THE EFFECT OF SILICON ON THE MICROSTRUCTURE AND SEGREGATION OF DIRECTIONALLY SOLIDIFIED IN738 SUPERALLOY

The effect of silicon on the microstructure and solidification segrega tion of directionally solidified IN738 nickel-based superalloy was stu died. Directional solidification at various solidification rates and p artial directional solidification plus rapid quenching were applied. M etallographic analysis and an electron microprobe were mainly used to observe and measure the microstructure and elemental segregation of th e alloy, respectively. It was found that silicon affected the morpholo gy of the liquid-solid interface of the alloy during solidification an d gave the alloy a tendency to form well-developed dendrites. The addi tion of silicon enlarged the solidus-liquidus temperature interval, an d the solidification rate also greatly influenced the interval. The in terval increased with increasing solidification rate. Silicon promoted the precipitation of the gamma/gamma' eutectic, and also affected its precipitation temperature. Silicon segregated mainly in interdendriti c regions, and promoted the segregation of other elements. All of the effects of silicon on the alloy related to the solidification rate.