Development of titanium alloys by the method of complex alloying

We study the effect of alloying on the mechanical properties of welded joints and base metal of titanium alloys of the system Ti-Al-Mo-V-Cr-Fe. We also formulate the theoretical aspects and principles of complex alloying of titanium alloys and the theory of alloying of additive materials for the welding of α-, (α + β), and β-alloys. It has been shown that (α + β)-(VT23) and β-(VT19) structural titanium alloys, developed on the basis of the proposed theory of complex alloying, provide high weight efficiency of construction of present-day flying vehicles. __________ Translated from Fizyko-Khimichna Mekhanika Materialiv, Vol. 42, No. 5, pp. 45–50, September–October, 2006.     

Processing of a porous titanium alloy from elemental powders using a solid state isothermal foaming technique

The authors have conducted a preliminary investigation with regard to the potential to manufacture porous titanium alloys for biomedical applications using toxic-free elemental powders, i.e., Ti, Nb, Ta, Zr, in combination with the pressurised gas bubble entrapment method and in contrast to standard processing routes that generally utilise prealloyed powder containing potentially toxic elements. Elemental powder compacts were either hot isostatic pressed (HIP-ed) at 1000°C and then foamed at 1150°C or else HIP-ed at 1100°C and foamed at 1350°C. Porous α + β alloys containing up to 45 vol% of porosity in the size range 20–200 μm were successfully produced, thus highlighting the potential of this manufacturing route. It was expected that further optimisation of the processing route would allow full development of the preferred β-Ti phase (from the point of view of elastic modulus compatibility between implant and bone) with this being the subject of future work by the authors.     

Investigation of the effects of microstructure on creep deformation in α2-based titanium aluminide intermetallics

The results of a systematic investigation of the effects of microstructure/substructure on the secondary creep behaviour of α2-based titanium aluminide alloys are presented. This includes a study of the effects of heat treatment on the steady-state creep behaviour of α2+β-processed Ti-24Al-11Nb and Ti-25Al-10Nb-3V-1Mo at 540, 650 and 760°C, and an investigation of the effects of creep deformation on dislocation substructures in Ti-24Al-11Nb. The parameters that control secondary creep deformation are identified for both alloys, and the results are compared with data obtained for conventional high-temperature near-α titanium alloys and β-forged Ti-24Al-10Nb-3V-1Mo. This revised version was published online in November 2006 with corrections to the Cover Date.     

Tungsten-free hard alloys based on titanium carbide

The properties of tungsten-free hard alloys based on titanium carbide prepared from chips of various titanium alloys were studied, and the conditions for the preparation of tungsten-free alloys were optimized. The properties of TiC-based alloys prepared from chips of the VT20, VT3-1, and VT25 titanium alloys, containing V, Mo, Zr, and Al, were shown to compare well with those of commercial analogs. Nickel vaporization during vacuum sintering of the hard alloys was studied, and the sintering conditions were optimized (residual pressure in the range 10–100 Pa, reduced sintering temperature)     

Effect of hydrogen on phase and structural transformations in titanium alloys of different classes

We study the laws of phase and structural transformations in titanium alloys under the action of dissolved hydrogen and in the course of subsequent degassing. We show the possibility to control structure formation in them with the help of alloying with hydrogen and to obtain structures that cannot be obtained by conventional technological methods. It has been established that the alloying system determines the character of interaction of these alloys with hydrogen in the course of hydrogenation. After additional alloying with hydrogen, intermediate hydrides are formed in titanium alloys with β-isomorphic stabilizers (V, Nb), Ti Cr₂ intermetallic compound appears in alloys with β-eutectoid stabilizer (Cr), and Ti₃Al compound is formed in alloys with high aluminum content. After vacuum annealing of hydrogen-containing specimens at 600°C, a composite heterophase (α + β + α₂) or (α + β + TiCr₂) structure is formed, and intermetallic particles in it have an incoherent boundary. __________ Translated from Fizyko-Khimichna Mekhanika Materialiv, Vol. 42, No. 3, pp. 33–39, May–June, 2006.     

