Preparation And Properties Of TiN And Ti Doped Tungsten Matrix Composites

High melting temperature,good thermal conductivity,and low sputtering rates are excellent properties that make W a potential plasma facing material(PFM)for the International Thermonuclear Experimental Reactor.However,serious problems that limit the use of W still exist,such as low-temperature brittleness,recrystallization embrittlement,and radiation embrittlement.Addition of second phase or alloying elements to tungsten alloys is a kind of preparation method to improve combination properties of tungsten alloys.In this paper,W–Ti–TiN composites were fabricated by mechanical ball-milling and spark plasma sintering method from the tungsten powders,nano titanium nitride(TiN)particles and titanium hydride powders.The effects of the contents of TiN,the parameter of mechanical ball-milling and the contents of Ti on the microstructures and properties of W–Ti–TiN composites were investigated.Moreover,the He~+irradiation performance of the W–Ti–TiN composites were studied.The following conclusions could be drawn:(1)W-(0.5,1,2,4)wt.% TiN composites were prepared by mechanical alloying and spark plasma sintering.The TiN particles were dispersed uniformly,attributing a strengthening effect on the W matrix.With the addition of TiN,the grain was refined,trans-granular fracture was achieved,and the micro-hardness was increased.Highest value was obtained for W-2 wt.% TiN composites,which had the highest density of98.73% and ultimate tensile strength of 180 MPa.(2)With the increase of milling time,the powder particles experienced the welding,fracturing,and rewelding processes.The grain size of the powders was refined to nanocrystalline;thereafter,an amorphous phase was determined after 80 h of milling.And only the WxTi1-x solid solution was determined after 80 h,thereby revealing the decomposition of TiH1.9 and the formation of the W-Ti solution.After sintering,a refined uniform distribution of the second phase was obtained.With the increase of milling time,80-h milling samples showed that an intermediate region between the W and Ti phases exists,which corresponds to the β(Ti,W)phase.Micro-hardness and thermal conductivity increased with the milling time,and the highest value for samples prepared by the 80-h milling(3)The different content addition of Ti into W–TiN composites had a significant effect on the densification and micro-hardness improving.The grain size wassignificantly refined to 0.51 μm by the addition of Ti.The properties of the alloy containing 4 wt.% Ti were the best among those of the other alloys obtained.During sintering,N probably diffused into other Ti lattices,resulting the formation of Ti/TiN solution.Furthermore,addition of Ti enhanced the He~+ irradiation resistance of the resultant alloys.The TiN peeled off after irradiation,and vacancies that could induce erosion were found at the grain boundaries.The sample with 8 wt.% Ti showed no secondary-phase peeling,and only small densities of blisters were found in its W-grain and Ti-rich phases.