Electroless nickel plating is a popular choice in many industries, from electronics to automotive to aerospace engineering. One of the primary reasons for its popularity is its hardness, which can be increased exponentially with heat treatment. Additionally, electroless nickel coating does not lose its other sought-after qualities – such as excellent corrosion resistance – when treated with heat.
In contrast to hard chrome, which softens in response to heat, electroless nickel coating can be treated with heat to subtly or drastically increase the hardness of the plating. In fact, with the right amount of heat, electroless nickel coating deposits can exceed 1,000 VHN – a deposit hardness comparable to that of hard chrome.
Heat treatments on electroless nickel plating can be used for stress relieving and de-embrittlement on both pre- and post-plate treatments. Some electroless plating companies will also use heat treatment for a sustained length of time to diffuse the layer of nickel into steel, making the coating more flexible. Despite the diffusion, this process does not affect the superior corrosion protection offered by nickel.
Due to the increased hardness of electroless nickel that can be achieved with heat treatment, it is common practice. Heating to 300C – 400C for the duration of an hour is the standard practice. However the amount of phosphorous in the deposit will have an effect on the hardness that can be achieved.
Above 400C, there are some unusual changes to the deposit. At 600C, phosphorous has been noted to migrate to the surface of the deposit and oxidise. At 800C, the phosphorous vapourises from the surface.
It is recommended that heat treatment takes place in an inert atmosphere (like nitrogen), as air can cause the deposit to yellow. However, electroless nickel with a high phosphorous content will often not yellow when heat-treated in air. To remove phosphorous from the surface, it is recommended to heat-treat in moist hydrogen or forming gas. This will make the electroless nickel plating easier to solder and weld – useful if it is intended for the electronics industry. For soldering and wire bonding ease, along with high electrical conductivity, nickel boron electroless nickel is a good choice.
With heat treatment, the already versatile electroless nickel coating gains an even more significant number of possible applications, being used in a vast amount of industries. Preparation by a knowledgeable electroless plating company results in an almost limitless number of possible applications for the metal, with heat treatment being an invaluable solution to the need for a hard, durable nickel plating.