**New Processing Routes for Functionally Graded Materials and Structures through Combinations of Powder Metallurgy and Casting**

Takahiro Kunimine, Hisashi Sato, Eri Miura-Fujiwara and Yoshimi Watanabe

Additional information is available at the end of the chapter

http://dx.doi.org/10.5772/62393

#### **Abstract**

New processing routes for metal-matrix functionally graded materials (FGMs) and structures through combinations of powder metallurgy and casting are described in this chapter. Centrifugal mixed-powder method is introduced as a processing meth‐ od for metal-matrix FGMs at first. The centrifugal mixed-powder method is a devel‐ oped technique of centrifugal casting by setting predesigned mixed powder in a spinning mold in advance. As an example of processed FGMs by this method in our previous studies, Cu-based FGMs with dispersed diamond particles are shown. Graded structures in the Cu-based FGMs are investigated through scanning elec‐ tron microscope (SEM) observations of microstructures. As the latest processing method for metal-matrix FGMs developed by our research group, centrifugal sin‐ tered-casting method is shown. The centrifugal sintered-casting method is a modi‐ fied processing technique of the centrifugal mixed-powder method. In the centrifugal sintered-casting method, FGMs are processed by the combination of centrifugal sintering and centrifugal casting. Al–Si alloy and Cu-based FGMs with dispersed diamond particles are introduced as examples. Applications of metal-ma‐ trix FGMs processed by the centrifugal sintered-casting method are also described. Fabricated metal-matrix FGMs can be used as grinding wheel and applied to carbon fiber-reinforced plastic (CFRP) machining.

**Keywords:** Functionally graded materials (FGMs), Metal-matrix composite, Powder met‐ allurgy, Centrifugal sintering, Centrifugal casting

© 2016 The Author(s). Licensee InTech. This chapter is distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/3.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

### **1. Introduction**

New processing routes for metal-matrix functionally graded materials (FGMs) and structures through combinations of powder metallurgy and casting are described in this chapter. FGMs are well known as a relatively new class of inhomogeneous composite materials having property gradient. The property gradient in the FGMs is caused by a position-dependent chemical composition, microstructure, or atomic order [1]. These FGMs are generally fabri‐ cated based on powder metallurgy, melt-processing technique, chemical vapor deposition, physical vapor deposition and so on.

**Figure 1.** A schematic illustration showing a typical fabrication process of FGMs by the powder metallurgy method through spark plasma sintering (SPS).

Figure 1 shows a schematic illustration of a typical fabrication process of FGMs by the powder metallurgy method through spark plasma sintering (SPS). At first, mixed powders with various ratios of materials A and B are prepared. Predesigned mixed powders are stacked inside a die for the SPS as shown in Figure 1. The case of six-graded composition layers is shown in Figure 1. The number of graded layers can be freely chosen. Then, FGMs with stepwise graded structure can be obtained by sintering these powders with an SPS machine. Ti–ZrO2 FGMs with stepwise graded structure were fabricated by this method in our previous study [2]. A continuous graded structure can also be obtained by this method with a green body having continuous graded composition. For example, Ti–ZrO2 FGMs were fabricated by this method in our previous studies [3, 4].

The melt-processing technique is also an effective way to fabricate continuous graded struc‐ ture. In terms of melt-processing techniques to fabricate metal-based FGMs, various kinds of centrifugal method were developed: centrifugal casting [5–7], centrifugal solid-particle method [8, 9], centrifugal *in situ* method [10, 11], and so on. The centrifugal casting is a processing method that uses centrifugal force caused by rotation of a mold. By the centrifugal force in the rotating mold including molten metal and solid particles, compositional gradient due to the difference of the material densities between the molten metal and the solid particles is generated. By controlling these phenomena, FGMs can be fabricated. Basically, both the centrifugal solid-particle method and the centrifugal *in-situ* method are based on the centri‐ fugal casting. The centrifugal solid-particle method can be conducted at a temperature of liquid–solid coexistence in alloy systems, such as Al–Ti [8, 9]. On the other hand, the centrifugal *in-situ* method can be made at a temperature of liquid phase in alloy systems, such as Al–Ni [10] and Al–Cu [11]. By using these processing techniques, various kinds of FGMs having specific graded distributions of reinforcement can be made.

As new melt processing techniques, centrifugal mixed-powder method [12–15] and centrifugal sintered-casting method [16, 17] have been recently developed. These two melt processing techniques are introduced in this chapter. Applications of metal-matrix FGMs processed by the centrifugal sintered-casting are also described. Fabricated metal-matrix FGMs can be used as grinding wheel and applied to carbon fiber-reinforced plastic (CFRP) machining [17].
