Effect of Fe additions on microstructure and mechanical properties of a multi-component Nb-16Si-22Ti-2Hf-2Al-2Cr alloy at room and high temperatures

The phase constitutions, microstructural evolutions, and mechanical properties of Nb-16Si-22Ti-2Hf-2Al-2Cr-xFe alloys (where x = 1, 2, 4, 6 at.%, hereafter referred to as 1Fe, 2Fe, 4Fe and 6Fe alloys, respectively) prepared by arc-melting were investigated. It was observed that the nominal Fe content affected the solidification path of the multi-component alloy. The as-cast 1Fe alloy primarily consisted of a dendritic-like Nb-SS phase and (alpha+gamma)-Nb5Si3 silicide, and the as-cast 2Fe and 4Fe alloys primarily consisted of an Nb-SS phase, (alpha+gamma)-Nb5Si3 silicide and (Fe + Ti)-rich region. In addition to the Nb-SS phase, a multi-component Nb4FeSi silicide was present in the as-cast 6Fe alloy. When heat-treated at 1350 C for 100 h, the 1Fe and 6Fe alloys almost exhibited the same microstructures as the corresponding as-cast samples; for the 2Fe and 4Fe alloys, the (Fe + Ti)-rich region decomposed, and Nb4FeSi silicide formed. The fracture toughness of the as-cast and heat-treated Nb-16Si-22Ti-2Hf-2Al-2Cr-xFe samples monolithically decreased with the nominal Fe contents. It is interesting that at room temperature, the strength of the heat-treated samples was improved by the Fe additions, whereas at 1250 degrees C and above, the strength decreased, suggesting the weakening role of the Nb4FeSi silicide on the high-temperature strength. As the nominal Fe content increased from 1 at% to 6 at.%, for example, the 0.2% yield strength increased from 1675 MPa to 1820 MPa at room temperature; also, the strength decreased from 183 MPa to 78 MPa at 1350 degrees C. (C) 2014 Elsevier Ltd. All rights reserved.