ASTM B764-04(2021)

Standard Test Method for Simultaneous Thickness and Electrode Potential Determination of Individual Layers in Multilayer Nickel Deposit (STEP Test)

SIGNIFICANCE AND USE
4.1 The ability of a multilayer nickel deposit to enhance corrosion resistance is a function of the difference in the electrode potentials of the nickel layers (as measured individually at a fixed current density in a given electrolyte versus a reference electrode) and the thicknesses of the layers. The potential differences must be sufficient to cause the bright nickel or top layer to corrode preferentially and sacrificially with respect to the semi-bright nickel layer beneath it.  
4.2 This test procedure allows the measurement of these potential differences directly on an electroplated part rather than on separate foil specimens in such a way that time determines the thickness of each layer, while the potential difference between nickel layers is an indication of the corrosion resistance of the total nickel deposit.  
4.3 The interpretation and evaluation of the results of this test should be by agreement between the purchaser and the manufacturer.
Note 1: This test may be used as a quality assurance test of the multilayer nickel coatings applied in production. It should be understood that due to many factors that influence the progress of corrosion during actual use of the part, the performance of different multilayer nickel deposits in the test cannot be taken as an absolute indicator of the relative corrosion resistance of these deposits in service.
SCOPE
1.1 This test method closely estimates the thickness of individual layers of a multilayer nickel electrodeposit and the potential differences between the individual layers while being anodically stripped at constant current density.2,3  
1.2 This test method does not cover deposit systems other than multilayer electroplated nickel deposits.  
1.3 This standard does not purport to address all of the safety concerns, if any, associated with its use. It is the responsibility of the user of this standard to establish appropriate safety, health, and environmental practices and determine the applicability of regulatory limitations prior to use.  
1.4 This international standard was developed in accordance with internationally recognized principles on standardization established in the Decision on Principles for the Development of International Standards, Guides and Recommendations issued by the World Trade Organization Technical Barriers to Trade (TBT) Committee.

General Information

• Status: Published
• Publication Date: 31-Mar-2021
• ICS: 25.220.40 - Metallic coatings
• Technical Committee: B08 - Metallic and Inorganic Coatings
• Drafting Committee: B08.10 - Test Methods

Relations

• Refers: ASTM B504-90(2011) - Standard Test Method for Measurement of Thickness of Metallic Coatings by the Coulometric Method
• Effective Date: 01-Oct-2011
• Refers: ASTM B456-11 - Standard Specification for Electrodeposited Coatings of Copper Plus Nickel Plus<br> Chromium and Nickel Plus Chromium
• Effective Date: 01-Jun-2011
• Refers: ASTM B456-11e1 - Standard Specification for Electrodeposited Coatings of Copper Plus Nickel Plus<br> Chromium and Nickel Plus Chromium
• Effective Date: 01-Jun-2011
• Refers: ASTM B456-03(2009) - Standard Specification for Electrodeposited Coatings of Copper Plus Nickel Plus Chromium and Nickel Plus Chromium
• Effective Date: 01-Sep-2009
• Refers: ASTM B504-90(2007) - Standard Test Method for Measurement of Thickness of Metallic Coatings by the Coulometric Method
• Effective Date: 01-Mar-2007
• Refers: ASTM D1193-06 - Standard Specification for Reagent Water
• Effective Date: 01-Mar-2006
• Refers: ASTM B456-03 - Standard Specification for Electrodeposited Coatings of Copper Plus Nickel Plus Chromium and Nickel Plus Chromium
• Effective Date: 10-Apr-2003
• Refers: ASTM D1193-99e1 - Standard Specification for Reagent Water
• Effective Date: 10-Feb-1999
• Refers: ASTM D1193-99 - Standard Specification for Reagent Water
• Effective Date: 10-Feb-1999
• Refers: ASTM B456-95 - Standard Specification for Electrodeposited Coatings of Copper Plus Nickel Plus Chromium and Nickel Plus Chromium
• Effective Date: 01-Jan-1995
• Refers: ASTM B504-90(2002) - Standard Test Method for Measurement of Thickness of Metallic Coatings by the Coulometric Method
• Effective Date: 23-Feb-1990
• Refers: ASTM B504-90(1997) - Standard Test Method for Measurement of Thickness of Metallic Coatings by the Coulometric Method
• Effective Date: 23-Feb-1990

Overview

ASTM B764-04(2021), "Standard Test Method for Simultaneous Thickness and Electrode Potential Determination of Individual Layers in Multilayer Nickel Deposit (STEP Test)," provides a comprehensive methodology for measuring both thickness and electrode potential of individual layers within multilayer nickel electrodeposits. Known as the STEP Test, this method allows direct measurements on electroplated parts, helping determine key properties important for assessing and improving corrosion resistance of nickel coatings. This test method is vital for quality assurance and process control in industries utilizing multilayer nickel electroplating to enhance product lifespan and durability.

