| Particle reinforced iron matrix composites have been taken significantly interests due to their high strength, high stiffness and high wear resistance properties. A two-stage resistance sintering with dynamic temperature control technology was employed to manufacture SiCp/Fe composites and influence of the sintering holding temperature and holding time of the technology on properties of composites were investigated. A mechanical impact metal coating technology was developed during powder blending by mechanical alloying ball mill to solve the reinforcing particle cluster in particle reinforced iron matrix composites which processed by powder metallurgy method. Effect of the mechanical impact coating parameters on properties of composites was investigated. The SiCp/Fe composites were manufactured by the optimal processing to investigate the influence of the particle volume fraction, single-sized particles and mix-sized particles on microstructure and properties of composites. The Eshelby particle-compound model and the three-dimensional finite element model for SiCp/Fe composites were also established to predict stress-strain curves and investigate the influence of particle volume fraction, single-sized particles and mix-sized particles on composite properties.The SiCp/Fe composites were condensed with increasing sintering holding temperature and holding time, which contributes to better properties. However, too high holding temperature and/or too long holding time caused deteriorative reaction in the SiC particles and iron mtrix interfaces. Experimental results indicated that properties of SiCp/Fe composites achieved optimal as the holding temperature and holding time were about 1200? and 200s, respectively. The study on the mechanical impact metal coating technology indicated that the reinforcing particles damage during mechanical alloying could be avoided and the reinforcing particles could be primely coated by the iron matrix when the ball-to-powder ratio was 5:1, the rotational speed was 225rpm and the coating time was 120min, respectively. Compared with conventional powder blending method, the new mechanical impact metal coating technology can significantly improve properties of the composites and also shows the better performance as the higher particle volume fraction. For instance, the tensile strength and relative density of 20vol%SiCp/Fe composites processed by the impact technology could be improved 42.3% and 5.5%, respectively, compared with conventional method.Hardness, wear resistance and tensile strength of the SiCp/Fe composite increased firstly and then decreased with increasing particle volume fraction from 5% to 20%. And the properties achieved optimal value as the particle volume fraction was 10%. However, the elongation of the composite monotonically decreased with the particle volume fraction increasing. Microstructure analysis revealed that reinforcing particle clusters and defects have been found in the 15vol%SiCp/Fe composite, which decreased its properties. The reinforcing particle size scarcely affected the hardness of SiCp/Fe composite; however, significantly influence the wear resistance. The tensile strength, ductility and wear resistance of the 10%vol SiCp/Fe composite increased when the particle size increased from 3.5?m to 13?m because the distribution of the reinforcing particles in SiCp/Fe composite trended to be homogeneous; but decreased with a further increase of the particle size, for a larger-size particle had a lower strength themselves which was easily fractured to failure as the composite under an external loading.Effects on the properties of the SiCp/Fe composites reinforced with mix-sized particles were studied in the present research. It indicated that that the properties of the SiCp/Fe composites could be optimized by a rational design of different size particles mixture. The SiCp/Fe composites achieved the best mechanical properties with the 13?m and 23 ?m nominal-sized particles mixed by the 1:1 mass mixing ratio, compared with that of 13?m+3.5?m and 13?m+38?m. The mass ratio of the 13?m and 23?m particles mixture also reached another optimal of 2:1 in the 10vol%SiC/Fe composite and 1:1 in the 20vol%SiCp/Fe composites. For the 2:1 mass ratio of the 13?m+23?m particles mixture, the tensile strength improved 9.7% and 38.3% compared with the single-sized 13?m and 23?m particles, respectively; however, the elongation showed little different in these threee cases. For mix-sized particles not only condensed the composites but also decreased the defects in composite indicated by microstructure and fracture surface observations so that the tensile strength of the composite was improved.An Eshelby particle-compound model included a fracture mechanism from the matrix micro-crack propagation base on the experiamental observations was firstly established to predict the stress-strain curves of SiCp/Fe composites, where the effective stress of the composites from the fracture stress of the matrix was corrected. The new stress-strain curves predicted by this Eshelby model well agreed with with experimental results. The stress in the reinforcing particles verus the strain of the composite was found much higner than that in the iron matix, which implied that the load was greatly transferred from the iron matrix to the reinforcing particles and proved that the load transfer mechanism determined strengthening the SiCp/Fe composite. A three-dimensional finite element model for SiCp/Fe composites was established to predict stress-strain curves of SiCp/Fe composite reinforced with particle random-distributed particle size of 7?m, 10?m,20?m and 30?m. The simulation results showed that the particle size had a great effect on yield strength of 10vol%SiCp/Fe composite. The composite achieved the highest yield strength reinforced by the particles, which were neither the smallest nor the largest size, in agreement with the experimental observation. So this implied that there was a critical particle size which had the best effective on blocking plastic deformation of the matrix. Also, compared with single-sized particle, the mix-sized particles improve yield strength of SiCp/Fe composite more effectively, which agreed with the experimental observation. However, the mixed mass ratio between different size particles showed little effect on properties of the composite, disagreed with the experiments, which indicated that defect quantity at interface between particle and matrix also contributed strengthing of the SiCp/Fe composite. |
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