Stability of a plane reaction front in the solid phase to small perturbations under conditions of a generalized plane stress state is studied with allowance of the coupled character of heat transfer and deformation processes and possible changes in the reaction rate under the action of internal stresses without external mechanical loading. The problem is solved analytically by the method of perturbations. Conditions of the loss of stability of various conversion regimes in some limiting cases are studied for different technological and physical parameters.Key words: plane reaction front, stability of conversion regimes, generalized plane stress state.
Introduction.A model of self-sustained synthesis of a coating on a substrate was proposed in [1]. Such a regime of coating synthesis can be ensured, for instance, with an electron beam unfolded into a line. An analysis of a stationary problem shows that there are different regimes of conversion, which are characterized by different temperatures of the products and different rates of conversion. In this case, there arises a question of conversion stability to small perturbations. It was shown [2, 3] that solid-phase conversion is more unstable to two-dimensional perturbations. In the present paper, we consider a simpler case: one-dimensional perturbations of the form exp (ϕτ ). This choice of perturbations is explained by the specific features of the reaction-front behavior described in [4] and caused by a possible dependence of the solid-phase reaction rate on the work of stresses.Problem for the Case of Small Perturbations. To formulate the problem of stability of the front to small perturbations, we write the nonstationary model with ignored heat release in the heat-conduction equations and without the kinetic equation in the coordinate system fitted to the moving reaction front [1]:Here T is the temperature, x is the spatial coordinate, t is the time, ε ij are the strain-tensor components, c ε is the specific heat at constant strain, ρ is the density, λ T is the thermal conductivity, λ, μ are the Lamé coefficients, K = λ + 2μ/3 is the bulk modulus, α T is the temperature coefficient of linear expansion, ε kk = ε 11 + ε 22 + ε 33 , and V n is the reaction-front velocity.