Functionally Graded Materials Samples Research Articles

The effect of Al2O3 content on the microstructure and properties of Al/Al2O3 functionally graded material

This study aims to survey effect of Al2O3 content on the microstructure and also the physical and mechanical properties of Al/Al2O3 which functionally graded material (FGM) that are manufactured by the powder metallurgy technique. For this purpose, five-layer Al/Al2O3 green part samples with Al:Al2O3 different weight ratios were fabricated by cold pressed under 620 MPa. After compaction, the samples were sintered for 1 h in a nitrogen atmosphere at a temperature range between 600 °C and 640 °C. An optical microscope and a field emission scanning electron microscope (FESEM) were used to evaluate the Microstructural characterization. The Archimedes density, Vickers hardness and flexural strength of sintered samples were measured. The highest relative density of 95 % was achieved at a sintering temperature of 640 °C on lower Al:Al2O3 weight ration variation on Al/Al2O3 FGM sample. The hardness values gradually changed in cross section of different FGM samples from 31 HV to 65 HV which depend on the sequence of Al2O3 content in different layers. However, the highest flexural bending strength of 70 MPa was obtained at the sample on Al/Al2O3 FGM included the compositions of 35, 25, 15, 5, 0 wt% Al2O3. By decreasing Al2O3 content along Al/Al2O3 FGM, the changing semi-brittle or brittle to ductile failure mechanism was observed. In some fabricated FGM samples observed a few cracks in the interfacial region between layers with high Al2O3 content.

Temperature distribution in CrMnNi steel-Mg-PSZ functionally graded material during FAST/SPS

Within the scope of this study, the macroscopic temperature distribution in the steady-state temperature condition during Field Assisted Sintering Technique/Spark Plasma Sintering (FAST/SPS) in functionally graded materials (FGM) was investigated. The sample material exhibited a diameter of 50 mm and a thickness of 9 mm. The FGM samples were composed of steel X2CrMnNi 16-7-6 and Mg-PSZ ceramic (MgO partly stabilized ZrO2). By varying the sintering tool setup, a specific modification of the macroscopic temperature distribution within the sample material and the sintering tool was achieved. The aim of the modifications was to optimize the temperature gradients in order to allow for the simultaneous compaction of all FGM layers under ideal circumstances. This involves achieving enhanced ceramic densification without inducing steel melting. Finite element method (FEM) simulations were carried out to get information about the temperature distribution within the sample material and the sintering tool. Furthermore, for this propose, thermocouple temperature measurements were conducted at various measurement points on pre-sintered FGM within the specific sintering tool setup. Additionally, all findings regarding the temperature distribution within the sample material and the sintering tool were compared with results concerning the temperature distribution from the microstructural and mechanical characterization of the center and edge regions of the FGM samples. The FGM samples exhibited a significant increase in temperature from the center to the edge in the radial direction depending on the used sintering tool setup. While the FGM samples showed only minor vertical temperature gradients in the center, the highest vertical temperature gradients were determined at the edge of the FGM sample using an asymmetric sintering tool setup.

Characterization of a functionally graded material produced using a new designed blender

Abstract One of the techniques widely used for fabrication of FGMs (Functionally Graded Materials) is powder metallurgy. However, producing a FGM with smooth gradient in its constituents mixture has remained a challenge yet to be met. The purpose of this research is design and manufacturing a blender for producing a functionally graded material with smooth gradient of its constituent materials. The blender was used to mix magnesium and titanium dioxide to produce Magnesium/titanium dioxide FGMs. The powder mixture was then compacted by Instron, drop hammer, and split Hopkinson bar at 600 °C. The microstructure and relative density of the functionally graded samples fabricated at different strain rates were studied in this work. SEM images clearly demonstrated a continuous and functional distribution of Mg and TiO2 particles in the produced FGM samples. It was also shown that increasing the compaction loading rate resulted in a higher relative density in the FGM samples. The maximum relative density (92%) was observed for the samples produced by Hopkinson bar. This level of density was 7% and 17% higher than the densities of the samples fabricated using drop hammer and Instron, respectively. The improvement of relative density in dynamic compaction methods is attributed to the increased compaction pressure and process being adiabatic.

