High density of micro cracks of chrome layer

Micro-cracks in Hard Chrome

The number of "cracks" in a given distance affects the properties of chrome plating. Almost all electroplated hard chromium deposits are cracked.

Cracking occurs during the plating cycle when internal stress exceeds the tensile strength of the chromium, which is hard and brittle. The width, depth and population density of these micro-cracks varies widely and is influenced by the following: the type of plating chemistry used (single-catalyst, mixed catalyst, proprietary), chromic acid concentration, type and concentration of catalyst, chromium-to-catalyst ratio, plating current-density, bath temperature, concentration of bath impurities (iron, copper, zinc, nickel, trivalent chromium, etc.) chromium deposit thickness surface condition of substrate.

If the conditions during plating cause the cracks to be coarse in nature, they are often referred to as macro-cracks.

Cross Section at 400 magnification
Standard chrome deposit. Large deep cracks extend down to base metal serve as pathways for corrosion.

Usually, chromium with this type of microstructure exhibits less desirable properties in service. It should be noted that macro-cracking can occur in chromium deposited over any type of substrate, not just those that are already stressed in tensile.

Generally speaking, a structure of high density of micro-cracks which is comprised of a high population density of narrow, shallow cracks is desirable, because the deposit tends to have a lower stress, higher lubricity, good wear resistance and better corrosion resistance.

Cross Section at 400 magnification
Standard chrome deposit. The greater number and smaller sized micro-cracks provide better lubricity and corrosion resistance. But the corrosion can still arrive at base material.

Multilayer chrome plating is the solution at this problem

Our chrome plating process is a combination of these two solutions (high density of micro cracks and multilayer chroming), to obtain at end a layer of chromium that may prevent corrosion of base steel.

Multilayer chrome deposit
The great number of micro cracks and their non-correspondence provide increased protection to the corrosion. The corrosion don't arrives at base steel.

Because the correspondence probability of micro cracks of each chrome layer tends to zero, the multi-layer process offers increased protection from corrosion and lower wear, with a three-layer structure with high density of micro cracks. The final result, with a total layer thickness of 60µm and more, assures superior corrosion protection and is less affected by thermal stress and wear.