MX2011010125A - Process for coating metallic components with nickel-boron alloys by chemical reaction. - Google Patents

Abstract

The present invention refers to a process for depositing, by immersion, a homogeneous film made of a nickel-boron alloy over metallic parts of ferrous alloys subjected to wear for increasing the hardness and resistance thereof to corrosion. The content of boron is of 3-6% by weight and 97-94% by weight of nickel, the thickness of the film may range from 2 Ám to 100 Ám, depending on the immersion time. The deposition does not require the use of an external electric current.

Description

Coating process of metallic components with nickel-boron alloys by chemical reduction.

Object of the invention The present invention relates to a process by which a homogeneous film of a nickel-boron alloy is deposited by immersion on metal parts of ferrous alloys subject to wear to increase its hardness and resistance to corrosion.

The boron content is 3-6% by weight and 97-94% by weight of nickel, and the thickness of the film can be carried out from 2 to 100 μm, depending on the immersion time. To perform the deposit, it is not necessary to apply an external electric current.

Background Since its implementation in commercially viable form in 1946 by Brenner and Riddell (Wolfgang Riedel, Electroless Nickel Plating, ASM International, Metal Park, Ohio USA, 1991), the processes for depositing nickel without the application of an electrical or electroless current for its name in English, they have grown from a laboratory curiosity to a multibillion dollar industry.

At present, progress is being made in the development of stable formulations and predictable behavior in long lifetimes of the baths and under different operating conditions. Electroless deposits are produced by the autocatalytic reduction of nickel ions in an aqueous solution, on the surface of a catalytic substrate using appropriate reducing agents (Wolfgang Riedel, Electroless Nickel Plating, ASM International, Metal Park, Ohio USA, 1991, Glenn O .

Mallory and Juan B. Hajdu; Electroless Plating Fundamentals and Applications, American Electroplaters and Surface Finishers Society (AESF) and Leena Das, Effect of Carbon Inclusion in Ferrous Substrate and Bath Stabilizer on the Porosity of Electroless Nickel Coating; Dissertation for the Degree PhD Chemical Engineering, June 10, 1996).

Ni-B coatings are being used in the aerospace, automotive, chemical, petroleum, electronics, textile and medical equipment industries, since there is a potential for applications that allow a better performance of the components that are coated with this alloy, These processes and the processes where Ni-P is applied have become the industrial catalytic coating processes normally in use with a growth rate of 5% per year as mentioned in Bolger Paul T. and Szlag David C. Investigation into the Rejuvenation of Electroless Spent Nickel Bats by Electrodialysis, Environ. Sci. Technol 2002 36, 2273-2278.

The first studies on acid baths to apply Ni electroless coatings, presented problems of stability of the baths, so that research work on stabilizing additives and depot speed improvers was initiated, for example, the work of Abd El- Rehim SS, Effect of Additives on Plating rate and Bath Stability of Electroless Deposition of Ni-Phosphorus-Boron on Aluminum, Metal Finishing, December, 29-33, (1996), who studied the influence of organic and inorganic additives; in the case of organic additives that had sulfonated anions, they improved the stability and the speed of Ni-PB coating on aluminum substrates, when they were added at low concentrations (100-300 mg / L), and at high concentrations they tend to decrease the deposit speed. In the case of inorganic additives, of which only C0CI2 was tested, it does not have an important influence on the deposition speed, the rest of the additives decrease the deposition speed.

Of the first works done with Ni-B are those of Shrivastava P.B., Venkatramani N., Rohatgi V.K., Totlani M.K. and Mital CK, Electroless Nickel Deposition on Ceramic and Cooper Surface, Metal Finishing, February, 65-70, (1985) and Doss S., Cañe F. and Ikeda H., Low Boron electroless nickel plated through hole process for printed and flexible circuit fabrication: advancements in quality, productivity and realiability, Sur-Fin (1997) 143-157, who developed Ni-B coatings with dimethylaminoborane or DMAB using Rochelle salt as a complexing agent. It can be seen in these works that the rate of deposit depends on the temperature, pH and concentration of the complexing agent. In Ni-B coatings there is no information as abundant as in Ni-P, Ni-B coatings have certain advantages over Ni-P, such as better substrate wettability characteristics, good weldability / brazability or brazing by its name in English and high melting point 1200-1400 ° C. In these works, the use of any bath stabilizing agent is not mentioned.

