Direct selective laser sintering (SLS) or selective laser melting (SLM) are additive manufacturing techniques that can be used to produce three-dimensional ceramic parts directly, without the need for a sacrificial binder. In this paper, a low laser energy density is applied to SLS/SLM high density powder layers of sub-micrometer alumina at elevated temperatures (up to 800̊C). In order to achieve this, a furnace was designed and built into a commercial SLS machine. This furnace was able to produce a homogeneously heated cylindrical zone with a height of 60mm and a diameter of 32mm. After optimizing the layer deposition and laser scanning parameters, two ceramic parts with a density up to 85% and grain sizes as low as 5μm were successfully produced

This paper presents the design and fabrication process of a spherical-omnidirectional ultrasound transducer for underwater sensor network applications. The transducer is based on the vibration of two hemispheres with a thickness of 1 mm and an outer diameter of 10 mm, which are actuated by two piezoelectric ring elements. Since the ultrasound wave is generated by the vibration of the two hemispheres, a matching layer is not required. Silicon Carbide (SiC) is used as the material of the hemispherical shells of the transducer. The shells were fabricated by laser sintering as an additive manufacturing method, in which the hemispheres were built layer by layer from a powder bed. All manufactured transducers with an outer dimension of $10\times 14.2$ mm and a center frequency of 155 kHz were measured in a water tank by a hydrophone or in mutual communication. The circumferential source level was measured to vary less than 5dB. The power consumption and the insertion loss of the transducer, ranging from 100 $\mathsf{\mu }$ W to 2.4 mW and 21.2 dB, respectively, along with all other measurements, prove that the transducer can transmit and receive ultrasound waves omnidirectionally at tens of centimeters intervals with a decent power consumption and low actuation voltage.

Additive manufacturing (AM) technologies for technical ceramics are rapidly emerging. Many of these processes rely on a polymer binder-assisted printing approach followed by de-binding and furnace sintering for densification. However, the required de-binding step is long and sensitive, and the presence of densification shrinkage requires a compensation in design. This study explores laser powder bed fusion (LPBF) as an additive manufacturing method for full net-shaping of reaction bonded silicon carbide (RBSC) and reaction bonded boron carbide (RBBC). During LPBF, silicon is used as a structural binder instead of traditional sacrificial polymer binders. By combining this with liquid silicon infiltration (LSI) as a densification method, long de-binding times and densification shrinkage are avoided. This leads to a net-shaping, additive manufacturing process for RBSC and RBBC ceramics with high Young’s modulus (285 and 308 GPa respectively), flexural strength (220 and 168 MPa) and hardness (2045 and 2242 HV).

This paper presents the design and fabrication procedure of a single-element omnidirectional piezoelectric ultrasound transducer, which can be utilized for under water communication. The transducer consists of a spherical silicon infiltrated silicon carbide (Si-SiC) body and is able to perform communication at 160 kHz with a Q factor of about 5.6 over a distance of more than one meter. The circumferential pressure amplitude of the beam pattern of the transducer varies less than 10 dB, which allows reliable communication between different transducers at an arbitrary orientation with respect to each other.