Liquid Metal Engineering; EXOMET and Metal-Matrixnanocomposites

Transcription

1 Liquid Metal Engineering; EXOMET and Metal-Matrixnanocomposites W. D. Griffiths, N. Adkins and D. Shevchenko School of Metallurgy and Materials, College of Engineering and Physical Sciences, University of Birmingham, Edgbaston, Birmingham, UK, B15 2TT.

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3 The EXOMET project 1. Aimed for a 50% increase in strength and ductility. 2. Creep-resistant Al alloys, up to around C institutions from 13 countries. 4. Runs The issues; 1. Nano-particle creation. 2. Prevention of nanoparticle agglomeration in the alloy. 3. Particle pushing / engulfment during solidification. 4. Casting to obtain desired mechanical properties. 5. Upscaling to industrial scales.

4 The EXOMET project 1. Physical Processing of Molten Light Alloys under the Influence of External Fields. 2. For grain refiners and nanocomposites TiBor+ grain refiners for Mg alloys. 4. Electromagnetic, ultrasonic and mechanical shearing.

5 The EXOMET project 1. Physical Processing of Molten Light Alloys under the Influence of External Fields. 2. For grain refiners and nanocomposites TiBor+ Mg grain refiners. 4. Electromagnetic, ultrasonic and mechanical shearing.

6 The EXOMET project 1. Physical Processing of Molten Light Alloys under the Influence of External Fields. 2. For grain refiners and nanocomposites. 3. Electromagnetic, ultrasonic and mechanical shearing.

7 1. Strengthening Mechanisms I Load Transfer σ 0.5 V σ Δσ load = 0.2 MPa Where Vp= volume fraction of particle = 1 or 2 vol.%

8 Strengthening Mechanisms II Orowan. Δσ Orowan = 2 MPa

9 Strengthening Mechanisms III Hall-Petch σ σ 0 = 20 MPa K = 0.04 MPa.m 1/2 d= 50 μm Δσ Orowan = 26 MPa

10 Strengthening Mechanisms IV Coefficient of Thermal Expansion Mismatch Δσ 3 β G b 12 V α T 1 V b d For ; dp= 50 nm and α Al = 22.2x10-6 K -1 For ; dp= 50 nm and α= 2.8x10-6 K -1 Δσ CTE = 211 MPa

11 Summary of the Strengthening Mechanisms σ Δσ load = 0.2 MPa Δσ Orowan = 2 MPa Δσ Hall-Petch = 26 MPa Δσ CTE = 211 MPa

12 2. Preform fabrication. Water based slurry preparation (2 48 hours) Mould heating for starch consolidation (2-3 hours) Preform firing to remove starch (4 20 hours)

13 The preform. Investigated the influence of Starch loading Slurry rolling time Starch consolidation time 1.5 hours consolidation time 2 hours consolidation time Optimal composition: 30 g of per 100 ml of water 43 g of starch per 100 gm of Maximum loading 27 vol% (39 wt% loading with AZ91) 2 hours rolling time 48 hours rolling time

14 The Hot IsostaticInfiltration Technique Before After HIPing details; Pressure up to 200 MPa Temperature 700 C Dwell time 10-30min Full infiltration of preform

15 The HIPpedpreform The wall thickness of top part of the can was increased by 2 mm preform infiltrated with AZ91

16 Masteralloymelting ISM crucible AZ31 solidified in the crucible

17 Tensile results, AZ31 and AZ31 + 2vol.% AZ31 + AZ31 True Stress MPa True Strain

18 AZ31 and AZ31+2vol.% 30.0 Modulus of Elastisity ( Gpa) AZ AZ Modulus of Elastisity (Gpa) AZ31 AZ31 + AZ31 63 MPa AZ Mpa + 24% PS 0.2

19 Element Weight% Atomic% Element Weight% Atomic% C K 9 17 O K Mg K 1 1 Si K Cu K 2 1 Totals 100 Particle sizes seems to be in agreement with manufacturer statement (40 nm). Particleswerefoundwithinthe Al-Si matrix. O K Si K Cu K 4 1 TEM BF image Totals 100 EDS incertitude ± 1% Element Weight% Atomic% C K 2 4 O K Mg K 1 1 Si K Cu K 3 1 Totals 100

