Caracterização térmica, mecânica e eletroquímica de ligas Ti50Ni50-xMox obtidas por fusão a plasma-skull.

Abstract

This work aimed the study of the aspects involved in the preparation, processing and characterization of a ternary alloy of titanium (Ti-Ni-Mo), with variation of molybdenum content to verify its influence on the microstructure, mechanical properties and corrosion resistance. The study was conducted on Ti50Ni50-xMox alloys with six distinct compositions, with the addition of 0; 0.5; 1.0; 2.0; 3.0 e 4.0 at.% of Mo. The alloys were fabricated by the Plasma-Skull Push-Pull process (PSPP), followed by injection molding in a metal mold. After the fabrication process, these alloys were characterized regarding the microstructure, chemical composition, thermal, mechanical and electrochemical properties. The results indicated that the Ni-Ti alloy microstructure was modified with the addition of Mo, showing different phases, precipitates (TiNi, Ti2Ni) and oxides (Ti4Ni2O, TiO, TiO2, TiO3, MoO e MoO3). It was observed with XRD results that there was an increase of R phase stability with increasing molybdenum content and that the monoclinic martensite (B19') phase was identified only in the Ni-Ti sample. The DSC results indicated that the addition of molybdenum to the Ni-Ti alloy caused the rise of the R phase and the increase of the content of this element in the ternary alloy generated a shift of phase transformation peaks to lower temperatures. The modification of the ternary alloy composition also resulted in a change in the microhardness and elasticity modulus results, which had a decrease in value with increasing molybdenum content. The corrosion results indicated that there is an increase in corrosion resistance with an increase in the Mo content. In general, Ti-Ni-Mo samples showed higher Rp and lower Icorr values than Ni-Ti film, which suggests that the addition of Mo positively influenced the corrosion resistance of Ti-Ni-Mo films. The heat treatment caused grain refinement, slight increase in hardness and increased corrosion resistance of alloys with higher Mo contents. Especially for Ti-Ni-Mo4 alloy that showed a Rp value three times higher after heat treatment. Thus, the increase of corrosion resistance of the Ti-Ni-Mo4 alloy is related to the refining of the grains and the higher percentage of molybdenum in this alloy that generated a mix of the oxides TiO and MoO3, forming a more stable passive layer.