Functional Graded Materials Research Articles

Synchronized in situ X-ray and infrared imaging of laser deposition

Laser deposition is a growing additive manufacturing process for its applications in repair and functional graded materials. This study investigates the influence of powder deposition for Ti-6Al-4V using synchronized X-ray and thermal infrared imaging. Melt pool geometry and their theoretical estimates as well as thermal histories are compared between a clad without and with powder deposition. The results show how powder deposition causes fluctuations in geometry and thermal histories. Fundamental understanding of the influence of powder deposition into a melt pool can lead to better prediction of melt pool geometry, thermal history, and better controlled processing.

BORONIZING MITIGATE FAILURE MECHANISMS WITH EXTENDED LIFE IN OIL/GAS STEEL PIPING UNDER ACOUSTIC INDUCED VIBRATION (AIV)

Oil and gas piping systems suffer from acoustically induced vibration, AIV, that end with hearing losses and consuming personnel’s lives. However, Leak-Before-Break (LBB) methodology was developed to mitigate failure, the primary piping systems exhibit an extremely low probability of rupture (xLPR). For understanding of piping failure mechanisms under AIV, 3-point bending tests are conducted to study structural integrity in oil/gas piping (ASTM A333 Carbon Steel GR.6 Seamless). Besides, for ultra-fast surface hardening and strengthening, a non-traditional powder pack boronizing technique is introduced at 950oC for 10 and 30 minutes. Mechanical characterization as well as microstructural analysis are conducted for continuous and incremental bending tests. In addition, FE modeling, ANSYS, is conducted on actual “case study” of oil/gas piping to study the changes in dynamic characteristics for both as-received (AR) and boronized steel Under AIV(173 dB). Failure mechanisms is established in AR sample with clear banding and early localized micro-plasticity at 0.2 flexural stress (sf). Void coalescence induce crack initiation at 0.3 sf. Crack propagation (at 0.5 sf), crack evolution (at 0.7sf) and catastrophic failure are captured. Boronizing with the diffusion of Boron into the outer surface dominate functional-graded materials (FGM), with surface and bulk hardening. Surface hardening via boronizing mitigate fracture mechanisms with no clear micro-plasticity, but with clear twinning and banding elimination. In addition, to investigate the sustainability of piping and the effect of boronizing, under AIV, FE modeling is introduced with two different steel piping systems (AR with strength 580 MPa, and boronized steel with strength 1390 MPa). Failure mitigation is introduced with the increase of endurance limit as well as increase of piping life. تعاني أنظمة أنابيب النفط والغاز من الاهتزازات الناتجة عن الصوت ، AIV ، والتي تنتهي بفقدان السمع واستهلاک حياة العاملين. ومع ذلک ، تم تطوير منهجية التسرب قبل الکسر (LBB) للتخفيف من الفشل ، حيث تظهر أنظمة الأنابيب الأولية احتمالية منخفضة للغاية للتمزق . (xLPR) لفهم آليات فشل الأنابيب بموجب AIV ، تم إجراء اختبارات الانحناء من 3 نقاط لدراسة السلامة الهيکلية في أنابيب النفط / الغاز المستخدمة (ASTM A333 Carbon Steel GR.6 Seamless) . إلى جانب ذلک ، من أجل تغطية وتقوية السطح بسرعة فائقة ، تم تقديم تقنية التغطية بالبورون غير التقليدية عند درجة حرارة 950 درجة مئوية لمدة 10 و 30 دقيقة. تم إجراء التوصيف الميکانيکي وکذلک تحليل البنية المجهرية لاختبارات الأنابيب –الإنحناءات المستمرة والمتقطعة. بالإضافة إلى ذلک ، يتم إجراء نمذجة FE ،بإستخدام ANSYS ، على حالة فعلية لأنابيب النفط / الغاز لدراسة التغيرات في الخصائص الديناميکية لکل من الفولاذ المغطي بالبورون المستلم (AR) والفولاذ البورونى تحت AIV (173 ديسيبل). تم دراسة آليات الإنهيار في عينة AR مع النطاقات الواضحة واللدونة الدقيقة الموضعية المبکرة عند 0.2% إجهاد الانحناء . (sf) يؤدي الاندماج الفارغ إلى بدء الشروخ عند %0.3 . sfتم التقاط انتشار الشروخ (عند %0.5 sf) ، وتم إکتشاف تطور الشقوق (عند %0.7 sf) ثم الفشل الکارثي المفاجئ. تؤدي التغطية بالبورون إلى انتشار البورون علي السطح الخارجي تدريجيا ويؤدي إلى تکوين مواد مرکبة- المواد المتدرجة الوظيفية (FGM) ، مع تصلب السطح والکتل. تصلب السطح الخارجي يؤدي إلى تخفيف آليات الکسر وزيادة التصلد بالبورون مع عدم وجود لدونة دقيقة واضحة ، ولکن مع إزالة التوأمة والنطاقات الواضحة (Banding). بالإضافة إلى ذلک ، للتحقق من استدامة الأنابيب وتأثير البورون ، في إطار AIV ، تم تقديم نمذجة FE مع نظامين مختلفين للأنابيب الفولاذية (AR) بقوة 580 ميجا باسکال ، والفولاذ بالبورون بقوة 1390 ميجا باسکال). يتم تقديم تخفيف الأعطال من خلال زيادة حد التحمل بالإضافة إلى زيادة عمر الأنابيب) .

