The titanium anodizations in 0.1 M sulfuric acid solution at different treated potentials and the effects of UV-irradiation on the anodized films were investigated by spectroscopic ellipsometry (SE), atomic force microscopy (AFM) and scanning tunneling microscopy (STM). The results showed that the thickness of anodized films decreased in air within 280 min over 500 mV vs. Ag/AgCl. The features of parameters tanΨ and cosΔ in SE were in accord with the polarization curve and the thickness of anodized films, respectively. UV-irradiation could greatly decrease the thickness of the anodized films and provably assisted the reconstruction of anodized titanium films from an amorphous and porous structure to a compact structure. Regardless of UV-irradiation, the cosΔ and tanΨ were still in good agreements with the thickness of anodized films and the polarization curve, respectively. It was also found that UV-irradiation could decrease the surface roughness and make a wider atomically flat terrace on the anodized titanium surface.
The microstructure and property of 15Cr1Mo1V steel welded joints after 70,000h service have been researched by OM, SEM, Vickers hardness test and small punch test (SPT). The microstructure of 15Cr1Mo1V steel welded joints after service became coarse and the grain boundary became vague. More carbide particles were observed in welded joints after service. The microhardness gradient curve of 15Cr1Mo1V steel welded joints before service was higher than that after service. The SPT properties gradient curves, including yield strength gradient curve and tensile strength gradient curve by SPT, had the same shape and trend as the microhardness gradient curve before and after service. The SEM fracture appearance of SPT specimens was the characteristic of ductile fracture, irrespectively of before or after service, though the dimple size was a little bit big and deep before service and some cluster particles were observed after service for the ripening of carbides.
The microstructure and property of T91/10CrMo910 dissimilar steel welded joints after one and two years service have been studied by OM, TEM, EDS and Vickers hardness test in this paper. The results showed that after one year service the microhardness of T91/10CrMo910 dissimilar steel welded joints increased clearly and after two years service chromium element diffused or transferred from the welding line or T91 matrix to 10CrMo910 matrix. Coarse lath martensite was the characteristic of the microstructure of T91/10CrMo910 dissimilar steel welded joints, and the martensite laths became fragment after one and two years service. More carbide particles had been observed after one year service than that after two year service, which had a good agreement with the results of the micro-Vickers hardness test.
For its two unique properties of superelasticity and shape memory, nitinol is widely used in medical applications. Traditionally, most nitinol stents are normally heat set at 485°C, which induces the formation of the Ni-rich second phases such as Ti2Ni3 and Ti3Ni4, increases the austenite finish temperature and reduces material strength and fatigue performance. The addition of 600°C heat setting was applied to the nitinol stents after 485°C heat setting process and its effect on the mechanical, dimensional and functional properties of the nitinol stents were investigated. The experimental results showed that the nitinol stent tubes with the addition of 600°C heat setting process had higher elastic modulus, ultimate tensile strength, elongation percentage, inner dimension and outer dimension than those of the nitinol stents with 485°C heat setting process. Moreover, after the addition of 600°C expansion step, the nitinol stents almost had the same average deployment force and deployment accuracy as those of the nitinol stents with 485°C heat setting process and higher average inner dimension (ID) and outer dimension than that of those without the 600°C expansion step. Either treated with the addition of 600°C heat setting process or only 485°C heat setting process, the average austenite finish temperature (Af ) of the nitinol stents was both lower than the body temperature and the average Af of the fomer was 8°C lower than that of the latter.
With the aircraft structure design criterion from traditional static strength design to damage tolerance design and with the independent research and development of new-type civil turbofan regional aircraft and the implement of the plan to develop the country's own large passenger jets in China, it is essential to do some researches on casting TC4 alloys for the lack of the data of fatigue properties. The detail fatigue rating cut-off (DFRcutoff) values of casting TC4 alloys are measured and calculated by double dots method, the thresholds in fatigue crack propagation and the fatigue crack growth rates at different stress ratios are studied and the fatigue fracture at different stress ratios are observed by scanning electron microscopy. The results show that DFRcutoff value by double-dot method is 375.83 Mpa. The thresholds of fatigue crack propagation decrease with the increase of the stress ratio, whereas the fatigue crack growth rates increase with the increment of the stress ratio and the relationship curves between fatigue crack propagation rates and the stress intensity factor range have been obtained. Moreover, SEM observations indicate that the fatigue trips become wide with the increasing of the stress ratio.
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