Classification and physical and mechanical properties of pure titanium and titanium alloys
High-purity titanium is a low-strength, plastic-rich metal. The most pure titanium is produced by the iodide method (i.e., by vacuum heating and dissociation of Ti). Iodide method titanium contains 0.05% impurities, mainly metal impurities, its ultimate strength C-215-255 meganewtons/m3; yield point 0.2=120-170 meganewtons/m3; elongation = 50-60% The reduction of the section is taken as 70-80%; the Brinell hardness is 1275 meganewtons/meter 3, and the impact toughness is >250 joules/cm 3 . The elastic characteristics of titanium with iodide method are as follows: volume elastic modulus = meganewtons/m3; standard elastic modulus or Young's modulus five = 10.6x10* meganewtons/meter shear modulus (=40xl0s meganewtons/meter 2; The looseness factor is 0.84U33.
Titanium is a transition element located in Group IV subgroup B of the Mendeleev periodic table. Titanium has two allotropes: a titanium below the polymorphic transformation temperature (882.5 ° C), which has a close packed hexagonal lattice; when the temperature is below the polymorphic conversion temperature but below the melting point, Cold titanium, which has a body-centered cubic lattice. "Titanium has a density of 4.51 g/cm3 at 25 ° C and cold titanium has a density of 4.32 g/cm 3 at 900 ° C. The lattice constant of a titanium is as follows: a = 0.2950 nm; c = 0.4683 nm; c / a = 1.587; at 900 ° C, a-0.3306 nm of cold titanium; at 25 ° 0, a = 0.3282 Nano. In terms of density, titanium is located between aluminum and iron, and it ranks fourth among the metals with the largest reserves (after aluminum, iron, and magnesium) in terms of its distribution in the earth's crust. However, titanium iodide has little application in the industry due to its low strength. Industrial pure titanium contains a small amount of impurities such as iron, silicon, hydrogen, oxygen and nitrogen. The presence of these elements, even in small quantities, greatly increases the strength of the titanium and significantly reduces its plasticity at room temperature.
Titanium alloys, the elements involved in the formation of alloys are divided into three categories according to their influence on the phenomenon of titanium polymorphism:
1. Can improve the elements of phase stability. Among the various metals, aluminum is a phase stabilizer and is contained in almost all industrial titanium alloys.
2. The elemental stabilizer which can improve the stability of the Lu phase can be subdivided into two subclasses. The first subclass of chromium, manganese, iron, nickel, lead, antimony and cobalt. When they are alloyed with titanium, phase inhomogeneous co-melt decomposition occurs at a relatively low level of precipitation. Such elements are called phase heterogeneous co-melt stabilizers. Vanadium, molybdenum, niobium, tantalum and tungsten niobium are in the second subclass. When they are alloyed with titanium, the dissolving body can be kept to room temperature. These elements are referred to as phase isomorphous stabilizers.
3. Elements such as tin and zirconium that do not significantly affect stability are classified as the third type. The heat treatment does not strengthen the titanium alloy. The superior performance of this alloy is that it has good solderability.