Defects, including keyhole and lack of fusion (LoF) pores and spattering, are frequently observed in parts produced by L-PBF, even when optimized processing parameters are used. This presents significant challenges for part and process qualification and certification. Understanding the formation of defects at the part scale becomes crucial, particularly when non-spherical powders are employed in laser powder bed fusion (L-PBF). Here, the central hypothesis is that the morphology, size, and powder interlocking characteristics of non-spherical powder will affect the interaction between heat source and particle and alter in-process defect formation and anomalies such as particle spattering and porosity. Keyhole porosity can occur during both stationary and scanning laser processes. It is caused by the rapid vaporization of the material. Depending on the local melt pool dynamics, gas bubbles may escape or remain trapped after solidification. Not all keyhole-mode melting activities result in keyhole porosity, and determining a threshold for its occurrence is crucial for achieving high-quality AM materials with a relative density of >99.5%.

The keyhole morphology method (see an example in Figure 1), based on the front wall angle and penetration depth, has shown success in predicting keyhole pore formation. It was found when the keyhole front wall angle (θ) <77°, stable keyhole mode is attained. By analyzing keyhole behavior using dynamic X-ray radiography (DXR), PI Mostafaei and his team will quantify keyhole fluctuation frequency and establish the relationship between keyhole depth and θ. Understanding this relationship will help determine optimum processing variables, mainly laser power and scan speed, to minimize keyhole porosity in L-PBF processed non-spherical powder.

The specific research goals for students are to be able to:

·         Exploring laser-powder interaction, melt pool analysis, and quantifying the spatial distribution of pores.

·         Study a transition regime (TR) between the stable (I) and unstable (II) keyhole regimes in L-PBF, in which the keyhole morphology changes from wide and shallow in region I to narrow and deep in region II. Pores can form in TR, mostly at the rear keyhole wall keyhole porosity is more common in region II with pores typically forming at the keyhole bottom [27].

·         Studying the keyhole collapse mechanism and related regime transition as well as keyhole dynamics in L-PBF non-spherical powder.

The specific learning goals for students are to be able to:

·         Explain the fundamentals of the L-PBF concept for advanced manufacturing of materials.

·         Describe defects in metal 3D printed parts, their formation mechanism and mitigation approaches.

·         Gaining experience in powder handling, designing parts for printing, operating our LaserTeh 30 SLM printer, metallography, phase analysis using X-ray diffraction, and mechanical testing.