Study On Phase, Microstructure And Corrosion Behavior Of Composite Cladding Of Intermetallic Compound Ni₃Si

Aimed at areo engineer turbine, a Ni₃Si base coating alloyed by the addition of element Ti, Nb and reinforced by a in-situ particle-reinforced TiC, NbC were fabricated on the nickel-matrix superalloy substrate GH864 by laser cladding. The microstructure of clad layers was characterized using XRD, SEM, EPMA and EDAX. The clad layers without pores and cracks were obtained, and an excellent bonding between the clad layers and the substrate was ensued by a strong metallurgical interface.The effects of the addition of element Ti, Nb on the phase structure of Ni-Si were investigated by Differential Scanning Calorimetry. The results indicated that the element addition of Ti, Nb had no effect on the phases of the composite, only changed the intensity of Ni-Si phase. The properties of corrosion resistance of the cladding layers which were in the H2SO4 solution were valued by weight gain test. The corrosion kinetic curves mainly followed linear parabolic rate law. As far as the Ni-Si-Ti clad layers, nearly before the 10h, the weight gain critically increased, at the about of 34h, the weight gain increased to a maximum, and then kept a steady state with a slow corrosion rate; As far as the Ni-Si-Nb clad layers, it exhibited a fast corrosion in the initial 13h of corrosion, at the about of 35h, the weight gain per unit increased to a maximum, and then kept a steady state with a slow corrosion rate. The cladding layers which were added the alloy elements had a good corrosion resistance.The oxidation resistance of Ni-Si-Ti-C, Ni-Si-C-Nb clad layers has been investigated by cyclic oxidation tests. The oxide scale, microanalysis and the composition of the samples were investigated by the scanning electron microscopy (SEM) and X-ray diffraction (XRD). The results showed that the oxidation kinetic curves mainly followed line-parabolic rate law for 48h under 1100℃. The oxidation scale were compact, smooth, and successive distributing. In the initial course of the oxidation, it exhibited a fast weight-gain. With time going, the speed of oxidation decreased. The oxidation kinetic curves kept a steady state. This showed that Ni-Si-C-Ti,Ni-Si-Nb-C clad layers had an outstanding oxidation resistance for 48h under 1100℃. The Ni-Si-Ti-C clad layers exhibited severely weight-gain for 95h under 1100℃, the oxidation scale was loose and porous, the oxidation badlydecreaced. The oxidation speed of the Ni-Si-Nb-C clad layers increased slowly after 95h, but when the addition of (C+Nb) was 15%, the oxidation scale was compact, which had an outstanding oxidation resistance.