Estudo do efeito de pulsos elétricos no auto-reparo da liga pré-deformada AA7075 (Al-Zn-Mg-Cu): comportamento mecânico e evolução microestrutural
Over the past few years, research into self-healing materials has gained increasing scientific attention. In this class of bioinspired materials, engineers and scientists rely on biological mechanisms to design new materials with unique characteristics. Advances in this sense are widely noted in...
Na minha lista:
| Autor principal: | |
|---|---|
| Outros Autores: | |
| Formato: | doctoralThesis |
| Idioma: | pt_BR |
| Publicado em: |
Universidade Federal do Rio Grande do Norte
|
| Assuntos: | |
| Endereço do item: | https://repositorio.ufrn.br/handle/123456789/58199 |
| Tags: |
Adicionar Tag
Sem tags, seja o primeiro a adicionar uma tag!
|
| Resumo: | Over the past few years, research into self-healing materials has gained
increasing scientific attention. In this class of bioinspired materials, engineers and
scientists rely on biological mechanisms to design new materials with unique
characteristics. Advances in this sense are widely noted in several classes of
materials. Specifically for metallic materials, processing by electrical pulses, EPT
(Electropulsing Treatment) is a new approach to self-healing that is increasingly
important in technology. Applying a controlled current of sufficiently high density
but with a low-temperature rise generates an electron flow with an energy capable
of modifying the microstructure, which may promote stress relief, the reduction of
microvoids and microcracks, or even the recrystallization. Given the importance
of techniques that increase the useful life of aeronautical components, the
purpose of this work is to establish a methodology with the development of
appropriate parameters for the self-healing process via electrical pulses in the
aluminum alloy AA 7075 (Al-Zn-Mg -Cu). Compositional and phase analysis was
performed via X-ray fluorescence (XRF) and X-ray diffraction (XRD). The
mechanical behavior and generation of crystalline defects were previously
evaluated in specimens machined according to the ASTM E8 standard under
interrupted tensile tests at deformations of 60%, 70%, 80%, 90%, and 95%
relative to rupture, increasing yield stresses and reduction of ductility. The most
hardened samples (90 and 95% deformed) were treated via EPT with peak
current (Ip) of 400 A, with a current density that varied from 23.5 A/mm2, initially
for specimens of cross-sectional area of 17 mm2, and 50 A/mm2 for specimens
with a reduced section area of 8 mm2. Experimentally, a specimen was tested
with an Ip of 500 A and a current density of 29.4 A/mm2; These samples used 0
A base current (I b ), peak time (T p ) and base time at 0.1 s (T b ). in a total
treatment time of 7s, 14s and 21s in cycles of 35, 70 and 105 respectively. The
most critical condition, referring to samples deformed to 95% of rupture, treated
by EPT (I p of 400 A) and current density of 50 A/mm2 with 7s, 14s, and 21s, was analyzed via residual stresses by XRD, proving the relief of residual stresses promoted by EPT due to of the application period, agreeing with the behavior under tension. The microstructural analysis considered the notched samples to
generate defects. A peak current Ip of 400 A was used with a current density of
80 A/mm2, with a base time (tb) of 0.1 seconds and peak residence time varying
from 0.1 to 0.3 seconds. The results showed that there was microstructural
evidence in the total and partial closure of microcracks in micrographs observed
via field emission scanning electron microscopy (SEM-FEG), thus corroborating
the results obtained in mechanical tests and via x-ray residual stress. |
|---|