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Hassan Preface Though titanium and its alloys are relatively new engineering materials, they have found wide application in the aerospace, shipbuilding, automotive, sports, chemical marciniaak food processing industries due to their extreme lightness, high specific strength and good corrosion resistance at temperatures below oC. They are also considered suitable materials for biomedical application due to their biological passivity and biocompatibility.
Biomateriaay, besides these bkomateriay properties titanium alloys have a number of adverse favorable properties which are related to their processing, machinability and long time use in open and corrosive environment.
Chemical reactivity of titanium with other materials at elevated temperature is high, which necessitates the development of non conventional melting, refining and casting techniques, making this material very expensive.
Numerous research is directed towards addressing these issues in order to ease their processing and further applications. This nine diverse chapters of this book are distributed under three sections and address problems related to the processing and application of this precious metal and its alloys. The book chapters are contributed by researchers who devoted long periods of their research career working on titanium and its alloys looking for marconiak to some of these specific problems.
From this perspective this book will serve as an excellent reference material for researchers whose works is in anyway related to titanium and marciniqk alloys – from processing to applications. The chapters are designed to address the issues that marcinia, at the material development, processing and the application stages.
For instance, the case formation defects that arise at the investment casting stage and the optimization aspects of the additive manufacturing AM processes through numerical biomateria and simulation has been addressed in two different chapters. Similarly, marcinia metallurgical defects resulting from entrapped gases during casting processes are common to titanium parts. The morphology of formation of these defects in the production of Ti6Al4V alloy is presented in another chapter of the book with the objective maricniak addressing effectively the problem at the casting stage.
Titanium parts are sometimes designed to work as die components or as projectiles and as such are subjected to high pressures and temperatures.
However, high pressure raises a number of scientific and engineering issues, mainly because under such pressures the relatively ductile phase may get transformed into a fairly brittle phase, which may significantly limit the use of titanium alloys in high pressure applications.
One of the chapters of the book deals X Preface with these issues and indicates how the formation of phase may be avoided through adoption of proper processing techniques. In the Chapter Hot Plasticity of alpha Beta alloys the authors have shared their invaluable experimental results explaining different aspects of hot plasticity of two-phase titanium alloys and have indicated techniques for developing appropriate microstructure yielding optimum plastic flow stresses under elevated temperatures.
The phenomenon of super plasticity is also addressed in the same chapter. Furthermore, application of titanium alloys under corrosive environment and friction requires additional strengthening through effective surface treatment. One chapter of the book addresses different aspects of a common chemico-thermal method – nitriding to apply an effective coating on titanium parts.
Specific issues related to the intricacies of the nitriding process suitable for application on titanium parts have been elaborated in the same chapter madciniak excellent illustrations. Titanium alloys are common options in biomedical and dental applications and biomtaeriay ternary alloys Ti-6Al-7Nb are widely used for these purposes due to their unique mechanical and chemical properties, excellent corrosion resistance and biocompatibility. Development of nanotube anodic layers for medical applications on these materials are addressed in one of the chapters while the mechanism of electrochemical deposition of calcium phosphate on titanium substrate and the related process parameters and optimization techniques are presented blomateriay another.
Titanium and biomateriya alloys are well known for their marcinizk machinability properties. Useful experimental materials are presented in one chapter dealing with machining of titanium alloys, specifically drilling, a common machining operation.
We hope the research materials presented in biomateriayy different chapters of this book will contribute to the ongoing research works on titanium and its alloys and help further improvement in the properties and application of titanium alloys. Acknowledgements The Editor would like congratulate the publishing team of INTECH for taking up this vital project and successfully steering it through its various reviewing, editing and publishing stages.
Deep appreciation is biomateriqy to all the authors of the book chapters for their contribution in composing this valuable book. He would also like to acknowledge his deep appreciation to the Publishing Process Managers of the book for their sincere cooperation in rendering Editor’s duties during biomaterjay entire period of the editing and compilation process.
Finally, he would like to express his gratefulness to the publisher for choosing him as the Editor of this book. Introduction It is easy to understand why industry and, especially, aerospace engineers love titanium. Titanium parts weigh roughly half as much as steel parts, but biomaeriay strength is far greater than the strength of many alloy steels giving it an extremely high strength-to-weight ratio. Most titanium alloys are poor thermal conductors, thus heat generated during cutting does not dissipate through the part and machine structure, but concentrates in the cutting area.
The high temperature generated during the cutting process also causes a work hardening phenomenon that affects the surface integrity of titanium, and could lead to geometric inaccuracies in the part and severe reduction in its fatigue strength [Benes, ].
On the contrary, additive manufacturing AM is an effective way to process titanium alloys as AM is principally thermal based, the effectiveness of AM processes depends on the material’s thermal properties and its absorption of laser energy rather than on its mechanical properties. Therefore, brittle and hard materials can be processed easily if their thermal properties e.
Cost effectiveness is also an important consideration for using additive manufacturing for titanium processing. In the aerospace industry, titanium and its alloys are used for many large structural components.
AM processes have the potential to shorten lead time and increase material utilization in these applications. The following sections 1. For the aerospace industry which is the biggest titanium market in the U.
