In a new model of alloy solidification in a square mold, the interface being followed by a front-tracking technique is representative of a curve joining the tips of growing solid dendrites. The coupled heat equation is solved via an Eulerian control-volume formulation. In the absence of convection, the nucleation and nonequilibrium growth of both a front of columnar grains and a single equiaxed grain have been modeled and animated. This is a major step toward the computationally efficient complete direct numerical simulation of the developing grain structure in a casting process.

Their inherent lack of dislocations and hence slip planes leads to exceptionally high strength and elasticity, approaching the theoretical limit. While oxide glasses and ceramics exhibit low toughness and brittle failure, BMGs can display toughness comparable to crystalline metals. [ 2 ] The lack of grain structure means that BMGs are homogeneous and exhibit isotropic behavior, even at sub-micrometer length scales, and, without grain boundaries or precipitates as oxidation sites, corrosion rates are significantly reduced compared to conventional metals.BMGs soften above an alloy-specifi c glass-transition temperature ( T g ) before eventual, time-dependent, crystallization at a higher, crystallization temperature ( T x ). In this supercooled liquid region (SCLR) between T g and T x , the viscous BMGs may be plastically shaped under low applied forces using polymer-processing techniques, such as hot embossing, extrusion, foaming, and injection and blow moulding, before again cooling to a solid metallic glass. With relatively low processing temperatures and no solidifi cation shrinkage, parts can be formed to netshape with excellent accuracy, and geometries, and surface patterns previously diffi cult in metals can be achieved with ease. [3][4][5][6][7] Such remarkable properties and behavior have led to significant interest in BMGs as engineering materials over the past 20 years, but it is only recently that their potential for use as a biomaterial has been studied. [ 8 ] To date, our understanding of material biocompatiblity has evolved mainly through empirical testing, observing the interaction of materials with cells and host tissue in vitro and in vivo. Materials can induce host responses varying from local and systemic infl ammation, hypersensistivity, toxicity, and even tumorogenesis, meaning that thorough evidence of material safety is required before regulatory approval and clinical translation. We now largely recognise the material characteristics that generate both favorable and undesired host responses, as outlined by Williams, [ 9 ] offering the opportunity for informed material design, while being cognisant that biocompatibility is specifi c to the application and host environment. [ 10 ] The original requirement of fi rst generation "biocompatible" materials was bio-inertness. [ 11 ] This included a resistance to corrosion in the body, and here Ti-and Co-based alloys scored highly. [ 12 ] Less-inert metals, such as Mg, were therefore not deemed suitable, although the ions released on dissolution are generally not harmful to the human body. However, current design requirements for biomaterials, including most recently biometals, include eliciting an appropriate host response, [ 13 ] and this can include the need to biodegrade and resorb. There are potential advantages for BMGs that span applications of With increasing knowledge of the materials science of bulk metallic glasses (BMGs) and improvements in their properties and processing, they have started to become candidate materials for biomedical dev...

The current review uses the material requirements of a new space propulsion device, the Variable Specific Impulse Magnetoplasma Rocket (VASIMR ® ) as a basis for presenting the temperature dependent properties of a range of dielectric ceramics, but data presented could be used in the engineering design of any ceramic component with complementary material requirements. A material is required for the gas containment tube (GCT) of VASIMR ® to allow it to operate at higher power levels. The GCT's operating conditions place severe constraints on the choice of material. A dielectric is required with a high thermal conductivity, low dielectric loss factor, and high thermal shock resistance. There is a lack of a representative set of temperature-dependent material property data for materials considered for this application and these are required for accurate thermo-structural modelling. This modelling would facilitate the selection of an optimum material for this component. The goal of this paper is to determine the best material property data values for use in the materials selection and design of such components. A review of both experimentally and theoretically-determined temperature-dependent & room temperature properties of several materials has been undertaken. Data extracted are presented by property. Properties reviewed are density, Young's, bulk and shear moduli, Poisson's ratio, tensile, flexural and compressive strength, thermal conductivity, specific heat capacity, thermal expansion coefficient and the factors affecting maximum service temperature. Materials reviewed are alumina, aluminium nitride, beryllia, fused quartz, sialon and silicon nitride.

Abstract. The development of MEMS and Microsystems needs a reliable massproduction process to fabricate micro components with micro/nano scale features. In our study, we used the micro injection molding process to replicate micro/nano scale channels and ridges from a Bulk Metallic Glass (BMG) cavity insert. High density polyethylene (HDPE) was used as the molding material and Design of Experiment (DOE) was adopted to systematically and statistically investigate the relationship between machine parameters, real process conditions and replication quality. The peak cavity pressure and temperature were selected as process characteristic values to describe the real process conditions that material experienced during the filling process. The experiments revealed that the replication of ridges, including feature edge, profile and filling height, was sensitive to the flow direction; cavity pressure and temperature both increased with holding pressure and mold temperature; replication quality can be improved by increasing cavity pressure and temperature within a certain range. The replication quality of micro/nano features is tightly related to the thermomechanical history of material experienced during the molding process. In addition, the longevity and roughness of the BMG insert was also evaluated based on the number of injection molding cycles.

Internal flow behaviour during melt-pool-based metal manufacturing remains unclear and hinders progression to process optimisation. In this contribution, we present direct time-resolved imaging of melt pool flow dynamics from a high-energy synchrotron radiation experiment. We track internal flow streams during arc welding of steel and measure instantaneous flow velocities ranging from 0.1 m s−1 to 0.5 m s−1. When the temperature-dependent surface tension coefficient is negative, bulk turbulence is the main flow mechanism and the critical velocity for surface turbulence is below the limits identified in previous theoretical studies. When the alloy exhibits a positive temperature-dependent surface tension coefficient, surface turbulence occurs and derisory oxides can be entrapped within the subsequent solid as result of higher flow velocities. The widely used arc welding and the emerging arc additive manufacturing routes can be optimised by controlling internal melt flow through adjusting surface active elements.