Overview Of Cast Titanium Alloys

Pure titanium is a gray-white light metal, small density, 4.54 sand m3, between Al and Fe, high melting point, about 1668 ℃, higher than iron, small coefficient of thermal expansion, poor thermal conductivity.

Pure titanium plasticity, low strength, easy to process molding, can be made into fine wire and sheet. Titanium alloy strength is very high, 0h up to 1400MPa, similar to some high-strength alloy steel, but also has good low-temperature mechanical properties.Ti has excellent corrosion resistance in the atmosphere and seawater, in sulfuric acid, hydrochloric acid, nitric acid, sodium nitrogen oxide, and other media are very stable, Ti's oxidation resistance is better than most austenitic stainless steel.

Ti in the solid state has an isotropic transition: 882.5 ℃ for the dense row of hexagonal lattice, said a-Ti; 882.5 ℃ until the melting point for the body-centered cubic lattice, said, β-Ti; 882.5 ℃ isotropic transition a-Ti ← → β-Ti, which has a very important significance for the reinforcement.

Industrial pure titanium contains H, C, 0, Fe, Mg and other impurity elements, a small amount of impurities can make titanium strength and hardness significantly higher, plasticity and toughness significantly lower. Industrial pure titanium according to the different content of impurities is divided into TA 1 . TA2. TA3 and so on three kinds of according to 15-1), the larger the number of impurities, can be made in 350 ℃ below the work, the strength requirements of the parts are not high.

Alloying elements dissolved in a-Ti, the formation of a solid solution, dissolved in the knife-Ti to form a β solid solution. Al, C, N.O "B, etc. to make the a-Ti-Moon-Ti transition temperature increases, known as a stabilizing elements. Fe, Mo, Mg, Cr, Mn, V, etc. to make the homogeneous isotropic transition temperature decreases, known as the β stabilizing elements. Sn . Zr, etc. do not have a significant effect on the transformation temperature and are called neutral elements.

According to the use of annealed state of the phase organization, titanium alloys can be divided into three categories: a titanium alloy, 18 titanium alloy and ((a + β) titanium alloy. The grades are expressed as TA, TB, TC plus a number. Titanium alloy grades and uses in Table 15-1, a titanium alloy Titanium stabilizing elements such as adding Al. B to obtain a titanium alloy. a titanium alloy strength at room temperature is lower than the β titanium alloy and (a + β) titanium alloy, but high temperature (500-600 ℃) strength is higher than they are and the organization of the stability, oxidation resistance and creep resistance is good, good welding performance. a titanium alloy can not be quenched to strengthen the main relies on the solid solution Strengthening, heat treatment is only annealed after the shape of the stress relief annealing or elimination of work hardening recrystallization annealing.

A typical grade of titanium alloy is TA7, composition Ti-5A1-2.5 Sn. Its use temperature does not exceed 5000C, mainly used in the manufacture of missile fuel tanks, supersonic aircraft turbine magazines.