What are the factors affecting Gr12 titanium alloy forgings?

Gr12 titanium alloy has small specific gravity, high melting point (about 1600 ℃), good plasticity, high specific strength, corrosion resistance, can work at high temperatures for a long time, and other advantages, and therefore has been used more and more as an important bearing parts of the aircraft and aircraft engines, in addition to titanium alloy material forgings, castings, fasteners and so on. Modern foreign aircraft using titanium alloy weight ratio has reached about 30%, the application of titanium alloy in the aviation industry has a broad future. Of course, titanium alloy also exists the following shortcomings: such as deformation resistance, poor thermal conductivity, notch sensitivity (1.5 or so), microstructure changes on the mechanical properties of the more significant impact, resulting in smelting, forging, processing and heat treatment complexity. Therefore, the use of non-destructive testing technology to ensure the metallurgical and processing quality of titanium alloy products is a very important topic. The following mainly introduces the defects that are easy to appear in the flaw detection of titanium forgings:

1, segregation type defects
In addition to β segregation, β spot, titanium-rich segregation and striated α segregation, Z dangerous is the gap type α stable segregation (I type α segregation), which is often accompanied by tiny holes and cracks around it, containing
Oxygen, nitrogen and other gases, brittle. There is also aluminum-rich α-stable segregation (type II α segregation), also due to cracks and brittleness and constitute a dangerous defect.
2,Inclusions
Mostly high melting point, high density metal inclusions. By the titanium alloy composition of high melting point, high density elements are not fully melted to stay in the matrix formation (such as molybdenum inclusions), but also mixed in the
Smelting raw materials (especially recycled materials) in the cemented carbide tool chipping or inappropriate electrode welding process (titanium alloy smelting is generally used in vacuum self-consumption electrode remelting method), for example
The high density of inclusions left behind by tungsten arc welding, such as tungsten inclusions, in addition to titanium inclusions.
The presence of inclusions can easily lead to the occurrence and expansion of cracks, so it is not allowed to exist defects (for example, the Soviet Union in 1977, titanium alloys X-ray radiography inspection found in the diameter of 0.3 ~ 0.5mm of high-density inclusions must be recorded).
3,Residual shrinkage
4,Hole
Holes do not necessarily exist individually, there may be more than one dense presence, will make the low-week fatigue crack expansion speed up, resulting in premature fatigue damage.
5,Crack
Mainly refers to forging cracks. Titanium alloy viscosity, poor fluidity, coupled with poor thermal conductivity, and thus in the forging deformation process, due to surface friction, internal deformation inhomogeneous
Obviously, as well as a large temperature difference between inside and outside, it is easy to produce a shear band (strain line) inside the forging, which leads to cracking in severe cases, and its orientation is generally along the direction of the Z large deformation stress.
6,Overheating
Titanium alloy thermal conductivity is poor, in the thermal processing process in addition to improper heating caused by forgings or raw materials overheating, in the forging process is also prone to deformation due to thermal effects caused by overheating, causing microstructural changes.
Heat, causing microstructure changes, resulting in overheating Weiss organization.