Characterization of Microstructure and Properties of Additively Manufactured Materials under Room and Elevated Temperatures

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Introduction
The fast progression of additive manufacturing (AM) technology in recent decades has brought forth a new age of material design and production.In contrast to conventional manufacturing techniques that frequently rely on subtractive procedures, additive manufacturing (AM) enables the fabrication of complicated and intricate structures with unparalleled precision.The aforementioned capabilities have facilitated the fabrication of materials and components that were previously considered unfeasible or even unattainable to fabricate.As several businesses aim to exploit these emerging design possibilities, it is crucial to conduct comprehensive examinations of the microstructure and characteristics of additively made materials in different scenarios, including both ambient and increased temperatures [1].Throughout history, there has been a significant amount of research conducted on material characteristics and microstructures within the realm of conventional production methods [2].Nevertheless, the distinctive method of layerby-layer deposition employed in additive manufacturing presents novel intricacies and potentialities for material characteristics.The aforementioned characteristics are frequently interconnected with the microstructural composition of the substance, which is controlled by several factors including the thickness of layers, the speed at which printing occurs, and the specific additive manufacturing technique utilised.This necessitates a thorough examination of the manner in which these factors impact the resultant microstructure and, subsequently, the mechanical and thermal characteristics of the fabricated materials [3].Comprehending these relationships is crucial for the effective incorporation of additively created materials in many applications, including aerospace, automotive, medical devices, and consumer items.The comprehension of these materials not only guarantees their dependability and performance, but also empowers engineers and designers to enhance their designs in order to use the distinctive attributes of additively generated materials.Additive manufacturing, also known as 3D printing, signifies a fundamental transformation in the fabrication process of materials.
The process entails the sequential application of material in layers, under the guidance of computerised designs, in order to fabricate three-dimensional things.The aforementioned procedure effectively removes several limitations commonly associated with conventional manufacturing techniques, hence allowing the fabrication of intricately detailed geometries and personalised structures that were previously unachievable [4].
Although additive manufacturing offers several benefits, it also presents novel problems.The process of layering can result in changes in microstructure and the occurrence of imperfections, such as porosity, which can have a substantial impact on the qualities of the material.In addition, the thermal gradients experienced during the process of additive printing can give rise to distinct phase changes and residual tensions inside the material.

Fig. 1 Steps in Additive Manufacturing
The growing use of additive manufacturing in many sectors necessitates a deeper comprehension of the microstructural changes that occur in these materials throughout the manufacturing process and post-production, as shown in fig. 1.The microstructure of a material, which includes parameters such as grain size, orientation, and porosity, is of utmost importance in the determination of mechanical strength, thermal conductivity, and several other material properties.Hence, it is imperative to conduct a comprehensive analysis of the microstructure in order to accurately anticipate the performance of additively made materials across various operational circumstances [5].The main objective of this study is to conduct a thorough analysis of the microstructure and characteristics of materials produced using additive manufacturing.The study places particular attention on evaluating the performance of these materials at both normal and high temperatures.
The research will span a wide array of materials, such as metals, polymers, and ceramics, which will be manufactured using different additive manufacturing techniques.This project tries to address the existing knowledge gap between theoretical understanding and practical implementation by conducting a comprehensive analysis of the microstructure and mechanical characteristics of these materials.This analysis will be carried out in controlled laboratory settings as well as at increased temperatures.The acquired insights will enhance the ability to make educated decisions about material selection, process optimisation, and design in sectors that necessitate materials to retain their integrity and usefulness throughout a wide range of temperatures [6].

Materials and Methods
The choice of materials, which includes metals, polymers, and ceramics, is an important component of this subject.Each material displays distinctive behaviours under various production circumstances; thus, it is crucial to evaluate them [7].In a current scenario, we will examine the selection of materials, namely a stainless-steel alloy (such as 316L), a thermoplastic polymer (such as ABS), and a ceramic (such as alumina), as shown in table.1.In terms of mechanical and thermal characteristics, these materials span a wide spectrum, enabling a thorough investigation.
Before the production process, the raw materials undergo preparation to achieve precise compositions, purities, and particle sizes.The stainless-steel powder undergoes thorough characterization to ensure consistent distribution of particles and chemical makeup.In a similar vein, the polymer pellets are carefully chosen based on their melt flow characteristics, while the ceramic powders undergo processes such as particle size reduction and homogenization to provide a uniform feedstock.In order to assure compatibility with the qualities of each material, suitable additive manufacturing procedures are used.In this scenario, the selection of the Direct Metal Laser Sintering (DMLS) technique is made for the fabrication of stainless-steel components, while the Fused Deposition Modelling (FDM) method is chosen for polymer-based materials.Additionally, the Binder Jetting procedure is opted for the production of ceramic objects.These methods exhibit different levels of accuracy, resolution, and compatibility with different materials [8].
