| Al2O3 particles and steel are combined by mechanical function, this lead to a weak interface of Al2O3 particles and steel, and a poor mechanical properties of composites. So it is always very important question that how to improve wettability of Al2O3 particle reinforced steel matrix (Al2O3p/steel matrix) composites and its performance. In the paper, activation substances are added in the preform, the wettability of ceramic particles and steel are studied after adding activation substances, and the structure and mechanical properties are analyzed, and the mechanism of activated substances are discussed.In this paper, the mesh of Al2O3 particles is 40 to 60,1065 steel is used to metal matrix, activation substances are Ti, TiO2 and Cr(15% wt of Al2O3), then Al2O3p/steel matrix composites was successfully prepared by 50 MPa pressure.Composites without activation substances is prepared and its infiltration depth is 4-5 mm, it is good interface quality, and no shrinkage. The wetting angle is 125°, and the hardness of composites is 35.8 HRC, three point bending strength is 588.7 MPa, the study shows that the fracture has obvious cracks, and some particles occur shed, crack has the obvious extension trend, and it showed brittle fracture. These suggest that interface of composite is combined by mechanical bonding.The infiltration depth of composites with Ti is 8-9 mm, the result shows that TiC is formed in interface, the matrix miscrostructure is ferrite. Wetting angle is 75°, so Ti powder has improved greatly on the wetting angle. The hardness of the composites is increased to 42.3 HRC, increased by 64%, and three point bending strength increased to 1018.0 MPa, increased by 72.9%. fracture SEM and subsurface analysis shows that TiC is formed in interface. It is improve the interface effectively, and the interface combine more firmly. These suggest that interface of composite is combined by metallurgical bonding.After adding TiO2 powder, the infiltration depth increase to 10-12 mm, the result indicates TiO2 can form Al2TiO5 with Al2O3, that and adding TiO2 are formed interface modification layer in the composite interface. The interface changed from simple mechanical combination to metallurgical combination. The wetting angle is 106°, the hardness of composites with TiO2 is 39 HRC, increased by 10%, three point bending strength is 748.9 MPa, increased by 26.36%, fracture SEM and subsurface analysis shows that composite with TiO2 have good interface, Al2O3 particles is main transcrystalline fracture, which show that TiO2 can improve interface bonding strength.After adding Cr powder, the composites for infiltration depth is 8-9 mm. The result shows the addition of Cr powder can form FeCr phase with liquid steel. The wetting angle curve is analyzed, the wetting angle is 109°. Although chemical reactions is occurred in composite interface, the microstructure of matrix are changed The hardness of composites with Cr is 50.7 HRC, increased by 95.6%, and three point bending strength is 669.5 MPa, increase by 13.7%. Fracture SEM and subsurface analysis shows that the fracture of composite materials is also brittle fracture, but the interface bonding strength is greatly improved.These analysis show that the interface combination of composite material change from mechanical bonding to metallurgical bonding by adding Ti, this make the wettability between particles and matrix reduce, and improve mechanical properties of composites. After adding TiO2, weak interface reaction are occurred between TiO2 and Al2O3 in the interface of particles and metal matrix efficiently, but the major role is transition layer of Al2O3-TiO2-Fe, this can improve properties of the composites efficiently. Although Cr doesn’t produce exactly the chemistry in the interface, and interface bonding method is always mechanical bonding, Cr powder can change the composition of liquid steel around the Al2O3 particles, and reduce composite interface energy, the wettability are improved. So the composites for mechanical properties can be improved. |
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