In the analysis of the etched microstructure of the additive manufactured nickel superalloy, micro pores in the nano-meter dimensions were found in the matrix and also on the dendrite structures. The distribution is random and so is the size of these pores.
Is this due to the lack of optimisation of the process parameters or any phase that has been dissolved by the etchant.
We have some issues during polishing additive manufactured nickel superalloys, because this kind of material tend to cover partially some pores during the material remotion. For this reason, I will recommend you to try electropolishing but take into account that this technique will make the pores coarse if it is not properly used.
The dimensions of the pores vary from half a micron to one micron, and is randomly dispersed in size as well as shape.
The powders used in the SLM process typically have pores in it of the similar dimension. But, these micro-pores are present throughout the microstructure in high magnification.
And how to be sure these are carbides?
Dear Roshan, Please also consider the following fact which may also cause porosity in the AM alloys
I am not sure about the process optimization but i think, the prior surface oxidation of metallic powder particles (especially active metals) may also produce porosity due to lack of fusion between particles during melting process. However high temperature per unit area (focused beam) may dissociate the oxides but sometime these may retain within the microstructure.
On the other hand, in order to diagnose the nature of inclusions (i.e. carbide, oxide etc.) i think you should measure the surface texture by using EBSD and/or electron diffraction studies etc. I hope this answers your question.
Hello,
Another factor, over and above mentioned by fellow researcher here, may be the Laser source. In general the Power/heat distribution is Gaussian in nature and hence we may have variation in the heat flux/temp in the beam spot diameter itself and this may result in differential heating/cooling of the material being deposited. The variation in solidification rate may induce micro/nano pores as observed.
Regards
Alok Singh Chauhan : Thank you for your answer. Is it too early to generalise that what ever the optimisation is done on the processing parameters, there will still be metallurgical porosity ( less than 1 micron) due to external factors as well as feedstock impurity?
You may say so, Even the cast components are also subjected to hot isostatic pressing to reduce the surface porosity present. You may also plan HIPPING of part produced through Additive Manuf, if porosity is of much concerned.
- Badges
- Science topic
- Similar topics
- Mathematics
- Algebra
- Matrix