Low Impedance Passivates for Electrical Connectors

S. M. Volz, J. B. Claypool, M. O'Keefe, and W. FahrenholtzMissouri S&T

S. GaydosBoeing

T. NahlawiDipsol of America

ASETSDefense Workshop6 Dec 2016

FY 15 SEED Statement of Need• Develop Technologies for the Passivation of Corrosion

Resistant Coatings used in DoD Electrical System Components that do not use Hexavalent Chromium

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• Must be Compatible with Low Hydrogen Embrittlement (LHE) alkaline ZnNi Coatings

γ-ZnNi Coating• Zn-14Ni Advantages

– Environmentally benign – Sacrificial to steel during

corrosion– Corrodes slowly – Low hydrogen embrittlement– Approved for aerospace

applications• Requires Passivation Coating:

– Maintain low contact resistance in corrosive environment

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Passivations Investigated• Dipsol passivations

– Trivalent chromium passivation (TCP); IZ-264– Cobalt-free trivalent chromium passivation (Co-Free)– Modified Cobalt-free trivalent chromium passivation (Co-Free Mod)– Hexavalent Chromate (CrCC) used as control; IZ-258

• S&T passivations– Cerium-based passivation (CeCC)

• Cerium Chloride or Cerium Nitrate deposition based solution

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Tri/Hex Chrome Deposition Procedure

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Rinse with DI water Surface Activated

Passivation Deposition Bath

Rinse with DI water

Rinse with DI water Embrittlement Bake

γ-ZnNielectroplated

onto Steel

Cerium-based Passivation Deposition Procedure

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Chemically Cleaned

Rinse with DI water Surface Activated

Passivation Deposition Bath

Rinse with DI water

Rinse with DI water CeCCPost-Treatment

Air Dry

γ-ZnNielectroplated

onto Steel

Sample Evaluation• Electrochemical analysis

– Cyclic Potentiodynamic Scan– Electrochemical Impedance Spectrocopy

• Electrolyte: 0.6 M (NH4)2SO4 and 0.6 M NaCl• Corrosion performance

– ASTM B117• Evaluated at 100 hr. intervals for 1000 hrs.

• SEM/EDS analysis• X-Ray Diffraction analysis• Contact resistance: MIL-STD-81706B

– 5 measurements on each panel – Measured 0 hrs., 100 hrs., and 1000 hrs. ASTM B117

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Coating System

Passivated ZnNi

Steel

2468

1012

0 50 100 150 200 250 300

Z (μ

m)

X (μm)

ZnNi Surface Roughness

Passivation Layer

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γ-ZnNi Coatings

01234567

10 20 30 40 50 60 70 80 90

Inte

nsity

(103 )

2θ (Degrees)

• Grain size is ~20 μm for as-deposited γ-ZnNi• XRD only detected γ-ZnNi• Passivations are ~100 nm thick

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0

2

4

6

8

10

12

CeCC-N CeCC-Cl Co-Free Co-Free Mod. Cr(III) CrCC

Cont

act R

esis

tanc

e (m

Ω)

As-Deposited Contact Resistance

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As Deposited Electrochemical Impedance Spectroscopy

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As Deposited Polarization Curves

2 2Zn H O ZnO H+ ⇔ +0.673E V= −

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Before and After Salt Spray Testing (SST) for 1000 Hours

CeCC-Cl

CeCC-N

Co-Free

Co-Free Mod

TCP

CrCC

CeCC-Cl

CeCC-N

Co-Free

Co-Free Mod

TCP

CrCC

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Electrochemical Impedance Spectroscopy After 1000 Hours of SST

Passivations that performed best in SST had higher frequency response

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Morphology After 1000 Hours of SST

CeCC-Cl CeCC-N Co-Free

Co-Free Mod TCP CrCC

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Corrosion Product CompositionAtomic % (EDS)

CeCC-Cl CeCC-N Co-Free Co-Free Mod TCP CrCC ZnNi (XRF)Ni 1 1 1 7 11 1 14Zn 60 43 39 23 63 52 86O 34 52 46 65 22 44 0

• Co-Free Mod and TCP surface had little/no corrosion product

• EDS detected higher Ni signal where no corrosion visible

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XRD After 1000 Hours of SST

CeCC-Cl

CeCC-N

Co-Free

Co-Free Mod

TCP

CrCCZnO/OH/CO3Corrosion Product

Minimal Corrosion Product Detected

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Electrical Contact Resistance

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Alternate Contact Resistance Method

Sample BYU Probe Resistance (ohms)

MIL-DTL-81706B Probe Resistance (ohms)

T-test comparison

TCP 0.0007 ± 0.0002 0.013 ± 0.001 >99% chance differentCo-Free 0.0013 ± 0.0005 0.00142 ± 0.00007 ~22% chance different

CrCC 0.0007 ± 0.0004 0.0062 ± 0.0009 >99% chance different

Adaptation of BYU Design/Fabricated Microprobe for Thin Film Battery Electrodes

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Summary• TCP and CeCC Passivations on LHE ZnNi Deposited with

Contact Resistance <5 mΩ/in2

• Electrochemical Response Dependent on Type of Passivation-CrCC and TCP-based Passivations Best Response

• IZ-264 TCP and Co-Free Modified IZ-264 TCP Electrical Contact Resistance <10 mΩ/in2 After1000 Hours of ASTM B117

• Four Line Microprobe Electrical Contact Resistance Test Method More Sensitive Than MIL-DTL-81706B

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