EP0470878A1 - Anti-wear coating on a titanium based substrate - Google Patents

Abstract

• a) rugosification du substrat par sablage,
• b) dépôt d'une sous-couche d'accrochage de nickel par pulvérisation cathodique,
• c) étape intermédiaire de nettoyage
• d) activation par immersion de la pièce dans un bain cyanuré,
• e) dépôt de la couche finale anti-usure en Ag ou choisie dans le groupe formé par Cr, Ni, Co pris seuls ou en mélange entre eux avec ou sans particules céramiques telles que SiC, Cr₂C₃ , Al₂O₃, Cr₂O₃.

A process for depositing an anti-wear coating in Ag or chosen from the group of materials formed by Cr, Ni, Co, taken separately or as a mixture with or without ceramic particles such as SiC, Cr₂C₃, Al₂O₃, Cr₂O₃, on a titanium-based substrate is described. According to the invention, it comprises the following stages:

• a) roughening of the substrate by sandblasting,
• b) deposition of a nickel bonding sublayer by sputtering,
• c) intermediate cleaning step
• d) activation by immersion of the part in a cyanide bath,
• e) depositing the final anti-wear layer in Ag or chosen from the group formed by Cr, Ni, Co taken alone or as a mixture with or without ceramic particles such as SiC, Cr₂C₃, Al₂O₃, Cr₂O₃.

Description

The field of the present invention is that of methods of depositing anti-wear coatings on titanium or titanium alloy parts and the coatings thus obtained.

It is very difficult to obtain very adherent deposits on titanium and its alloys because of the great passivity of these.

It has already been proposed to subject a preliminary treatment to the parts to be coated before proceeding with the actual anti-wear deposit, in order to improve the adhesion thereof. It has thus already been proposed to carry out the following preliminary treatments:

Anodic attack in glycol mixtures - hydrofluoric acid, acetic acid;

Zinc predepot from glycol-metal fluoride mixtures or aqueous mixtures based on fluoroboric acid, hydrofluoric acid and metal salts;

Long-term pickling in hydrochloric or sulfuric acid - concentrated hydrochloric acid followed by iron, nickel or cobalt deposits in very acid baths.

In all these methods, it is necessary or recommended to combine the preliminary treatment with a heat treatment between 400 ° C and 800 ° C in a non-contaminating atmosphere with respect to titanium in order to improve the resistance of the metallic coating. However, this outfit is never excellent. In particular, the coating obtained does not withstand machining or grinding.

It has also been proposed in document FR-A-1 322 970 to carry out a preliminary treatment by chemical means in an oxidizing medium consisting in subjecting the part to the action of a bath of chromic anhydride, alkaline phosphate and acid hydrofluoric for 5 to 30 min at a temperature between 35 ° C and 100 ° C. However, this range has the double disadvantage of generating hydrides in the coating and of ensuring undesirable penetration of hydrogen into the substrate during subsequent electrolytic operations.

The invention therefore aims to overcome the aforementioned drawbacks, by eliminating the generation of hydrides by eliminating the prior chemical treatments of the substrate and by slowing the penetration of hydrogen into the substrate during the electrolytic process of depositing the anti-wear layer.

The invention also aims to allow an anti-wear deposit on titanium parts while reducing the fatigue drop compared to the previous methods and thereby allowing the use of coated titanium substrates for parts subjected to a cyclic fatigue, where the parts obtained by the previous processes do not allow it.

The object of the invention is therefore to produce a range of deposition in which the techniques of deposition of nickel by magnetron sputtering are combined in order to ensure a underlay particularly adherent to the substrate with an electrolytic deposit allowing the deposition of a final anti-wear layer.

The object of the invention is more particularly to define nickel deposition parameters by sputtering, compatible with subsequent electrolytic deposits.

• a) rugosification du substrat par sablage,
• b) dépôt d'une sous-couche d'accrochage de nickel par pulvérisation cathodique ;
• c) étape intermédiaire de nettoyage ;
• d) activation électrolytique par immersion de la pièce dans un bain cyanuré ;
• e) dépôt d'une couche de nickel électrolytique ;
• f) dépôt de la couche finale anti-usure en Ag ou choisie dans le groupe formé par Cr, Ni, Co, pris seuls ou en mélange entre eux avec ou sans particules céramiques telles que SiC, Cr₂C₃, Al₂O₃, Cr₂O₃.

