Experimental Studies on Polyester - Titanium Functionally Graded Materials

In the present work an attempt has been made to fabricate Polyester based Titanium Functionally Graded Materials. Titanium particles are produced through conventional filing operation, by rotating Titanium rod of 50 mm diameter on lathe machine. Filing operation has been carried out at 650 rpm using a course file. The obtained powder was demagnetized to remove the foreign material related iron. Powders are subjected to sieving operation to get desired range of particle size i.e 300 microns. FGMs with 2.5 gm, 5 gm and 10 gm titanium by weight are fabricated through sedimentation technique. The quality of the FGMs is examined through liquid penetrant non-destructive testing. FGMs are tested and analyzed from density, hardness and optical microscopy point of view. Obtained results are compared and analyzed.


1.Introduction
The scientific community has created a great deal of novel materials in today's inventive environment.High strength/weight and stiffness ratio composite materials that are the lightest in weight have found effective uses in the aircraft industry and other engineering fields.Functionally graded materials (FGMs) are a novel class of composite materials that have garnered a lot of attention lately.By layered mixing two materials with distinct thermo-mechanical properties and volume ratios, one can create Functionally Graded Materials (FGM) by progressively altering each layer until the final layer has the highest volume/weight ratio of the first phase and only a small number of particles from the second phase.In order to maximize heat resistance and mechanical properties, functionally graded materials (FGMs) distribute the material functions throughout the material body.This makes them perfect for spacecraft, where one side may be exposed to extremely high temperatures and the other side to extremely low temperatures.Many of the analytical techniques created for conventional composites with distinct phases may not be directly applicable to FGMs due to the constantly changing material properties that are a characteristic of FGMs.Functionally graded materials have gained a lot of attention lately due to their many uses in industries including energy, defense, aerospace, electronics, and medicine.The type of processing method employed determines the final characteristics of FGM.The two primary processes in the creation of FGMs are consolidation, which entails placing the graded structure on a substrate, and nonhomogeneous spatial gradation of the component parts.FGMs with compositional gradients are created using a variety of techniques.The segregation phenomenon, which is brought on by the different specific gravities of the alloy liquids and reinforcement particles, makes it possible to produce Functionally Graded Materials (FGMs) with gradient distributed reinforcement particles using centrifugal casting.By managing the solidification process, the gradient can be preserved.
IOP Publishing doi:10.1088/1742-6596/2765/1/012013 2 Metal and ceramic-based systems have been the subject of the majority of research.Sedimentation is a specific process used in the production of particle reinforced FGMs.The difference in density between the particle and the matrix is the basis for the sedimentation process.If gravitational force is used properly, a graded structure can be created.Hassanin and Jiang [1] developed Multi-layer FGMs using highly stable alumina/zirconia suspensions.Suspension stability was achieved by controlling both pH and the concentration of dispersant with respect to the powder weight.
Materials with varying functional grades are useful in a wide range of applications.FGMs made of Al2O3/Y and ZrO2 are utilized in medical applications like knee or hip prostheses [2].The energy industry [3], high current connectors, sensors, and capacitors [4][5][6] all use graded dielectrics.When Youngming et al. [7] studied the Al2O3/Ti3SiC2 FGM system, they found that as the weight percentage of Al2O3/Ti3SiC2 content increased, the FGM's electrical conductivity increased as well.Additionally, it was discovered that the Al2O3/Ti3SiC2 content of the FGM directly correlated with its increased hardness.Afzal et al. synthesized a bio FGM zirconia, hydroxyapatite, and alumina matrix and examined its structural integrity [8].Das et al. [9] summarized current advances in engineering and the processing of materials have led to a new class of graded multilayered materials called functionally graded materials (FGMs).This article looks at the best processing technologies and applications of the advanced, high quality products generated in FGMs.It also highlights about the future research scope in FGMs.
According to Jha et al. [10], the tailored structural properties, including morphological properties, are the primary advantage of FGMs over other composites.When comparing FGMs to non-graded FGMs, Pan E found that the residual stresses were lower in FGMs [11].Thermal barrier coatings are used in gas turbine engine components and tungsten-coated dampers, according to research by Kim, J.H. et al.The thermal mismatch between the coating material and the base, however, presents one of the main obstacles in the development of thermal barrier coatings [12].Andrew et al. [13] demonstrated that thixotropic casting successfully produced regular gradients in hydroxyapatite-316L stainless steel biomaterial FGMs.An impeller dry blending (IDB) case study in this chapter showed the potential of IDB for producing excellent linear gradients in metalceramic FGMs.A hydrostatic shock forming case study showed its potential as a densification method for continuous bulk FGMs for which the metal and ceramic components have greatly differing melting points.Ti-TiB FGMs were fabricated using pressure-assisted densification for ballistic applications.The disadvantages of residual stresses were addressed by the developed Ti-TiB FGMs.It has been reported that mechanical characteristics like the modulus of elasticity, thermal coefficient of expansion, and ballistic performance are significantly impacted [14].Functionally graded polyster was created, and its mechanical properties were examined by Lucignano and Quadrini [15].
