Gas Release Behavior of Cu-TiH<Subscript>2</Subscript> Composite Powder and Its Application as a Blowing Agent to Fabricate Aluminum Foams with Low Porosity and Small Pore Size

Compared to traditional pore structure with high porosity (≥ 80 pct) and large pore size (≥ 3 mm), aluminum foams with low porosity (60 to 70 pct) and small pore size (≤ 2 mm) possess higher compressive property and formability. In order to achieve the goal of reducing pore size, Cu-TiH₂ composite powder prepared by ball milling preoxidized TiH₂ with Cu powder was used as a blowing agent. Its gas release behavior was characterized by thermogravimetric analysis and differential scanning calorimetry. The results show that the ball milling treatment can advance the gas release process and slow the gas release rate at the same time. All these changes are favorable to the reduction of porosity and pore size. Such Cu-TiH₂ composite powder provides an alternative way to fabricate aluminum foams with low porosity and small pore size.     

Effect of LiF as Sintering Agent on the Densification and Phase Formation in Al<Subscript>2</Subscript>O<Subscript>3</Subscript>-4 Wt Pct Nb<Subscript>2</Subscript>O<Subscript>5</Subscript> Ceramic Compound

Different amounts of LiF were added to an Al₂O₃-4 pct Nb₂O₅ basic ceramic, as sintering agent. Improved new ceramics were obtained with LiF concentrations varying from 0.25 to 1.50 wt pct and three sintering temperatures of 1573 K, 1623 K, and 1673 K (1300 °C, 1350 °C, and 1400 °C). The addition of 0.5 wt pct LiF yielded the highest densification, 94 pct of the theoretical density, in association with a sintering temperature of 1673 K (1400 °C). Based on X-ray diffraction (XRD), this improvement was due not only to the presence of transformed phases, more precisely Nb₃O₇F, but also to the absence of LiAl₅O₈. The preferential interaction of LiF with Nb₂O₅, instead of Al₂O₃, contributed to increase the alumina sintering ability by liquid phase formation. Scanning electron microscopy (SEM) results revealed well-connected grains and isolated pores, whereas the chemical composition analysis by energy dispersive energy (EDX) indicated a preferential interaction of fluorine with niobium, in agreement with the results of XRD. It was also observed from thermal analysis that the polyethylene glycol binder burnout temperature increased for all LiF concentrations. This may be related to the formation of hydrogen bridge bonds.     

An Experimental and Modeling Study of Synthesis,Consolidation and Aging Behavior of AA2014 Composite Reinforced by TiB<Subscript>2</Subscript> via Powder Metallurgy Method

Aluminum 2014 alloy composite reinforced with TiB₂ particulates with different volume% of TiB₂ (5, 10 and 15%) has been successfully synthesized by P/M route. The composite powders were consolidated by cold uniaxial compaction pressure followed by sintering at 590 °C in N₂ atmosphere. The Al 2014–TiB₂ composites were aged at 160 °C between 0 and 8 h followed by microstructural characterization and hardness evaluation. Scheil cooling and equilibrium calculations were performed using FactSage for qualitative understanding of the microstructural evolution during sintering and aging operations. In addition, the thermo-physical properties such as hardness, density and transverse rupture strength of the sintered samples were evaluated.     

Synthesis,Characterization and Mechanical Properties of AA7075 Based MMCs Reinforced with TiB<Subscript>2</Subscript> Particles Processed Through Ultrasound Assisted In-Situ Casting Technique

AA7075/TiB₂ composites have been synthesized through both in situ salt-melt reaction method and ultrasound assisted in situ process. Microstructural studies reveals that ultrasound assisted in situ method improves the dispersion of TiB₂ particles and reduces the porosity level. Moreover, the ultrasonic treatment refines the reinforcement particle size along with improvement in particle dispersion. The mechanical property assessment confirms that ultrasonic treatment improves the mechanical properties of composite. The hardness of the AA7075 alloy is increased from 55 H_V to 74 H_V by the addition of 5% TiB₂ particles and it further increased to 82 H_V by ultrasonic treatment. A similar trend is also observed when weight percentage of particles increases to 7.5%. Addition of 5% in situ TiB₂ particles increases the ultimate tensile strength of AA7075 alloy by 60 MPa and it is further enhanced by 80 MPa upon ultrasound assisted process. Composites have shown a small reduction in ductility when compared to un-reinforced alloy, though 81% ductility of matrix alloy has been retained. Similar trend has been observed in composites fabricated using ultrasonic assisted casting.