These guys seem to say cobalt chrome. I think Betz also said that in his youtube interview with Cyborg4Life but I believe that video was removed from youtube
https://www.google.com/search?q=betzbone+cobalt+chrome&oq=betzbone+cobalt+chrome&aqs=chrome..69i57.2969j0j1&sourceid=chrome&ie=UTF-8https://jlimblengthrecon.org › article
betzbone cobalt chrome from jlimblengthrecon.org
A second-generation Betzbone nail introduced the use of cobalt-chrome as a nonferrous metal instead of surgical steel. In 2001, the intramedullary skeletal ...
Cosmetic limb lengthening procedure at the BETZINSTITUTEhttps://www.youtube.com › watch
10:51
... chromium-cobalt (non-iron-steel), invented and made in Germany. Please watch a detailed description of the advantages of the BETZBONE® ...
YouTube · Yvonne Betz · Jun 6, 2018
I think Betz/Becker is just a great choice, I mean you can get the cobalt chrome betzbone option for tibias and have weight bearing. I am aware that the youtube video above does not depict tibias though