Phase transformation in High Entropy Bulk Metallic Glass (HE-BMG) and Lamellar Structured-High Entropy Alloy (HEA)

An investigation into the phase transformation of metastable alloys such as high entropy alloys (HEAs) and high entropy bulk metallic glasses (HE-BMGs) was performed. Bulk metallic glasses (BMGs) and HEAs were known to have a metastable phase at high temperature, while HEAs was reported to have a sluggish diffusion at high temperature. Besides, the drawback of many single phase HEAs is that they are mechanically unstable due to the presence of single phase either body centred cubic (BCC) or face centred cubic (FCC) structures. Here, a systematic study on the crystal structure, physical and mechanical properties of TiZrHfNiCu HE-BMG and FeCoNi(BxAl1-x)0.1Si0.1 (0 ≤ x ≤ 1) lamellar structured HEA were explored. It was revealed that, a phase transformation occurred in HE-BMG in isothermal and non-isothermal conditions, yet the nucleation and growth behaviour was relatively slow at high temperature compared to most Zr-based amorphous alloys. This phenomenon was proven by the attained data of activation energy and crystallisation mechanism which reflect the crystallisation resistance of the alloy. The addition of boron as a substitution of aluminium in FeCoNi(BxAl1-x)0.1Si0.1 alloy changed the phase formation, phase stability, morphology characteristics and mechanical properties of the alloy. The unique lamellar herringbone-like structure was formed with increasing boron content and led to improvement of mechanical properties of the alloy such as the hardness from B0.4 to B1.0. Lamellar structured-HEA was designed to obtain a balance in strength and ductility for FeCoNi(Bx Al1-x)0.1Si0.1 HEA where it can be tailored by modifying the boron content. The optimum balance of strength (1550 MPa) and ductility (19%) was attained at 0.5 at% boron content

Investigation of regression rate end-burning typed hybrid rocket motor

Hybrid Rocket Motor (HRM) has a critical weakness that impacts performance: low regression rate. Due to this, extensive investigation has been done on end-burning type HRM to enhance the regression rate. Experimental works were conducted on the end-burning HRM compared to the conventional HRM. The present investigation is focused on single port HRM, paraffin wax, and gas oxygen as the fuel and oxidizer, respectively. The results show that combustion occurs only at the fuel end in end-burning mode, which permits the burning area and fuel mass flow rate to remain constant, enhancing the motor's performance and ensuring that the oxidizer-to-fuel ratio does not fluctuate. HRM performance has also been evaluated by calculating thrust and specific impulses. According to this study, end-burning HRM has a 33% less regression rate but around a 50% increase in thrust and specific impulse compared to conventional HRM. The low regression is due to the small initial combustion area. Mass flux is the more prominent factor in increasing the regression rate and thrust of the end-burning HRM compared to the fuel length. Further improvement to the design of the HRM can maximize the potential of the end-burning mode

Non-isothermal crystallization kinetics of a rapidly solidified as-cast TiZrHfNiCu high entropy bulk metallic glass

This paper aims to investigate the thermal behavior and crystallization kinetics of TiZrHfNiCu high entropy bulk metallic glass (HE-BMG) alloy using the standard procedure of Differential Scanning Calorimetric (DSC) annealing technique. The alloy was produced using an arc melting machine with a critical diameter of 1.5 mm. The crystallization kinetics and phase transformation mechanism of TiZrHfNiCu HE-BMG was investigated under the isochronal condition at a single heating run based on the Johnson-Mehl- Avrami (JMA) theory. In isochronal heating, the apparent activation energy for glass transition and crystallization events was analyzed by Kissinger and Ozawa methods. The average activation energy value for crystallization of TiZrHfNiCu amorphous alloys in isochronal modes was 226.41 kJ/mol for the first crystallization and 297.72 kJ/mol for second crystallization stages. The crystallization mechanism of the first step was dominated by two- and three-dimensional growth with increasing nucleation rate, while the crystallization mechanism in the second stage was dominated by two-dimensional crystallization growth with a constant nucleation rate. The diffusion mechanism result proved the theory of sluggish atomic diffusion of HEA at elevated temperature

High entropy alloy as metal additive for hybrid rocket propellant

A typical solid propellant used in rocket propulsion systems is made from polymeric fuel, crystalline liquid binder and additives. In comparison to conventional propulsion systems, hybrid propulsion is more safe, reliable and environmentally friendly. However, the hybrid systems have some drawbacks, including low fuel regression rates and low combustion efficiency. As a result, several approaches have been developed to increase the rate of solid fuel regression rate including the introduction of metal additives to the system. Nowadays, high entropy alloys (HEA) are among the most advanced materials for high performance applications. This alloy has a potential to replace the existing metal additives in hybrid propulsion systems. The present work proposes a new composition based on Paraffin wax fuel, loaded with high entropy alloy as a metal additive for hybrid propulsion systems using the following ratio of 80:20. Therefore, this research explores the efficacy of high entropy alloys as additives for hybrid propulsion systems. Characterizations and thermal analysis of solid fuel using X-ray diffraction (XRD), differential scanning calorimetry (DSC) and thermogravimetric analysis are carried out to determine the structure, thermal decomposition and energy characteristics of the solid fuel with the HEA as additive. XRD result shows that HEA in a form of solid solutions produces BCC and FCC structures. Thermal analysis of paraffin wax with the addition of HEA gives the maximum value of 136.34 J/g for the total latent heat of the mixture. It is concluded that HEA increases the energy released from the fuel by 86.92 % compared to pure paraffin wax fuel. The mixture of paraffin and HEA fuel has a prospect to be used as future rocket fuel

