Volume 13A - Corrosion Fundamentals, Testing, and Protection Part 12 ppsx

Introduction to Methods of Corrosion Protection Introduction Introduction to Methods of Corrosion Protection Paul Natishan, Naval Research Laboratory Factors Affecting Corrosion Behav

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α

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High-Temperature Gaseous Corrosion Testing

David A Shifler, Naval Surface Warfare Center

References

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α

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High-Temperature Gaseous Corrosion Testing

David A Shifler, Naval Surface Warfare Center

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Introduction to Methods of Corrosion Protection

Introduction

Paul Natishan, Naval Research Laboratory

Factors Affecting Corrosion Behavior

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Galvanic Couples

Coatings

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Inhibitors

Introduction to Corrosion Resistance of Bulk Materials

Introduction

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Alloying

Fig 1 The effect of alloying is shown as the influence that various elements have on the corrosion rate of

a base 19Cr-9Ni casting alloy in boiling 65% nitric acid The specimens were solution annealed and quenched Composition of the base alloy was 19Cr, 9Ni, 0.09C, 0.8Mn, 1.0Si, 0.04P (max), 0.035S (max), and 0.06N (Ref 1)

Reference cited in this section

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Metallurgical Factors

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Fig 2 The relationship between microstructure and corrosion behavior From the phase diagram (top), alloys with differing compositions—and thus differing relative amounts of alpha and beta phase particles—are selected A profile of the material in a corrosive medium is shown when alpha is active and beta is noble The bottom line illustrates when alpha is more noble than beta (adapted from Ref 2)

Mechanical Treatments

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Corrosion Resistance of Aluminum Alloys

Jack Snodgrass and Jim Moran, Alcoa, Inc

Alloying to Improve Corrosion Resistance

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Mechanical Treatments to Improve Corrosion Resistance

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Surface Treatment to Improve Corrosion Resistance

μ

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μ

References cited in this section

Processing to Improve Corrosion Resistance

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Selection of Fabrication Operations

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Ba(OH) 2 saturated

Fig 2 Corrosion rates as a function of time for commercially pure magnesium Curve A, distilled water vented to air through a caustic trap; curve B, distilled water vented to atmospheric CO 2 Source: Ref 2 Table 3 Corrosion rate of commercially pure magnesium in various media

mm/yr mils/yr Humid air

Humid air with condensation

Distilled water

Distilled water exposed to acid gases

Hot deionized water (100 °C) (14 days stagnant immersion)

Hot deionized water inhibited with 0.25 NaF

Seawater

3M MgCl2 solution

3M NaCl (99.99% high-purity Mg with <10 ppm Fe)

Table 4 Typical magnesium alloy systems and nominal compositions

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UNS Al Zn Mn Ag Zr Th Re AM60

Corrosion Resistance of Magnesium Alloys

Revised by Barbara A Shaw, Pennsylvania State University

Metallurgical Factors

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Fig 3 Effect of iron content on the corrosion rate of commercially pure magnesium subjected to alternate immersion in 3% NaCl Source: Ref 4

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Fig 4 Effect of alloying and contaminant metals on the corrosion rate of magnesium as determined by alternate immersion in 3% NaCl solution Source: Ref 5

Table 5 Contaminant tolerances and manganese limits for magnesium die castings

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Table 6 Known contaminant tolerance limits in high- and low-pressure cast forms

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Fig 6 Effect of heating temperature on corrosion rate of die-cast AZ91D and AM60B in salt-spray test for 10 days using ASTM B 117 method Data are for test specimens that were heated from 0.5 to 36 h Source: Ref 12

Table 7 Contaminant tolerance limits versus temper and cast form for AZ91 alloy

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Causes of Corrosion Failures in Magnesium Alloys

Fig 7 Effect of heavy-metal contamination on the salt-spray performance of sand-cast AZ91 samples in the T6 temper, as determined by ASTM B 117 method The samples, containing less than 10 ppm Ni and less than 100 ppm Cu, were simultaneously exposed for 240 h The sample at left contained 160 ppm Fe and had a corrosion rate of 15 mm/yr (591 mils/yr) The sample at right contained 19 ppm Fe, and the corrosion rate was 0.15 mm/yr (5.9 mils/yr)