Spark plasma sintering (SPS) is one of the most popular solid phase methods for fabricating FGM [16][17][18].The SPS technique is useful for producing nano products, metal matrix composites, fiber reinforced metal matrix composites, intermetallic compounds, FGMs, and a wide range of other materials with high wear resistance, including sandblasting nozzles [19].The SPS process is appropriate for the creation of FGMs because it can produce varying phase melting temperatures.Compared to other conventional techniques, the SPS technique offers comparatively easy activation and purification of the powders.Current activated tip based sintering was explained by EI -Desounky et al., who also demonstrated a direct correlation between green density and FGM size [20].Using phenolic resin and nanofibers and a powder metallurgy process, Bafekrpour et al. [21][22][23] created polymeric functionally graded nano composites and studied their viscoelastic and thermo mechanical properties.Furthermore, their findings showed that the composites with the highest percentage of graphite in the top and bottom layers and the lowest percentage in the center showed improvements of about 97% in thermo mechanical properties and 34.7% in creep resistance.Ashish et al. [24] presented an overview of FGM is presented regarding the concept, need, and manufacturing methods used to manufacture FGM to date and mathematical models representing the FGM effective properties are discussed.Current trends regarding the application of AM methods on manufacturing FGM are discussed from both the academic and industrial points of view.Watanebe et al. [25] investigated the viability of using centrifugal casting to create Nialuminide steel clad pipe.Jedamark et al. [26] used the electrochemical gradation technique to fabricate the W/Cu FGM system.The manufactured FGM produced the necessary chemical gradient for the FGM and revealed that certain process parameters, including electrolytic porosity, resistivity, density, and geometry, had an impact on the morphological structure and shape.Ankush Mehta et al. [27] proposed an FGM using two separate materials in the form of adhesive and silicone-based gels (A and B).The 3D bio-printer was used for developing an FGM in the form of tensile specimens and mechanical, and electrical results for the developed FGM were highlighted.Also, two possible combinations of FGM (A + B, B + A) in the same weight proportion were explored in the 3D bioprinter, and the variation in the thickness or non-uniformity in the shape was observed which led to the change in dielectric properties of FGM.
Wilson and Shin [28] used the laser deposition technique to create Ni-based FGMs.It was stated that adding more TiC powder to Inconel 690 powder would result in a more refined structure.A liquid precursor dissolved in a liquid solvent is used in the straightforward chemical solution deposition (CSD) thin film processing method.The mechanical behavior of ZrO2/Al2O3 and WC/Co, which were created using the electrophoretic deposition technique, was investigated by Put et al. [29].For the ZrO2/Al2O3 system, the hardness value variation was found to range from 13.5 GPa at the core to 19.5 GPa at the edges; in contrast, for the WC/Co FGM system, the hardness value variation ranged from 21 GPa to 9 GPa from the core to edges.The Al2O3-W FGM system was created by Katayama et al. [30] by employing the slip casting process and then sintering it at a temperature of 18,000 C. A higher percentage of dispersant was found to increase the raw materials' dispersibility.Additionally, a gradual change in W's grain size was noted along with the composition of the layer.The gel casting technique is one of the most popular methods for creating intricately shaped ceramics with a dense and porous structure.One method for processing colloidal materials that has a high yield at a low cost, a high green capacity, and a short formation time is gel casting.Al2O3/ZrO2 FGM system was created by Park et al. [31] by dip coating substrates that had been prepared using the gel casting technique.Mechanical and microstructural characteristics of the manufactured FGM system were described.There was a smooth transition in hardness from the substrate to the outer layer.Ion plating, chemical vapour deposition, and plasma spraying are a few examples of gas-based techniques.In the case of vapour deposition systems, the gradient composition of the deposited products is determined by the control of the production system and the ratio of the phase's reaction.For coating applications, compositional gradient composites made using liquid phase techniques are widely used.The type of processing technique used determines the final property of the FGM.The primary challenges in the production of FGMs are the non-uniform spatial gradation of the component parts and consolidation, which entails placing the graded structure on a substrate [32].Metal and ceramic-based systems have been the subject of the majority of research.Consequently, there aren't many research studies on the processing methods for polymeric-based FGMs.
Metal and ceramic-based systems have been the subject of the majority of study.As a result, there are few research reports on the processing methods for FGMs based on polymers accessible.Hence, in the present work an attempt has been made to fabricate polyester based titanium FGMs through sedimentation technique and evaluating density, microstructure and hardness properties.

