Study On Preparation Of B ₄ C / Al Composites By High Energy Ball Milling

As a special ceramic material, B4C has excellent physical and chemical properties such as high strength, extreme hardness, low density and well neutron absorbtion ability etc. However, there has some kind of defects like low fracture toughness property, too high sintering temperature, bad antioxidant ability and so on with in B4C itself leads to its restriction use in manufacture. Because of the reason above, many related researchers pay attention to the study of B4C reinforced metal matrix composites, which can not only develop high electrical conductivity, good thermal conductivity of metal material but exert the advantage of B4C reinforced particle. Because the density of Al is close to the density of B4C, low melting point, extensive material source and maintains the light quality and improves strength when compounding with B4C, and B4C reinforced Al matrix composites becomes the most popular research subject.The mainly existing problems about B4C particle reinforced Al matrix composites are the dispersion of B4C particle in Al matrix and interface reaction. To solve those problems above, high-ball milling and vacuum hot pressing process are adopted in manufacturing B4C/Al composites.(1) Using single factor method to study the impact on composite powder that caused by different parameters such as the content of B4C, milling time, agitation shaft rotation speed, ball percentage and the content of stearic acid and then analyze the different ball milling parameters on composites particle size, morphology, and composites phase. The results show that, the size of B4C/Al powder are refined, B4C partices realize uniform distribution, and no impurity phase generated when the ball mill parameter are:the mass fraction of B4C is 20%, the mass fraction of stearic acid is 1.5%, ball milling time is 2.5h and the agitation shaft rotation speed is 500/700rpm(2) Optimize the ball mill parameters by using response surface methodology (RSM). After the single factor experiment and the optimization of parameters, the best ball mill parameters are:the mass fraction of B4C is 20%, the mass fraction of stearic acid is 1.2%, ball milling time is 2.3h and the agitation shaft rotation speed is 500/700rpm. In this condition, the B4C/Al composites show the best comprehensive performance.(3) Through experimental analysis, the most reasonable hot press process and the best content of B4C is as follow:hot pressing temperature is 600℃, hot pressing pressure is 100MPa and the mass fraction of B4C is 20%, in this condition, the density of composites is 97.2%, B4C can get homodisperse and good interface bonding, and the tensile strength and hardness are 385.7MP and 135.4Hv.(4) The fracture analysis shows that the fracture way of B4C/Al composites is the detachment of B4C and Al matrix and the cooperation of the tear up of Al matrix and the fracture of B4C, and plastic fracture and brittle fracture make up tensile fail, and strengthening mechanism is about refined crystalline strengthening and second phase strengthening.