AMORIM, F. A.; http://lattes.cnpq.br/8321435564685497; AMORIM, Fernando Andrade.
Resumen:
NiTi alloys enabled revolutionize many traditional engineering projects with
uniques properties of superelasticity (SE) and shape memory effect (SME).
Interested on incorporating these materials in different applications and devices,
developments of efficient welding technology for NiTi alloys becomes necessary
due to the fact that this type of process can provide many differents geometric
shapes and combinations of similar and dissimilar materials. In this context, this
study had as main objective to determine variations in thermomechanical
properties for NiTi welded wires. For this work, superelastic NiTi SMA wire (ASTM
F2063) with 0.9 to 0.4 mm in diameter were divided into two groups: (a) wires
without heat treatment (NiTiA) and (b) heat treated wires at 400 ° C for 20 minutes
(NiTi400). Then, these wires were welded by autogenous welding process, using
the Micromelt machine (EDG, Equipment and Controls). The thermomechanical
characterization of as received and as welded wires was performed by using
differential scanning calorimetry (DSC), dynamic mechanical analysis (DMA)
uniaxial tensile test at different temperatures (30°C to 70°C), optical microscopy
(OM), scanning electron microscopy (SEM) and Vickers micro indentation. The
results showed a good efficiency of TIG welding for every NiTi wire studied
groups. DSC curves demonstrates that welding process can cause a
metallurgical changes into NiTi wires, promoting changes in phase transformation
temperatures. The mechanical properties of the welded wire presented a tensile
rupture strength of 750 MPa (NiTi~70 °C) and strain values up to 8.5% (NiTiA).