Materials and Methods
In the present work, polyester resin used as matrix material and titanium powder particles as reinforcement material.Table 1 and 2 shows the properties of pure polyester and titanium.

Production of Reinforcements (particles)
Titanium particles are produced through conventional filing technique.Figure 1 shows the production of powder particles.Titanium rod of diameter 50 mm was subjected to filing operation on a lathe machine using course file with an operating speed of 650 RPM. Figure 2 shows the obtained powder particles.The produced powder is subjected to demagnetization in order to remove ferrous particles.In order to select certain range of particles, the obtained powder was subjected to sieving for 10 minutes.Figure 3 shows the sieving operation.The Ti particles are sieved up to 300 microns as per IS 460:1982 standards.

Fabrication of FGMs 2.3.1 Sedimentation Method
PVC pipe of diameter 2.4 cm and length 4.2 cm is taken for manufacturing of polyester -Ti FGM's by sedimentation technique.Sieved Ti particles are taken with varying percentages of 2.5, 5 and 10 gms by weight for fabricating of FGM's.Measured Ti (2.5gm) particles are mixed with polyester and poured in the prepositioned pipe which is placed in vertical direction.After pouring, settling time of 1hr to 2 hrs is allowed for sedimentation.Figure 4 shows the process of sedimentation, similar procedure was adopted for the production of polyester-5Ti and polyester-10Ti FGM's.For the purpose of comparison pure polyester (without titanium powder) was also fabricated under similar processing conditions.Figure 5 shows the obtained specimens with varying percentages of Ti, i.e., pure polyester, 2.5gm Ti particles, 5gm Ti particles, 10 gm Ti particles.

Testing
The fabricated FGMs were subjected to the following testing for quality estimation and properties evaluation.

2.4.1Dye penetrant test
Any homogenous substance can be inspected using the penetration approach.The current test makes use of both red penetrant and white developer.The test section is now treated with a dry powder after the penetrant has seeped in.This powder expands the region of penetrant indication by pulling the penetrant from the defect and acting as a sponge.

Density
After the fabrication, each sample was weighed and their densities were estimated using the following formula Ρ = Mass/Volume

Hardness Test
All the samples were subjected Vickers hardness test both on top and bottom surface at a constant load of 0.5 kg.Three readings were taken on each sample and average values are reported.

Microscopic examination
The fabricated samples are subjected microscopic examination after following the sequential polishing techniques.Both top and bottom surfaces were subjected microscopic examination inorder to witness the presence of titanium particles and as well as polyester base.