The Direct Metal Laser Sintering (DMLS) process involves the use of a high-energy laser to selectively induce melting and fusion of metal powder particles in a sequential layer-by-layer manner, resulting in the formation of a compact and solid structure [9].The Fused Deposition Modelling (FDM) process involves the sequential extrusion and deposition of a thermoplastic filament, which is then fused together layer by layer to fabricate the ultimate component.Binder Jetting is a manufacturing process wherein a liquid binder is precisely deposited onto layers of ceramic powder, resulting in their cohesive bonding prior to the subsequent sintering stage.Every process encompasses distinct characteristics, including laser power, layer thickness, build speed, extrusion temperature, and binder saturation, which dictate the microstructure and qualities of the ultimate product.Fig. 2 Working of Direct Metal Laser Sintering (DMLS) [10] Various analytical approaches are utilised to evaluate the generated microstructures.It may be posited that optical microscopy is capable of discerning macroscopic characteristics such as layer borders and flaws.Conversely, scanning electron microscopy (SEM) offers the ability to generate intricate visual representations of grain patterns and porosity [11].X-ray diffraction (XRD) is employed to ascertain the phase composition of sintered materials.Optical microscopy, akin to the naked eye, allows for the observation of the distinct layers present.On the other hand, scanning electron microscopy (SEM), comparable to a magnifying glass, enables a closer examination of the grains inside each layer.Finally, X-ray diffraction (XRD), similar to a chemical analysis, facilitates the identification of the specific materials utilised [12].The evaluation of mechanical properties is a crucial component in the thorough analysis of materials produced by additive manufacturing techniques, especially when examining their performance at normal and high temperatures [14].Within this particular framework, the process of mechanical property testing encompasses the act of exposing the fabricated specimens to a series of standardised tests in order to quantitatively assess their reaction to external pressures and to get insights into the influence of their microstructure on their overall performance.
Conventional mechanical tests, such as tensile testing, hardness testing, and fracture toughness analysis, are typically performed under ambient conditions.Tensile tests offer valuable insights into many mechanical properties of materials, including their load-bearing capacity, yield strength, ultimate tensile strength, and elongation.The process of hardness testing evaluates the ability of a material to resist indentation or scratching, providing valuable insights into its hardness characteristics across various locations.Fracture toughness testing is a method used to assess the ability of a material to resist the propagation of cracks, which is a crucial characteristic for components that experience stress concentrations or have possible faults [15].
In the context of high temperatures, the importance of mechanical property testing is heightened since it might reveal changes in material behaviours [16].The purpose of conducting high-temperature tensile tests is to determine the ability of a material to maintain its strength, measure its ductility, and identify the point at which plastic deformation begins when exposed to extreme temperatures.These tests serve the purpose of identifying possible vulnerabilities in the structural integrity of the material when the temperature rises.Creep testing is a method that entails submitting specimens to prolonged durations of increased temperatures while maintaining constant loads [17].This testing approach is employed to assess the material's propensity for time-dependent deformation when subjected to stress.This knowledge has significant importance in situations where materials are subjected to prolonged exposure to high temperatures.
The correlation between mechanical property testing and microstructure is indisputable [18].The mechanical characteristics of materials in additive manufacturing are dramatically affected by the introduction of flaws, residual tensions, and phase shifts.Hence, these examinations not only yield numerical data but also provide valuable insights into the correlation between microstructural characteristics and macroscopic phenomena.The data obtained from these tests plays a crucial role in validating computer models, facilitating the optimisation of processes, and eventually facilitating the identification of suitable materials for specific applications in additive manufacturing.Additionally, these tests take into consideration the influence of different temperature situations.Mechanical property testing plays a crucial role in establishing a connection between the microstructure of materials produced by additive manufacturing and their mechanical behaviour at both ambient and increased temperatures [19].