Key Topics

• Measurement Approach: Utilizes coulometric principles to simultaneously determine the thickness and electrode potential differences of individual nickel layers while being anodically stripped at a constant current density.
• Corrosion Resistance Assessment: Evaluates the effectiveness of multilayer nickel systems by analyzing the potential differences between layers, which is a critical indicator of prioritized and sacrificial corrosion behavior.
• Direct Testing on Components: Unlike traditional techniques that may require separate foil specimens, the STEP test is performed directly on the electroplated part, improving the relevance and immediacy of the assessment.
• Quality Assurance Use: Provides a rapid, destructive test for production environments, enabling manufacturers to monitor and maintain coating integrity during routine manufacturing.
• Result Interpretation: Requires cooperation between purchaser and manufacturer to agree upon meaningful evaluation criteria, as STEP test results may vary based on several operational and material factors.

Applications

• Electroplated Nickel Quality Control: Widely used in industries producing automotive parts, appliances, electronic components, and decorative hardware, where multilayer nickel offers superior corrosion protection.
• Process Optimization: Enables plating facilities to adjust nickel layer compositions and thicknesses to achieve desired performance targets based on real measurement data.
• Corrosion Resistance Validation: Assures end users and purchasers that multilayer nickel coatings meet specified performance standards for corrosion protection by validating the presence and effectiveness of bright and semi-bright nickel layers.
• Research and Development: Supports material scientists and engineers in developing new or improved nickel electrodeposit formulations by providing empirical data on electrochemical properties of layered coatings.
• Benchmarking and Calibration: Serves as a calibration tool for thickness testing equipment, relying on traceable reference standards to ensure consistency and traceability in measurement.

Related Standards

• ASTM B456 - Specification for Electrodeposited Coatings of Copper Plus Nickel Plus Chromium and Nickel Plus Chromium; closely related in defining requirements for multilayer nickel and nickel-chromium systems.
• ASTM B504 - Test Method for Measurement of Thickness of Metallic Coatings by the Coulometric Method; foundational to the electrochemical stripping principles utilized in the STEP Test.
• ASTM D1193 - Specification for Reagent Water; ensures purity requirements for test procedures are maintained.
• National Institute of Standards and Technology (NIST) SRM 2350 – Provides certified reference materials for coating thickness and potential difference calibration.

Practical Value

Adhering to ASTM B764 ensures effective quality assurance and standardized reporting for multilayer nickel deposit systems. By measuring both thickness and electrode potentials simultaneously, manufacturers can confirm that coatings will perform as intended in real-world environments, thus reducing the risk of premature failure or costly corrosion-related issues. The standard promotes international trade by supporting consistent test practices and compliance with widely recognized methodologies.

Keywords: multilayer nickel, STEP Test, electrode potential, nickel coating thickness, corrosion resistance, quality control, ASTM B764, electroplating standards, electrodeposited nickel, surface finishing.

Standards Content (Sample)

