2-1- Introduction

2-2- 3D printing techniques for metallic biomaterials

2-3- 3D printed metallic biomaterials

2-4- Challenges, potential and current active research in 3D printing of metallic biomaterials

2-5- Conclusion References

2-1- Introduction

Among the three-dimensional (3D) printing, or officially known as additive manufacturing (AM), techniques, the powder bed fusion (PBF) and directed energy deposition (DED) are most commonly used to process metals directly as they have the capability to produce high-quality parts that are fully dense. According to ISO/ ASTM 52900:2017, PBF is a group of AM processes in which thermal energy selectively fuses regions of a powder bed, while DED is another group of AM processes in which focused thermal energy is used to fuse materials by melting as they are being deposited. In the academia, there has been extensive studies applying 3D printing in tissue engineering (Sudarmadji et al., 2011; Yeong et al., 2009; Wiria et al., 2007; Yang et al., 2002). For example, tissue scaffolds for cardiac and bone have been fabricated successfully (Chua and Yeong, 2014; Yeong et al., 2004). These applications have mainly focused on using polymers; however, in recent years, there has been growing interest in using metallic biomaterials to create implants. This is made possible with the advancement in 3D printing and accelerated development of printable materials. In this chapter the application of these two groups of AM technologies in fabrication of metallic biomaterials is described, with specific focus on metals that are biocompatible and commonly used such as 316L stainless steel, titanium-6aluminum-4vanadium (Ti6Al4V), and cobalt-chromium-molybdenum (CoCrMo).

1- Introduction

2- Deposition techniques for 3D printing of biomaterials

3- Materials for 3D printing of biomaterials

4- Applications of 3D printed biomaterials

5- 4D printing and its applications for biomaterials

6- Conclusions and future perspectives

References

Introduction

Three-dimensional printing (3D printing) or additive manufacturing (AM) promises to produce complex devices formulated from biomaterials and bioinspired materials from designs that are patient-specific. Since its advent as presurgical visualization technique and fabrication of tooling molds, 3D printing has evolved to yield bespoke devices, implants, scaffolds, diagnostic devices, and drug-delivery systems. As a result of recent public interest and affordable printing platforms, there is the desire to utilize this exciting technology for personalized health care. However, before AM can become a ubiquitous tool for the regeneration of complex tissues, such as bone, cartilage, muscles, vessels, nerves, and complex organs with multifaceted three-dimensional microarchitecture (e.g., kidneys, lymphoid organs), a number of technological limitations must be overcome. The development of advanced bioinks for 3D and 4D printing through the rational design of novel materials and their implementation as functional biomaterials through ever-expanding deposition techniques has improved the diversity and functionality of printed constructs outside of the traditional biofabrication window [1]. While there is the necessity for a compromise between suitability for purpose and biocompatibility, recent developments in materials science and bioink formulations have resulted in an improved range of solutions for biofabrication platforms. New biologically relevant printing formulations with highly consistent and accurate deposition parameters, attractive mechanical properties, high cytocompatibility, and the ability to modulate cellular functions are now being developed and offer prospects as biomaterials for use in a multitude of different applications; however, further work is needed before these novel materials become common place. In this chapter, we explore some of the approaches being pursued to achieve these targets in common 3D and 4D printing techniques, including an overview of the state-of-the-art technologies and formulations used in novel materials and bioinks, which are currently being developed, the techniques which are being utilized to produce 3D and 4D constructs, and the applications for which these new materials may be employed in. Key examples are highlighted to demonstrate the progress of this emerging technology and limitations to its development identified.

