GR5 (Ti-6Al-4V) is a martensitic a/3 type two-phase titanium alloy with good comprehensive properties, and its service temperature can reach 450°C. It is widely used in important structural parts of the aviation industry, such as wing blades, aero-engine wheel discs, etc. Since the GR5 titanium rod is a two-phase titanium alloy, if the composition of the micro-region is not uniform, it will inevitably lead to abnormal macro-structure and micro-structure, resulting in a significant difference in the hardness between the abnormal region and the normal region, so that the material as a whole exhibits uneven performance. It leads to the source of fatigue cracks, which brings great hidden dangers to the safety of parts and reduces the service life of the alloy. Aiming at the black streak defect found in the low magnification inspection of a GR5 titanium alloy bar product, in order to accurately determine the type of defect, the metallographic structure was observed with a metallographic microscope to determine the abnormal area of the metallographic structure. Then, the chemical composition segregation defects of Mo-rich and Al-poor in the black stripe area were analyzed by scanning electron microscope. The composition segregation in the black streak region was determined to be non-brittle segregation by microhardness testing.
The experimental results show that the composition segregation and types of GR5 titanium alloy can be effectively determined according to the above method. And it is determined that this type of defect will not affect use and can be delivered after removal. Such defects can be reduced or eliminated by controlling the selection of raw materials for titanium alloy ingots, material mixing, electrode preparation and voltage and current during smelting. The segregation of titanium alloys can be divided into hard segregation (hardness higher than normal area, also called brittle segregation) and soft segregation (hardness lower than normal area, also called non-brittle segregation). If there are only non-brittle segregations in the product and all properties meet the product standard requirements, the product can still be delivered for use after the segregation has been eliminated. Brittle segregation is not allowed to be delivered after dismantling and should be discarded in batches.
A. For the black stripe defect of GR5 titanium rod found by visual inspection, the microstructure was observed by metallographic microscope, and the defect area was not much different from the normal area, so the type of defect could not be judged; in addition, the chemical composition of the defect area of the titanium rod was analyzed by scanning electron microscope, The defect region was found to be a segregation of chemical elements rich in heavy and depleted in aluminum. Finally, combined with the microhardness test, it is determined that the segregation type of the GR5 titanium rod is non-brittle segregation with rich aluminum and poor aluminum. The composition segregation and type of GR5 titanium alloy can be effectively determined by microstructure observation, micro-area composition analysis and micro-hardness test.
The segregation in the B.GR5 titanium alloy bar is a non-brittle segregation rich in heavy and poor in aluminum, which does not affect the use, and can be continuously transported after cutting; by controlling the selection of raw materials, mixing and electrode preparation parameters, as well as the voltage and current in the smelting process, it can be reduce or eliminate this defect.
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Nicole
Company: Baoji Jimiyun Dynamic Co., Ltd
Cuntry:China
Add:Baoti road,Jintai,Baoji city,Shaanxi,China
Cel:+86 13369210920
Gmail:nicole@jmyunti.com
Website:www.jm-titanium.com
