Study On The Effect Of Mechanical Alloying On The Solid-phase Reaction Synthesizing Of Laves Phase TaCr₂Alloys

Laves phase TaCr2is an intermetallic with topologically closed-packed structure.It has the potential applications as novel high temperature structural materials due to itsexcellent high-temperature properties,such as high melting point, high strength, highcreep resistance,and good oxidation resistance at high-temperatures. However, thispotential is retarded by its brittleness at room temperature. How to improve thebrittleness of Laves phase TaCr2at room temperature turns into one of the hot topics inmaterial research fields.This article investigated synthesizing of Laves phase TaCr2by soild phase thermalreaction and explored whether it is feasible for using mechanical alloying(MA) todecrease solid phase reaction temperature and the effect of ball milling time on thestructure and morphology of Cr-33Ta mixed powder, besides, the relationship ofmilling time, relatively density and vicker hardness is investigated. The researchplays an important role for overcoming the brittlenss of Laves phase TaCr2.The results indicate that original Cr-33Ta elemental powders will be graduallyevolved into Cr（Ta）and Ta（Cr）non-equilibrium supersaturated solid solution during0-8h milling time. But Laves phase TaCr2can not be directly synthesized until50h MAtime. The obvious angular original Cr-33Ta elemental powders will evolve into similarspherical particles and the grain sizes of Ta and Cr are significantly homogeneous. Theabove results will provide an important guidance to reduce the annealing temperatureand time aiming to developing high strength and high toughness synthesizing ofhomogeneous composition and fine grains up to high tough Laves phase TaCr2.With the increasing ball milling time, the grain sizes and micro strains of Ta andCr will gradully increase. After8h milling time, the grain sizes of Ta and Cr are3.935nm and13.833nm and the micro strains of Ta and Cr are6.112%and0.537%respectively.According to the effect of milling times, annealing temperature,and annealingtimes on synthesizing of Laves phase TaCr2, it is found that the milled times,duringwhich synthesizing reaction can be sufficiently accomplished, has a threshold which is30h for an annealing of900℃×3h. Under a3h annealing time, the lowest annealingtemperature,at which synthesizing reaction can be sufficiently accomplished for30hmilled powders, is1000℃. Under a1000℃annealing the shortest annealingtime,during which synthesizing reaction can be sufficiently accomplished for15h milled powders, is1.5h.The results of the microstructural observations and performance examinations ofCr-33Ta alloys with the different ball milling time and HP in1250℃×3h indicate thatin the beginning the mechanics properties of Cr-33Ta samples increases and themicrostructure is more uniform and finer as the ball milling time increases. But themechanical properties of Cr-33Ta samples decreases as the ball milling time moreincreases. The best properties were obtained from the sample prepared from the ballmillinged30h powders with the relative density of98%, the Vickers hardness of11GPa.