Investigations Of Preparation Technology And Interface Microstructure Of SHS Composite Pipes

As a new type of synthesis process of materials, self-propagating high-temperature synthesis (SHS) rose at the end of 1960's to get compounds in a short time by means of the combustion heat generated by reaction itself. SHS has been paid more attention and industrialized step by step because of its simple equipments, controllable technological parameters and components and high densification of products. Because the quality problem of composite pipes is reflected in preparation technology and properties of interface aspects, it is necessary to conduct the research into preparation technology and interface microstructure of composite pipes.In this paper, the additive is added to change intrinsicformulation to produce new types of composite pipes by SHS-gravitational and SHS-centrifugal process. The physical and mechanical properties of composite pipes have been analysed by means of density test, hardness test, joining strength test and heat-shock test and so on. Microstructures and phases of the ceramic layer and the interlayer are analysed by means of optical microscope and SEM and X-ray diffraction analysis. The effects of filling density, centrifugal force, component of additive and the interface microstructure on properties of composite pipes have been studied. The phase separation and solidification law of SHS-gravitational have been discussed through the model of phase separation and solidification of SHS-gravitational.It was indicated that the ceramic layer of composite pipe is smooth, uniform and has perfect properties when the filling density is 1.6g/cm3 and SiO2 content is 2%~4%. TiO2 is favorable to diffusion of micro particle of A12O3 crystal defect nearby, which will not only activate AI2O3 crystal lattice, promote combustion process, increase the density and strength of ceramic, but also narrow the solidification temperature interval of ceramic anddecrease the tendency of hot cracking. When Na2B4O7 is added as reactant, the infiltration between A12O3 and Fe in the interface area is improved. As a result, the mismatch between ceramic and metal, the joining strength and mechanical properties are improved greatly. In SHS-centrifugal process, the pipe is being rotated at centrifugal acceleration of 20~40G. The structure of composite pipe is three layers of steel pipe—interlayer—ceramic layer in radial turn when 15%~20% Ti and Ni are added as reactant. The interlayer is joined metallurgically with the steel paper and the interface microstructure is fine columnar crystal with dendrite cross; and the interlayer is joined mechanically with the ceramic layer with interlocking, which increases the joining strength of ceramic-lined and improves the mechanical properties of composite pipes greatly.