TESTING & MEASUREMENT
Electroless Nickel Plating Thickness Measurement and Phosphorous Analysis
What is Electroless Nickel Plating ?
Electroless Nickel Phosphorous ( ENP ) is a nickelphosphorous alloy ( NiP ) deposited by a chemical process , unlike the galvanic process of nickel electroplating that requires an electric current .
but can be significantly increased by heat treatment . Typical applications are in oil and gas exploration , where the environment can be corrosively acidic
In all cases the deposit is of uniform thickness , even in recesses and internal surfaces . However , agitation of the plating solution is needed to ensure a flow of solution over complex shapes and through internal bores .
How can we measure and verify that an ENP coating meets specification ?
Key deposit parameters are thickness , phosphorous content (% P ) and hardness
Thickness Measurement - primarily a function of immersion time , although the plating rate can vary with changes in plating solution chemistry , temperature , and pH , so regular checks and adjustments are needed .
A handheld Fischer DELTASCOPE ® FMP30 can be used for nondestructive thickness measurement of high phosphorous deposits ( non-magnetic when P > 10 %) on steel substrates .
DELTASCOPE ® FMP30 portable gauge with interchangeable probes for thickness measurements of high phosphorous electroless nickel on steel .
Phosphorous content (% P ) ranges from 2 % P to 14 % P , and specific plating bath formulations produce deposits with low phosphorous ( 2 % to 5 %), medium phosphorous ( 6 % to 9 %), and high phosphorous ( 10 % to 14 %) content .
Thickness ranges from a few microns for electronic applications to more than 75 microns for heavy duty corrosion resistance on rough surfaces .
Thickness and phosphorous tolerances are important parts of a coating specification and verification of compliance is vital to ensure correct functionality of the coating .
What is Electroless Nickel Plating good for ?
Low Phosphorous content (< 6 % P ) deposits exhibit a high hardness range as deposited and can be heat treated to further increase hardness and wear resistance . At maximum hardness it approaches the hardness of hard chrome , but with better corrosion resistance especially in alkaline environments such as chemical processing plants .
Medium Phosphorous content ( 6 % – 8 % P ) deposits are used for general corrosion resistance on steel , copper , or aluminium alloys , and provide a bright uniform hardwearing finish . It has a high plating rate and is used in decorative , industrial , and electronic applications .
High Phosphorous content (> 10 % P ) deposits are used where the greatest corrosion resistance is required . At > 10 % P the deposit is amorphous with no grain or phase boundaries that would otherwise provide initial corrosion sites . Hardness is relatively low as deposited
A portable FISCHERSCOPE ® X-RAY XAN ® 500 XRF system can be used for non-destructive thickness measurement for low , medium , and high phosphorous content ENP on steel and other substrates , especially for components that are too large for conventional chambers .
Extremely powerful portable XRF gun for electroless nickel thickness measurement on a wide range of substrates
Thickness measurement range using XRF is ~ 0.01 microns to 40 microns , depending on phosphorous content .
Conventional XRF ENP thickness applications use a fixed phosphorous
Extremely powerful portable XRF gun for electroless nickel thickness measurement on a wide range of substrates .
CONTINUED ON PAGE 58
56 OCTOBER 2021 read online : www . surfaceworld . com