Crack formation in iron-nickel alloys under stress in alkaline media

The corrosion resistance and the character of crack formation in iron, nickel, and iron-nickel alloys under stress in a boiling NaOH solution were studied. The character of fracture of two-phase alloys was found to be related to the presence of an -phase at the grain boundaries. In the absence of the ferrite constituent, Fe-Ni alloys fail by intercrystalline fracture and the time-to-rupture decreases with increasing stacking fault density.     

Hydrogen embrittlement of an HSLA 80 steel in sea water under cathodic charging conditions

Abstract

Hydrogen embrittlement of a copper precipitation strengthened and niobium microalloyed HSLA 80 steel on cathodic charging in synthetic sea water has been studied using a slow strain rate technique. The effects of strain rate and potential applied for hydrogen charging have been studied. Hydrogen measurement at different potentials has also been carried out. A loss in ductility in terms of a drop in percentage elongation and percentage reduction in area has been observed, the effect being prominent at potentials beyond —800 mV(SCE). Fractography by SEM shows a dominance of microvoid coalescence with increasing quasicleavage features at higher negative potentials. A hardening effect of hydrogen charging up to —600 mV(SCE) followed by a softening effect has been observed. The results are discussed in the light of the existing models of hydrogen–dislocation interaction and hydrogen induced microvoid coalescence.     

Corrosion of titanium alloys in aqueous solutions of hydrochloric acid

We investigate the kinetics of corrosion of α-, (α+β)-, and β-titanium alloys in aqueous solutions of hydrochloric acid. It is shown that the process of dissolution obeys a parabolic law and is accompanied by the formation of an oxide (TiO₂ rutile) film on the metal surface. We demonstrate that corrosion processes are intensified as the amount of the β-phase in titanium alloy increases. Karpenko Physicomechanical Institute, Ukrainian Academy of Sciences, L'viv. Translated from Fizyko-Khimichna Mekhanika Materialiv, Vol. 33, No. 3, pp. 112–115, May–June, 1997.     

The characteristics of TiAl-based alloys melted in graphite crucibles

ABSTRACT

In the paper, the phase composition, microstructure, and selected mechanical and operational properties at room and elevated temperature of a TiAl intermetallic alloy from the TNB group – Ti–45Al–8Nb–0.5(B, C), induction melted in special graphite crucibles, are characterised. Selected properties of this alloy were compared to those of the reference TNB-V2 alloy with similar chemical composition, prepared with technologies currently used in the world. The result of this comparison was a positive recommendation for the proposed melting technology as an alternative to this and other groups of TiAl-based alloys.

This paper is part of a thematic issue on Titanium.     

Effects of ageing after cathodic charging in austenitic stainless steels

Ageing after cathodic charging resulted in a number of significant structural changes as the hydrogen diffused out of the specimen. The -phase is formed during hydrogen charging of the 316 steel. The weight fraction of the -martensite decreased with increasing ageing time. It is suggested that the transformation might be taking place during hydrogen release. Techniques for quantitative phase distribution in the stainless steel after various ageing times were used.     

Corrosion resistance of nitrided titanium alloys in aqueous solutions of hydrochloric acid

It is shown that vacuum heating prior to nitridation contributes to the formation of nitrided layers on a surface. The layers adequately protect titanium alloys from corrosion in aqueous solutions of hydrochloric acid. Moreover, vacuum heating makes it possible to perform effective nitridation at low temperatures. Karpenko Physicomechanical Institute, Ukrainian Academy of Sciences, L'viv. Translated from Fizyko-Khimichna Mekhanika Materialiv. Vol. 34, No. 1, pp. 108–110, January–February, 1998.     

Texture effects under tension and torsion loading conditions in titanium alloys

The paper derives from a major research programme on texture evolution and characterisation in the titanium alloys Ti-6Al-4V and Ti550. The present publication focuses on the mechanical characterisation of the texture in rolled plate. It focuses specifically on monotonic strengths and strain control fatigue under tension and torsion loading. Dependencies of fatigue performance on specimen orientation are interpreted through EBSD evaluation of basal and prism plane intensities within the present materials. The cyclic deformation and mechanisms of failure are related to the relative magnitude of tensile and shear stress components in the tension and torsion loading modes. Stress relaxation is shown to play an important part in these processes. Its relationship to available slip systems is discussed     

The formation of omega phase in titanium and zirconium alloys: A review

The omega phase is a metastable phase which forms in alloys of titanium and zirconium with most transition metals. In this paper the available data from both alloy systems on the occurrence, the structure, the mechanism of formation, and the morphology of the phase are reviewed and compared. The effect of omega phase on the mechanical behaviour and on the superconducting properties is then discussed. It is concluded that uncertainties still exist on the mechanism of the omega transformation during quenching and on the mechanism of the effect of omega on the mechanical properties.     

