What grade of titanium are "memory titanium" glasses made of?

Question

I've worked with different grades of titanium. Mostly with grade 5, and also grade 1 which is ductile.

I know that some glasses are made of titanium and are called "memory titanium", I guess because they bend back to their original shape?

My question is, which grade of titanium would that be?

Answer 1

Those glasses are made out of Shape Memory Alloys (SMA), from which the most common ones include nickel, titanium, copper, zinc, or iron in their composition. I don't think the tag: grade of titanium, is applicable for SMAs even it they contain a high percentage of titanium.

As a functional materials, their properties and applications are so different that they have their own system. For example, one of the most recognizable brands of SMAs, Nitinol (nickel-titanium):

...offers different grades of Nitinol, which are distinguished by the austenite start temperature of the ingot:

• Nitinol #1 (superelastic) -35 to -10 °C

• Nitinol #2 (superelastic) -45 to -15 °C

• Nitinol #4 (superelastic) -10 to +10 °C

• Nitinol #5 (shape memory) ≥ +85 °C

• Nitinol #6 (shape memory) +35 to +85 °C

• Nitinol #8 (shape memory) +10 to + 35 °C

• Nitinol #9 (superelastic) ≥ +35 °C

From: https://cdn.thomasnet.com/ccp/00956637/229312.pdf

It is possible to tune the shape-memory and superelasticity properties of the alloy by modifying its composition. And speaking about the glasses (spectacles), you are more interested in the superelasticity behavior of the material rather than in its shape memory effect.

Answer 2

Titanium used for frames is either 99% pure or, for memory frames 75% Titanium and 25% of nickel or copper.

You can read more here (the result of a google search) : https://www.zennioptical.com/blog/whats-so-terrific-about-titanium-frames/