Nickel Electrodeposition Process For Improving High-temperature Ductility

Abstract

A process of electroplating nickel using an electrolyte containing a sulfte. The process is conducted at a temperature of 27.degree. C. or lower. The electrolyte may be used in either an acid or an alkaline bath.

Description

STATEMENT OF GOVERNMENT INTEREST

The invention defined herein may be manufactured and used by or for the Government of the United States of America for governmental purposes without the payment of any royalties thereon or therefor.

CROSS-REFERENCE TO RELATED APPLICATIONS

The process described in this application is closely related to an application Ser. No. 829,215 now U.S. Pat. No. 3,582,480, filed June 2, 1969 for Heat Treating Process for Improving High Temperature Ductility of Electrodeposited Nickel and Nickel Alloys in the name of Juan Chorne.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The invention relates to the field of electroplating and, more particularly, to the electrodeposition of nickel at low temperatures.

2. Description of the Prior Art

A process known as the Barrett Sulfamate Nickel-Plating Bath and described in U.S. Pat. No. 2,318,592 to Martin E. Cunery is used to deposit nickel or nickel alloy. It consists of an electrolyte containing a sulfamate, which may be used in either an acid or an alkaline bath. An example bath would be made of sulfamic acid and nickel carbonate. It has been found that when the finished product is heated to temperatures above 450.degree. C. a severe embrittlement occurs. This embrittlement is a serious defect. The cause of this embrittlement is hydrogen which is deposited with the nickel. U.S. Pat. No. 2,534,911 recognizes this problem and attempts to remedy it.

SUMMARY OF THE INVENTION

The invention using a well-known process and altering the steps of this process is eliminating the embrittlement found in present whisker-reinforced composites at high temperatures and has increased the specific strength (strength-to-density) ratio.

The object of the invention is to change the present process of preparing whisker-reinforced composites by controlling the temperature to develop whisker-reinforced composites having high strength-to-weight ratios at elevated temperatures.

It is another object of the present invention to present a process similar to that of the known Barrett Sulfamate process but by carrying out the new process at low temperatures to produce a product that will be free of embrittlement when used at high temperatures.

It is a further object of this invention to provide a process for the electrodeposition of nickel so that the finished product will be ductile at high temperatures as well as normal working temperatures.

It is a further object of the present invention to provide a process for the electrodeposition of nickel, the process to be carried out at low temperatures to prevent the codeposition of hydrogen along with the nickel.

It is a still further object of the present invention to provide a process for the deposition of nickel at which the process is carried out at temperatures lower than 27.degree. C.

Other objects, advantages and novel features of the present invention will become apparent from the following detailed description of the invention when considered in conjunction with the accompanying drawing.

DESCRIPTION OF THE DRAWING

FIG. 1 is a graph showing minimum percent elongation in room temperature with relation to current density; and

FIG. 2 is a graph showing minimum percent elongation at room temperature relative to plating both temperature.

DESCRIPTION OF PREFERRED EMBODIMENTS

It is expected to achieve a specific strength of 600,000 (strength-to-density ratio) inches at 2,000.degree. F. in a conventional tensile test. The development of a technique for preparing whisker reinforced high-temperature metals, such as nickel or nickel alloys which reproducibly exhibit strength greater than 200,000 inches at 1,800.degree. F. The feasibility of reinforcing metals with high strength whiskers was demonstrated previously using what may be considered a model system of A1.sub.2 O.sub.3 whiskers in a silver matrix. Composites prepared by infiltering the A1.sub.2 O.sub.3 whiskers with molten silver exhibited strength-to-density values as high as 725,000 inches at room temperature with 24 volume percent whiskers and 320,000 inches at 1,600.degree. F. with 45 volume percent whiskers.

Later a more refractory matrix metal was selected in order to meet the elevated temperature criteria. The matrix selected was nickel, since it is the base for many of the high temperature, oxidation resistant alloys. It was found that molten nickel dissolved all metallic coatings applied to the whiskers resulting in dewetting, poor penetration and poor bonding. Several potential methods for fabricating nickel and nickel alloy matrix composites were explored and on the basis of these studies, it was concluded that the achievement of higher strength-to-density ratios at temperatures close to 2,000.degree. F. are feasible since small composites prepared by an electroforming technique exhibited specific strength values as high as 320,000 at 1,850.degree. F. However, these high strength values could not be achieved in larger electroformed specimens due to incomplete penetration of the whisker bundle of the electroplated nickel. Voids and other matrix irregularities resulted which greatly reduced the effective cohesive strength of the matrix and limited the transfer of stresses to the fibers at elevated temperatures. To heal these various matrix defects incurred during electroplating, an additional step, pressure bonding, was introduced.

Referring to FIG. 1 the minimum percent elongation in room temperature is shown relative to changes in current density expressed in amperes per square foot. Results are shown for a plating temperature of 58.degree. C., 41.degree. C. and 27.degree. C.

FIG. 2 illustrates the improvement in ductility with reduction of the plating bath temperature. While actual tests have not been conducted, as yet, below a 27.degree. C. temperature, calculations indicate the curve will follow the course shown in dashed lines.

With the electroplating pressure bonding process the results were marred by the embrittlement of the electroplated nickel matrix during exposures to the high temperatures used in the bonding process. The nature of the matrix embrittlement was concluded to be caused by a deposition of hydrogen along with the nickel during the electroplating process. The steps taken to avoid this embrittlement form the basis for the invention.

The making of high-strength composites by incorporating A1.sub.2 O.sub.3 whiskers in a nickel matrix employs an electroplating process followed by pressure bonding.

The following steps are the basic steps in this process:

1. The A1.sub.2 O.sub.3 whiskers are first given a thin metallic coating by a cathodic sputtering process using a variety of metals including W, Ti, Mo and others.

2. The coated whiskers are formed into an oriented mat.

3. The coated whisker mats are then given an additional coating of nickel by an electroplating process carried out at a temperature not exceeding 27.degree. C. and with a critical electric current density which is increased with a decrease in temperature to form a "prepreg" which is partially consolidated.

4. The "prepregs" are placed in a suitable die and heated to elevated temperatures in the range of 1,000.degree. to 1,400.degree. C. and then pressed in the die for final consolidation.

5. The resulting composites are tested in the temperature range ultimately intended for their use, 900.degree. to 1,100.degree. C. A "prepeg," as noted above, is an art term meaning preimpregnated and refers in this instance to the composite, whisker and nickel coating previous to the bonding step.

The electroplating of nickel without the addition of the whisker produces like results with regard to embrittlement.

While this is a comparatively small change, the results are that the ductility of the composite is greatly improved, the embrittlement of the nickel is almost eliminated and a useful composite is produced.

Obviously many modifications and variations of the present invention are possible in the light of the above teachings.

Claims

What is claimed is:

1. In the process of electrodepositing nickel using an electrolyte containing a sulfamate, the improvement which comprises conducting said electroplating at a temperature no higher than 27.degree. C.