ABSTRACT
SiCp/Al composites have excellent physical properties and are widely used in aerospace and other fields. Because of their poor machinability, they are often machined by non-traditional machining methods such as electrical discharge machining (EDM). In the process of EDM, due to the "shielding" effect of the reinforced particles of SiC, the local ejection force is low during the processing process, and it is difficult to throw the reinforced particles smoothly, which ultimately leads to a low material removal rate and poor surface quality. In this paper, a high-low-voltage composite ejecting-explosion EDM power supply is developed to explore the explosive effect of reinforced particles in the ejecting-explosion EDM process and the unique process law of the explosion process. The experiment platform uses self-developed CNC machining machine tools based on an ejecting-explosive EDM power supply, and the influence of a detonation-increasing wave on the processing of SiCp/Al composites with different volume fractions was studied by changing four factors: the open-circuit voltage difference, pulse current difference, pulse phase difference, and pulse width difference of the back wave behind the step front. The material removal rate and surface roughness were measured. The research results showed that the material removal rate could be increased to 164.63%, and the material surface roughness could be increased to 30.03% by adjusting the high and low pulse current difference from 1 A to 8 A. When the voltage difference between high and low wave (HLW) pulses increases from 40 V to 120 V, the material removal rate can be increased to 150.39%, and the material surface roughness can be increased to 20.49%. The material removal rate increases with the increase in pulse phase difference and open-circuit voltage difference. With the increase in peak current difference and pulse width difference, the material removal rate becomes faster at first and then slower. The surface roughness of materials increases with the growth of open-circuit voltage difference, peak current difference, pulse width difference, and pulse phase difference.
ABSTRACT
Composite material uses ceramic reinforcement to add to the metal matrix to obtain higher material properties. Structural design is an important direction of composite research. The reinforcement distribution of the core-shell structure has the unique advantages of strong continuity and uniform stress distribution. In this paper, a method of preparing boron carbide (B4C)-coated titanium (Ti) powder particles by ball milling and preparing core-shell B4C-reinforced Ti matrix composites by Spark Plasma Sintering was proposed. It can be seen that B4C coated on the surface of the spherical Ti powder to form a shell structure, and B4C had a certain continuity. Through X-ray diffraction characterization, it was found that B4C reacted with Ti to form layered phases of titanium boride (TiB) and titanium carbide (TiC). The compressive strength of the composite reached 1529.1 MPa, while maintaining a compressive strain rate of 5%. At the same time, conductivity and thermal conductivity were also characterized. The preparation process of the core-shell structure composites proposed in this paper has high feasibility and universality, and it is expected to be applied to other ceramic reinforcements. This result provides a reference for the design, preparation and performance research of core-shell composite materials.
ABSTRACT
In the present study, the effects of SiC nanowires (SiCnws) with diameters of 100 nm, 250 nm and 450 nm on the microstructure and mechanical behavior of 20 vol.% SiCnws/6061Al composites prepared by pressure infiltration were studied. It was found that the interface between SiCnws and Al matrix was well bonded, and no interface product was found. The thicker SiCnws are beneficial to improve the density. In addition, the bamboo-like and bone-like morphologies of SiCnws produce a strong interlocking effect between SiCnws and Al, which helps to improve the strength and plasticity of the material. The tensile strength of the composite prepared by SiCnws with a diameter of 450 nm reached 544 MPa. With a decrease in the diameter of SiCnws, the strengthening effect of SiCnws increases. The yield strength of SiCnws/6061Al composites prepared by 100 nm is 13.4% and 28.5% higher than that of 250 nm and 450 nm, respectively. This shows that, in nano-reinforced composites, the small-size reinforcement has an excellent improvement effect on the properties of the composites. This result has a guiding effect on the subsequent composite structure design.
