Titanium alloys hydrogenated

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. 

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

Titanium alloyed with kon is a candidate for soHd-hydride energy storage material for automotive fuel. The hydride, FeTiH2, absorbs and releases hydrogen at low temperatures. This hydride stores 0.9 kWh /kg. To provide the energy equivalent to a tank of gasoline would thus requke about 800-kg... 

HYDROGEN AS A USEFUL ALLOYING ELEMENT IN TITANIUM ALLOYS... 

There are several reasons which made hydrogen processing most applicable to titanium alloys ... 

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). 

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. ... 

Mechanical properties of hydrogenated titanium alloys are strongly dependent on the applied stress tensor, especially on its hydrostatic component. This was illustrated by the high-pressure tensile and extrusion tests on the Ti-6Al-2.5Mo-2Cr alloy and the same alloy hydrogenated to a = 0.15 wt.%H. Tests were carried out using the apparatus at the Institute of Metal Physics UD RAS operating at hydrostatic pressures of machine oil to 15 kbax and temperatures to 250°C. 

It is rather likely that pressure-induced phase transformations can also occur in hydrogenated multicomponent industrial titanium alloys. However, there were no available data on the high-pressure behavior of such alloys. 

Thus, there are rather many microscopic processes which contribute to result in hydrogen-improved workability. To elucidate all contributions to this beneficial phenomenon, further study of the plastic flow of titanium alloys is necessary both at microscopic and macroscopic levels. 

Hydrogen alloying increases ductility of titanium alloys by 10 to 45 times at moderate temperatures of 400 to 750 C. 

Hydrostatic pressure considerably increases workability of hydrogenated titanium alloys. Thus, their ductility at 20-250 C exceeds that of the hydrogen-free alloys in the pressure range of 10 kbar. 

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

B.A. Kolachev and V.K. Nosov, Hydrogen plasticization in hot deforming of titanium alloys, in Titanium Science and Technology, Proc. V Intern. Conf. on Titanium, vol. 1, G. Liitjering, U. Zwicker and W. Bunk, eds., DGM, Oberursel (1985) 625. 

V.K. Nosov and B.A. Kolachev, Hydrogen Plasticization at Hot Working of Titanium Alloys, Metallurgia, Moscow (1986). 

O.N. Senkov, I.O. Bashkin, S.S. Khasanov, and E.G. Ponyatovsky, Grain structure of titanium alloy VT20 after hydrogen treatment and deformation at moderate temperatures, Fiz. Met. Metallovedeniye, 76 128 (1993). 

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). 

Tantalum-Titanium Bishop examined the corrosion resistance of this alloy system in hydrochloric, sulphuric, phosphoric and oxalic acids and found that alloys containing up to about 50% titanium retained much of the superlative corrosion resistance of tantalum. Under more severe conditions, a titanium content of below 30% appears advisable from the standpoint of both corrosion resistance and hydrogen embrittlement, although contacting or alloying the material with noble metals greatly decreases the latter type of attack. Tantalum-titanium alloys cost less than tantalum because titanium is much cheaper than tantalum, and because the alloys are appreciably lower in density. These alloys are amenable to hot and cold work and appear to have sufficient ductility to allow fabrication. 

The proposed mechanism includes the production of HCl from the pyro-hydrolysis of the metal chlorides. Similar reactions are likely for bromides and iodides. Fluorides however are relatively stable and would not be expected to hydrolyse. It was considered that this might account for the inability of fluorides to cause cracking. Hydrogen absorption by titanium alloys exposed to chloride salts at elevated temperatures has been detected and found to be proportional to the amount of moisture participating in the reaction. 

Similarly, Allen, Alsalim and Wake 45,46 determined that alkaline hydrogen peroxide was the best pretreatment for titanium alloys. This pretreatment was found to preferentially etch the P phase, while also undercutting some of the a grains and redepositing needle-like crystals on the P grains. The very rough surfaces that resulted were found to enhance adhesion by mechanical aspects. 

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