You can use toArray() of eloquent as below.
The toArray method converts the collection into a plain PHP array. If the collection’s values are Eloquent models, the models will also be converted to arrays
$comments_collection = $post->comments()->get()->toArray()
From Laravel Docs:
toArray also converts all of the collection’s nested objects that are an instance of Arrayable to an array. If you want to get the raw underlying array, use the all method instead.