Titanium alloy has a small specific gravity (about 4.51 kg / CM3), a high melting point (about 1650 ° C), good plasticity, high specific strength, good corrosion resistance, and can work at high temperatures for a long time. ° C), and has been increasingly used as an important bearing component of aircraft and aircraft engines. At present, the application proportion of titanium alloy materials in aircraft has reached about 30%, and titanium alloy materials have a bright future in the fields of aviation, navigation, petroleum, power, electronics, and other fields. However, titanium alloys also have the following defects: large deformation stress, poor thermal conductivity, and large notch sensitivity (about 1.5). Now the change in structure has a significant impact on mechanical properties, etc., which leads to smelting, forging processing and heat treatment. Complexity. Therefore, using non-destructive testing technology to ensure the processing quality of titanium alloy materials is an important link. The following introduces the defects that are easy to occur in titanium alloy materials during flaw detection:
Segregation defect
Common segregation defects are β-segregation, β-spots, titanium-rich segregation, and strip-shaped α segregation. The most dangerous gap-type stable α segregation (type I α segregation) is often accompanied by small holes, cracks, and oxygen. Nitrogen and other gases are more brittle. There is also aluminum-rich α stable segregation (type II α segregation), which is also a dangerous defect due to cracks and brittleness.
2. Inclusions are mostly metal inclusions with a high melting point and high density. It is formed by the high melting point and high-density elements in titanium alloys that are not fully melted and left in the matrix (such as molybdenum inclusions). There are also carbide chipping or improper electrode welding processes mixed with smelting raw materials (especially recycled materials) ( Titanium alloy smelting generally uses the vacuum consumable furnace electrode remelting method), such as tungsten electrode arc welding, leaving high-density inclusions, such as tungsten inclusions, in addition to titanium compound inclusions. The existence of inclusions easily leads to the occurrence and expansion of cracks, so it is an impermissible defect.
3. Residual shrinkage
4. Holes, holes may not exist individually or maybe densely located, which will accelerate the growth of peripheral fatigue cracks and cause early fatigue damage.
5. Crack mainly refers to forging crack. Titanium alloy has large viscosity, poor fluidity, and poor thermal conductivity. Therefore, during forging deformation, due to large surface friction, obvious internal deformation non-uniformity, and large internal and external temperature differences, it is easy to generate shear lines inside the forging ( Strain line), which causes cracking when severe, and its orientation is generally in the direction of the maximum deformation stress.
6. Overheating, titanium alloy has poor thermal conductivity. In addition to overheating caused by improper heating during the hot working process, it is also easy to cause overheating due to thermal effects during deformation during the forging process, causing microstructural changes and overheating Weiss organization.
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Segregation defect
Common segregation defects are β-segregation, β-spots, titanium-rich segregation, and strip-shaped α segregation. The most dangerous gap-type stable α segregation (type I α segregation) is often accompanied by small holes, cracks, and oxygen. Nitrogen and other gases are more brittle. There is also aluminum-rich α stable segregation (type II α segregation), which is also a dangerous defect due to cracks and brittleness.
2. Inclusions are mostly metal inclusions with a high melting point and high density. It is formed by the high melting point and high-density elements in titanium alloys that are not fully melted and left in the matrix (such as molybdenum inclusions). There are also carbide chipping or improper electrode welding processes mixed with smelting raw materials (especially recycled materials) ( Titanium alloy smelting generally uses the vacuum consumable furnace electrode remelting method), such as tungsten electrode arc welding, leaving high-density inclusions, such as tungsten inclusions, in addition to titanium compound inclusions. The existence of inclusions easily leads to the occurrence and expansion of cracks, so it is an impermissible defect.
3. Residual shrinkage
4. Holes, holes may not exist individually or maybe densely located, which will accelerate the growth of peripheral fatigue cracks and cause early fatigue damage.
5. Crack mainly refers to forging crack. Titanium alloy has large viscosity, poor fluidity, and poor thermal conductivity. Therefore, during forging deformation, due to large surface friction, obvious internal deformation non-uniformity, and large internal and external temperature differences, it is easy to generate shear lines inside the forging ( Strain line), which causes cracking when severe, and its orientation is generally in the direction of the maximum deformation stress.
6. Overheating, titanium alloy has poor thermal conductivity. In addition to overheating caused by improper heating during the hot working process, it is also easy to cause overheating due to thermal effects during deformation during the forging process, causing microstructural changes and overheating Weiss organization.
titanium rectangular bar medical titanium sheet titanium foil strip medical grade titanium wire
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