Grinding of Fe-B4C powder charge in an inertial cone mill

Abstract

621.762The use of an inertial cone mill to grind iron and boron carbide powder mixtures is examined. The dependence of the particle-size distribution in the mixture after grinding on the maximum particle size is analyzed. It is established that the content of coarse-grained fractions (larger than 100 μ m) substantially decreases as compared with the initial powder even after three grinding cycles. If the number of grinding cycles is increased to 20, the content of finer fractions (smaller than 63 μ m) is only 6 to 8% higher than in powders subjected to 3-12 grinding cycles in the inertial cone mill. Therefore, more than 3 or 6 cycles to produce Fe-B 4 C powder with the optimal content of the ≤100≤63μ m fraction are unreasonable.Recently, the attention of researchers has been focused on iron-based boron alloys owing to their high strength, hardness, and wear resistance and relatively low cost. Thus, they can be regarded as promising materials for making wear-resistant alloys [1,2]. For example, the study [3] shows that the wear resistance of coating composite materials based on the Fe-B-C system is comparable with and, on occasion, greater than that of materials based on tungsten carbide, which is more expensive.Boron carbide not only hardens the material, but also activates sintering because eutectic transformation occurs in the Fe-B-C system, contact melting occurs in the iron-boron carbide powder mixture at temperatures above 1100°C, and the liquid phase activates consolidation [4]. The heterogeneous structure of the material, which is an alloyed matrix with hard inclusions of complex carbides and borides, is responsible for high wear resistance [2].To produce low-porosity samples from a Fe-B-C charge by liquid-phase sintering, the particles of the starting powder, according to different authors, should not be larger than 60-100 µm [3][4][5], whereas standard watersprayed iron powders used for structural purposes include coarser fractions that amount to about 30% of the total mass. One of the effective methods to improve the agglomeration of such powders is grinding. Thus, it is necessary to develop an efficient method for grinding sprayed powders. This paper examines the possibility of using an inertial cone mill (ICM) to grind powder mixtures of iron and boron carbide. This mill is distinguished from mills of other types by a specific way the load is applied to particles being ground. For example, most mill designs apply a concentrated load of random magnitude and site of application to the powder (which quite often leads to nonselective breaking and balling of particles), whereas the particles in the ICM are in a triaxial stress state due to cyclic loading in the chamber [6]. Since entering the grinding chamber, a particle suffers more than hundred processes of compression, shear, bending, and unloading. During motion, the particle changes the shear vector, which promotes its breaking on the weakest planes. Figure 1 shows the ICM design. External grinding cone 2 and spherical support 4 of internal grinding c...