Preparation And Performance Study Of Dispersion Strengthening Vanadium Alloys

Developing fusion energy is an important measure to solve the energy crisis, becauseof the harsh conditions of the fusion, looking for the ideal lining materials of fusionreactor is particularly significant. The special properties of vanadium alloy such asmaintaining good dimensional stability and low activation characteristics under neutronirradiation, good compatibility with liquid lithium, resistance expansion induced byradiation determine it to be an appropriate choice of being lining structure material innuclear fusion reactor. However, the low tensile strength of vanadium alloy hinders theprocess of engineering application.In order to improve the strength and plastic of the vanadium alloy, mechanicalalloying method was adopted in this paper, appropriate amount of YH₂and Ti₃SiC₂wereadded in the matrix of V-4Cr-4Ti alloy powder to make a series of alloy powder ofV-4Cr-4Ti-1.8YH₂-xTi₃SiC₂（x=0,0.4,0.8and1.2）.Two mass ratios of ball and powderand a series of ball milling times were set up in this experiment in order to study thereasonable process parameters of mechanical alloying. The reasonable process parametersof ball mill were drawn by contrast that the better mass ratio of ball and powder was7:1and the best ball milling time was50h. The alloy powder had not been detected anycontaminate brought by ball mill pot and grinding balls in this phase and mechanicalalloying of powders could be achieved completely.The technological process of spark plasma sintering and hot isostatic pressing （SPS-HIP） were used to fabricate vanadium alloy ingot, followed with post-processing. Thestudy of the density and hardness of vanadium alloy ingot found that vanadium alloy ingothad already showed a high density just by means of SPS and could be made furtherdensification by HIP treatment.The protective measures such as coated vanadium alloypowder and ingot with Ta slice and Zr foil could effectively solve the problem ofcarburizing and oxygen-absorbing. This series of processing method could not only makehigh density of vanadium alloy, but also eliminate the stress of vanadium alloy andincrease the toughness of the alloy so as to improve its processing and mechanicalperformance. The mechanical tensile experiments of vanadium alloys annealed indifferenttemperature shown that different heat treatment temperature immensely affected themechanical properties of the alloys, adding different mass of Ti₃SiC₂could significantlychange the tensile strength, yield strength and elongation of the matrix ofV-4Cr-4Ti-1.8YH₂-xTi₃SiC₂alloy. The vanadium alloy which had the best comprehensivemechanical properties of the series of alloy was V-4Cr-4Ti-1.8YH₂-0.4Ti₃SiC₂annealedin1100℃which yield strength was875MPa, tensile strength was1108MPa andextension was16.8%.The microstructure of V-4Cr-4Ti-1.8YH₂-0.4Ti₃SiC₂alloy was characterized andanalyzed. The grain size mostly was0.5μm and there were many internal high-densitydislocation. The solid solution of V-4Cr-4Ti was found in large amounts whose grain sizewas about400nm. Ti₃SiC₂phase whose grain size was about100nm distributed in thesubboundary of V base phase, playing the role of dispersion strengthening. Thehydrogenated yttrium （YH₂） added in the alloy powder was turn into Y in hightemperature through dehydrogenation reaction, which could absorb oxygen in the grainboundary and turn into Y2O3whose grain size was20nm, dispersing around the vanadiumphase. The Y2O3grain had not only absorbed oxygen and purified grain boundary, but alsoplayed the role of fine-grain strengthening and dispersion strengthening which couldhinder the movement of dislocation and improve the mechanical properties and plastic ofvanadium alloy.