VAC uses rapid solidification technology to cast thin metallic ribbons from molten metal with extremely high cooling rates of 106 K/s, high casting speeds of 100 km/h, and automatic reel changing during winding. This allows the production of amorphous or nanocrystalline soft magnetic alloys with superior properties for applications such as magnetic cores and inductive components. Various single crystal growth methods are used to eliminate grain boundaries, including floating zone, Czochralski crystal pulling, and hydrothermal synthesis using water as a mineralizing agent. Twin-roll and twin-belt casting are continuous casting methods that produce thin strips with fine grain structure and high casting rates.
Titanium is named after the Titans, the
powerful sons of the earth in Greek mythology.
• Titanium is the forth abundant metal on
earth crust (~ 0.86%) after aluminium, iron and
magnesium.
Titans
homepage.mac.com
Rutile (TiO2)
mineral.galleries.com
Ilmenite (FeTiO3)
• Not found in its free, pure metal form in
nature but as oxides, i.e., ilmenite (FeTiO3)
and rutile (TiO2).
• Found only in small amount in Thailand...
Isothermal forging represents a possible alternative to produce near net and net shape forgings.The basic principle of isothermal forging consists of a plastic forming process during which die and work piece temperatures are identical or very similar.
Titanium is named after the Titans, the
powerful sons of the earth in Greek mythology.
• Titanium is the forth abundant metal on
earth crust (~ 0.86%) after aluminium, iron and
magnesium.
Titans
homepage.mac.com
Rutile (TiO2)
mineral.galleries.com
Ilmenite (FeTiO3)
• Not found in its free, pure metal form in
nature but as oxides, i.e., ilmenite (FeTiO3)
and rutile (TiO2).
• Found only in small amount in Thailand...
Isothermal forging represents a possible alternative to produce near net and net shape forgings.The basic principle of isothermal forging consists of a plastic forming process during which die and work piece temperatures are identical or very similar.
This lecture gives an overview about the possibilities to produce aluminium foilstock and wire-bar in a continuous way. Continuous casting is the preferred casting method in modern plants because it offers higher productivity. But there are limitations in the use of this technology because not all alloys can be cast. The product shows properties that can differ from conventional material. This lecture demonstrates the principal of operation; technologies for continuous casting; types of casters; areas of application; properties of the products; behaviour of the products in further processing. General knowledge in materials engineering, some knowledge about aluminium alloy constitution and heat treatment, engineering background in manufacturing processes and basic knowledge of foundry practice is assumed.
Metal matrix composites (MMCs) possess significantly improved properties including highspecific strength; specific modulus, damping capacity and good wear resistance compared to unreinforced alloys. There has been an increasing interest in composites containing low density and low cost reinforcements. Among various discontinuous dispersoids used, fly ash is one of the most inexpensive and low density reinforcement available in large quantities as solid waste by-product during combustion of coal in thermal power plants. Hence, composites with fly ash as reinforcement are likely to overcome the cost barrier for wide spread applications in automotive and small engine applications.
Wear Properties of Thixoformed Al-5.7Si-2Cu-0.3Mg Aluminium AlloyDr. Manal Abdullatif
Earlier work has shown that Al-5.7Si-2Cu-0.3Mg aluminium alloy is suitable for
thixoforming process. Here, the dry sliding wear behaviour of the alloy, in the as-cast and
thixoformed conditions were investigated. The cooling slope technique was used to produce the alloy
with globular microstructure for the thixoforming process. Both the thixoformed and cast samples
were subjected to T6 heat treatments prior to the wear tests. The tests were carried out using a
pin-on-disc tribometer, against a hardened M2 tool steel disc of 62 HRC at different loads, under dry
sliding conditions at fixed sliding speed and sliding distance of 1 m.s–1 and 5 km respectively. The
microstructural response, worn surfaces was thoroughly and carefully examined using various
methods such as scanning electron microscopy, energy dispersive spectroscopy, and differential
scanning calorimetry. The density of the heat treated thixoformed alloys showed significant increase
in the hardness property, among others, due to its reduced porosity. Their wear test results also
observed that the weight loss of materials increase with an increase in the input load and the sliding
distance for all samples. However, the as-cast alloy displayed higher wear rate compared with the
thixoformed alloys. In general, the wear mechanisms showed a mixture of abrasive, oxidative and
delamination wear (mild wear) at low applied loads and mainly an adhesive (severe wear) at high
applied loads.
