Possible Mechanism of Autoignition of Titanium Alloys in Oxygen

Mechanism of metal ignition due to fracture

“…3, which also shows the results of experiments under uniaxial extension of various titanium-based alloys in oxygen up to their fracture [5]. In the coordinates used, the experimental points are fairly well approximated by straight lines for all materials tested and both methods used to induce material fracture.…”

“…The criterial equation [6], with allowance for the hypotheses put forward in [1,5], has the following form for ignition of a fracture fragment:…”

“…This assumption is based on results obtained by measuring layer-by-layer microhardness of samples of titanium-based alloys after their fracture in oxygen [5].…”

“…(The assumption made in [5,7] that the primary initiators of ignition are massive conical parts of the halves of the fractured sample was not validated experimentally.) Ignition of the microfragments mentioned above in both mechanisms of metal fracture occurs when they are located in the fracture crack filled by oxygen at an operating pressure.…”

“…By an example of titanium alloys, it was demonstrated that the critical pressure p * of alloy ignition in oxygen (minimum pressure of oxygen at which sample fracture in this medium leads to material ignition) decreases with increasing temperature T * . The assumption put forward in [5] implies that the limiting stage of oxygen-titanium interaction during fracture is dissociative chemical adsorption of O 2 molecules on the juvenile metal surface, which determines the form of the reaction rate as a function of the medium pressure [∂m/(∂t) ∼ p 0.5 ], and the critical conditions of ignition of fragments formed due to fracture are described by the criterial equation of the theory of the thermal explosion for a heterogeneous reaction [6]. Based on experimental data and results of [7], the mechanism described in [1,5] is extended in the present work to other metallic materials; results of studying the nature and conditions of heat transfer between ignition initiators are given; kinetic parameters of the reaction between oxygen and the juvenile surface of metals are calculated.…”