Study On Compressive Properties Of Al₂O₃ Particles Reinforced Steel Matrix Composites With Hierarchical Structure

The concept of hierarchical structure was introduced to steel matrix composites for the first time,and the effects of different powders,matrix,preform sphere diameters and preform arrangement on the organization and compressive properties of steel matrix composites were mainly investigated.Cracking behavior of the composites were discussed.The main findings were as follows.In this paper,a new alumina particle(Al₂O₃p)/steel matrix with hierarchical structure is investigated.Both matrix and reinforcing phase are divided into grade ? and grade ?.Micron-sized Al₂O₃p(Grade ? reinforcement)first forms millimeter-sized composite ball with the steel matrix(Grade ? matrix).The composite ball(Grade ? reinforcement)then forms a monolithic composite with the steel matrix(Grade ? matrix).The reinforcing phase is regularly distributed in the composite material in a"non-uniform"manner to achieve the regulation of strength and toughness.The effects of preform addition of reduced iron powder and Fe320 alloy powder on the organization of high manganese steel matrix and 40Cr steel matrix composites with hierarchical structure were investigated.The Al₂O3 particles were dispersed uniformly in the composite zone and did not have obvious defects.The diffusion and reaction of multiple elements occurred in the composite zone.When the matrix is high manganese steel,the migration of Mn elements is obvious,and the interface exists Mn₂SiO₄,Al_xFe_xSi_x,and microcrystalline glass phase:Na₂O·Al₂O₃·SiO₂.When the matrix is 40Cr steel,Al_xFe_xSi_x exists at the interface,and Ni and Cr elements in Fe320alloy powder and Fe form Fe-Cr and Fe-Ni solid solution with each other.The effects of preform addition of reduced iron powder and Fe320 alloy powder on the microhardness of high manganese steel matrix and 40Cr steel matrix composites were investigated.The effect of reduced iron powder on the microhardness of high manganese steel matrix composites was better than the addition of Fe320 alloy powder.The effect of Fe320 alloy powder on the microhardness of 40Cr steel-based composites was better than the addition of reduced iron powder.The addition of micronized powder changes the matrix composition within the composite area.As high manganese steel is a high alloy steel,the addition of reduced iron powder makes the Mn element diluted,which makes the matrix composition approximate to that of medium manganese steel.After heat treatment,the metallographic organization of martensite and austenite combination is formed,which improves the hardness of the matrix.On the contrary 40Cr steel as a low alloy steel,the addition of Fe320 alloy powder improves the microhardness of the matrix due to the mutual solid solution of Ni and Cr elements with Fe.The effect of preform addition of reduced iron powder and Fe320 alloy powder on the compressive properties of composites was investigated.For the high Mn steel matrix composites,the compressive properties of the composites with the addition of reduced iron powder were better than Fe320 alloy powder,while for the 40Cr steel matrix composites,on the contrary,the addition of Fe320 alloy powder was better than that of reduced iron powder.The effects of different preform spherical diameters(6,7 and 8 mm)and different preform arrangements(parallel and staggered)on the compressive properties of reduced iron powder-Al₂O₃p/high manganese steel matrix composites with hierarchical structure were investigated.The yield strength and compressive strength increased when the spherical diameter was reduced.The composite obtained better compressive properties when the preforms were staggered compared with parallel arrangement.The cracking behavior of Al₂O₃p/steel matrix composites were studied,and the cracking patterns of the composites with hierarchical structure were summarized.Cracking initially occurs at the macroscopic interface between the preform frame junction(spherical preforms are positioned at wire mesh junctions,followed by gravity cast infiltration to obtain composites with hierarchical structure)and the grade ? reinforcing phase,and the grade ? and grade ? matrix exhibit significant deflecting and crack-stopping effects on crack expansion from the microscopic and macroscopic perspectives,respectively,so that more energy is consumed for crack expansion.The toughening of the composites is mainly attributed to the synergistic strengthening effect between the steel matrix frame and the composite zone frame,where the steel matrix bears the load and hinders the crack expansion generated in the composite zone frame,which has an energy-absorbing effect.