This international standard was developed in accordance with internationally recognized principles on standardization established in the Decision on Principles for the
Development of International Standards, Guides and Recommendations issued by the World Trade Organization Technical Barriers to Trade (TBT) Committee.
Designation: B764 − 04 (Reapproved 2021)
Standard Test Method for
Simultaneous Thickness and Electrode Potential
Determination of Individual Layers in Multilayer Nickel
Deposit (STEP Test)
This standard is issued under the fixed designation B764; the number immediately following the designation indicates the year of
original adoption or, in the case of revision, the year of last revision. A number in parentheses indicates the year of last reapproval. A
superscript epsilon (´) indicates an editorial change since the last revision or reapproval.
1. Scope 3. Summary of Test Method
1.1 This test method closely estimates the thickness of
3.1 This procedure is a modification of the well-known
individual layers of a multilayer nickel electrodeposit and the
coulometric method of thickness testing (Test Method B504).
potential differences between the individual layers while being
It is also known as the anodic dissolution or electrochemical
2,3
anodically stripped at constant current density.
stripping method.
1.2 This test method does not cover deposit systems other
3.2 Coulometric thickness testing instruments are based on
than multilayer electroplated nickel deposits.
the anodic dissolution (stripping) of the deposit at constant
1.3 This standard does not purport to address all of the
current, while the time is measured to determine thickness.As
safety concerns, if any, associated with its use. It is the commonly practiced, the method employs a small cell that is
responsibility of the user of this standard to establish appro-
filled with an appropriate electrolyte, and the test specimen
priate safety, health, and environmental practices and deter- serves as the bottom of the cell. To the bottom of the cell is
mine the applicability of regulatory limitations prior to use.
attached a rubber or plastic gasket whose opening defines the
1.4 This international standard was developed in accor- measuring(stripping,anodic)area.Ifametalliccellisused,the
dance with internationally recognized principles on standard-
rubber gasket also electrically insulates the test specimen from
ization established in the Decision on Principles for the the cell.With the specimen as the anode and the cell or agitator
Development of International Standards, Guides and Recom-
tube as the cathode, a constant direct current is passed through
mendations issued by the World Trade Organization Technical the cell until the nickel layer is dissolved. A sudden change in
Barriers to Trade (TBT) Committee.
voltagebetweentheelectrodesoccurswhenadifferentmetallic
layer starts to dissolve.
2. Referenced Documents
3.3 Each different metal or species of the same metal
2.1 ASTM Standards:
requires a given voltage to keep the current constant while
B456 Specification for Electrodeposited Coatings of Copper
being stripped. As one nickel layer is dissolved away and the
Plus Nickel Plus Chromium and Nickel Plus Chromium
next layer becomes exposed, there will be a voltage change
B504 Test Method for Measurement of Thickness of Metal-
(assuming a constant current and difference in the electro-
lic Coatings by the Coulometric Method
chemical characteristics of the two nickel layers). The elapsed
D1193 Specification for Reagent Water
timeatwhichthisvoltagechangeoccurs(relativetothestartof
the test or previous voltage change) is a measure of the deposit
thickness.
ThistestmethodisunderthejurisdictionofASTMCommitteeB08onMetallic
and Inorganic Coatings and is the direct responsibility of Subcommittee B08.10 on
3.4 At the same time, the amplitude of the voltage change
Test Methods.
canbeobserved.Thatis,theease(ordifficulty)withwhichone
Current edition approved April 1, 2021. Published May 2021. Originally
approved in 1986. Last previous edition approved in 2014 as B764 – 04(2014) .
layer can be dissolved or stripped with reference to another
DOI: 10.1520/B0764-04R21.
layer can be compared. The lower the voltage needed the more
For discussion of this test, see Harbulak, E. P., “Simultaneous Thickness and
active the metal or the greater the tendency to corrode
Electrochemical Potential Determination of Individual Layers in Multilayer Nickel
Deposits,” Plating and Surface Finishing, Vol 67, No. 2, February 1980, pp. 49–54. preferentially to a more noble metal adjacent to it.
3.5 Where the metallic layers are of such a similar nature
U.S. Patent 4,310,389. Assignee: The Chrysler Corp., Highland Park, MI
48203.
that change of the stripping voltage is small, there can be
For referenced ASTM standards, visit the ASTM website, www.astm.org, or
problems in detecting this change if the voltage between the
contact ASTM Customer Service at [e-mail]. For Annual Book of ASTM
deplating cell (cathode) and the sample (anode) is measured.
Standards volume information, refer to the standard’s Document Summary page on
the ASTM website. As the sample is dissolved anodically, cathodic processes are
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United States
B764 − 04 (2021)
