MPIF 2016 kmj

Royal Military College - College Militaire Royal
Microstructural Studies of
Tungsten–Manganese–(Chromium
or Titanium) Alloys Prepared by
Mechanical Alloying
MPIF 2016
Boston, MA
O. Elsebaie and K.M. Jaansalu
Department of Chemistry and Chemical Engineering
Royal Military College of Canada

2
Outline
 WHA & Adiabatic Shear
 Background – Binary Phase Diagrams
 Short Term and Long Term Objectives
 Alloying, Sintering, XRD and SEM/EDX
 Resulting Microstructure and Solubility
 Conclusions
 Future Work

3
Introduction
 Tungsten heavy alloys (WHAs) have high strength and high density
 Desire to replace depleted uranium (DU) alloys with WHAs in KE
projectiles
 Challenge: produce microstructure that will form adiabatic shear
bands (ASBs) under hypervelocity impact
 Characteristics sought: fine microstructure, low thermal diffusivity
 Approaches: modification of the matrix, cold working of the alloy,
and alloying of the tungsten itself
 Alloying tungsten  requires a different approach and phase
diagrams

4
Background
Tungsten Alloys
 Some characteristics of the alloying elements
Property Alloying elements
W Mn Ti Cr
Thermal conductivity
(W/mK)
173 7.81 19 93.9
Density
(g/cm3)
19.25 7.21 4.506 7.19
Heat of Mixing
(kJ/mol)
- +6 +2.4 +7.4

5
Background
Tungsten Heavy Alloys (WHAs)
 Consist of W grains bounded by a lower
melting point alloy matrix (Ni, Co, Fe)
 In literature, a theoretical calculation1
of
∆H mix for W-Mn system is positive, +4 to
+8 kJ mole-1
 Energy provided during mechanical milling
 A finer microstructure and some solubility of
Mn in W is observed
1. F. R. de Boer, R. Boom, W. C. M Mattens, A. R. Miedema, and A. K. Niessen, Cohesion in
Metals, (Amsterdam: North-Holland Physics Publishing, 1988)

6
Background
Phase Diagram Calculation
 Principles behind the computer calculation of phase
diagrams are well established
 Programs use similar approaches (FactSage, ThermoCalc)
 Self-consistent databases for commercial light alloys, steels,
slags, copper alloys, superalloys, molten salts, etc are available
 Several tungsten binary systems assessed, but no
database
 Cr-W, Cr-Mn, Ti-W, Ti-Mn
 Mn - W not known
 W and δ-Mn both have bcc crystal structure
 Mn is soluble in Cr and Mo

7
Background
Manganese
 Limited terminal solid solubility
 δ-Mn has high vapour pressure and affinity for oxygen
 W displays a limited solubility in α-Mn

8
Background
Titanium
 Fully soluble in tungsten at high temperature(1)
 Displays a limited solubility in α-manganese
 Titanium itself is prone to adiabatic shear band formation(2)
∆Hmix = 2.4 kJ / mole (3) ∆Hmix = -3.1 kJ / mole (3)
1- http://www.crct.polymtl.ca/fact/documentation/BINARY/BINARY_Figs.htm
2- Y. Bai, B. Dodd, Adiabatic Shear Localization Occurrence, Theories and Applications, (2002) 24-53.
3- F. R. de Boer, R. Boom, W. C. M Mattens, A. R. Miedema, and A. K. Niessen, Cohesion in Metals, (Amsterdam: North-Holland Physics
Publishing, 1988)

9
Background
Chromium
Cr-W
 Cr soluble in W (1)
 Miscibility gap
∆Hmix = +7.4 kJ / mole (2)
-
Cr-Mn
 Mn soluble in Cr (1)
 Intermetallic compounds
∆Hmix = -3.1kJ / mole (2)
1- http://www.crct.polymtl.ca/fact/documentation/BINARY/BINARY_Figs.htm
2- F. R. de Boer, R. Boom, W. C. M Mattens, A. R. Miedema, and A. K. Niessen, Cohesion in Metals, (Amsterdam: North-Holland Physics
Publishing, 1988)

10
Objectives
Short term:
 Understand the effects of Ti and Cr addition on the microstructure
of the W-Mn alloys
 Study the solubility of Mn in W in the presence of Ti and Cr and
compare to extrapolated phase diagrams
Long term:
 Identify potential WHAs to replace DU alloy in KE projectiles