1- Introduction

2- Materials and experiments

3- Model formulation

4- Model implementation

5- Numerical results

6- Conclusions

References

Abstract

The one-way and two-way shape memory effects (SMEs) as well as the thermal hysteresis represent fundamental properties when dealing with the design of detachable and thermally-stable connection systems based on shape memory alloys (SMAs). Such properties can be induced and tuned by thermo-mechanical processes that include thermal treatments and severe pre-deformation in martensitic state, causing the onset of plastic strains. In such complex conditions, material modeling is of great importance to support the design. This paper proposes a generalization of the three-dimensional phenomenological constitutive model by Souza et al. (1998), in order to describe the behavior of severely pre-strained NiTi-based SMAs. The proposed model allows to describe pseudoelasticity, one-way and two-way SMEs, as well as additional physical phenomena evidenced experimentally, such as transformation temperatures’ evolution, thermal hysteresis, phase transformations at low stresses, thermal strains, and phase-dependent elastic properties. Several numerical simulations, ranging from uniaxial tests to the finite element analysis of two case-studies, are performed. Model results are in good agreement with the results of a performed experimental campaign and allow to discuss SMA behavior under such complex loading conditions.

Introduction

Shape Memory Alloys (SMAs) are widely applied in various fields of engineering and medicine thanks to their unique strain recovery capabilities (Jani et al., 2014; Otuska and Wayman, 1998; Duerig et al., 1990), that can be obtained either by heating or by stress release, through the so-called Shape Memory Effect (SME) and Pseudoleastic Effect (PE), respectively. SME and PE are due to reversible solid-state microstructural transitions, the so-called thermoelastic martensitic transformations (TMT), between the parent body-centered cubic austenitic phase (B2) and the product monoclinic martensitic one (B19’). TMT can be induced either by temperature changes (TIM, ThermallyInduced Martensite) or by mechanical loads (SIM, Stress-Induced Martensite), providing the SME and PE, respectively. B2 phase is stable at high temperature and low stress, while B19’ is stable at low temperature and high stress. Thanks to TIM, the material is able to change its microstructure reversibly when varying the temperature between the so-called Transformation Temperatures (TTs). Direct transformation (B2-B19’) can occur when cooling the material below the martensite TTs, while reverse transformation takes place during heating above the austenite TTs. The difference between martensite and austenite TTs, namely ΔTT, is regarded as the thermal hysteresis of the material. Thermal hysteresis, and the associated stress-strain hysteresis, is a limiting phenomenon in SMA-based fast actuation systems, as it represents a source of inefficiencies due to the increased energy loss and time response. Nevertheless, thermal hysteresis could be a beneficial feature when a large thermal stability range is needed, such as in some fasteners or connectors operating in constrained recovery mode (Jani et al., 2014; Duerig et al., 1990; Humbeeck, 2001). In such systems recovery forces are generated as the SMA element, previously deformed in martensitic state, is heated up to the austenite TTs in a constrained shape, i.e. against a mechanical obstacle. This is due to the so-called One-Way Shape Memory Effect (OW-SME) and it is the basic principle of many successful systems, e.g. permanent fasteners, couplers, or SMA hybrid composites (Humbeeck, 2001; Duerig et al., 1990; Jani et al., 2014; Kirkby et al., 2008).

1- Introduction

2- Test specimen fabrication

3- Test results

4- Conclusions

References

Abstract

Resin transfer molding (RTM) is a mass production process that can replace autoclave processes, and composite lap joints are extensively used in composite structures. When a tensile load is applied to a single-lap joint, both shear and tensile peel stresses are generated owing to the eccentric load effect. Reinforcing the composite joint in the thickness direction can reduce the shear and peel stresses generated in the joint, which can contribute considerably to the increase in the strength of the composite joint. Several reinforcing methods have been developed to improve the directional properties along the material’s thickness. Accordingly, a stitching process is typically used. However, the conventional stitching process has disadvantages because a) it requires complex equipment, and b) it cannot use highly elastic brittle fibers, such as carbon fibers. Recently, we proposed an I-fiber stitching process to minimize the bending of carbon fibers to prevent their fracture. In this study, composite, single-lap joint specimens were fabricated with RTM using an I-fiber stitching process, and their strengths were evaluated. The strengths of composite joint specimens fabricated at different stitching intervals and with the use of different patterns were compared with those of specimens fabricated without the use of the stitching process.

