Authors: P Bassani P Giuliani A Tuissi C Zanotti
Publish Date: 2009/07/02
Volume: 18, Issue: 5-6, Pages: 594-599
Abstract
Samples obtained from relatively large powders 150 µm with total porosity in the range 3068 were characterized mainly from a morphological point of view Total porosity as well as pore size shape and distribution was analyzed Sample microstructure was also investigated indicating that the main phase produced during the selfpropagating hightemperature synthesis SHS reaction is Ti reach NiTi phase as confirmed by calorimetric analyses Moreover the presence of secondary phases suggested by the low transformation enthalpy was confirmed by SEM observations In fact EDS microanalyses and EBSD mapping helped in the identification of such secondary phases such as Ni3Ti Ti2Ni and Ti4Ni2O x Other samples were successively produced starting from the same powders but introducing a different powder compression methodology and operating conditions In this way the obtained samples showed higher porosity featured by more uniform size shape and distribution while from a microstructural point of view no significant differences were observed Mechanical compression tests were carried out at room temperature and on selected samples also above A f in order to highlight the influence of pore shape and distribution Results obtained at room temperature show that the mechanical properties decrease with the porosity augmentation For higher temperatures the samples presented a pseudoelastic behavior Dilatometric tests were also performed and the results well indicated the martensite to austenite transformation at the same temperature showed by the DSC analyses Thermal analysis was completed by evaluating the thermal diffusivity temperature and porosity dependence using an experimentalnumerical approach especially developed
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