Fabrication Of Porous Titanium-based Material And Its Application

Abstract:Previous works for fabricating porous TiAl intermetallics by Kirkendall have been reported.For industrial application requirements, high permeate flux porous TiAl and gradient pore size TiAl intermeallics were fabricated.The pore structure properties,mechanical properties and environment corrosion resistivities were further investigated by various advanced testing methods.In order to enhance the corrosion resistance performance of porous material,a novel porous Ti3AlC2ceramic was fabricated.A thermodynamic estimation method was proposed to speculate the reaction diffusion path of Ti,Al and C.The effects of Al content and reactive sintering temperature on porous Ti3AIC2ceramics, and pore forming mechanism were taken into consideration.Finally, the porous TiAl intermetallics were successfully applied in the solid-liquid separation of suspended TiCl4raw liquid in industry production procedure.More details were given as follows.High permeate flux porous TiAl intermetallics were fabricated by space-holder of ammonium carbonate and urea, independently. The effect of space-holder addition amount on pore size,permeability, porosity and volume expansion were investigated systematically. According to the mass conservation law, the relation of porosity ?S and space-holder amount w was established,and the relationships between permeability and pore structure parameters were investigated as well.The tensile strength of porous TiAl ?b and porosity ? match the ?a????H equation ?b=K?0(1-?)m.Different pore size TiAl substrates were fabricated by powder metallurgy technique with different particle size of Ti,Al elemental powder. The results indicated that the pore size and permeability were increasing with particle size increase.The gradient porous TiAl intermetallics were prepared through spraying fine Ti/Al powders on porous TiAl substrate surface,and then the samples were sintered in vacuum furnace.The pore size of substrate and the particle size of powders were the main factors for the matching of substrate.The powder piling model was proposed to simulate the spraying membrane process, the result revealed that when the particle size D50?(?2-1)dm,the decrease rate was64.6%,which was approximate to the experimental data63%.The relations between membrane thickness and pore structure parameters were considered. The porous TiAl membrane with uniformly pores, narrow pore size distribution has a metallurgical bonding with matrix, and can withstand8MPa impact force, which is satisfied the industrial demand.Porous Ti3AlC2was fabricated through reactive synthesis technique with TiH2, Al and graphite. The effect of Al content on the phase constitution and pore structure parameters was discussed. The phase TiC firstly decreased and then increased with increase of Al content, while the variation of pore size and permeability showed contradictory trends to that of TiC alteration. The pore forming mechanism is as follows:(1)At first, TiAl was formed previously by Ti and Al, during this stage, the permeability increased, while the pore size and permeability remained largely unchanged.(2) During the second stage, Ti reacted with C to synthesis TiC, and then TiC will diffuse into TiAl alloy to yield Ti3AlC2.With more and more TiC diffusing into TiAl, TiC will deviate its original position, the porosity will increase. At the same time, with TiC diffusing into TiAl, the volume of original TiAl could expand, that will extrude the pores produced by Kirkendall effect, so, the pore size and permeability decreased. When TiC diffused into TiAl completely, the effect of diffusion is the main factor, then the pore size and permeability increased as well.Finally, the fabricated porous TiAl intrmetallics material was successfully applied to the solid-liquid separation of suspended TiCl4raw liquid in industry procedure. The sealed, continuous and long-term filtration procedure was realized using the filtration-backwash technology and porous TiAl intrmetallics tubes as filtration elements, which can alleviate dramatically or even avoid raw material loss and severe environment pollution. The filtration tubes exhibited long-term,stable and high flux and filtration accuracy. The deposition characteristic can be described by the forces balance of a particle in the immediate vicinity of the membrane or cake layer given by Altmann and Ripperger, and the calculated particle deposition size is4.6-5.2?m.Membrane with average pore size of3.5?m was selected for TiCl4filtration.According to Darcy equation, the process of filtration is divided into two stages:at the initial stage of filtration, the particles which are equal to the pore size rush into pore quickly, causing the porosity of membrane decreases, filtration resistance increases and filtration flux decreases as well.At the second stage, fine particles are deposited at the membrane even for high cross-flow velocity and contribute to cake layer formation. During the pore-blocking stage, the membrane resistance is3.00×1011m-1. Compared with all these physical methods, the adhesive force binds particles together and makes cake layer strong and dense that reverse filtration is an effective method to remove cake layer. However, chemical cleaning method is a better method for the alternative, the flux grew quickly and reached a steady state of1.202m3/m2·h.