Introduction

Resin transfer molding (RTM) process is a mass-production process that can replace the autoclave process. In recent years, RTM processes have increasingly been applied to aircraft structures that are co-cured. Thick composite structures produced by co-curing have the disadvantage that their mechanical properties are weak in the thickness direction [1]. In order to compensate for this weakness, various methods have been developed for reinforcing the mechanical properties of the composite along the thickness direction. Some of these methods, including z-pinning and stitching, are being extensively used. The z-pinning process is a method for reinforcing the mechanical properties along the thickness direction by inserting pins made of various materials and shapes into the prepreg material. Son et al. [2] and Ko et al. [3] studied the fatigue characteristics of single-lap joint specimens reinforced with stainless steel and jagged pins exposed to various environmental conditions. Chang et al. [4] studied the tensile and fatigue characteristics of single-lap joint specimens reinforced with z-pins, and evaluated the optimization of the insertion pins. Park et al. [5] studied the tensile properties through pull-off tests of T-joint specimens reinforced with z-pins. The conventional stitching process is a method of reinforcing the mechanical properties in the thickness direction by intersecting the upper and lower fibers of the preform. Mouritz et al. [6] performed tensile, compressive, shear bending, and fatigue tests on the stitched composite specimens, and studied the characteristics of the stitching process. Beylergil et al. [7] studied the strength of the stitched composite, singlelap joint, and proved that the stitching process decreases the peel and shear stresses along the thickness direction and increases the joint strength. Aymerich [8] conducted fatigue testing on a single-lap joint specimen using a stitching process, and evaluated the stiffening effect of stitching.

Introduction

Metal casting is considered as a 7000-year-old technology which offers a large range of routes in order to produce the components with a range of sizes, shapes, quantities, quality and metal requirements (Akarte et al., 1999). Metal casting is the simplest process in which mostly gives a direct routing to the shape of the product and it gives least expensive. The process of metal casting requires a mould cavity with the desired shape and metal that is molten is poured over the mould cavity. The main objective of the metal casting is produced beneficialimplements for the human consumption and also for the beautiful work of art. From the ancient art casting, it is clear that modern industrial casting has their production which has significant skill and technological skill. In the ancient times learned and traditional skill has been used for the ages and experiences in order to produce acceptable casting. The quality of the metal casting is affected by a number of parameters which are found at the different process stages. For example, defects that may result from improper parameters of the moulding and core sand include pinholes due to the presence of hydrogen, sand deformation, gas fractures, and shape imperfections. Defects that may result from improper construction or improper assembly of the pattern andmouldsare fractures, shape imperfections, sand presence, is runs, cracks, gas presence, surface defects, mechanical damage, knob, flash, mismatch, pushing up, warping. Gases tend to dissolve in the liquid steel at all stages of the production of castings, i.e. during melting in the furnace, during tapping, during pouring of moulds, and even after pouring of the mouldsbefore complete solidification of the casting. Therefore, reducing or eliminating casting defects such as blowholes, voids in the cast structure, pinholes, non-metallic presence or porosity, and scaling on the surface of casting requires strict control of the whole process of melting and casting. The control of charge and compliance with the technological regime during melting of alloys in a furnace for casting are particularly important in the absence of vacuum treatment of liquid metal (in an induction furnace or ladle). Possible defects caused by incorrect melting include is runs, slag presence, tears (caused by excessively high temperature), gas presence, incorrect chemical composition, and pinholes(Wilk-Kołodziejczyk et al., 2014). The systematic review of the designer and robust in a way for evaluating the options that are available for identifying the best. The process selection is a manufacturing task in order to choose a method to transform the materials in to the one or more processes. The process considered to be more economical, and they are subjected for the meeting of technical constraints(Dieter, 1991). The manufacturing and material processing is a selection process problem in which multi-attribute decision-makingproblem. The decision is made during the preliminary design of an environment that is uncertain in the parameters, relationship and requirements. Material and process selection (MPS) occurs before the beginning of design for manufacturing (DFM) (Karthik et al., 2003).The study indicates that the product cost is around 5% of the total product cost, and the design is made of the stage effect of the product cost (Chen and Feng, 2000).

