Research Of Micro-mechanism Of Energy Deposition In Explosive Consolidation Of Powders

Explosive compaction of powders is a new technique that employs shock waves to compress powder to form solid components under high temperature and high pressure instantaneously and is the idiographic application of shock wave physics in engineering. As a technique of powder metallurgy to obtain newfashioned materials explosive compaction is now widely used in the fabrication of fine ceramic, metal alloys, metal-matrix composite materials, nano-crystalline, metastable alloys and superhard materials. To obtain compacts with high quality the research of the micro-mechanism of explosive compaction of powders, especially to establish the influence of powder's size, distribution of granularity, shape, exterior state, mechanical and calorific capability on the quality of compacts is of great importance and at the same time it is also in favor of the research of porous equation of state.In the beginning of the thesis documents on the state of equation of powders as well as the macroscopical and microcosmic mechanism of explosive compaction of powders is introduced so as to develop the microcosmic mechanism of explosive compaction of powders further. Then mechanisms of deformation and energy deposition between particles are divided into micro-explosive welding, micro-friction welding, micro-void collapse, micro-shock waves etc. recur to experiments and numerical simulation on the basis of the model of stacked particles. Systemic and in-depth research of the mechanism mentioned above has been carried out. The main research products of this paper are as follows:1 Representative materials (powders and fibres of steel and copper) have been chosen to do a lot of experiments of explosive compaction of plastic materials, brittle materials and mixture of plastic and brittle materials. Mechanical and metallurgic phenomenon have been researched recur to metallography of the compacts so as to apply the bases to establish the mechanisms of energy deposition, position and condition on which the mechanism mentioned above will occur is analyzed.2 Energy deposition at the interface of particles caused by micro-explosive welding in explosive compaction of metal powders is solved with uncompressible ideal liquid symmetrical impaction model and the influence of approaching flow velocity and impactangle on energy deposition and temperature field near welding interface.3 A slanting impaction model of two parallel plates was proposed to research the effect of friction between particles during explosive compaction of powder. The change tendence of the interface friction of the particles with the change of temperature is analyzed and influence of shock compression, grain size of powders and intensity of material on the time for the voids to close is researched by LS-DYNA program. The temperature rise at the interface of particles caused by the therm-force coupled friction is calculated by integration. Size effect is considered during the calculation and the critical size in which it takes effect is also given.4 A one-dimension model of hollow sphere is used to research the last stage of void collapse in powders. Effect of heat conduction is added to the equations for the one-dimensional flow of spherical symmetric and the temperature distribution during the collapse of the hollow sphere is solved by finite-difference under the condition that the material is rigid-plastic fluid and the constitutive equations are thermo-visco-plastic.5 For building up a porous equation of state(EOS) which can suit to total pressure history, a new p- a model including melting effect is constructed, the model can arrive at the dense state of α =1. The porous EOS is obtained by generalizing the Hugoniot data of dense materials along equal-pressure lines.6 An impact model of multi-flyer plates is proposed to research the arising and dissipation of micro-shock waves in explosive compaction of powders as well as the rules of energy deposition and distribution.