Titanium intermetallics

Modem machining deals with an increasingly wide range of materials which includes, in addition to the traditional metals, high-chromium and nickel stainless steels, titanium, intermetallics, refractory metals, ceramics, glasses, fiber-reinforced composites, and many others. These materials have widely different properties. They react differently to machining and each presents a special machining problem. 

Current research in metal hydrides has been stimulated by the possibility of storing hydrogen as a solid hydride. Rare-earth and titanium intermetallic alloys have been most investigated for this purpose, but there is also a continuing interest in the Pd/H system because its comparative simplicity makes it popular as a model system. 

Aluminium-Titanium. Intermetallic phases with a significantly higher melting point (dissociation tempera-... 

Refractory metals give only rise to few intermetallic compounds, due to the very high temperature of the liquidus of their alloy systems, though de Lepinay et al have obtserved the formation of copper-titanium intermetallic compounds during the electrodeposition of titanium [40]. 

The second form consists of Pt metal but the iridium is present as iridium dioxide. Iridium metal may or may not be present, depending on the baking temperature (14). Titanium dioxide is present in amounts of only a few weight percent. The analysis of these coatings suggests that the platinum metal acts as a binder for the iridium oxide, which in turn acts as the electrocatalyst for chlorine discharge (14). In the case of thermally deposited platinum—iridium metal coatings, these may actually form an intermetallic. Both the electrocatalytic properties and wear rates are expected to differ for these two forms of platinum—iridium-coated anodes. 

Alloys of the P type respond to heat treatment, are characterized by higher density than pure titanium, and are more easily fabricated. The purpose of alloying to promote the P phase is either to form an aE-P-phase aEoy having commercially useful quaUties, to form aEoys that have duplex a- and P-stmcture to enhance he at-treatment response, ie, changing the a and P volume ratio, or to use P-eutectoid elements for intermetallic hardening. The most important commercial P-aEoying element is vanadium. 

Welding (qv) of titanium requires a protected atmosphere of iaert gas. Furthermore, parts and filler wire are cleaned with acetone (trichloroethylene is not recommended). The pieces to be welded are clamped, not tacked, unless tacks are shielded with iaert gas. A test sample should be welded. Coated electrodes are excluded and higher purity metal (lower oxygen content) is preferred as filler. Titanium caimot be fusion-welded to other metals because of formation of brittle intermetallic phases ia the weld 2oae. 

Titanium and zirconium intermetallics. Various metals of practical relevance (Ti, and also Nb, Fe, Ni) form several fields of solid solutions with aluminium in presence, often, of rather complex phase equilibria. Several investigations and re-examinations of such systems, performed in the course of time, have been reviewed and assessed during the European Congress EUROMAT 2005... 

Individually indexed alloys or intermetallic compounds are Aluminium amalgam, 0051 Aluminium-copper-zinc alloy, 0050 Aluminium-lanthanum-nickel alloy, 0080 Aluminium-lithium alloy, 0052 Aluminium-magnesium alloy, 0053 Aluminium-nickel alloys, 0055 Aluminium-titanium alloys, 0056 Copper-zinc alloys, 4268 Ferromanganese, 4389 Ferrotitanium, 4391 Lanthanum-nickel alloy, 4678 Lead-tin alloys, 4883 Lead-zirconium alloys, 4884 Lithium-magnesium alloy, 4681 Lithium-tin alloys, 4682 Plutonium bismuthide, 0231 Potassium antimonide, 4673 Potassium-sodium alloy, 4646 Silicon-zirconium alloys, 4910... 

Researchers have tried to fabricate plates using many different metals— mainly, stainless steel, aluminum alloys, titanium alloys, nickel alloys, copper alloys, intermetallic alloys, and metal-based composites such as carbon fiber-reinforced aluminum alloys, carbon fiber reinforced copper alloys, etc. [26]. Although Ta, Hf, Nb, Zr, and Ti metals show good corrosion resistance and chemical stability [6], the cost of fhese metals is too high for them to be used as materials in metal plates. That is why relatively cheaper iron-based alloys, particularly stainless steel, have been popularly studied as plate material. In the following secfions, we will infroduce sfainless sfeel (SS) and SS plates, which have been extensively investigated and show promise for the final applications [6,11]. 

