Composition Design And Laser Fabrication Of Nickel-based Intermetallic Compound Alloys

Intermetallic compounds have been extensively investigated and applied in the area of petrochemical and aerospace industries,particularly Ni-Al and Ni-Si system intermetallic compounds,as candidate materials for high temperature structural and coating applications..They are well known for their abnormal relationship between temperature and strength,relatively low densities and excellent oxidation and corrosion resistance.In the present work,nickel-based intermetallic compounds were fabricated successfully by preplacing Ni-25Si,Ni-25Si+Cr/Nb, Ni-13Si-9Ti+Cr/Nb and Ni-Al-Si powders using a continuous wave 10 kW carbon dioxide laser under optimum processing parameters.The phase, microstructure,chemical characterization and phase transformation of the synthesized alloys were characterized using X-ray diffractometer(XRD), optical microscopy(OM),scanning electronic microscopy(SEM),energy dispersive spectrometer(EDS),electron probe microscopy analysis(EPMA) and differential scanning calorimetry(DSC).The microhardness of these alloys was also measured using HX-1000TM type microhardness tester.The Ni-25Si alloy was mainly composed ofγ-Ni solid solution and Ni₃Si.The microhardness of the Ni-25Si alloy was 740HV.The phases of the Ni-25Si alloy with the addition of Cr were made ofγ-Ni solid solution, Ni₃₁Si₁₂and Ni₃Si intermetallic compounds.The microstructure of the Ni-Si-Cr ternary alloys showed a great change from typical dendritic structure to netlike structure with increasing the content of Cr.The phase of the Ni-25Si+5at.%Nb alloy containedγ-Ni solid solution,Ni₃₁Si₁₂,Ni₃Si and Nb₃Ni₂Si.The microstructures of the Ni-25Si with addition of Nb were fine,uniform and dense.The microhareness of the Ni-25Si+4at.%Nb was 747HV.The phase of the Ni-13Si-9Ti alloy was composed ofγ-Ni solid solution and Ni₃(Si,Ti)intermetallic compound.With the addition of Cr element,a new phase,namelyÏ„₆(Ni_16Si7Ti6,was identified.The microstructures of the Ni-13Si-9Ti alloy with increasing the addition Cr content became more fine and dense.While adding Nb to the Ni-13Si-9Ti alloy,the phase consisted ofγ-Ni solid solution,Ni₃(Si,Ti)and Nb₃Ni₂Si. The microstructures of these alloys showed dendritic and eutectic structure. The microhardness of the Ni-13Si-9Ti alloy was improved evidently through addition of Nb.The Ni-13Si-9Ti+5at.%Nb had the highest hardness value of 870.6HV,comparing with the Ni-13Si-9Ti alloys with addition of 2 and 8 at.%Nb.The phases of the Ni-Al-Si alloys mainly consisted of Ni-Al intermetallics and small amount of Ni solid solution.The microstructures showed a great change from three different morphologies for the Ni-25Al alloy to irregular block shape for the Ni-5A1-20Si alloy.Among these alloys, the Ni-15Al-10Si alloy had the highest hardness value of 914HV. Particularly,the uniform Ni3A1 alloy without cracks can be obtained using laser processing technical under optimum processing parameters.