Alloying mechanics in moving melt pool during laser solid forming from blended elemental powders

The laser solid forming (LSF) titanium alloys from blended elemental powders are investigated. By combining the computation of the melting time of powder particles with the motion analysis of the solid-liquid interface of the melt pool, the formation mechanism of the unmelted powder particles during LSF from blended elemental powders is disclosed. That the powder particles inject into the "unmelted zone" is the main reason leading to the formation of the unmelted particles. The morphologies of the unmelted particles are presented as "crescent" or sphere when the spherical elemental powder particles are used as the deposited materials. The theoretical analysis agrees well with the experimental results. The morphology and formation condition of the composition segregation band during LSF Ti-xAl-yV from blended elemental powders are investigated. It is found that the composition segregation band is prone to occur when the V content in the Ti-xAl-yV alloys is near or higher than the critical concentration of element V, and this is caused by the low melt flow velocity near the solid-liquid interface in the melt pool. The uniform composition in the alloying clad layers can be obtained by controlling the powder delivery parameters, powder characteristics, and the processing parameters.