How Does Titanium Achieve Its Color and Texture?

How are titanium products endowed with exceptional appearance and texture? This relies on a variety of surface treatment technologies. This article will provide an in-depth look at the 7 core surface treatment processes for titanium, guiding you through the details.

1. Anodizing

Anodizing is a widely known and mature process. Besides common aluminum alloys, titanium is also suitable for anodizing, and indeed, most titanium coloring is achieved through this process. Anodizing can bestow titanium with a rich array of colors and patterns (such as ice crystal effects, threading, etc.), creating significant differentiation. Beyond decoration, it forms a dense oxide layer on the product surface, enhancing mechanical properties, improving wear and corrosion resistance, providing insulation, and increasing coating adhesion.

It's worth noting that the anodizing effects on titanium alloys differ from those on aluminum alloys. Although titanium anodizing costs are relatively high, the hardness of the formed oxide film may actually be lower than that of the titanium substrate itself. Therefore, many manufacturers prefer to apply anodizing treatment to products made from pure titanium. For example, aside from the natural titanium finish, the other three color variants (Black Titanium, White Titanium, and Blue Titanium) of the iPhone 15 Pro utilize anodizing technology for coloring, followed by a PVD process for functional protection.

2. PVD Coating (Physical Vapor Deposition)

PVD, or Physical Vapor Deposition, is a mature vacuum coating technology. Applying PVD treatment to titanium alloy surfaces primarily aims to add functional coatings for protection and shielding. Currently, while PVD performs adequately as a functional coating, there is still room for improvement in its durability, which heavily depends on the performance of the underlying base material.

Taking the iPhone 15 Pro as an example again, its three colored versions feature a PVD coating applied over the anodized layer to enhance surface performance. However, subsequent reports of color fading highlight the current limitations in PVD's durability. Nevertheless, PVD technology can also achieve coloring effects and, overall, significantly elevate the design quality and grade of a product.

3. CNC Machining (Computer Numerical Control)

The application of CNC machining in the titanium field primarily involves shaping and finishing. One of its core challenges lies in severe tool wear. Due to the high hardness of titanium alloys, machining them is considerably more difficult than processing common metals. During machining, tools must withstand high temperatures, significant cutting forces, long friction distances, and issues like vibration deformation and built-up edge, leading to rapid wear. Conventional tools are often inadequate, necessitating the use of specialized coated tools, or even diamond tools or CBN (Cubic Boron Nitride) tools for effective processing. For instance, in the production of smartwatch casings, an average of one tool might be consumed for every four casings produced, resulting in substantial cost pressure.

4. Grinding & Polishing

Grinding and polishing are essential steps in the processing of virtually all materials. The goal is to achieve more precise dimensions and a finer surface texture on the product. This typically involves using fine polishing media to meticulously treat all areas of the product surface. By adjusting the process parameters, diverse effects such as a high-gloss mirror finish or a matte, frosted look can be achieved.

5. Brushing

Creating a brushed finish on a titanium surface yields a unique matte texture. This treatment is highly prevalent in consumer electronics products, favored by consumers for its combination of a smooth tactile feel and visual appeal.

6. Laser Processing (Laser Engraving/Marking)

Laser processing of titanium mainly includes techniques such as laser drilling and laser welding, enabling high-precision localized treatment.

7. Sandblasting

Sandblasting treatment on titanium alloy surfaces primarily serves functional purposes: improving surface adhesion for subsequent coatings, extending service life (by removing surface impurities like oxides and scale), and enhancing surface smoothness and aesthetics. It can be considered a preparatory step that facilitates other surface finishing processes.

A previous Apple patent mentioned applying sandblasting to titanium alloys. By combining new sandblasting techniques with etching and anodizing, superior surface results can be achieved, effectively refining the surface, enhancing protection, and improving appearance. It is understood that the titanium frame of the iPhone 15 Pro underwent a sandblasting process.

In the realm of surface treatment for titanium products, particularly in precision consumer electronics, an advanced approach involves using dissimilar metal composite structures followed by aesthetic finishing. The main difficulty lies in the high cost – requiring the preservation of each metal's specific properties while also meeting the demands for mass production. For instance, the latest iPhone 15 Pro adopts a novel structure: a titanium frame encloses a substructure made of 100% recycled aluminum. This is achieved through thermo-mechanical processing and other techniques, utilizing ultra-high pressure for solid-state diffusion to create a high-strength bond between the two metals. However, the practical results still have room for improvement, indicating that surface treatment technologies for titanium continue to be explored and refined.