爆炸粉末烧结是将炸药爆轰所产生

爆炸粉末烧结是将炸药爆轰所产生的冲击能量以激波的形式作用于粉末,使其在瞬态、高温、高压下发生烧结的一种材料合成的新技术,是激波物理学在工程中的具体应用。作为爆炸加工领域的第三代研究对象和一种获得新型高性能材料的粉末冶金技术,爆炸粉末烧结正广泛应用于精细陶瓷、金属间化合物、金属基复合材料、纳米块体以及微晶、准晶、非晶等亚稳合金以及超硬材料的合成与烧结当中,同时也可用于高分子聚合物的激波改性当中。对爆炸粉末烧结的细观机理的研究,尤其是正确确立对爆炸烧结影响很大的粉末颗粒大小、粒度分布、颗粒形状、表面状态、微粒力学性能和热学性能对爆炸压实与结合的影响,有利于促进爆炸烧结材料向更细微的材料学领域发展并有利于促进多孔材料本构关系与状态方程的研究,为之提供更丰富的理论依据,因而具有很高的理论意义与应用价值。 论文开篇从多孔材料冲击状态方程、爆炸粉末烧结的宏观机理和细观机理三个角度入手介绍了作者对爆炸粉末烧结的机理的文献追踪,其重点放在对其细观机理的调研方面,为进一步发展爆炸粉末烧结的细观机理提供了坚实的基础。接下来,以密排球堆积模型为基础借助于实验手段和数值模拟辅助分析将爆炸粉末烧结中颗粒间的变形和沉能机制划分为微爆炸焊接、微摩擦焊接、微孔隙闭合、微冲击波耗能几种主要形式并分别对其进行了较为系统而深入的研究,论文的主要研究成果有: 1 选择具有代表性的模型材料(铜铬的混合粉末,钢、铜的纤维),进行了大量的塑性材料、塑性与脆性粉末混合物的爆炸烧结实验,以金相观察结果研究区分了其中的力学、冶金现象,为各种沉能机制的建立提供了实验依据,并通过相关理论分析了各种沉能机制存在的位置和条件。 2 以理想流体对称碰撞模型在考虑传热效应的基础上计算了由微爆炸焊接引起的颗粒界面附近的温度场和熔化层厚度,并计算分析了来流速度和碰撞角对焊接界面附近区域升温的影响。 3 针对爆炸粉末烧结过程中颗粒间的摩擦效应建立了高压楔入模型,分析了烧结过程中颗粒间摩擦力随颗粒温度的变化规律,借助于LS-DYNA有限元程序研究了冲击压力、颗粒大小、材料强度等因素对孔隙闭合时间的影响,并在此基础上用积分法对颗粒间热力
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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.