Fusion welded joints between Titanium and Aluminium present certain problems in detection and interpretation of defects during conventional Non Destructive testing by Radiography and Ultrasonic Testing methods. While porosity is a common defect that occurs in Aluminium weldments, the most common defect that occurs in a weld joint between Titanium and Aluminium is incomplete fusion. This may be because of large difference in the melting points (of Aluminium and Titanium), in their densities, thermal conductivities, thermal expansions, grain sizes, nature of oxides they form during welding. Detecting these defects in these weld joints by conventional Radiography is very difficult owing to the large difference in the densities of Aluminium and Titanium. If the test parameters are set based on Titanium then the film on Aluminium side becomes dark, masking all the defects lying on Aluminium side, rendering evaluation impractical.
Similarly detection of the defects by conventional ultrasonic test method is extremely difficult owing to two main reasons:
- Titanium is a fine grained material while Aluminum is a coarse grained material.
- Both porosity and incomplete fusion give similar kind of indications making the identification of the defect difficult.
Experiments have been carried out to detect detects by Radiography method varying parameters like kVA of Source, Source to film distance, Angle of source with joint etc., Experiments have also been carried out by ultrasonic test methods varying parameters like angle of probe, size of probe, frequency of crystals etc. While the experiments with radiography failed to detect the defects, ultrasonic method met with some success with less degree of reliability. A skilled and trained person who is able to distinguish between incomplete fusion and porosity taking into consideration the fine grained titanium on one side and coarse grained Aluminum on the other side, is able to assess the joint with good degree of accuracy. In this paper Authors enumerated the ways and means through which the defects in such joints can be detected with good degree of accuracy.
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