Nickel plating is an important electro deposition process for preserving steel, brass and other basis metals from corrosion. Plated as a bright deposit often combined with chromium, nickel is the most effective electroplated coating for preserving a decorative appearance for extended periods of time in corrosive environments. Nickel electro deposition is also popular for engineering applications as a non-decorative functional plate.
Bright nickel electroplated for decorative uses differs appreciably from non-decorative nickel deposits. The high sulfur content (>0.05%) of the bright deposit reduces its ductility and corrosion resistance. Bright deposits are typically deposited from the watts formulation (see below) with the addition of organic-sulfur brightening systems. Functional deposits are typically deposited from the watts bath without the addition of brighteners (commonly referred to as watts non-bright) or from sulfamate nickel chemistries (see below).
Brightness in nickel deposits is induced with organic-sulfur compounds that decompose at cathode surfaces forming very small particles of nickel sulfide which refine the grain size of the deposit at the cathode surface (plated part) by at least two orders of magnitude. The selection of brightener additions to the plating bath affects ductility, internal stress, electrical conductivity and corrosion resistance of the deposit, all in a negative manner. Nickel coatings stressed in tension reduce the fatigue strength of steel. Nickel deposits lose corrosion resistance, ductility and electrical conductivity as the amount of co-deposited sulfur or other impurities increases from the brightening system. The change of the above characteristics is a rather complex subject which is primarily dependent on the bath chemistry, but also to a lesser extent on the operational parameters of that chemistry. The following charts will provide general trends/properties of nickel as deposited from the three (3) traditional chemical systems: watts non-bright, watts bright (watts with organic brighteners) and sulfamate.
ELECTRICAL RESISTIVITY Type of Bath Resistivity, microhm-cm Watts, Organic brightener 10.00 Sulfamate 8.60 Watts 7.76 DUCTILITY Type of Bath Elongation % Watts, Organic brightener 4-5 Sulfamate 20-30 Watts 5-30 INTERNAL DEPOSIT TENSILE STRESS Type of Bath Stress, PSI Avg. Range Watts, Organic brightener 30,000 0-60,000 Sulfamate 0 15,000 Compressive-20,000 Watts 18,000 10,000-60,000Corrosion Resistance:
The corrosion resistance of nickel deposits is very complex and the object of much study. In general, as any impurity is added to the deposit, the nickel plate loses its ability to fight off corrosion. The most common deposit impurities are hydrogen, oxygen, carbon, sulfur, chloride and metallic impurities. Because the watts non-bright and sulfamate formulations do not co-deposit sulfur and carbon from a brightening system, they are more corrosion resistant.
In summary, for engineering applications where ductility and corrosion resistance of the deposit take precedence over a decorative finish, a watts non-bright or sulfamate formulation is the deposit of choice. If low internal stress is also a concern for parts that will be significantly deflected or bent, sulfamate nickel processes are superior. However, bear in mind that these deposits are not bright and as such do not have as high of an aesthetic appeal. The old adage “bright is right” does not always apply for engineered coatings!
In the first installment of our plating series, we covered the best methods for plating aluminum: chem film and anodize. Here, we’ll explore electroless nickel plating, a versatile finishing method that works well with many metals, including steel, copper, and aluminum alloys.
Electroless nickel plating uses a chemical reduction process to deposit an alloy of 90% nickel and 10% phosphorus onto the surface of a metal part. Promising excellent durability and an attractive cosmetic appearance, RoHS-compliant electroless nickel is a popular choice for various applications.
Parts we commonly send to our trusted third-party vendors for electroless nickel plating services include:
Shafts
Handles
Cosmetic Parts that require durable surfaces
Medical components
Connectors
Electroless nickel plating is a precision machine shop-friendly finishing method that boasts many benefits.
An excellent choice for parts that must withstand extreme environments, electroless nickel plating is highly resistant to salt water, carbon dioxide, hydrogen sulfide, and oxygen.
Because this plating method doesn’t require electric current, it can penetrate easily into a part’s corners, edges, and recesses, resulting in a highly consistent coating. The exceptional consistency makes it a great choice for assemblies requiring soldering.
Nickel-plated parts have a hardness level of 48 Rockwell C, which can be increased to up to 70 Rockwell C through heat treating.
Compared to finishing methods such as anodizing, which can add an unpredictable amount of buildup to a part’s surface, electroless nickel plating adds only about 0.001” of buildup, allowing us to hold the tightest tolerances of any plating method.
Electroless nickel plating is popular for its shiny silver appearance, which makes it a desirable choice for external parts. The luxe coating has a look similar to steel for a lower price point. It also resembles chrome without requiring an electricity-based finishing process.
As with all plating methods, there are factors you’ll need to consider when requesting electroless nickel plating services.
Features with internal or external threading may need to be masked to prevent buildup from accumulating on the threads. If you are unsure whether masking is necessary, just ask our team!
Although electroless nickel plating adds less buildup to parts than most finishing methods, it’s still important to plan for the 0.001” buildup it does produce. Be sure to communicate with your precision machining partner about your specified tolerances so that they can account for anticipated buildup during machining if necessary.
Reata subcontracts plating services to well-vetted members of our vendor network. Our high-level project management capabilities ensure you’ll receive exceptional electroless nickel plating services for your precision parts without having to do the heavy lifting yourself.
Request a quote today!