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What does a materials person do?
 Producing a product provides an excellent framework on which to
introduce the role of a materials person. First, we need to define
our product and the operating conditions. These operating conditions
can then be related to the properties and behavior of the materials.
We might then consider some materials that could meet these conditions.
Coupled with the choice of materials one needs to consider how
one can process the material to produce the product. Once produced
the performance of the product needs to be evaluated and the process
improved or changed to meet the needs of the product. Effective
industrial design requires these factors and involves also the
production techniques, cost, and marketing conditions. The materials
person plays key roles in the manufacturing of any product. The
materials selection is just the beginning. There are four basic
elements of the field that come to play:
- Processing: This is key to the question that needs to be answered. How can
I produce this product? There are four general categories of processing
types and these four categories are the cornerstones on which
the materials person interacts with other engineers in the manufacturing
of a product. These are:
- Solidification Processing (utilizes the liquid state in the process) The structural processing
of most metals begins by forming an alloy in the molten state,
where it is relatively easy to mix the components. This process
is also utilized in glasses and some polymers. Once the proper
temperature and composition is achieved, the melt is cast. Castings
can be divided into two types, depending on the subsequent processing
steps. The first type is shape casting, which takes advantage
of the fluidity of liquid metal to form complex shapes directly.
Because of the complexity of their part geometries, these castings
generally cannot be mechanically worked to a significant degree
and any changes in microstructure or properties must be achieved
during solidification or through heat treatments afterwards Casting,
crystal growth, atomization, welding, etc.
- Powder Processing (utilizes powders in the process) Slip casting, powder pressing, hydroplastic
forming followed by drying and firing or hot pressing- Bulk ceramics
are usually processed in powder form since their high melting
points and low formability prohibit solidification and/or deformation
processing. Metals and polymers can also be processed from powders.
Powder processing involves consolidation (packing) of particulate
to form a "green body". Densification follows, usually by sintering.
There are essentially two basic methods of consolidating powders.
Dry powder can be compacted in a die (dry-pressing) or the particles,
if small enough.
- Deposition Processing (utilizes evaporation and/or condensation in the process) Electroplating,
spray coating, sputtering, laser ablation, chemical vapor deposition
(CVD), etc. - Deposition processing is a chemical surface modification
such as used in semiconductor processing or for decorative or
protective coatings generally involves the deposition of a chemical
vapor or ions onto a surface. Vapor source methods require a vacuum
to transport the gaseous source of atoms to the surface for deposition.
Common vapor sources are thermal evaporation ( similar to boiling
water to create steam), sputtering (uses energetic ions to bombard
a source and create the gas state), or laser light to ablate (remove)
remove atoms from surface to create the gaseous state. Other sources
use carrier media such as electrochemical (ions in a solution
transported by an electrical field to the surface for depositions)
or spray coating (ions or small particles transported by gases,
liquids, and/or electrical field).
- Deformation Processing (utilizes crystal plasticity or a viscous flow in the process)
Rolling, forging, drawing, extrusion, spinning, cutting, turning,
milling, etc.- Deforming a solid to generate a desired shape is
a common process. It generally involves the use of a large force
to deform the material. Many techniques heat the material to reduce
the force needed to deform it. Sometimes a mold is used to define
the shape. Forging, an old method that heated a metal and deformed
the metal by hammer blows is used today with multi-ton hammers.
Rolling to reduce thickness of a plate is another common process.
Some glasses when heated can be formed with tools or molds. Machining
methods like drilling to make holes or milling are examples of
other common deformation processing methods.
| Hot Rolling process at Inland Steel Corporation. |
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- Structure: This is key to the question of characterizing the material and
to form a basis for understanding the state or condition of the
material. Characterizing a material involves the understanding
of the ways the components of the material are arranged from atomic
to a macro (visual with the eye) scale. These arrangements are
correlated with the processing and coupled strongly with the material
properties. Understanding these levels of the structure of materials
is a basic part of the role of a materials person and this structural
information serves as a means to understand and control the processing
stages and to provide a similar basis for the physical properties
of the material. Structural information comes in a series of size
scales.
| Structural Level |
Standard Technique |
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| unaided eye |
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| Optical microscope |
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| Scanning Electron Microscope (SEM) |
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| Transmission Electron Microscope (TEM) |
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| Field Ion Microscope (FIM) and Scanning Tunneling Microscopes
(STM) |
- Properties: The physical properties of the material are generally a basic
reason for selecting the material for the needed product performance.
The performance of a product frequently requires various behaviors
and thus types of properties. It is frequently found that a compromise
among the needed properties must be made to be consistent with
the processing selected and the structural state desired or possible.
Most of the useful properties are related to the structural state
of the material. Typical properties of interest may be classified
into:
- Mechanical: Tensile strength, fracture toughness, fatigue strength, creep
strength, hardness, etc.
- Electrical: Conductivity or resistivity, ionic conductivity, semiconductor
conductivity (mobility of holes and electrons),etc.
- Magnetic: Magnetic susceptibility, Curie Temperature, Neel Temperature,
saturation magnetization, etc.
- Optical and Dielectric: Polarization, capacitance, permittivity, refractive index, absorption,
etc.
- Thermal: Coefficient of thermal expansion, heat capacity, thermal conductivity,
etc.
- Environmental Related: Corrosion behavior, wear behavior, etc.
- Performance: The composite of the other three elements of the field is integrated
into how the product performs. This evaluation may be made in
the various stages of manufacturing as well as in the final use
of the product. Testing and characterization is frequently employed.
Analysis of failed products is used to obtain feedback into the
processing and its control as well as the initial selection of
both the material and the stages of processing. Testing is usually
related to product meeting performance requirements, testing of
some material property, and the characterization of the levels
of structure of interest in the product. In many products the
control of the processing is closely coupled with some property
test and/or a structural characterization.
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| Failure testing machines are capable of cycling enormous loads
on small samples. |
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Photo courtesy: Images of Materials
SEM micrograph of a failure of an alumina ceramic during bending. |
Site related questions or comments? Contact crc@tms.org
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