Additive manufacturing of Inconel625-HSLA Steel functionally graded material by wire arc additive manufacturing

Functional graded materials (FGMs) have been widely applied in many engineering fields, and are very potential to be the substitutions of dissimilar metal welding joints due to their overall performance. In this work, the Inconel625-high-strength low-alloy (HSLA) Steel FGM was fabricated by wire arc additive manufacturing (WAAM). The chemical composition distribution, microstructure, phase evolution and mechanical properties of the FGM were examined. With the increasing of HSLA Steel, the chemical composition appeared graded distribution, and the primary dendrite spacing was largest in graded region with 20%HSLA Steel and then gradually decreased. And the main microstructure of the FGM transformed from columnar dendrites to equiaxed dendrites. Laves phase precipitated along dendrites boundary when the content of HSLA Steel was lower than 70% and Nb-rich carbides precipitated when the content of HSLA Steel exceeded to 70%. Microhardness and tensile strength gradually decreased with ascending content of HSLA Steel, and had a drastic improvement (159HV to 228HV and 355Mpa to 733Mpa) when proportion of HSLA Steel increased from 70% to 80%.

Functionally Graded Scaffolds with Programmable Pore Size Distribution Based on Triply Periodic Minimal Surface Fabricated by Selective Laser Melting.

Functional graded materials are gaining increasing attention in tissue engineering (TE) due to their superior mechanical properties and high biocompatibility. Triply periodic minimal surface (TPMS) has the capability to produce smooth surfaces and interconnectivity, which are very essential for bone scaffolds. To further enhance the versatility of TPMS, a parametric design method for functionally graded scaffold (FGS) with programmable pore size distribution is proposed in this study. Combining the relative density and unit cell size, the effect of design parameters on the pore size was also considered to effectively govern the distribution of pores in generating FGS. We made use of Gyroid to generate different types of FGS, which were then fabricated using selective laser melting (SLM), followed by investigation and comparison of their structural characteristics and mechanical properties. Their morphological features could be effectively controlled, indicating that TPMS was an effective way to achieve functional gradients which had bone-mimicking architectures. In terms of mechanical performance, the proposed FGS could achieve similar mechanical response under compression tests compared to the reference FGS with the same range of density gradient. The proposed method with control over pore size allows for effectively generating porous scaffolds with tailored properties which are potentially adopted in various fields.