The subject of the invention is therefore a method of depositing an anti-wear coating in Ag or chosen from the group of materials formed by Cr, Ni, Co, taken separately or as a mixture between them, with or without ceramic particles such as SiC Cr₂C₃, Al₂O₃, Cr₂O₃ on a titanium-based substrate characterized in that it comprises the following stages:

• a) roughening of the substrate by sandblasting,
• b) deposition of a nickel bonding sublayer by sputtering;
• c) intermediate cleaning step;
• d) electrolytic activation by immersion of the part in a cyanide bath;
• e) deposition of an electrolytic nickel layer;
• f) deposition of the final anti-wear layer in Ag or chosen from the group formed by Cr, Ni, Co, taken alone or as a mixture with or without ceramic particles such as SiC, Cr₂C₃, Al₂O₃, Cr₂O₃.

• b1) décapage ionique du substrat dans une enceinte à vide à une pression comprise entre 1.10ml et 50 Pa
• b2) nickelage par pulvérisation cathodique sous atmosphère inerte obtenue par introduction d'argon dans l'enceinte, à une pression comprise entre 2.10⁻¹ et 5 Pa.

According to a feature of the invention, step (b) can be carried out in two successive sub-steps, (b1) and (b2), carried out under an inert gas atmosphere, the two sub-steps being:

• b1) ionic pickling of the substrate in a vacuum enclosure at a pressure between 1.10 ml and 50 Pa
• b2) nickel-plating by sputtering under an inert atmosphere obtained by introducing argon into the enclosure, at a pressure between 2.10⁻¹ and 5 Pa.

Advantageously, step (b2) will be carried out by sputtering with a magnetron cathode, and preferably at a pressure between 0.4 and 0.8 Pa.

Other characteristics of the process will be specified below.

• Une couche de Ni déposée par pulvérisation cathodique magnétron et l'épaisseur comprise entre 3 et 7 microns.
• Une couche de Ni électrolytique obtenue par prénickelage en bain acide suivie d'un nickelage en bain sulfamate, ladite couche ayant une épaisseur comprise entre 18 et 20 microns.
• Une couche finale anti-usure en Ag ou d'un matériau choisi soit dans le groupe formé par Cr, Ni, Co, pris seuls ou en mélange entre eux avec ou sans particules céramiques telles que SiC Cr₂C₃, Al₂O₃, Cr₂O₃ ladite couche ayant une épaisseur supérieure à 80 microns.

The subject of the invention is also the parts thus obtained on a titanium-based substrate and comprising from the substrate to the surface:

• A layer of Ni deposited by magnetron sputtering and the thickness between 3 and 7 microns.
• An electrolytic Ni layer obtained by pre-nickel plating in an acid bath followed by nickel plating in a sulfamate bath, said layer having a thickness of between 18 and 20 microns.
• A final anti-wear layer of Ag or of a material chosen either from the group formed by Cr, Ni, Co, taken alone or as a mixture with or without ceramic particles such as SiC Cr₂C₃, Al₂O₃, Cr₂O₃ said layer having a thickness greater than 80 microns.

Other characteristics of the process according to the invention will be described in the supplement which follows, accompanied by 2 plates representing fatigue test curves in rotary bending on toroidal test pieces in TA6V, according to various finish states indicated. in legend for parts produced according to the state of the art defined by patent FR-A-1 322 970 or according to the invention.

The curves give the admissible stresses in rotary bending according to the number of cycles carried out.

• des barreaux de diamètre 30mm et de hauteur 80mm
• des plaques de 100 X 20 X 2 mm
• des alésages de diamètre 30mm et de hauteur 12mm percés dans des barreaux.

To describe the invention in more detail, the range of deposition will be explained on the basis of example of deposits made on test pieces of titanium alloy TA6V in the cast state. The test pieces used were as follows:

• bars of diameter 30mm and height 80mm
• plates of 100 X 20 X 2 mm
• bores of 30mm diameter and 12mm height drilled in bars.

We first carried out an operation of roughening the substrate, by dry sandblasting with corundum of 50 microns or by wet sandblasting with quartz of 40 microns, an operation which tests had demonstrated desirable to then obtain a satisfactory adhesion of the deposited nickel. in the following operations.

The parts are then placed in a vacuum enclosure in the range of high secondary vacuum, ie at a pressure between 3.10⁻⁴ and 3.10⁻¹ ^Pa.

