Ecm Titanium 1 61 Cracked ((BETTER))

Ecm Titanium 1 61 Cracked

The crack patterning of Ti films on PDMS substrates is shown in Figure 3. The crack patterning of Ti films was performed for the Ti films of 80, 180, and 250 nm thicknesses. The crack patterns on the PDMS substrate with a crack-free region were examined by EB reflection microscopy, which confirmed the presence of a crack-free region. The titanium film samples were scratched to remove and investigate the crack lines. The Ti film of 80 nm thickness had no crack lines, as shown in Figure 3a. The crack lines in the Ti film of 180 nm thickness showed the cracks in four directions, as shown in Figure 3b. The crack patterns in the Ti film of 250 nm thickness consisted of lines running in two directions, as shown in Figure 3c.

The strain-dependent cracking behaviors of the Ti films on PDMS substrates were examined first at the microscale using an optical microscope (Olympus BX 51,Olympus Corporation, Tokyo, Japan). To stereoscopically investigate the patterns and sizes of the cracks at the smaller scale, the samples were three-dimensional (3D)-scanned using a 3D laser scanning microscope (Olympus CLS 4000). In addition, scanning electron microscopy (SEM, Hitachi S4800, Hitachi High-Tech, Tokyo, Japan) was utilized to closely observe individual cracks. The resistances of the cracked Ti films on PDMS substrates were measured by a simple two-probe method, using a probe station connected to a high-resolution, multi-purpose electrical characterization system (Keithley 4200-SCS, Keithley Instruments Inc., Cleveland, OH, USA). The extremely high-resolution system enabled to detect a femto-ampere-level current and to measure a resistance of more than 1 T. The resistance was monitored not only under normal tension, but it also measured under non-planar straining along a curved surface.

The authors are not aware of any service cases of sustained load cracking, dwell fatigue or ripple fatigue in commercially pure titanium. Whilst sustained load cracking phenomena may well occur in these grades, it seems likely that they are significantly less susceptible than the high strength alloys. Thus, although no definitive data are available, comfort can be drawn from the many years of successful application of this material in structures designed following ASME requirements. However, sustained load cracking and dwell/ripple fatigue failures have occurred in high strength alloys, such as Ti-6Al-4V. Thus, it is considered prudent to design structures made from these grades employing parameters such as K ISLC or K IRLC (the threshold toughness values below which no SLC occurs) instead of K IC and conventional fatigue limits, where appropriate. For Ti-6Al-4V applications where flaw tolerance is required, it is recommended that extra-low interstitial (ELI) grades (such as ASTM grades 23 and 29) in the beta-annealed condition are employed, with an aluminium content less than, say, 6.4%. However, whilst this recommendation seems reasonable given present knowledge, it must be considered tentative at present. In the author’s opinion, the majority of information available on crevice corrosion behaviour in titanium alloys relates to the second generation alloys that are being increasingly applied to marine structures. Crevice corrosion is strongly affected by a number of factors. Thus, microstructures of the alloy in its parent materials and in the welds are important, but so are the surface treatment and the electrode current density. Surfaces that exhibit a low passivation resistance to crevice corrosion are less susceptible to this phenomenon. On the other hand, the surface area of the deposit is also important and can be determined from the weight of corrosion product deposited. In low depth corrosion, surfaces exposed to sea water are heavily corroded whereas a tapered surface, having a weight of deposit corresponding to the depth of corrosion, would have a lower susceptibility. The TiAl ELI types exhibited a weight of deposit corresponding to a depth of corrosion of about 0.01 mm per year. TiAl ELI welds showed a low susceptibility to crevice corrosion. 5ec8ef588b