Metal Injection Moulding of Ti and Ti alloys (MIM-Ti)

Metal Injection Moulding
of Ti and Ti alloys
(MIM-Ti)

Motivation:
 Producing small-to-medium sizes and very complex
designs of titanium parts.
Problem definition:
 It`s difficult to make parts from titanium duo to high
oxygen affinity of titanium.

Solution methods:
 Forming process
 Casting process
 Machining
 Metal Injection Moulding “M
(MIM)

Level of solution:
 Although forming is a good choice to minimize cost, the Metal
Injection Moulding is better choice for specific circumstances.
 we can notice that in low
production the cost of MIM is
high, but in mass production
the cost of MIM is nearly
equal to the cost of forming
process

Introduction:
 MIM process is an established net-shape manufacturing
process that combines:
MIM Process
Powder
Metallurgy
Plastic
Injection
Moulding
• Flexibility of composition
selection.
• Inexpensive raw materials.
• Ability to manufacture
complex parts.
• It is particularly suited to
mass production.

Challenges which face MIM-Ti nowadays.
 It`s hard to get fine spherical powder (≤ 45 μm).
• Gas atomization
• Plasma wire-based atomization process
 The high affinity of titanium for oxygen and carbon.
• It requires special considerations specially in binder system.

Gas atomization:
It is a process to manufacture high
quality metal powders.
It offers a perfectly spherical shape
combined with a high cleanliness level.
Plasma wire-based atomization process:
 A titanium wire is atomized by 3 inert gas
plasma jets to form spherical metal
powders.
 the powders obtained is very pure.

MIM Process:
1. Mixing
• The materials are mixed under a protective atmosphere.
• At a temperature slightly higher than the melting point of the
binder.
2. Injection Moulding
• Injection molding machines are used to inject the green part
3. Debinding system.
• First step (Chemical)
• Second step (Thermal debinding)
4. Sintering
• Brown part is sintered at a high temperature and in a high
vacuum to form a solid component.

Mechanical properties:
 Most of parts need moderate properties, although superior mechanical
properties are always desired. Density, interstitial content (oxygen,
carbon and nitrogen), microstructure and alloying content can all affect
mechanical properties.
1. Density
To get a fine powder (≤45 μm) with a high sintered density (98%) in
MIM-Ti parts to reduce the surface porosity and improved the fatigue
strength by 100 MPa
• Add Small additions of alloying elements such as iron, nickel or boron
• Hot isostatic pressing (HIP) is a common process used to improve the
density and mechanical properties and improve the ductility of MIM by
reduce the porosity

2. Interstitial elements
 Oxygen is the main element decreases ductility,
cold workability, fatigue strength and
corrosion resistance of Ti and its alloys.
 nitrogen, carbon and hydrogen could have a
detrimental influence on the properties but these
elements are negligible in comparison with
oxygen
• It is necessary to limit the oxygen content to 0.3 wt% for a commercially
pure Ti component and to 0.2% for a Ti-6Al-4V component .
• It is necessary to limit the carbon content to 0.08 wt% to avoid titanium
carbide formation within the structure.

3. Microstructure
• A uniform, fine microstructure, including grain size, lamellar size, phase
distribution and morphology is necessary to improve the mechanical
properties.
• Due to the high temperature in sintering process led to coarse
microstructure, controlling that by morphology and size of α and β lathes
and grains is necessary for achieving the desired final mechanical
properties.
• sintering heat treatments may improve the ductility and strength of MIM
components through their modification of microstructure.

Showing examples of general microstructures obtained in MIM of different Ti
alloys. The presence of a coarse microstructure is clear especially for pure Ti
(Fig. a) and Ti-6Al-4V (Fig. b). Also, illustrates a large improvement in the
microstructure and density of Ti-6Al-4V components by addition of 0.5% boron
to the feedstock.

4. Alloying
• Improvements to the mechanical properties of Ti components by
small (or large) additions of other elements such as (CP-Ti, Ti-
6Al-4V, Ti-Nb, Ti-Mo, Ti-Mn, Ti-Ni shape memory and Ti-Al
alloys)
• addition of small amounts of alloying elements such as B and rare
earth elements (Ce, La, Y2O3)

Dimensional accuracy of MIM-Ti components :
Dimensional reproducibility, uneven shrinkage and distortion are significant
challenges for Ti-MIM. These challenges, which are common for MIM of all
materials.
The most important categories:
• Component factors:
Component size, geometry and wall thickness can significantly influence the
distortion and dimensional stability of sintered parts
especially for large-sized parts This is because the large components carry a
greater chance of containing residual binder, which generally limit the part size
for MIM to 50 mm, wall thickness of 5.0 mm and weight 50 g.

