can sub-process default model be made to Enterprise BPMN collaboration diagram from Enterprise BPMN process diagram?
No, this is not possible, even by the BPMN 2.0 standard specification. Reason: You cannot have Pools inside of a sub-process, not even lanes. It must be possible to show the model of the sub-process in the expanded version of the sub-process symbol of the parent process. It also wouldn’t make sense to define further first-citizen processes (represented by pools) inside a sub-process.
Here is another idea: You can use a Call acitivty. This will spawn an entirely new process, which may contain collaborations like any other process and is re-usable from multiple call activities, even in different processes.