Of course, there are more-or-less standard definitions of Turing machines as a certain type of mathematical object formalized in some theory (Say, ZFC), but what I am looking for is a first order theory of Turing machines themselves. Is there a standard notion of such a first order theory of Turing machines in the literature? The basic properties I would be looking for would be the following (or something similar):
The main objects in the language of the theory would be Turing machines, and the only atomic propositions of the theory are of the form $\mathrm{halts}(T,a,t)$ which says intuitively something like "The Turing machine $T$ halts on input $a$ at time $t$ in the execution".
In particular, I am interested in the connections between such a theory and Peano Arithmetic, and wish to find a result in the literature stating that these be equiconsistent theories.