SPIS TRECI CONTENTS
This chapter will focus on fusion-based AM processes with application to titanium. Numerical modeling and simulation is a very useful tool for assessing the impact of process parameters and predicting optimized conditions in AM processes.
Marciniao processes involve many process parameters, including biomateray power and power intensity distribution of the energy source, travel speed, translation path, material feed rate and shielding gas pressure. These process parameters not only vary from part to part, but also frequently vary locally within a single part to attain the desired deposit shape [Kobryn et al.
The variable process parameters together with the interacting physical phenomena involved in AM complicate the development of process-property relationships and appropriate process control.
I Stanisaw GuzowSkI, Maciej MIchnej Yuan-jian YAnG, weiwen
Thus, an effective numerical modeling of the processing is very useful for assessing the impact of process parameters and predicting optimized conditions. Currently process-scale modeling mainly addresses transport phenomena such as heat transfer and fluid dynamics, which are closely related to the mechanical properties of the final structure.
For example, the buoyancy-driven flow due to temperature and species gradients in the melt pool strongly influences the marconiak and thus the mechanical properties of the final products. The surface tension-driven free-surface flow determines the shape and smoothness of the clad. In this chapter, numerical modeling of transport phenomena in fusion-based AM processes will be presented, using the laser metal deposition process as an example.
Coaxial laser deposition systems with blown powder as shown in Fig. The material studied is Ti-6Al-4V for both the substrate and powder. Numerical modeling of the solidification of metal alloys is very challenging because a general solidification of metal alloys involves a so-called mushy region over which both solid and liquid coexist and the transport phenomena occur across a wide range of time and length scales [Voller, ].
A rapidly developing approach that tries to resolve the smallest scales of the solid-liquid interface can be thought of as direct microstructure simulation. To this approach belong phase-field [Beckermann et al.
Due to the limits of current computing power, the above methods only apply to small domains on a continuum scale from about 0. Based on the REV concept, governing equations for the mass, momentum, energy and species conservation at the process scale are developed and solved.
Two main approaches have been used for the derivation and solution of the macroscopic conservation equations. However, the numerical procedures of this model are fairly involved since two separate sets of conservation equations need to be solved and the interface between the two phases must be determined for each time step [Jaluria, ].
This places a great demand on computational capabilities. In addition, the lack of information about the microscopic configuration at the solid-liquid interface is still a serious obstacle in the implementation of this model for biomaterriay applications [Stefanescu, ].
This model uses the classical mixture theory [Muller, ] to develop a single set of mass, momentum, energy and species conservation equations, which concurrently apply to the solid, liquid and mushy regions.
The numerical procedures for this model are much simpler since the same equations are employed over the entire computational domain, thereby facilitating use of standard, single-phase CFD procedures.
In this study, the continuum model is adopted to develop the governing equations. The techniques to find the shape of the free surface can be classified into two major groups: Lagrangian or moving grid methods and Eulerian or fixed grid methods.
In Lagrangian methods [Hansbo, ; Idelsohn et al. A continuous re-meshing of the bimoateriay or part of it is required at each time step so as to follow the interface movement. A special procedure is needed to enforce volume conservation in the moving cells.
All of this can lead to complex algorithms. They are mainly used if the deformation of the interface is small, for example, in fluid-structure interactions or small amplitude waves [Caboussat, ]. In Eulerian methods, the interface is moving within a fixed grid, and no re-meshing is needed.
While Lagrangian techniques are superior for small deformations of the interfaces, Eulerian techniques are usually preferred for highly distorted, complex interfaces, which is the case for fusion-based additive manufacturing processes.
For example, in AM processes with metallic powder as feedstock, powder injection causes intermittent mergers and breakups at the interface of the melt pool, which needs a robust Eulerian technique biomatetiay handle. In this method a scalar indicator function, F, is defined on the grid to indicate the liquid-volume fraction in each computational cell. Volume fraction values between zero and unity indicate the presence of the interface. The VOF method consists of an interface reconstruction algorithm and a volume fraction advection scheme.
The features of these two steps are used to distinguish different VOF versions. VOF methods have gone through biimateriay continuous process of development and improvement. The current generation of VOF methods approximate the interface as a plane within a computational cell, and are commonly referred to as piecewise linear interface construction PLIC methods [Gueyffier et al. Some important terms for the melt pool have been added in the momentum equations, including the buoyancy force term and surface tension force term, while some minor terms in the original derivation in [Prescott et al.
The molten metal is assumed to be Newtonian fluid, and the melt pool is assumed to be an incompressible, laminar flow. The solid matciniak liquid phases in the mushy zone are assumed to be in local thermal equilibrium.
Schematic diagram of the calculation domain for laser metal deposition process For the system of interest, the conservation equations are summarized as mafciniak The continuum densityvector velocity V, enthalpy h, and thermal conductivity k are defined as follows: To calculate these four quantities, marcinia, general practice is that gl or gs is calculated first and then the other three quantities are obtained according to the following relationships: For the target biomateriy Ti-6Al-4V, it is assumed that gl is only dependent on temperature.
Here the mushy zone is considered as rigid i. Here Boussinesq approximation is applied. The fifth terms on the right-hand side of Eqs. The term S in Eq. S S F n 13 where is surface tension coefficient, the curvature of the interface, n the unit normal to the local surface, and S the surface gradient operator.