Structure and physicomechanical properties of eutectic Ti-Si-X alloys

We study the structure and physicomechanical properties of various eutectic alloys of Ti-Si-Zr, Ti-Si-B, and Ti-Si-Ga systems. It is shown that Ti-Si-Zr alloys with elevated concentrations of Zr reveal, due to the presence of (Ti, Zr)₂ Si dispersed silicides with sizes of about several hundred nanometers, improved mechanical properties as compared with the properties of alloys based on Ti₅Si₃ silicides. The cast eutectic alloy of the Ti-Si-Zr-Sn system with a plasticity of ∼ 1.7% is obtained for the first time. The formation of superfine eutectics based on the Ti₆Si₂B ternary compound in alloys of the Ti-Si-B system enables one to obtain titanium composites with improved refractory properties and elevated moduli of elasticity (of about 150 GPa or, after additional alloying, as high as 165 GPa). This can be promising for the development of new refractory titanium composite materials with elevated stiffness. The analysis of the combined effect of gallium and silicon in Ti-Si-Ga alloys reveals the possibility of getting titanium materials with high heat resistance, i.e., materials based on the (α-Ti(α₂-Ti₃Ga) + Ti₅ (Si, Ga)₃ binary eutectics. Translated from Fizyko-Khimichna Mekhanika Materialiv, Vol. 44, No. 3, pp. 35–42, May–June, 2008.     

Effects and mechanisms of grain refinement in aluminium alloys

Grain refinement plays a crucial role in improving characteristics and properties of cast and wrought aluminium alloys. Generally Al-Ti and Al-Ti-B master alloys are added to the aluminium alloys to grain refine the solidified product. The mechanism of grain refinement is of considerable controversy in the scientific literature. The nucleant effects i.e. which particle and its characteristics nucleate α-Al, has been the subject of intensive research. Lately the solute effect i.e. the effect of dissolved titanium on grain refinement, has come into forefront of grain refinement research. The present paper attempts to review the literature on the nucleant effects and solute effects on grain refinement and addresses the importance of dissolved titanium in promoting nucleation of α-Al on nucleant particles.     

Corrosion and mechanical properties of titanium alloyed with aluminum, iron, and molybdenum

We study the influence of Fe, Al, and Mo on the corrosion and mechanical properties of titanium. It is shown that the corrosion resistance of titanium becomes 3.5 times lower as the concentration of iron increases from 0.1 to 5%. The microalloying of Ti-Al-Fe-Mo alloys with molybdenum inhibits corrosion. We develop new low-alloy structural and corrosion-resistant titanium alloys of the Ti-Al-Fe-Mo system. Their innovative character is confirmed by patents of the Ukraine. __________ Translated from Fizyko-Khimichna Mekhanika Materialiv, Vol. 42, No. 5, pp. 41–44, September–October, 2006.     

Production of conversion oxide-ceramic coatings on zirconium and titanium alloys

We consider the possibilities of surface hardening of zirconium and titanium alloys with conversion oxide-ceramic coatings. These coatings have been produced by the method of plasma-electrolytic treatment in alkaline solutions. We have established that the plasma temperature in discharge spark channels reaches (6–9) · 10³ K. The thickness of the coatings is 100 to 120 and 30 to 40 μm, and their microhardness is ∼ 800 and ∼ 1000 MPa for zirconium and titanium alloys, respectively. The functional properties of the coatings depend on the synthesis conditions, including the electrolyte composition, the cathode and anode current densities, and also the treatment time. We have evaluated the thickness, microhardness, and wear resistance of the coatings under conditions of dry friction and cavitation as well as their fatigue strength and corrosion resistance. We have established that this treatment provides a high wear and corrosion resistance of the alloys under study with insignificant decrease in their fatigue strength. __________ Translated from Fizyko-Khimichna Mekhanika Materialiv, Vol. 42, No. 2, pp. 117–124, March–April, 2006.     

The effect of metastability on room temperature deformation behavior of β and α + β titanium alloys

The deformation behavior of single-phase metastable β-titanium alloys and two-phase α+metastable-β alloys strongly depends on the degree of stability of the β-phase. Recently, it has been shown that the tensile deformation behavior, as well as the creep deformation behavior at low temperatures (<0.25T _m), is strongly influenced by the degree of metastability. For example, the titanium β-alloy Ti–13.0wt%Mn, which has higher stability than the titanium β-alloy Ti–14.8wt%V, deforms by slip only; whereas the latter deforms by slip and twinning. In addition to the mechanical properties, the deformation mechanisms also depend on the degree of metastability. Further, the deformation mechanisms of a given metastable β-alloy depend on whether the β-phase is present by itself as a single-phase alloy, or in the presence of α-phase in the form of a two-phase alloy. For example, it was found that a metastable Ti–V alloy deforms by slip and twinning when it is in the form of a single-phase alloy, but deforms by slip and martensitic transformation when the same metastable β-phase is present in a two-phase α + β alloy. The mechanical properties of the metastable β alloys in turn depend on these deformation mechanisms. These recent developments are reviewed in this article.     

