The precipitation behavior of carbide in K416 B superalloy was investigated by means of creep measurement and microstructure observation. The results show that nanometer M6 C particles discontinuously precipitate in the γ matrix or along the γ/γ′ interface of the alloy during high temperature tensile creep. Thereinto, the amount of fine M6 C carbide increases as creep goes on, and the coherent interfaces of M6 C phase precipitating from the γ matrix are {100} and {111} planes. The thermodynamics analysis indicates that the solubility of element carbon in the matrix decreases when the alloy is deformed by the axial tensile stress during creep, so as to cause the carbon segregating in the regions of stress concentration and combining with carbide-forming elements M（W, Co）, which promotes the fine M6 C carbide to precipitate from the γ matrix.
Hot corrosion behavior of FGH96 powder metallurgy(P/M) superalloy in 25 % NaCl + 75 % Na_2SO_4 molten salts at 650, 700, and 750 ℃ was investigated in this paper. The methods of mass loss measurement, X-ray diffraction(XRD), scanning electron microscopy(SEM),and energy-dispersive spectroscopy(EDS) were used here.The experimental results show that hot corrosion kinetics follows a square power law at 650 ℃, while a linear one at 700 and 750 ℃. The corrosion layer is detected to be composed of Cr_2O_3, NiO, and Ni2S_3 at each temperature.The cross-sectional morphologies and corresponding elemental maps indicate that the corrosion layer is a stratified structure of oxide and sulfide. The results and analyses confirm that the hot corrosion mechanism of FGH96 P/M superalloy is a cooperate process of oxidation and sulfidation. Furthermore, the relatively higher concentrations of Cr, Co, and Ti provide better corrosion resistance to the attack of S and Cl^-.
He JiangJian-Xin DongMai-Cang ZhangLei ZhengZhi-Hao Yao
As one of the new additive manufacturing processes,electron beam melting(EBM)has seen its promising potential in the fabrication of metal matrix composites(MMCs)components with complex geometries.In this work,WC_P/NiBSi MMCs were fabricated by EBM and plasma-transferred arc welding(PTAW)for a comparative study.The microstructures of both samples were examined using a scanning electron microscope(SEM)equipped with an electron backscattered diffraction(EBSD)detector.The macrohardness was tested using a Rockwell hardness method(Type C),while the microhardness was measured using different loadings(0.5-1.0 N)based on different phases.The anti-abrasion performance was tested as per the ASTM G105 standard.The corrosion behavior of the MMCs was also assessed by potentiodynamic polarization.The results indicate that the EBM bulk and the PTAW cladding MMCs exhibit different microstructures due to the different local solidification conditions.This is believed to lead to the varied mechanical properties and corrosion resistance of the MMCs,and the possible mechanisms were also discussed.
