PSI - Issue 2_A

Osmar de Sousa Santosa et al. / Procedia Structural Integrity 2 (2016) 1443–1450 Osmar de Sousa Santos/ Structural Integrity Procedia 00 (2016) 000–000

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and the PBII treated wire (dashed line). One can see in the Table 5, the maximum value of internal friction is 0.215, occurring at 34.4 °C on cooling, which is 10% higher than that of the reference wire with internal friction value of 0.195 at 33.7°C. The peak temperatures taken from a DMA curves are about 15 °C lower than that obtained by DSC results as seen in Table 3.

Reference PBII wire

Heating

Cooling

Internal friction, tan δ

Temperature (°C)

Fig. 7 . Internal friction curves of the reference wire and the PBII treated wire. For the heating curves, the value of internal friction is 0.193, which is the same for both samples, occurring at 82.9 °C for the reference wire and at 82.0 °C for the PBII treated wire. One can note that the values found for the A p from Table 3 are almost the same for values found for the temperature peaks of internal friction on the heating curves.

Table 5. Values of internal friction for the reference wire and the PBII treated wire.

Sample

Curve

tan δ Peak Temperature (°C)

0.195 0.215

33.7 34.4 82.9 82.0

Reference Cooling

PBII wire

Reference Heating 0.193

0.193

PBII wire

4. Conclusions The thermomechanical properties of the NiTi wire with the modified surface by plasma based ion implantation was investigated. The evaluation of mechanical properties in this study showed that stress-strain tests for the reference wire and the PBII treated wire indicated that the PBII treatment did not change significantly the mechanical properties of NiTi wire, where the SME was the same and the upper plateau stress are very close for both samples. As shown in Figure 6, there are cracks perpendicular to loading direction on the implanted surface due to stress strain cycles, these cracks could lead to a fracture if the sample were submitted to a higher stress or a cycling load, which is not desirable in applications as a biomaterial. The MTT for the reference wire and the PBII treated wire are very close one another with the highest difference for MTT occurring for the A s values, which was of 3%. The PBII treated wire and the reference wire presented the same values for the peak of internal friction for the heating curves, and values very close for the cooling curves. As shown in this work, the PBII treatment practically does not alter the thermo-mechanical properties of NiTi SMA wire compared to the reference wire. This is an important result taking into account practical aspect such as design devices using the advantages of having a PBII treated surface associated to SME of NiTi alloy.