An Al3Zr-reinforced Al matrix composite using metal powders was fabricated via in-situ synthesis in vacuum; these were subjected to a pin-on-disc wear test with a SUS304 disc specimen under oil lubrication. The elemental mixture of Al and ZrH2 particles was sintered in vacuum for the in-situ-formed Al3Zr. ZrH2 particles were thermally decomposed in the reaction with the Al matrix to form hard Al3Zr intermetallic compounds. The friction coefficient and wear volume values of the Al–Al3Zr composites were significantly lower than those of the pure Al specimen. This is attributed to the uniform dispersion of Al3Zr particles in the Al matrix, which prevented the metallurgical bond from falling and blocked the direct contact between the Al matrix and SUS304 disc.
The wide applicability of titanium (Ti) has prompted the analysis to improve its mechanical strength through the addition of different alloying elements. Among these, Ti materials with pre-mixed pure Ti and titanium nitride (TiN) powders as the starting materials have exhibited improved mechanical properties and tribological performance. In this study, the tribological properties of Ti matrix composites with ring-shaped TiN dispersoids were evaluated. The materials were fabricated from pre-mixed pure Ti powder and core–shell structured Ti–(N) powder, which were prepared by heat treatment at 1273 K under N2 gas. The tribological behavior of the Ti–TiN composites was studied by varying the applied load using a ball-on-disk wear test under oil lubrication conditions. The initial familiarity period of the Ti–TiN composites decreased. Subsequently, compared to the pure Ti specimen employed as a reference material, the friction coefficient was significantly lower and more stable. This is attributed to the ring-shaped, hard TiN dispersoids, which prevented the adhesion phenomenon and improved the oil film formability owing to the increase in microhardness and abrasive wear resistance of the nitrogen solid solution in the core region.
Powder metallurgy (PM) Al 3 Zr reinforced aluminum (Al) composites were fabricated by in-situ reaction during spark plasma sintering (SPS) using the pre-mixed Al and zirconium hydride (ZrH 2 ) powders. The diffusion behavior of Al and zirconium (Zr) elements in Al matrix were studied. It was clarified that ZrH 2 decomposed at around 773 K and dissolved Zr elements reacted with Al matrix to form Al 3 Zr layers around ZrH 2 particle. Al 3 Zr compounds grew toward the center of ZrH 2 particle due to a faster diffusion rate of Al compared to Zr element. The tribological behavior of the composite material was investigated by using pin-on-disk wear test under lubricated condition. Friction coefficient and wear volume of Al-Al 3 Zr composite were much lower than those of pure Al. SEM observation and SEM-EDS analysis on wear track of pin and disk specimens were investigated. The sliding surface of SUS304 stainless steel counterpart after wear test showed very slight damages and no seizure phenomenon with the pin specimen. It is concluded that PM Al-Al 3 Zr composite had a good tribological property and wear resistance due to hard Al 3 Zr particles dispersed in Al matrix preferentially contacting the counterpart material to prevent the soft Al matrix in direct contact with SUS steel surface.
In application of amorphous silica originated from rice husks to industrial raw materials, fine particles less than a few microns are strongly required in the market. A long-time mechanical milling process is necessary to refine raw silica materials due to their high hardness, and results in a remarkable advance of the products cost. In this study, high efficiency refining technique of silica materials using the conventional milling process was proposed. When burning rice husks at 450 600 without air supply, the organic elements such as cellulose, hemi-cellulose and lignin are completely changed to very brittle carbides, and resulted in formation of layer-structures consisting of silica and carbides in the ashes. These brittle carbides easily lead to the fragmentation of hard silica materials, and very fine particles are successfully prepared by milling process. Raman spectroscopy and SEM-EDS analysis was effective to optimize the burning temperature of rice husks to obtain the carbide layers in the ashes. For example, when more than 34 wt% carbonized elements are contained in the ashes, one hour conventional milling process is enough to prepare fine amorphous silica particles with a mean particle size less than 1 μm. In comparison with silica materials with no carbide, the above refining technique remarkably reduced the milling process time to about 1/10. Finally after the secondary combustion of the refined ashes to thermally resolve the carbides and remove the carbon elements, the application of the optimized combustion temperature from 750~850 resulted in high-purity fine silica particles with a low carbon content less than 0.06 wt%.
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