Parametric optimization and impact behaviour of AA7075/SiC FGM fabricated by hot compaction powder metallurgy process

The current investigation focuses on developing multilayered AA7075/SiC functionally graded material (FGM) with high hardness and impact toughness. The FGM was fabricated using a hot compaction powder metallurgy process. Critical process parameters such as compaction pressure, temperature, and holding time were optimized using Taguchi's L9 orthogonal array coupled with grey relational analysis. Charpy impact and Vickers hardness tests were performed to measure the toughness and microhardness of the specimens, respectively. The fabricated FGM samples were analyzed using SEM, EDS, and XRD to determine their morphology, fracture surface, elemental composition, and evolved phases. The results showed that parameter setting with a compaction pressure of 400 MPa, a temperature of 400 ℃, and a holding time of 15 min yielded the highest grey relational grade. The optimized parameter revealed an improvement of 25.05% and 28.08% in toughness and microhardness, respectively, compared to run no. 1. The microstructural analysis of the sample with optimum properties showed that the SiC reinforcement particles were evenly dispersed throughout the AA7075 matrix, and there was strong interfacial bonding between the layers of FGM. It was found that the mixed mode of brittle and ductile fracture can absorb impact energy before failure.

Machinability of fabricated Al/Mg-based functionally graded material with Pb interfacing foil using liquid processing route

The present experimental study attempts to develop functionally graded materials (FGMs) using aluminum alloy 7075 and magnesium alloy AZ91D using a gravity die-casting process. The said non-conventional FGM samples with lead (Pb) interfacing foils were made to estimate the machinability during the electric discharge machining (EDM) process. In particular, an attempt is made to determine the effects of input parameters such as peak current(Ip), gap voltage(Vg), and pulse on time (Ton) on the responses. These results confirmed that the responses, namely, material removal rate (MRR) and electrode wear rate (EWR), are observed as low for the FGM sample made with lead foil when compared with pure Al7075 and AZ91D.

Tribological analysis of laser deposited SS316L/Co27Cr6Mo functionally graded materials using adaptive neuro-fuzzy inference system

Image processing, power engineering, robotics, industrial automation etc., have all found successful uses for artificial intelligence (AI) techniques such as artificial neural networks (ANN) and neuro-fuzzy logic (FL). In this study, an adaptive neuro-fuzzy inference system (ANFIS) modelling of machine learning (ML) has been implemented to estimate the tribological properties of functionally graded materials (FGM). These FGMs were developed using a direct energy deposition (DED) technique of additive manufacturing (AM) from SS316L and Co27Cr6Mo alloys. The input data for this ANFIS modelling is acquired from the experiments done on FGM samples using the Pin on Disc (PoD) apparatus. The main objective of this work is to predict the tribological parameters of FGM samples by creating a data-driven predictive model called ANFIS. From the findings, the ANFIS was found to be the efficient method to estimate the wear rate of FGM samples.

A novel approach to develop and characterize bi-directional aluminum-copper functionally graded material

A substantial increase in research activity on functionally graded materials (FGMs) was foreseen in the past few decades owing to their high strength and stiffness, design flexibility, and multi-functional features. However, the majority of the literature was confined to uni-directional (1D) gradation in material constituents. As a result, their usage was limited to a few advanced applications such as aircraft frames and shuttles, propulsion systems, and machine elements wherein the temperature is distributed along two or more directions. Thus, there is a demand for FGM that shows property variations in bi (2D) or tri (3D) directions. The present research work is an attempt made to design and develop bi-directional functionally graded material (2D FGM) with aluminum (Al) and copper particles. A 2D FGM sample in the form of a rectangular slab having material variation along x and y directions was produced through powder metallurgy using a 3D-printed cuboid. Variations in microstructure and hardness confirm the material gradation in two directions. Change in erosion wear at different locations was also observed on the sample. Furthermore, worn-out surfaces using scanning electron micrographs revealed a ductile fracture.

