MPIF 2016 kmj

Royal Military College - College Militaire Royal

Microstructural Studies of Tungsten–Manganese–(Chromium

or Titanium) Alloys Prepared by Mechanical Alloying

MPIF 2016Boston, MA

O. Elsebaie and K.M. Jaansalu Department of Chemistry and Chemical Engineering

Royal Military College of Canada

Royal Military College - College Militaire Royal 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


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


BackgroundTungsten 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


BackgroundTungsten 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)


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


BackgroundManganese

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


BackgroundTitanium

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.htm2- 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)


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.htm2- 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)


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


Experimental ProceduresAlloy 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

CompactionMilled 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

TungstenManganese

TitaniumChromium

99.95%99.60%99.50%99.00%

1-1.5 µm<10 µm<44 µm<44 µm

Inframat Advanced ChemicalsAlfa AesarAlfa AesarAlfa Aesar


Experimental ProceduresAlloy Characterization

X-Ray Diffraction: Scintag XRD PANalytical X’Pert Pro MPD The diffraction angle range

(2θ) was 20º-130º


Experimental ProceduresAlloy 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


Results & DiscussionXRD 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 ÅW from lit ~ 3.1648 Å

1. W phase2. MnTi2O4

3. TiN

3 -

TiN

(20

0)

3 -

TiN

(11

1)

2 -

MnT

i 2O4

(311

) 1- W

pha

se


Results & Discussion

SEM Analysis – W-20Mn-17Ti

at 1275°C/30 min at 1425°C/30 min

Oxides Tungsten phase

Coalescence

15


Two phases: W-rich and oxides

Overall compositions selected for Laves phase appearance

18


Ternary Phase Diagram: Mn - W - Ti


Two phases: W rich and oxides

Decreasing solute content in tungsten due to: oxidation (SEM / XRD) and nitration (XRD)




Results & DiscussionXRD 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 ÅW from lit ~ 3.1648 Å

1. W phase2. MnCr2O4

3. Cr phase

3 - C

r-pha

se

1-W

pha

se

2 - M

nCr 2O

4


Results & Discussion SEM Analysis - W-17Mn-18Cr

at 1275°C/30 min

22

at 1425°C/30 min

Chromium phase

Chromium phase

oxide phase

Oxides


Results & Discussion SEM Analysis - W-50Mn-20Cr

at 1275°C/30 min

23

at 1425°C/30 min

Manganese phase

Manganese phase

Oxide phase

Oxide



Ternary Phase Diagram: Mn - W - Cr

Note extensive chromium rich solid solution

Loss of manganese Two or three metal alloy

phases present plus oxide



Ternary Phase Diagram: Mn - W - Cr Composition at Mn-Cr side

corresponds with sigma phase Possible precipitated on

cooling Presence not yet confirmed

Relatively higher manganese loss



Ternary Phase Diagram: Mn - W - Cr Agreement between

predicted phase diagram and experimental data reasonable considering manganese loss and oxidation


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


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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