Study On Microstructure And Mechanical Properties Of Hastelloy Surface Modification

Hastelloy X is a nickel-chromium-iron-molybdenum alloy with excellent oxidation resistance and high temperature strength.It is widely used in gas turbine engines such as combustion chambers,tailpipes and cabin heaters.With the development of the aviation industry,the requirements for the properties of Hastelloy have further increased.In this paper,the effect of the bombardment times by the high-current pulsed electron beam(HCPEB)on the surface microstructure and properties of Hastelloy X was investigated.The microstructure of the bombarded surface was characterized by scanning electron microscope(SEM),energy dispersive spectrometer(EDS),electron backscattered diffraction(EBSD),and x-ray diffraction(XRD).The phase composition,grain orientation,the elastic modulus,microhardness and the friction properties by nanoindenter,microhardness tester,friction-abrasion testing machine and phase shift microXAM-3D.The results showed that:(1)After bombardment by HCPEB,the surface of the metal melted.Impurities vaporized and flied out,causing deformable structures such as melting pits.The ultra-fast cooling and solidification showed a corrugated morphology,and the grains were refined.Among them,the grains size of samples bombarded 5 times and 20 times were smaller.After etching,the grain boundaries of the original sample were corroded,and white carbides were formed at the grain boundaries of the sample after bombardment;the corrosion resistance of the sample increased as the rise of bombardment times.The difference in the morphologies of the samples before and after bombardment is due to the rapid remelting of the bombarded surface,which formed a remelted layer of about 2 ?m.(2)After bombardment there is a grain orientation of the surface.Frequently,the samples bombarded 5 times and 20 times trend to have(111)surface orientation.(3)The nano-indentation experiment showed that the elastic modulus and micro-hardness of the sample decreased after bombardment.Among the samples after bombardment,the micro-hardness and average modulus of elasticity of the sample bombarded 5 times were larger.(4)The analysis of surface roughness and friction properties showed that the surface roughness of the sample is the smallest after 5 bombardments.The surface roughness changed with the time of bombardment.The wear amount of the sample bombarded 5 times is the smallest and the depth of its wear scar is shallow.