in Electroless Nickel Plating:
| Electroless nickel is far
superior to electrolytic nickel plating. It is characterized by the
Nickel has long been used as a plating material because of its excellent appearance coupled with good corrosion resistance. Prior to 1946, nickel coatings were applied to most substrates by using electricity (electroplating). However, in that year a process was discovered whereby a nickel phosphorous alloy coating was produced by chemical reduction on a catalytic metal surface – electroless nickel plating. Since that time methods have been developed that allow electroless nickel plating of most metals and also many nonmetallic substrates.
Most electroless nickel coatings contain 5 to 15% phosphorus. The high nickel, low phosphorous alloy deposited by chemical reduction without electric current is mil for mil more corrosion resistant than electroplated nickel. On properly prepared substrates it is virtually pore free. Also, unlike electrolytic nickel the thickness of electroless deposits is distributed evenly over the entire surface even of complex parts. Blind holes, threads, small diameter holes, recesses or internal areas receive the same amount of plating as sharp corners, edges or flat surfaces. Therefore, total thickness can often be reduced, close tolerances can be maintained, and although electroless nickel can be machined, subsequent machining to size is frequently eliminated.
One of the chief uses of electroless nickel has been preventing corrosion of metals. Thus electroless nickel has found ready acceptance in fields such as missiles and rocketry, oil refineries, chemical plant equipment, tank interiors, and many other mechanical and electrical applications. Due to its hardness, wear resistance, and uniform deposit thickness, electroless nickel has also found wide usage in the field of pumps, compressors, hydraulic pistons and other moving parts. In fact, electroless nickel should be considered wherever there is need for a hard, smooth, corrosion resistant, and uniformly distributed metallic coating. Since it has a natural lubricity and, therefore high resistance to abrasion, it has often proved superior to hard chrome plate. (Top of Page)
When applied to correctly prepared surfaces, electroless nickel deposits generally afford more corrosion resistance than equal amounts of electroplated nickel as demonstrated by years of successful commercial application. The low porosity combined with the characteristic uniformity of the deposit and its high inherent corrosion resistance results in excellent coatings for use in corrosive service.
To obtain maximum protection the importance of the surface preparation cannot be over emphasized. For example: salt spray corrosion generally starts out as pits. These pits form centers of galvanic corrosion, which in turn seem to accelerate additional pit formation. Any foreign matter included in the deposit such as slag, oxides, rust, or silicates from improper cleaning or rinsing, can easily form these centers (or cores) of the pits. Since proper surface preparation will eliminate many of these pits, it is of prime importance. Detailed corrosion test data listing over 170 common corrosive environments is presented in an article by W.H. Metzger, Jr. (Top of Page)
With proper surface preparation, excellent adhesion can be obtained. Metzger has reported bond strengths of 30,000-60,000 lbs. per square inch for electroless nickel on mild steel. On other substrates our electroless is generally lower.
Our electroless nickel coating has passed the 180 degree bend test specified by MIL-C 26074 without any sign of flaking. There will usually be macroscopic and microscopic cracks in the coatings parallel to the direction of bending. On properly prepared surfaces this cracking is not accompanied by flaking, but demonstrates that adhesion of the coating is greater the cohesion of the deposit. (Top of Page)
As plated, our electroless nickel deposits have an average Vickers (DPH) micro-hardness of 400-600. This can readily be increased to approximately 1,000 by heat treating at 400°C (750°F) for one hour. Further heating above 400°C tends to reduce the hardness, but at the same time increases the ductility due to the growth in crystal size. (Top of Page)
Due to the unusually high purity of the solution, our electroless nickel deposits are bright as compared to most other electroless nickel deposits. However, it must be clearly understood that by “bright electroless deposits” one must not think in terms of bright nickel deposits such as are common in commercial electroplating. Some solutions do build brightness but not to the same degree as electrolytic nickel baths. Our solutions preserve any of finish of the substrate surface. Thus, precision machined parts may frequently be plated with 1 to 3 mils of electroless nickel and put into service without further machining or polishing. (Top of Page)
Because our electroless nickel deposits are uniform in thickness, they permit the complex plating of intricate shapes and patterns. Industrial diamonds as small as 125 grit and the cavity of a 7 ton steel mold for molding plastic have been successfully plated with electroless nickel.
In electroplating, the distribution of nickel plate varies with current density. Since edges and sharp corners are high current density areas, there is a build up of electroplated nickel at these points. With the uniform deposit of electroless nickel, these variations are eliminated. If one mil of electroless nickel is deposited on the outside of a tube, then one mil will be deposited on the inside. A needle plated with electroless nickel is still a needle without nodular growth found in electroplated deposits. (Top of Page)
Electroless nickel deposits are covered by MIL-C-26074 entitled “Coatings, Electroless Nickel, Requirements for” and by SAE specifications AMS 2404A and AMS 2405.
These specifications spell out the requirements for the final coating and not the requirements of the solution or the process used to obtain the coating.
The requirements of specification MIL-C-26074 call out specific thickness, sampling procedures and special treatments such as baking for the relief of hydrogen enbrittlement. These, of course, are under the control of the plant doing the actual plating and not under that of the supplier of the plating solution. (Top of Page)
Options in Electroless Nickel Plating:
Erie Hard Chrome's newly-outfitted nickel plating facilities deliver the best surface preparation, process chemicals, finishes, and overall results currently obtainable. Several options are available:
Coefficient of Static Friction <0.1
Excellent wear resistance
Great material release
55 RC as plated, Heat treated to 62RC
Uniform deposit distribution of Boron Nitride particles
Click Here for more data on our Millenium KR product
- Excellent Corrosion reduction
- Mold Based (water lines)
- Parts in a corrosive environment
- Uniform distribution
- Repairs and sizing can be done precisely
- Natural Lubricity
- Excellent release
- Anti-galling properties
- Molding and sliding areas
- Non-erosive characteristics
- Low porosity
- Excellent adhesion
- Best for parts exposed to wear in corrosive environment
Hardness rating of 62RC
Replacement for chrome in certain applications
Close tolerances can be easily maintained
- High lubricity
- Great for use on slides
- Excellent release
- Has resolved some stubborn sticking problems