Investigation of indentation response of bi-directional functionally graded materials

Functionally graded materials made of more than two material constituents have been recently introduced in order to control stiffness and contact response. In the present study, effects of bidirectional gradation of the mechanical properties of functionally graded materials, made of more than two distinct material constituents, upon the indentation response are investigated. Utilizing isoparametric graded finite elements formulation to realize the gradation of material properties, the problem is handled in the framework of the mechanics of functional graded materials coupled with contact mechanics to investigate the nonlinearity inherent with indentation problems. The obtained results showed that the bidirectional gradation of the material properties and the indenter radius have significant effects on the indentation response of bidirectional functionally graded materials. Also, it is indicated that the indentation configuration can be effectively controlled by imposing a bidirectional gradation in an elastic material.

Universal material template for heterogeneous objects with applications to additive manufacturing

Additive manufacturing processes enable the fabrication of the material with multiscale complexities. However, to efficiently model the material compositions and microstructures on multiple design scales is an issue for most existing heterogeneous object modeling methods. To solve this problem, a universal material template and its associated heterogeneous object model are developed in this paper. The developed material template aims to provide a standardized description of the material’s microstructures. The material descriptors defined in the material template can be used in the developed heterogeneous object model to describe the spatially varied material compositions and microstructures on multiple design scales. In addition to that, a multiscale rendering method is also developed in this paper which can reconstruct the microstructure of multiscale materials defined in the material template. Both mesh and voxel models can be generated by the developed rendering technique for visualization and fabrication purposes. To further validate the effectiveness of the proposed template and rendering methods, the microstructures of three different types of commonly used materials in additive manufacturing processes are reconstructed from the pre-defined material templates. A heterogeneous object model with functional graded multiscale materials is also successfully generated and fabricated by an existing commercial additive manufacturing process. In general, the developed material template and its associated modeling and rendering methods provide the foundation for the multiscale design and modeling of parts fabricated by the additive manufacturing process.

CORROSION PROPERTIES OF Ti-B4C/CNF FUNCTIONALLY GRADED MATERIALS

This study aims to investigate corrosion properties of Ti-B4C/CNF functional graded materials (FGMs). FGMs are produced in three layers by traditional cold pressing and sintering method. While B4C was incorporated into the Ti matrix at 5%, 10% and 15% percent, the CNF was only 0.5% by volume. Corrosion properties of FGMs are determined by potentiodynamic method. 3 M HCl was preferred as the corrosion solution. Corrosion rates were calculated from the Tafel curve and the corrosion surface was examined by using SEM-EDS. The results show that the corrosion process of composite material in 3 M HCl showed different corrosion resistance, in which corrosion rate showed the evolution trend of initial increase and subsequent decrease, while amount of reinforcement changed. While the best corrosion resistance among the FGMs was determined in the sample with 5%B4C additive, the worst corrosion resistance was determined with 15%B4C+0.5% CNF additive.

Investigation of multibody receding frictional indentation problems of unbonded elastic functionally graded layers

In multibody indentation problems of functionally graded materials, characteristics and gradation of material constituents are greatly influence the response of these problems. The objective of the present study is two folds. The first is to develop a comprehensive and efficient 2D nonlinear inequality constrained variational finite element model capable of analyzing multibody frictional indentation problems of FGMs considering a realistic friction model. The second fold is to investigate the effects of material properties of the constituents of functional graded materials and their gradation, coefficient of friction, and indenter size on the response of multibody frictional indentation systems. For multibody contact configuration, different types of contact at different contact interfaces are modeled in the framework of contact mechanics. To overcome the drawbacks of classical Coulomb's law of friction, friction at the indentation interfaces is modelled using the nonclassical nonlinear local friction model to realize the tangential frictional stress and relative tangential displacements. All frictional contact constraints at all contact interfaces are exactly fulfilled without any penalty parameters. The isoparametric graded finite element formulation is utilized to realize the material properties of FGMs. Application of the developed model is verified with analytical models available in the literature and very well agreement is found. A case study of an unboned elastically graded layered homogeneous elastic substrate indented by a flat rigid indenter subjected to simultaneous normal and tangential loadings is comprehensively investigated. A detailed parametric study is conducted to explore the effect of the layer gradation index, coefficient of friction, and indenter width on the indentation response, which including contact pressure, tangential frictional stress and displacement field at the indenter-graded layer interface and graded layer-elastic substrate interface. Results show that the receding frictional contact response of FGMs can be controlled by appropriate choice of the layer gradient index.