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Acknowledgment

References

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Corrosion Resistance of Stainless Steels and Nickel Alloys

Introduction

Table 1 Compositions of selected stainless steels and related higher alloys

C Mn P S Si Cr Ni Mo Others (a) PREN (b)

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S32760 (c)

J95150

J94224

S32615

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Table 2 Compositions of selected copper-nickel and nickel-base alloys

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N08330

N08800 N08825 N08904 N10276 N10665

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A John Sedriks, Office of Naval Research

Stainless Steels

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Fig 1 Compositional and property linkages for stainless steels

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Nickel-Base Alloys

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Fig 2 Compositional and property linkages for nickel-base alloys

γ′

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Corrosion Resistance of Titanium Alloys

Introduction

Steven Yu, 3M Company

Corrosion Resistance of Titanium and Titanium-Base Alloys in Aqueous Environments

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Passivating Titanium Oxides

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Fig 1 Potential-pH equilibrium diagram for the titanium-water system at 25 °C (77 °F) The diagram was established by considering, as derivatives of the tri- and tetravalent titanium, the hydroxide Ti(OH) 3

and the hydrated oxide TiO 2 -H 2 O Lines a and b establish the stability region of water Consult Ref 7 for further explanation

Table 1 Lattice parameters of crystalline titanium oxide

TiO 2 -(anatase) tetragonal

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TiO 2 -(rutile) tetragonal

TiO 2 -(brookite) orthorhombic

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Corrosion Vulnerability of Titanium and Titanium Oxides: The Effect of Selected Environments

•

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Table 2 Pitting potential of commercially pure titanium

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11.5%Mo-6%Zr-4.5%Sn) It is evident that the alloying additions of molybdenum, zirconium, and palladium were beneficial in raising the 70 °C (158 °F) threshold for crevice corrosion Source: Ref 6

→

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Fig 3 Electrochemical polarization tests of titanium and titanium-base alloys, including Ti-6%Al-4%V (Ti-6-4), Ti-15%Mo-3%Nb-3%Al (Ti-15-3-3), Ti-13%Nb-13%Zr (Ti-13-13), Ti-55%Ni, and commercially pure (CP) titanium (grade 2), revealed that titanium and titanium-base alloys are

spontaneously passive in a deaerated 0.1 M NaCl solution The potentiodynamic scans were conducted at

a scan rate of 0.1 mV/s SCE, saturated calomel electrode

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Effects of Alloying on Active Anodic Corrosion of Titanium

αβ

β

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Fig 4 Electrochemical polarization tests of titanium and titanium-base alloys, including Ti-6%Al-4%V (Ti-6-4), Ti-15%Mo-3%Nb-3%Al (Ti-15-3-3), Ti-13%Nb-13%Zr (Ti-13-13), Ti-55%Ni, and

commercially pure (CP) titanium (grade 2), in a deaerated 5 M HCl solution The potentiodynamic scans

were conducted at a scan rate of 0.1 mV/s SCE, saturated calomel electrode

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Fig 5 Open-circuit potentials of commercially pure (CP) titanium in deaerated 0.1 M NaCl solution and deaerated 5 M HCl solution at 37 °C (99 °F) In 0.1 M NaCl, CP titanium did not exhibit the drop in

open-circuit potential that is characteristic of surface activation after oxide dissolution SCE, saturated calomel electrode

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Fig 6 Open-circuit potentials of Ti-45%Nb and Ti-50%Zr (bulk alloys), initially with air-formed oxides,

in deaerated 0.1 M NaCl and 5 M HCl solutions at 37 °C (99 °F) Ti-45% Nb and Ti-50%Zr did not exhibit surface reactivation in 0.1 M NaCl solution (pH ~ 6.8) In contrast, both alloys exhibited surface reactivation in 5 M HCl due to chemical dissolution of the oxide SCE, saturated calomel electrode

Fig 7 Potential-pH equilibrium diagram for Ti-H 2 O system of 37 °C (99 °F) The dissolved titanium species are at an activity of 10 -6 Lines a and b define the region of water stability The experimentally recorded open-circuit potentials (OCP) of commercially pure (CP) titanium, Ti-45%Nb, and Ti-50%Zr

