Design and development of SiC/(W,Ti)C gradient ceramic nozzle

Abstract

The idea of functionally gradient material (FGM) theory was used to design ceramic nozzle based on the erosion wear behaviors of the ceramic nozzles and the outstanding properties of FGM. The purpose is to reduce the tensile stress at the entry region of the nozzle during sand blasting processes. The design theory and methods of gradient ceramic nozzle were proposed. The physical, micromechanical, and composition distribution models of gradient ceramic nozzle were established. The optimum composition distribution of the gradient ceramic nozzle material was determined from the solution of the multi-objective optimization calculation by constructing the models of the composition distribution versus the structural integrity of the compact in fabricating process. Results showed that compressive residual stresses appeared at the entry area of the gradient ceramic nozzle. The optimized component distribution exponent p is 0.5. An SiC/(W,Ti)C gradient ceramic nozzle material was synthesized by hot-pressing according to the design result. Results showed that the surface Vickers hardness of the FGM-1 gradient ceramic nozzle materials was greatly improved in comparison with that of the other layers.ceramic nozzle, erosion wear, function gradient material, stress, Finite element analysisThe nozzle is the most critical part in the abrasive jet machining (AJM) equipment, and is widely used for surface strengthening, surface modification, surface clearing and rust removal, etc. The surface quality, the cost, and the efficiency of the AJM were affected by the nozzle wear resistance. Ceramics have intrinsic characteristics, such as high melting point, high hardness, and good chemical inertness that make them promising candidates for wear-resistance components. However, the application of ceramics to wear is usually limited by the variability of their mechanical strength and their poor fracture toughness.

Research and Development of Design Technologies for Functionally Gradient Ceramic Materials

“…Assuming the volume fraction of component A of every gradient layers is fixed, when n<1, from interior layer to exterior layer, every gradient layer changes gradually from thin to thick as the exponent distribution law. When n>1, from interior layer to exterior layer, every gradient layer changes gradually from thick to thin as the exponent distribution law [6]. Principles of determining exponent n are as following:…”

The effect of easily ionized elements Na and K on the performance of pulsed plasma thruster using water propellant

“…For the improvement of the impulse, it is necessary to increase the stored energy value to increase the thermal ionization of propellant or to reduce the total resistance R all . The traditional way for the improvement of PPT performance is to optimize the storage energy and electrode structure or storage energy and propellant feed rate [9][10][11], and the increase of storage energy value can merely influence the plasma density and can not actually increase the low electron temperature (T e ) or low electron collision frequency which leads to high resistance. This is the main cause for the low thrust power ratio of the water propellant PPT-Fully ionized plasma resistivity, not depending on plasma density, is in proportion to (kT e ) 3/2 .…”