Of the problems presented by the baths of Ni alloys, it is identified that the stability of the baths is of the most important, many investigations have been made with different stabilizers such as those that have ions of lead, ions, odato, 2-Mercaptobensotiazol or 2-MBT, malic acid and sulfonate anions; it was determined that the stabilizers retard the deposition speed on the substrate and the carbon inclusions, decrease the phosphorus content in the coating and in addition sulfur and lead are co-deposited in the presence of 2-MBT and lead ions, respectively. An important aspect that was determined in the work: L. Das and D.T. Chin, Effect of Bath Stabilizers On Electroless Nickel Deposition On Ferrous Substrate, Plating & Surface Finishing, Agust 1996, pp 55-61; it is the porosity of the coating, which decreases when the MBT content is below 0.5 ppm, but increases linearly with the increase in the concentration of 2-MBT.

Another work, with Ni-P-B baths, where bath stabilizers such as cadmium sulfate, lead chloride, 2-MBT and sodium saccharin were used, was conducted by A. Talaat El-Mallah, M.Hassib, M.S. Morsy and E.M. Abdel-Meguid, Autocatalytic Alkaline Ni-P-B., Metal Finishing, July, 7-10, 1991; It was determined that there is a greater increase in stability when using PbC and 2-MBT in concentrations of 0.1 to 0.2 mg / L. Ni-P-B coatings with 2-MBT as a stabilizer produce coatings with the largest grain size, are not glossy and apparently have no attractive appearance We have basically identified two commercial processes to deposit Ni-B, processes where the reducing agent is based on borohydrides and baths where the reducer is DMAB, of the properties that have been identified from these deposits it can be mentioned that when the Ni deposits -B contain < of 2% by weight of B, the structure consists of solid solution of boron in microcrystalline nickel, when the boron content is about 6% by weight, the deposits are amorphous and when the content of B is 2-6% by weight it is a mixture of microcrystalline and amorphous phases. It is determined that the structure in the cross section is columnar which is the result of the nucleation and hemispheric growth of the deposits. With suitable thermal treatments, hardness higher than hard chromium can be achieved. It has also been determined that they exhibit surprising wear resistance. The only disadvantage that has been determined is that they have a slightly lower corrosion resistance to Ni-P alloys as mentioned in the article by Duncan RN, The Properties of Electroless Nickel Coatings Reduced with Boron Compounds, Journal of Applied Surface Finishing 1, (2), 2006, 133-142.

In most Ni-electroless coatings, lead is used to prevent spontaneous decomposition of baths and cadmium is used as a polish but decreases corrosion resistance; the levels in a working solution are below 2 ppm, but the codeposited quantity is 0.025-0.1% for lead and 0.1-0.2% for cadmium, but the problems are due to the cumulative effect on health and the impact on the environment environment, including ELV guidelines of the European Union, are requiring the disposal of hazardous materials such as lead, cadmium, hexavalent chromium and mercury, to make the vehicles easier to recycle and recover as mentioned in Kimberly's works Tress, Heatbath Corporation, Sprinfield, Massachusetts, Converting to Lead, Cad Free Electroless Nickel, Sur-End 2005 and Crotty DE, Lead and Cadmium Free Electroless Nickel Process for The 21st Century, Sur-Fin Proceeding 2005.

In all the Ni-B baths that are studied and developed for functional applications at present, the problematic regarding the stability of the baths during a relatively long time of use or waiting that they present when they are used as agents must be highlighted. reducers dimethylaminoborane or alkali metal hydrides; of all the consulted bibliography and mainly the US patents 3062666, 3234031, 3338726, 3373447, 3674447, 3738849, 4019910, 4407869, 4484988, 4983428, 5017410, 5019163, - 5269838, 5706999, 6183546 Bl, 6319308 Bl and the application for US2006 / 0151525 Al, stabilizers have been used to prevent spontaneous decomposition of baths, such as glycolic acid, organic compounds with bivalent sulfur, lead chloride, lead acetate, thallium sulfate, sodium cyanoborohydride, polyhydric acids, ions zirconil or vanadil, ethylene glycol, thiocarbanilide, lead nitrate, lead chloride and thallium mixture, thallium nitrate and thallium sulfate, and lead tunsgtanate.