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in deaerated 0.1 M NaCl and 5 M HCl solutions before and after surface activation at 37 °C (99 °F) are

presented SCE, saturated calomel electrode NHE, normal hydrogen electrode

Effects of Alloying Additions on Titanium Passivity

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Fig 8 Polarization measurement of titanium-palladium alloys in acidic sodium chloride solution (deaerated, sweep rate = 0.2 V/min, NaCl = 250 g/L, pH = 0.5, and boiling) SCE, saturated calomel electrode; CP, commercially pure Source: Ref 51

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Formation of Amorphous or Vitreous Oxide

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Reduction of the Potential Gradient across Surface Film

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Fig 9 Schematic of the active metal/passive oxide/Helmholtz double layer/solution interfaces that are present on a passivated metal surface

Enhancement of Atomic Bond Strength

ε

Δ

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Table 3 Data for enthalpy of adsorption (oxygen), ΔHads , and atomic bond strength, ε M-M , for a selection

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Lowering of the pH of Zero Charge

Repassivation Behavior of Titanium and Titanium-Base Alloys

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Δ Δ

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References

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Phosphate Conversion Coatings

Introduction

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Kevin Ogle, Irsid, Arcelor R&D (Maizières-lès-Metz, France); Michael Wolpers, Henkel KGaA (Düsseldorf, Germany)

Structure and Function of the Phosphate Film

Table 1 Characteristics of different types of phosphate coatings and associated processes (general formulas)

Heavy phosphating Alkali

phosphating (iron

phosphating)

phosphating (dry-in-place phosphating)

No-rinse-Low-zinc phosphating Standard-zinc phosphating (a)

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needed for tanks

Application method

mg/L (d)

c(Na + ), g/L c(NO 3 - ), g/L

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Fig 1 Scanning electron micrographs and x-ray diffraction patterns comparing crystalline and amorphous phosphate layer (a) Tri-cation phosphate layer of a spray process (b) Tri-cation phosphate layer of a no-rinse process Substrate is electrogalvanized steel

Table 2 Phosphate compounds found in conversion coatings

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Fig 3 Trend of paint delamination of steel products (a) Cold rolled steel (b) Hot dip galvanized steel (c) Galvannealed steel (Fe-Zn alloy) Coating is approximately 25 μm electrophoretic paint with and without phosphate treatment Artificial damage by Van Laar scratch, scalpel comparable to a ball-point pen, then exposed in a cyclic corrosion test Test cycle was 1 day salt spray fog, plus 4 days condensed water exposure plus 2 days dry period Creepage is defined as the distance between the artificial damage and the border of delamination Note that the y-axes are different in scale Source: Ref 6

Fig 4 Delamination of painted steel substrates treated with different zinc phosphatations after 1 year outdoor exposure Substrate CRS, cold rolled steel; EG, electrogalvanized Coating electrophoretic paint + filler + top-coat Artificial damage by Clemen scratch, like a cut with a scalpel

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Fig 5 Delamination of painted steel substrates treated with four different alkali phosphatations after

504 h exposure in salt spray fog Coating, electrophoretic paint + filler + top-coat Artificial damage, Van Laar scratch

Phosphating Steps

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Table 3 Typical process sequences in different industries

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Table 4 General formulas of alkaline cleaning products

°C °F Steel

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Phosphating

→

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Physical and Chemical Properties

Table 7 Stripping solutions for phosphate layers

°C °F Iron, steel

Zinc

Aluminum

Magnesium

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Processing Equipment and Control

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•

ΔΔ

•

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References

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Chromate and Chromate-Free Conversion Coatings

R.G Buchheit, The Ohio State University; A.E Hughes, CSIRO

Historical Perspective

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Chromate and Chromate-Free Conversion Coatings

R.G Buchheit, The Ohio State University; A.E Hughes, CSIRO

Chromate Conversion Coating Formation

Fig 1 Speciation of soluble Cr(VI) as a function of pH and concentration The labels indicate the predominant soluble chromium species in a given pH-concentration domain Many commercial CCC bath formulations have Cr(VI) concentrations that fall in the shaded box so that the primary film- forming species is dichromate (Equilibrium constants from Ref 16)

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