Since those early days of the birth of what became known as the “jet age,” titanium alloys have found a strong demand by manufacturers. Heat treatment of the titanium alloy is important for its best mechanical properties to be exhibited. The general method of heat treatment of a titanium alloy involves low pressure (vacuum).
Aerospace was also instrumental in the development thin-film, hard-coatings techniques because the deposited surface was able to produce extraordinarily high surface hardness values as well as excellent mechanical strength.
With the new term that was being developed (thin-film surface heat treatment) the benefits shown in Figure 2 were observed.
General Attack Corrosion
Also known a uniform attack corrosion, general attack corrosion is perhaps the most common type of corrosion, and it is generally caused by a chemical or electrochemical exposure over time. It has the potential to initiate a corrosive condition that will likely result in the deterioration of the entire exposed surface of a metal. Ultimately, the metal deteriorates to the point of failure.
General attack corrosion accounts for the greatest amount of metal destruction by corrosion but is considered a safe form of corrosion because it is predictable, manageable and often preventable.
Unlike general attack corrosion, localized corrosion specifically targets one area of the metal structure. Localized corrosion is classified as one of three types.
- Pitting: Pitting results when a small hole, or cavity, forms in the metal, usually as a result of de-passivation of a small area. This area becomes anodic, while part of the remaining metal becomes cathodic, producing a localized galvanic reaction. The deterioration of this small area penetrates the metal and can lead to failure. This form of corrosion is often difficult to detect due to the fact that it is usually relatively small and may be covered and hidden by corrosion-produced compounds.
- Crevice corrosion: Similar to pitting, crevice corrosion occurs at a specific location. This type of corrosion is often associated with a stagnant micro-environment, like those found under gaskets and washers and clamps. Acidic conditions or a depletion of oxygen in a crevice can lead to crevice corrosion.
- Filiform corrosion: Occurring under painted or plated surfaces when water breaches the coating, filiform corrosion begins at small defects in the coating and spreads to cause structural weakness.
Look for more on this topic in our next blog.