Aerodynamic assessment and development of Smokey SAM Prototype (TRL-6)

This paper presents an aerodynamic assessment on the "Smokey Sam Prototype (TRL-6) Start (X)". Initially, the rocket prototype was designed by using OpenRocket open source software, where all of the user's design requirements and objectives are considered. The TRL-6 Smokey Sam Star (X) is expected to fly within 400 m with the operating Mach number 0.2 as a comparable to US GTR-18A. This research evaluates the aerodynamics performance of the design Smokey Sam prototype rocket using a computational fluid dynamics (CFD) approach. The aerodynamics analyses were started with an initial speed of 25 m/s, and the procedures were repeated for 40 m/s and 54.6m/s. For instance, the CFD study assessed the flight performance and stability once launched, such as lift coefficient, drag coefficient and pitching moment. The turbulence model is employing K-omega (k-ω) model to express turbulent properties of flow to a reckoning for history effects like convection and diffusion of turbulent energy. The actual pressure distribution was compared with the conventional rocket material's exact pressure distribution to inspect the best rocket material to sustain the best strength to weight ratio at high-speed trajectory operation. Several observations were made into the modelling process, such as surrounding velocity and pressure. It is found that the flight is in stable mode since the obtained pitching moments are almost zero at all assessed speed. For the flight trajectory validation, the model was printed using a 3D printer and tested experimentally by launching it into the air

Enhancement of fenton process using high entropy alloy powder as catalyst

The Fenton process is one of the chemical oxidation degradation processes widely used in wastewater management due to being environmentally safe. The Fenton process is a reaction in which iron-catalyzed hydrogen peroxide to generate hydroxyl radical. Even though the Fenton process can degrade the azo dye solution, there are still substantial limitations, such as high sludge production and limited catalytic activity. This study focus on improving the azo dye degradation process in the Fenton process. Thus, a novel alloy material known as High Entropy Alloy (HEA) powder has been proposed for use as a catalytic material in the Fenton process. Mechanical alloying method was used to produce HEA powder, which is expected to considerably improve its efficiency in the degradation of azo dyes. The result shows the presence of HEA as catalyst improves the Fenton reaction by providing additional actives sites. This research contributed to the development of an appealing, low-cost, and efficient approach for HEA functional applications in wastewater management

Synthesis and characterization of nickel boride nanoparticles for energy conversion catalyst materials – the effect of annealing temperature

In the recent technology development, fuel cell has been widely used in many applications, including transportation and industry. Platinum catalysts are used to catalyst the reaction at the oxygen electrode, but they are expensive and has limited supply. A nickel-boron nanoparticle catalyst is proposed as a substitute for fuel cell catalyst material. The objectives are to evaluate the effect of the annealing process and to determine the characteristics of the annealed nanoparticles using scanning electron microscopy - energy dispersive X-ray (SEM-EDS), inductively coupled plasma optical emission spectroscopy (ICP-OES) analysis, total organic carbon (TOC) analysis and X-ray diffraction (XRD). A wet chemical method was used to synthesize nickel-boron nanoparticles by chemical reduction (co-reduction) of nickel chloride and sodium borohydride. As-synthesized nickel-boron nanoparticles were annealed at temperatures of 200, 300, 400, 500, and 700 °C in an argon atmosphere for 2 h. From the experimental results, nickel-boron nanoparticles annealed at 300 °C with equal dispersion of crystalline Ni and crystalline Ni3B showed the highest catalyst performance. The yield of nickel-boron nanoparticles sized 1.1364 nm was smaller than in the literature (37 nm). The size of Ni-B nanoparticles was calculated by using the Scherrer equation with the values of full width half maximum (FWHM) obtained by peak fitting following the Gaussian model. Smaller Ni-B nanoparticles have a higher surface-area-to-volume ratio, which increases the exposure of the active sites (crystalline Ni and crystalline Ni3B phase) to the reactants (methanol) and improves catalytic activity

Morphological study of Superabsorbent polymer hydrogels from sago starch

This paper comprises of the characterizations of superabsorbent polymer hydrogels based on sago starch (SS) prepared via graft copolymerization method with acrylic acid (AA) in the presence of ammonium persulphate (APS) and N, N-metylenebisacrylamide. The morphology of sago-g-acrylic (SAG) was evidenced by scanning electron microscope (SEM) images. The remarkable feature of this SAG is the porosity distribution with different amount of crosslinker. Less amount of crosslinker leads to increment in porosity distribution as well as water absorbency. This SAG with excellent water absorbency properties, being biodegradable in nature could be useful in sanitary products, horticulture and agriculture