In the present invention a new process for applying a Ni-B film on steels, copper alloys, aluminum alloys and on engineering metal alloys is presented. The objective is to obtain a process to apply an electroless Ni-B film free of Pb, Cd and Ta. Make a coating process, on metallic pieces of steel to increase the resistance to wear and corrosion that must be practical and easy to control, that contaminates less than the traditional electrolytic method, easy to scale at an industrial level and that can be automated.

Detailed description of the invention to the Alkaline Cleaning Bath An important step, in general for all coatings, is the initial cleaning of the parts to be coated, therefore extreme care should be taken at this stage. The recommended cleaning for the parts to be treated is known as alkaline cleaning.

The composition and operating conditions of this bath can be found in Table 1: Table 1 The pieces should be as clean as possible of the grease coming from the machining process, polishing and / or handling. Surface oxides due to inadequate storage will always provide a problem of adhesion and color change of the deposited material.

How to prepare the bathroom: I. The tribasic sodium phosphate is dissolved in a volume of water corresponding to 75% of the one to be used to prepare the bath, with constant agitation with a propeller-type stirrer at 200 rpm.

II. In another 12.5% of the volume of the water the sodium carbonate dissolves, until its total dissolution and it is added to the tribasic sodium phosphate solution.

III. Slowly add the sodium hydroxide to the solution containing tribasic sodium phosphate and sodium carbonate.

IV. Care should be taken to rinse the containers thoroughly, with the remaining 12.5% of the volume of water; taking into account that the liquid level of the solution to be prepared must be adjusted. b) Rinse with clean water Rinsing with clean water should be done by submerging the pieces several times and allowing the excess water to drain off the pieces. Countercurrent rinsing is recommended, however it can be done in standing water in a tub, considering that this water should be changed periodically, to avoid contamination of subsequent baths. c) Acid Pickling (Electroly cleaning) This surface pretreatment step of the parts and the above are designed to assist in the control of hydrogen embrittlement and to ensure maximum adhesion of the coating on the substrate.

The purpose of acid etching is to completely remove traces of oxide on the surface of the parts to be coated with Ni-B. The intensity of the treatment must be kept at the minimum required for the process. The concentration and conditions of this bath are shown in Table 2: Table 2 How to prepare the bathroom It is recommended to slowly add the acid to the water, with constant agitation with a propeller type agitator at 200 rpm, in such a way that the acid can drain through the walls of the bath container. d) Rinse with clean water Repeat the rinsing equal to that of stage b). e) Anodic Acid Attack (Activation) It is important to apply an anodic acid attack and its subsequent rinsing with water as final steps in the preparation of the surface of ferrous alloys to be subjected to the electroless Ni-B process to ensure a good Ni-B coating adhesion. The materials and operating conditions of this stage are shown in Table 3.

Table 3 Mode of preparation of activation bath or anodic acid attack: The acid is added to the water slowly with constant agitation with a propeller agitator at 200 rpm, until a homogeneous solution is obtained. This operation must be done in such a way that the acid can drain on the walls of the bathroom container. f Rinse with clean water Repeat the rinsing equal to that of stage b). i \ Electroless Ni-B Bath The procedures for the preparation of the surface of the parts to be coated should follow the methodology previously described to ensure the success in the coating. It is recommended to use the shortest possible time recommended in each stage of surface preparation. The concentration and application conditions of the Ni-B bath can be seen in Table 4.

TABLE 4 The boron content is 3-6% by weight and 97-94% by weight of nickel, and the thickness of the film can be carried out from 2 to 100 μm, depending on the immersion time. To perform the deposit, it is not necessary to apply an external electric current.

