Study On The Microstructures And Properties Of Ti-Ni-Fe Alloys

In recent years,the intermetallic compounds have activated in many fields such as semiconductors,superconductors,magnetic materials,memory alloy with its unique function features.As structural materials,they have lots of advantages like corrosion resistance,oxidation resistance and high strength/density ratio co mparing with alloys.Unfortunately,low ductility of the intermetallic compounds attained so far restrict their applications.Therefore,it is a significant issue that to research and development a new intermetallic compound as structure materials.In this paper,we selected the TiNiFe alloy as the object to explore and improve its mechanical properties as structural materials.We preparated series of TiNiFe,TiNiFeC alloys and investigated the microstructure and mechanical properties of these al oys in as-cast or hot rolling.First of all,we used high purity titanium,nickel,iron,raw material to prepare Ti_95-XNi_XFe₅（X= 47.5,46.5,46,45.2）series alloys.Research results show that these alloy were composed of second phase Ti₂Ni and matrix phase TiNi.Certainly,Fe in two phase are solid solution,and the priority is dissolved in the matrix.The mesh shape second phase is distributed in the matrix grain boundary.With the increase of the content of Ni,Ti₂Ni phase in the alloy decrease.On the contrary,the content of TiNi phase was adding.The yield strength of the alloy was enhancing,however,the alloy become brittle.We realized that the Ti49 Ti498 have no phase transformation after the hot rolling in 850 degrees and water quenching.The second phase distribution along the rolling direction were streamlined.Along with the increase in Ni content,the tensile strength of the alloy increase,the tensile elongation decreases.Secondly,we investigated the effect of the microstructure and mechanical properties by adding a small amount of C into Ti_95-XNi_XFe₅（X=47.5,46.5,46,45.2）alloys.Comparing with the pure alloys,in addition to the formation of TiC in the two alloys,the second phase Ti₂Ni strip along the grain boundary distribution has mottled shape are dispersed on the substrate in Ti47.5C and Ti48.5C alloys.The yield strength of the Ti47.5C alloy dropped from 1844 MPa to1800MPa,but compression strain from 7.8% to 12.8% and the Ti48.5C alloy dropped from 1231 MPa to1164MPa,but compression strain from 23.7% to 25.2%.Due to the amount of Ti₂Ni in alloys were high,so the micromorphology of the Ti49 and Ti49.8 have not changed obviously with little C.The yield strength of the Ti49 C alloy increase to 877 MPa from 929 MPa,but compress strain has little change.The yield strength of the Ti49.8C alloy increase to 422 MPa from 557 MPa and they present a very high ductility without any cracks and fracture in the compression test.Through measure the length of primary dendrite and secondary dendrite,we discover that with the increase Ni,the length of dendritic were enhanced.So the Ni element can promote the growth of TiC.The tensile properties of Ti49 C and Ti498 C a lloys with hot rolled compare with the Ti49 and Ti498 al oys.It is obviously that the effect of C elements on alloy is inconsistent.