Tribological behaviour of Ti/HA and Ti/SiO2 functionally graded materials fabricated at different strain rates

Functionally graded materials (FGMs) have found extensive applications in the biomedical industry, due to their excellent mechanical and tribological properties. However, new FGM fabrication techniques are yet to be examined for possible enhancements in their properties. This study investigates the tribological properties of Titanium/Hydroxyapatite (Ti-HA) and Titanium/Silicon oxide (Ti-SiO2) FGM samples fabricated by three die compaction techniques for the application of dental implants. The constituting powder particles were functionally dispersed and mixed using a newly-designed mixer and consolidated by hot dynamic and quasi-static compaction techniques at three different strain rates. Microstructure, hardness, wear resistance, wear penetration depth, and friction coefficient of the FGM samples were then studied in this work. Optical microscopy images exhibited smooth dispersion of powders conforming to a linear grading function. Vickers hardness values of the FGM samples was found to be directly proportional to the strain rate and inversely proportional to the content of the reinforcing phase (HA or SiO2). Higher strain rate also resulted in higher wear resistance and lower wear penetration depth in all FGMs, with the highest wear resistance being observed in the samples prepared using the Split Hopkinson Bar. Similarly, the coefficient of friction was also shown to be the lowest in Ti-HA samples prepared using Split Hopkinson Bar. Further, microscopic observations revealed that adhesion, delamination and abrasion as the dominant wear mechanisms in all FGM samples. It was concluded that the Ti-HA sample produced by the SHB method enjoyed superior tribological properties, being comparable to that of natural human teeth.

Influence of Cu and Al interfacing foil on Al7075/A360 FGMs fabricated by gravity casting

Functionally graded materials (FGMs) are innovative and manipulated modern engineering materials with customized performance or function due to the spatial gradation in morphology. The present research work attempts to fabricate the FGMs with and without interfacing layers by adopting the gravity casting methodology. The fabricated FGM samples were investigated for microstructural and mechanical characteristics, namely, with Cu and Al foils and without an interfacing layer. The FGM samples with Cu, Al foils, and without interfacing foils exhibited microhardness values of 85Hv, 88Hv, and 92Hv, respectively. The microhardness of the fabricated FGM sample without interfacing foil, compared to the FGM sample made with interfacing foil, namely, Cu and Al, is observed as high. The said result may be due to the presence of the intermetallic compounds in the absence of interfacing foil which is confirmed by Scanning Electron Microscope (SEM) and Energy-dispersive X-ray spectroscopy (EDS)analysis.

Microstructural examination and mechanical characterization of Ti/HA and Ti/SiO2 functionally graded materials fabricated at different loading rates

Functionally graded material (FGM) is a heterogeneous composite material that consists of two or more constituent phases with continuous changes in the microstructure from one material to another with adjustable through thickness properties. FGMs are utilized in medical applications, such as dental implants, due to their excellent mechanical and tribological properties. In this study, the powder metallurgy method (PMM) is used to produce Titanum/Hydroxyapatite (Ti/HA) and Titanum/Silicon dioxide (Ti/SiO2) FGM samples. A new designed blender is employed to mix the particles constituting the FGM samples. The mixed particles are then compacted at different strain rates from quasi static loading, using a universal testing apparatus, to dynamic loadings, using a drop hammer and a split Hopkinson bar. The effect of strain rate on mechanical properties and microstructure of specimens is studied by conducting various tests such as indentation and compression tests and by microstructural examinations using scanning electron microscopy (SEM). The results showed that the relative density of fabricated specimens was increased with the increase of the strain rate. The highest relative density for the Ti/HA composite was achieved for the specimens produced by the split Hopkinson bar. For both of Ti/HA and Ti/SiO2 FGMs the maximum indentation force and indentation energy, obtained from the load-penetration depth curve, and the ultimate strength, obtained from the compressive stress-strain curve, were increased with the increase in strain rate. The results also indicated that the increase in volume fraction of reinforcing ceramic particles (HA or SiO2) led to the decrease of the maximum indentation force and indentation energy.

