The United States Patent and Trademark Office recently published a patent from Apple, which shows that Apple is still exploring the possibility of using titanium on its equipment.
Apple pointed out in the patent document that, in the process of producing equipment, it is ideal if it can produce dark gray or black, low-cost hard metal casings. Usually, zirconium or zirconium alloys can be used to produce dark-colored metal materials, but this kind of material itself is expensive, heavy, and difficult to process.
Titanium alloy is a relatively hard and light alloy, and the surface of this alloy can also be anodized or surface coated. However, traditional oxidation or anodizing treatment usually creates a certain thickness on the surface. Coloring on the metal surface can be accomplished by PVD coating or plating by physical vapor deposition. For example, the darker part of the shell can be directly obtained by using PVD chromium carbide coating on the steel or titanium substrate. However, there is not much research related to primary oxidation on the surface of titanium metal.
