DTIC ADA450540: Hydrogen Environment Assisted Cracking of pdf

DTIC ADA450540: Hydrogen Environment Assisted Cracking of

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Precipitation hardened martensitic AetMet(tradeMark) 100 is a high purity ultra-high strength steel with exceptional plain strain fractare toughness (K(sub IC) 130 MPa square root to m) and high yield strength (sigma YS 1725 MPa). The hydrogen envfronment assisted cracking (FlEAC) behavior of this modem steel is not w#1 understood, and was characterized in neutral 3.5% NaCl solution at various applied potentials (E(sub App)) relevant to coated applications in marine environments. A novel short crack specimen was stressed under constant displacement-rate, and monitored using a high resolution electrical potential crack monitoring technique to determine the Stage II crack growth rate (da/dt(sub II)) and threshold stress intensity (K(sub TH)) typically of the chemically short crack reghne (250 to 1000 micronmeter). AerMet(TradeMark) 100 is susceptible to severe transgranular (TG) HEAC when stressed in neutral 3.5% NaCl and at near free corrosion potentials, as quantified by reduced Km, to as low as 10% of K(sub IC), and da/dt(subII) as high as 0.5 micronmeter/s.

Applied electrode potential (E(sub App)) is a critical variable. As EApp increases from -1.1 volts vs. saturated calomel electrode (V(sub SCE)) to 0.625 V5CE, operationally defined Km increases from the very low level of 9 MPa square root to m to a maximum of 40 MPa square root to m, and da/dt(sub II) decreases monotonically from 500 nm/s to 1 nm/s. Additional polarization to -0.5 V(sub SCE), typical of free corrosion in aerated solution, produces a decrease in Km to l6MPa square root to m and increase in da/dt(sub II) to 100 nm/s. The mechanism for this behavior is crack tip hydrogen embrittlement. The effect of electrode potential is understood based on occluded crack acidification at the anodic conditions and cathodic polarization at lower potentials, each favoring H production and uptake

• Creator/s: Defense Technical Information Center
• Date: 1/1/2006
• Year: 2006
• Book Topics/Themes: DTIC Archive, Lee, Yongwon, VIRGINIA UNIV CHARLOTTESVILLE DEPT OF MATERIALS SCIENCE AND ENGINEERING, *HIGH STRENGTH ALLOYS, *STEEL, *HYDROGEN EMBRITTLEMENT, *CRACK TIPS, *STRESS CORROSION, POLARIZATION, ENVIRONMENTS, HIGH RATE, HYDROGEN, COATINGS, SOLUTIONS(GENERAL), ELECTRODES, ANODES, AERATION, SQUARE ROOTS, OCEAN ENVIRONMENTS, MODEMS, LOW LEVEL, HIGH STRENGTH, CATHODES, SATURATION, THRESHOLD EFFECTS, CRACKS, INTENSITY, TOUGHNESS

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