Design of an additively manufactured functionally graded material of 316 stainless steel and Ti-6Al-4V with Ni-20Cr, Cr, and V intermediate compositions

This study presents a method for designing a computationally informed gradient pathway to fabricate a functionally graded material (FGM) with terminal alloys of 316 stainless steel (SS316) and Ti-6Al-4V via directed energy deposition additive manufacturing with powder feedstock. The grading is accomplished through the introduction of intermediate elements and alloys (Ni-20Cr, Cr, and V) to avoid the brittle Fe-Ti intermetallic phases that form in the direct liquid phase joining of Ti-alloys and stainless steels. Using a combination of equilibrium calculations and Scheil-Gulliver simulations, a compositional pathway was designed to avoid deleterious phases. FGM samples were fabricated and experimentally characterized to determine the viability of the pathway. A change in phases from fcc to bcc was predicted to occur within the Ni-20Cr/Cr gradient region, and this was validated through experimental characterization. No detrimental phases (intermetallic, Laves, or σ phases) formed along the gradient path, demonstrating a successful computationally-informed design and fabrication of an FGM from SS316 to Ti-6Al-4V.

Experimental evaluation of additively deposited functionally graded material samples-microscopic and spectroscopic analysis of SS-316L/Co-Cr-Mo alloy

<abstract> <p>The gradual and uniform variation in the composition of the material, generally two, is called functionally graded materials (FGM). These FGM are used in practical applications to advantage both material properties. Several methods are used to fabricate the FGM components. The current article is research on the direct energy dispersive technique of 3D Printing employed for depositing the SS316L and Co-Cr-Mo alloy FGM samples. L9 orthogonal array of Taguchi method is used. Process parameters like laser power, powder feed rate and scan speed have been used for deposition. Their structural properties are analysed using scanning electron microscopy, X-ray diffraction, element dispersive technique, and Fourier transform impedance spectroscopy. The results reveal that defect-free samples were deposited, and all the samples have Body Centered Cubic structure except one. Good elemental bonding was observed between SS316L and Co-Cr-Mo alloy.</p> </abstract>

Micromechanical modeling and experimental characterization for the elastoplastic behavior of a functionally graded material

Functionally Graded Materials (FGMs) are characterized by the distribution in composition and structure gradually over volume, which were recently designed and developed as a key component of a multifunctional building envelope for the high performance of energy efficiency. It was realized by mixing aluminum particles and fine High-Density Polyethylene (HDPE) powders through a vibration-sedimentation process. To investigate the elastoplastic behavior of FGMs, an elastoplastic model based on micromechanics with pairwise particle interactions is developed in this study. The particle phase is assumed to remain in its linearly elastic state while the matrix phase undergoes elastoplastic deformation. The corresponding yield function for the FGMs is investigated, where the pairwise interaction and probabilistic spatial distribution of particles are utilized to accommodate the gradation of particle volume fraction. Accordingly, the overall elastoplastic behavior of FGMs is established through the microscopic homogenization. The proposed algorithm is validated with uniaxial compression test of FGM samples, where the authentic particle distribution is captured statistically through image processing method. Finally, the effect of volume fraction distributions on the overall effective elastoplastic behavior of FMGs is investigated.

Experimental study on mechanical properties of Ni/TiO2 FGM processed by pressureless sintering technique

In the present work, an experimental investigation and characterization of Functionally Graded Materials (FGMs) is carried out. The Nickel (Ni) and Titanium dioxide (TiO2) materials are taken as principal materials and the powder metallurgy technique is used for the preparation of specimens. The Nickel powder has a particle size of 20 μm with more than 99% purity and Titanium dioxide powder having 35 μm particle size with more than 99% purity is used for this study. The FGM specimens are prepared with five layers, with pure Nickel on one side and pure Titanium dioxide on opposite side of the specimen; and the three intermediate layers comprising of mixture of Nickel and Titanium dioxide. The five layered FGM samples are prepared with one inch diameter round die and the compacted samples are heated up to 1200°C in an inert gas (argon) atmosphere. The microscopic result shows that the microstructure of Ni/TiO2 FGM has varied layer-by-layer and the interface between the layers are observed. As a part of mechanical characterization, both green and sintered FGM sample densities are measured for each layer of the sample. The Rockwell hardness test method is used to find the hardness of the each layer in the samples. Linear shrinkage of the specimen is calculated with the help of green sample dimensions. The Compression test is conducted on the sintered specimens by using universal testing machine; stress-strain behaviour and maximum stress reported.