Chapter 10 provides an exhaustive description of how these techniques can be applied to a large number of industrial alloys and other materials. This includes a discussion of solution and substance databases and step-by-step examples of multi-component calculations. Validation of calculated equilibria in multi-component alloys is given by a detailed comparison with experimental results for a variety of steels, titanium- and nickel-base alloys. Further selected examples include the formation of deleterious phases, complex precipitation sequences, sensitivity factor analysis, intermetallic alloys, alloy design, slag, slag-metal and other complex chemical equilibria and nuclear applications. 

Titanium iron hydrides are among the materials which, at the present time, appear to have potential for practical applications as an energy-storage medium (7). The formation and properties of titanium iron hydride have been studied by Reilly and Wiswall (3), who found that the reaction proceeds in two steps as indicated by Reactions 5 and 6. Both hydrides have dissociation pressures above 1 atm at room temperature in contrast to TiH2 which is very stable. Titanium iron is representative of intermetallic compounds that consist of an element (titanium) capable of forming a stable hydride and another element (iron) that is not a hydride former or at best, forms a hydride with great difficulty. Iron presumably plays a role in destabilizing the hydrides. Titanium also forms a 1 1 compound with copper (there are other intermetallic compounds in the titanium-copper system) and this fact, coupled with the observation that copper... 

The intermetallic compounds were prepared from the best grade of metals commercially obtainable. The rare earth metals, obtained from Research Chemicals, Inc., were 99.9% pure, and cobalt and nickel, obtained from the United Mineral Corp., were 99.999% pure. After each element was weighed to obtain the correct stoichiometric amounts, the compounds were formed by induction melting in a water-cooled copper boat under an argon atmosphere, purified by passage through a titanium-gettering furnace. 

The oxides, hydrides, halides, sulphides, sulphate , carbonates, nitrates, and phosphates are considered with the basic elements the other compounds are taken in connection with the aoidio element. The double or complex salts in connection with a given element include those associated with elements previously discussed. The carbides, silicides, titanides, phosphides, arsenides, etc., are considered in connection with carbon, silicon, titanium, etc. The intermetallic compounds of a given element include those associated with elements previously considered. 

Several fiber types have been mentioned so far, and several other types have been neglected that have been worked on over the past few years. Some of those not discussed may become important fibers for reinforcement in the years ahead. To date though, they have not been available in sufficient quantity for thorough evaluation in composite specimens. Included in this group are boron carbide, spinel, polycrystalline alumina and silica, titanium diboride, and miscellaneous silicides and intermetallics. Ten years from now as we look back on the 70s we no doubt will have an entirely different view of some of these materials. 

Metals and ceramics (claylike materials) are also used as matrices in advanced composites. In most cases, metal matrix composites consist of aluminum, magnesium, copper, or titanium alloys of these metals or intermetallic compounds, such as TiAl and NiAl. The reinforcement is usually a ceramic material such as boron carbide (B4C), silicon carbide (SiC), aluminum oxide (A1203), aluminum nitride (AlN), or boron nitride (BN). Metals have also been used as reinforcements in metal matrices. For example, the physical characteristics of some types of steel have been improved by the addition of aluminum fibers. The reinforcement is usually added in the form of particles, whiskers, plates, or fibers. 

The alloy niobium-titanium (NbTi) and the intermetallic compound of niobium and tin (Nb>Sn) are the most technologically advanced LTS materials presently available. Even though NbTi has a lower critical field and critical current density, it is often selected because its metallurgical properties favor convenient wire fabrication. 

Figure 11.4.6 shows the pressure (P) versus composition (x) isotherms for the hydrogen-iron-titanium system. This system is an example of the formation of a ternary hydride from an intermetallic compound. 

The melting point of titanium is 1670°C, while that of aluminium is 660°C.142 In kelvins, these are 1943 K and 933 K, respectively. Thus, the temperature 625°C (898 K) amounts to 0.46 7melting of titanium and 0.96 melting of aluminium. Hence, at this temperature the aluminium atoms may be expected to be much more mobile in the crystal lattices of the titanium aluminides than the titanium atoms. This appears to be the case even with the Ti3Al intermetallic compound. The duplex structure of the Ti3Al layer in the Ti-TiAl diffusion couple (see Fig. 5.13 in Ref. 66) provides evidence that aluminium is the main diffusant. Otherwise, its microstructure would be homogeneous. This point will be explained in more detail in the next chapter devoted to the consideration of growth kinetics of the same compound layer in various reaction couples of a multiphase binary system. 

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