The substrate is then subjected to an ionic pickling which cleans the substrate by removing material. To do this, the parts are placed in an inert gas atmosphere, for example argon injected into the enclosure under a pressure of between 1.10⁻¹ and 50 Pa while applies a negative voltage to the substrate in order to attract the ions to the substrate during the luminescent discharge produced in the enclosure. The operation can be performed in a range of power densities between 0.05 and 0.4 W / cm².
The tests showed that the preferred range was 0.1 to 0.15 W / cm² for a period of between 15 and 20 minutes.

After this ionic stripping operation on the substrate, a nickel bonding layer is deposited. For the reasons indicated above, the choice of deposition method fell on sputtering deposition.

Recall that this technique is a vacuum deposition process operating cold, in luminescent plasma, in a gas maintained at reduced pressure from 0.1 to 10 Pa. The material to be deposited, here nickel, called target and placed in cathode , is introduced into the vacuum enclosure in the form of a plate a few millimeters thick. The substrate is arranged in an anode.

At the residual pressure of the enclosure, the electric field created between the 2 electrodes causes the ionization of the residual gas which creates a luminescent cloud between the electrodes.

The substrate is then covered with a layer of the same material as the target, due to the condensation of atoms coming from the target under the impact of positive ions contained in the luminescent gas and attracted to the target due to its negative bias.

More precisely, in the invention, the choice was made to deposit the bonding nickel by sputtering with a magnetron cathode in order to increase the quality of adhesion of the nickel and to increase the speed of the deposit in order to obtain a range of a duration compatible with the requirements of industrial production.

With a magnetron cathode we combine with the electric field an intense magnetic field perpendicular to the previous one, ie parallel to the target. This superposition of the two fields has the effect of winding the electronic trajectories around the magnetic field lines, considerably increasing the chances of ionizing a gas molecule in the vicinity of the cathode. The ionization efficiency of the secondary electrons emitted by the cathode is increased due to the lengthening of their trajectories. This increase in ion density near the target results in a significant increase in the ion bombardment of the latter, hence an increase in the quantity of atoms ejected for the same applied voltage.

According to the invention the substrate to be coated placed in the anode position, has been polarized at a voltage between -20 and -500V.

The best results have been obtained between -100 and -150 V.

The target was made of pure nickel and it was bombarded with a power density between 70 and 700 W / dm², the choice of the bombardment power density of the target being made as a function of the temperature admissible by the substrate to be covered.

The spraying was carried out under an inert atmosphere in a pressure range between 0.2 and 5 Pa, the best results being obtained between 0.4 and 0.8 Pa.

To obtain a nickel deposit of 5 to 7 microns, durations of between 45 and 60 minutes have been sufficient, which has a notable advantage compared to the prior techniques which required several hours.

The part then undergoes an alkaline degreasing by soaking for 3 to 7 minutes (typically 5) in an aqueous bath containing 30 to 45 g / l of Turco 4215 NCLT or 40 to 60 g / l of Ardrox PST 39 (registered trademarks).

The part is then rinsed with cold water, checking the continuity of the water film.

An electrolytic activation of the part is then carried out by soaking it for one minute under a current density (ddc) of 1.5 to 3 A / dm² in an aqueous bath comprising from 60 to 80 g / l of KCN and from 10 to 50 g / l of K₂ CO₃.

The part is then rinsed again with cold water and electrolytic nickel-plating operations are carried out.

These are carried out in two successive stages:

- température

: 50 ± 5°C

- d.d.c.

: 6 ± 1A / dm² pendant 3mn
puis 4 ± 1 A/dm² pendant 10mn

dans un bain contenant :

- NiCl₂, 6H₂O

: 280 à 350 g/l

- Ni métal

: 69 à 86 g/l

- H₃BO₃

: 28 à 35 g/l

-e1) pre-nickel plating in an acid bath (pH 1.1) in the following operating conditions:

- temperature

: 50 ± 5 ° C

- ddc

: 6 ± 1A / dm² for 3 minutes
then 4 ± 1 A / dm² for 10 minutes

in a bath containing:

- NiCl₂, 6H₂O

: 280 to 350 g / l

- Ni metal

: 69 to 86 g / l

- H₃BO₃

: 28 to 35 g / l

The average thickness deposited is 15 microns.

The part is then rinsed with cold water.

- température

: 50 ± 5°C

- d. d. c.

