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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Fig. 3. SEM micrograph of the PBII treated wire surface.

The Figure 4 shows the EDS linescan measurement for a precipitate on the surface of the sample. As shown in Table 1, the alloy has medium carbon content (0.29%at) and by the analysis on the chemical composition of the linescan, it is possible to infer that the precipitate on the surface of the sample is TiC associated to the melting process using a graphite crucible. It is noted that the precipitates are more exposed on the surface due to etching used before PBII treatment.

Ti K 1

cps

Ni K 1

Linescan

N Kα1

C Kα1

O Kα1

µm

Fig.4. EDS analyses of PBII treated wire.

The Figure 5 shows the stress-strain curves for the reference wire (solid lines) and the PBII treated wire (dashed lines). The samples were loaded at 25 °C, therefore below M f temperature being the martensite the only stable phase. Then the samples were unloaded and then heated up to 120°C, above A f , monitoring the shape recovery by strain gage. Using tangent lines method, it is possible to approximate the detwinning start (σ s ) and finish stresses (σ f ). The Table 4 shows information on the mechanical properties of twinned martensite, calculated for 4% strain. One can see in the Table 4, the values found for σ s , σ f and upper plateau stress are very close each other for both samples. Note also that the total strain was recovered after the temperature increase to 120 °C (see Figure 5).