Titanium cogs plated?

I thought my 7800 series Dura Ace cassette cogs were made of titanium but, it turns out they are plated. When I bought my wife’s and my bicycles in 2004, I also purchased 12-21, 12-23 and 12-25 cassettes for each of them. Neither of us have ridden for the last ten years however I have gotten back...