Preparation And Mechanical Properties Of NiCr Alloy Foam

Nickel based alloy foam has the advantages of high melting point,high temperature strength,excellent high temperature oxidation resistance and corrosion resistance.It has broad application prospects in high temperature filtration,high temperature heat exchange and high temperature catalyst carrier.However,the strength and elastic modulus of the existing nickel based alloy foams are relatively low,which is difficult to meet the requirements of light weight,high strength and high temperature resistant materials in the aerospace field,which limits their further development and application.In this paper,three dimensional reticulated open cell NiCr alloy foams with small pore size,homogeneous composition,high porosity and high strength were prepared by means of pack cementation and homogenizing heat treatment with Ni foam as substrate.Al diffusion coating on the surface of NiCr alloy foam was prepared by pack cementation.The morphology,composition and microstructure of the NiCr alloy foams were characterized by SEM,EDS and XRD.The quasi-static compressive properties and energy absorption properties of the NiCr alloy foams were tested by the universal testing machine.?1?The Cr layer with different thickness can be prepared on the surface of the Ni foam by pack cementation.The Cr layer is metallurgical bonded with the substrate,and its thickness increases gradually with the extension of pack cementation time.After homogenization heat treatment,the NiCr alloy foam can form homogeneous single phase austenite structure,and maintain the three-dimensional reticulated structure of Ni foam.The Cr content and relative density of NiCr alloy foam increased with the extension of pack cementation time.?2?The compressive strength,specific strength and energy absorption capacity of the NiCr alloy foam are affected by the pack cementation time,which increases with the extension of the pack cementation time.Compared with the Ni foam,the compressive strength,specific strength and energy absorption capacity of the Ni-29Cr alloy foam prepared by pack cementation for8 h were improved by 3.3 times,1.5 times and 2.9 times,respectively.Under the same preparation process,increasing the density of Ni foam can also improve the compressive strength and energy absorption capacity of foam NiCr alloy,but has no obvious effect on its specific strength.?3?The thickness of the Al coating increases with the extension of the pack cementation time.The Al coating prepared by pack cementation method can be divided into?-Ni₂Al₃ and Cr₅Al₈ layer,?-NiAl and?-Cr layer and??-Ni₃Al layer,in which the?-Ni₂Al₃ and Cr₅Al₈ layer occupy most of the coating.The Cr element in the NiCr alloy foam inhibits the inward diffusion of the Al element,and the higher the Cr content,the stronger the inhibition effect.?4?Al coating can significantly improve the mechanical properties of foamed NiCr alloy.Its compressive strength,specific strength and energy absorption capacity increase with the increase of surface Al coating thickness,but the coating will greatly increase the brittleness of the NiCr alloy foam.The NiCr alloy foam can maintain its plasticity after 20 min of pack cementation,but after 40 min and 60 min,the surface coating will undergo severe cracking and spalling during compression,which will seriously reduce its plasticity.The energy absorption capacity of the NiCr alloy foam increases first and then decreases with the extension of the pack cementation time,and the energy absorption efficiency decreases with the extension of the pack cementation time.