Fundamentals, synthesis and applications of Al2O3-ZrO2 compositesTANDRA MOHANTA
When the word “Ceramic” comes to our mind, we usually associate them with plates, saucers, cups and mugs. But, the word “Ceramic” encompasses more than just the word “plates” or “saucers”. Indeed, ceramic materials are hard and inherently brittle, but this is just the tip of the iceberg. They have multifarious properties and have acquired a status of high technical importance in the field of scientific research. Ceramics are the soul of the modern day’s structural applications owing to their high mechanical and thermal stability under different challenging conditions. They exhibit remarkable properties such as high hardness, high wear resistance, high corrosion resistance, high elastic modulus, high melting point and the ability to retain high strength at elevated temperatures. Alumina (Al2O3) is one such remarkable ceramic material known for its unique optical, mechanical and electrical properties. But the brittle nature of Al2O3 limits its use in certain engineering applications. Therefore, the strength of Al2O3 and Al2O3- based ceramics can be enhanced by tailoring the microstructural design through the application of strategic techniques that may involve secondary phase particle inclusion (such as Zirconia, ZrO2)
1. RAPID SOLIDIFICATION TECHNOLOGY
VAC is one of the pioneers in Rapid Solidification Technology to cast thin metallic ribbons of
thickness 15 -50 µm in a single process step directly from the molten metal.
Special features of this process are:
extremely high cooling rates of 106 K/s (i.e. from about 1400°C to less than 400 °C in
one millisecond)
high casting speeds of 100 km/h
in-line winding of the thin ribbon
automatic reel change during winding without process interruption
Rapid Solidification Technology allows the production of metallic ribbons in the amorphous
(glassy) state. The lack of long range atomic order results in superior soft magnetic properties.
Via a special annealing treatment some amorphous compositions may be transformed into
nanocrystalline materials
Amorphous and nanocrystalline soft magnetic alloys are the basis for many innovative
applications as magnetic cores, inductive components or in labels for electronic article
surveillance (EAS).
2. Typical strengths and elastic limits for various materials. Metallic glasses are unique
3. Single-Crystal Casting:
FIGURE 17 Single-crystal solidification process for casting superalloy turbine blades to eliminate grain
boundaries. From Gell, Duhl, and Giamei. Reprinted with permission.
4. Single-Crystal Processing:
The use of single crystals in metallurgical research and in microelectronic devices is well known,
but it was only in 1982 that monocrystalline alloys first entered service as a critical structural
component. It was a high-technology application in every sense of the word, following two
decades of research and development on cast super alloy turbine blades. As a result, singlecrystal gas-turbine blades are now performing advantageously in both commercial and military
aircraft engines.
There are high-temperature applications in which the grain boundaries and random grain
orientations of polycrystalline super alloys are undesirable, in part because of thermal
fatigue failure and creep rupture along such interfaces. This motivated the development of
directional solidification during the 1970s to produce columnar grains with controlled orientation
and with grain boundaries parallel to the main stress direction. The next major step was to
eliminate the grain boundaries entirely; this was made possible and practical by the single-crystal
casting process shown schematically in Figure 17.30 The helical
6. Figure 2. The growth of single crystals by the floating-zone method in the image furnace
a. The ends of the tow sample rods enter the hot zone, melt, and are pushed together to form a
connection section of melt.
b. The two melt-connected rods are lowered slowly, initially at different velocities. As soon as the lower
rod moves downward, melt begins to crystallize at the rod's upper surface, with the grains of the sintered
powder acting as nuclei. If the lowering rate remains below a certain level (determined by the material),
the grains simultaneously increase in size and decrease in number.
c. As the diameter of the growing rod is reduced to about 1-2 mm (by lowering the lower rod faster than
the upper rod), grains are eliminated until only one large grain -- the desired singe crystal -- remains.
d. After that, varying the rates at which the rods are lowered allows the single crystal to grow in
diameter to the final size, typically 5-10 mm; then the crystal of this diameter continues to grow in length
as long as the feeding material -- the upper rod -- lasts.
7. CRYSTAL PULLING METHOD:
HYDROTHERMAL SYNTHESIS
Water medium
High temperature growth, above normal boiling point
Water acts as a pressure transmitting agent
Water functions as solublizing phase
8. Often a mineralizing agent is added to assist with the transport of reactants and crystal
growth
Speeds up chemical reactions between solids
Crystal growth hydrothermally involves:
Temperature gradient reactor = autoclave (bomb !!)
