Impacts of Lubricant Type on the Densification Behavior and Final Powder Compact Properties of Cu-Fe Alloy under Different Compaction Pressures.

A Cu-15Fe alloy was fabricated using a powder metallurgy (PM) route, with the addition of different solid lubricants (i.e., paraffin wax (PW) and stearic acid (SA) as well as their composites (PW+SA)). Green compacts were produced via cold compaction at different pressure levels of 50 MPa, 200 MPa, and 350 MPa, then sintered for 60 min under vacuum at 1050 °C. The systematic evolution of the densification, porosity, and pore-size behavior were studied. Vickers Hardness Tests were used to measure hardness. The analysis of the morphological alterations was performed using scanning electron microscopy (SEM) and X-ray diffraction (XRD) techniques. Moreover, under dry sliding conditions, pin-on-disk wear tests were conducted in order to determine tribological properties such as the coefficient of friction (µ), specific wear rate (K), and friction temperature gain. Results revealed that the lubrication process and compaction pressure play a crucial role in defining the characteristics of the final compact. Higher sintered densities and hardnesses were achieved at 50 MPa when PW was used as a solid lubricant, and became reduced as the compaction pressure increased. In contrast, in the case of SA, higher sintered densities and hardnesses were obtained at a compaction pressure of 350 MPa, and increased with increasing pressure. Moreover, PW samples exhibited lower coefficients of friction and wear properties. The addition of SA improves the wear loss of friction materials as well as their coefficients of friction. Compared to blank and PW samples, SA samples show a nearly 50% reduction in wear rate.

Microstructure and Superior Corrosion Resistance of an In-Situ Synthesized NiTi-Based Intermetallic Coating via Laser Melting Deposition.

A nickel-titanium (NiTi)-based intermetallic coating was in-situ synthesized on a Ti-6Al-4V (TC4) substrate via laser melting deposition (LMD) using Ni-20Cr and TC4 powders. Scanning electron microscopy, X-ray diffraction, a digital microhardness tester and an electrochemical analyzer were used to evaluate the microstructure, Vicker's microhardness and electrochemical corrosion resistance of the intermetallic coating. Results indicate that the microstructure of the intermetallic coating is composed of NiTi2, NiTi and Ni3Ti. The measured microhardness achieved is as high as ~850 HV0.2, ~2.5 times larger than that of the TC4 alloy, which can be attributed to the solid solution strengthening of Al and Cr, dispersion strengthening of the intermetallic compounds, and grain refinement strengthening from the rapid cooling of LMD. During the electrochemical corrosion of 3.5% NaCl solution, a large amount of Ti ions were released from the intermetallic coating surface and reacted with Cl- ions to form [TiCl6]2 with an increase in corrosion voltage. In further hydrolysis reactions, TiO2 formation occurred when the ratio of [TiCl6]2- reached a critical value. The in-situ synthesized intermetallic coating can achieve a superior corrosion resistance compared to that of the TC4 alloy.

An efficient mechanochemical synthesis of alpha-aluminum hydride: Synergistic effect of TiF3 on the crystallization rate and selective formation of alpha-aluminum hydride polymorph.

α-AlH3 is one of the most promising hydrogen storage materials due to its high gravimetric hydrogen capacity and low dehydriding temperature. In present work, a convenient and cost-efficient solid-state mechanochemical reaction is proposed to obtain α-AlH3 nano-composite. With the addition of TiF3, α-AlH3 nano-composite was formed in a short period by milling of LiH and AlCl3. Based on XRD and NMR results, the average grain size of the α-AlH3 in the nano-composite was 45 nm. The reaction pathway as well as the synergistic effect of TiF3 on the solid state reaction between LiH and AlCl3 were confirmed. In the α-AlH3/LiCl nano-composite, TiF3 reduced the temperature of dehydriding reaction and improved dehydrogenation rate of α-AlH3. Within the temperature range between 80 and 160 °C, dehydrogenation of the as-milled α-AlH3 nano-composite showed fast kinetics. At 160 °C, a maximum hydrogen desorption of 9.92 wt% was obtained within 750 s, very close to the theoretical hydrogen capacity of α-AlH3.

An insight into the process and mechanism of a mechanically activated reaction for synthesizing AlH3 nano-composites.

The reaction pathway as well as the mechanism of the solid state reaction between MgH2 and AlCl3 has been a mystery so far. Based on SEM, TEM and NMR (Nuclear Magnetic Resonance) analyses, an amorphous intermediate (AlH6)n was preferentially formed and recrystallized as a γ phase at the final stage of the reaction. As a novel finding, this research provides a deep insight into the process and mechanism of this mechanically activated reaction.