The Study On Solidification And Room Temperature Mechanical Properties Of Ni-Al-Zr Eutectic Alloy

High-temperature structural materials of intermetallic compounds have always been one of the research hotspots in the field of materials,but the main problems of intermetallic compounds as high-temperature structural materials are:insufficient high temperature strength,brittleness at room temperature,and poor oxidation resistance.In recent years,Ni-Al-Zr eutectic alloy,as a new type of high-temperature structural material,has attracted wide attention of scholars at home and abroad due to its low density,good oxidation resistance and high strength.The solidified structure and phase composition of Ni-Al-Zr alloy is expected to further improve the room temperature fracture toughness and high temperature strength of the alloy.In this paper,Ni-Al-Zr eutectic alloy was prepared by vacuum arc melting and directional solidification.Firstly,the solidification characteristics and as-cast structure of Ni75.5AlxZr24.5-x eutectic alloy were systematically studied.Ni75.5Al13.5Zr11 and Ni88Al4Zr8 two typical eutectic components were selected and analyzed by XRD,SEM,TEM and DSC Methods The solidification path and microstructure of the alloy were studied,and the mechanical properties of the alloy were analyzed using micro Vickers hardness,compression test,tensile test and three-point bending test.The main conclusions are as follows:(1)Ni75.5AlxZr24.5-x as-cast alloy is mainly composed of Ni3Al and Ni7Zr2 two phases.With the increase of Al content,the composition of Ni75.5AlxZr24.5-x alloy changes from hypoeutectic?eutectic?hypereutectic,the primary phase changes from Ni7Zr2(hypoeutectic)?Ni3Al(hypereutectic),and then two eutectic transformation L? Ni7Zr2+Ni3Al.As the Al content increases,the yield strength and compressive strength of the as-cast alloy gradually increase,and the formation of primary Ni3Al dendrites significantly improves the work hardening ability of the alloy.(2)Ni75.5Al13.5Zr11 alloy is mainly composed of Ni3Al and Ni7Zr2 intermetallic compound phases.When the withdrawal rate V=5 ?m/s and 500 ?m/s,the directional solidification structure is Ni3Al primary phase+(Ni3Al+Ni7Zr2)eutectic;when V=10 ?m/s,the alloy structure is(Ni3Al+Ni7Zr2)eutectic.As the withdrawal rate increases,the interlayer spacing of Ni75.5Al13.5Zr11 alloy,the volume fraction of primary phase Ni3Al and the fracture toughness value at room temperature are gradually reduced,while the Vickers hardness and yield strength of the alloy are increased.V=500 ?m/s,the alloy has the highest Vickers hardness and yield strength.(3)Ni88Al4Zr8 alloy is mainly composed of ?-Ni phase with Fcc solid solution structure and intermetallic compound Ni5Zr phase.When the withdrawal rate V increases from 5 ?m/s to 500 ?m/s,the quenching interface of the directional solidification structure presents a typical dendritic interface.As the withdrawal rate increases,the primary and secondary dendrite spacing(?1 and ?2),primary phase volume fraction and interlayer spacing gradually decrease.(4)As the withdrawal rate increases,the Vickers hardness and yield strength of the Ni88Al4Zr8 alloy both increase.Under the condition of a high withdrawal rate of V=500 ?m/s,the hardness and yield strength of the alloy reach the maximum,respectively 420 HV and 1105.3 MPa,which is about 1.7 times and 2.1 times the alloy-related properties at low withdrawal rates.During the deformation of the alloy,the dislocation motion is first excited in the ?-Ni phase solid solution,and then the dislocation is accumulated in the ?-Ni phase/Ni5Zr layered interface,and then transferred to the Ni5Zr phase to make the dislocation slip prior to cleavage fracture.