In a polycrystalline material, mechanical properties are controlled primarily by the material's inherent microstructure characteristics—grain size, grain shape, grain orientation, and composition of materials. These characteristics can change significantly with different processing methods and conditions, thereby changing the mechanical properties. Due to the complex nature of the additive manufacturing process where the material is subjected to repetitive heating cycles, the resulting microstructure is very inhomogeneous and different for different process parameters, creating variability in mechanical properties (see Akram, et. al. [1]). Using a Microstructure Simulation in Additive Science, you can predict the changes in microstructure—grain size, grain shape, and grain orientation—for a given set of process parameters.

Grain size can be used to predict the mechanical property of yield strength. The relationship between yield strength and grain size is described mathematically by the Hall-Petch equation:

where is the yield strength, is a materials constant for the starting stress for dislocation motion, is the strengthening coefficient (constant for a material), and is the diameter of a grain. This relationship shows that the grain size is inversely proportional to yield strength. The smaller the grain size, the higher the yield strength, and vice versa. This relationship holds true for most materials and is a widely accepted model to express the yield strength relationship with grain size. If you know the material constants, you can use the grain size obtained from a Microstructure Simulation to predict the yield strength of a material.

Grain orientation plays a major role in the directional nature of a part's mechanical properties. If the grain size and orientation is uniform in all three orthogonal planes, this indicates the part's properties are isotropic. If grain orientation is predominant in one of the planes, this indicates that the printed part will be highly anisotropic. As-built parts printed by AM are usually anisotropic, meaning different build orientations give different mechanical properties. The grain orientation data obtained from a Microstructure Simulation can provide insights into the grain orientation in the part produced using different process parameters such as laser power, speed, scan pattern, hatch spacing, powder layer thickness, etc. Ultimately, the goal in AM simulation is to enable you to design a part based on your specific requirements. For example, if your part requires anisotropy in one of the directions, you can design the part by choosing the parameter set that results in the desired anisotropic microstructure.