occurring on the deplating cell (cathode) surface that can also 5.2 Constant Current Source—This should supply a con-
give rise to voltage changes, due to alterations of the cathode stant current that can be varied between 0 and 50 mA (typical
surface, thus obscuring the anode voltage change. This diffi-
25 to 35 mA). A current of 30 mA corresponds to a stripping
culty can be avoided by measuring the potential of the
rate of 7.8 µm/min at 100 % current efficiency when used with
dissolving anodic sample with respect to an unpolarized third
a gasket providing 0.08 cm stripping area. (This is achieved
electrode (reference) placed in the cell. By recording this
with the solution stated in 5.1.) Most commercial coulometric
potential any difference in electrochemical activity between
thickness testers can be used as the current source.
layers is more readily detected. The equipment may be
5.3 Electrolyte Agitation Source—All commercial coulo-
calibrated against standards with known STEP values.
metric thickness testers incorporate a means to agitate the
3.6 The thickness of any specific nickel layer may be
solution. It is possible to purchase these types of units
calculated from the quantity of electricity used (current multi-
separately, if so desired, to be used externally in conjunction
plied by time), area dissolved, electrochemical equivalent of
with other power supplies.
nickel, anode efficiency, and density of the nickel layer.
5.4 Recorder—Any time-based recorder with an input im-
3.7 Commercial instruments using this principle are avail-
pedance of at least 1.0 MΩ and capable of running at
able. They are usually a combination coulometric and STEP
approximately 0.5 mm/s (3 cm/min) can be used.
instrument. Reference standards are available to calibrate the
instrument. The STEPTest, as is the Coulometric Test, is rapid
5.5 Deplating Cell—The cell may be similar in construction
and destructive to the coating.
to commercially available coulometric deplating cells. It is
usually a cup-shaped cell of either 316 stainless steel, copper-
4. Significance and Use
nickel alloy, or plastic that engages a round rubber or plastic
4.1 The ability of a multilayer nickel deposit to enhance
gasket to the work piece or sample. The opening through the
corrosion resistance is a function of the difference in the
cell and gasket allows contact of the electrolyte to the test
electrode potentials of the nickel layers (as measured individu-
specimen and defines the stripping area.
ally at a fixed current density in a given electrolyte versus a
NOTE 2—A coulometric deplating cell could be constructed of plastic
reference electrode) and the thicknesses of the layers. The
using a cylindrical stainless steel or copper-nickel alloy sheet cathode
potential differences must be sufficient to cause the bright
located in the larger upper area of the cup. The advantages of such a cell
nickel or top layer to corrode preferentially and sacrificially
are the prevention of whisker growth and the choking off of the small bore
with respect to the semi-bright nickel layer beneath it.
opening, and the ease of cathode removal for cleaning or replacement.
4.2 This test procedure allows the measurement of these
5.6 Reference Electrode—Either silver or platinum wire of
potential differences directly on an electroplated part rather
approximately 1.5 mm in diameter can be used. Silver is
than on separate foil specimens in such a way that time
probably the better choice due to its ability to form a
determines the thickness of each layer, while the potential
silver-silver chloride electrode when used in a chloride con-
difference between nickel layers is an indication of the corro-
taining electrolyte. The tip of the reference electrode should
sion resistance of the total nickel deposit.
extend so that the distance between the tip of the electrode and
4.3 The interpretation and evaluation of the results of this the bottom of the agitator tube is approximately 5 mm.
test should be by agreement between the purchaser and the
NOTE 3—It is necessary to condition the silver electrode before using in
manufacturer.
order to form the silver-silver chloride surface. This is easily done by
anodically treating approximately a 75-mm length of wire in 1 N
NOTE 1—This test may be used as a quality assurance test of the
hydrochloric acid solution for 10 to 15 s using 35-mAanodic current.This
multilayer nickel coatings applied in production. It should be understood
will form a gray film on the wire, which should always be present. Once
that due to many factors that influence the progress of corrosion during
the gray film is formed, it is not necessary to repeat the conditioning
actual use of the part, the performance of different multilayer nickel
treatmentunlessthefilmhasbeenremoved.Itmaybeadvisable,however,
deposits in the test cannot be taken as an absolute indicator of the relative
to recondition the electrode after a prolonged period of inactivity or when
corrosion resistance of these deposits in service.
the electrode has been allowed to remain dry for an extended period of
time. Drying off the electrode should be avoided by immersion in either
5. Apparatus
the hydrochloric acid conditioning solution, the step test solution, or
5.1 Composition of the Electrolyte :
distilled water when not in use.
Nickel Chloride (NiCl ·6H O) 300g/L
