Padauk MCUs: Everything You Wanted To Know And More About The OTP And MTP Parts

The first method of encryption that Cisco provides is through the command service password-encryption. This command obscures all clear-text passwords in the configuration using a Vigenere cipher. You enable this feature from global configuration mode.

The last password looks random and was still not cracked when the password cracker stopped running three days later. The problem is remembering a password like this one. See the upcoming sidebar, Choosing and Remembering Strong Passwords for tips on choosing an appropriate password.

Trace Mode 5 Crack

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Next is level 1, the default user level. This level provides the user with many more commands that allow the user to display router information, telnet to other systems, and test network connectivity with ping and traceroute. Level 2, which is not enabled by default, adds a few additional show and clear commands, but provides no opportunity for a user to reconfigure the router. Finally, level 15 allows full access to all router commands.

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Contact-mode high-speed atomic force microscopy (HS-AFM) has been utilised to measure in situ stress corrosion cracking (SCC) with nanometre resolution on AISI Type 304 stainless steel in an aggressive salt solution. SCC is an important failure mode in many metal systems but has a complicated mechanism that makes failure difficult to predict. Prior to the in situ experiments, the contributions of microstructure, environment and stress to SCC were independently studied using HS-AFM. During SCC measurements, uplift of grain boundaries before cracking was observed, indicating a subsurface contribution to the cracking mechanism. Focussed ion beam milling revealed a network of intergranular cracks below the surface lined with a thin oxide, indicating that the SCC process is dominated by local stress at oxide-weakened boundaries. Subsequent analysis by atom probe tomography of a crack tip showed a layered oxide composition at the surface of the crack walls. Oxide formation is posited to be mechanistically linked to grain boundary uplift. This study shows how in situ HS-AFM observations in combination with complementary techniques can give important insights into the mechanisms of SCC.

Conjoint corrosion and stressing of a metal or alloy can result in the development of cracks which propagate through the material, causing failure due to the reduced fracture resistance1,2. This phenomenon is known as stress corrosion cracking (SCC). Forms of localised corrosion, such as SCC, can occur without any obvious outward signs of damage accumulation, whilst causing significant deterioration of component structural integrity1. Furthermore, subtle changes in environment can lead to considerable differences in SCC behaviour, resulting in its occurrence being difficult to predict. As a result, SCC is often undetected, giving rise to sudden and unexpected failure. This has resulted in a significant number of failure events across numerous structural engineering applications in a range of industries including gas, oil, and nuclear3,4,5.

The unpredictable nature of SCC calls for considerable research into the associated mechanisms. Techniques in which SCC processes can be imaged non-destructively and in situ are of particular importance for understanding the physical mechanisms, and the sequence in which they occur. A plethora of techniques have been implemented in previous studies. These include surface and volume measurements such as optical microscopy, electron microscopy techniques and atom probe tomography (APT), and reaction sensing techniques such as electrochemical noise and scanning vibrating electrode technique6,7,8,9,10,11. These techniques operate over a range of length- and time-scales; however, techniques that offer the highest resolution seldom facilitate the conditions necessary for in situ measurements. The work presented here uses a newly developed contact-mode high-speed atomic force microscope (HS-AFM) to obtain the high temporal and spatial resolution necessary for such measurements.

Within the work presented here, the HS-AFM technique was applied with the aim of better understanding the underlying mechanisms occurring within this IGSCC system. IGSCC is the result of a combination of three factors: susceptible microstructure, environment, and local tensile stress11. Within the first part of this study, these three factors were studied separately to deconvolute their individual contributions to IGSCC. It is well recognised that these factors act synergistically and that their behaviours will differ when isolated, this in itself being a strong driver for in situ studies where all factors are acting simultaneously. In the second part of the study the three factors are brought together to initiate and study IGSCC. In addition to HS-AFM analysis, complementary measurements of crack tip chemistry are performed by APT and energy dispersive X-ray spectroscopy (EDX), and subsurface cracking is evaluated by focussed ion beam (FIB) and scanning electron microscopy (SEM). This combination allowed for a more complete characterisation of the IGSCC phenomenon.

