Pressure tubes pick up hydrogen while they are in service within CANDU reactors. Sufficiently high hydrogen concentration can lead to hydride precipitation during reactor shutdown/repair at flaws, resulting in the potential for eventual rupture of the pressure tubes by a process called Delayed Hydride Cracking (DHC). The threshold stress intensity factor (KIH) below which the cracks will not grow by delayed hydride cracking of Zr-2.5Nb micro pressure tubes (MPTs) has been determined using a load increasing mode (LIM) method at different temperatures. MPTs have been used to allow easy study of the impact of properties like texture and grain size on DHC. Previous studies on MPTs have focused on creep and effects of stress on hydride orientation; here the use of MPTs for DHC studies is confirmed for the first time. Micro pressure tube samples were hydrided to a target hydrogen content of 100 ppm using an electrolytic method. For DHC testing, 3 mm thick half ring samples were cut out from the tubes using Electrical Discharge Machining (EDM) with a notch at the center. A sharp notch with a root radius of 15 µm was introduced by broaching to facilitate crack initiation. The direct current potential drop method was used to monitor crack growth during the DHC tests. For the temperature range tested the threshold stress intensity factors for the micro pressure tube used were found to be 6.5-10.5 MPa.m1/2 with the value increasing with increasing temperature. The average DHC velocities obtained for the three different test temperatures 180, 230 and 250oC were 2.64, 10.87 and 8.45 x 10-8 m/s, respectively. The DHC data obtained from the MPTs are comparable to the data published in the literature for full sized CANDU pressure tubes. / Thesis (Master, Mechanical and Materials Engineering) -- Queen's University, 2009-04-24 12:55:36.917

No presente trabalho foi estudado o comportamento de um aço inoxidável austenítico do sistema Fe-Cr-Mn-N, nas condições como recebido, solubilizado e sensitizado, quando submetidos à meios contendo cloretos. Para analisar a suscetibilidade à corrosão sob tensão foram utilizados corpos de prova dos tipos DCB (\"Double Cantilever Beam\") e C(T) (\"Compact- Tension\"), pré-trincados em fadiga, com entalhes laterais e carregados com cunhas. Os meios empregados foram as soluções aquosas 45% em peso de MgCl2 na temperatura de ebulição de 154°C, água do mar sintética na temperatura ambiente e de ebulição de 100°C e 3,5% em peso de NaCI na temperatura ambiente. A suscetibilidade à corrosão sob tensão foi avaliada em termos do fator limite de intensidade de tensão, KISCC, e foram caracterizados os aspectos fractográficos dos corpos de prova em que ocorreram propagação de trinca por corrosão sob tensão. Foi verificado que apenas os corpos de prova do aço E3949 nas condições como recebido e sensitizado, foram suscetíveis à corrosão sob tensão em solução aquosa de 45% em peso de MgCl2 na temperatura de ebulição. Também foi determinado o comportamento eletroquímico do material nas condições citadas acima com relação aos meios empregados. Os resultados das curvas de polarização obtidas mostraram que o material apresenta baixa resistência à corrosão, principalmente em meios de MgCl2. / The present work studies the stress corrosion cracking behavior in austenitic Fe-Cr-Mn-N stainless steel, in as received, solubilized and sensitized conditions, when submited to several chlorides environments. To evalued the stress corrosion cracking susceptibility, DCB (\"Double Cantilcver Beam\") and C(T) (\"Compact- Tension\") specimens, fatigue precracked, side grooved and wedge loaded were used. The environments employed were boiling solution of 45 wt% of MgCl2 at 154ºC, synthetic sea water at room and 100°C temperatures, and a solution with 3,5 wt% of NaCI at room temperature. The susceptibility to stress corrosion cracking has been evaluated in terms of the threshold stress intensity factor, KISCC, and the fracture surface appearance of those specimens whose the crack propagation took place was characterized. The results showed that only the specimens in the as received and sensitized conditions, were suceptible to the stress corrosion cracking effect in the solution with 45 wt% of MgCl2 at the boilling temperature. Also, it has been verified the electrochemical behavior of this steel when submited in the above environments. The results of polarization curves showed that the material presents low corrosion strength, mainly in MgCl2 environments.