Mechanical characterisation and machining evaluation of ceramic cutting tools functionally graded with six layers

Functionally graded materials (FGMs) are composites graded in one or more directions by the mean volume fraction variation of their constituents in a continuous or stepwise design. The objective of this study is to apply the FGM concept to ceramic cutting tools to widen its application range. Thus, two cutting tool materials were selected: cemented carbide, owing to its higher toughness, and alumina-based ceramic, owing to its high wear resistance at elevated temperatures. Ceramics based on alumina were functionally graded with cemented carbide and sintered using the spark plasma sintering technique. The thermal residual stresses were predicted; additionally, the microstructure, relative density, and Vickers hardness and fracture toughness for the alumina layer were evaluated, and flexural strength and machining tests were conducted. From the results, cracks were not observed in the microstructure and full density was obtained. In general, the hardness and fracture toughness values were close to those in the literature. A flexural strength improvement of at least 50% on FGM samples was observed in comparison to homogeneous ceramic ones. The FGM cutting tools supported approximately 1000 N of machining force without catastrophic failure when turning martensitic stainless steel into a conventional lathe. The values of surface roughness (Ra and Rz) agree with those in the literature under similar cutting and geometry conditions.

Study on Strength and Stiffness of WC-Co-NiCr Graded Samples.

This work deals with the investigation of the strength and the stiffness of samples built of step-variable functionally graded material (FGM). The considered FGM samples consist of two main components: WC and NiCr with some content of Co as a conjunction of structure. The samples were fabricated on the basis of the detonation gun layer deposition method which is regarded as a novelty in the case of FGM production. The analyzed samples possess a finite number of layers with different varying fractions of each constituent across the wall. The basic tests of bending were conducted to assess the influence of used components in adequate proportions on the stiffness and the total strength in bending. In addition, to validate the numerical approach, simulations of samples under similar loads with truly reflected material distributions were carried out. The material properties of components were determined due to micro-nano-hardness by instrumental indentation techniques. The numerical calculations were performed with the use of the material characteristics for each material and with a consideration of large deflections. Furthermore, by means of an electron microscope, the composition of materials and distribution of chemical elements across the thickness of samples were examined. This paper reveals the experimental results of FGM samples manufactured by detonation gun layer deposition which allows the creation of layer by layer moderately thin-walled structures. It was shown that the indentation method of a determination of Young’s modulus gave higher values in comparison to values attained in the bending test. Moreover, it was stated that a modelling of FGM still requires the study of each layer separately to clearly predict the strength of the whole FGM structure.

Junction Characterization in a Functionally Graded Aluminum Part.

Aluminum alloys are widely used to produce automotive components, thanks to their great mechanical properties–to–density ratio. Engine components such as pistons are conventionally produced by casting of Al–Si eutectic alloys (Silumin alloys) such as EN AC 48000. Due to the harsh working conditions and the lower ductility if compared to aluminum–silicon alloys with lower silicon content, pistons made of this alloy are prone to fatigue failures in the skirt region. In order to overcome such limits, the use of a Functionally Graded Material (FGM) in the production of a piston is proposed. The adoption of a functionally graded architecture can maximize the properties of the component in specific areas. A higher level of thermal resistance in the crown of the piston can be achieved with EN AC 48000 (AlSi12CuNiMg), while higher elongation at rupture in the skirt region would be conferred by an EN AC 42100 (AlSi9Mg0.3). The FGM properties are strictly related to the metallurgical bonding between the alloys as well as to the presence of intermetallic phases in the alloys junction. In the present article, the characterization of gravity casted FGM samples based on Al–Si alloys with respect to microstructure and mechanical testing is presented, with a specific focus on the characterization by impact testing of the joint between the two alloys.

