

One object of the present invention is to enable the production of a consistant coating of titaniferous hard material on nickel-base alloys and highly nickeliferous steels.

According to the present invention we propose a method in which the base material of nickelbase alloy or highly nickeliferous steel is first exposed to a gaseous phase containing, apart from inert gas and/or hydrogen, only that species of gas which donates the non-metallic component, and in which subsequent deposition of the titaniferous hard material is achieved from the gaseous phase. It has been shown that said method will produce a strongly adhering and extremely dense layer, which accordingly will resist corrosion also at high-temperature conditions and which exhibits excellent wearinhibiting properties.

For the pre-treatment, use is preferably made of carbon for carbide and carbon nitride surface layers, of boron for boride surface layers, and of carbon or boron for carbon boride surface layers.

Suitable carbon donors are hydrocarbons containing at least three carbon atoms for each molecule, such as propane, butane or benzol.

Suitable boron donors are boron trichloride, boron tribromide and boranes of sufficiently easy handling properties.

Where temperatures below 1 0000C are used, the boron halogenides are preferably directed together with the hydrogen over the parts to be coated to suppress the formation of slowly evaporating metal halogenides in accordance with 4 Me+2 BX3 3MeX2+MeB2 (Me=Fe, Ni, Cr) since these will cover the surface and cause poor bonding.

In the pre-treatment a carbide or boride layer of a certain porosity forms on the surface of the alloy by diffusion-controlled reaction of one or several metals in the alloy with the carbon or boron from the gaseous phase. The remaining porosity of the layer will in the subsequent deposition of the hard material, lead to the formation of Ni3Ti to exactly a degree conducive.

to good bonding as a result of anchoring effect.

The concentration of the reactive gas components, the temperature and the exposure time are preferably selected such that the activity of the titanium in the gaseous phase is maintained at a relatively low level in both absolute terms and in comparison with the activity of the reactant donating the nonmetallic component of the hard material.

Preferably, the conditions are such as to permit deposition to take place at a temperature between 8000 and 1 1000C and a gaseous phase containing maximally 2% TiCI4.

For producing a TiC layer, the temperature range from 9500 to 1 0500C has proved especially advantageous. For producing a TiB4 layer, the temperature range between 9000 and 10000 and a TiCi4 content of maximally 0.5% has proved especially advantageous.

Example 1 A nickel-base alloy, e.g. of a composition of 22% Cr, 9% Mo, 19% Fe, Si, Mn, remainder nickel, as known by its trade name of Hastelloy X, was coated with TiC as follows.

After evacuation and flushing and deposition facility as commonly practiced in chemical vapor deposition (CVD) work, the parts to be coated were heated to a temperature of 9500 to 1 0500C in inert gas (e.g. argon). Thereafter, propane, butane or benzol was admitted until its content amounted to 5% to 10% by volume and directed over the parts to be coated. The process was continued for 30 to 60 minutes at the lower temperature limit, and for 10 to 20 minutes at the upper temperature limit. In the process a carbide layer of a certain residual porosity was formed.

The hydrocarbon was then removed by flushing with argon. The subsequent deposition of TiC took place at a consistent temperature and at a pressure of 50 to 200 mbar. For the formation of TiC, use was made of TiCI4 and CH4 in a hydrogen atmosphere, which were directed over the parts to be coated at a molar ratio CH4:TiCI4=5:1. The hydrogen content of the gaseous phase was 89%.

Example 2 In the coating of a nickel-base alloy in accordance with Example 1 with TiB2 the parts to be coated are heated to 9000 to 10000C in inert gas. A nearly continuous metal boride layer is formed on the surface of the parts by directing 5 to 10% by volume BCI3 flow is simultaneously reduced so that the resulting gaseous phase is 1 96% H2, 0.1 to 0.5% TiC14 and 0.5 to 3.5% BCI3.

The molar ratio TiCI4:BCI3 should be between 3 and 10, preferably 5 to 7.

In the two examples above the molar ratio CH4:N2 (or NH3) or BX3 (X=CI, Br):N2 to be selected for the deposition of the mixed phases TiCxN,~x and TiBxN,~x depends on the stoichiometry desired. This has no bearing on the principal intention to set a high nonmetal-to-Ti ratio in the gaseous phase.

In the examples above, hard material layers were produced which gave excellent bond and density, which makes them excellent corrosioninhibiting layers. They also had excellent wearinhibiting properties.

Claims

1. A method for coating nickeliferous materials with titaniferous hard material layers, wherein, the base material is pre-treated by exposure to a gaseous phase which apart from inert gas and/or hydrogen contains only that species of gas which denotes the non-metallic component, and thereafter, deposition of the titaniferous hard material from the gaseous phase is effected.

2. A method according to Claim 1, wherein the base material is exposed during the pretreatment, to the gaseous phase at a temperature between 9000C and 1 1000C for a duration of from 10 to 60 minutes.

3. A method according to Claim 1 or 2, wherein the non-metallic component is carbon or boron, propane, butane or benzol, or boron trichloride or boron tribromide, being used as donators.

4. A method according to any one of the Claims 1 to 3, wherein during deposition of the titaniferous hard material the activity of the titanium in the gaseous phase is maintained at a relatively low level in both an absolute sense and in comparison with the activity of the reactant donating the non-metallic component of the hard material.

5. A method according to any one of the Claims 1 to 4, wherein for the deposition of the titaniferous hard material, use is made of TiCI4 together with a reaction gas.

6. A method according to any one of the Claims 1 to 4, wherein for the deposition of the titaniferous hard material, use is made of TiCI4 and CH4 in a hydrogen atmosphere at a CH4:TiCI4 molar ratio greater than 3:1, preferably 5:1.

7. A method according to any one of the Claims 1 to 4, wherein for the deposition of the titaniferous hard material, use is made of TiCI4 and BCI3 in a hydrogen argon atmosphere at a TiCI4:BCI3 molar ratio between 3 and 10, preferably 5 to 7.

8. A method according to any one of the preceding Claims, wherein for producing a TiC hard material layer, the deposition process takes place at a temperature between 8000C and 1 1000C, especially between 9500 and 10500C, at a pressure of 50 to 200, bar and a gaseous phase containing maximally 2% TiCI4.

9. A method according to any one of the Claims 1 to 7, wherein in that for producing a TiB2 hard material layer, the deposition process takes place at a temperature between 8000 and 1 1 000 C, especially between 9000 and 100000 and a gaseous phase containing maximally 0.5% TiCI4.

1 0. A coated nickel-base alloy or highly nickeliferous steel, when produced by this method according to any one of the preceding claims.

11. A coated nickel-base alloy or highly nickeliferous steel, substantially as hereinbefore described.