Thermal analysis techniques refer to a set of analytical methods employed to investigate the thermal properties and behaviour of materials [20].These techniques involve the measurement and analysis of several thermal parameters.Thermal analysis techniques [21] are of utmost importance in the field of materials characterisation as they contribute significantly to the comprehension of materials' thermal behaviour, stability, and phase transitions.Differential Scanning Calorimetry (DSC) and Thermogravimetric Analysis (TGA) are two prominent methods that provide significant contributions in the examination of thermal characteristics exhibited by various substances.Differential Scanning Calorimetry (DSC) [22] is a commonly employed technique for investigating the thermal transitions of materials in relation to temperature by analysing the heat flow, as shown in fig. 3. Differential scanning calorimetry (DSC) is a technique that enables the determination of specific heat capacity, enthalpy, and temperature range associated with phase changes such as melting, crystallisation, and glass transitions.This is achieved by quantifying the heat received or emitted during these transitions.During a differential scanning calorimetry (DSC) experiment, controlled temperature variations are applied to both a sample and a reference material.The energy necessary to maintain both the sample and the reference material at an equivalent temperature is then quantified.Phase transitions can be identified by observing variations in energy input, which enables the measurement of transition temperatures and the corresponding enthalpy changes.The comprehension of the impact of additive manufacturing procedures on material crystallinity, glass transition, and other temperature-dependent behaviours is contingent upon a comprehensive grasp of Differential Scanning Calorimetry (DSC) [23].
Thermogravimetric Analysis (TGA) [24], in contrast, is primarily concerned with quantifying alterations in the mass of a substance in relation to variations in temperature.Thermogravimetric analysis (TGA) is a highly valuable technique in the investigation of thermal breakdown, oxidation, and volatilization phenomena.In the context of a thermogravimetric analysis (TGA) experiment, the sample undergoes controlled heating or cooling, while its corresponding weight variation is continually observed.Any alteration in weight, whether it be a decrease or increase, may be attributed to chemical processes or phase transitions taking place inside the substance.Thermogravimetric analysis (TGA) offers valuable insights into the thermal stability, composition, and reaction kinetics of many materials.Within the realm of additively built materials, thermogravimetric analysis (TGA) serves as a valuable tool for discerning the existence of volatile constituents, like binders or residual solvents, alongside identifying degradation patterns that might potentially impact the material's efficacy under heightened thermal conditions [25].
The combined utilisation of Differential Scanning Calorimetry (DSC) and Thermogravimetric Analysis (TGA) provides researchers with the opportunity to investigate the complex thermal characteristics shown by materials produced using additive manufacturing techniques.By elucidating the manner in which these materials react to alterations in temperature, phase transitions, and chemical reactions, these methodologies provide a more profound comprehension of their appropriateness for certain applications, guaranteeing the ideal design and efficacy of materials in diverse thermal settings.

Results and Discussion
In the realm of mechanical testing, it is possible to utilise data to exemplify the varied responses of stainless-steel alloy (316L), a thermoplastic polymer (ABS), and a ceramic (alumina) under the influence of mechanical stress [27].Tensile testing provides valuable insights into the mechanical properties of materials.The experimental findings for stainless steel (316L) indicate a measured yield strength of 450 MPa, an ultimate tensile strength of 620 MPa, and an elongation at fracture of 25%.On the other hand, the thermoplastic polymer known as acrylonitrile butadiene styrene (ABS) has a yield strength of 50 MPa, an ultimate tensile strength of 60 MPa, and an elongation at break of 15%.It is worth mentioning that ceramics, such as alumina, possess inherent brittleness, which deviates from the conventional measures of yield and ultimate tensile strength [28].Conversely, the fracture toughness value of 4 MPa√m and the modulus of elasticity value of GPa offer significant insights into the material's behaviour under mechanical stress.The evaluation of material hardness is an additional crucial aspect conducted during testing.Stainless steel (316L) has been seen to possess a hardness of around 200 HV (Vickers) or 40 HRC (Rockwell C), whilst the thermoplastic polymer ABS is known to have a Shore D hardness of 80.When comparing the two materials, it is evident that ceramic alumina has a significantly greater Vickers hardness value of 1500 HV [29].
In addition, the evaluation of fracture toughness is of great importance, particularly in the context of analysing a material's ability to resist crack propagation [30].Stainless steel (316L) has a notable fracture toughness (KIC) of 50 MPa√m, hence highlighting its exceptional resistance to crack propagation.In contrast, the measurement of fracture toughness in polymers is less frequently conducted as a result of their non-linear characteristics [31].The fracture toughness of ceramic alumina is measured at around 4 MPa√m, indicating its inherent brittleness.The aforementioned data sets highlight the substantial diversity in mechanical characteristics shown by various materials.Stainless steel has a favourable combination of strength and ductility, whilst ABS showcases a higher degree of pliability [32].On the other hand, ceramic alumina exhibits exceptional hardness but is characterised by brittleness.The complex interaction of characteristics influences the choice of materials for particular uses, guaranteeing the best possible performance in response to different mechanical pressures [33].
