In today's highly demanding technological environment, one of the main challenges in new material design is combining seemingly irreconcilable thermomechanical properties in the same component (e.g., high heat and corrosion resistance, high strength in elevated-temperature applications and high resistance to wear, and high toughness in load-bearing elements). In many cases, the problem may be solved by using coatings or by layering dissimilar materials. From a structural viewpoint, a major disadvantage of these techniques, particularly in ceramic coating of metals, has been the resulting high thermal and residual stresses and relatively poor bonding strength. Thus, in thin films, coatings, and layered materials, surface cracking and debonding or delamination have been common forms of mechanical failure. One effective way of reducing residual and thermal stresses and enhancing bonding strength has been to eliminate material-property discontinuities by grading the material composition near the interfaces or through the coating. These new materials, with continuously varying compositions or volume fractions, are known as functionally graded materials (FGMs).In developing FGMs, research on the mechanics, and particularly on the fracture mechanics of these inhomogeneous materials, is needed to provide technical support to materials scientists and to manufacturing and design engineers. In the past, fracture mechanics has been useful both as a screening tool during material processing and as a design and maintenance tool for service-life assessment. Broadly speaking, fracture mechanics involves studying the effect of the applied loads, the component/flaw geometry, and the environmental conditions on the fracture of engineering materials.

Fracture Mechanics of Functionally Graded Materials

Functionally graded materials: A review of fabrication and properties

Functionally Graded Composite Materials: An Overview

Bending and free vibration response of layered functionally graded beams: A theoretical model and its experimental validation

Fabrication of ZrO2–NiCr functionally graded material by powder metallurgy

The fabrication of disk shaped functionally gradient material with an optimum distribution of composition for thermal stress reduction in a specific material combination of PSZ/Stainless Steel is described. The thermal stress generated during cooling from sintering temperature was analized by finite element method as a function of conpositional distribution and sample size.According to the optimum compositional gradient, the sintered compact of the PSZ /SUS304 functionally gradient material was successfully fabricated.

Microstructural Designing and Fabrication of Disk Shaped Functionally Gradient Material by Powder Metallurgy

A powder spray stacking apparatus has been developed for fine stacking of mixed powders. Functionally gradient material has been successfully fabricated using this process, which has fine microstructural transition from stainless steel to zirconia ceramics.Mixing ratio of metal and ceramic powders in the suspension using ethanol as a solvent was varied gradually by the computer control. Deposited products, which were prepared by spraying and depositing the suspension on preheated substrates, were CIP'ed, encapsulated and HIP'ed. Detailed observation of the microstructure has revealed that this process could precisely control the various composition profile with the minimum control size of 0.01mm. It has been shown that the thermal shock resistance of spray formed FGM'was significantly higher than that of monolithic zirconia ceramics.

https://www.jstage.jst.go.jp/article/jjspm1947/37/7/37_7_922/_pdf

Fabrication of Sintered Functionally Gradient Material by Powder Spray Forming Process

In order to evaluate fracture strength for Y2O3-ZrO2, 3mol% Y2O3-ZrO2 (PSZ) /SUS 304 composite materials, Macor as a machinable ceramics and comercially available ceramics (SiC, Si3N4, PSZ, Al2O3), fracture toughness tests were carried out by use of RCT or bending specimens. On the other hand, the fracture strength of these materials was evaluated and inspected the correlation between fracture toughness and fracture stress of small punch (SP) or modified small punch (MSP)test data to predict the fracture toughness value by using miniaturized specimens. Characteristic of the MSP testing method is the ability to evaluate elastic modulus (Young's modulus), fracture strength, yield strength, fracture strain, and fracture energy, etc., with high accuracy and good reproducibility for brittle materials. For a series of metal/ceramics composites which from ductile to brittle, this paper clarified clear the applicable range for SP and MSP testing methods, which suggested that the simultaneous use of SP and MSP test methods can evaluate the fracture strength of metal/ceramics composites.

Ryuzo Watanabe

Papers

Microstructural Designing and Fabrication of Disk Shaped Functionally Gradient Material by Powder Metallurgy

Fabrication of Sintered Functionally Gradient Material by Powder Spray Forming Process

Evaluation of Fracture Toughness for Metal/Ceramics Composite Materials by Means of Miniaturized Specimen Technique

Temperature gradient sintering process of PSZ/Mo Powder Compacts by Laser Beam Irradiation

Hot powder vehicle compaction of an atomized stainless steel powder