dissertation global and local fracture properties of metal matrix ...

More documents

Recommendations

Info

Section 7 7. Application of ECAP to improve the homogeneity of the particle distribution in MMCs This work is a part of a big project on the deformation and fracture behavior of MMCs. It was originally planned to investigate (in addition to the cast MMCs) powder metallurgy MMCs with particle sizes between 100 µm and 1 µm. We found, however, that the as-received material with small particle sizes could not be used for our investigations since the material properties were extremely bad due to the appearance of large particle clusters. This part of the work deals with the problem of the homogeneity of the particle distribution in powder metallurgy MMCs: a method of equal channel angular pressing is proposed to solve this problem, and the effect of this method on the global and local fracture properties is studied. 7.1. Material An Al6061 based powder metallurgy MMC reinforced by 20% of Al2O3 particles is chosen as a material for this investigation. The alumina particle size scatters in the range between 1 and 5 µm. A few, single particles having larger sizes are observed. The size of the matrix powder is 40 µm. The composite was supplied in a form of a rod with a diameter of 25 mm: the extrusion ratio was 10:1. A metallographic section of the rod shows that the as-fabricated material has a strongly clustered particle distribution (Fig. 7.1). Fig. 7.1. Microstructure of the as-fabricated PM MMC. 79 30µm
Section 7 7.2. A model by Tan and Zhang for the case of combination of extrusion and equal channel angular pressing Tan and Zhang [23] proposed a model to predict the homogeneity of the particle distribution in PM-MMCs. They suggest that a homogeneous particle distribution can be expected only when the reinforcement size is not less than a critical value, dc, which is determined as a function of the matrix powder size, dm, the particle volume fraction, f, and the reduction ratio of extrusion, R, namely d c d = 1 ⎡⎛ π ⎞ ⎢⎜ ⎟ ⎢ f ⎣⎝ 6 ⎠ In the case of rolling, the criterion becomes [23] d c m / 3 80 ⎤ −1⎥ ⎥⎦ R . (7.1) d m = , (7.2) 1/ 3 ⎡⎛ π ⎞ ⎤ 1 ⎢⎜ ⎟ −1⎥ ⎢ 6 f ⎥ 1− R' ⎣⎝ ⎠ ⎦ where R’ is the percentage of reduction in thickness. In the case of a combination of extrusion with rolling, the critical value of reinforcement size can be derived as [23] d c d m = . (7.3) 1/ 3 ⎡⎛ π ⎞ ⎤ R ⎢⎜ ⎟ −1⎥ ⎢ 6 f ⎥ 1− R' ⎣⎝ ⎠ ⎦ One can see from all three criteria that the extrusion or (and) reduction ratio for a given material is (are) the only parameter(s) responsible for the homogeneity of the particle distribution in the PM-MMCs during its processing: its (their) increase decreases the dc-value. Theoretically, a homogeneous distribution of reinforcements could be achieved in any material, independently of the particle and matrix powder size or the particle volume fraction, if enough deformation is induced into the sample. However, a great shortcoming of extrusion and rolling is a significant decrease of the sample section with increasing extrusion or (and) reduction ratio. Thus, the extrusion or (and) reduction ratio is (are) often limited by a fixed final dimension of the sample required for industrial application.
Page 1 and 2:
MONTANUNIVERSITÄT MONTANUNIVERSIT
Page 3 and 4:
TABLE OF CONTENTS 1. Introduction 5
Page 5 and 6:
7.4.4. The effect of ECAP on the lo
Page 7 and 8:
Section 1 The main results of this
