MATERIAL SELECTION CRITERION BY
JAMES M MUTUA
DEPARTMENT OF MECHANICAL ENGINEERING- JKUAT, KENYA
Selection constraints for research material ranges from;
1. Properties of the material (mechanical, chemical and physical
properties)
2. Cost
3. Availability
4. Ease of processing
Parameter for consideration when selecting a material of choice.
Properties
Maraging steels
Maraging steels are one of the steel categories that are characterised by
good dimensional stability, high fatigue strength, and post processing
capability.
They contain iron as the main alloying element while Silicon, Manganese,
Chromium, Molybdenum, Nickel, Titanium, phosphorus, cobalt and very small
quantities of carbon as the other alloying elements. Typical composition is
shown below.
Properties
1. Good dimensional stability during and after processing
2. High strength
3. High hardness
4. Good fracture toughness
5. Their properties can be enhanced through age hardening.
6. Low carbon content- reduced/no quench cracking
7. High nickel content and absence of carbides-good corrosion/high wear
resistance.
8. Exhibits high cooling rates- favours epitaxial solidification
Properties
High fracture toughness
High strength
Excellent dimensional stability
Good weldability
Good corrosion resistance
Has high cooling rates
Additive manufacturing technology produces maraging steel products with
significantly higher yield strength and fracture toughness. This can also be
enhanced by the ability of the MS to undergo age hardening. Post process
heat treatment leads to improved hardness, tensile strength. However, the
%elongation is significantly reduced.
The low carbon content (<0.03 C %Wt.) guards the products against quench
cracking. On the other hand, high nickel content and the absence of carbides
in its structure contributes to the good corrosion resistance and wear
resistance nature of the material.
The material possess low thermal expansion coefficient which is responsible
for its excellent dimensional stability after solidification.
High cooling rates favours epitaxial solidification of the material during the
complicated thermal transformation that take place. This high solidification
rates ensure precipitation and uniform distribution of Ni- rich intermetallic
compounds in the lathe martensite as well as minimising the reversion of
metastable martensite. These are the ingredients to associated with the high
strength and high fracture toughness exhibited by the materials.
Powder characteristics
Diameter- maraging steel powder can be generated using both water
atomization (WAP) and the gas atomization processes GAP). The GAP is
highly preferred due its ability to produce near-spherical morphology and
smooth surfaced powder despite its high cost.
To a high degree of accuracy, uniform diameter powder particles can be
made from maraging steels (diameters in the range of 20- 100 m have
been generated and used in metal 3D printing using maraging steels).
Stability- due to their low affinity for oxygen, maraging steel material
are regarded as moderately stable during 3D printing. However, precautions
should be taken to provide inert environment during the part printing.
Flowability- due to the uniform diameter exhibited by the powder,
their flow rate can easily be controlled and therefore provide the optimum
required material flow rate an important parameter in optimizing 3D printing
process.
Apparent density
Processing
Temperature
Compound transformation and their significance
Post production processing and their significance
Cost
The cost of maraging steel is slightly higher compared that of
austenitic stainless steels (specific costs per kg=19,000 /kg)
Applications
Structural/Sub- structural
Finds a lot of application in the aerospace, automobile industry
[rocket motor casings, landing gears] due to their superior
mechanical properties)
Non-structural (..)
Tooling applications such as making dies, drill chunks, moulds
fasteners etc
Conformal cooling channels- high cooling rate..
Maraging (Vascomax) in Aerospace
Maraging (Vascomax) is stronger than most standard steel yet still malleable. It can be flow formed over
mandrels as a thinner rocket or missile skin at any length. Thinner means more
room for payloads and fuel.
Maraging for the Military
Our armed forces rely on weapons that perform reliably over long periods in harsh environments. Maraging
(Vascomax) retains its strength and has minimum distortion and deterioration, even after heat and pressure. It
is a key material in the manufacture of all types of firing pins and breech blocks.
Maraging in Transportation
Maraging's superior strength and ductility make it the preferred material for
critical parts such as landing gear in all types of civilian and military aircraft.
Temperature changes and sudden or constant applications of pressure,
impact or torque, have little effect on parts made from Maraging. It is the ideal
material for high performance internal engine components such as shafts,
gears and fasteners.
Maraging in Manufacturing
Maraging's ability to expand without cracking make it the material of choice
for drill chucks. Its uniform machinability and durability make it ideal for
producing gears in sophisticated robotic arms in assembly lines, and its high
strength and wear resistance make it perfect for grippers in automation lines. Other Maraging (Vascomax)
benefits for the manufacturing arena include excellent polishability and weldability with pre- or post heating.
Maraging in Tool & Die Making
Maraging (Vascomax) has a significant cost advantage over other alloys. Uniform predictable
shrinkage during heat treatment means Maraging does not require excessive reworking. It is easily
machined. Its hardness and strength allow it to withstand the repeated pressures of compression
molding for longer tool life with a very good surface finish.
Availability
Enough quantity for mass production of 3D products to meet the
emerging demand is necessary.
Material availability will greatly affect the rate of Am adoption as
a tool for mass production.
Opportunities for new knowledge
Existing literature
Stainless steels
Properties
1. Good ductility
2. High strength
3. High corrosion resistance
4. Relatively low cost
5. Relatively light weight
Powder characteristics
Diameter
Stability
Flowability
Apparent density
Processing
Temperature
Compound transformation and their significance
Post production processing and their significance
Cost
Applications
Structural
Sub- structural
Non-structural (..)
Availability
Enough quantity for mass production of 3D products to meet the
emerging demand
Opportunities for new knowledge
Existing literature
