X-ray non-destructive testing of titanium alloy castings
Titanium alloys are widely used in petrochemical, aerospace, chemistry, electric power, metallurgy, medicine, marine engineering, sports and leisure and other fields due to their excellent corrosion resistance, low density, high specific strength and other advantages. With the development and improvement of modern titanium alloy casting technology, titanium alloy castings are widely used in aerospace complex aircraft parts, engine frames, hydraulic cylinders and other structures with strict requirements due to their technical advantages of high material utilization and complex structures. , marine engineering, petrochemical pump and valve equipment, sports and leisure and other fields. In order to ensure the safe use of products, the aerospace, petrochemical and shipbuilding industries have high requirements for the quality of titanium alloy castings, and have high limits on the level of defects allowed in castings. Defects in products should be detected qualitatively, quantitatively and locally using non-destructive testing methods.
Defects in titanium alloy castings can be divided into internal defects and surface defects. The internal defects of titanium alloy castings mainly include pores, shrinkage cavities, shrinkage porosity, cracks, high-density slag inclusions, low-density slag inclusions, etc.; surface defects mainly include hot cracks, cold cracks and cold partitions.
Due to the low density of titanium alloy and the low radiation absorption coefficient, the radiation should be selected with low energy and soft quality (long-wave radiation). This is reflected in the fact that the radiation equipment uses high-current mobile radiation equipment, and it is best to use soft-ray X-ray inspection equipment for thin workpieces.
The transmission process parameters of titanium alloy radiation detection mainly depend on the thickness of the transmission part. The thickness of the transmitted part, the size and focal length of the radiation source must be taken into consideration when selecting pipeline voltage, pipeline current and exposure time. The selected radiation energy should be compatible with the material and thickness of the transmissive object. When ensuring the blackness value of the film, try to use low voltage, but the energy should not be too low, otherwise it will be difficult to obtain sufficient exposure within an appropriate time.
At present, there is no special X-ray inspection standard for titanium alloy castings at home and abroad. It only stipulates the allowable degree of various defects in the manufacturing specifications of titanium alloy castings. Standard films are used for comparative rating. However, these standard films are standard films for steel castings. Due to the material Different casting processes have different types and shapes of internal defects.
Casting standards in the aerospace field include GJB 2896-2007 "Specifications for Titanium and Titanium Alloy Investment Precision Castings" and HB 5448-90 "Titanium and Titanium Alloy Investment Precision Castings". Casting products are divided into Ⅰ, Ⅱ, Category III and IV, different casting parts require levels A, B, C, and D respectively. The quality of aviation products is generally Category I and requires level B. The X-ray testing process and specifications are carried out in accordance with GJB 1187A-2001 "Ray Inspection". The test result grade assessment is based on the reference standard film of ASTM E-192. The standard film is divided into 8 levels. The quality assessment is relative to the ASTM-E446 standard film. More stringent.
