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Over the past two decades, a considerable amount of work has been done on zirconia-toughened alumina (ZTA) to take advantage of the recognized toughening effect induced by ZrO2. In fabricating customized or complex-shaped ZTA parts, conventional manufacturing processes, including slip casting and powder metallurgy, are regarded as time-consuming and cost-intensive. In response to these problems, directed energy deposition (DED) has been proposed and utilized to fabricate customized ZTA parts with highly flexible features in a shorter cycle time at a lower cost. Investigations have been reported on studying effects of input variables (such as laser power) in DED of ZTA parts, however, there are very limited investigations on effects of the ZrO2 content. In this investigation, the effects of the ZrO2 content on microstructures and mechanical properties of DED-fabricated ZTA parts are studied. Experimental results show that at lower levels of ZrO2 contents (5 wt%, 10 wt%, and 20 wt%), a novel three-dimensional quasi-continuous network (3DQCN) microstructure is tailored, whereas at higher levels of ZrO2 contents (30 wt%, 35 wt%, and 41.5 wt%), eutectic microstructure dominates the whole part. Both the 3DQCN microstructure and the eutectic microstructure are beneficial for toughening ZTA parts. In addition, the 3DQCN microstructure contributes to hardening ZTA parts. [ABSTRACT FROM AUTHOR]

Laser engineered net shaping (LENS) has become a promising technology in direct manufacturing or repairing of high-performance metal parts. Investigations on LENS manufacturing of Inconel 718 (IN718) parts have been conducted for potential applications in the aircraft turbine component manufacturing or repairing. Fabrication defects, such as pores and heterogeneous microstructures, are inevitably induced in the parts, affecting part qualities and mechanical properties. Therefore, it is necessary to investigate a high-efficiency LENS process for the high-quality IN718 part fabrication. Ultrasonic vibration has been implemented into various melting material solidification processes for part performance improvements. However, there is a lack of studies on the utilization of ultrasonic vibration in LENS process for IN718 part manufacturing. In this paper, ultrasonic vibration-assisted (UV-A) LENS process is, thus, proposed to fabricate IN718 parts for the potential reduction of fabrication defects. Experimental investigations are conducted to study the effects of ultrasonic vibration on microstructures and mechanical properties of LENS-fabricated parts under two levels of laser power. The results showed that ultrasonic vibration could reduce the mean porosity to 0.1%, refine the microstructure with an average grain size of 5 µm, and fragment the detrimental Laves precipitated phase into small particles in a uniform distribution, thus enhancing yield strength, ultimate tensile strength (UTS), microhardness, and wear resistance of the fabricated IN718 parts. [ABSTRACT FROM AUTHOR]