Studies of thermally sensitised Type 304 stainless steel in thiosulfate solutions without applied stress have been performed in other works with varying reports26,31. Some studies found that thiosulfate does not result in anodic activity or localised corrosion in the absence of stress22,23,24,31. However, in other works thiosulfate was found to initiate and propagate localised corrosion processes in such a way that the role of stress was considered to be secondary26. However, these experiments were performed by reaction sensing techniques and precise reaction sites were not reported. The observations made in this study show that thiosulfate does indeed have a corrosive effect on the sample surface, and this occurs at the GB carbide precipitates positioned on sensitised GBs. This dissolution process may occur at the crack tip during IGSCC, resulting in stress accumulation at the resultant micro-pits. However, this process may not occur during IGSCC due to the synergistic nature of the individual factors.

IGSCC was observed to occur as a smooth, continuous process rather than a stepwise process. This contrasts with previous studies where cracks were found to grow as discrete microcracks, considered to be indicative of a hydrogen fracture mechanism24,25. However, it must be noted that the observations were performed at the surface, and it is possible that any subsurface cracking progressed in a stepwise fashion. The deformed region at the crack tip may contain strain-induced martensite, as measured in other works40; however, in this study this behaviour was not clearly observed.

As the crack becomes wider and deeper, the resultant topographic maps begin to exhibit imaging artefacts due to the nature of AFM. In particular, as the crack deepens, the measurement is affected by tip convolution. For this reason, HS-AFM is most suited for the dynamic in situ measurement of crack initiation and the very early stages of SCC, rather than the later stages. These are the stages that other techniques struggle to image due to environmental requirements and both spatial and temporal resolution limitations. By combining the strengths of multiple techniques, a more complete picture of the SCC process can be achieved.

In summary, combining dynamic HS-AFM measurements with complementary composition and subsurface analysis by APT, FIB, and electron microscopy has enabled a detailed analysis of the IGSCC processes occurring on a model system across a range of sub-micrometre length-scales. Drawing together the measurements performed within this study suggests that subsurface crack propagation is a key phenomenon within this system, where limited diffusion allows for a build-up of aggressive electrolyte chemistry within the occluded crack interior. An oxide layer with a layered composition was present on the walls of the subsurface cracks. The oxide layer did not fill the cracks suggesting that the SCC process was stress driven. However, within measurements performed closer to the crack tip the oxide was observed to fill the crack, indicating a possible pre-oxidation phenomenon. This was supported by GB uplift observations as the oxide layer occurred on a similar length scale to the observed GB uplift effect, suggesting a possible mechanistic connection. It may be postulated that oxide formation at and ahead of the subsurface crack tip may result in uplift of the GBs at the surface prior to rupture. Furthermore, in situ measurements showed a smooth crack propagation process. Whilst the oxide observations may support a film rupture mechanism similar to that proposed in previous works22, inherent contributions from other mechanisms such as hydrogen induced fracture cannot be ruled out. However, it is clear from the measurements performed that the crack growth process is highly localised and combines both chemical and mechanical processes. Whilst the presented study does not explicitly favour a particular model for cracking, some key mechanisms have been observed that are previously unreported, including GB uplift, the role of an oxide layer and the precedence of subsurface crack propagation.

To conclude, high-resolution measurements have provided important insights into the SCC system studied and may be applied to other systems in future. In situ observations of surface crack propagation performed by HS-AFM allows for better understanding of the evolution of the cracking process as it happens, rather than only characterising the failed specimen after cracking has finished. Combining these observations of real-time quantitative morphology evolution with chemical composition and structural information using other cutting-edge techniques such as APT is essential to inform models of SCC and provide evidence for SCC mitigation methodologies. 2ff7e9595c