Preparation,Microstructure And Mechanical Properties Of Ni-Al Intermetallic Laminated Sheet

Nowadays,the lightweight and high-temperature resistant structural materials are needed to replace Ni-based superalloys due to the rapid development of aerospace industry.Under this background,Ni-Al intermetallic compound with the advantages of low density,high specific strength,high service temperature,good structural stability and oxidation resistance can be used as a preferred material to achieve the goal of structural weight reduction and high temperature bearing.However,due to its intrinsic brittleness,poor plasticity and toughness at room temperature,the preparation of thin-walled structural plates is difficult,and the strength of single-phase Ni-Al intermetallic is low at high temperature.Based on this,this project attempts to prepare high-performance Ni-Al intermetallic structural sheets with the improved high-temperature strength and toughness by introducing a plastic layer.The Ni-Al intermetallic laminated sheets were synthesized by hot-pressing reaction under vacuum atmosphere using 70?m thick pure nickel foil and 20?m,50?m,80?m,100?m pure aluminum foil.The microstructures of the laminated sheets were studied using optical microscope(OM),X-ray diffractometer(XRD),and scanning electron microscope(SEM).The optimal hot-press diffusion process was determined,and the evolution of the structure during the reaction preparation process was revealed.The results show that the reaction preparation process is divided into two stages:first-level diffusion reaction and second-level diffusion reaction.In the first-level diffusion reaction stage,the Al phase is almost completely diffused and transformed into NiAl₃ and Ni₂Al₃ phases,and the final formed phase are Ni+Ni₂Al₃.In the second-level diffusion reaction stage,the remaining Ni phase and Ni₂Al₃ phase continue to react to form NiAl and Ni₃Al phases.The final formed phase is NiAl when the thickness of Al foil is 100?m and 80?m and Ni+Ni₃Al+NiAl phase is formed when the thickness of Al foil is 50?m and 20?m.The laminated sheets with uniform structure and good density can be obtained under the preparation conditions of640?/20MPa/6h+1200?/20MPa/1h.The microstructure will change by adjusting the content of Ni and Al.With the decrease of Al content,the microstructure changes from single NiAl phase to Ni+Ni₃Al+NiAl mixed phases.Tensile properties at room temperature and high temperature,bending properties at room temperature of Ni-Al intermetallic laminated sheets with different thickness of Al foil were studied,and the fracture mechanism was analyzed.The results show that the NiAl alloy sheet is brittle at room temperature when the thickness of Al foil is 100?m,showing a mixed fracture mode of intergranular fracture and brittle transgranular fracture.The laminate has better tensile properties at room temperature when the thickness of the Al foil is 20?m.Its tensile strength and elongation reach 642.0 MPa and 15.6%,respectively,showing obvious plastic fracture.At 800??900?and 1000?,the laminates have high plasticity,and the elongations reach 61.3%,71.4%and 101.3%when the thickness of the Al foil is 80?m,respectively.In addition,the laminates have high strength,and the tensile strength reach350.3MPa?230.5MPa and 140.2MPa at aforementioned temperatures when the thickness of Al foil is 50?m.The tensile fracture of the laminate changes from plastic fracture to quasi-cleavage fracture with the thinning of the Al foil.When bearing the bending load at room temperature,the bending deformation ability of the laminate is poor when the thickness of Al foil is 100?m and 80?m and the bending deformation ability of the laminate is stronger when the thickness of the Al foil is 20?m.While,the bending strength is greater when the thickness of the Al foil is 50?m.