Ti-Based Alloys

Titanium alloys may be processed like stainless steel. This leads to a cost effective production of a wide range of semi-finished and finished products and parts. If the tendency to oxidation and welding above approximately 350 and the low thermal conductivity are taken into account, parts can be manufactured fromTi alloys, quite similar to manufacturing from stainless steels. A wide variety of working, joining, and coating processes is well established. 

Alloy composition Alloy type Tensile Yield Density Young s Main Standard 

Ti6A15Zr0.5MoSi near a 950 880 4.45 125 High-temperature strength 3.7155 

8A14Sn3.5Zr0.7Nb 0.5Mo0.2Si0.05C near a 1030 910 4.55 120 High-temperature strength  

1 Alloy 1 1 Alloy type II Year of introduction II Useful maxiinuiii°C  

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Addition of rare earths to Ti-base alloys results in a profound effect on recrystallized grain size and other microstructural features as shown in Table 12.6. 

Rare earths have low solubilities in a-Ti and hence can function as dispersionstrengthening agents. Rapid solidification and deformation processing of Ti-base alloy containing rare earths was used to obtain a fine dispersoid of rare earth oxides, sulphides and oxysulphides. The data on improved strength, stress rupture life and creep resistance of Ti-base alloys with added rare earths are given in Table 12.10. 

They also contain low amounts of other metals such as Al, V Nb, Ta, Mn, Zr and/ or Sn. The only pure metals used for medical devices are Ti and Ta. The only binary alloys applied for biomaterials are Ti-base alloys, for example, Ti30Nb, Ti30Ta Ti(n)Mn, and memory super alloys NiTi (Bradley 1994 Breme 1994 Breme and Wadewitz 1989). 

Precious, semi-precious, most Pd-base alloys, Ti-base alloys and stainless steel also produce excellent biological responses with a survival rate of 98% to 70% for the highest concentration. Two semi-precious alloys with high Ag-content reflect the cytotoxic effect of pure silver (Figure 5.1). Ni-Cr alloys (14% and 23%) induce a strong cytotoxic action, and dental amalgams produce total cell death at very low concentrations. 

Fig. 5.4 Typical feature of LI 32 cells corresponding to control cultures or to cultures exposed to Au, Pd, or Ti or to precious, semi-precious and Ti-base alloys.

Van Orden, A. 1985. Corrosive response of the interface tissue to 316L stainless steel, Ti-based alloy and cobalt-based alloys. In The Dental Implant, R. McKinney and J.E. Lemons (Eds.), pp. 1-25, Littleton, PSG. 

Table 7.3 shows an example of galvanic corrosion rates of aluminium alloys in 3.5% NaCl solution when coupled to different materials. For instance, it is seen that the contact with low-alloy steel gives considerably higher galvanic corrosion rates on aluminium than does contact with the - from a practical point of view - more noble stainless steels as well as Ni- and Ti-based alloys (regarding material descriptions, see Section 10.1). The table reflects the cathodic efficiency of the various materials coupled to aluminium (with the exception of cadmium, zinc and aluminium alloys) in the actual environment. 

Boz] used the Bozzolo-Ferrante-Smith (BFS) method, one of the family of quantum approximate methods, to analyze site substitution behavior of Cr additions to the binary TiFe compound. The decomposition of (3Ti in step-quenched Ti base alloys was studied by [1952Phil] and discussed in [1952Phi2]. 

Figure 17.7 The length of the incubation crack as a function of the stress amplitude B - an Al-based alloy C - a Ti-based alloy D - a low-alloy steel E - a superalloy F - a stainless steel. See Table 17.1 for details.

It is obvious from curves in Figure 17.7 that, under stress amplitudes of more than 300 MPa, the length amcub is of the order of 1—2 pim for Al- and Ti-based alloys. The crack begins to grow almost at once. Other alloys give the amcub value of 4—5 im and the crack growth occurs later. 

For steels and superalloys under a stress amplitude of from 150 to 300 MPa, the embryo length is found to be 4—10 pim. The values of Njncub and Nf increase correspondingly in comparison with Al- and Ti-based alloys. The stress amplitude from 100 to 150 MPa for these alloys does not lead to the crack-embryo propagation. As... 

Five groups of materials based on Ti may be distinguished [1.51-53] commercially pure (i. e., commercially available) Ti (cp-Ti), low-alloy Ti materials, Ti-base alloys, intermetallic Ti-Al materials, and highly alloyed functional materials TiNi shape memory alloys, Nb-Ti superconducting materials (Sect. 4.2.1), and Ti-Fe-Mn materials for hydrogen storage. 

Titanium undergoes a structural phase transformation at 882 °C. Like in steels, this transformation is crucial for the microstructural design and the mechanical properties of Ti-based alloys. The low temperature phase a-Ti has an almost close packed hexagonal (A3) structure that is somewhat compressed along the c axis. Its... 

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

Roue L, Guay D, Schulz R (2000) Hydrogen electrosorption in nanociystalline Ti-based alloys. J Electroanal CJiem 480 64—73. doi 10.1023/ A 1026441532352... 

Stainless steels, as well as A1-, Ni-, and Ti-based alloys have been studied extensively as possible candidates for bipolar plates. One of the most well-studied materials for bipolar plates is SS 316/316L (16-18% Cr, 10-14% Ni, 2% Mo, rest Fe) other candidates are 310,904L, 446, and 2205. Bare stainless steel plates form a passive 2-A nm chromium oxide surface layer under PEMFC conditiOTs that leads to unacceptably high ICRs. A similar trend is observed for the other alloys and therefore surface modification or surface coatings on selected substrate material has to be considered as a pathway to meet the technical targets of low ICR and high corrosion resistance. 

Ti-based alloys have long been known to be susceptible to hot-salt stress corrosion (e.g. Gray, 1973). Recent work (Nicholls et al., 1997) indicates that TiAl-based alloys suffer from accelerated hot-salt corrosion attack in the temperature range 650 to... 

Property Ti-based alloys TisAl-based intermetallic materials TiAl-based intermetallic materials Ni-based superalloys... 

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