Organizational changes during heat treatment of titanium and titanium plate

In order to improve the performance of titanium and titanium alloys , except alloys Outsider through the necessary general but also the use of appropriate heat treatment.

Organizational changes during heat treatment of titanium and titanium alloys

Titanium and titanium alloys in addition to the heating process of recovery and recrystallization cold outside the organization , as well as solution of the compound and a → β polymorphic transformation.
The second type of stress most of the process of recovery process to eliminate titanium and titanium alloy is also at a certain temperature , generated by the movement of vacancies and dislocations when making deformation . Recovery process occurs at a temperature below the recrystallization temperature, typically at 500 ~ 650 ℃.

Like other metals, titanium and titanium alloy recrystallization process is also in the organization after deformation , born in the crystalline grain nucleation and growth process. In this case the lattice type does not change, but the change of mechanical properties . This process is subject to the degree of cold deformation , heating temperature and holding time , and through the cold deformation rate, heating temperature and recrystallized grain size of the three-dimensional re- crystallized.

Titanium alloying elements on the recrystallization temperature began to influence the preceding section has been described before. In addition , niobium and cobalt , the commonly used alloying elements and impurity elements could increase the recrystallization temperature of titanium .

It should be noted , in titanium and titanium alloys , recrystallization process is often accompanied by other organizational changes . For example , the smaller the content of the β stabilizing elements near a a + β alloys and alloys , accompanied with a change in phase and the dissolved β components ; β in the heat-treatable alloy recrystallization often performed simultaneously with the re -crystallization process, or cause birth effects on subsequent aging . In addition, different types of the alloy microstructure in a different room , the deformation of the alloy phase involved different recrystallization process and characteristics are not the same surgical implant titanium. a recrystallization of the alloy in a major phase. In addition to industrial pure titanium addition , a metal cold deformation capacity is small, and therefore difficult to grain refinement effect in β -type alloy recrystallization mainly in β phase. β alloy cold deformation capacity is big, the degree of crushing grain , can be changed by recrystallization original organization . However, due to β alloy grain growth tendency of large , so the grain refinement is still more difficult. As a + β alloys, will depend on the participation of the main phase deformation , depending on the circumstances analysis, such as recrystallization TC4 alloy is mainly a phase recrystallization .

Determination of recrystallized microstructure observation and mainly uses a combination of X -ray diffraction method . When recrystallization , fine equiaxed grains appear on the fibrous tissue after deformation , while x-ray back reflection Laue diffraction ring on the start phase diagram becomes disconnected spots . For heat treatable β alloys can also be used incomplete aging (500 ℃ / 4 ~ 8 hours, air-cooled ) method displays recrystallized structure , not by incompletely recrystallized grains after aging after corrosion was dark .

It was determined that began TA2 titanium recrystallization temperature is about 550 ℃, TA7 titanium is about 600 ℃,medical titanium bar TC4 titanium alloy is about 700 ℃, TB2 alloy is 750 ℃.