How does crack develop in Laser powder bed fusion additive manufacturing after solidification of material.?
How does the dendritics growth occur?
Is it due to small pores or residual stress while cooling down or cooling rate?
Welding cracks are always the result of critical tensile stresses. In turn, tensile stresses arise due to shrinkage of the molten material during cooling:
The volume of the deposited material decreases during cooling, and the cold substrate oppose this deformation, creating tensile stresses in the deposited layer. If the stress reaches the strength limit of the surfacing material, then cracks form in it.
In welding technologies it is impossible to avoid shrinkage during cooling, but it is possible to reduce the stresses it causes and avoid the formation of cracks. There are many methods for this, three of which are the most important and universally applicable:
1. Use of surfacing materials with high plastic deformation and low elastic modulus.
2. Heating the substrate before surfacing to the highest possible temperatures.
3. Use of high-temperature annealing after welding or surfacing.
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