Promising functional graded materials for compact gaseous insulated switchgears/pipelines

The electric field distributions along gas-solid interfaces determine the reliability, lifetimes and sizes of gaseous insulated switchgears/pipelines (GIS/GIL), which also affect the reliability of power systems. In this study, the characteristics of steady and transient electric field distributions were first introduced, followed by the concept of functionally graded materials (FGMs). The development histories of FGM applied in electrical engineering and the related optimisation methods were described in detail. The field regulation effect and fabrication technology of different FGM insulators were also compared. To overcome the limitations of traditional FGM insulators, the design of surface FGM (SFGM) was proposed, together with their preparation methods and electrical performance. Furthermore, the future development prospects of FGM and SFGM insulators for compact GIS/GIL were summarised.

Fabrication and characterization of novel layered materials produced by electroless plating and hot pressing

In this study, two types of three-layer functional graded materials (FGMs) were produced by hot pressing method. For the fabrication of the FGMs, electroless silver coated copper powders with flake-like morphology were used in the first layer on the spherical copper core layer. For the fabrication of Cu–Ag–Cr samples, surface of the electroless silver coated copper powders was coated with chrome. On the other hand, for synthesize of Cu–Ag–Ni compacts, the surface of the electroless silver coated copper powders was coated with nickel. The hardness and electrical conductivity of the Cu core and Cu–Ag samples were approximately 82 HB, 95% IACS and 100 HB, 100% IACS, respectively. The hardness and electrical conductivity of the Ni layer in the Cu–Ag–Ni samples were 125 HB and 76% IACS, while that of Cr layer had 115 HB and 75% IACS in the Cu–Ag–Cr compacts. It was determined that the materials fabricated by using layered metallic powders provide both high conductivity and good oxidation resistance. Results show that the oxidation resistance of Cu–Ag–Cr and Cu–Ag–Ni materials was about 20 times higher than that of conventional copper materials.

Optimization of entropy generation in nonlinear stratified Powell–Eyring fluid with convective boundary conditions

Entropy generation phenomenon is applied in reactors, turbines, natural convection, chillers, functional and regular graded materials. Irreversibility of a system and surroundings in Powell–Eyring fluid is analyzed in this research article. Flow is deformed by an inclined sheet. Measure of irreversibility is also called entropy. Rate of Entropy generation is calculated by considering heat transfer, radiation and viscous dissipation phenomena. Thermal stratification (nonlinear) and heat generation/absorption are incorporated in heat transport while solutal stratification (nonlinear) and chemical reaction have taken part in mass transport. Mixed convection phenomenon is also accounted here. To obtain the analytical solutions of nonlinear and non-dimensional governing equations homotopic analysis method is applied. The behavior of emerging parameters is discussed comprehensively via velocity, temperature and concentration profile. Entropy generation can be minimized by small values of Prandtl number and Eckert number. Thus, these physical phenomena can be used as a cooling agent in various industrial processes.

Microtopography‐Guided Radial Gradient Circle Array Film with Nanoscale Resolution

Distribution of multimaterials at arbitrary positions with nanoscale resolution and over a large area substrate is essential to future advances in functional graded materials. Such stringent requirements are highly beyond the reach of current techniques, although newly developed 3D printing technologies are addressed. Here, a radial gradient circle array film with the distribution accuracy up to ≈18 nm is fabricated by using microtopographic substrate. A mathematical model is developed to guide the distribution of position, size, shape, and type of materials on an arbitrary section for the given morphology of substrate. The periodic electrical and mechanical properties of the radial gradient circle film are identified, which can be beneficial for further functionalization and applications, such as gradient refractive index lenses, microcoils, and microantennas.

