Evolution of Slip Morphology and Fatigue Crack Initiation in Surface Grains of Ni200

Abstract

The evolution of slipbands into fatigue cracks in surface grains of commercially pure Ni, in wt pct), was studied at ambient temperature. Round-bar specimens with electropolished surfaces were fatigued under displacement-controlled, fully reversed conditions at four strain amplitudes under a nominal strain rate of 1 9 10 À3 s À1 . Low-cycle fatigue tests were periodically interrupted to characterize the slip morphology at various fatigue cycles using scanning electron microscopy. The results showed that the distribution of slip in Ni200 varied considerably in individual surface grains at a given strain amplitude. Some grains were deformed more severely and exhibited more intense slipbands than others, while some surface grains showed the absence of slip lines with no evidence of plastic deformation. The evolutions of slipband width and spacing in deformed surface grains were followed as a function of fatigue cycles in order to assess the slipband morphology at the onset of fatigue crack initiation.

Fatigue behaviors of laser hybrid welded AA7020 due to defects via synchrotron X‐ray microtomography

“…Besides evaluating the defect location tending to a crack based on stress concentration factor, a theoretical model to determine the crack nucleation lifetime was proposed by introducing the stress concentration factor due to defects where K t is the stress concentration factor of defects, Δ σ is the applied stress range, r * is the distance ahead of pores dominated by crack initiation, ρ is the local radius of pores, Δ σ e is the endurance limit, N i is the crack initiation life, α is the fatigue life exponent, and ζ is the fatigue life coefficient.…”

Cyclic Deformation Response of β-Annealed Ti-5Al-5V-5Mo-3Cr Alloy Under Compressive Loading Conditions

“…[37] However, there are indeed major differences in the surface slip band development between the present alloy and those planar slip alloys such as 70Cu-30Zn alpha brass, [36] Cu-16 at. pct Al alloy, [37] Ni200, [41] and Zircaloy-2 alloy. [42] One of the new and significant findings of this investigation is that only limited slip bands were developed even in samples cycled at high stress levels with large cycling numbers; whereas for those typical planar slip materials, the number of slip bands would keep increasing with further cycling and sometimes they would cover the entire gage surface.…”

“…[42] One of the new and significant findings of this investigation is that only limited slip bands were developed even in samples cycled at high stress levels with large cycling numbers; whereas for those typical planar slip materials, the number of slip bands would keep increasing with further cycling and sometimes they would cover the entire gage surface. In fact, Chan et al [41] reported that in Ni200, some surface grains were deformed severely and exhibited a rough surface topography due to the formation of extrusions and slip steps of planar slip bands, while some surface grains showed the absence of slip lines with no evidence of plastic deformation. This behavior is very similar to the present alloy.…”

Avaliação da propagação de trinca associada à corrosão da liga 7475 T7351 submetida a carregamentos de voos simulados

“…Em pesquisa de Huang e Ren (1991), foi observado o surgimento de micro trincas nesses microentalhes em amostras da liga GH33A, além de observarem, que a rugosidade e o endurecimento da superfície provocam uma deformação localizada, sendo este o principal fator que diminui a vida em fadiga de baixo ciclo. No entanto, a tensão residual e também a rugosidade foram apontadas como principais agentes para diminuir a vida em fadiga de alto ciclo.…”

“…Estes deslizamentos são representados através de linhas paralelas que se movimentam quando os materiais sofrem tanto o carregamento cíclico quanto monotônico. As irregularidades provocadas pelas intrusões formam concentradores de tensão e as extrusões, são responsáveis pela rugosidade da superfície dos grãos, figura 2.3 (Chan et al 2009;Stephens et al 2001).…”