Papers by Author: Walman Benício de Castro

Abstract: It is important to control the martensitic transformation start temperature (Ms) of Ti–Ni alloys because it determines the temperature range over which the shape memory effect and superelasticity appear. Powder metallurgy (PM) is known to provide the possibility of material-saving and automated fabrication of at least semi-finished products as well as net-shape components for NiTi alloys. In this study powder with different particle sizes was subjected by gas atomization. The evolution of the control the martensitic transformation start temperature (Ms) was studied by differential scanning calorimetry. The effect of the particle size of powders on the transformation temperatures behaviors was discussed.

Abstract: Melt spun Ni-Cr-P alloy ribbons were used as filler metal to join Al2O3 substrates together using a vacuum brazing process. The influence of the brazing load, brazing temperature and holding time on the shear resistance of brazed joints was evaluated. The experimental results showed that the holding time was the most important parameter. At a brazing temperature of 1060°C, the shear resistance value increased from 6.17 to 93.7 MPa with increasing brazing time from 20 to 100 min, respectively.

Abstract: Rapid Solidification Processing (RSP), of metals and alloys, is establish by increasing of the undercooling applying high cooling rates (102 - 106 K/s) or by reduce nucleation sites using low cooling rates (1 K/s). Melt undercooling opens new solidification pathways for new nonequilibrium phases and unusual microstructures. Several techniques have been developed to reduce nucleation sites and produce increased undercooling in metals and alloys including the fluxing technique. The aim of this paper is to study the influence of the undercooling level on microstructures of eutectic Sn-57wt%Bi alloy by using the fluxing technique. A morphological change from eutectic to eutectic plus primary dendrites bSn was observed when the undercooling increase from 10 K to 19 K and a refinement of the primary dendrites bSn was observed when the undercooling increase from 19 K to 29 K. Increasing the undercooling led to a higher growth rate, hence morphological refinement occur.