Titanium ring, titanium block, titanium target and other titanium alloy forgings flaw detection prone to defects

Titanium alloy specific gravity is small (about 4.5), high melting point (about 1660 ℃), good plasticity, has a high specific strength, corrosion resistance, can work at high temperatures for long periods of time (the current hot strength of the titanium alloy has been used for 500 ℃), and other advantages, and therefore has been increasingly used as an aircraft and aircraft engine important bearing parts, in addition to titanium alloy material forgings, there are casting, plate (such as aircraft skin), fasteners and so on. In addition to titanium alloy forgings, there are castings, plates (such as aircraft skins, fasteners and so on. Modern foreign aircraft using titanium alloy weight ratio has reached about 30%, visible titanium alloy application 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, which leads to complexity in smelting, forging processing and heat treatment. 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 alloy forgings:

1, segregation-type defects In addition to β segregation, β spot, titanium-rich segregation and striated α segregation, the most dangerous is the interstitial type α stabilized segregation (I-type α segregation), which is often accompanied by tiny holes and cracks around it, contains oxygen, nitrogen and other gases, and is more brittle. There are aluminum-rich α-stable segregation (type II α segregation), also due to cracks and brittleness and constitute a dangerous defect.

2, inclusions are mostly high melting point, high density metal inclusions. By the titanium alloy composition of high melting point, high density elements are not sufficiently melted to stay in the matrix formation (such as molybdenum inclusions), but also mixed in the smelting of raw materials (especially recycled materials) in the cemented carbide cutting tool debris or inappropriate electrode welding process (the smelting of titanium alloys is generally used in the vacuum self-consuming electrode remelting method), such as tungsten electrode arc welding, leaving high-density inclusions, such as tungsten inclusions, in addition to the 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, the information provided by the titanium alloy X-ray radiographic inspection found in the diameter of 0.3 ~ 0.5mm of high-density inclusions must be recorded).

3, residual shrinkage See examples.

4, hole hole is not necessarily a single presence, there may be more than one dense presence, will make the low-week fatigue crack expansion speed up, resulting in early fatigue damage.

5,Crack mainly refers to forging cracks. Titanium alloy viscous, poor fluidity, coupled with poor thermal conductivity, and thus in the process of forging deformation, due to surface friction, internal deformation unevenness is obvious, as well as the temperature difference between inside and outside the large, easy to produce in the forging internal shear band (strain line), which leads to cracking in severe cases, its orientation is generally along the direction of the maximum deformation stress.

6, overheating The thermal conductivity of titanium alloy 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 microstructure changes, resulting in overheating of the Weiss organization.