Accelerating sample preparation of graded thermoelectric materials using an automatic powder feeding system

In recent years, the development of techniques for the controlled preparation of functional graded materials (FGMs) has become a vigorous research field. In this study, to improve the efficiency and accuracy of sample preparations, an automated feeding system based on gravimetric principles for dry powder with three dosing feeders is designed and realized. The feeding rate and accuracy can be regulated by coordinating the protruded length L (mm) and rotational speed V (r/min) of the feeder stirrer. To demonstrate this automatic sample preparation system, the well-known thermoelectric material BixSb2−xTe3 (x = 0.3, 0.4, 0.5, 0.6, 0.7 and 0.8) is selected and prepared by the developed system, and the composition distribution of the functional graded material is characterized. Experimental results show that the BixSb2−xTe3 (x = 0.3–0.8) functionally graded material crystalizes in the rhombohedral phase after hot-pressing sintering and annealing and the prepared sample has a good gradient composition distribution. This verifies the reliability and accuracy of the feeding system. The concept of samples with a gradient component and application of the automatic powder feeding system could considerably accelerate the research and development of new materials.

Surface functional graded spacer for compact HVDC gaseous insulated system

Electrical field distortion induced flashover is a bottleneck for the stable operation of HVDC gas insulated system (GIS). Functional graded materials (FGM) have attempted to homogenize the electrical field distribution along the gas-solid interface; however, the complicated fabrication process and huge dielectric loss makes it difficult into industrial application. This paper proposed a novel concept as that a spacer with functional surface was fabricated by magnetron sputtering ZnO onto the epoxy resin forming a surface conductivity gradient, namely surface functional graded materials (SFGM). The feasibility was first demonstrated by simulating the electrical field distribution. Two kinds of disc-type spacers with SFGM were designed as linear and inverse proportional annular gradients. Results show that the more uniform electrical field distribution contributes to the improved surface flashover voltage of the SFGM spacer. Therefore, the SFGM epoxy spacer has great potential in HVDC GIS insulation.

Continuous graded Gyroid cellular structures fabricated by selective laser melting: Design, manufacturing and mechanical properties

Functional graded cellular materials (FGCMs) have attracted increasing attentions for their improved properties when compared to uniform cellular structures. In this work, graded Gyroid cellular structures (GCSs) with varying gradient directions were designed and manufactured via selective laser melting (SLM). As a reference, uniform structures were also manufactured. The surface morphology and mechanical response of these structures under compressive loads were investigated. Results indicate high manufacturability and repeatability of GCSs manufactured by SLM. Optimized density distribution gives these structures novel deformation and mechanical properties. GCSs with density gradient perpendicular to the loading direction exhibit deformation behaviours similar to uniform ones, while GCSs with the gradient parallel to the loading direction exhibit layer-by-layer deformation and collapse behaviour. A novel phenomenon of sub-layer collapses is found in GCSs with gradient parallel to the loading direction. Furthermore, mathematical models were developed to predict and customize the mechanical properties of graded cellular structures by optimizing the relative density of each layer. These significant findings illustrate that graded cellular structures have high application prospect in various industries, particularly given the fact that additive manufacturing has been an enabler of cellular structure fabrication.

Micromechanical analysis of the effective properties of lattice structures in additive manufacturing

Lightweight design is an area of mechanical engineering that becomes increasingly important in many industries, as they pursue reduced mass and more efficient parts. A special class of materials for load-bearing structures are metallic cellular materials with cubic unit cells, which can be manufactured conveniently through laser beam melting (LBM). Such materials exhibit a rather complex microstructure and can be analysed using analytical and numerical methods wherein the determination of properties such as relative density, effective elastic and yield strength properties is of special interest. This paper addresses closed-form analytical methods based on beam theories for the determination of the effective properties of additively manufactured microstructures such as lattices, and a comparison with experimental results [1,2] which leads to excellent agreements for relative densities lower than 40%, although results reveal a great dependency on the manufacturing strategy. Lastly, a classification concerning the topology of the cellular units is presented as well in order to help the engineer choose appropriate geometries for specific application purposes. In conclusion, this structural concept may be applied in many fields such as bioengineering and in functional graded materials as they are applied in lightweight engineering.

