Tungsten is used for the filament, but raw filament cathodes went out around the time Edison died. Recent cathodes have a tungsten filament folded up inside a metal sleve (filament is coated with an insulating material so the folds don't short out).

The metal sleve is coated with a rare earth material that is a much better emitter of electrons than tungsten. Unfortunately, this coating will eventually become poisoned by stuff that evaporates off the internal components of the CRT.

Back in the '50s, when TV tubes were really expensive, there were "do or die" devices that would overvoltage the filament, hopefully not enough to blow it, but enough to boil the contaminents off the sleve.

Color tubes don't seem to burn images like monos did, thought the phosphor may degrade with time, so screen savers have been primarily entertainment in recent years.

Disclaimer: I am not an expert in cathode ray tubes, but having been involved with vacuum tubes since well before the CK722, and a [link|http://www.geekculture.com/geekculturestore/webstore/tubesrock.html|vacuum tube enthousiast] to the present day, and having had a father who worked as a process engineer (now known as a "manufacturing engineer") for Tung-Sol when it was a major manufacturer of vacuum tubes, I am not entirely unaware of issues involving cathodes (or anodes, for that matter).

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PS I own one of those big 4-pin carbon anode transmitting triodes just like on the Ts (see link). It's about 8" high.