FUNCTIONALLY GRADED MATERIALS

JITHIN JOSE (P2MFG15007)

K.PAVAN KUMAR (P2MFG15008)

INTRODUCTION

Pure metals and non metals

Alloys

Composites

Functionally graded materials

DEFINITION

Functionally graded materials (FGM) are composite materials which are designed to present a particular spatial variation of their properties

This is usually achieved by forming a compound of two components whose volume fraction is changed across a certain direction.

For example, the toughness of a metal can be mated with the refractoriness of a ceramic without any compromise in the toughness of the metal or the refractoriness of the ceramic.

ORIGIN

The “first” FGM was developed in Japan in 1984-85 as the result of a space-plane project. Although the concept of FGM is recent, many materials that fit the description have existed for decades

Some FGM also occur naturally: Bones and teeth Seashells Bamboo tree Human skin

SOME NATURALLY OCCURRING FGMS

HUMAN SKIN BONE

BAMBOO TREE

WHY FGM?

Better adherence of a protective layer (against corrosion, for instance)

Minimization of interfacial stresses between different materials (e.g. due to temperature variation)

Relocation of maximum stresses on a load bearing component

Increase in local fracture toughness

FGMs allow better customization and tailoring of materials for specific tasks

More variety in material selection for engineering design

Stiffer at clamped end Softer at clamped end

CLASSIFICATION OF FGMS

FGMs may be compositionally or micro-structurally graded

Depending upon the nature of gradient, the functionally graded materials (composites) may be grouped into following types

1) Fraction gradient type

2) Shape gradient type

3) Orientation gradient type

4) Size (of material) gradient type

Based on gradation FGMs are classified into

1) Continuous

2) Stepped

Continuous Stepped

FGMs come in several types, depending on their constituents (e.g. ceramic-metal, metal-metal…)

EXAMPLES

TUNGSTEN-COPPER

Tungsten surface:Hard, refractory material

Copper surface:Good electric and thermal conductivity

TITANIUM CARBIDE-NICKEL

TITANIUM CARBIDE-NICKEL

Maximum fracture toughness is achieved for 30 wt.% Ni. The metal phase surrounds the TiC particles and hence acts as a toughening phase.

Peak in hardness and flexure strength due to metal phase changing its behavior from dispersive to connective

MULLITE (Al6Si2O13) -MOLYBDENUM

ALUMINUM-POLYCARBONATE

This type of materials is being researched for its special properties of full wave transmission on one side (Al) and full dissipation on the other, making it suitable for NDT (Non-Destructive Testing) probes.

PROCESSING METHODS

Thin FGM: It consist of relatively thin sections or thin surface coating.

1.Vapour Deposition techniques(i.e. PVD,CVD)

2.Plasma Spraying

3.Self-propagating High temperature synthesis (SHS)

4.Ion Beam Assisted Deposition (IBAD)

Bulk FGM: It consist of volume of materials which require more labour intensive processes.

1.Powder metallurgy technique

2.Centrifugal casting method

3.Solid freeform technology

VAPOUR DEPOSITION TECHNIQUE

PLASMA SPRAYING

SELF PROPAGATAING HIGH TEMPERATURE SYNTHESIS

ION BEAM ASSISTED DEPOSITION

POWDER METALLURGY TECHNIQUE

CENTRIFUGAL CASTING PROCESS

SOLID FREE FORM TECHNOLOGY

APPLICATIONS

AEROSPACE APPLICATIONS They have the added advantage that the metal side can be

bolted onto the airframe rather than bonded as are the ceramic tiles used in the Orbiter.

Other possible uses include combustion chamber insulation in ramjet or scramjet engines

NUCLEAR FUSION REACTORS Modification to heat exchangers in tokomak fusion

reactors

FUEL CELL TECHNOLOGY Creating a porosity gradient in the electrodes, the

efficiency of the reaction can be maximized