3. Write a short note on shape memory alloys (SMA)?

Alloy :
An alloy is a material composed of two or more elements, at least one of which is
a
metal. These elements are combined in varying proportions to create a new
material
with properties that may differ from those of the individual elements. Alloys are
designed to achieve specific characteristics such as enhanced strength, durability,
corrosion resistance, or other desirable properties for various applications.
Shape Memory Alloys(SMA)
Shape Memory Alloys (SMAs) are a remarkable class of materials with the unique
ability to "remember" their original shape and return to it when subjected to
certain
stimuli. This intriguing behavior is attributed to their phase transformation
characteristics and has led to a wide range of practical applications.
The most common type of SMA is based on an alloy of nickel and titanium, known
as
Ni-Ti or Nitinol. These alloys exhibit two distinct phases at different temperatures:
austenite, the high-temperature phase, and martensite, the low-temperature
phase. The
transition between these phases is reversible and can be triggered by changes in
temperature or mechanical stress.
The key features and applications of shape memory alloys:
• Shape Memory Effect (SME): SMAs can undergo deformation at a certain
temperature and return to their original shape when heated above a critical
temperature. This ability to recover their shape makes them suitable for various
applications, from medical devices to aerospace engineering.
• Superelasticity: SMAs also possess the property of superelasticity or
pseudoelasticity. This means that they can endure significant strains while still
reverting to their initial shape. This behavior is due to the reversible phase
transformation and makes them useful in applications like stents, braces, and
eyeglass frames.
Applications:
• Biomedical Field: SMAs have found extensive use in medical applications, such
as self-expanding stents, orthodontic wires, and minimally invasive surgical
instruments.
• Aerospace and Engineering: They're utilized in deployable structures for
satellites and spacecraft due to their compactness and shape-changing abilities.
• Robotics: SMAs can be integrated into robotic mechanisms, enabling soft
robotics and more adaptable and efficient movement.
• Consumer Goods: They're used in various consumer products like eyeglass
frames that adjust to the wearer's face and shape-adapting clothing.
• Automotive Industry: SMAs are employed in actuators for various automotive
systems, including active suspension systems and engine components.
• Challenges: While SMAs offer numerous benefits, they also present challenges.
Their response can be sensitive to temperature fluctuations and stress levels.
Additionally, the engineering and processing of these alloys can be complex,
impacting their commercial viability.

4. Enumerate the difference among Soldering, Brazing and Welding

Soldering, brazing, and welding are all methods used to join materials together,
typically metals. Each process has its own characteristics, temperature ranges,
and
applications. Here are the key differences among soldering, brazing, and welding:
Soldering:
a. Soldering involves melting a filler metal called solder, which typically has a
lower melting point than the materials being joined.
b. Soldering temperatures are relatively low, usually below 450°C (840°F).
c. The parent materials remain mostly unchanged; the solder forms a bond by
adhering to the surface through capillary action.
d. Soldering is commonly used for electrical and electronics applications, such as
soldering components onto circuit boards
Brazing:
a. Brazing utilizes a filler metal, called brazing alloy, with a higher melting point
than solder but lower than the base materials.
b. The temperature used in brazing is higher than soldering, typically between
450°C to 1150°C (840°F to 2100°F).
c. Brazing results in a stronger joint compared to soldering, as the filler material
interacts metallurgically with the base materials to form a solid bond.
d. This method is often used in applications where a stronger joint is required but
the base materials shouldn't be melted, such as in plumbing and HVAC systems.
Welding:
a. Welding involves melting the base materials themselves, or in some cases,
adding a filler metal to create a strong joint.
b. Welding temperatures are the highest among the three processes, ranging
from
a few thousand degrees Celsius for arc welding to even higher temperatures for
processes like laser welding.
c. The melted materials fuse together to form a single, continuous piece.
d. Welding creates very strong joints suitable for load-bearing applications, such
as construction, automotive manufacturing, and aerospace.
Recite the classification of metals
Metals can be classified into several categories based on various criteria, including
their properties, uses, and positions in the periodic table. Here's a general
classification of metals:
• Alkali Metals: These are the elements in Group 1 of the periodic table,
including lithium (Li), sodium (Na), potassium (K), rubidium (Rb), cesium
(Cs), and francium (Fr). They are highly reactive and are typically soft metals.
• Alkaline Earth Metals: These are the elements in Group 2 of the periodic table,
including beryllium (Be), magnesium (Mg), calcium (Ca), strontium (Sr),
barium (Ba), and radium (Ra). They are also reactive, but less so than alkali
metals.
• Transition Metals: These are the elements in the d-block of the periodic table,
located from Group 3 to Group 12. They are known for their various oxidation
states, colorful compounds, and ability to form complex ions. Examples include
iron (Fe), copper (Cu), and gold (Au).
• Inner Transition Metals: These are the elements in the f-block of the periodic
table, which includes the lanthanides and actinides. Lanthanides are used in
various technologies, while actinides are often radioactive.
• Post-Transition Metals: This is a category of metals that includes elements
with properties intermediate between those of transition metals and nonmetals.
Examples include aluminum (Al), tin (Sn), and lead (Pb).
• Basic Metals: This category includes metals that are commonly found and used.
They are generally good conductors of heat and electricity. Examples include
iron (Fe), copper (Cu), and zinc (Zn).
• Noble Metals: These metals are resistant to corrosion and oxidation in moist
air. They include elements like gold (Au), silver (Ag), and platinum (Pt).
• Precious Metals: This term is often used interchangeably with noble metals and
refers to metals that have high economic value due to their rarity and various
uses. Examples are gold (Au), silver (Ag), and platinum (Pt).
• Reactive Metals: These metals are highly reactive, especially with water and
oxygen. They include alkali metals and alkaline earth metals.
• Non-Ferrous Metals: These are metals that do not contain significant amounts
of iron. They are often used for their desirable properties like low weight, high
conductivity, and resistance to corrosion. Examples include aluminum (Al),
copper (Cu), and titanium (Ti).
a. Ceramics:
Ceramics are a class of inorganic, non-metallic materials that are known for
their hardness, high melting points, and excellent resistance to heat and
corrosion. They are typically composed of compounds between metallic and
non-metallic elements, such as oxides, nitrides, and carbides. Ceramics can be
found in various forms, including traditional pottery and modern engineering
materials.
Properties of ceramics:
• Hardness: Ceramics are known for their hardness and are often used in
applications requiring wear resistance, such as cutting tools.
• Brittleness: Ceramics are generally brittle, meaning they are prone to cracking
and shattering under stress.
• High melting points: Ceramics have high melting points, making them suitable
for high-temperature applications like kilns and heat shields on spacecraft.
• Electrical insulators: Most ceramics are excellent insulators of electricity, which
makes them useful in electrical and electronic components.
• Chemical resistance: Ceramics are often resistant to chemical reactions, making
them suitable for applications involving exposure to harsh chemicals.
• Biocompatibility: Some ceramics are biocompatible and can be used in medical
implants and dental applications.
10. Describe the construction & Working of Arc Welding Process with neat sketch
Welding is a fabrication process that involves joining two or more pieces of metal
or
thermoplastic materials by melting their edges and fusing them together. This
process
creates a strong and permanent bond between the materials, resulting in a single,
continuous piece.
Welding is commonly used in various industries, including manufacturing,
construction, automotive, aerospace, and more. It is a fundamental technique for
creating structures, components, and products that require the integration of
different
parts. The goal of welding is to produce a joint that is as strong and reliable as the
original materials being joined.
Arc Welding Process: Construction and Working
Arc welding is a welding process that involves the creation of an electric arc
between
an electrode (usually made of a consumable or non-consumable material) and the
workpiece. The intense heat generated by the arc melts the base metal and the
electrode,
forming a molten weld pool that cools and solidifies to create a welded joint. Let's
delve
into the construction and working of the arc welding process, accompanied by a
neat
sketch.

