Alpha strengthened

The Zn—A1 system permits manipulation of the mechanical properties by suitable heat treatment. The aluminum-rich alpha phase is especially suitable for solution hardening since it can be supersaturated by as much as 30 wt % zinc. Furthermore, both alpha and beta phases can be strengthened by precipitation because of decreasing solute solubiUty with decreasing temperature. 

The use of specific additives such as alpha-hydroxy acids, urea, or glycerol may strengthen some of these changes.25-28 The effects of additives can be studied in RCTs and lead to recommendation of specific additives for specific purposes, for example, urea to increase hydration. 

Table 2 summarizes the best data obtained in three groups of alloys namely binary, ternary and complex alloys with combined strengthening with borides and silicides. The binary alloys is practically quasi-binary ones because contain enough content of iron, which transforms these formally alpha-alloys into practical pseudo-alpha ones containing small but important amount of beta-phase. 

These alloys have an hep crystal structure known as alpha phase. The beta-transus temperature of CP titanium alloys is -910 15 °C (1670 27 °F), depending on the oxygen content (Ref 1). These alloys are not strengthened by heat treatment, like some other titanium alloys. They also have excellent corrosion resistance in seawater and marine environments. 

The combination of low-aluminum, medium-zirconium, and high-tin strengthens and stabilizes the alpha phase. Considerable strengthening at all temperatures is derived from the active eutectoid compound TixSiy. The alloy may be classified as both a weakly stabiHzed, martensitic alloy and an active eutectoid. It displays the isothermal transformation characteristics of two-phase titanixim alloys. 

IMI 829 is a near-alpha titaniiim alloy of me-diiim strength and high-temperature capability up to 540 °C (1000 °F). IMI 829 develops its properties from a combination of sohd-solution strengthening and beta heat treatment which produces an acicular transformed structure. IMI 829 is lean in beta stabilizers in order to give high creep resistance. It therefore has hmited har-denability good property levels being achieved in sections up to 75 mm (3 in.) thick. 

IMI 550 is an alpha-beta titanimn alloy of medium strength with a typical ultimate tmisile strength of 1100 MPa (159 ksi) and temperature capability up to about400 °C (750 °F). The alloy derives its properties om solid solution strengthening and age hardening. Because of the significant level of beta stabilizer content, IMI 550 exhibits a useful aging response in sections up to 150 rmu (6 in.) thick. 

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