Titanium: A Technical Viewpoint
All You Wanted To Know About Titanium
Posted by Raymond on March 26, 1998 at 15:24:57:
In Reply to: Raymond, sorry I’ve the same query for real, please tell: posted by Julian Jameson on March 26, 1998 at 12:27:15:
:With a material science trainning background, (sorry, not even metallurgy) I saw many posts here providing valuable information on materials use in watch industry. Meanwhile there are still a few misunderstandings concerning the “mighty” metal “titanium” and its applications in the watch industry.
Firstly I want to clarify some points, I am not any expert in titanium and I don’t even own a titanium watch. All the titanium I can play with is in the heads of my golf clubs. I have a few of them.
Titanium is a light and strong material with Superior Strength-to-Weight Ratios. “The densities of titanium-based alloys range between .160 Ib/in3 (4.43 gm/cm3) and .175 Ib/in3 (4.85 gm/cm3). Yield strengths range from 25,000 psi (172 MPa) commercially pure (CP) Grade 1 to above 200,000 psi (1380 MPa) for heat treated beta alloys. Titanium is not renowed in its hardness.
The combination of high strength and low density results in exceptionally favorable strength-to-weight ratios for titanium-based alloys. These ratios for titanium-based alloys are superior to almost all other metals and become important in such diverse applications as deepwell tubestrings in the petroleum industry and surgical implants in the medical field. “
The other distinctive advantage is the chemical inertness of the titanium surface. Titanium and most of its alloys has one of the most inert surface amongst all metals. It is due to the fact that titanium metal itelf is rather reactive particularly in higher temperature, a thin layer of titanium oxide is formed almost immediately after the fresh metal surface is exposed to air. Titanium oxide is hard (again titanium metal and alloys themselves are not particularly hard). Since it is difficult to find titanium oxide (TiO2) solid big enough to measure its hardness as commonly done with aluminium oxide and chromium oxide, I cannot find the figures. The inertness come from this hard oxide layer. Besides, titanium surface is reported to be the most bio-compatible.
Commerially, processing titanium involve vaccum/inert gas blanketing due to it reactiveness.
Mirror surface polish is hard to be achieved as the titanium might react to the material in the polishing wheel with the heat generated in the process, and a uniform oxide layer to provide mirror reflection is hard to be obtained. At least such surface are rarely be seen.
All the titanium watches I came across have shot blasted finished, some are with anodizing treatment for enhancing thickness of the oxide layer. Titanium surface tends to gall while having extended contact with surface of titanium or other metal. Problems of various wears were widely reported. One shall expect such happening in wearing a titanium watch with a matching barcelet.
Finally, refinishing/polishing titanium surface will involue stripping the oxide layer. Due to the strong adhesion and the hard surface, it can only be done by mechanical brushing or shot blasting, and the later process shall generally give a more satisfactory result. In order to develope a uniform oxide layer, the stripping shall ideally be done under vaccum and anodize the surface immediately afterward. I do not think any watchmaker in town has the equipment and technology to do it right.
Since I am no expert, please correct me if there is any mistake.
Many thanks in advance,