Preparation Technology Of Bi-continuous Graded TiC/Fe Composites

The preparation technology of bi-continuous phase TiC/Fe and graded TiC/Fe composites are studied in this thesis for the application of wear-resistant materials.The structure relationship of bi-continuous composites makes the ceramic reinforcement and metal matrix restrict and fill each other,which improved the properties of the composites.In the experiment,organic sponge was used as the template to prepare uniform TiC porous ceramics and graded TiC porous ceramics as the reinforcing phase of Fe matrix composites by using the slurry impregnation and pressureless sintering process.By studying the impregnation and sintering processes of porous ceramics,the optimized material formula and process parameters within the experimental range were obtained.The experimental results showed that both the uniform and graded TiC porous ceramics presented continuous and complete three-dimensional network structure at the micro level,and there were no other impurity phases except TiC.The rib diameter,porosity and volume density of TiC porous ceramic can be controlled by dipping different aperture of templates and adjusting the impregnation process.Porous ceramics which prepared by small pore size of sponge(with high PPI)as the template has low porosity,high volume density and high compressive strength.The compressive strength of 40 PPI porous ceramics by dipping 6 times can reach up to 3.49 MPa.Uniform and graded bi-continuous phase TiC/Fe composites were prepared by melt pressureless infiltration process.The relationship between the microstructure and mechanical properties of the composites were researched.The results show that the bond of the interface between the TiC ceramic phase and metal matrix in the composite is tight without obvious defects.There was a significant difference in ceramic content between the two sides of the graded interface of the graded composites.The ceramics ribs have the continuous transition at the interface,and the metal matrix penetrated into the gap of the ceramic reinforced phase,forming a bi-continuous graded structure.The bi-continuous phase TiC/Fe composite showed good mechanical properties and friction performance.The volume fraction of the TiC ceramics reinforcement,which prepared with 40 PPI organic sponge template and dipping 5 times,is about 14.4%.The highest tensile strength of the composites can reach to 1260 MPa,and the compressive strength,bending strength and Vickers hardness of the composites are 1084 MPa,635 MPa and 4.98 GPa,respectively.The properties of bi-continuous phase TiC/Fe composite are much better than that of the particle reinforced TiC/Fe composites with the same ceramics content.The hardness of the graded composites showed a graded distribution.Hardness of the 40 PPI layer is significantly larger than that of another layer with less ceramics content.The interlayer shear strength of the graded composites increased with the decrease of ceramics content difference between the two layers,and the maximum shear strength is 346MPa for the 35 PPI-40 PPI graded composites.The friction and wear tests were carried out on composites with different ceramic contents,and the variational rules of the friction coefficient and wear rate were obtained.The results showed that the friction coefficient of bi-continuous TiC/Fe composite decreased with an increase in TiC content,and the friction coefficient of 35 PPI TiC/Fe composite is 0.52.The friction coefficients of the composites under different pressure have a little variation within a range of 0.51-0.56,which shows appropriate wear resistance and stable friction coefficients.The minimum wear rate and wear depth of 35 PPI TiC/Fe composites are 0.15×10-9 mm3/N·m and 2.96 ?m,respectively.