20 TEM observation of a Mg-nanocomposite By KeeHyun Kim

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22 Other images (the scale marker bar is 200 nm)

23 Polycrystalline Tilting particles are crystalline and polycrystals, confirmed by diffraction patterns

24 Magnified images Matrix Matrix Matrix Matrix

25 Oxidation of the matrix -MgO

26 Silicon particles Some particles are pure Si not!!! Please see and compare with point analysis

27 Summary of work to date., Al 2 O 3, AlN, Al(OH) 3 nanopowdersinvestigated as candidate materials for preforms. and Al 2 O 3 materials were selected. (AlNreacts with water). Slurry composition has been optimised. and Al 2 O 3 preforms have been infiltrated with AZ91 Tensile testing of AZ31+2vol.% was undertaken and showed significant performance improvement, (Young s Modulus and PS 0.2 ).

28 3. Electromagnetic Stirring and Cavitation in an Induction Furnace Designed by Pericleous and Valdez at Greenwich University, and built by ALD.

29 Electromagnetic Stirring and Ultrasonic Cavitation (K. A. Pericleous, Greenwich University)

30 4. Positron Emission and Annihilation PEPT uses a radioactive isotope which decays by releasing a positron (β+); the positrons collide with local electrons to produce two back-to-back γ-rays.

31 Positron Emission Tomography Positron Imaging uses a particular type of radioactive isotope, (specifically, 18 F), that decays by releasing a positron (β + ). The positron collides with a local electron giving off 2 γ-rays emitted backto-back. Detection of the γ-rays allows the original location of the particle, along a line, to be found. Detection of multiple pairs allows the particle location to be to be found by triangulation.

32 In this example a rat has been dosed with a radioactive glucose compound, (containing C-11), that accumulates in the kidneys and the pituitary gland, which allows their function to be studied.

33 Positron Emitting (β+) Isotopes Nuclide Half-Life 82 Rb 78 s 15 O 122 s 13 N 10 min. 11 C 20.3 min. 68 Ga 68 min. 18 F 110 min. 45 Ti 3.1 h. 62 Zn / 62 Cu 9.2 h. 66 Ga 9.7 h. 64 Cu 12.7 h. 140 Nd / 140 Pr 3.4 days. 124 I 4.2 days. 82 Sr / 82 Rb 25 days 68 Ge / 68 Ga 271 days 22 Na 2.6 years.

34 Labelling Methods 1. Bombardment of an oxide particle by 3 He. Oxygen in the outer layers is converted to 18 F. Detectable particles are typically submm, μm. 2. Bombardment of water by 3 He produces water containing 18 F. This is adsorbed onto the particle surface, (either alumina or an ion-exchange resin). Smaller, <100μm, or more active, particles can be made.

35 Effect of casting temperature a) b) c) d) Casting Temperatures (a) 85, (b) 110, (c) 87 and (d) 87

36 The sand casting.

37 Results of Al plate castings. Initial Particle Location b) a) Two particle tracks for alumina particles entrained in Al alloy sand-cast plate castings. (a) size = 355 to 425 µm. (b). size = 425 to 710 µm

38 View of particle simulation after 3 seconds of simulated time. (~1000 particles.s -1 ) Flow Velocity Higher velocities displayed darker Flow Direction Particle locations Flow Direction

39 Modelled inclusion trapping in liquid Al in a sloping launder.

40 The PEPT Experiment

41 600 µm particle track

42 Summary Previous attempts at metal-matrix failed due to processing problems. Current attempts at making nanocompositesare to deploy a wider range of novel processing techniques and have a greater chance of success.

43 Future Work 1. The manufacture of Al-MMnC s. 2. The introduction of Mg-MMnC s into Al alloys. 3. The use of electromagnetically-generated cavitation to disperse MMnC s. 4. The use of electromagnetic stirring to disperse the MMnC s. 5. The use of PEPT to study particle behaviour during electromagnetic stirring.