Titanium hydrogen effect

This induced an increasing number of papers devoted to the study of the hydrogen effect on the mechanical properties of titanium alloys -lo SQjjjg interesting effects of hydrogen in titanium and its alloys are discussed below on the basis of the experimental data obtained at ISSP RAS (the early experiments were carried out in co-operation with the Institute of Metal Physics UD RAS). 

Hydrogen effect on the mechanical properties discussed below was studied on several a and a+fi alloys with the following nominal composition of metallic components (Russian trade marks given in parentheses) commercial titanium of nominal purity 99.3% (VTl-0), Ti-6Al-2Zr-1.5V-lMo (VT20), Ti-6A1-4.5V (VT6), Ti-6Al-2.5Mo-2Cr (VT3-1), Ti-4Al-1.5Mn (OT4), Ti-6.5Al-4Mo-2Sn-0.6W-0.2Si (VT25u) and others. The main features of their stress-strain behavior due to hydrogenation were much similar, but some individuality was characteristic of each alloy. 

The hydrogen effect on ductility and the flow stress will be considered first on the example of non-alloyed titanium. The Ti - H phase diagram is given in Fig. 1, and Fig. 2 shows the temperature dependence of ductility of Ti-a H alloys, A , for several X values. Tensile tests were run at a rate e 10" s . Ductility of the commercial... 

These and other hydrogen effects can be useful for improvement of processing of industrial high-strength titanium alloys. 

The group IV B elements titanium, zirconium, and hafnium exhibit the normal isotope effect. Most of the data for the titanium-hydrogen system have been obtained at elevated temperatures. However, extrapolation of the available data (II, 13,31) to room temperature indicates a normal effect for hydrogen and deuterium. The group VB metals vanadium, niobium, and tantalum, on the other hand, exhibit inverse isotope effects indeed, these are the only pure metals that exhibit the inverse effect near room temperature. Extensive data have been reported for these systems. The P-C-T data obtained by Wiswall and Reilly (32) for vanadium hydrogen and deuterium clearly show a greater stability for... 

Although the pure titanium-hydrogen system exhibits the normal isotope effect, many titanium alloys show the inverse effect. The exchange of pro-tium-tritium mixture with the hydrided phase of these alloys has demonstrated an inverse protium-tritium isotope effect in Ti-V, Ti-Mo, Ti-Cr, Ti-Mn, and the ternary alloy TiCrMn (1). On the other hand, Ti-Co, Ti-Fe, and Ti-Ni systems exhibit the normal isotope effect. Clearly much can be learned from a study of these systems. 

Cremaschi P and Whitten J L 1987 The effect of hydrogen chemisorption on titanium surface bonding Theor. Chim. Acta. 72 485-96... 

The a — 0 transformation has a large hysteresis in hydrogenated titanium alloys, and different thermal treatments change their phase content. Various degrees of metastability due to hysteresis are implicit for the alloys after different thermal treatments. Metastable phases undergo transformation to a more equilibrium state during deformation, which can effect the flow of the alloy. Below we consider the effect of the thermal pre-strain treatment on ductility on the strength of the Ti-6A1-2Zr-1.5V-lMo-rH alloys. ... 

In the previous Sections, bulk specimens were alloyed with hydrogen from the gas phase. It was interesting to see whether hydrogen affects the mechanical properties of titanium in a similar way if metal is in a powder state and hydrogen is introduced by mechanical mixing of the metal powder with titanium dihydride, or the interparticle boundaries axe an insurmountable obstacle for hydrogen an eliminate the effects observed in bulk specimens. 

Fig. 10 shows that the flow stress of the hydrogen-alloyed compacts is essentially less than that of the outgassed ones at all test temperatuics. The flow stress relation between the hydrogen-alloyed and outgassed compacts depended on the strain. At equal strains at test temperatures, this ratio could achieve 2 or more. Thus, the effect of hydrogen on the properties of compacted powders is much similar to that observed on bulk titanium. 

Compacted powder mixtures of titanium and titanium dihydride demonstrate the hydrogen-enhanced plasticity effects on deformation over 500 C, like titanium alloys hydrogenated from the gas phase. 

I.O. Bashkin, E.G. Ponyatovsky, O.N. Senkov, and V.Yu. Malyshev, The strain-rate effect on the hydrogen-induced workability improvement of titanium alloy VT20 at temperatures 500-800°C, Phys. Met. Metall., 69 167 (1990). 

O.N. Senkov, E.V. Konopleva, and E.G. Ponyatovsky, The effect of initial phase content and structure on workability of a hydrogen-alloyed titanium alloy, Fiz. Met. Metallovedeniye, 77 142 (1994). 

T emary alloys Ti-Al based materials mechanical properties of Titanium alloys hydrogenated stram effects pressure effects Tight-binding LMTO CPA... 

Mansfeld, F., The Effect of Water on Passivity and Pitting of Titanium in Solutions of Methanol and Hydrogen Chloride , J. Electrochem. Soc., H8, 1412 (1971)... 

There are also occasions, particularly in hydrogen-containing atmospheres, when surface contamination of the titanium with iron can result in localised corrosion and embrittlement. This effect can be countered by avoidance of undue contamination with iron during fabrication, by postfabrication cleaning and by post-fabrication anodisingIt should be emphasized, however, that in general use in the marine and chemical industries discussed below, iron levels up to 0-2% do not adversely affect corrosion resistance. 

The addition of a small percentage of a noble metal to a base metal such as stainless steel or titanium can provide sites of low overvoltage for the cathodic reduction of dissolved oxygen or hydrogen ions. This permits larger currents and hence more positive potentials to be obtained at the anodic region, and promotes passivation under some circumstances . This effect has been demonstrated for stainless steels but has not been adopted in practice, since under other conditions the noble metal addition accelerates corrosion . 

The method is more useful with titanium, and the effect of alloying titanium with a small amount of palladium is described in Section 5.4. The use of platinum in the prevention of hydrogen embrittlement in tantalum. 

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