Richard A. Haber

High frequency ultrasound phased array characterization of SiC mirror blanks

Silicon carbide mirror blank materials were characterized using ultrasound phased array technology to determine the feasibility of using this method for rapidly characterizing material homogeneity and locate anomalous flaws. A 10MHz 64 element linear probe was used to measure and image the top and bottom surface reflected signal peak amplitudes. C-scan images located the presence of possible sub-surface heterogeneities as well as surface scratches invisible to the eye. Bottom surface scans located variations in homogeneity within the sample bulk. High frequency ultrasound phased array was found to be well suited for detailed characterization of SiC mirror blanks.

Ultrasonic NDE of silicon carbide lightweight systems

Silicon carbide (SiC) high energy mirrors from M-Cubed, Schafer Corp, Poco and Trex Inc. were investigated using nondestructive ultrasound C-scan imaging. Reflected signal amplitude variations from the top surface of the SiC mirrors were imaged to locate surface and subsurface inhomogeneities. Where possible, the bottom surface reflected signal amplitude and material velocity were mapped to evaluate bulk properties. Elastic property mapping was also performed on a dense SiC mirror sample to look for regional variations in Poissons ratio, Youngs modulus, shear modulus, and bulk modulus. These ultrasound techniques were successfully utilized for detection of subsurface inhomogeneities in the SiC mirror samples.

Aluminium magnesium boride: synthesis, sintering and microstructure

ABSTRACT AlMgB14 ceramics were reported as high-hardness materials over a decade ago. While different synthesis routes for processing of AlMgB14 ceramics were reported in the past, however the synthesis routes are still not optimised and present a significant challenge to the manufacturers. In this work six different synthesis routes were explored for the synthesis of AlMgB14 powder. The synthesised compositions were characterised by XRD, where weight fractions of each phase were calculated by Rietveld refinement. The bulk ceramics were sintered using powder with the highest yield (93.2%) of AlMgB14 phase by spark plasma sintering at 1315°C and 50 MPa. Both phase composition and microstructure of the sintered AlMgB14 were characterised by XRD and SEM/EDS, which revealed the existence of AlMgB14, MgAl2O4 and a small amount of unreacted Al. Hardness and indentation fracture resistance of AlMgB14 ceramics were measured to be 26.7 ± 2.2 GPa and 5.59 ± 0.42 MPa m1/2, respectively by Vickers indentation technique.