Rapidly solidified titanium alloys for high-temperature applications

The application of rapid solidification technology (RST) to titanium alloy systems is relatively new and became the subject of active research since it was demonstrated that novel titanium alloys of higher temperature capability can be synthesized through new alloy design based on rapid solidification processing. The effects of rapid solidification on the occurrence of metastable phases, microstructures and mechanical properties in binary and ternary titanium alloys are reviewed. In particular, earlier results from RS-Ti alloy research have shown that many different novel dispersoids, some of which are coarsening-resistant at elevated temperatures (600 to 800° C), can be created in the matrix through RST. The alloys containing novel dispersoids also exhibit good creep resistance at elevated temperatures. Further studies on/- and-Ti alloys through RST, in conjunction with the development of various processing technologies for bulk alloy manufacturing, are clearly desirable.     

Spongy titanium alloyed with oxygen for the production of titanium alloys

We study the influence of alloying of spongy titanium with oxygen on the structure, mechanisms of fracture, and mechanical properties of titanium. It is shown that, within the range of concentrations 0.05–0.30%, oxygen insignificantly affects both the structure and the mechanism of fracture of cast titanium but strongly increases its strength with preservation of plasticity within the admissible range specified for standard titanium alloys of this grade. Translated from Fizyko-Khimichna Mekhanika Materialiv, Vol. 44, No. 3, pp. 78–80, May–June, 2008.     

Hydride formation under cathodic charging of titanium and TiAl-based alloys in alkaline solutions

The electrochemical methods and the data of X-ray diffraction analysis are used to determine the parameters of cathodic polarization for the hydrogenation of α-Ti and alloys based on the TiAl intermetallic phase without formation of the hydride phase or with formation of hydrides. In α-Ti, the increasing cathodic polarization in a 0.1 M NaOH solution leads to the dissolution of hydrogen in the metal lattice and its modification and to the increase in the amount of hydrides. The hydride phase is not recorded TiAl-based alloys even for much higher levels of absorption of hydrogen as compared with pure titanium. However, hydrogen affects the phase composition of alloys and the lattice parameters of the phases. Published in Fizyko-Khimichna Mekhanika Materialiv, Vol. 44, No. 3, pp. 103–106, May–June, 2008.     

Status of the titanium production,research, and applications in the CIS

We present a survey of the research and development of titanium alloys, mill products, processes, and applications in the CIS between the tenth and eleventh Titanium World Conferences. Driven by an increased world-market demand, the titanium industry of the CIS has become an important contributor to the global expansion of titanium in volume and applications. Unfortunately, the domestic shipments of titanium and, especially of mill products, remain low because of the inadequate consumption of titanium by domestic end-users, such as aerospace, chemical, and marine (shipbuilding) industries. Although the titanium-research activity remains not as extensive as earlier, it is characterized by a certain recovery motivated by both performance-driven and cost-driven applications. In numerous cases, the studies are performed through broad international cooperation. Due to its application-oriented nature, these trends of activities are moving from academic institutions to industrial research groups. Hence, the fundamental studies of the complex nature of titanium-based materials are gradually shifted to the applied research aimed at the development and scaling up of advanced alloys, processes, and new applications. The “Titan” Interstate Association realizes an important mission by keeping the titanium industry and science in the CIS united, coherent, and cooperative despite the disintegrative political and economic trends in the countries of the former Soviet Union. Translated from Fizyko-Khimichna Mekhanika Materialiv, Vol. 44, No. 3, pp. 7–20, May–June, 2008.     

