Preparation, Properties And Modeling Of Iron Matrix Composites Reinforced By Different Types Of Ceramic Particles

Particulate reinforced iron matrix composite, which has high strength, high stiffness and high wear resistance properties, is one of the metal matrix composites with potential value of industrial applications. However, investigations in the literature have been focused on individual sole type of particle reinforced iron matrix composites respectively and the results have no comparability each other to evaluate different reinforcements due to the enormous difference on preparation technology and on materials microstructure. It is significant to conduct systematically an investigation with respect to preparation, properties and modeling of iron matrix composites reinforced by different types of ceramic particles.First, the improved specimen current heating dynamic hot press sintering technology was applied to study the effect of the holding time on properties of10%TiC/Fe composite to investigate whether the technology is equally applicable to the preparation of iron matrix composites reinforced by other types of reinforcing particles rather than SiC reinforcement. Then, tensile properties and wear performance of the iron matrix composites reinforced by different types of ceramic particles (Cr3C2、SiC、TiC、Ti(C,N)、Si3N4、TiB2、B4C and Al2O3) prepared by the same technology were studied experimentally as well as to examine the effect of different types of mixed particles and the influence of reinforcing content. Moreover, the mechanical properties of different types of composites were simulated by Eshelby equivalent inclusion mechanical model to reveal the strengthening mechanisms of different types of iron matrix composites in order to provide necessary experimental data and theoretical fundament for the development of particle reinforced iron matrix composite.The study on the influence of holding time on properties of10%TiC/Fe composites indicated that the sintering of the composite is insufficient with lots of defects in microstructure and the properties of the composites are low if the holding time is less than 200s. When the holding time is200s, it is shown that TiC particles have no reaction as well as good bond with the iron matrix by sufficient sintering, so the composite exhibited excellent properties. As the increase of holding time further, TiC particles would react with the iron matrix severely to produce graphite plates by TiC decomposing into iron matrix to disserve its continuity, and this results in a decrease in the properties of the composite. The properties of both TiC/Fe and SiC/Fe composites can achieve optimal when the holding time is200s, which implies that the best preparation parameters for the eight types of composites are same and the specimen current heating dynamic hot press sintering technology has good stability and flexibility.The investigation on the effect of eight types of ceramic particles on mechanical properties of iron matrix composites showed that SiC reinforcing particles present the strongest effect on improving strength experimentally, and Cr3C2reinforcing particles take the next best effect with the AI2O3reinforcing particles being the worst. It was seen by microstructure observations that the TiC and the Ti(C,N) particles have no reaction with the iron matrix to leave a pure Ferrite microstructure of the matrix, whereas the Cr3C2and the SiC particles took a slight reaction with iron to form some Pearlite in the matrix. The rest types of composites not only have pure Ferrite microstructure in the matrix but also have some micro-voids and micro-cracks at the interfaces between the reinforcing particles and the matrix. It is concluded that the slight reaction between Cr3C2or SiC reinforcing particles and the iron matrix increases the interfacial bonding, which is beneficial to raise the strength of composites as well as the reactive product, Pearlite, increases matrix strength to enhance the composites. The SiC has higher fracture toughness than the Cr3C2, as well as low coefficient of thermal expansion and highest thermal conductivity and those also help the SiC become the best reinforcing particles in the investigation. The TiC and the Ti(C,N) particles do not react with the matrix to produce Pearlite and do not result in micro defects in the matrix neither so that their strengthening effect is moderate. On the other hand, the other four types of reinforcing particles such as AI2O3not only didn’t increase matrix strength by producing Pearlite but also results in the interface micro defects due to their low electric conductivity and chemical inertness, which make them poor types as the reinforcing particles.The iron matrix composites reinforced by different types of ceramic particles (SiC, TiC, and Ti(C,N)) were selected to investigate the effects of reinforcing particles on wear behaviors. It is shown that the wear loss of all the iron matrix composites is less than15%of that of typical carbon tool steel. The Ti(C,N) particles presented the strongest effect on improving the wear resistance among the four types of investigated ceramic particles and the effect of the other reinforcing particle types on wear property falls a series of SiC, TiC and Cr3C2from high to low. It was surprisingly noticed that there is no clear relationship between the wear performance and hardness of the composites. The reinforcing particles such as Ti(C,N) particles which are endurable to a certain deformation on the interfaces can improve wear resistance more significantly.The preliminary results of the iron matrix composites reinforced by mixed types of ceramic particles showed that the addition of other types of ceramic particles helps Cr3C2particles be dissolved in the iron matrix to strengthen the composites. The addition of other types of particles results in intensive interface reaction between the SiC particles and the iron matrix to lower properties of the composite. The relative density, hardness, tensile strength and wear resistance of the mixture reinforced composites can be all improved if SiC particle size is increased. This is an interesting phenomenon and is worthwhile for a further research.The stress-strain curves of the different iron matrix composites were simulated by Eshelby equivalent inclusion mechanical model to reveal strengthening mechanisms. The results showed that the stress-strain curves by the modeling agree well with those of the experiments on TiC/Fe and Ti(C,N)/Fe composites, but the modeling results are much lower than the experiments on SiC/Fe and Cr3C2/Fe composites, and the modeling results are much higher than the experiment on the other composites. Further more, stress in matrix of the iron matrix composites reinforced by different types of particles has been calculated. The modeling results suggested that the strengthening mechanism in10%TiC/Fe and10%Ti(C,N)/Fe composites chiefly relies on load sharing of the reinforcements only, while the strengthening mechanisms in the SiC/Fe and Cr3C2/Fe composites rely not only on load sharing of the reinforcement but also on increasing matrix strength. The other composites are strengthened by load sharing of the reinforcement but the matrix strength is lowered due to micro defects so that the strength of the composites is almost the same as that of the iron matrix alloy. The modeling offers a good support to interpret the experiments. The tensile strength and yield strength of all the eight types of composites showed a maximum value at10%volume fraction of reinforcing particles experimentally whereas the yield strength should be increased continuously with the increase of the volume fraction by the modeling. The theoretical analysis and microstructure observations were carried out to suggest a good explanation for the experiments:When the reinforcement volume fraction is low, the effect of load sharing mechanism is insufficient and composite strength is low. When the reinforcement volume fraction achieves to10%, the strengthening of load sharing mechanism is increased meanwhile the reinforcements are still distributed homogeneously with no harmful effect on the strength. When the volume fraction is further increased up to15%for example, the reinforcement distribution is uneven with many clusters, which have weak bond with the matrix to contribute nothing in load sharing effect and break the continuity of the matrix to lower matrix strength because of the micro-cracks between the particles in the clusters, so that the composite strength is lower than that of the10%fraction composite.