PSI - Issue 60

Sarath Chandran Nair S. et al. / Procedia Structural Integrity 60 (2024) 564–574 Sarath Chandran Nair S./ Structural Integrity Procedia 00 (2023) 000 – 000

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Table 5. Test procedure Step

Test condition / inspection method

1

Tensile/compressive test to the required strain at room temperature – 1 cycle

2

Dye Penetrant inspection

3

Heating the specimen to 790K/820K without any load – 1 cycle

4

Dye Penetrant inspection

5

Tensile/compressive test to the required strain at 790K/820K – 3 cycles

6

Dye Penetrant inspection

7

Tensile/compressive test to the required strain at 790K/820K – 3 cycles

8

Dye Penetrant inspection

9

Tensile/compressive test to the required strain at 790K/820K – 3 cycles

10

Dye Penetrant inspection

11

Tensile/compressive test to the required strain at 790K/820K – 3 cycles

12

Dye Penetrant inspection

13

Tensile/compressive test to the required strain at 790K/820K – 3 cycles

14

Dye Penetrant inspection

5. Results and discussion Total 20 specimens were tested among them

• 5 Nickel coated specimens for tensile strain of 0.4% at 790K • 3 Nickel coated specimen for compressive strain of 0.7% at 790K • 7 Nickel and Chromium coated specimens for tensile strain of 0.2% at 820K • 5 Nickel and Chromium coated specimens for compressive strain of 1.5% at 820K

All the specimens had undergone 15 strain cycles at high temperature and DP test carried out as mentioned in table 5. Nickel coated specimen was tested initially and cracks were found during testing as shown in fig. 7 and 8. Cracks were observed in high temperature tests in both tension and compression cases. As the number of strain cycles was increased the cracks were found to be severe. From fig.9 it can be seen that the stress-strain curve deviates from its normal behaviour at 0.6% strain which attributes to the reduction in the strength due to cracking of coating in the specimen. Peeling of coating is also observed as the testing progressed. Accordingly, coating parameters were changed to improve the ductility by reducing its hardness. Specimens were prepared with the improved coating parameters and further testing were done. Similarly, changes were made for Nickel and Chromium coating to improve ductility.

Fig. 7. Cracks seen on Nickel coating in visual inspection