Rapid directionally solidified microstructure characteristic and fracture behaviour of laser melting deposited Nb–Si–Ti alloy

摘要

Aiming at achieving fine and directionally-solidified microstructure of Nb-Si based alloy,Nb,Si and Ti powder particles were utilized as the raw materials,and laser melting deposition（LMD） experiments were conducted with1500 W and 2000 W laser power,respectively.The microstructure characteristic,micro-hardness,and indentation fracture toughness were examined by scanning electron microscope（SEM）,X-ray energy dispersive spectrometer（XEDS） and X-ray diffraction（XRD）.The results showed that the two kinds of as-deposited Nb-17 Si-23 Ti alloy samples were mainly composed of Nbss,（Nb,Ti）3 Si and Ti-rich Nbss,and the microstructure presents rapid directionally-solidified characteristic,in which the ＜100＞ crystallographic direction of Nbss and ＜110＞ crystallographic direction of（Nb,Ti）3 Si tend to be parallel to the LMD building direction.With the laser power increasing from 1500 W to 2000 W,the microstructure became more oriented and homogeneous.For the sample at 2000 W,the dendrite spacing was only about 1-2 μm,and Nbss and（Nb,Ti）3 Si couples grow alternately and they are parallel to the building direction strictly.In the meantime the micro-hardness and indentation fracture toughness reached 1075 HV and 20.3 MPa·m1/2,respectively,indicating significant improvement by the directional growth of fine Nbss and（Nb,Ti）3 Si phases,and the dimple fracture mode of the Nbss dendrites.