Bath preparation method: i. In 50% of the volume of water that will be used for the bath, the nickel sulphate dissolves, taking care that it does not present undissolved particles. ii. Add the sodium citrate little by little, trying a constant agitation until the salt dissolves in its entirety. iii. Add 2-mercaptobenzothiazole little by little until a complete solution is observed iv. Add the dimethylaminoborane complex also little by little until its complete dissolution. v. Let stand 24 hours before use. h) Rinse with clean water Repeat the rinsing equal to that of stage b).

\) Rinse with hot water As a final step and to help the drying of the pieces, a final rinse with water at 85-100 ° C for 3 minutes must be carried out, to then remove the pieces and pass them to the final inspection.

Claims (16)

Claims

1) A process for depositing by immersion a homogeneous film of a nickel-boron alloy on metal parts of ferrous alloys subject to wear, to increase the hardness and resistance to corrosion, characterized in that it comprises the following steps: a) Alkaline cleaning bath; b) Rinse with clean water; c) Acid pickling; d) Rinse with clean water; e) Anodic Acid Attack; f) Rinse with clean water; g) Electroless Ni-B bath; h) Rinse with clean water; i) Rinse with hot water.

2) A process for depositing by immersion a homogeneous film of a nickel-boron alloy on metal parts of ferrous alloys subject to wear to increase the hardness and resistance to corrosion, according to claim 1, characterized in that the composition and the conditions of operation of the alkaline cleaning bath of a) is comprised of: Sodium Carbonate (Na2C03), Sodium Hydroxide (NaoH) and Tribasic Sodium Phosphate (Na3P04 »12H20), at a temperature of 80 to 90 ° C, with a time of immersion of between 15 to 30 seconds and a cathodic current density of 30 - 55 A / dm2.

3) A process for depositing by immersion a homogeneous film of a nickel-boron alloy on metal parts of ferrous alloys subject to wear to increase the hardness and resistance to corrosion, according to claim 1, characterized in that the preparation of the cleaning bath alkaline of a) is carried out in the following way: I. The tribasic sodium phosphate is dissolved in a volume of water corresponding to 75% of the one to be used to prepare the bath, with constant agitation with a propeller-type stirrer at 200 rpm; II. In another 12.5% of the volume of the water the sodium carbonate dissolves, until its total dissolution and it is added to the tribasic sodium phosphate solution; III. Slowly add the sodium hydroxide to the solution containing tribasic sodium phosphate and sodium carbonate; IV. Care should be taken to rinse the containers thoroughly, with the remaining 12.5% of the volume of water; taking into account that the liquid level of the solution to be prepared must be adjusted.

4) A process for depositing by immersion a homogeneous film of a nickel-boron alloy on metal parts of ferrous alloys subject to wear to increase the hardness and resistance to corrosion, according to claim 1, characterized in that the rinsing with clean water of b), it must be done by submerging the pieces several times and allowing the excess water to drain off the pieces; countercurrent rinsing is recommended, however it can be done in standing water in a tub, considering that this water should be changed periodically, to avoid contamination of subsequent baths.

5) A process for depositing by immersion a homogeneous film of a nickel-boron alloy on metallic parts of ferrous alloys subject to wear to increase the hardness and resistance to corrosion, according to claim 1, characterized in that the composition and the conditions of Operation of the acid etching bath of c) is comprised of: Hydrochloric Acid (HCI at 35 vol.%), at a concentration of 40 to 50%, at room temperature, with an immersion time of 50 seconds and a current density cathode of 16 A / dm2.

6) A process for depositing by immersion a homogeneous film of a nickel-boron alloy on metal parts of ferrous alloys subject to wear to increase the hardness and resistance to corrosion, according to claim 1, characterized in that in the acid etching bath from c), the acid is added slowly to the water, with constant agitation with a propeller-type stirrer at 200 rpm, in such a way that the acid can drain through the walls of the bath container.

7) A process for depositing by immersion a homogeneous film of a nickel-boron alloy on metal parts of ferrous alloys subject to wear to increase the hardness and resistance to corrosion, according to claim 1, characterized in that the rinsing with clean water of e), it must be done by submerging the pieces several times and allowing the excess water to drain off the pieces; countercurrent rinsing is recommended, however it can be done in standing water in a tub, considering that this water should be changed periodically, to avoid contamination of subsequent baths.

