The production of neutrons from D + D reactions in thermally cycled titanium deutende (TiDx) (x ≈ 2) is investigated in depth. Special attention is given to cubic-tetragonal (δ-ϵ) phase transition that TiDx experiences near room temperature as a possible triggering mechanism of “cold nuclear fusion reactions.” The TiDx (x ≈ 2.00) samples, possessing well-known properties about the δ-ϵ transition, are cycled at temperatures (from −60 to 60°C) where the phase transition takes place. The cold fusion signature is investigated by measuring the neutron flux of the sample during the experiments. No significant neutron signal above the background level is found during thermal cycling of the TiDx samples. It is concluded that in the samples investigated, no correlation exists between the δ-ϵ transition and the trigger of the D + D reactions. Background deviations give an upper limit of the rate of the D + D → 3He + n reaction of λ < 10−23 fusion/p-d·s.