: 2 A/dm² pendant 5 mn
puis 4A/dm² pendant 5 mn.

dans un bain contenant

- Ni sulfamate

: 75 à 90 g/l

- NiCl₂, 6H₂O

: 18 g/l

- ion chlorure Cl⁻⁻

: 3,75 à 5,60 g/l

- H₃BO₃

: 30 à 40 g/l

e2) nickel plating in a sulfamate bath under the following operating conditions:

- temperature

: 50 ± 5 ° C

- ddc

: 2 A / dm² for 5 min
then 4A / dm² for 5 min.

in a container bath

- Ni sulfamate

: 75 to 90 g / l

- NiCl₂, 6H₂O

: 18 g / l

- Cl⁻⁻ chloride ion

: 3.75 to 5.60 g / l

- H₃BO₃

: 30 to 40 g / l

The thickness of nickel deposited is between 3 and 5 microns.

The part is then rinsed with cold water.

The part can then receive its anti-wear coating such as coatings in Cr, Ni-Co, Ni Co SiC or Ag-Ni.

- température

: 54° ± 1°C

- d.d.c.

: 25 A/dm² pendant 10mn puis
: 20 A/dm² pendant 12 heures

dans un bain contenant :

- CrO₃

: 225 à 275 g/l

- H₂SO₄

: 2 à 3 g/l

- Cr ⁺⁺⁺

: 2,5 à 8 g/l

avec CrO₃ / H₂ SO₄ compris entre 90 et 120.A first example can be given with an electrolytic chromium coating obtained under the following operating conditions.

- temperature

: 54 ° ± 1 ° C

- ddc

: 25 A / dm² for 10 minutes then
: 20 A / dm² for 12 hours

in a bath containing:

- CrO₃

: 225 to 275 g / l

- H₂SO₄

: 2 to 3 g / l

- Cr ⁺⁺⁺

: 2.5 to 8 g / l

with CrO₃ / H₂ SO₄ between 90 and 120.

The average thickness obtained is between 120 and 150 microns.

Another example of an anti-wear coating is 29% Ni-Co.

The Ni / Co mass ratio used is 20 and the Ni + Co sum in solution is 87.5 g / l.

- température

: 50° ± 2°C

- pH

: 3,9 ± 0,1

- d.d.c

: 2 A/dm² pendant 10 mn puis
4 A/dm² pendant 3h25mn.

Nickel and cobalt are introduced into the bath in the form of nickel sulfamate Ni (NH₂ SO₃) ₂, 4 H₂O and cobalt sulfamate Co (NH₂SO₃) ₂, 4H₂O under the following operating conditions:

- temperature

: 50 ° ± 2 ° C

- pH

: 3.9 ± 0.1

- ddc

: 2 A / dm² for 10 min then
4 A / dm² for 3h25mn.

the parts are placed on a rotating assembly and the bath stirred with compressed air.

The average thickness obtained is 120 to 140 microns.

After obtaining one of the aforementioned anti-wear coatings, the part is rinsed with cold water then dried with compressed air, then undergoes degassing at 200 ° + 5 ° C for 3 h.

In order to determine the fatigue strength of titanium-based parts coated with anti-wear deposits according to the invention, fatigue tests in rotary bending on toric test pieces were carried out.

Coated test pieces according to the invention were therefore compared to coated test pieces according to the state of the prior art represented by the teaching of document FR-A-1322970.

The attached tables illustrate the operations that have been carried out. These tables are an integral part of this description.

Table 1 shows the treatment ranges applied to 56 test pieces, some of which were left at various stages of the coating process before subjecting them to rotary bending fatigue tests.
Table 2 illustrates the precise operating conditions for electrolysis carried out during the operations indicated in table 1.

The curves of plates 1 and 2 illustrate these results by showing, during the rotational bending fatigue tests, the variation of the stresses as a function of the number of cycles according to the state of finish of the parts and according to whether they were obtained by the invention. or according to the state of the art.

The curves show that the coated parts according to the invention have a much lower fatigue drop in rotary bending than those produced according to the state of the art illustrated by patent FRA 1,322,970.

The maximum admissible stresses after 10⁸ cycles, can be summarized from this table as follows, depending on whether the coatings (nickel plating alone, Ni Co, Cr) have been produced by means of the invention or according to the state of the art

Table 3 shows the results of vibration fatigue tests carried out, depending on the nature of the treatment carried out on each sample, the number of cycles and the maximum stresses applied.

