Titanium alloy has the advantages of small proportion (about 4.5), high melting point (about 1600 degrees C), good plasticity, high strength, strong corrosion resistance, long-term operation at high temperatures (currently used in hot titanium alloy 500 degrees C), and so on, so it has been increasingly used as an important carrier part of aircraft and aircraft engines, in addition to titanium alloy material forging, there are castings, plates (such as aircraft skin), fasteners and so on. The weight ratio of titanium alloy used in modern foreign aircraft has reached about 30%, which shows that the application of titanium alloy in the aviation industry has a broad future. Of course, titanium alloy also has the following disadvantages: such as large deformation resistance, poor thermal conductivity, gap sensitivity (about 1.5), microscopic tissue changes have a significant impact on mechanical properties, 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 subject. The following main introduction of titanium forgings in the exploration of defects prone to:
1, partial defects.
In addition to beta partiality, beta spot, titanium-rich analysis and strip alpha partiality, the most dangerous is the gap-type alpha stable partial analysis (I-type alpha partial analysis), which is often accompanied by small holes, cracks, containing oxygen, nitrogen and other gases, brittle. There is also aluminum-rich alpha stable bias (type II alpha partial analysis), which also poses a dangerous defect due to its cracks and brittleness.
2, mixed with debris.
Most are high melting point, high density metal debris. By the titanium alloy composition of high melting point, high density elements are not fully melted to form in the substitum (e.g., tantalum mix), but also mixed in the smelting raw materials (especially recycled materials) carbide tool chip or inappropriate electrode welding process (titanium alloy smelting generally uses vacuum self-consumption electrode remelting method), such as tungsten electrode electrode welding arc, leaving high density clamping debris, such as tungsten clamping, in addition to titanium.
The presence of debris can easily lead to cracks and expansion, so defects are not allowed (e.g. the Soviet Union's 1977 data stipulated that high density debris with diameters of 0.3 to 0.5 mm must be recorded during x-ray examinations of titanium alloys).
3, residual shrink hole.
See example.
4, hole.
Holes do not necessarily exist in a single place, may also appear more than one dense presence, which will speed up the expansion of low-week fatigue cracks, resulting in early fatigue damage.
5, cracks.
Mainly refers to forging cracks. Titanium alloy viscosity, poor mobility, coupled with poor thermal conductivity, so in the forging deformation process, due to large surface friction, internal deformation unevenness and internal and external temperature difference, etc. , easy to produce shear belt (strain line) inside the forging, seriously lead to cracking, its orientation generally along the maximum deformation stress direction.
6, overheating.
The thermal conductivity of titanium alloy is poor, in addition to improper heating in the heating process caused forgings or raw materials overheating, in the forging process is also easy because of the thermal effect of deformation caused by overheating, causing microscopic tissue changes, resulting in overheated Wei's tissue.
