Studies On Microstructures And Mechanical Properties Of Fe-15Al-10Nb In-situ Composite And TiC Reinforced Ni-Cr-Mo Matrix Composite Coatings

High temperature metal matrix composites have great potentials for civil and military applications. Two structural material systems for high temperature applications were studied:Fe-15Al-10Nb in-situ composite with fibrous structure and in-situ TiC reinforced Ni-Cr-Mo composite coatings.The as cast ingots with the nominal composition Fe-15Al-10Nb (at.%) were selected, some of which were heat treated as well as directionally solidified. The microstructures of disordered α-(Fe,Al) and (Fe, Al)2Nb Laves phase within as cast(AC), heat treated(HT) and directionally solidified(DS) samples were observed through scanning electron microscopy (SEM) and transmission electron microscopy (TEM). As for the macro-mechanical properties, the yield strength, fracture toughness and creep properties were examined by a Gleeble3800physical simulator under step-wise increased load and a universal electromechanical testing machine. The small-scale mechanical properties of DS sample were examined by a nanoindenter instrument. After directional solidification, all dendrites and lamellae were transformed into cell structures, in which fibrous Laves phase was dispersed in a-(Fe,Al) matrix. Because of the anisotropic feature of fibers, the nano-hardness and elastic modulus presented different values in longitudinal and transverse directions. The yield strength of DS sample at different temperatures was lower than those of AC and HT ones, and the fracture toughness was lower than that of AC sample.For the sake of studying the effect of Mo composition and changes of Ni-Mo composition on microstructures and erosion resistance of coatings, two composition series of in-situ TiC reinforced Ni-Cr-Mo claddings were fabricated by lasers on316L steel plates. SEM was used to observe the microstructure evolutions, and anti-abrasion properties of the coatings were investigated by wet sand rubber wheel abrasive wear tests and high temperature erosion tests. As results turned out, the addition of Mo could make coatings more homogenous, improve their microhardness, but impair erosion resistance. Adjusting the relative compositions of Ni-Mo could also change the porosity of coatings, which further affected high temperature erosion properties. When Ni is22wt.%and Mo is10wt.%, the high temperature erosion resistance is the best.