2 2 NOTE 4—A ceramic junction reference electrode that does not require
Sodium Chloride (NaCl) 50g/L
conditioning is available commercially.
Boric Acid (H BO)25g/L
3 3
A
pH 3.0
5.7 Millivolt Meter (optional)—When using a sensitive and
well-calibrated recorder, a millivolt meter is not necessary. If
A
The pH may be adjusted with diluted hydrochloric acid or sodium hydroxide, as
one is desired, however, any sensitive, high-input impedance
required, and is more critical than the composition of the electrolyte.
meter can be used.Astandard pH meter with a millivolt setting
Prepared in Purified Water—Type IV or better as specified
would be satisfactory.The meter should have a range from 0 to
in Specification D1193.
2000 mV. If a millivolt meter is used which has low-output
impedance facilities, it can be used in parallel to drive the
5 recorder and will serve as a buffer amplifier. Most laboratory
Electrolyte can be obtained commercially that meets the requirements of this
test. pH meters have such output terminals.
B764 − 04 (2021)
6. Procedure 6.10 Stop the test by turning off the agitator, constant
current source, recorder, and milliampere meter. Remove the
6.1 Set up equipment as recommended by the manufacturer.
electrode assembly, if necessary, and empty the cell of the
If necessary, turn on the recorder and the millivolt meter and
strippingsolution.Washthecellthreetimeswithpurifiedwater
allow them to warm up.
(Type IV or better as specified in Specification D1193) before
6.2 If chromium is present on the nickel surface, remove it
continuing to the next test.
with concentrated hydrochloric acid. Make sure the nickel
6.11 This test is based on a measured current-time relation-
surface is clean. Rinse well and dry off the surface.
ship necessary to remove a given amount of nickel from a
specific area.
NOTE 5—Chromium can be removed by using the coulometric deplat-
ingcellasisdoneonmanycommercialcoulometrictesters.Ifthisisdone,
Example: if the constant current source produces 30 mA, the
secure the cell and gasket to the test piece as in 6.3 and 6.4 but do not
recordertimebaseis30mm/min,andthedeplatingareais0.08
insert the electrode assembly. Fill the cell with a common test stripping
cm , it would take 19.2 s to deplate 2.5 µm of nickel.The chart
solution for chromium (Test Method B504) and hook up only the cell and
would travel 9.6 mm.Ageneral equation that may be used is as
test piece to the power supply. Apply the current until all the chromium
hasbeenremoved.Adenseblanketofbubblesonthesurfaceofthesample
follows:
indicates that all the chromium is removed. Remove the stripping solution
SL A I
~ !~ !~ !
fromthecellwithoutmovingordisturbingthesealofthegaskettothetest
5 T (1)
surface. Wash the cell three times with purified water (Type IV or better ~0.303! S
as specified in Specification D1193) and once with the step test solution.
where:
Proceed to 6.5.
SL = chart scan length, mm,
6.3 Positionthetestspecimeninasecurehorizontalposition
S = chart speed, mm/min,
sothatthechromium-strippednickelsurfaceisdirectlybeneath
I = cell current, mA,
the cell gasket.
A = deplating area, cm,
T = nickel thickness, µm, and
6.4 Lower the coulometric deplating cell assembly; secure
0.303 = constant calculated from the electrochemical
by sealing the gasket to the nickel surface. A flat test area of
equivalent and density of nickel.
approximately 10 mm in diameter is desirable but not required.
NOTE 7—Commercial units are available that will modify and may
The criterion is that there be no leakage of the electrolyte. If
simplify the above procedure.
leakage does occur, discontinue test and start a new one.
6.5 Fill the coulometric deplating cell to the appropriate
7. Factors Affecting the Accuracy of the Method
level with the step test solution making sure that no air is
7.1 Excessive Metal Build-Up in Coulometric Deplating
trapped within the solution.
Cell—Excessive buildup of deposited nickel or the formation
6.6 Lower the reference electrode assembly into the coulo-
of “whiskers” on the inside of the coulometric deplating cell
metric deplating cell, if necessary. The positioning of the
(cathode), especially near the gasket hole, can cause erratic
reference electrode should be such that the distance from the
results and produce “noisy” curves. When buildup is observed,
end of the electrode to the test specimen is reproducible to
remove it completely according to the manufacturer’s instruc-
within 1 mm and be held constant throughout the test.
tions or as follows:
7.1.1 If a metallic cell is used as a cathode:
NOTE 6—The insertion depth of the electrolyte agitation tube which
7.1.1.1 Ream with a round, fine file. (Adrill or reamer may
includes the reference electrode is important and should always be the
same. The difference of potential rather than the absolute potential is the be used.)
important measurement.
7.1.1.2 Soak for 15 to 20 s in a solution of four parts
6.7 Check all electrical connections. Make sure all connec- concentratedsulfuricacidandonepartconcentratednitricacid.
If 316 stainless steel is used for the cell, it may be soaked in
tions are secure and that no corrosion exists at the contact
points and that all contact points are secure. concentrated nitric acid until all nickel is dissolved.
7.1.1.3 Rinse in water (Type IV or better as specified in
6.8
...