Preparation and Thermal Properties of BN and LPSO Hybrid Reinforced Magnesium Matrix Composite

Hexagonal boron nitride (h-BN) is a ceramic material with high thermal conductivity (TC) and low coefficient of thermal expansion (CTE), which can improve multiple thermal properties of metal-matrix composites as a reinforcing particle, but its wettability with metal melt is very poor. In order to enhance the wettability between the h-BN and magnesium alloy melt, the electroless plating was used to coat a thin layer of pure nickel on h-BN particles, which was proved to be effective and efficient in this study. The results showed that by adding Y element to magnesium alloy melt to consume Ni element melted from the nickel-plating layer, the long period stacking ordered (LPSO) structure composed of Mg-Ni-Y was successfully formed, and the magnesium matrix composite reinforced by hybrid h-BN and LPSO structure was obtained. After ultrasonic treatment (UT), the TC of the magnesium composite containing 3 vol% h-BN and 14.16 vol% LPSO is 99.92 W/(m·K), which is a 8.3% enhancement compare to the composite without UT. The average CTE (293-373 K) of the composite is 18.36×10-6 K-1, which is reduced by 29.4% compared with pure magnesium.

Revealing the Influence of Microparticles on Geopolymers’ Synthesis and Porosity

Geopolymers are zeolites like structures based on hydrated aluminosilicates units of SiO4 and AlO4. These units, known as poly(sialate), poly(sialate)-siloxo or poly(sialate)-disiloxo are chemically balanced by the group I cations of K+, Li+, or Na+. Simultaneously, the chemical reaction of formation, known as geopolymerization, governs the orientation of the unit, generating mesoporous structures. Multiple methods can be used for pore structure and porosity characterization. Among them, nuclear magnetic resonance (NMR) relaxometry allows the detection of the porous structure in a completely nonperturbative manner. NMR relaxometry may be used to monitor the relaxation of protons belonging to the liquid molecules confined inside the porous structure and, thus, to get access to the pore size distribution. This monitoring can take place even during the polymerization process. The present study implements transverse relaxation measurements to monitor the influence introduced by the curing time on the residual liquid phase of geopolymers prepared with two different types of reinforcing particles. According to our results, the obtained geopolymers contain three types of pores formed by the arrangement of the OH− and Si groups (Si-OH), Si-O-Si groups, Si-O-Al groups, and Si-O rings. After 48 days, the samples cured for 8 h show a high percentage of all three types of pores, however, by increasing the curing time and the percentage of reinforcing particle, the percent of pores decrease, especially, the gel pores.

3D Printing and Stretching Effects on Alignment Microstructure in PDMS/CNT Nanocomposites

The alignment of high aspect ratio reinforcing nanoparticles within a polymer matrix can have significant effects on the mechanical, electrical, and thermal properties of the nanocomposite. Therefore, in order to tailor the properties of the composite, it is imperative to develop novel methods to control the alignment of these filler particles in various polymeric matrices. This paper reports a unique approach to alter the alignment of carbon nanotubes (CNT) within polydimethylsiloxane (PDMS) nanocomposites using 3D printing technology. A line of the reinforced PDMS resin is printed on a PDMS substrate using direct ink writing technology, which can produce alignment in the print direction depending on printing parameters, the loading of the reinforcing particle, and the rheology of the ink. Then, the substrate is stretched and placed in an oven to cure the printed nanocomposites line with increased alignment in the stretch direction. These two techniques have the advantage of simplicity over other techniques and can efficiently manufacture nanocomposites with the alignment of nanoparticles. Optical microscopy will be used to quantify the alignment within the printed line. Electrical and mechanical properties will be tested to determine the effects of the different alignments within the elastomer. The ability to control the alignment of elastomeric CNT composites is advantageous for the growing field of polymer-based electronics.

Microstructure analysis and mechanical properties of phosphorus-reinforced ZCuPb20Sn5 alloy

An investigation was carried out to assess the effect of the P content on the microstructure and mechanical properties of ZCuPb20Sn5 alloy. Alloys of various compositions, (0.05, 0.1, 0.2, 0.3, 0.5% wt.% P) were melted in a melting furnace under 1200 °C and cast into metal mould, the hardness, strength and elongation of alloy castings which adding P or not in melting process were tested and the casting mircostructure was analyzed. The results show that the second phase appeared and gradually increased in amount with the content of P elements increased. Also, the microstructure of ZCuPb20Sn5 alloy was refined, and the average size of lead inclusions was reduced and formed a dispersed network of eutectoid inclusions.The addition of P had a beneficial effect on the microstructure and properties of ZCuPb20Sn5 alloy. The hardness and tensile strength of ZCuPb20Sn5 alloy increased, but the elongation increased at first, then decreased, when the P content increased. When the P content was less than 0.1 wt.%, the functions of phosphorous copper mainly was used as a deoxidizing initial gas, but when exceeded 0.1 wt.%, a second phase reinforcing particle formed with copper or nickel together, which improved the mechanical properties of the alloy. However, the elongation was lowered due to the brittle phosphide phase.

Effects of Nano TiC Particles on Recrystallization and Mechanical Properties of Al-Zn-Mg-Cu Alloy

The recrystallization and mechanical properties of 7085 alloy and TiC/7085 composites with different nano TiC content (0.1, 0.3, 0.5, and 1 wt%) were investigated in this work. Results showed that as the TiC content increased from 0.1 to 1 wt%, dynamic recrystallization was promoted in which the composites proceeded by hot deformation; after T6 treatment, static recrystallization was hindered. In addition, the ultimate strength of composites first increased and then decreased with the increase of nano TiC particle content from 0.1 wt% to 1 wt%. When the content of nano TiC particles reached 0.5 wt%, the tensile strength of the nanocomposites was improved to 608 MPa, 12% higher than that of 7085 alloy, via the reinforcing particle strengthening mechanism. Due to the grain coarsening and the TiC particle cluster, the ultimate tensile strength of 1 wt% TiC/7085 composite decreased to 585 MPa.

Fabrication and Characterization of Aluminium-Rice Husk Ash Composite Prepared by Stir Casting Method

Metal Matrix Composites (MMCs) constitute an important category of design and weight-efficient materials. This article highlights on the work where an attempt is taken to fabricate aluminium matrix composite reinforced with rice husk ash (RHA) particles, an agricultural byproduct with high amount of silica. RHA particles, upon analysis, are incorporated into the Al matrix melt by stir casting. Magnesium (~1%) is used as a wetting agent between matrix and reinforcement. 3, 6 and 9% wt. of RHA are added into the matrix. The microstructure analysis reveals the reinforcing particle distribution inside the matrix which indicates successful fabrication of the composites. The density and mechanical properties such as strength and hardness are measured for both unreinforced metal and composites. The results found in the tests show a decrease in density with increasing reinforcement while increasing yield strength, ultimate strength and hardness of the composites with increasing reinforcement from the unreinforced condition.