Functionally Graded Materials

Functionally graded material (FGM) belongs to a class of advanced composite materials that is characterized by variation in composition, microstructure, as well as properties across the dimension of the material. The properties of FGM are different from any of the individual materials that make up the composite. In this chapter, an introduction to the functionally graded material is presented. A brief background to the functionally graded material and the presence of FGM in nature are also discussed. The chapter ends with a summary.

Functionally graded materials (FGMs) are advanced composite materials that are used to solve a number of engineering problems, as well as in the biomedical implant applications for the replacement of human tissues. These materials are used to eliminate the stress singularities that occur, as a result of the property mismatch in the constituent materials in a composite. There are different types of FGMs that are used today, depending on the type of application, for which the material is intended. In this chapter, the different types of FGMs are presented. The areas of application of this novel material are also explained.

Functionally graded materials (FGMs) are novel engineering composite materials with the properties varying across the volume of a composite material. There are different kinds of manufacturing methods for producing functionally graded material (FGM)—depending on whether it is functionally graded material thin coating or bulk functionally graded material. The various processing techniques of the functionally graded materials, such as the physical vapour deposition process, or the chemical vapour deposition process that are used for the production of thin-film functionally graded material coatings and the processes, such as the powder metallurgy technique and the centrifugal casting method for the production of bulk functionally graded materials. These are discussed in this chapter. The thin functionally graded material coatings are used to improve the surface properties of the coated part or the substrate. The bulk functionally graded materials, on the other hand, are produced when a variation in properties is desired across the whole bulk of the material.

Functionally graded materials (FGMs) are advanced materials that are used to prevent the problems that arise when composite materials with sharp interfaces are used in a harsh working environment, which includes stress singularities due to property mismatchs, poor adhesion, and delamination. A number of conventional manufacturing processes have been used to produce functionally graded materials and some of these manufacturing processes were presented in Chap. 3. Additive manufacturing (AM) technology is an advanced manufacturing process that offers many advantages and possibilities for the fabrication of complex three-dimensional products through material addition, as against the material removal in the conventional machining processes. Some of the AM technologies have the capability of fabricating complex parts that are made with the functionally graded material (FGM) in a single manufacturing process. Some of the AM technologies that are used to produce functional FGM parts include: selective-laser sintering, selective-laser melting, the laser-metal deposition process, and fused-deposition modelling. These AM technologies are presented in this chapter; and some of the research work using these technologies for the fabrication of FGMs are also reviewed.

In this chapter, a case study on the laser metal deposition (LMD) process of functionally graded material (FGM) of titanium-alloy composite is presented. A functionally graded composite material of an important titanium alloy—Ti64/TiC or Ti6Al4V/TiC was fabricated using the LMD process with the different TiC percentage. The TiC of up to 50 W.% on the Ti64 substrate was produced. The first layer of the FGM is 100% Ti64; the next layer consists of a mixture of 95% and 5% TiC. The percentage of Ti64 was continuously reduced by 5% and the percentage of TiC increased by 5% in the mixture for each subsequent layer up to the last layer of 50% Ti64 and 50% of TiC. The microstructure, the mechanical, and the tribological properties of the produced FGM were studied using an optical microscope, a microhardness tester, and the wear tester. The microstructure of the fabricated FGM showed a continuous microstructure, without any sharp interface between the substrate and the deposited layers. To compare the properties of the FGM produced, a traditional composite of Ti64/TiC was also produced, using the LMD process. The properties of the FGM, the composite and the substrate are compared; and the results are presented and discussed in this chapter. The results indicate that the microstructure of the traditional composite showed a sharp interface between the deposited layers and the substrate. The fabricated FGM has improved mechanical and tribological properties, compared with the conventional composite and the Ti64 substrate.

Functionally Graded Materials (FGMs) are a class of advanced engineered materials characterized by a variation in composition or/and a variation in microstructure, with a corresponding variation in properties, such as the mechanical, the thermal, and the electrical properties. The main aim of FGM is to eliminate the sharp interface that is present in the conventional composite materials, where failure mostly begins because of the high stress concentration at this site. The sharp interface is replaced with the gradual variation of composition, as well as the microstructural composition through the non-uniform distributions of the reinforcement phase (s) dispersed gradually, according to their position in the structure. The functionally graded material (FGM) was initially developed for a thermal barrier application, but with the new developments in the industries and modern fabrication processes, the application areas have increased substantially. Such application areas now include those for the general use as structural components in extreme working environments, such as high-temperature and high-pressure environments. Functionally graded material is one of the most efficient materials in achieving sustainable development in industries. In this chapter, the future research requirements for FGMs are presented, together with an extensive summary of this book.