Microstructure And Mechanical Properties Of NiAl-Based Multi-Component Eutectic Alloys

In NiAl-based eutectic alloys,NiAl-28Cr-6Mo eutectic alloy is expected to as ideal high-temperature structural materials due to its high melting point,low density,and good oxidation resistance.However,the ductility and strength of alloy are still not enough.In this paper,NiAl-28Cr-6Mo eutectic alloy is selected as the base alloy,and the mechanical properties of the eutectic alloy are further improved by using a combination of strengthening phase and ductile phase as a multi-component eutectic composite material or alloying.According to relevant researches,this paper combines the advantages of multicomponent and eutectic alloys,and uses this idea to design multi-component eutectic alloys based on NiAl-28Cr-6Mo eutectic alloys.Ni3Al(FCC)and Cr(Mo)(BCC)eutectic microstructures are expected be formed to achieve a balance of strength and plasticity.The microstructures and mechanical properties of(Ni1.0-3.5Al)66-28Cr-6Mo(in molar ratio(NixAl),x=1.0.1.5,2.0,2.5,3.0 and 3.5,denoted by Ni1.0,Ni1.5,Ni2.0,Ni2.5,Ni3.0 and Ni3.5,respectively)alloys were investigated using SEM,EDS.TEM,microhardness and compression tests.The micro structure of NiAl-28Cr-6Mo(Ni1.0o)alloy consists of NiAl and Cr(Mo)eutectic phases.With increasing the Ni content to 2.0,the microstructure changes from eutectic(Ni1.0)to eutectic + primary NiAl dendrite(Ni1.5 and Ni2.0).When the Ni content increases further,besides eutectic and primary NiAl dendrite,the gray phase emerges in these alloys(Ni2.5,Ni3.0 and Ni3.5).The gray phase is identified as an ordered fce(Ni,Cr)3(Al,Mo)phase(Ll2)by SEM-EDS and TEM.Among the investigated alloys,both Ni2.0 and Ni2.5 alloys possess the higher fracture strength and microhardness.This paper also tried to introduce plastic toughening element Fe into NiAl-28Cr-6Mo eutectic alloy,new NiAl-Cr(Mo)-xFe(in molar ratio(NiAl),x=0.5,10,15,20,25 at%denoted OFe,5Fe,10Fe,15Fe,20Fe,25Fe,respectively)eutectic alloys are formed.The microstructure is still composed of NiAl phase and Cr(Mo)phase in 5 Fe and 10Fe alloys,and Fe dissolves into those both phases.When the Fe content further increases,Cr(Mo)primary dendrite appeares in the alloy,and the volume fraction increases obviously with increasing the Fe content.In these multi-component eutectic alloys,the 5Fe and 10Fe multi-component eutectic alloys exhibit higher strength.Since NiAl-Cr(Mo)eutectic alloy is derived from NiAl-Cr eutectic alloy,this paper also tried to add elemental Fe into NiAl-Cr alloy.It is found that NiAl-34Cr-2Fe is still a eutectic alloy(eutectic).The two phases in eutectic alloys are NiAl and Cr(Fe).The microstructure is still composed of NiAl phase and a-Cr phase,and Fe dissolves into those both phases.Moreover,the content solubility of Fe in NiAl phase is lower than in a-Cr phase.When the Fe content further increases,Cr(Fe)primary dendrite appeares in the alloy,and the volume fraction increases obviously with increasing the Fe content.In addition,with increasing the Fe content,the strength of those alloys show a decreasing trend.