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