Formation of Sub-grain Structure Induced by Composition Segregation and Stacking Faults in Laser-Deposited Premixed Near-α Titanium Alloy and Ti2AlNb Alloy Powders
Near-α titanium alloy and Ti2AlNb alloy powders premixed with different proportions were prepared on the near-α titanium alloy substrate by laser deposition technique,and the microstructure characteristics were analyzed and discussed.Results show that numerous river-like sub-grain structures are formed inside the equiaxed B2 grains of the laser-deposited premixed titanium alloy powders with the proportion of Ti2AlNb above 40wt％,whereas the needle-like structure within coarse columnar β grains exist with the proportion of Ti2AlNb below 40wt％.It is noteworthy that the decrease in laser power and scanning speed can accelerate the formation of sub-grain structures.Based on the analysis of experimental results,it can be inferred that the formation of sub-grain structure not only is related to the precipitation of O phase due to composition micro-segregation at sub-grain boundaries,but also is inseparable from the stacking faults caused by the internal stress during the laser deposition.
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