Evolution of microstructures and mechanical properties of spark plasma sintered Fe-Cr-Nb alloys

Present study investigates microstructural stability and mechanical properties of spark plasma sintered Fe-Cr-Nb alloys for its nuclear first wall reactor application. The nanostructured alloys were prepared by mechanical alloying (MA) for 25 h in argon atmosphere (purity < 10 ppm O-2) using SPEX 8000 M high energy ball mill. After evaluation of thermal stability of the alloy powders, spark plasma sintering was performed at 800, 900 and 1000 degrees C at a heating rate of 100 degrees C/min with a holding period of 5 min. X-ray diffraction phase analysis followed by TEM-SAED pattern analysis of the sintered samples confirmed the stability of complete solid solubility of the Fe-Cr-Nb alloys after sintering even at 1000 degrees C. Relative sintered density and microhardness values were found to increase with increase in the sintering temperatures. The microhardness value of the sintered Fe-15Cr-1Nb sample was measured to be 9.5 GPa corresponding to the relative sintered density of similar to 98%. The compressive strength was assessed to be quite high (2400 MPa) for the Fe-15Cr-1Nb sample sintered at 1000 degrees C. Retaining of nanostructures (confirmed by TEM analysis) after sintering at 1000 degrees C is ascribed for such high hardness and compressive strength. Analysis of strengthening mechanisms and their quantitative estimation have been made for solid solution strengthening, grain size strengthening and dislocation strengthening and are found to correlate well with experimentally measured compression strength results.