Frequency analysis of sandwich beam with FG carbon nanotubes face sheets and flexible core using high-order element

ABSTRACTIn the present paper, the vibrational behavior of sandwich beam with a flexible core and anti-symmetric functionally graded carbon nanotubes face sheet is investigated. Carbon nanotubes are considered as functional graded materials in the thickness of the faces and their properties change along the thickness of the face sheets. For the modeling of sandwich beam behavior, the Euler–Bernoulli theory is used for face sheets and the semi-3D elasticity is used for the core, which allowed us to investigate the flexibility of the core. Differential equations of motions are derived using the virtual displacement principle. In this research, a high-order element is presented for solving equations of motion, and then by using this element, the finite element formulation has been extracted and solved. Numerical results are obtained for various boundary conditions, which include simply support, clamped, free-clamped, and simply support-clamped. Also, different volumes of carbon nanotubes have been investigated for different distributions. The results showed that the distribution of the FG-X pattern carbon nanotube leads to the highest natural frequency of the beam. The main conclusion of this research is that, in most cases the FG-O pattern has the lowest natural frequencies and in some cases the FG-Λ pattern has the lowest natural frequencies. In other words, generally, it can be say that the lowest natural frequencies of the sandwich beam with functionally graded carbon nanotubes faces depend on the boundary conditions, thickness ratio, and also the volume fraction of carbon nanotubes. In this paper also the effect of geometric angles of the beam, such as the thickness of the core and face sheet thickness on natural frequency of the system is also investigated.

A review of functionally graded thick cylindrical and conical shells

Thick shells have attracted much attention in recent years as intelligent and functional graded materials because of their unique properties. In this review paper, some critical issues and problems in the development of thick shells made from Functionally graded piezoelectric material (FGPM) are discussed. This review has been conducted on various types of methods which are available for thick shell analysis and mainly focuses on elasticity theories, shear deformation theory, simplified theories and mixed theories since they were widely used in the modeling of FG thick shells. It is expected that this comprehensive study will be very beneficial to everyone involved or interested in the shell models.

Physics-Informed Network Models: a Data Science Approach to Metal Design

Functional graded materials (FGM) allow for reconciliation of conflicting design constraints at different locations in the material. This optimization requires a priori knowledge of how different architectural measures are interdependent and combine to control material performance. In this work, an aluminum FGM was used as a model system to present a new network modeling approach that captures the relationship between design parameters and allows an easy interpretation. The approach, in an un-biased manner, successfully captured the expected relationships and was capable of predicting the hardness as a function of composition.

Aluminium Matrix Composites Fabricated by Friction Stir Processing A Review

Aluminum alloys widely use in production of the automobile and the aerospace becausethey have low density, attractive mechanical properties with respect to their weight, better corrosion and wear resistance, low thermal coefficient of expansion comparison with traditionalmetals and alloys. Recently, researchers have shifted from single material to composite materialsto reduce weight and cost, improve quality, and high performance in structural materials.Friction stir processing (FSP) has been successfully researched for manufacturing of metalmatrix composites (MMCs) and functional graded materials (FGMs), find out new possibilitiesto chemically change the surfaces. It is shown that the technique of FSP is very promising tomodify the microstructure of strengthened metal matrix composite materials. There has thebenefit of decline in distortion and flaw of material when FSP uses instead of othermanufacturing processes. The aim of the present work is to give a review of technology of (FSP)as a method to produce the aluminium matrix composite, and conclusions of this review will bedemonstrated.