SOARES, R.L.; http://lattes.cnpq.br/0494374289705105; SOARES, Roniere Leite.
Abstract:
The objective of the present study was to obtain Ni50Ti50-XHfX .at% alloys with EMF by
means of three types of processes: (i) plasma arc casting (SPP method) on EDG
Discovery camera All Metal ; (ii) fast solidification by the melt spinning method; (iii)
arc melting. Then, it continues with the thermal characterization (by means of the
DSC technique) and microstructural characterization (by the XRD, OM and SEM/EDS
tests). In the thermal characterization were recorded and discussed the
transformation temperatures [TTs], heat flows [W/g], energy densities [J/g] and
thermal hystereses [ΔP and ΔT]. These results were correlated with qualitative and
quantitative phase analyzes that was detected by XRD in the 5 substituting
compositions studied (Hf = 8, 11, 14, 17 and 20 .at%). The Rietveld method was
used to make structure refinement and to determinate the variables such as specific
density, percentage of phases, network parameters [a b c; α ȕ Ȗ], indexing of
crystallographic planes (h k ), calculation of the relative degree of crystallinity [Xc]
and amorphous percentage, in addition to measuring the chemical compositions of
the observed phases. Based on non-linear regressions, the results of the X-ray
diffraction experiments were also used as a statistical tool to establish a
mathematical relationship between the interplanar distance [d, Å] & crystalline
identification fraction 1/d2
with the Bragg angle [2ș, o]. Afete that, the cold-embedded
samples were chemically attacked by optical microscopy (OM) and scanning electron
microscopy (SEM) with the objetive to observe surface aspects, textures, contours
and grain sizes (width, length, perimeter and area). The EDS technique was used to
determine the atomic percentage (.at%) of the elements of the alloys in specific
areas. It was demonstrated in this work that although Ni-rich alloys were prepared
using the same methodology, materials and nominal compositions, the thermal and
microstructural results were considered very distinct, with peculiarities that direct us
to the individualized discussion in each of the 3 processes.