Study On Microstructure Of Multi-layer Laser Cladding Nb-Si Based In-situ Composites

Nb-Si Baesd in-situ composites has been considered as the most potential of aircraft engine blade materials because of its good esughness at room temperature and high-temperature comprehensive performance. It’s one of the research hotspots by ad出ng alloying elements es improve its ductility at room temperature and oxidation resistance at high temperature. In this paper, Nb-!Si situ composite samples of Nb-18Si-24 Ti and Nb-18Si-24Ti-6Cr were prepared by laser cladding method. We had used two kinds laser（including YAG and semiconductor lasers）to optimize the process parameters, then mainly to study the effects of adding alloying dements Cr and Y on microstructure of Nb-Si-Ti in-situ composiess by using 3kW semiconductor laser. The aim of the papers was es evaluate the alloying elements added and its contents on microstructure and its formation mechanism in a quick way by preparing Nb-Si in-situ composite samples successfully. At last,antioxidant properties of Nb-Si in-situ composi es samples were studied.The optimal parameters of single-pass laser cladding Nb/NbsSi3 in-situ composites had been conofirmed.YAG laser parameters: laser pulse current was 150 A, defocus amount was20 mm,the pulse frequency was 20 Hz, and the pulse width was 3.0ms; semiconductor laser:power was 1500 W,ese defocus amount was 310mm:ese scaiming speed was 4G0inm/mm.Based on which we prepared multilayer laser cladng samples of Nb-Si-X（Ti,Cr,Y）.The microstructures of Nb/Nb₃Si₃ in-situ composi"tes were analyzed by OM,XRD, SEM and TEM methods. The results show that the phase of Nb-Si based in-siUi composiess were composed of Nbss and its SUicon compounds. Compared with YAG laser,which power is500 W, the microstructures of ese semiconductor laser cladding Nb-Si-Ti system werecomposed of NbssjNb₃Si₃ and Ti single quality,NbsSi has disappeed,and the proportion ofese eutectic（Nbss+Nb₃Si₃）356(1,ese Nbss+NbsSi] and Nbss+CrsNb eWectic mixture ese appeared by adtion Cr. As the Cr content increases, CrzNb also increased. The microstructures of Nb/Nb₃Si₃ in-situ composites had been refined by adding trace rare elements Y（1 at.%）.Nb/Nb₃Si₃ in-situ composites of Nb-18Si-24 Ti and Nb-18Si-24Ti-60 samples were oxidized treatment at 850 °C,the outer oxide film grew thicker while the extension of oxidized me for both of the two samples. The microstructures had a great fference between the inner and outer oxide layer, the inner oxide layer was relatively dense than the outer oxide layer, microns holes distributed randomly in bo& samples whose size was aboutlOjxm.The oxidation rate of Nb-18Si-24 Ti was 20mm/h while that of the Nb-18Si-24Ti-6Cr is 15mm/h. shows esat the addition of Cr element can fiirther improve the antioxidant activity of Nb-Si-basedin-situcomposites.