Ti-based composites

Key words Ti-based composites, fatigue crack growth, high temperature... 

An operating temperature of conventional titanium alloys is limited by 300 - 500 °C. The known Ti-based composites possess high strength under... 

The first carbonitride alloys based on Ti(C,N)—Ni—Mo were iatroduced ia 1970 foUowed by (Ti, Mo)(C,N)-based compositions having fine microstmctures that provided a balance of wear resistance and toughness (4). Continued research on the titanium carbonitride alloys, often called TiC—TiN cermets, ia the 1980s led to the developmeat of complex cermets having a variety of additives such as molybdeaum carbide(2 l) [12069-89-5] M02C, TaC, NbC, zirconium carbide [12020-14-3], ZrC, hafnium carbide [12069-85-1], HfC, WC, vanadium carbide [12070-10-9], VC, chromium carbide (3 2)... 

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]. 

Several attempts to induce orientation by mechanical treatment have been reviewed 6). Trans-polyacetylene is not easily drawn but the m-rich material can be drawn to a draw ratio of above 3, with an increase in density to about 70% of the close-packed value. More recently Lugli et al. 377) reported a version of Shirakawa polyacetylene which can be drawn to a draw ratio of up to 8. The initial polymer is a m-rich material produced on a Ti-based catalyst of undisclosed composition and having an initial density of 0.9 g cm-3. On stretching, the density rises to 1.1 g cm-3 and optical and ir measurements show very high levels of dichroism. The (110) X-ray diffraction peak showed an azimuthal width of 11°. The unoriented material yields at 50 MPa while the oriented film breaks at a stress of 150 MPa. The oriented material, when iodine-doped, was 10 times as conductive (2000 S cm-1) as the unstretched film. By drawing polyacetylene as polymerized from solution in silicone oil, Basescu et al.15,16) were able to induce very high levels of orientation and a room temperature conductivity, after doping with iodine, of up to 1.5 x 10s S cm-1. 

In the copolymerisation of butadiene and isoprene with Ti-based catalysts, both monomeric units of the copolymers obtained are essentially of a ciy-1,4 structure the microstructure of monomeric units in the copolymers does not differ substantially from that in the homopolymers [196-198], Nd-based catalysts provide butadiene/isoprene copolymers with more than 95% cis-1,4 monomeric units [89,199,200], On the other hand, Co-based catalysts give copolymers in which the structure of the monomeric units depends markedly on copolymer composition [19,201,202], Similarly, the structure of the monomeric units depends on copolymer composition in copolymers of butadiene and 2,3-dimethylbutadiene obtained by copolymerisation with Co-based catalysts [201,203],... 

BN fibers are used in aluminum matrices because they are one of the few materials easily wet by molten aluminum. hBN-AlN composites are described ". Gel methods resulted in an hAlN-turbostratic hBN composite. zBN-based composites, e.g., with Al, Si, Ti nitride matrices, were reported. A nanostructure composite was made by low temperature conversion of an aqueous solution of simple Al, B, and N-containing compounds to intermediate precursor (gel) materials. BN-AIN composite fabrication is also described . 

The effects of the V/Ti/P composition on the catalytic performance were studied in the reaction of methanol with acetic acid in the presence of oxygen with fixed acetic acid/methanol/oxygen/nitrogen feed rates of 25/50/25/350 mmol/h. Over a V phosphate catalyst with a P/V atomic ratio of 1.06, the yields of acrylic acid and methyl acrylate reach 37 and 15 mol%, respectively, based on the charged acetic acid. From a study with a series of catalysts with VTi2P composition, where x is varied from 4.0 to 7.0, it is found that the activity decreases steadily as the phosphorus content increases, while the highest selectivity to the condensation products (acrylic acid and methyl acrylate) is obtained with the X = 6.0 catalyst. The yields of acrylic acid and methyl acrylate reach 45 and 20 mol%, respectively, based on the charged acetic acid the selectivity to the two condensation products reaches 89 mol% based on acetic acid. From a study with another series of [(Ti... 

Hindryckx, R, Dubois, R, Jerome, R., Teyssie, R, and Garcia Marti, M. 1997. Rolymeiization-filled composites prepared with highly active filler-supported Al/Ti/Mg catalysts. 1. Synthesis of homogeneous polyethylene-based composites. Journal of Applied Polymer Science 64 423-438. 

The preceding discussion was based on the situation where an alloy component vaporizes or sublimates directly to characteristic species that can be measured easily. This situation is not the case in some reactive alloy systems because one component may not vaporize directly or its vapor pressure may be too low to measure. However, its activity can be calculated through an additional equilibrium between the components and easily measurable vapor species. Ti-Al-O is an important example of this type of system. Here interstitial O has a very high solubility in Ti-rich compositions, and O... 

Table 3.1-19 Chemical composition and mechanical properties of Ti-base alloys at room temperature (minimum values)...

Based on systematic variations and optimizations such as those shown in Fig. 4.2-8, commercial Nb—Ti superconducting composite wires are provided for a wide range of specifications. Figure 4.2-10 shows a typical wire cross section and Table 4.2-9 lists some characteristic data. 

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