Crack growth process in Ni-Single crystal with hydrogen cathodic charging

Notched tensile tests {orientation tensile axis [001] and ${[\bar{1}\bar{1}1]}$ , direction of notching: [010], [011], [112]} were performed to investigate the crack growth process in Ni-single crystal with hydrogen cathodic charging. It was investigated that the crack growth direction tends to be <011> on {001} with any tensile direction. Y-shaped hillocks and striation-like pattern were observed on the fracture surfaces of hydrogen embrittled specimens using a scanning electron microscope (SEM) and an atomic force microscope (AFM). The striation-like patterns were not matched on both fracture surfaces of specimens, though the Y-shaped hillocks were exactly matched. Moreover, it was indicated that the striation-like pattern is perpendicularly formed to the crack growth direction on the fracture surface behind the crack tip and its shape results in an obtuse angle with respect to the fracture surface. The Y-shaped hillock was formed between micro-cracks located at crack tip by shear fracture. Furthermore, we proposed a crack growth model in Ni-single crystal at hydrogen atmosphere from the observation of the fracture surfaces.     

Hydrogen depth profile in phosphorus-doped, oxygen-free copper after cathodic charging

Spent nuclear fuel, in Sweden, is planned to be put in 50-mm thick copper canisters and placed in 500-m depth in the bedrock. Depending on the conditions in the repository, an uptake of hydrogen in the copper may occur. It is therefore necessary to establish how a hydrogen uptake affects the microstructure in both the surface and the bulk. Phosphorus-doped, oxygen-free copper has been cathodically charged with hydrogen for up to 3?weeks. The amount of hydrogen as a function of the distance from the surface was measured by two methods: glow discharge optical emission spectrometry and melt extraction. The penetration of the increased hydrogen content was about 50?μm. Extensive bubble formation took place during the charging. A model has been formulated for the diffusion of hydrogen into the copper, the bubble formation and growth. The model can describe the total amount of hydrogen, the number of bubbles and their sizes as a function of the distance from the surface. Bubbles close to the surface caused the surface to bulge due to the high hydrogen pressure. From the shape of the deformed surface, the maximum hydrogen pressure could be estimated with the help of stress analysis. The maximum pressure was found to be about 400?MPa, which is almost an order of magnitude larger than previously recorded values for electroless deposited copper.     

Formation of functional layers on titanium alloys under nonstattonary conditions

We formulate basic thermodynamic ideas concerning the relationship between the physicochemical processes and the accumulation of defects in materials. The accumulation of damage results in, generally speaking, nonstadonary conditions of interaction in the metal-medium system. To describe the kinetics of the processes of high-temperature interaction of binary alloys with gaseous media, we formulate the corresponding initial-boundary-value diffusion problem and obtain analytic expressions for the distributions of impurity and alloying elements, for the thickness of the newly formed phase, and the increment of mass. We also perform the verification of the proposed approach. The numerical solutions adequately reflect the observed tendencies in the behavior of the parameters of corrosion of OT4 alloy in oxygencontaining media under the conditions of thermal cycling and static loading. Translated from Fizyko-Khimichna Mekhanika Materialiv, Vol. 36, No. 2, pp. 65–75, March-April, 2000.     

Difference in surface reactions between titanium and zirconium in Hanks' solution to elucidate mechanism of calcium phosphate formation on titanium using XPS and cathodic polarization

Titanium and zirconium were immersed in Hanks' solution with and without calcium and phosphate ions, and the surfaces were characterized with X-ray photoelectron spectroscopy (XPS) to determine the mechanism of calcium phosphate formation on titanium in simulated body fluids and in a living body. In addition, they were cathodically polarized in the above solutions. XPS characterization and cathodic polarization revealed differences in the surface properties in the ability of calcium phosphate formation between titanium and zirconium. The surface oxide film on titanium is not completely oxidized and is relatively reactive; that on zirconium is more passive and protective than that on titanium. Neither calcium nor phosphate stably exists alone on titanium, and calcium phosphate is naturally formed on it; calcium phosphate formed on titanium is stable and protective. On the other hand, calcium is never incorporated on zirconium, while zirconium phosphate, which is easily formed on zirconium, is highly stable and protective. Our study presents new information regarding the surface property of titanium and demonstrates that the characteristics of titanium and zirconium may be applied to various medical devices and new surface modification techniques.