Density
Table 3 shows the summary of densities obtained for Pure polyster, 2.5gm Titanium, 5gm Titanium and 10gm Titanium FGMs. Figure 7 shows the variation of densities for pure polyester, 2.5Ti, 5Ti and 10Ti FGMs.The obtained values are 1.33 gm/cm 3 for 2.5Ti FGM and 1.40 gm/cm 3 for 5Ti FGM and 1.59 gm/cm 3 for 10Ti FGM.Increase in density can be observed with respect to Titanium increment.This is true because the Titanium density is higher as compared to pure polyester as a result FGMs are with high density.Sedimentation process aided in more densification, hence the incremental values.Rate of increment in density is also proportional to the addition of Ti content in polyester resin.For a given volume, the increment in density depends on how effectively the Ti powder particles have been doped.From the results it is evident that the doping was effective and sedimentation technique is successful.9 shows the Vickers hardness values for 2.5 gm FGM. Figure 8 represents the pure polyester side, where as Figure 9 reveals the hardness on titanium side.It is understood that pure polyester side is soft, depth of indentation is more and hardness is less.However, hardness value is 613HV at Ti side.For a given load, small impression of indenter indicates hard material, and the opposite is true for large impressions.Figure 12 and Figure 13 shows the hardness images for 10Ti FGM. Figure 12 shows the value corresponding to polyester side and Figure 13 shows the value corresponding to Ti rich side.Ti rich IOP Publishing doi:10.1088/1742-6596/2765/1/01201310 side the hardness value is 897HV.This is highest as compared to 2.5 Ti and 5 Ti FGMs.The material's elastic limit, or yield strength, determines hardness to a greater extent than the work hardening coefficient.The modulus of elasticity also has an impact on hardness.However, the resin side the value is much low i.e. 103 HV.

3.4Optical Microscopy
Figure 14 shows the optical microscope image of pure polyester resin.Since it is the image taken only on polyester there are no traces of metallic inclusions.i.e. titanium powder.Figure 15 shows the optical microscope image of 10 Ti FGM on rich side.It can be seen that dominant metallic presence of titanium powder.However, rare presence of polyester that was impregnated in to metallic zones can also be witnessed.Figure 16 shows the optical microscope image of 5 Ti FGM on rich side.The presence of titanium powder evidence is less as compared to 10 Ti content FGM.Increased content of polyester which appears to be deposited/ covered the presence of Ti powder.This can be attributed to good bonding between powder particles makes the FGM more strong and sustainable.Figure 17 shows the optical microscope image of 2.5 Ti FGM on rich side.It can be seen that poor evidence related to metallic titanium powder presence.However, presence of polyester can also be seen which appears to be in smoke colour deposited on metallic surfaces.

Figure 6
shows the sample obtained from liquid penetrant test.The red colour indicates the cracks or flaws on the specimen.The defects in the specimen finds out after the developer (white colour) has IOP Publishing doi:10.1088/1742-6596/2765/1/0120137 been applied to the specimen.It is evident from the figure that except at the tip there are no significant defects that are present in the specimen.

Figure 12 .
Figure 12.Hardness values of Pure Polyester Side.

Figure 14 .
Figure 14.Optical microscope image of pure polyester resin.

Figure 17
Figure 17 Optical microscope image of 2.5 Ti FGM.

1 )
Polyester based Titanium with varying weight fractions are successfully fabricated using sedimentation technique.2) Liquid penetrant NDT method revealed that the samples are of good quality without any cracks and porosity.3) With increasing titanium content, increased values of hardness has been observed from polyester rich surface to titanium rich surface.4) Improved densities are observed for 2.5Ti, 5Ti, 10Ti FGMs with increasing titanium content.5) Optical microscope images corroborate the concept of functionally graded materials.

Table 1 .
Properties of Polyester

Table 2 .
Properties of Titanium

Table 3 .
Summary of densities for FGMs S.