Effect of the heating rate on the microstructure of a ferritic ODS steel with four oxide formers (Y-Ti-Al-Zr) consolidated by spark plasma sintering (SPS)

The proposed ODS ferritic steel alloyed with (Y-Ti-Zr-Al) was produced by mechanical alloying (MA) and spark plasma sintering (SPS) to obtain a complex nanostructure. To densify the material, a sintering cycle by SPS was performed at 1100 degrees C using fast heating rates (from 100 to 600 degrees C/min). During the attrition of MA powders, the uneven distribution of deformation level and of alloying elements has produced an inhomogeneous recrystallization during the consolidation step. Influence of processing condition was studied by modifying the heating rate of SPS to promote a heterogeneous material with bimodal grain size distribution. The final microstructures were characterized by X-ray diffraction and electron microscopy (SEM and TEM). The mechanical behaviour at R.T. was characterized by means of the Vickers microhardness and micro tensile tests. The good balance obtained between ductility (similar to 22-26%) and yield stress (800-910 MPa) at room temperature is provided by the bimodal grain size distribution. To predict the experimental values depending on the processing conditions, a yield strength model is presented. This model covers the contribution of different strengthening mechanism from solid solution, grain size, dislocation density and oxides precipitation. The model indicates the dislocation density as the major strengthening contribution. In addition, small punch (SP) tests were performed to analyse the response of the material at high temperatures where remarkable properties have been achieved.Authors want to acknowledge Ferro-Ness project and Ferro-Genesys project funded by MINECO under National I+D+I program MAT2016-80875-C3-3-R and MAT2013-47460-C5-5-P.Publicad