Dissolution of reactants at one end
Transport with help of mineralizer to seed at the other end
Crystallization at the other end
Hydrothermal growth of quartz crystals
Water medium, nutrients 400 oC, seed 360 oC, pressure 1.7 kbar
Mineralizer 1M NaOH
Uses of single crystal quartz: Radar, sonar, piezoelectric
transducers, monochromators, XRD
Annual global production hundreds of tons of quartz crystals
Hydrothermal crystal growth is also suitable for growing single
crystals of:
Ruby: Cr3+/Al2O3
9. Corundum: a-Al2O3
Sapphire: Cr2
6+/Al2O3
Emerald: Cr3+/Be3Al2Si6O18
Berlinite: a-AlPO4
Metals: Au, Ag, Pt, Co, Ni, Tl, As
Role of the mineralizer:
Control of crystal growth rate:
choice of mineralizer, temperature and pressure
Solubility of quartz in water is important
TWIN-ROLL CASTING:
Twin-roll casting relates to the continuous casting methods using traveling "endless" molds
(rolls, belts, wheels). The method is characterized by zero relative movement between the mold
(two rolls) and casting surfaces.
Twin-roll casters are used for manufacturing cast strips of Aluminum based bearing materials.
In twin-roll casting process a melt is fed through a ceramic nozzle into the gap between two
rotating water-cooled rolls. The melt cools down and solidifies between the rolls. Additionally
the solid strip exerts hot rolling with the thickness reduction of about 5-20%.
Sticking between the roll and the solidified strip is prevented by means of a parting agent applied
to the roll surface. The agent contains Graphite or magnesium hydroxide.
Twin-roll casting process provides extremely high cooling rate up to 1000ºF/s (550ºC/s).
10. Benefits of twin-roll casting:
Very fine Grain structure. High cooling rate results in very fine Grain structure of aluminum and
homogeneous distribution of tin, silicon particles and other constituents.
Surface machining is not required. Surface defects do not form due to negligible relative
movement of the rolls and the solidifying alloy. The cast strips may be coiled and further
processed (rolled) without surface machining (milling) in contrast to those cast in stationary
molds (water-cooled graphite mold, submerged graphite mold).
Very high casting rate. Extremely high cooling rate allows to increase the withdrawal rate to 40
inch/min (1000 mm/min).
Non-intermittent withdrawal regime. No cracks form in the surface layer therefore pauses and
reverse steps are not required in the withdrawal cycle (intermittent withdrawal regime
produces periodic non-homogeneous structure, which may cause cracks during cold rolling
operation).
Easy coiling. Thin castings with a thickness of 0.24”/6 mm are obtained.
11. Disadvantages of twin-roll casting:
Expensive equipment.
Low casting thickness. It is more difficult to clad thin cast strips with pure aluminum.
High internal thermal stresses caused by very fast cooling and solidification. The castings should
be annealed prior to rolling.
TWIN BELT CASTING:
Twin-belt casting relates to the continuous casting methods using traveling "endless" molds
(rolls, belts, wheels). The method is characterized by zero relative movement between the mold
(two belts) and casting surfaces.
Twin-belt casters are used for manufacturing cast strips of Aluminum based bearing materials.
In twin-belt casting process a melt is fed through a ceramic nozzle into the gap between two
rotating endless thin belts held in tension.
The belts are supported and chilled by two water-cooled copper plate. The melt cools down and
solidifies between the belts.
The cast strip is pulled out by a withdrawal unit synchronized with the drive of the belts.
Benefits of twin-belt casting:
Surface machining is not required. Few surface defects form due to the absence of the relative
movement of the belts and the solidifying alloy.
High casting rate. The absence of tearing friction forces applied to the casting “skin” allows to
increase the withdrawal rate.
Low internal stresses. Low cooling rate produces low internal stresses.
12. Non-intermittent withdrawal regime. No cracks form in the surface layer therefore pauses and
reverse steps are not required in the withdrawal cycle (intermittent withdrawal regime
produces periodic non-homogeneous structure, which may cause cracks during cold rolling
operation).
Easy coiling. Thin castings are obtained.
Disadvantages of twin-belt casting:
Relatively coarse Grain structure caused by low cooling rate.
Short service life of the belts.
More expensive equipment as compared to the methods of casting in stationary molds.