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Metallurgy is a domain of materials science that studies the physical and chemical behavior of metallic elements, their intermetallic compounds, and their mixtures, which are called alloys. It is also the technology of metals: the way in which science is applied to their practical use. The term is nowadays distinguished from the craft of metalworking.
 Metallurgists study the microscopic and macroscopic properties using
metallography. In metallography, an alloy of interest is ground flat
and polished to a mirror finish. The sample can then be etched to
reveal the microstructure and macrostructure of the metal. A
metallurgist can then examine the sample with an optical or electron
microscope and learn a great deal about the sample's composition,
mechanical properties, and processing history.
Crystallography, often using diffraction or x-rays or electrons, is
another valuable tool available to the modern metallurgist.
Crystallography allow the identification of unknown materials and
reveals the crystal structure of the sample. Quantitative
crystallography can be used to calculate the amount of phases present
as well as the degree of strain to which a sample has been subjected.
The physical properties of metals can be quantified by mechanical
testing. Typical tests include tensile strength, compressive strength,
hardness, impact toughness, fatigue and creep life.
Nondestructive testing (NDT):
Nondestructive testing (NDT), also called nondestructive evaluation
(NDE) and nondestructive inspection (NDI), is testing that does not
destroy the test object. NDE is vital for constructing and maintaining
all types of components and structures. To detect different defects
such as cracking and corrosion, there are different methods of testing
available, such as X-ray (where cracks show up on the film) and
ultrasound (where cracks show up as an echo blip on the screen). This
article is aimed mainly at industrial NDT, but many of the methods
described here can be used to test the human body. In fact methods from
the medical field have often been adapted for industrial use, as was
the case with Phased array ultrasonics and Computed radiography.
While destructive testing usually provides a more reliable assessment
of the state of the test object, destruction of the test object usually
makes this type of test more costly to the test object's owner than
nondestructive testing. Destructive testing is also inappropriate in
many circumstances, such as forensic investigation. That there is a
tradeoff between the cost of the test and its reliability favors a
strategy in which most test objects are inspected nondestructively;
destructive testing is performed on a sampling of test objects that is
drawn randomly for the purpose of characterizing the testing
reliability of the nondestructive test.
Spark testing:
Spark testing metals is done by noting the type of sparks that issue
from a piece of steel that has been put to a grinding wheel, From this
one can deduce with some accuracy the type of alloy present (for
instance; percentage carbon, vanadium, chromium).
Spark characteristics to note are:
1. color
2. length
3. branching
One of the simplest tests is to note how the sparks branch. Higher
carbon steels will produce shorter streams of sparks with a large
amount of branching, in contrast low carbon steel will produce a longer
stream with less branching. Additionally wrought iron will produce
practically no branching, and cast iron extremely short stream with
excessive branching.
Salt spray test:
Salt spray test is a standardized test method used to check corrosion
resistance of coated samples. Coatings provide corrosion resistance to
metallic parts made of steel, zamak or brass. Since coatings can
provide a high corrosion resistance through the intended life of the
part in use, it is necessary to check corrosion resistance by other
means. Salt spray test is an accelerated corrosion test that produces a
corrosive attack to the coated samples in order to predict its
suitability in use as a protective finish. The appearance of corrosion
products (oxides) is evaluated after a period of time. Test duration
depends of the corrosion resistance of the coating; the more corrosion
resistant the coating is, the longer the period in testing without
showing signs of corrosion.
There is no correlation between the duration in salt spray test and the
expected life of a coating, since corrosion is a very complicated
process and can be influenced by many external factors. Nevertheless,
salt spray test is widely used in the industrial sector for the
evaluation of corrosion resistance of finished surfaces or parts.
Electromagnetic Testing (ET):
Electromagnetic Testing (ET), as a form of nondestructive testing, is
the process of inducing electric currents or magnetic fields or both
inside a test object and observing the electromagnetic response. If the
test is set up properly, a defect inside the test object creates a
measurable response.
The term "Electromagnetic Testing" is often intended to mean simply
Eddy-Current Testing (ECT). However with an expanding number of
electromagnetic and magnetic test methods, "Electromagnetic Testing" is
more often used to mean the whole class of electromagnetic test
methods, of which Eddy-Current Testing is just one.
Magnetic flux leakage:
Magnetic flux leakage (MFL) is a magnetic method of nondestructive
testing that is used to detect corrosion and pitting in steel
structures, most commonly pipelines and storage tanks. The basic
principle is that a powerful magnet is used to magnetize the steel. At
areas where there is corrosion or missing metal, the magnetic field
"leaks" from the steel. In an MFL tool, a magnetic detector is placed
between the poles of the magnet to detect the leakage field. Analysts
interpret the chart recording of the leakage field to identify damaged
areas and hopefully to estimate the depth of metal loss.
Liquid Metal Embrittlement:
Liquid Metal Embrittlement is a phenomenon of practical importance,
where certain ductile metals experience drastic loss in tensile
ductility or undergo brittle fracture when tested in the presence of
specific liquid metals. Generally, a tensile stress, either externally
applied or internally present, is needed to induce embrittlement.
Exceptions to this rule have been observed, as in the case of aluminium
in the presence of liquid gallium.[1] People have studied this
phenomenon from the beginning of the 20th century. Many of its
phenomenological characteristics are known and several mechanisms were
proposed to explain it.[2] The practical significance of liquid metal
embrittlement is revealed by the observation that several steels
experienced ductility losses and cracking during hot dip galvanizing or
during subsequent fabrication.
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