SHOCK COMPRESSION OF REACTIVE POWDER MATERIALS M.A. Dmitrieva, V. N. Leitsin, T.V. Kolmakova

2 Increase of reactivity of reactive the mixture – mechanical activation Intensive mechanical loading Compression → decrease of reactive cell size → increase of thermal conductivity Plastic strain Distruction of oxide and adsorbed layers from the particles surface (kinetics of damage level development is taked into account) Dynamic heating of powder mixture Chemical reactions Reactionary heating of powder mixture Phase transfers Melting (kinetics of phase transfer is taking into account) → convective mass transfer Complex criterion Lateral flow (vortices) Ultra-fast conversions Computer Simulation Concept

3 Dynamic model of fracture [1] Kashtanov, A.V. and Petrov, Yu.V., Tech. Phys., 2006, vol. 51, no. 5, pp. 604–614. [2] Glebovskii, P.A. and Petrov, Yu.V., Phys. Solid State, 2004, vol. 46, no 6, pp. 1051–1054. σ В – is the breaking point of a powder component K Ic – is the fracture toughness and с is the velocity of elastic waves Further development of material fracture is defined by the incubation period  [2]: A criterion for complete fracture of material The kinetic equation of material damage The instantaneous damage ω0 as a function of applied pressure р can be written [1] in the form:

4 A necessary condition for ultra-fast transformations at the initial stage of synthesis is the emergence of cross-flows: 1 Mescheryakov Yu. I. // Control in Physicotechnical Systems, Fradkov, A.L., Ed., St. Petersburg: Nauka, 2004, pp. 222–245. Mescheryakov's statistical criterion 1 Condition of second stage of compression The fulfilment of non-stationary criterion results in the wave flow of medium characterised by the loss of mass velocity in the shock pulse direction. Cross-flows ensure the convective transport of components in the microvolumes of reactive mixture, thus the non-stationarity criterion determines one of the necessary conditions for the formation of the substructure of synthesis product as well as for the opportunity for the implementation of ultrafast chemical transformations on the rising edge of shock impulse. The achievement of the required degree of mechanical activation Computer Simulation Concept

1 2 Wave front 3 1 – model; 2 – “window” material; 3 – radiation detector The radiation temperature is represented by a thermal component and a fluorescent one: The radiation temperature is represented by a thermal component and a fluorescent one: 5 Where T is thermodynamic temperature of near surface layer, λ is a wavelength ε λ is the monochromatic emissivity, c 2 = const. T b = T t + L, 1/T t – 1/T= –λlnε λ /c 2, Computer Simulation Concept

6 The burning of the powder-mixture particles gives rise to chemiluminescent flashes where ρ is the powder density; c p is the heat capacity; C i is the concentration of one of the powder components. where E is the Young modulus;  T is yield point;  в is breaking point;  is thermal-expansion coefficient; ε is ultimate strain; d is destructed particle size; ξ is a defect size. The destruction of the powder-mixture particles gives rise to mechanoluminescent flashes destruction due to thermal expansion destruction in unloading wave Computer Simulation Concept

7 Algorithm Macrokinetics Filtration Mechanical Modification Thermal Balance Every model parameters are refined via the iterations. The changes of components concentration, porosity, phase state are taken into account.

8 The non-uniformity of particles plastic deformation Curve 1 – П 0 =0,3; Curve 2 – П 0 =0,4; Curve 3 – П 0 =0,5. Ni + 31,5 мас. % Al =NiAl+Q b/a=1,5; П 0 =0,3÷0,5; d Ni =d Al =5 мкм; Т 0 =293 К; P f = 2 ГПа; t imp = 1 мкс а0а0 b0b0 c At a low intensity of dynamic impact or low porosity, the thermal effect of shock-induced chemical transformations will not cause particle heating in this layer, which is necessary for the thermal initiation of reaction in the non-deformed parts of reactive components. the product of mechanochemical transformations will be a composite consisting of the structural elements of initial mixture components and the reaction product. Ni Al I II I t, MKC  I II

9 Relative volume of zones of possible ultrafast transformations  b/a =1,1 b/a =1,3 b/a =1,5  Ni + 31,5 мас. % Al =NiAl+Q b/a=1,1÷1,5; П 0 =0,4; d Ni =d Al =5 мкм; Т 0 =293 К; P f = 2 ГПа; t imp = 1 мкс There is a threshold value of initial porosity, the excess of which results in a sharp increase in the relative volume of ultrafast transformation

Ni Al porosity b C, P The distribution of component concentration and specified pore volume t,  s I ch / I chm T t, K   b E a, kJ/mol The distribution of thermal radiation temperature, T t, and relative chemiluminescence intensity, I сh / I сhm, The distribution of activation energy values in the subareas of reaction cell facing the rear surface

t,  s I ch / I chm T t, K   t,  s T bt The distribution of radiation temperature, T bt, in view of the thermal and chemiluminescent radiation of the rear surface of model samples after the shock pulse arrival The distribution of thermal radiation temperatures, T t, and relative chemiluminescence intensity, I сh / I сhm, of the rear surface of model sample in the visible spectrum after the shock pulse arrival

12 Conclusion Our research offers a composite criterion for the implementation of non-stationary process of dynamic compaction of reactive powder mixture, which determines necessary conditions for ultrafast physiochemical transformations on the rising edge of shock pulse. There is a threshold value of initial porosity, the excess of which results in a sharp increase in the concentration of zones of non-sationarity mode of dynamic compaction.

13 Radiation temperature defines the intensity of physiochemical processes on the surface of model samples and provides information about the implementation of different physiochemical transformation stages, structure modification, and a number of other parameters of a reactive powder body, both on the surface and inside the material. The non-uniformity of plastic deformation and the kinetics of development of damageability of powder particle material is a deciding factor in the mechanical activation of powder components of a reactive powder. Conclusion Thank You for Your attention