Transcript Advanced materials

Ipcowala Institute of Engineering & Technology- Dharmaj
Seminar Topic
on
Advanced Materials
Prepared By:
Guided By:
131010119010
131010119011
Prof. Bhavin A. Gajjar
Advanced materials
Super alloys
Ferro electric and piezoelectric materials
Advanced magnetic materials
Advanced engineering polymer materials
Advanced ceramic and composite materials
photo conducting and photovoltaic materials
electro-optic materials
Lasers, smart materials
Biomaterials–
Determining
mechanical
properties and their applications
• Recent trends in Bio-Material Characterization.
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• A super alloy or high performance alloy is
an alloy, that exhibits excellent mechanical
strength and resistance to creep at high
temperatures; good surface stability; and
corrosion resistance.
• Super alloys typically have a matrix with an
austenitic face centered cubic crystal structure.
A super alloy's base alloying element is
usually nickel, cobalt or iron.
• Typical applications are in the aerospace,
industrial gas turbine and marine turbine
industry, e.g. for turbine blades for hot
sections of jet engines, and bi-metallic engine
valves for use in diesel and automotive
applications.
Case study
• Used in Gas Turbine Rotor:
* oxidation resistance and strength
* creep strength
* design of rotor must not be only on the
basis of yield strength.
• Creep is a slow mechanism of strain.
• At low temperature, fine grained metals are
generally stronger than the coarse grained ones,
because grain boundaries interfere with the
progression of the dislocation movements.
• At elevated temperatures, the situation is
reversed.
High temperature strength
Classes of High-Temperature Alloys
Base
Class
Super 12% Cr Martensitic Stainless
Steels
Fe
20-23% Cr Austenitic Valve Steels
Fe-Ni
Age-Hardenable Super alloys
Fe-Ni-Co
Age-Hardenable, Low-Expansion
Superalloys
Alloying Element Effects –High Temperature Alloys
Nickel (0-75%)
stabilizes
austenite,
forms
strengthening
phases,
improves
high-temperature
stability
and
strength.
Chromium (11-23%)
forms protective oxide layer for
oxidation and corrosion resistance.
Molybdenum and Tungsten
(0-15%)
Strengthening elements;
improve corrosion resistance.
Structural aspects of super alloys
• Super alloys used for high temperature
applications usually have FCC structure based on
combination of Ni, Fe, Co and Cr.
• Chromium is provided to obtain the oxidation
resistance.
• Cobalt is used to replace a part of the iron or
nickel. It dissolves in solid solution and strengthen
the material.
• Aluminum and titanium provide a very fine
precipitate γ’, which structurally very near to the γ
solid solution.
• The formula for γ’ is Ni3Al. Some of the aluminum
can be replaced with titanium with only small
change in a0.
• The structure of γ’ is an ordered substitutional
solid solution.
• Aluminum or titanium atoms occupy the corners
of the unit cell and Ni atoms are in the face
centers.
• Precipitates are in the form of cubes. These
precipitates are responsible for high strength of
super alloys.
Effects of other alloying elements
• Molybdenum adds strength of the matrix in super
alloys and also forms complex carbides which reduce
creep rate.
• Small amount of zirconium and boron are added for
their beneficial effects on carbide size refinement.
• The carbon content is about 0.1 to 0.2%.
• Practically all grades of super alloys are cast only few
are wrought, because with increased creep strength,
hot working process becomes difficult.
• Also some of the alloys have low ductility that is
adequate for service but not for rolling.
• Investment casting process is the most widely used
method. Any intricate shape can be produced using
this method.
• and a lower bound, or limit:
• In these expressions, E and V denote the
elastic modulus and volume fraction,
respectively, whereas the subscripts c, m and
p represent composite, matrix, and particulate
phases.
Plot of upper and lower bound Ec v/s Vp curves
for a copper–tungsten composite,
tungsten: particulate phase;
experimental data points fall between the two curves.
Photomicrograph of a WC–Co cemented carbide
Light areas: Cobalt Matrix
Dark regions: Particles of tungsten carbide
• The yield stress of a submicron-sized crystal may
be as high as several GPa, but its thermal stability
may not be great.
• The torsional strength of metallic whiskers, as
well as the nanoindentation hardness on
crystalline specimens, often exhibit a significant
rise as the material size decreases.
Flat-end diamond punch used
for microcompression
Bio-nanotechnology
• Nanotechnology is increasingly being used in medicine, via
biomaterials.
• These include carbon nanotubes in an ultra-sensitive DNA
detector, release of drug molecules controlled by nanoporous
membranes with pores marginally larger than the drug
molecules and surface nanoreceptors to provide drug release
specifically to damaged tissue.
• Diabetes is one condition becoming more prevalent
worldwide and where it is aimed to implant drugs beneath
the skin to deliver as needed to maintain a steady blood
glucose level.
• Biodegradable nanobeads coated with specific molecules are
able to mimic the ability of white blood cells to reduce
inflamed blood cell walls by traveling through the
bloodstream and target the inflammation site.
Nanocomposite contact lenses for
diabetes detection
• Transport wound dressings have been developed from
nano-structured membrane material which protects
the skin from bacterial infection.
• Cells may be grafted onto the dressing to promote
tissue regeneration.
• Another innovation is to incorporate drug delivery in
the membrane to provide controlled medication.
• Bacteria infection itself may be treated with a new
class of material called ‘peptide nanotubes’.
• These are about 3 nm in diameter and 6 nm long and
are made to perforate bacterial membranes without
harming healthy cells.
• The nanoparticles can be directed at a tumor with
accuracy to have negligible effect on the other tissues,
and allow higher doses to be administered.