Delayed cracking in air has been studied for three types of titanium alloys. Delayed cracking tests were carried out in air during sustained loading, and also in pure water, ethyl alcohol and vacuum in order to examine the effect of those environments on the delayed cracking. Compact specimens of 6mm thickness were cut from Ti-6Al-4V alloys annealed, and solution-treated and aged, Ti-5Al-4Mo-4Cr-2Sn-2Zr and Ti-15V-3Cr-3Sn-3Al alloys solution-treated and aged. In the Ti-6Al-4V alloy, the delayed cracking occurred markedly in specimens annealed in comparison with specimens solution-treated and aged. Its susceptibility increased from in vacuum, to in ethyl alcohol, air and pure water in the order described, and hence the delayed cracking in air might occur due to moisture and a very small amount of hydrogen retained in specimens. In addition, in-situ observation of the crack growth during loading revealed that the delayed crack extended mainly in alpha phases and was arrested by beta phases in the specimens annealed.
Anti-corrosion resistance of the coatings deposited by the Chemical Vapour Deposition (CVD) is considered to be influenced by the characteristics of the coatings, such as chemical composition, impurity, micro-pores, crystallographic orientation and so on. Study aims to examine the characteristics and corrosion resistance of titanium nitride coating deposited by Radio-Frequency (RF)-plasma CVD of TiCl4+N2+H2 reactants. The corrosion resistance of the coating is found to be influenced by the deposition conditions such as the substrate temperature and N2/TiCl4 mixing ratio to a great extent. A highly crystalline stoichiometric TiN coating with excellent anti-corrosion resistance in acidified solution could be synthesized at the substrate temperature higher than 923K and N2/TiCl4 mixing ration of 3. This coating contains very few chlorine in it and low prefered crystallographic orientation.
Corrosion of zinc under an organic coating was studied with a specimen of zinc in galvanic contact with steel exposed into environment separately inside an artificial defect introduced. The corrosion tests consisted of repeated 24 hour cycle of immersion in NaCl solution followed by drying in the air. Corrosion current decayed shortly in the drying period of early cycles, while it remained larger than 2nA in the whole drying period of later cycles, when underfilm corrosion of zinc began to start with such wet situation at the coating-zinc interface. Qdry, the ratio of electricity integrated for all the drying periods to the total one, depended significantly on test conditions and increased with higher NaCl concentration, shorter immersion time (or longer drying time) and higher humidity. The Qdry value more than 20% made high probability of initiation of underfilm corrosion of zinc, combined with the total electricity, Qt, more than 21C/cm2, equivalent to 10μm depth of anodic dissolution of free surface zinc.
Pinhole of CVD, PVD ceramic film coated on stainless steel was evaluated, using electrochemical measurement in various electrolytes. Cosequently, ratio of active dissolution current of a coated and a non-coated specimen in 1N HCl+0.01M KSCN solution gave the most reliable evaluation of pinhole. Results obtained are summarized as follows: (1) The pinhole ratios evaluated by this method are reproducible accurately as the substrate exposed to the electrolyte through penetrated pinholes is activated in 1N HCl+0.01M KSCN solution immediately after immersion. (2) Fewer pinholes can be evaluated compared with pre-studied methods as the anodic current by ceramic film is small and active dissolution current at pinhole is larger than ordinary electrolytes.
X-ray microanalysis provides useful information on the identification, location and quantitation of elements within a sample down to the micrometer level of size. Described in this article are the principle, sample preparation, quantitation, state analysis and the related applications such as sectional analysis of the filiform corrosion and individual image presentation of CuO and Cu2O.