No presente trabalho foi estudado o comportamento de um aço inoxidável austenítico do sistema Fe-Cr-Mn-N, nas condições como recebido, solubilizado e sensitizado, quando submetidos à meios contendo cloretos. Para analisar a suscetibilidade à corrosão sob tensão foram utilizados corpos de prova dos tipos DCB (\"Double Cantilever Beam\") e C(T) (\"Compact- Tension\"), pré-trincados em fadiga, com entalhes laterais e carregados com cunhas. Os meios empregados foram as soluções aquosas 45% em peso de MgCl2 na temperatura de ebulição de 154°C, água do mar sintética na temperatura ambiente e de ebulição de 100°C e 3,5% em peso de NaCI na temperatura ambiente. A suscetibilidade à corrosão sob tensão foi avaliada em termos do fator limite de intensidade de tensão, KISCC, e foram caracterizados os aspectos fractográficos dos corpos de prova em que ocorreram propagação de trinca por corrosão sob tensão. Foi verificado que apenas os corpos de prova do aço E3949 nas condições como recebido e sensitizado, foram suscetíveis à corrosão sob tensão em solução aquosa de 45% em peso de MgCl2 na temperatura de ebulição. Também foi determinado o comportamento eletroquímico do material nas condições citadas acima com relação aos meios empregados. Os resultados das curvas de polarização obtidas mostraram que o material apresenta baixa resistência à corrosão, principalmente em meios de MgCl2. / The present work studies the stress corrosion cracking behavior in austenitic Fe-Cr-Mn-N stainless steel, in as received, solubilized and sensitized conditions, when submited to several chlorides environments. To evalued the stress corrosion cracking susceptibility, DCB (\"Double Cantilcver Beam\") and C(T) (\"Compact- Tension\") specimens, fatigue precracked, side grooved and wedge loaded were used. The environments employed were boiling solution of 45 wt% of MgCl2 at 154ºC, synthetic sea water at room and 100°C temperatures, and a solution with 3,5 wt% of NaCI at room temperature. The susceptibility to stress corrosion cracking has been evaluated in terms of the threshold stress intensity factor, KISCC, and the fracture surface appearance of those specimens whose the crack propagation took place was characterized. The results showed that only the specimens in the as received and sensitized conditions, were suceptible to the stress corrosion cracking effect in the solution with 45 wt% of MgCl2 at the boilling temperature. Also, it has been verified the electrochemical behavior of this steel when submited in the above environments. The results of polarization curves showed that the material presents low corrosion strength, mainly in MgCl2 environments.

Due to the increasing use of cyclically loaded cast aluminum components in automotive and aerospace applications, fatigue and fatigue crack growth characteristics of aluminum castings are of great interest. Despite the extensive research efforts dedicated to this topic, a fundamental, mechanistic understanding of these alloys' behavior when subjected to dynamic loading is still lacking. This fundamental research investigated the mechanisms active at the microstructure level during dynamic loading and failure of conventionally cast and SSM Al-Si-Mg alloys. Five model alloys were cast to isolate the individual contribution of constituent phases on fatigue resistance. The major constituent phases, alpha-Al dendrites, Al/Si eutectic phase, and Mg-Si strengthening precipitates were mechanistically investigated to relate microstructure to near-threshold crack growth (Delta Kth) and crack propagation regimes (Regions II and III) for alloys of different Si composition/morphology, grain size, secondary dendrite arm spacing, heat treatment. A procedure to evaluate the actual fracture toughness from fatigue crack growth data was successfully developed based on a complex Elastic-Plastic-Fracture-Mechanics (EPFM/J-integral) approach. Residual stress-microstructure interactions, commonly overlooked by researches in the field, were also comprehensively defined and accounted for both experimentally and mathematically, and future revisions of ASTM E647 are expected.