If I set up in a Turkish free zone, do I stop paying corporate tax?

That is not how it works. What creates the exemption is not that the company sits in a free zone. It is where the product manufactured in the zone is sold. If the product goes abroad, into the same zone, or into another free zone, the earnings fall within the exemption. If it is sold into Turkey proper, outside the free zones, those earnings are taxable. Moving into a zone produces no tax outcome on its own; the direction of the sale does.