Silicon carbide (SiC) devices have become one of the key research directions in the field of power electronics. However, due to the limitation of the SiC wafer growth process and processing capacity, SiC devices, such as SiC MOSFET (Metal-oxide-semiconductor Field-effect Transistor), are facing the problems of high cost and unsatisfied performance. To improve the precise machinability of single-crystal SiC wafer, this paper proposed a new hybrid process. Firstly, we developed an ultrasonic vibration-assisted device, by which ultrasonic-assisted lapping and ultrasonic-assisted CMP (chemical mechanical polishing) for SiC wafer were fulfilled. Secondly, a novel three-step ultrasonic-assisted precise machining route was proposed. In the first step, ultrasonic lapping using a cast iron disc was conducted, which quickly removed large surface damages with a high MRR (material removal rate) of 10.93 μm/min. In the second step, ultrasonic lapping using a copper disc was conducted, which reduced the residual surface defects with a high MRR of 6.11 μm/min. In the third step, ultrasonic CMP using a polyurethane pad was conducted, which achieved a smooth and less damaged surface with an MRR of 1.44 μm/h. These results suggest that the ultrasonic-assisted hybrid process can improve the precise machinability of SiC, which will hopefully achieve high-efficiency and ultra-precision machining.

To refine the grain size and improve the mechanical properties of ultrahigh-strength aluminum alloy (Al-10Zn-1.9Mg-1.6Cu-0.12Zr), the Al-Ti-B-Er grain refiner was prepared by the melt reaction method using the aluminum melt and Al + Ti + B precursor. The results exhibit that the Al-Ti-B-Er grain refiner is mainly composed of a block TiAl₃ phase, and loose agglomerated nano-sized TiB₂ and Al₃Er phases. The microstructure of ultrahigh-strength aluminum is significantly affected by the Al-Ti-B-Er refiner, which changes from dendrite to equiaxial grain with increasing Al-Ti-B-Er content, and the size of the eutectic phase is significantly refined. The high-efficiency refinement of Al-Ti-B-Er is due to Er promoting the uniform distribution of TiAl₃ particles and the formation of loose agglomerated nano-sized TiB₂ particles. The optimal addition content of Al-Ti-B-Er into ultrahigh-strength aluminum alloys is 1 wt%, whose grain size is approximately 40 µm. Additionally, the strength and ductility of ultrahigh-strength aluminum alloys are simultaneously improved by adding 1wt% Al-Ti-B-Er after the T6 treatment, reaching 756 MPa and 20%, respectively. This enhancement in strength and ductility is mainly attributed to grain refinement and the eutectic phase refinement.

The effects of Sn and Mo alloying elements on the microstructure and electrochemical properties of TiZrTaNb high entropy alloys were studied by optical microscope (OM), scanning electron microscopy (SEM), X-ray diffraction (XRD) and electrochemistry. TiZrTaNb, TiZrTaNbMo and TiZrTaNbSn alloys with equal atomic ratio were prepared by the arc melting method. The results showed that the microstructure of the high entropy alloys was dendritic structure with single BCC structure. The addition of Mo and Sn elements promoted the growth of the dendritic structure and accelerated the interdendritic segregation of the TiZrTaNb alloy. The TiZrTaNbMo alloy exhibited excellent corrosion properties compared to TiZrTaNb and TiZrTaNbSn alloys based on corrosion parameters I_corr, φ_corr, I_pass. The corrosion mechanism is discussed based on the corrosion morphology. The alloying elements have an important effect on the microstructure and electrochemical properties of a high entropy alloy.