Nucleation and growth kinetics of reaction-product formation for copper–titanium and silver–titanium alloys on alumina

A nucleation and growth mechanism is proposed for the formation of the reaction product at the interface between polycrystalline alumina and liquid-metal alloy drops containing titanium. The reaction product had been previously identified to be an oxide of titanium. The growth of reaction product islands was clearly observed at the alumina–metal interface using optical microscopy after dissolving the metal droplets with acid. The fractional coverage was quantified as a function of time and, by assuming Avrami-type reaction kinetics, surface reaction rate constants, k, were calculated for copper–titanium and silver–titanium alloys on alumina. Reaction rate constants between 1.4 × 10^-4 and 18 × 10^-4 s^-2 were obtained for copper–titanium alloys on alumina. The k values for silver–titanium alloys were found to be an order of magnitude lower (2.5 × 10^-6 and 7.2 × 10^-6 s^-2) then the k values obtained for copper–titanium alloys on alumina. This revised version was published online in November 2006 with corrections to the Cover Date.     

Control of the structure of titanium alloys by the method of thermohydrogen treatment

We show the possibility of controlling the structure of titanium alloys of different classes by means of their thermohydrogen treatment and consider the process of structure formation in shaped castings of VT20L alloy under additional alloying with hydrogen. Depending on the hydrogen content in the course of thermohydrogen treatment, the transformation of a course-lamellar structure into a fine-lamellar one with α-particle sizes from several micrometers to nanometers is possible. We describe the mechanism of phase and structural transformations in titanium alloys with a heightened content of β-eutectoid stabilizers (Ti-12Cr) or aluminum (VT6, VT23) under the action of hydrogen. We also show the possibility of producing a composite structure of the β-phase and TiCr₂ intermetallic compound or noncoherent particles of the α₂-and α-phases, depleted with aluminum. Translated from Fizyko-Khimichna Mekhanika Materialiv, Vol. 44, No. 3, pp. 28–34, May–June, 2008.     

Properties and structural-phase state of the surface layers of titanium after combined nitriding

We study the simultaneous nitriding of titanium alloys by two methods: thermodiffusion saturation and ion implantation. Prior to nitrogen implantation, a thin oxynitride film and a thick nitride one were formed on the surface of VT6 titanium alloy of the (α + β)-class (Ti-6Al-4V). We show that nitrogen implantation changes the state of the surface of titanium and increases the surface microhardness of nitride and oxynitride coatings. An increase in the hardness of the surface without loss of its quality is possible in the case of nitrogen implantation into a thin oxynitride film. __________ Translated from Fizyko-Khimichna Mekhanika Materialiv, Vol. 43, No. 3, pp. 65–70, May–June, 2007.     

Phase formation in Mg-Sn-Zn alloys — thermodynamic calculations vs experimental verification

Alloy development requires investing huge efforts in the selection of the alloying elements and in the determination of potential compositions and their heat treatments. This effort can be reduced by “intelligent” selection of alloys and processing based on thermodynamic considerations. As an example, we would like to report on the design of heat-treatable Al-free Mg-based alloys, their heat treatment and on the expected precipitation phases during aging following solution treatment as well as exposure to elevated temperatures without precedent heat treatment. The thermodynamically predicted phase formation will be compared with experimental results.     

Titanium alloy production technology,market prospects and industry development

Titanium alloy with a low density, high specific strength, corrosion resistance and good process performance, is the ideal structural materials for the aerospace engineering. Based on the microstructure of titanium alloys, it can be divided into α-type titanium alloys (heat-resistant titanium alloys), β-type titanium alloys and α + β-type titanium alloys. The research scopes also include the fabrication technology of titanium alloys, powder metallurgy, rapid solidification technology, and other military and civilian applications of titanium alloys. Titanium and its alloys have become the ideal structural materials used for the fuselage, and accounted for a significant part of the structural quality in most military aircrafts. Titanium’s future market expectations need to be considered in the macro level market. Apart from the supply and demand trends of titanium market, it is necessary to consider the impact of technological innovations that can help to reduce the cost of titanium production.     

Influence of N and Fe on α-Ti precipitation in the in situ TiC–titanium alloy composites

High strength with high ductility can be achieved in the titanium alloys by using metal precipitated ceramic particle as reinforcement. In this work, α + β or β-Ti alloy composites were prepared with α-Ti precipitated TiC particles. A series of Ti–Fe–C–N alloys were prepared and a constitutional diagram was constructed as a function of N and Fe contents. Two criteria were identified for the formation of α-Ti precipitation. One is the existence of Ti₂C phase and the other is the presence of α-Ti phase in the matrix. The mechanism of α-Ti formation from the Ti₂C phase is discussed.