The investigation of microstructure plays a fundamental role in the thorough examination of materials produced by additive manufacturing, offering valuable understanding of their underlying structure and how it influences their qualities.This investigation incorporates a variety of methodologies that collectively reveal essential information regarding the microstructure of the material [35].The process of Grain Structure Analysis entails the investigation and evaluation of the spatial organisation and distinctive attributes of grains present in a given material.Methods like as optical microscopy and electron microscopy enable researchers to observe and analyse the characteristics of grain boundaries, sizes, and orientations.The deposition of materials in an additive manufacturing process occurs in a layer-by-layer fashion, resulting in distinctive patterns of grain development [36].These patterns have a significant influence on the mechanical strength and several other attributes of additively made materials.As an example, it is possible for stainless steel (specifically 316L) to display noticeable columnar grains as a result of the directed solidification that is inherent in specific additive manufacturing techniques, as shown in fig. 4. Fig. 4 Grain structural analysis of stainless steel (316L) [37] The assessment of porosity has great importance in the examination of microstructure, given that the presence of voids or pores inside a material can have a substantial impact on its mechanical characteristics.Imaging methods like as scanning electron microscopy (SEM) may be employed to quantitatively assess the extent of porosity, which may exhibit heightened prominence in additive manufacturing processes owing to inadequate fusion between successive layers.The assessment of porosity in thermoplastic polymers, such as ABS, can provide valuable information into their appropriateness for load-bearing applications [38].
The process of Phase Composition Determination entails the identification of several phases inside a material, including but not limited to crystalline, amorphous, or distinct chemical compositions [39].X-ray diffraction (XRD) [40] is a technique that is capable of precisely identifying the different phases present in a sample [41].On the other hand, energydispersive X-ray spectroscopy (EDS) is a method that allows for the examination of the composition of a sample [42].The comprehension of the crystalline phases and potential phase alterations resulting from processing is of utmost importance in the analysis of the thermal properties of ceramic materials such as alumina [43].The Comparative Analysis with Conventional Materials enhances the comprehension of microstructural characteristics by conducting a comparison between materials produced using additive manufacturing and those generated using conventional methods [44].This comparative analysis elucidates disparities in the morphological characteristics of grains, degrees of porosity, and compositions of phases.For example, a comparison between the microstructure of stainless steel (316L) [45] produced using additive manufacturing and stainless steel produced through traditional processing can provide insights into the impact of the layer-wise fabrication method on the grain structure and presence of flaws [46].By means of conducting microstructural investigations, researchers get a comprehensive comprehension of the manner in which additive manufacturing procedures impact the internal structure of materials.The understanding of microstructure and its relationship to qualities forms the foundation for comprehending material behaviour across different circumstances.These insights play a crucial role in customising the parameters of additive manufacturing, maximising the performance of materials, and guaranteeing their appropriateness for a wide range of applications, including aerospace and medical equipment [47]- [50].

Conclusion
This thorough work has generated substantial insights in the exploration of the complex correlation between microstructure and characteristics of additively made materials.The key points of the study are listed below: • The stainless steel (316L) demonstrated notable mechanical properties, including a significant yield strength of 450 MPa, an ultimate tensile strength of 620 MPa, and an elongation at break of 25%.• The thermoplastic polymer ABS exhibited a yield strength of 50 MPa, an ultimate tensile strength of 60 MPa, and an elongation at break of 15%, indicating its mechanical properties.• Due to its inherent brittleness, ceramic alumina exhibits deviations from traditional values of yield and ultimate tensile strength.However, the fracture toughness of the material is measured to be 4 MPa√m, while its modulus of elasticity is determined to be 350 GPa, both of which provide valuable insights into its inherent properties.

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The stainless steel (316L) exhibited notable hardness, as evidenced by Vickers and Rockwell C values of 200 HV and 40 HRC, respectively.•The thermoplastic polymer known as ABS had a Shore D hardness value of 80, indicating a moderate level of hardness.• The use of microstructural analysis has been helpful in comprehending the impact of additive manufacturing procedures on the internal structure of materials., 011 (2023) E3S Web of Conferences ICMPC 2023 https://doi.org/10.1051/e3sconf/20234300110101 430