a) Power Source: The power source for arc welding is typically an electric power
supply that provides the necessary voltage and current to maintain the arc.
b) Electrode Holder/Clamp: This device securely holds and positions the welding
electrode. It is designed to provide an electrical connection to the electrode.
c) Ground Clamp: This clamp connects the workpiece to the power supply's
ground or earth terminal, completing the electrical circuit.
d) Welding Cable: Heavy-duty cables are used to connect the electrode
holder/clamp and the ground clamp to the power supply. These cables carry the
current required for welding.
e) Protective Gear: Welders wear protective clothing, gloves, helmets with dark
visors (to shield against intense light), and sometimes respiratory protection to
safeguard against sparks, UV radiation, and fumes.
f) Shielding Gas (if applicable): In some arc welding processes, such as Gas Metal
Arc Welding (GMAW), a shielding gas is used to protect the molten metal from
atmospheric contamination.
Working:
a) Preparation: The workpiece surfaces to be welded are cleaned to remove dirt,
rust, and any contaminants that could affect the quality of the weld.
b) Electrode Selection: Depending on the welding process and material to be
welded, an appropriate electrode is chosen. Electrodes can be consumable (they
melt into the weld) or non-consumable (they do not melt).
c) Setting up the Equipment: The electrode holder/clamp is connected to the
positive terminal of the power supply, and the ground clamp is connected to the
negative terminal. This establishes the electrical circuit needed for the arc to
form.
d) Arc Formation: When the electrode is brought close to the workpiece, the
electric potential difference causes a high-intensity electric arc to form. This arc
produces extremely high temperatures, melting both the electrode tip and the
workpiece.
e) Melting and Depositing: As the arc heats the electrode and workpiece, the
metal
at the point of contact begins to melt. In the case of consumable electrodes, the
molten metal from the electrode tip transfers to the workpiece, forming the weld
pool.
f) Solidification: As the molten metal cools, it solidifies and fuses with the base
metal, creating a welded joint.
g) Slag Removal (if applicable): Some welding processes, like Shielded Metal Arc
Welding (SMAW), use a flux coating on the electrode that forms a layer of slag
over the weld. Once the weld cools, this slag must be chipped or brushed away
to reveal the finished weld.
h) Cooling: The welded joint is allowed to cool gradually to achieve the desired
strength and metallurgical properties.
Throughout the process, it's crucial to maintain proper electrode positioning, arc
length,
and welding speed to ensure a high-quality weld. The protective gear and proper
ventilation are essential to ensure the safety of the welder.