11
Experimental Procedures
Alloy Preparation
 Ternary alloys: W-20Mn-17Ti, W-25Mn-10Ti, W-18Mn-17Cr, W-50Mn-20Cr
 Milling: Planetary ball mill (Retsch PM 100) at 400 rpm with 1 % wax,
tungsten carbide balls for 4 hr (charge ratio 10:1) under argon
Chemical composition of powder used to prepare the alloy
 Compaction
Milled powders consolidated into green discs, 1.27 cm in diameter, under a
pressure of 460 MPa for 1 min
 Sintering
Alloy samples were sintered in a LECO TF-1 tube furnace, under a
controlled atmosphere of high purity argon, followed by dry hydrogen gas
at 1225°C for 1 hr, at 1275°C, 1350°C, 1425°C for 30 min
Material Purity Size Supplier
Tungsten
Manganese
Titanium
Chromium
99.95%
99.60%
99.50%
99.00%
1-1.5 µm
<10 µm
<44 µm
<44 µm
Inframat Advanced Chemicals
Alfa Aesar
Alfa Aesar
Alfa Aesar

12
Alloy Characterization
 X-Ray Diffraction:
 Scintag XRD
 PANalytical X’Pert Pro MPD
 The diffraction angle range
(2θ) was 20º-130º

13
Alloy Characterization
Examination of the microstructural
constituents and surface chemical
analysis
 Scanning Electron Microscopy
(SEM), 20kV
 Philips VP-30XL,
 FEI Quanta
 FEI FEG NanoSEM
 Energy Dispersive X-ray
Spectrometry
 EDAX Apollo Detector, Genesis
software
 Bruker XFlash detector and Esprit
software

14
Results & Discussion
XRD pattern - W-20Mn-17Ti
MnO
The 25-50º region shown here
Standard detected peaks
1- W (110)
2- MnTi2O4 (311)
3- TiN (200)
Lattice parameter
W-rich phase ~ 3.1636 Å
W from lit ~ 3.1648 Å
1. W phase
2. MnTi2O4
3. TiN
3-TiN(200)
3-TiN(111)
2-MnTi2O4(311)
1-Wphase

SEM Analysis – W-20Mn-17Ti
at 1275°C/30 min at 1425°C/30 min
Oxides
Tungsten phase
Coalescence
15

18
 Two phases:
 W-rich and oxides
 Overall compositions
selected for Laves phase
appearance
18
Ternary Phase Diagram: Mn - W - Ti

19
 Two phases:
 W rich and oxides
 Decreasing solute content
in tungsten due to:
 oxidation (SEM / XRD) and
 nitration (XRD)

20
 Two phases:
 W rich and oxides
 Decreasing solute content
in tungsten due to:
 oxidation (SEM / XRD) and
 nitration (XRD)

21
XRD pattern- W-18Mn-17Cr
The 25-50º region shown here
Standard detected peaks
1- W phase (110)
2- MnCr2O4 (311)
3- Cr phase (110)
Lattice parameters
W-rich phase ~ 3.1362 Å
W from lit ~ 3.1648 Å
1. W phase
2. MnCr2O4
3. Cr phase
3-Cr-phase
1-Wphase
2-MnCr2O4

SEM Analysis - W-17Mn-18Cr
at 1275°C/30 min
22
at 1425°C/30 min
Chromium phase
Chromium phase
oxide phase
Oxides

SEM Analysis - W-50Mn-20Cr
at 1275°C/30 min
23
at 1425°C/30 min
Manganese phase
Manganese phase
Oxide phase
Oxide

26
Ternary Phase Diagram: Mn - W - Cr
 Note extensive chromium
rich solid solution
 Loss of manganese
 Two or three metal alloy
phases present plus oxide

27
 Composition at Mn-Cr side
corresponds with sigma
phase
 Possible precipitated on
cooling
 Presence not yet confirmed
 Relatively higher
manganese loss

28
 Agreement between
predicted phase diagram
and experimental data
reasonable considering
manganese loss and
oxidation

29
Conclusions
This study investigated the effects of Ti or Cr additions in
a W-Mn alloy:
 Oxidation and nitration a factor with the addition of Ti
 Maximum solubility observed for Mn in W observed at 1275°C for
both Ti and Cr ternary systems
 Solubility of Mn in W decreases modestly at 1350 and 1425°C,
vapourization of Mn also a concern
 Experimental data for Mn-W-Cr alloys in modest accord with
predicted (extrapolated) ternary phase diagram

30
Future Work
 Alternative sintering methods (and elements) to overcome the
oxidation and vaporization of manganese
 Application of post heat-treatment process for homogenization of
the microstructure
 Thermodynamic modelling (using FactSage) to assess other
possible ternary systems eg W-Mo-Mn
 Investigate the mechanical properties of ternary W-Mn-Cr and W-
Mo-Mn alloys

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