In Situ Formation of Composite Layer on Cast Steel and Ni_3 Al by Casting Process

摘要

Within the framework of this study, a new multiplex technology of the synthesis of functionally gradient composite materials was developed. The said technology is a hybride combination of the casting process and an SHS technique,and enables fabrication of cast gradient composite materials of the Ni_3AI/NbC,cast steel/TiC and cast steel/NbC type,containing ceramic phases. The said phases are formed "in situ" in a metallic bath as a result of the SHS reaction initiated by contact achieved in substrates applied on a die holding the liquid metal at a temperature of 1823K. The process of fabrication of the above mentioned materials was carried out in a Balzers vacuum furnace and conducted the process in the atmosphere of argon at gas pressure of 0.05 MPa. The liquid metal was poured into dies with the applied layer of powdered material taking part in the SHS reaction. The carbide phase formed in the process of synthesis was next dispersed and rested in a subsurface layer of the casting,producing in this layer the required gradient structure. The thickness of thus produced composite layers was from 200 to 900(m,this depending on the number of substrates participating in reaction and on the process parameters. The size of the NbC and TiC carbides produced in a metallic bath was from 0,5 to 5(m. The functionally gradient materials of the Ni_3AI/NbC, cast steel/NbC and cast steel/TiC type, as fabricated by the above described process,were next examined by SEM,EDX and XRD.