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Laser powder bed fusion is a metal additive manufacturing technique that has received significant scientific and industrial attention over the past decades. However, the quality and reproducibility of parts manufactured by this technique is still a problem. Overcoming this issue requires an understanding of multiple complex physical phenomena which occur simultaneously during the process. This work illustrates a powerful new technique which synchronizes high-speed x-ray imaging with high-speed infrared imaging to study laser powder bed fusion processes in real time. Using this technique, we demonstrate the simultaneous observation of multiple phenomena including three-dimensional melt pool visualization, vapor plume dynamics, spatter formation, thermal history, and point cooling rates. The paired observation of these dynamic phenomena is critical to understanding the fundamentals of laser powder bed fusion, and the overall impact of process parameters on print quality.

Premature failures associated with microstructural degradation, i.e. white etching cracks (WECS), are becoming commonplace as applications are requiring tribological components to operate under extreme conditions. Although the specific drivers of WECs are still debated, the failures are often found in applications where cyclic loading is combined with added energy from stressors such as slip, impacts, or stray current. The aim of the current work is to elucidate effect that variable current has on premature failure. Numerous commercially available lubricants were tested, and both lubricant base oil type and additive package were found to have an effect on WEC failure time.

A review is presented of the design of suitable materials systems for joining by high-temperature plastic deformation, details of the joining techniques, microstructures and properties of the resulting composite bodies, and prospects and limitation for this type of joining technology. Joining parameters and resulting forms are discussed for Al2O3/mullite particulate composites, Y2O3-stabilized ZrO2 particulate/Al2O3 particulate and whisker-reinforced composites, hydroxyapatite bioceramics, La0.85Sr0.15MnO3 electronic ceramics, MgF2 optical ceramics, and Ni3Al intermetallics. Results are contrasted with those obtained by other methods of joining brittle, high-temperature materials, with special focus on durability and mechanical properties.

A plastic deformation process was demonstrated to self-join 3 mol.% yttria partially stabilized zirconia (3Y-TZP)/hydroxyapatite (HA) composites. The 3Y-TZP/40 vol.% HA composites were fabricated by conventional ceramic processing by cold pressing premixed 3Y-TZP and HA powders into pellets. Densification ( approximately 90%) of composites was achieved by sintering composite powder compacts at 1450 degrees C for 5h. Optimum self-joining of 3Y-TZP/40 vol.% HA composites was obtained at 1300 degrees C for a strain rate of 5 x 10(-5)/s. The flow stress during joining was 40 MPa. Microstructural and mechanical characterizations of the joint interface demonstrated that there were no discernible differences between the joint and the composite material away from the interface.

A plastic deformation process was demonstrated to self-join hydroxyapatite (HA), fabricating pore-free joints at 1275°C at a strain rate of 10−5 s−1. To determine optimum joining conditions, high-temperature compressive deformation of HA was investigated for strain rates between 5 × 10−6 and 10−4 s−1 at temperatures 1175–1275°C. X-ray diffraction revealed primarily the HA phase with the presence of tri- and tetra-calcium phosphate phases. Steady-state flow stresses were 0.6–45 MPa and increased with increasing strain rates. Stress exponents of ≈1 indicated a viscous diffusion-controlled deformation mechanism with an activation energy of ≈354±36 kJ/mol. Absence of cavitation and grain shape changes was consistent with grain boundary sliding.

This paper presents the results of the study on mechanical and tribological performance enhancement of 6061 aluminum alloys by incorporation of B4C particle via friction stir processing (FSP). The incorporation of B4C particles reduced friction by 30% and reduced wear by two orders of magnitude compared to unprocessed base material. FSP alone without particles addition did not have a significant effect on the tribological behavior of the aluminum alloy studied.