Materials Science Forum Vols. 828-829

Abstract: This paper presents simulation of molecular dynamics for the deposition of Titanium (Ti) and Nickel (Ni) particles on Ti substrate during Cold Gas Dynamic Spray (CGDS) process. The influencing factors of the deposition process, such as particle incident velocity, particle size and particle temperature are taken into consideration. Ti and Ni were selected because of their potential applications in the aerospace, marine and bio-medical industries. CGDS is preferred because it is a state of the art technique by which coatings are created without significant heating of the sprayed powder. In CGDS, particles are accelerated to supersonic velocities using a high speed gas stream. However, there are inherent difficulties in relating particle deposition characteristics with influencing factors of the deposition process. Moreover, there is limited literature on molecular dynamics simulation of CGDS process. For this reason, this paper develops a simulation process for Ti and Ni particles under influence of many factors using molecular dynamics. In this process, particles are allowed to interact for a short time, giving a view of their motion. The trajectories of these particles are determined by numerically solving the Newton's equations of motion for a system of interacting particles, in which the forces between the particles are defined. The results of the simulation process show that higher incident velocities and larger particle sizes result in stronger interface between the particle and the substrate. Further, higher temperatures of the substrate and particles improve the bond strength.

Abstract: The Interdependence model currently uses an analytical expression for a moving planar interface to calculate the solute diffusion length designated as x’_dl in the model. Upon nucleation within an alloy melt (i.e. when the solid embryo starts to grow), the interface grows with a spherical front which then breaks down into a dendritic interface. The time required for this breakdown is a subject for separate research. In this paper, we explore the validity of using a planar interface in the early stages of nucleation and growth of metal alloys as used in the Interdependence model. The diffusion field ahead of a planar interface, in theory, has an exponentially changing composition of infinite length. In the Interdependence model, x’_dl is assumed to be where this exponentially decreasing composition profile in the liquid ahead of the interface (for k < 1) reduces to within 1% of a quantity proportional to the nominal alloy composition, C₀, far from the interface. A numerical solidification model, μMatIC, is used to simulate the growth of a single grain with a dendritic interface in 2D and 3D. The numerical model is capable of generating the solute profile ahead of the growing grain which is used to evaluate the solute diffusion length that can be compared with the results obtained from the planar interface model. The comparisons were made with both 1% and 0.1% cut-off criteria. The results indicate that the 1% assumption being used in the planar front diffusion length calculation is a good approximation for the Interdependence model.

Abstract: Natural aging during storage of Al-Mg-Si alloys at room temperature can significantly reduce the maximum strengthening potential (T6) during artificial aging and, therefore, is a key topic in aluminium research and industry. Many different strategies to understand and reduce the negative effect of natural aging have been investigated during the last decades, including analysis of different thermal pre-treatments and considering the effect of different microalloying elements. From these investigations, the vacancy evolution and the formation of clusters containing Mg and Si were found to be the governing aging mechanisms behind natural aging. In this work, we present a model to simulate and predict the behavior of these alloys when subjected to room temperature aging after solutionizing and demonstrate the effects of different thermal routes and chemical composition variations. In the implemented model, the evolution of excess quenched-in vacancies and the effect of solute vacancy traps are considered. Special emphasis is placed on co-cluster formation and its contribution to strengthening. The thermokinetic software MatCalc is used for the simulations and the results of the simulations are validated by experimental investigation.

Abstract: Selective laser melting (SLM) is a modern method for producing objects with complex shape and fine structures in one working cycle from metal powders. Combination of the advanced technology of SLM with unique properties of Ti6Al4V alloy allows creating complex 3D objects for medicine or aerospace industry. Since properties of SLM parts depend on the geometrical characteristics of tracks and their cohesion, optical monitoring is actually used to for control the process. Temperature gradient determines the microstructure and mechanical properties of the SLM part, so studies about temperature fields are primarily important. On-line monitoring during laser scanning of Ti6Al4V alloy and formation of a single track in real-time with high-speed IR camera was studied. Numerical simulation allowed estimation the temperature distribution during processing. Conclusion regarding control system based on the online monitoring of deviations of the signal from IR camera during the SLM process was done.

Abstract: The automotive manufacturing industry, worldwide, has been engaged in a race to produce lightweight vehicles. Consequently, the industry continues to deploy significant resources in developing and utilising advanced lightweight materials and cutting-edge technologies in the manufacture of new vehicle models that are energy efficient, more reliable, safer, more user-friendly and less polluting; without compromising the other important vehicle attributes such as, size, cargo space and payload, structural integrity, power and acceleration. Mass reduction is one consistent and cost-effective strategy that can be combined with other efficiency improvement strategies and technologies to meet the requirements of fuel economy and emission reduction. The materials used in automotive light-weighting must fulfil several criteria imposed by regulation and legislation with the environment in addition to satisfying customer requirements. The choice for light, high strength automotive materials is between advanced high-strength steel (AHSS) on one hand, and composites of aluminium (aluminium metal matrix composites (AlMMCs)), magnesium and polymers, on the other. In this paper, the potential of AlMMCs as a replacement for most steels and aluminium alloys in the manufacture of automotive parts and components is discussed as well as their current status and future trends of utilisation in automotive light-weighting.

Abstract: Light metals are contributing significantly to the weight saving of components and structures of transport means. Regarding airliners FAA recently published a report on the development of a flammability test for magnesium alloys to be used in aircraft seat construction which opens up the options to introduce specific parts in next seat models. In former projects, it was shown that magnesium alloys are offering interesting mass reduction and-by this-fuel & emissions saving potentials in air transport. The major concern is the behaviour of Mg alloys in case of an aircraft fire which was investigated by FAA for particular alloys of Magnesium-Neodymium-Gadolinium, Magnesium-Yttrium-Rare Earth as well as Magnesium-Aluminium-Zinc composition in course to the test methods development. While clearly the AZ31 alloy fails in such a laboratory test, the other two types pass flawlessly by exhibiting a self-extinguishing behaviour shortly after removing the fire source. None of them are specifically usable for high pressure die casting or thixomolding processes which both are common production methods. From the typically used thixomolding alloys like AZ91D, AM50A, AM60B or AJ62A, the Magnesium-Aluminium-Zinc again is likely to fail in flammability tests due to the low-temperature melting network of eutectic phase. Therefore, the development focussed on Magnesium-Aluminium-Manganese and Magnesium-Aluminium-Strontium type alloys. Calcium – well known for the ability to improve the flammability behaviour – was added in certain concentrations to those alloying systems and investigated regarding self-extinguishing performance, manufacturing issues as well as mechanical properties. The results of these examinations are presented in the following paper.

Abstract: The functional requirements of lower extremity paediatric prostheses in developing regions and the materials used in the manufacture thereof is presented in this paper. Specific advantages and disadvantages of materials used in relation to the African paediatric amputee are highlighted. The paper examines the critical issues for which further research and development is needed into material and manufacture tailoring to meet the functional requirements of a paediatric prosthetic. The applicability of light metal alloys in meeting these requirements is emphasised.