Twin-roll casting is an energy-efficient technology for the magnesium strip production consisting of casting and rolling combined in one process step. Producing magnesium strips in an adequate quality-price ratio requires the application of material flow cost accounting to identify hidden improvement potentials. In the following, a material flow cost accounting analysis is carried out for the twin-roll casting process of AZ31 twin-roll-cast strips. Based on the findings, inefficient process steps of the twin-roll casting process are to be revealed, and actions for cost reduction from the point of a stable process management are to be assessed. Overall, an economic process and efficient material consumption can be designed for twin-roll casting considering the strip property development.

Introduction
Value for money is an important criterion for the acceptance of magnesium components by Original Equipment Manufacturers for an industrial application. Beside external business process optimization in the context of supply chain quality individual process steps need to be further improved to achieve the required quality-price ratio [1]. Especially in case of the twin-roll casting technology for the production of magnesium strips [2] the detection of saving potentials is considerable challenging. Compared with other production routes it is an economic and resource-saving procedure combining casting and rolling in one process step [3, 4].To realize additional cost savings, hidden material and energy inefficiencies need to be detected deriving measures for improvement. Supporting transparency of material and energy consumptions and its environmental and financial consequences material flow cost accounting is a useful tool to identify concealed inefficiencies [5, 6]. Therefore, the objective of this paper is to carry out a material flow cost accounting analysis for the twin-roll casting of magnesium AZ31 twin-roll-cast strips at the pilot plant of the Institute of Metal Forming at the TU Bergakademie Freiberg [7]. For this purpose, the twin-roll casting process is initially briefly described. Building on this, the material flow cost accounting analysis is conducted enabling a detailed view of all material and energy flows during twin-roll casting via material flow models. In the next step, the identified energy and material flows are illustrated as Sankey diagram proportional to their mass and energy content. To identify weak points, cost drivers and optimization potentials a material flow cost matrix was developed, whose results will be evaluated in this paper. Based on the technology’s limitations appropriate improvement actions are proposed for further research.

The microstructure of advanced steels is usually controlled by sophisticated thermo-mechanical processing or heat treatments post hot rolling [1]. Depending on chemical composition and process control, the microstructure of such steels may consist of a range of different phases. If the microstructure consists of more than one phase, the properties of the material strongly depend on the type and distribution of the respective phases [2]. Therefore, it is crucial to determine the type and amount of the different phases in order to assess the underlying structure-property relationship. Traditionally, microstructures of steels are characterized by using standard metallographic procedures based on chemical etching and light optical microscopy (LOM) and they are classified by comparing the microscopy images with reference series. Especially for steel and its complex microstructures the comparison with reference series is strongly dependent on the expert’s subjective opinion. Nonetheless, steel is still one of the most widely used materials because of its excellent mechanical properties and the huge variety of applications [3]. Therefore, there is significant interest in the devolvement of objective quantification techniques for steels. In order to characterize steel, the microstructures can be etched for example with a structure etching such as Nital [4] or color etching techniques like Beraha‘s etchant [5]. Due to different contrasts obtained by etching the ferritic matrix can be distinguished from a pearlitic, bainitic or martensitic second phase. However, these etchings are limited to empirical approaches and quickly reach their limits, especially for the discrimination of different phase constituents in steels that exhibit more than two phases. Furthermore, the microstructures of complex multi-phase steels are usually too fine to be resolved by light optical microscopy. A proper characterization requires modern metallographic techniques such as high resolution scanning electron microscopy (SEM) or electron back-scatter diffraction (EBSD) [6,7]. Therefore, any approach aiming at identifying the phase constituents of multi-phase steels has to rely on morphological or crystallographic parameters accessible by these techniques [8–13]. Recently, several studies have focused on EBSD for the microstructural characterization of steels, as this technique can provide direct information on the phase composition [6,7,8,14]. For example, in Ref. [14] a multitude of steel grades from different manufactures has been studied and an EBSD-based classification model was proposed. It was shown that the kernel average misorientation (KAM) deduced from EBSD measurements can be used to distinguish between ferrite, bainitic ferrite and martensite. Although those EBSD-based approaches have proven to work out for some steels, the phase separation by means of EBSD is very subjective as it strongly depends on a proper selection of  the preparation, measurement and evaluation parameters [14].