Composition control in the direct laser-deposition process

Laser-engineered net shaping (LENS) is a solid freeform fabrication process that has the capability of producing functionally graded material (FGM) components by selectively depositing different powder materials in the melt pool at specific locations in the structure during part buildup. The composition in each layer of an FGM is dependent upon the degree of dilution between the substrate (or previous layer) and powder material. A study on the effects of LENS processing parameters (laser power, travel speed, and powder mass flow rate) on dilution was conducted for deposits of H-13 tool steel and copper powder on H-13 tool steel substrates. When varying a single processing parameter while holding all others constant, the dilution was found to increase with increasing laser input power and travel speed and decrease with increasing powder mass additions into the melt pool. A method for estimating dilution in LENS deposits was developed from knowledge of LENS process efficiencies and material thermophysical properties. A reasonable correlation was shown to exist between the experimentally measured dilution and the dilution calculated from the model.