Materials for high temperature permanent molding

Hi,

I am working on design of mold, for gravity die (permanent mold) casting.

I know this technic is used for low temperature alloys but in my case the pooring temp. is around of 1500 °C it is as Ni base super alloy.

I would like to use this mold at least 100 times or more. What kind of material could be suitable for this application

I saw, some of them are using cast iron ?

I heard also some copper alloys could be suitable due to high thermal conductivity

One of them suggested me Tungsten alloys but i have no idea about the life time, it cost high as material and as machining

What about the some steel grade ?

Any other material to suggest me ? Is ther any ceramic or composite materials suitable for permanent molds

Thanks

Pierre