If we compare the results of these tests on parts with the same level of coating, depending on whether the coating is obtained according to the invention and according to the state of the art, we can see the following points:

The fall in fatigue limit after 10⁸ cycles of parts having undergone only the nickel plating (therefore before final coating) is 61% if the part is obtained according to the state of the prior art, but only 23% if the part is obtained by PVD nickel and then electrolysis as recommended by the invention.

In the coated state, for chrome coatings 0.1 mm thick, the fatigue limit drop is 52% for parts according to the prior art and only 15% for parts according to l 'invention.

For 0.1mm nickel-cobalt coatings, the difference is even greater since the drop in fatigue limit of 67% for the state of the art, drops to 27% for the parts according to the invention.

The results indicated above show that the invention makes it possible to significantly limit the lowering of the fatigue limit of the parts coated with protective deposits relative to the uncoated substrate, both in vibration fatigue and in fatigue by rotary bending.

By thus realizing an industrially exploitable process (because of its comparatively limited durations compared to the state of the art) for producing reliable and durable anti-wear deposits on titanium alloy substrates, the invention makes it possible to make coated titanium, parts which previously could not have been used in a restrictive environment.

It is therefore possible to use titanium substrates, which are much lighter than the materials usually used for parts subjected to lasting fatigue stresses, both in rotational bending and in vibration fatigue.

Claims (11)

Method for depositing an anti-wear coating in Ag or chosen from the group of materials formed by Cr, Ni, Co, taken separately or as a mixture with or without ceramic particles such as SiC, Cr₂C₃, Al₂O₃, Cr₂O₃, on a titanium-based substrate characterized in that it comprises the following steps: a) roughening of the substrate by sandblasting, b) depositing a nickel bonding sublayer by sputtering, c) intermediate cleaning step d) activation by immersion of the part in a cyanide bath, e) deposition of an electrolytic nickel layer, f) deposition of the final anti-wear layer in Ag or chosen from the group formed by Cr, Ni, Co, taken alone or as a mixture with or without ceramic particles such as SiC, Cr₂C₃, Al₂O₃, Cr₂O₃. Deposition process according to claim 1, characterized in that step (b) consists of two successive substeps b₁ and b₂ carried out under an atmosphere of inert gas, said substeps being - b₁) ion stripping of the substrate in a vacuum enclosure at a pressure between 1.10⁻¹ and 50 Pa. - b₂) nickel-plating by sputtering under an inert atmosphere obtained by introducing argon into the enclosure, at a pressure between 2.10⁻¹ and 5Pa. Deposition method according to claim 2 characterized in that the sub-step b₂ is carried out at a pressure between 0.4 and 0.8 Pa. Deposition method according to one of claims 2 or 3 characterized in that step (b₂) is carried out by sputtering with a magnetron cathode. Deposition method according to one of claims 2 or 3 characterized in that the substrate to be coated placed in the anode position is polarized at a voltage between -20 and -500V. Deposition method according to claim 5, characterized in that the substrate is polarized at a voltage between -100 and -150V. Deposition method according to claim 6 characterized in that the target is made of pure nickel and in that it is bombarded with a power density of between 70 and 700 W / dm², the choice of the bombardment power density of the target being made as a function of the temperature admissible by the substrate to be covered. Deposition method according to any one of Claims 1 to 7, characterized in that the cleaning step c) is carried out by soaking the part in an alkaline bath for 3 to 7 min, followed by rinsing with water cold. Deposition method according to any one of Claims 1 to 7, characterized in that step (e) consists of two successive substeps: - e1) pre-nickel plating in an acid bath at 50 ° C + 5 ° C under a ddc of 6 ± 1 A / dm² for 3 minutes then under a ddc of 4 ± 1A / dm² for 10 minutes. - e2) nickel plating in a sulfamate bath under a ddc of between 2 and 4 A / dm² for 5 minutes. Deposition method according to claim 9 characterized in that it comprises rinsing with cold water between each of the steps d, e1, e2, and f. Part whose substrate is based on titanium, characterized in that it comprises from the substrate to the surface - a layer of Ni deposited by magnetron sputtering and with a thickness between 3 and 7 microns. a layer of electrolytic Ni obtained by pre-nickel plating in an acid bath followed by nickel plating in a sulfamate bath, said layer having a thickness of between 18 and 20 microns. - a final anti-wear layer in Ag or in a material chosen from the group formed by Cr, Ni, Co, taken alone or as a mixture between them, with or without ceramic particles such as SiC, Cr₂C₃, Al₂O₃, Cr₂O₃, said layer having a thickness greater than 80 microns.

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