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ADVANCES IN ULTRAFINE-GRAINED MATERIALSWHAT ARE ULTRAFINE-GRAINED MATERIALS?Ultrafine-grained materials are solids with grain sizes less than 1m(1000nm) in size.The physics of these materials can be very different from the same material comprising conventionally sized grains.They are produced through the application of severe plastic deformation(SPD) to conventional coarse-grained metals.METHODS FOR PRODUCING UFG MATERIALSTHERE ARE 2 TYPES OF METHODS BOTTOM-UPASSEMBLES POLYCRYSTALLINE METALS FROM INDIVIDUAL ATOMS USING DEPOSITION TECQNIQUES OR FROM NANO SCALE BUILDING BLOCKS ARE PRODUCED

TOP-DOWNIN WHICH BULKY FULLY DENSE COARSE GRAINED POLYCRYSTALLINE SOLIDS ARE PROCESSED BY SPD

The principle of hpt

The sample is generally in the form of a thin disk .It is placed between two massive anvils and subjected to a pressure P.Then it is torsionally strained through rotation of either the lower or upper anvil.THE principle of ecapThe processing is conducted using a die that contains a channel, bent through a sharp angle near the center of the die.The sample billet is machined in such a way so as to fit within the channel.A plunger is used to press it through the die under an applied pressure P.

Since the billet is constrained to remain within the channel, it emerges as shown in following figure.Since the cross-sectional dimensions remain unchanged in the pressing operation, repetitive processing may be undertaken in order to impose very high strains.

MICROSTRUCTURES AFTER PROCESSINGBY ECAP THROUGH INCREASING NUMBER OF PASSNature of microstructures produced by spd processingA study has been done on a high purity (99.99%) aluminium after processing by ECAP for up to a maximum of 12 passes.The initial grain size before ECAP was ~1mm.After 1st pass there is an array of elongated subgrains.Later the microstructure gradually evolves into arrays of reasonably equiaxed grains.After 12 passes, average grain size was ~1.2m.

Nature of microstructure during hpt processA Cu-0.1%Zr alloy was processed at room temperature under a 6.0Gpa pressure.After processing through 1 turn, it was observed that there is inhomogeneous microstructure with average grain sizes measured as ~580nm in center and ~410nm at edge.Microstructure becomes more equiaxed after 5 turns and the grain size is ~500nm in center and ~410nm at edges.

Development of hardness homogeneity in spd processingAt the end of 1/4th turn, there is an extensive region of lower hardness in central region of disk.But after 5 turns, the hardness values become essentially homogeneous over the total area of the disk.Generally the hardness values are taken on cross-sectional planes of the disk .PROPERTIES OBTAINED BY MATERIAL AFTER SPD PROCESSING(1).THEY ACHIEVE HIGH STRENGTH

EX-The increase in 0.2% proof stress with increasing numbers of ECAP passes for a range of commercial aluminum alloys

14(2).THEY ACHIEVE SUPERPLASTIC PROPERTIES WHEN TESTING IN TENSION AT ELEVATED TEMPERATUREEX-Exceptional super-plasticity in an extruded ZK60 magnesium alloy processed by ECAP for 2 passes and then tested in tension at 473 K: the elongation of 3050% is the highest elongation recorded to date in any magnesium-based alloy processed under any conditions

APPLICATIONSMEDICAL DEVICES.

TRANSPORTATION AND CONSUMER PRODUCT INDUSTRIES.

FABRICATION OF COMPONENTS FOR MICRO ELECTRO MEHANICAL SYSTEM(MEMS).

SPORTS PRODUCTS AND AERONAUTICAL SYSTEMS.

DEFENSE EQUIPMENTS.

BIOMEDICAL AAPLICATIONS

(A)-SKULL BUTTON CLOSURE;(B)-BONE STERUM CLOSURE PLATE;(C)-SPINE LATE;(D)-MAXILLOFACIAL PLATE; AND (E)-RECONSTRUCTION TEMPOROMANDIBULAR PLATE.

FUTURE DEVELOPMENT IN SPD PROCESSING ADVANCEMENT IN ECAP PROCESS

TENSILE STRENGTH INCREASED BY COMBINING SPD PROCESSING WITH SUBSEQUENT FORMING SUCH AS COLD ROLLING.

EFFORTS ARE DONE TO EXTEND ECAP PROCESS TO INCLUDE PRESSING OF FLAT SAMPLES

DEVELOPMENT IS DONE IN HCP PROCESSING TO INCLUDE CYLINDRICAL BULK SAMPLES AND THE DEVELOPMENT PROCESSING TECHNIQUE FOR USE OF RODS AND WIRE

ConclusionThe processing of ultrafine grained metals through the use of SPD processing has now to critical stage. Sufficient laboratory results are available to demonstrate the general feasibility of this approach and it is recognized that these materials have a high innovation potential.

Accordingly, it is reasonable to anticipate significant new developments in this field and new applications for these UFG materials.

THANK YOU!!NANDITA GHODKIAKSHAY GAURKHEDEPHANEENDRA PEDAMALLUPAWAN KUMAR