And here is how you manufacture a "blisk", that's a combination "blade" and "disk" assembly. I think the cooling issues on the newer engines may be attributable to the problems of cooling and heating "blisks" in a uniform manner. A big chunk of metal with thin blades machined integrally to that chunk is not likely going to cool or heat evenly.
https://www.youtube.com/watch?v=FCfZQMPQa7g