| Powder metallurgy (P/M) parts, which have many excellent and unique properties, such as net shape, economization on material and energy, cost-effective, unpolluted and good integrated properties, have drawn increasing attentions in many industrial applications. Consequently, it is considered that P/M parts are the most valuable and exploitative natural engineering materials with great potential application in this century.The working environment of valve seats in automobile engine is very severe. Its working temperature is as high as about 700℃, and it is also corroded by exhaust gas at the same time. Therefore, valve seats suffer not only the mechanical impingements but also the scour and cauterization of high temperature gas as while as the abrasion of combustion product and the dust in the cylinder. Consequently, it is prone to be deformed, burnt out and even ruptured. In addition, the abroad use of non-lead gasoline causes serious wear due to the absence of lead lubrication during the use of valve seats. These phenomena require high performance for the valve seat because the original casting valve seats have not been adapted to the new demand. The P/M valve seats possess the characteristics such as high degree of freeness in materials design, small machining allowance, high using ratio of materials and suitable for volume-produce. Comparing with the casting ones, P/M valve seats have the trait of fine grain, little segregation, stable metallographic microstructure. Moreover, other trace elements can be added into the alloy.This thesis is mainly aimed at the preparation of double layers with superior performance and well unitary matching using P/M method for the sake of improving the heat conduction, prolonging the life span, decreasing the quantity of alloy elements and reducing the production cost. In the experiments, orthogonal test is employed to optimize the composition of Co,Cr,Mo,Ni and Cu.Furthermore, carbusintering and conventional sintering are investigated to study the effect of sintering methods on microstructures and properties. The microstructures and properties of the carbusintering materials are also studied in detail using SEM with EDS, XRD, MTS810 electromechanical testing machine and MM-200 wear testing machine. Conclusions are listed as follow:1. The optimal chemical composition (wt.%) of the working layer and non-working are Fe-3Co-1Cr-1Mo-2Cu-2Ni-0.4C and Fe-2Cu-2Ni-0.4C, respectively. The calculated heat expanding coefficients of these two layers show that the difference between the two heat expanding coefficients is very small and the two layers match well in thermal properties.2. The dominant phases areα-Fe and Fe-Cr-Ni in the working layer by XRD analysis, andγ-Fe,Mo2C and Cr7C3 appear in the carbusintering but absent in the conventional sintering. The microstructure is composed of fine sheet pearlite, a few ferrite, austenite rich in Ni, ferrite rich in Cr and holes in the carbusintering materials, while after quenching, the microstructures are needle martensite, retained austenite and small quantities of holes.3. Some mechanical properties are measured after sintering for both carbusintering and conventional sintering. The results show that the properties of carbusintering are better than that of conventional sintering. 4. Although dimples are the most composition of fracture morphology for both two kinds of specimens, the ruptures still show brittle deformation in stead of plasticity deformation in macroscopic due to the presence of holes.5. Under lower load, slight abrasion takes place in the Fe-based sintering materials, and the abrasion mechanisms are oxidative abrasion and adherence abrasion.
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