• Feedstock factors
Powder characteristics such as size, shape and distribution, binder systems,
mixing processes and powder loading can significantly influence distortion
and dimensional accuracy of MIM products. Also, coarse powders have been
found to show more distortion compared with fine powders.
• Processing factors
Injection molding parameters as well as debinding and sintering
parameters can severely influence dimensional accuracy, Therefore,
extreme care is required to optimize all steps of the MIM-Ti process in
order to control shrinkage and prevent distortion in the final products.

Developments in MIM-Ti:
A great effort has been made in the last decades for the
developments of MIM-Ti to obtain a:
• High dimensional precision
• Low oxygen content
• High mechanical properties.

Patent JP2005281736
Brief: They found a new solution for low cost manufacturing of MIM-Ti alloy components.
Method: They mixed different fractions of TiH2 (25 wt %), HDH titanium (75 wt %) and
60Al-40V pre-alloyed powders to manufacture Ti-6Al-4V components.
Result: Low oxygen (0.31%) and excellent mechanical properties, YS =910 MPa, UTS =
950 MPa and El = 14%.
Patent CN105382261
Brief: They found a solution to improve the dimensional accuracy of MIM-Ti components.
Method: They mixed titanium powders with different average particle sizes to produce
MIM feedstock.
Result: They obtained a high dimensional precision, low oxygen level of (˂ 0.25 wt %) and
high mechanical properties.

Patent US7883662B2
 Brief: A new binder system (ex: Aromatic binder 80) for control of the oxygen
and carbon content in MIM-Ti components as it helps to retain the shape of the
molded article and is removable via relatively low temperature means.
Method: The components is
shown in this figure
Result:
Oxygen content < 2000 ppm
Carbon content < 800 ppm
Nitrogen content <500 ppm

Important industrial Ti alloys
Commercially pure titanium (CP-Ti)
• CP-Ti is common in industrial applications (automotive,
marine and medical) and having the greater acceptable
tolerances for oxygen content, which can be up to 0.4% for
grade 4.
• This process is able to manufacture components with
chemical composition as well as mechanical properties.

 Ti-6Al-4V alloy (Ti64)
• It used extensively in the aerospace industry.
• Tensile strength up to 800MPa and elongation of 15% are
achievable through this process.
• This figure indicates that a typical lamellar structure with a
small fraction of remaining porosity exists in the
microstructures.

 Ti-10V-2Fe-3Al (Ti-10-2-3)
• It is a near beta alloy with a superior combination of strength and
toughness as well as high fatigue life.
• It's has been manufactured Ti-10-2-3 super elastic components
by MIM processing followed by solution treatment and aging.
• Properties: Under optimized MIM conditions, they reached a
high density of 97%, tensile strength of 1050 MPa and
elongation of 5.0%
• Applications: used in aircraft parts and aerospace components.

Titanium aluminides (Ti Al)
• with high strength-to-density ratio and
excellent resistance to creep and oxidation
at high temperature are structural
materials for various applications.
• This figure indicates that while as MIM
samples have a large fraction of porosity
an almost pore free microstructure is
obtained after Hot Isostatic Pressing
(HIP) processing.
• the ductility of the samples failed to
improve after HIP due to the high oxygen
level.

 MIM of porous Ti and Ti alloys
• MIM combined with space holder techniques has
the potential to manufacture porous components.
• Used in biomedical applications.
• It can be used KCl and NaCl as a space holders.
• micrographs of porous Ti
samples manufactured by MIM
and space holder technique. a)
42% porosity, b) 52% porosity,
c) 62% porosity, d) 72%
porosity

Application of MIM for the manufacture of
Ti components:
In biomaterial and implant fields, MIM can be used to manufacture
both high density and porous components.
As medical implants usually need porous structures, many attempts
have been made to manufacture porous Ti components.
Military and particularly the firearms industry are major
consumers of metal injection moulded products because MIM is a
flexible process that can produce high quality, precise net shape parts
while eliminating the need for expensive secondary processes

Examples of a) industrial and b) medical implant parts manufactured
using MIM-Ti process.

Metal Injection Moulding of Ti and Ti alloys (MIM-Ti)

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