No they are not. They often get lumped togehter, but here are the differences between the two design fields
First, lets define what these two terms mean:
UX = User Experience
UI = User Interface
UX is about the experience: the why, and the how something should work.
UI is about the presentation: the what, the how something should look.
You need a good UX, before you start on UI. UX adds the ‘makes sense’ to the UI, makes it feel intuative Lets break each design discipline down further.
UX does the research on what a feature should do and how it should works. UX designers talk to customers and stakeholders, conduct inverview and workshops to understand what it is a customer wants to achieve and how they do it. They then take all of this reasearch and put together personas, user flows and user stories in order to transfer this understanding of the customer and their needs to a UI designer.
UI then implements the requirements into a tangable product for users to use. UI designers take the deliverables from UX and create the templates, buttons, pages - basically everything that a user will “physically” ineract with as they do their work.
A good UI with a poor UX ends up being a frustrating experience. A good UX with a poor UI makes it difficult to get the intended user goal done. Both design disciplines really work hand and hand and feedback into each other.