PSI - Issue 3

A. Strafella et al. / Procedia Structural Integrity 3 (2017) 484–497 A. Strafella, A. Coglitore, E. Salernitano / Structural Integrity Procedia 00 (2017) 000–000

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Table 2. Matrix of the main tests.

Material

Temp. [°C]

Stress [MPa]

300

400

560

575

15-15Ti(Si)

550°C

   ,  

where “  ” represents the creep test performed in air and “  ” that in lead. A particular cell, showed in Figure 2, was specifically designed and manufactured for tests in lead.

Fig. 2. Cell designed and manufactured for tests in lead, mounted on a MAYES machine.

The cell is mounted on a MAYES machine; specimen was fixed to the grips of cell, filled with solid lead, heated up to the lead melting temperature and then the test temperature and load were applied. Data points were acquired every 1 h. After rupture, the specimens were cut under fracture surface to be analyzed with a SEM Leo 438 VP to characterize the morphology and microstructure of the fracture surfaces. The observations were performed in high vacuum, with no need of surface preparation treatments. Both the secondary (SE) and backscattered electron (BSE) detectors were used to point out morphological and chemical features. SE are emitted from the sample top surface atoms providing information relating exclusively to the surface morphology, while BSE are issued from the deeper layers of the material (up to about one micron deep) providing information relating to the composition and to the topography of the sample. 3. Results and discussion

3.1 Creep curves in air

The specimens were tested at 550°C under constant loads, corresponding to the initial tensile stresses in the range of 300-560 MPa, and the experimental data allowed to obtain the typical creep curves of 15-15Ti(Si). The most relevant curves were depicted in Figure 3, where the evolution of the creep strain with time at various stress levels is plotted.