Study On The Preparation And Properties Of Tungsten Coating And Titanium Carbide Doped Tungsten Matrix Composites

Tungsten metal was considered to be the most promising candidate for Plasma Facing Materials(PFMs)in fusion reactor.However,tungsten metal used as PFMs is also facing serious brittleness in several aspects i.e.low-temperature brittleness,high-temperature brittleness or recrystallization brittleness and radiation induced brittleness.The effective way to solve the brittleness of tungsten is the doping of second phase in tungsten matrix.In the thesis,First the dispersion of titanium carbide was studied.Then,precipitation-coating processes were utilized to prepare the tungsten-based composites.Finally,the fabrication of tungsten coating by metal organic chemical vapor deposition(MOCVD),the preparation process of tungsten coating was studied.Influence of preparing process on composites performance were studied.The main results are as follows:(1)The experiment results showed that the TiC suspension was satisfactorily dispersed with the dispersant(DMF and PEG)at pH 9.5,both electrostatic stabilization and steric stabilization were deduced to be the main mechanisms for well dispersion.(2)When TiC was dispersed with the dispersant(DMF and PEG)at pH 1,in the saturated solution of AMT,the well-dispersed spherical tungsten-based doped powders with a diameter of 200nm,which were prepared by high-purity hydrogen reduction(holding at 600? for lh and 800? for 30 min continuously).Study found that the second phase particles are uniformly distributed in the matrix W by spark plasma sintering(SPS)at this time.Moreover,the relative density of TiC/W composite material reaches the maximum of 94.6%,the maximum bending strength of 739MPa5 than the SPS sintering pure-W(345MPa)strength increased about 114%.In addition,micro-hardness of TiC/W composites about 486HV,micro-hardness values than the pure-W increased about 98%.(3)Well-dispersed TiC/W core-shell nanoparticles were synthsized by chemical reaction and high-purity hydrogen reduction process.When the concentration of hydrochloric acid solution for 50ml/240ml,slurry dispersant for DMF and PEG addition amount of 1:1,the tungsten-based doping powders would be more uniform with diameter about 200nm.The products were mainly composed of larger particles with diameters about 200 nm,companied by minor particles of ca.50nm can be obtained by two-step reduction.The three steps reduction results in severe hard agglomeration with particle size of about 1?m,these particles were " sintered" together.EDS spectrum was analyzed to found the core component consisting of Ti-W-C,TEM images demonstrate that TiC nanoparticles were well-encapsulated by W shells.(4)The tungsten membranes with ultra microstructure on CuCrZr alloy and CLAM substrates have been prepared by metal organic chemical vapor deposition(MOCVD),and constantly adjusting the deposition parameters during the experiment.The membranes were produced by pyrolysing the tungsten hexacarbonyl in low pressure,at air and argon atmosphere.When formed at 270?600?,the sublimation temperature of the tungsten hexacarbonyl at 70?90?,all the membranes consist of tungsten in the ?-W.The experiment confirmed the deposition temperature is the most important factor of the final W-coating properties,when the deposition temperature is 500?,the properties of tungsten membranes had been greatly improved.Then annealed at 700?800?,?-W will be converted into ?-W.Moreover,these membranes have stable chemical composition and microstructure.The bonding properties and polish of surface could be enhanced greatly.The coating on CuCrZr alloy has better properties than CLAM.