On the Short Surface Fatigue Crack Growth Behavior in a Fine-Grained WC-Co Cemented Carbide
Abstract
:1. Introduction
2. Materials and Methods
2.1. Material
2.2. Specimens
2.3. Experimental Procedure for Fatigue Tests
2.3.1. Rotating Bending Fatigue Tests (R = −1)
2.3.2. Four-Point Bending Fatigue Tests (R = 0.1)
3. Results
3.1. S-N Curve at R = −1
3.2. Fatigue Crack Growth (FCG) Behavior of Short Surface Cracks
3.3. Observation of the Crack Growth Path
3.4. Effect of the Microstructure on the Rate of FCG
4. Discussion
4.1. Difference in the FCG Behavior Between Short Surface Cracks and Long Through-Thickness Cracks
4.2. Effect of the Maximum Stress Intensity Factor, Kmax, on the Crack Growth Path
5. Conclusions
- There was little effect of the stress ratio on the da/dN-Kmax relation for short surface fatigue cracks.
- Short surface fatigue cracks have a longer region where fatigue crack growth is stable than long through-thickness fatigue cracks. In other words, long through-thickness fatigue cracks grow in a more brittle and unstable manner than short surface fatigue cracks. The FCG behavior of the short surface cracks is more susceptible to repeated stress than that of long through-thickness cracks. Thus, the FCG behaviors of both types of crack are clearly different.
- The crack growth paths were classified into four types: (1) within WC grains, (2) within the Co phase, (3) along WC/WC boundaries, and (4) along WC/Co boundaries. The percentage of crack growth paths along WC/WC boundaries decreased from 50 to 30% when Kmax was increased from 6.0 MPam1/2 to 7.5 MPam1/2, while the percentage of transgranular cracks within the WC grains increased from 20% to 40%.
- At low values of Kmax, it is not easy for a crack to grow within WC grains (transgranular cracking). Instead, fatigue crack growth occurs discontinuously along weak WC/WC interfaces or along WC/Co boundaries. On the other hand, at high values of Kmax, cleavage fractures of WC grains are more common and the area in which cleavage fractures occur is wider than at low values of Kmax. Moreover, cracks tend to be straighter than those for a low Kmax. Thus, cracks grow more rapidly for a high Kmax because of the higher crack driving force and the fewer bridging parts.
Acknowledgments
Author Contributions
Conflicts of Interest
References
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Co | Cr | W and C |
---|---|---|
13.0 | 0.51 | Bal. |
Young’s Modulus (GPa) | Fracture Toughness (MPam1/2) | Bending Strength (MPa) | Vickers Hardness (HV) |
---|---|---|---|
550 | 12.1 (11.8–12.6) | 4100 (3800–4350) | 1480 (1410–1520) |
Symbols Shown in Figure 14 | Co% (wt %) | dWC (μm) | λCo (μm) | KIc (MPam1/2) | Crack Length | R (-) | Reference | |
---|---|---|---|---|---|---|---|---|
a | 13 | 0.45 | 0.09 | 12.4 | Long | 0.1 | Mikado et al. [4] | |
b | 6 | 1.0 | 0.093 | 8.2 | Long | 0.1 | Fry et al. [12] | |
c | 6 | 0.39 | 0.15 | 7.5 | Long | 0.1 | Llanes et al. [14] | |
d | 10 | 1.1 | 0.216 | 9.1 | Long | 0.1 | Fry et al. [12] | |
e | 10 | 0.50 | 0.25 | 9.2 | Long | 0.1 | Llanes et al. [14] | |
f | 13 | 0.45 | 0.09 | 12.4 | Short | −1 | This work | |
g | 18 | 0.45 | 0.11 | 13.7 | Short | −1 | Mikado et al. [24] | |
h | 13 | 0.45 | 0.09 | 12.4 | short | 0.1 | This work |
Kmax (MPam1/2) | rp (μm) |
---|---|
6.0 | 0.34 |
6.5 | 0.40 |
7.0 | 0.46 |
7.5 | 0.53 |
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Mikado, H.; Ishihara, S.; Oguma, N.; Kawamura, S. On the Short Surface Fatigue Crack Growth Behavior in a Fine-Grained WC-Co Cemented Carbide. Metals 2017, 7, 254. https://doi.org/10.3390/met7070254
Mikado H, Ishihara S, Oguma N, Kawamura S. On the Short Surface Fatigue Crack Growth Behavior in a Fine-Grained WC-Co Cemented Carbide. Metals. 2017; 7(7):254. https://doi.org/10.3390/met7070254
Chicago/Turabian StyleMikado, Hiroko, Sotomi Ishihara, Noriyasu Oguma, and Shingo Kawamura. 2017. "On the Short Surface Fatigue Crack Growth Behavior in a Fine-Grained WC-Co Cemented Carbide" Metals 7, no. 7: 254. https://doi.org/10.3390/met7070254