Titanium alloys thermal properties

Note Thermal conductivity and electrical resistivity were determined using the Kohlrausch apparatus. Thermal conductivity values accurate within 5% are obtained by the Kohlrausch mediod. Source R. Taylor and H. Groot, Thermal Conductivity of Titanium and Titanium Alloys, Thermophysical Properties Research Laboratories, Purdue University, 1986... 

Source R. Taylor and H. Groot, Thermal Conductivjty of Titanium and Titanium Alloys," Thermophysical Properties Research Laboratories, Purdue University, 1906... 

The thermophysical properties of titanium alloys may also contribute to difficulty encountered during friction stir welding. Some numerical simulations of the FSW process indicate that low thermal diffusivity can contribute to the formation of advancing side wormhole or tunnel defects in friction stir welds the thermal diffusivities of titanium alloys are among the lowest of all metals. 

A comparison of thermophysical and thermomechanical properties for all three alloys is given in Table 7.12. Values for thermal conductivity, heat capacity, density, thermal diffusiv-ity, flow stress (800 °C, or 1470 °F, and strain rate =10 s ) and beta-transus temperature are given. Also recall that the CP titanium alloy has an hep crystal structure, the Ti-15-3 alloy has a bcc structure, and the Ti-6A1-4V alloy has a dual hcp/bcc structure. Furthermore, it is important to note that the total alloy content increases from CP titanium to Ti-6A1-4V to Ti-15-3. Study of the various properties suggests that ease of welding may be dependent on crystal structure, thermal conductivity, and beta-transus temperature. However, much more work is needed to understand differences in the FSW response of the three alloys. 

The thermal and dynamic mechanical behaviors of triblock copolymers with a styrene/isoprene/styrene architecture were investigated in order to understand their adhesive properties. Both copolymer free films and films bonding together two titanium alloy plates were found to have thermal and mechanical response that was strongly dependent on joint preparation. Microphase separation in the melts of these triblock materials was felt to contribute to the observed phenomena namely, the presence of residual stresses in thin films which had been cooled while under high pressure. 

Therefore, the basic properties of titanium and its alloys strongly depend on their basic metallurgical structure and the way in which this is manipulated in their mechanical and thermal treatment during manufacture. Four main types of titanium alloy have been developed, and hence titanium alloys fall into the four categories alpha, near alpha, alpha plus beta, and beta. 

Table 4.57. Thermal and electrical properties of selected titanium alloys...

Metals share excellent mechanical and conductivity (electrical and thermal) properties ideal for high stress apphcations such as heart valves. Titanium—nickel alloys have become the most common material for metaUic cardiovascular applications (stents and valves) due to unique properties shape memory effect, super-elasticity, high degree of biocompatibility moreover, they are almost completely inert and nonmagnetic. 

The use of titanium alloy provided reduc ed weight, greater mechanical strength, and significantly improved thermal properties, which yielded extended thermal lifetimes, leading to remarkable improvements in the battery s specific energy. The... 

Unique thermal properties of advanced titanium alloy provide extended thermal lifetimes. 

Zirconium is a lustrous, grayish white, ductile metal. A listing of the physical properties of zirconium is given in Table 22.1. However, a few comments can be made. First, zirconium s density is considerably lower than those of iron-and nickel-based stainless alloys. Second, zirconium has a low coefficient of thermal expansion, favoring equipment that requires a dose tolerance. The coefficient of thermal expansion of zirconium is about two-thirds that of titanium, about one-third that of type 316 stainless steel (S.S.), and about one-half that of Monel. Third, zirconium has high thermal conductivity that is more than 30% better than those of stainless alloys. These properties make zirconium very fabricable for constructing compact, efficient equipment. 

Source C. Dotson, Mechanical and Thermal Properties of High-Temperature Titanium Alloys, AFML-TR-67-41, Apr 1967 reported in Aerospace Structural Metals Heui X)ok, Vol 4, Code 3718, Bat-telle Columbus Laboratories, June 1978... 

Source C. Dotson, Mechanical and Thermal Properties of High-Temperature Titanium Alloys, AFML-TR-67-41, Apr 1967... 

Cathodic chaining of hydrogen onto unalloyed titanium surfaces is not recommended when temperatures exceed 80 °C (175 F). At metal temperatures below 80 °C (175 F), thin surface hydride films may form on a titanium alloys these are usually not detrimental fium the standpoint of corrosion or mechanical properties. However, veiy high cathodic current densities may lead to enhanced hydride film growth and eventual wall penetration and embrittlement even at room temperature. Surface thermal oxides on titanium appear to inhibit hydrogen uptake effectively under moderate cathodic charging conditions, but can broak down at high current densities. 

Annealing of titanium and titanium alloys serves primarily to increase fi"ac-ture toughness, ductihty at room temperature, dimensional and thermal sta-bihty, and creep resistance. Many titanium alloys are placed in service in the annealed state. Because improvement in one or more properties generally is obtained at the expense of some other property, the annealing cycle should be selected according to the objective of the treatment. Common annealing treatments are ... 

Titanium alloys are used for mechanical parts in the aircraft and space industries due to their high strength-to-weight ratio. Titanium is difficult to machine due to its low thermal properties, and its tendency to form strong bonds with metal oxides. 

Low Expansion Alloys. Binary Fe—Ni alloys as well as several alloys of the type Fe—Ni—X, where X = Cr or Co, are utilized for their low thermal expansion coefficients over a limited temperature range. Other elements also may be added to provide altered mechanical or physical properties. Common trade names include Invar (64%Fe—36%Ni), F.linvar (52%Fe—36%Ni—12%Cr) and super Invar (63%Fe—32%Ni—5%Co). These alloys, which have many commercial appHcations, are typically used at low (25—500°C) temperatures. Exceptions are automotive pistons and components of gas turbines. These alloys are useful to about 650°C while retaining low coefficients of thermal expansion. Alloys 903, 907, and 909, based on 42%Fe—38%Ni—13%Co and having varying amounts of niobium, titanium, and aluminum, are examples of such alloys (2). 

Nickel—Copper. In the soHd state, nickel and copper form a continuous soHd solution. The nickel-rich, nickel—copper alloys are characterized by a good compromise of strength and ductihty and are resistant to corrosion and stress corrosion ia many environments, ia particular water and seawater, nonoxidizing acids, neutral and alkaline salts, and alkaUes. These alloys are weldable and are characterized by elevated and high temperature mechanical properties for certain appHcations. The copper content ia these alloys also easure improved thermal coaductivity for heat exchange. MONEL alloy 400 is a typical nickel-rich, nickel—copper alloy ia which the nickel content is ca 66 wt %. MONEL alloy K-500 is essentially alloy 400 with small additions of aluminum and titanium. Aging of alloy K-500 results in very fine y -precipitates and increased strength (see also Copper alloys). 

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