8) A process for depositing by immersion a homogeneous film of a nickel-boron alloy on metal parts of ferrous alloys subject to wear to increase the hardness and resistance to corrosion, according to claim 1, characterized in that the composition and the conditions of operation of the anodic acid attack bath of e) is comprised of: Sulfuric Acid (H2SO4 at 35 vol.%), at a concentration of 300-400 ml / L, at room temperature, with an immersion time of 60 seconds and a cathodic current density of 10-43 A / dm2.

9) A process for depositing by immersion a homogeneous film of a nickel-boron alloy on metal parts of ferrous alloys subject to wear to increase the hardness and resistance to corrosion, according to claim 1, characterized in that the rinsing with clean water of f), it must be done by submerging the pieces several times and allowing the excess water to drain off the pieces; countercurrent rinsing is recommended, however it can be done in standing water in a tub, considering that this water should be changed periodically, to avoid contamination of subsequent baths.

10) A process for depositing by immersion a homogeneous film of a nickel-boron alloy on metal parts of ferrous alloys subject to wear to increase the hardness and resistance to corrosion, according to claim 1, characterized in that the concentration and the conditions of Application of the electroless Ni-B bath of g) is comprised of: Nickel Sulphate (N1SO4 · 6H20) at a concentration of 50 to 60 g / L, Dimethylaminoborane Complex (BH3NH (CH3) 2 at a concentration of 20 to 25 g / L, Sodium citrate (C6H5Na307 · 2H20) at a concentration of 40 to 50 g / L, 2- Mercaptobenzotiasol (C7H5N S2) (2MBT) at a concentration of 10 to 15 mg / L at a temperature of 60 to 70 ° C, with an immersion time of 30 minutes, at a pH of 6.0 and with constant agitation with a propeller type stirrer at 200 rpm.

11) A process for depositing by immersion a homogeneous film of a nickel-boron alloy on metal parts of ferrous alloys subject to wear to increase the hardness and resistance to corrosion, according to claim 1, characterized in that the preparation of the cleaning bath alkaline of a) is carried out in the following way: i. In 50% of the volume of water that will be used for the bath the nickel sulphate dissolves, taking care that it does not present undissolved particles; ii. Add the sodium citrate little by little, trying a constant agitation with a propeller type agitator at 200 rpm, until the salt dissolves in its entirety; iii. Add 2-mercaptobenzothiazole little by little until a complete solution is observed; iv. Add the dimethylaminoborane complex also little by little until its complete dissolution.

12) A process for depositing by immersion a homogeneous film of a nickel-boron alloy on metal parts of ferrous alloys subject to wear to increase the hardness and resistance to corrosion, according to claim 1, characterized in that the rinsing with clean water of h), it must be done by submerging the pieces several times and allowing the excess water to drain off the pieces; countercurrent rinsing is recommended, however it can be done in standing water in a tub, considering that this water should be changed periodically, to avoid contamination of subsequent baths.

13) A process for depositing by immersion a homogeneous film of a nickel-boron alloy on metal parts of ferrous alloys subject to wear to increase the hardness and resistance to corrosion, according to claim 1, characterized in that the rinse with hot water of i), it is carried out with water at 85-100 ° C for 3 minutes, to then remove the pieces and pass them to the final inspection.

14) A process for depositing by immersion a homogeneous film of a nickel-boron alloy on metal parts of ferrous alloys subject to wear to increase the hardness and resistance to corrosion, according to claims 1 and 10, characterized in that the boron content it is 3-6% by weight and 97-94% by weight of nickel.

15) A process for depositing by immersion a homogeneous film of a nickel-boron alloy on metal parts of ferrous alloys subject to wear to increase the hardness and resistance to corrosion, according to claims 1 and 10, characterized in that the thickness of the Film can be carried out from 2 to 100 μ? t ?, depending on the immersion time.

16) A process for depositing by immersion a homogeneous film of a nickel-boron alloy on metal parts of ferrous alloys subject to wear to increase the hardness and resistance to corrosion, according to claims 1 and 10, characterized in that in order to perform the Nickel-boron alloy deposit is not required to apply an external electric current.