Defects that are prone to occur in titanium alloy forgings:

1. Segregation type [i] defects

In addition to β segregation, β spot, titanium-rich segregation and strip α segregation, the most dangerous is interstitial α stable segregation (type I α segregation), which is often accompanied by small holes and cracks around it, containing oxygen, nitrogen and other gases , is more brittle. There is also aluminum-rich α stable segregation (type II α segregation), which also constitutes a dangerous defect due to cracks and brittleness, and also reduces the thermal stability and other properties of the alloy.

2. Inclusions

There are inclusions on the surface of the billet, and cracks are often formed along the inclusions during forging, or obvious foreign bodies appear after the forging is corroded, most of which are metal inclusions with high melting point and high density. It is formed by the high melting point and high density elements in the titanium alloy composition that are not fully melted and left in the matrix (such as molybdenum inclusions), and there are also carbide tool chippings or inappropriate electrode welding processes mixed in smelting raw materials (especially recycled materials). The smelting of Titanium Industrial Rod generally adopts the vacuum consumable electrode remelting method [ii]), such as high-density inclusions left by tungsten arc welding [iii], such as tungsten inclusions, and titanium compound inclusions. Titanium alloy forgings with inclusions are not allowed to be put into use.

3. Holes

The holes do not necessarily exist alone, but may also exist in a plurality of clusters, which will accelerate the growth of low-cycle fatigue cracks and cause premature fatigue failure.

4. Cracks

Mainly refers to forging cracks. Titanium alloys have high viscosity, poor fluidity, and poor thermal conductivity. Therefore, in the process of forging deformation, due to large surface friction, obvious internal deformation unevenness, and large temperature difference between inside and outside, it is easy to get inside the forging. A shear band (strain line) is generated, and cracking occurs in the direction of the maximum deformation stress in severe cases.

5. Overheating

The thermal conductivity of titanium alloys is poor. In addition to overheating of forgings or raw materials caused by improper heating during hot working, it is also easy to cause overheating due to thermal effects during deformation during forging, causing changes in microstructure and overheating Widmanderin [iv] ].

In order to ensure the quality of titanium alloy forgings, in addition to strictly controlling the quality of raw materials, attention should also be paid to the ultrasonic flaw detection of forging blanks and semi-finished products to prevent some deformation and physical properties during subsequent heating and processing.