Page 9 and 10:
Section 2 2.2. The influence of the
Page 11 and 12:
Section 2 high strength, fine reinf
Page 13 and 14:
Section 2 etched to mark the inclus
Page 15 and 16:
Section 2 (4.) The specimen prepara
Page 17 and 18:
Section 3 Fig. 3.1. The digital ele
Page 19 and 20:
height [µm] height [µm] 10 0 -10
Page 21 and 22:
Section 3 Fig. 3.5. The observation
Page 23 and 24:
Section 3 3.3.2. The determination
Page 25 and 26:
Section 3 The Eshelby tensor does n
Page 27 and 28:
equivalent stress Section 3 Fig. 3.
Page 29 and 30: Assume σ m eq Calculate matrix sec
Page 31 and 32: Section 4 Table 4.1. Chemical compo
Page 33 and 34: 4.1.1.3. Fracture mechanics tests S
Page 35 and 36: Section 4 Fig. 4.4. A view of a com
Page 37 and 38: Section 4 Table 4.3. Mechanical pro
Page 39 and 40: εfr [%] εfr [%] N 16 12 8 4 0 150
Page 41 and 42: Section 4 4.2. The effect of the he
Page 43 and 44: Section 4 It should be noted that n
Page 45 and 46: CODi [µm] 40 30 20 10 0 Section 4
Page 47 and 48: Section 4 Table 4.4. Results of the
Page 49 and 50: CODi [µm] COD i [µm] CODi [µm] 2
Page 51 and 52: Cast MMCs 10%-RT 10%-8h 10%-24h 10%
Page 53 and 54: COD vi [µm] COD vi [µm] CODvi [µ
Page 55 and 56: CODvi [µm] CODvi [µm] 80 60 40 20
Page 57 and 58: Section 4 Table 4.6. The values of
Page 59 and 60: σ p max [MPa] σ p max [MPa] σ p
Page 61 and 62: σ p max [MPa] σ p max [MPa] 1200
Page 63 and 64: σ interf max [MPa] σ interf max [
Page 65 and 66: Section 4 4.5. The relation between
Page 67 and 68: Section 4 Table 4.9. Conditions for
Page 69 and 70: Ln(Ln(1/(1-F σ))) Ln(Ln(1/(1-F σ)
Page 71 and 72: Section 5 diameter of 2…8 µm and
Page 73 and 74: MnS-inclusion r θ MnS-inclusion Se
Page 75 and 76: σ interf [MPa] σ interf [MPa] σ
Page 77 and 78: Section 6 where n is the number of
Page 79: Ji [kN/m] J i [kN/m] 25 20 15 10 5
Page 83 and 84: Section 7 its initial length, li. O
Page 85 and 86: 1 µm Section 7 5 µm Fig. 7.3. A s
Page 87 and 88: Section 7 a) b) c) Fig. 7.4. Micros
Page 89 and 90: Section 7 It is important that no p
Page 91 and 92: Section 7 between the Rtot and the
Page 93 and 94: Section 7 Fig. 7.8. The fracture su
Page 95 and 96: 10 z [mm] 5 -10 -15 Section 7 0 -20
Page 97 and 98: Section 7 Table 7.3. Data on measur
Page 99 and 100: 8. Summary Section 8 This work deal
Page 101 and 102: Section 8 The effect of the homogen
Page 103 and 104: Table 9.1. Data on stress for Speci
Page 113 and 114: Table 9.11. Data on stress for Spec
Page 119 and 120: Table 9.17. Results of the stereoph
Page 121 and 122: 1 2 1 2 3 3 4 5 6 5 9 119 7 7 8 9 6
Page 123 and 124: 8 9 10 6 10 122 11 12 13 14 11 12 1
Page 125 and 126: 9 10 11 12 13 124 50 µm Fig. 9.6.
Page 127 and 128: 1 2 1 2 3 3 4 4 126 5 5 6 9 7 50 µ
Page 129 and 130: 1 1 2 2 3 4 3 4 5 5 128 6 7 6 7 50
Page 131 and 132:
Fig. 9.12. Fracture surface with ma
Page 133 and 134:
1 2 3 1 2 3 4 5 6 7 8 9 10 4 5 132
Page 135 and 136:
Page 137 and 138:
Page 139 and 140:
Page 141 and 142:
Page 143 and 144:
Page 145 and 146:
Page 147 and 148:
Page 149 and 150:
Page 151 and 152:
Page 153 and 154:
Page 155 and 156:
Fig. 12.36. Fracture surface of the
Page 157 and 158:
[14] Lewandowski JJ, Liu C, Hunt WH
Page 159 and 160:
[42] Rice JR, Rosengren GF. Plane s
Page 161 and 162:
[70] ASTM E1820-01, “Standard Tes
show all

dissertation global and local fracture properties of metal matrix ...

Create successful ePaper yourself

Delete template?

Save as template?