Fabrication and characterization of nHA/titanium dental implant

In this work, functionally graded material (FGM) of Titanium/nano-hydroxyapatite were fabricated using powder metallurgy method as dental implant and their biocompatibility, static strength and fatigue characteristics in different volume fraction exponents were investigated using experimental and numerical methods. For producing hydroxyapatite powder, for the first time, drilling method was used instead of ball milling. First, cow bones were drilled using a 2 mm drill and the resulting powder was converted to nanostructured hydroxyapatite through specific heat treatment. Then FGM of titanium/nano-hydroxyapatite at different volume fractions and features such as bioactivity, hardness, microstructures, and fatigue strength of the FGM implants were investigated using empirical and numerical methods. The effect of changes in volume fraction exponents on each of these parameters was also investigated. According to the results, biocompatibility of titanium/hydroxyapatite FGM dental implants was confirmed after submerging in simulated body fluid (SBF) using scanning electron microscope (SEM) and ion concentration measurement (ICP) methods and were obtain that with increase in the soaking time in SFB, the rate of formation of bone-like apatite on the surface of the sample had an increasing trend and the concentration of calcium and phosphorous ions in the solution decreases which shows the formation of apatite. The samples were also in the safe zone after fatigue loading using finite element analysis. The result of numerical analysis of fatigue life for the fabricated dental implants showed that after 5 years, just %45 of the critical layer life which is pure HA remained; it means the fabricated dental implant can be work at least for 9 years without fatigue fracture. The effect of volume fraction exponents of FGM samples on a change gradient of mechanical properties and biocompatibility was investigated and according to the results, volume fraction exponent of N = 2/3 showed the best performance.

Characterisation of four-layered Al-Al2O3 functionally graded material prepared through powder metallurgy and pressureless sintering

In this research study, four-layered aluminium-aluminium oxide (Al-Al2O3) functionally graded material (FGM) was prepared through powder metallurgy (PM) route considering 0%, 10%, 20% and 30% weight percentage of ceramic concentration. The sintering temperature and time used are 620°C and 120 min following two-step sintering cycle. The prepared FGM samples were characterised by densification and shrinkage. Microstructural and elemental analyses were carried out by scanning electron microscopy (SEM) and energy dispersive X-ray spectroscopy (EDS). Mechanical characterisation was carried out using Vickers microhardness tests. It was observed that cylindrical FGM specimens (green compact) were successfully prepared and diameter of cylindrical structure was decreased after sintering process. It was also observed that there was no existence of macro-crack or micro-crack within the individual layer or at the interface and smooth transition occurred from one layer to next layer. Elemental analyses confirmed the gradient distribution of material composition layer by layer.

Microstructure and properties of functionally graded materials Ti6Al4V/TiC fabricated by direct laser deposition

PurposeThis paper aims to manufacture Ti6Al4V/TiC functionally graded material (FGM) by direct laser deposition (DLD) using Ti6Al4V and TiC powder. The objective is to investigate the effect of process parameters and TiC composition on microstructure, Vickers hardness and mechanical properties.Design/methodology/approachPowder blends with three different volume percentages of Ti6Al4V and TiC were used as feed material for DLD process. Five experiments with different values of laser power and scan speed were conducted to investigate the effect on microstructure and Vickers hardness for different compositions of feed material. Mini-tensile tests were performed to evaluate the mechanical properties of the FGM samples. Digital image correlation (DIC) was applied to estimate Young’s modulus and ultimate tensile stress (UTS) of heterogeneous material.FindingsThis paper indicates that primary carbide, eutectic carbide and un-melted carbide phases are formed in the FGM deposit. As the energy density was increased, the primary and secondary dendrite arm spacing was found to increase. As TiC composition was increased, Young’s modulus increased and UTS decreased. The dendritic morphology of primary TiC growth was expected to cause low resistance for crack propagation, causing lower UTS values. Tensile specimens cut in vertical orientation were observed to possess higher values of Young’s modulus in comparison with specimens cut horizontally at low carbon content.Originality/valueCurrent work presents unique and original contributions from the study of miniature FGM tensile specimens using DIC method. It investigates the effect of specimen orientation and TiC content on Young’s modulus and UTS. The relationship between energy density and dendritic arm spacing was evaluated. The relationship between laser power and scan speed with microstructure and Vickers hardness was investigated.