Compositional Variation In Inconel718 Alloy Fabricated By Selective Laser Melting

Composition are the basic factors that influence the properties of the alloy.Precise control of composition for the alloy is central to obtain high performance metal methods.In the process of selective laser melting, when the laser scanning powder, especially large energy input density, the instantaneous temperature is very high, even can reach several thousand degrees Celsius, which easily lead to the evaporation of components and cause the change of the alloy composition. Therefore, this article mainly through the aspects of thermodynamics, dynamics and experiment to study the law of elements’ evaporation of IN718 alloy in the process selective laser melting.The thermodynamic parameters which affect the components’ volatilization trend is calculated: activity coefficient and the saturation vapor pressure. The thermodynamic parameters were calculated mainly by Miedema model and Kolher ternary solution model. The results show that in the IN718 alloy which Cr-Fe-Ni as the main components,Cr has the biggest activity coefficients and saturated vapor pressure,Ni second,and Fe relatively minimum. The activity coefficient and saturated vapor pressure of the main elements increases with the increase of melt temperature.Analyzed the calculation results of the main volatile components evaporation rate,and find that the evaporation rate of Cr and Fe elements increases very fast with the temperature rise, especially after 2100 K,the change is obvious;According to the whole situation,The volatilization rate of the elements Cr is 10 times of the evaporation rate of Fe basically, indicating that there are more Cr element volatilize in a unit time per unit area; Studied the influence of different process parameters in the SLM process on the main elements of IN718 alloy volatilization rate.Results show that with the increase of laser power, scanning speed and spacing decreases, so as to increase the evaporation rate of the elements Cr and Fe,and Cr volatilization rate changes more obvious than Fe volatilization rate.In the experiment, the research mainly on the influence of different scan parameter to the components’ volatilization and respectively forging under single layer and single channel scan strategy,single layer and multi-channel scan strategy,multi layer and multi channel scan strategy.The experiment results show that when forging under single layer and single channel scan strategy and single layer and multi-channel scan strategy, with the laser power increased,scanning speed reduced, or the scanning interval decreased,the melt temperature rised, and the volatilization of Cr aggravated, the mass percentage in the alloy will decline; and the content of Fe element in the alloy will be increased,contrary to the changing trend of Cr elements,this is mainly affected by the Fe element which come from substrate.When forging through multi layer and multi channel scanstrategy, found with the laser power increased, scanning speed reduced, or the scanning interval decreased, the melt temperature raised, but the effect on the volatilization of Cr elements and Fe elements is not obvious, but in this experiment, the weight percentage content of Fe element has declined, because with the increase of forming height, the volatilization of Fe element in substrate decreased, so the effect of the Fe element to the elements in melt decreased.