PSI - Issue 14

Premkumar Manda et al. / Procedia Structural Integrity 14 (2019) 467–474 Author name / Structural Integrity Procedia 00 (2018) 000–000

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The hydrogen analysis of the damaged cooling duct of fighter aircraft is given in Table 2. It is reported that the hydrogen is the only gas that is appreciably soluble in Al and its alloys. Its solubility directly increases with increasing temperature. Hydrogen solubility is considerably greater in the liquid than in the solid state. Actual liquid and solid solubility of hydrogen in pure aluminium, just above and below the solidus temperatures are 0.65 and 0.034 ml / 100 g, respectively [Davis et al., 1993]. These values are equivalent to 0.65 and 0.034 ppm in liquid and solid, respectively. It is to be noted that the analyzed value of hydrogen is significantly higher in damaged cooling duct than the reported value (Table 2) [Davis et al., 1993].

Table 2. Hydrogen analysis of cooling duct of fighter aircraft.

Element

ppm

H

12.4  0.8

4.2. Microstructures The optical microstructures taken from damaged cooling duct are shown in Fig. 3. The microstructure is very fine. The BSE SEM microstructures taken at high magnification exhibit the presence of dispersion of insoluble particles of (Fe, Mn)Al 6 (large) and Al-Mn-Si particles (both large and small) (Fig. 4). The above mentioned particles (selected particles) are analyzed in detail by EPMA. The EBSD microstructure (IPZ map) reveals the presence of elongated grains with high aspect ratios along with fine elongated and / or equiaxed grains. The microstructure is partially recrystallized and volume fraction of recrystallized grains is quite less. Interestingly, microstructure does not the show the presence of hydrogen induced blisters.

Fig. 3. The optical microstructure of the damaged cooling duct.

Fig. 4. The BSE SEM microstructure of the damaged cooling duct.