First, segregation type defects
In addition to β segregation, β spot, titanium-rich segregation and strip α segregation, the more dangerous is the gap type α stable segregation (I type α segregation), which is often accompanied by fine holes and cracks around it, and it is brittle, containing oxygen, nitrogen and other gases. Aluminum-rich type α-stable segregation (type II α segregation) is also accompanied by cracks and brittleness, constituting a dangerous defect.
Second, inclusions are defects caused by high melting point and high density metal inclusions
It is formed by the titanium alloy composition of the high melting point, high-density elements are not sufficiently melted and remain in the matrix (such as molybdenum inclusions), but also smelting raw materials (especially recycled materials) mixed in the carbide tool fragments or electrode welding process is not appropriate (titanium alloy smelting is generally used in the vacuum self-consumption electrode remelting method), such as tungsten arc welding, leaving tungsten inclusions, titanium inclusions and other high-density inclusions. The presence of inclusions can easily lead to cracking and expansion, so there is no defect (for example, in the Soviet Union in 1977 data, in order to X-ray inspection of titanium alloys, it is necessary to record the diameter of 0.3-0.5mm of high-density inclusions).
III. Defects caused by residual shrinkage
See examples.
IV. Holes
The hole is not necessarily a single one, but may be multiple and dense, which accelerates the rate of expansion of low-week fatigue cracks and leads to premature fatigue damage.
V. Cracks
Mainly refers to forging cracks. Titanium matrix viscosity, poor fluidity, poor thermal conductivity, so in the process of forging deformation, due to the surface friction, internal deformation is not uniformly obvious, the temperature difference between the inside and outside, etc., is easy to produce shear bands within the forging (strain lines), which can cause cracks in severe cases, and its orientation is usually along the direction of the larger deformation stress.
Six, defects caused by overheating
Titanium alloy has poor thermal conductivity, in addition to forging or improper heating of raw materials, due to the thermal effect of deformation in the forging process, easily caused by overheating.
