Complexion: A new concept for kinetic engineering in materials science
Interfaces and the movement of atoms within an interface play a crucial role in determining the processing and properties of virtually all materials. However, the nature of interfaces in solids is highly complex and it has been an ongoing challenge to link material performance with the internal interface structure and related atomic transport mechanisms. Interface complexions offer a missing link to help solve this universal problem. We have theoretically predicted the existence of multiple interface complexions by thermodynamics, but the present work represents the most comprehensive characterization and proof of their existence in a real material system. An interface complexion can be considered as a separate phase, which can be made to transform into different complexions (phases) with vastly different properties by chemistry and heat treatment, thereby enabling the engineering control of material properties on a level not previously realizable. As such, complexions offer a solution to outstanding fundamental scientific mysteries, such as the origin of abnormal grain growth in inorganic materials, a problem which leading researchers in the field have struggled to explain for the past 50 years. It is also described how interface complexions will likely have widespread impact across all branches of material science and related disciplines. [1]
Ligament tissue engineering: An evolutionary materials science approach
The anterior cruciate ligament (ACL) is important for knee stabilization. Unfortunately, it is also the most commonly injured intra-articular ligament. Due to poor vascularization, the ACL has inferior healing capability and is usually replaced after significant damage has occurred. Currently available replacements have a host of limitations, this has prompted the search for tissue-engineered solutions for ACL repair. Presently investigated scaffolds range from twisted fiber architectures composed of silk fibers to complex three-dimensional braided structures composed of poly (l-lactic acid) fibers. The purpose of these tissue-engineered constructs is to apply approaches such as the use of porous scaffolds, use of cells, and the application of growth factors to promote ligament tissue regeneration while providing mechanical properties similar to natural ligament. [2]
Overview of the lattice Boltzmann method for nano- and microscale fluid dynamics in materials science and engineering
The article gives an overview of the lattice Boltzmann method as a powerful technique for the simulation of single and multi-phase flows in complex geometries. Owing to its excellent numerical stability and constitutive versatility it can play an essential role as a simulation tool for understanding advanced materials and processes. Unlike conventional Navier–Stokes solvers, lattice Boltzmann methods consider flows to be composed of a collection of pseudo-particles that are represented by a velocity distribution function. These fluid portions reside and interact on the nodes of a grid. System dynamics and complexity emerge by the repeated application of local rules for the motion, collision and redistribution of these coarse-grained droplets. The lattice Boltzmann method, therefore, is an ideal approach for mesoscale and scale-bridging simulations. It is capable to tackling particularly those problems which are ubiquitous characteristics of flows in the world of materials science and engineering, namely, flows under complicated geometrical boundary conditions, multi-scale flow phenomena, phase transformation in flows, complex solid–liquid interfaces, surface reactions in fluids, liquid–solid flows of colloidal suspensions and turbulence. Since the basic structure of the method is that of a synchronous automaton it is also an ideal platform for realizing combinations with related simulation techniques such as cellular automata or Potts models for crystal growth in a fluid or gas environment. This overview consists of two parts. The first one reviews the philosophy and the formal concepts behind the lattice Boltzmann approach and presents also related pseudo-particle approaches. The second one gives concrete examples in the area of computational materials science and process engineering, such as the prediction of lubrication dynamics in metal forming, dendritic crystal growth under the influence of fluid convection, simulation of metal foam processing, flow percolation in confined geometries, liquid crystal hydrodynamics and processing of polymer blends. [3]
Electrochemical Deposition of Lead Sulphide (PbS) Thin Films Deposited on Zinc Plate Substrate
Lead sulphide (PbS) thin films were deposited at different times on a zinc plate substrates using electrodeposition technique at room temperature. The results showed that PbS thin films resistivity has a direct proportionality with time. The optical properties of the thin film were measured using M501 UV-visible spectrophotometer in the wavelength range of 300 nm-1500 nm. The highest and lowest optical absorbance value of 0.253 and 0.219 at 5 mins and 1min respectively were recorded. The transmittance value of 0.582% and 0.966% at 3 mins were recorded in the infrared and ultraviolet regions respectively. The peak reflectance value was attained at 5 mins in both regions, while the minimum was obtained at 1min in the near infrared and visible regions. Refractive index, optical conductivity, extinction coefficient, real dielectric constant and imaginary dielectric constant were examined as a function of the photon energy. Further analysis revealed the band gap to be in the energy range of 1.9eV-2.6eV. These results show that lead sulphide can be used for mass production of solar cells and others photovoltaic devices. [4]
Structural Changes of Surface Layers of Hard Turned Parts by Wiper and Conventional Geometry
Aims: The aim of this paper is to achieve information about surface and sub-surface layers after hard turning by mixed ceramic tool with different geometry – Wiper and conventional and to compare achieved results to find out advantages of its use. Second aim is to obtain graphs of the influence of the tool wear on the surface structural changes.
Study Design: The experiment on hard turning was carried out with differently shaped mixed ceramic tools.
Place and Duration of Study: Slovak University of Technology in Bratislava, Faculty of Materials Science and Technology, Institute of Production Technologies and Institute of Materials Science, between November 2013 and May 2014.
Methodology: In the case of cutting tool wear and structural changes measurement this experiment was carried out on two different workpiece sizes – 1. 125 mm long cylinder to achieve cutting tool wear, 2. 10 mm long rings for structural changes. Microscopy for cutting tool wear measurement and X – ray diffraction for structural changes measurement was used. Cutting tool wear was represented by VB parameter and structural changes were represented by structural phase content, crystallites and lattice.
Results: Information about structural phase contents was achieved. There are some differences between surface and sub-surface layers after hard turning by mixed ceramic tool. Surface layer consists of more austenite phase than sub-surface layers. But there were not very big differences between used cutting tool geometry and its influence on the cutting tool wear. Both geometries were used more than 40 minutes till the flank wear parameter VB reached to 0.25 mm. The thickness of the surface heat influenced layer depends on the cutting tool wear and it is influenced by the cutting tool geometry – application of the Wiper geometry leads to thinner “white layer”.
Conclusion: It is very important to take into consideration cutting tool geometry when dealing with surface integrity after hard turning. But all achieved results depend on the used cutting parameters, cutting tool material, workpiece material, cutting force components, machine stiffness in specific experiments. [5]
Reference
[1] Dillon, S.J., Tang, M., Carter, W.C. and Harmer, M.P., 2007. Complexion: a new concept for kinetic engineering in materials science. Acta Materialia, 55(18), pp.6208-6218.
[2] Laurencin, C.T. and Freeman, J.W., 2005. Ligament tissue engineering: an evolutionary materials science approach. Biomaterials, 26(36), pp.7530-7536.
[3] Raabe, D., 2004. Overview of the lattice Boltzmann method for nano-and microscale fluid dynamics in materials science and engineering. Modelling and Simulation in Materials Science and Engineering, 12(6), p.R13.
[4] Lucky Ikhioya, I., Ehika, S. and N. Omehe, N. (2018) “Electrochemical Deposition of Lead Sulphide (PbS) Thin Films Deposited on Zinc Plate Substrate”, Journal of Materials Science Research and Reviews, 1(3), pp. 1-11. Available at: https://journaljmsrr.com/index.php/JMSRR/article/view/13161 (Accessed: 4December2020).
[5] Samardziova, M., Neslusan, M. and Kusy, M. (2014) “Structural Changes of Surface Layers of Hard Turned Parts by Wiper and Conventional Geometry”, Current Journal of Applied Science and Technology, 6(4), pp. 335-341. doi: 10.9734/BJAST/2015/14506.
