Effect Of Operation Parameters On Grain Morphology Of Inconel 718 Superalloy Fabricated By Laser Additive Manufacturing

Laser additive manufacturing has been used in manufacturing and repair of high value parts and components of complex geometry.It has commercially been applied in repair of turbine blades subjected to abrasive wear.As the mechanical properties of the laser built depend upon microstructure,which again is highly affected by the operation parameters,a study on the relationship between microstructure and operation parameters is always essential to get optimal parameters before any repair work is carried out.In this context,the influence of operation parameters i.e.laser power and laser scan speed on the grain morphology of the Inconel 718 fabricated by laser additive manufacturing has been studied.Two approaches were taken in this research.First,images from optical micrographs of the specimens produced by laser deposition under different operating conditions were investigated to understand growth morphology with respect to operating conditions.OM images reveal that laser deposited region mostly has equiaxed dendritic morphology at medium laser power and medium scan speed condition.Laser power of 600-650W and scanning speed of 6 mm/s seem propitious for equiaxed grain formation,from the experiments performed during the study.Secondly,columnar to equiaxed transition criteria(KCET)was used to predict the grain type of Inconel 718 according to the local solidification conditions measured from temperature profile of the melt pool from the simulation result performed at operating parameters of 600W laser power and 6 mm/s scan speed.The simulations results were in coherence with the experimental result.Next,KCET value for solidification of Inconel 718 has also been formulated using the Gaumann's modified model.The Kurz-Giovanola-Trivedi(KGT)dendrite growth model has been used to compare the primary dendrite arm spacing(PDAS)of the columnar dendrites.The PDAS measured from the OM images were slightly lower than theoretical values.The effects of heat treatment and boronization on hardness of laser deposited samples were also studied.