Efeito da deformação cíclica nas propriedades mecânicas de uma liga níquel-titânio superelástica

AUTOR(ES)
FONTE

IBICT - Instituto Brasileiro de Informação em Ciência e Tecnologia

DATA DE PUBLICAÇÃO

23/03/2005

RESUMO

The effect of cyclic rotary bending strains on martensitic and reverse transformation temperatures, on mechanical properties and on recovery strain capacity, was investigated in this work, using wires of a superelastic NiTi alloy with 1.0mm in diameter. The influence of rotational speed on the materials fatigue resistance was analyzed as well. The material was characterized by X-ray diffraction, optical and scanning electron microscopy and electron microprobe analysis. Cyclic rotary bending straining was performed by turning the wires, previously bent in a specific radius of curvature, around its axis, to allow maximum tensile strain amplitudes of 2,0, 3,0 and 4,5% at the wires surface. Specimens were initially tested until rupture by fatigue, in order to determine the average number of cycles to failure in each deformation condition. Next, wires strained to ¼ and ¾ of this number of cycles and wires not strained were employed in tensile, load-unload tensile and differential scanning calorimetry tests. A martensite stabilization effect was observed in wires subjected to cyclic strains amplitudes of 4,5%. This effect was manifested as an increase in the transformation temperatures and a decrease in the critical stress for inducing martensite, and took place, probably, due to the internal stress associated with dislocations and residual martensite generated during cycling. Also, degradation on the materials recovery strain capacity, as consequence of dislocations and residual martensite generated during cyclic rotary bending, was observed. In the analysis of the influence of rotational speed, it was observed that the fatigue life decreases as the speed increases, probably due to the increase in the wires temperature during the tests, which increases the critical stress for inducing martensite. Higher stresses contribute to the occurrence of plastic strains and support the nucleation and growth of cracks, decreasing the materials fatigue life.

ASSUNTO(S)

engenharia metalúrgica teses. metalurgia física teses. ligas de niquel-titanio propriedades mecânicas. teses.

ACESSO AO ARTIGO

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