That big block of metal is inconel, an extremely tough "austenitic nickel-chromium-based superalloy", one of the strongest metals known to humans, used in "in extreme environments subjected to pressure and heat" like nuclear plants. How do you cut such a hard thing? Let's watch a video.
That's a ceramic head rotating at very high speed. There are other ways -- like water cutters -- but only ceramic cutters can machine inconel at high speed.