PSI - Issue 6

S.A. Atroshenko et al. / Procedia Structural Integrity 6 (2017) 190–195 Author name / Structural Integrity Procedia 00 (2017) 000 – 000

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Table 1 shows the results of measuring the percentage of fiber on the fracture surface for the Grade 5 Ti alloy after the HPT and after the ECAP. The greater the percentage of fiber on the fracture surface, the more viscously the material is damaged, and a decrease in this index indicates more brittle fracture. Table 1. The percentage of viscous fracture (shear %) measured on the contact surface of the HPT and ECAP processed Grade 5 Ti alloy. The materials after HPT The materials after ECAP Air flow/powder V,m/s Powder, μm Shear, % Air flow/powder V,m/s Powder, μm Shear, % 50/36 230 91,4 50/36 230 91,4 100/57 93,9 100/57 94,2 150/71 93,6 150/71 93,5 250/88 93,1 250/88 93,5 50/36 109 94,6 50/36 109 91,6 100/57 95,1 100/57 95,0 150/71 94,9 150/71 94,2 250/88 94,6 250/88 94,5 As one may see from the presented data, erosion with a larger powder leads to more brittle type of fracture. With an increase in the erosion rate of the material both after the HPT and after the ECAP, the percentage of brittle fracture reaches its maximum for a 50 m/s the airflow velocity. An increase in the airflow velocity (up to 100 m/s) leads to a decrease of the brittle fracture percentage down to its minimum. For the flow velocities higher than 100 m/s the percentage of brittle fracture increases monotonically with the growing flow speed. Probably, if the airflow velocity exceeds 100 m/s, the damage is healed. The increase in the brittle fracture percentage in samples after the treatment of the HPT and ECAP is also associated with grain refinement and an increase in grain boundaries and junctions, where destruction begins. The change in the brittle component of the Grade 5 Ti alloy after the HPT in the process of high-speed erosion is similar to the same alloy after the ECAP processing and the quantity has approximately the same values. In the structure of the Grade 5 Ti alloy subjected to HPT after the erosion tests, regions of dynamic recrystallization with a finer-grained structure are observed (Fig.5a, b), while such regions are absent in the material, subjected to ECAP after erosion tests. At the same time, the thickness of the damaged layer in the material after the ECAP is smaller (Fig. 5c).

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Fig.5. The structure of the VT6 alloy after the erosion test at the airflow velocity of 50 m/s (powder size 230 μm) after the HPT (a, b) and after ECAP (c).