lamellar features on the fracture toughness
Conclusions
(1)
Three microstructures with different lamellar features were prepared by controlling the cooling rates after β forging. The final microstructure characterized by short rod-like α platelets was obtained by Ti-17 alloy through water quenching, which are about 3–10 μm in length and 1–1.5 μm in thickness. The final microstructure characterized by thin needle-like α platelets were obtained by Ti-17 alloy through air cooling, which are about 10–20 μm in length and around 1 μm in thickness. The slow air cooling method can provide the Ti-17 forging the lowest cooling rates among the three cooling methods. Thus the longest and the thickest α platelets were obtained by Ti-17 alloy through slow air cooling, which are about 20–40 μm in length and around 1.5 μm in thickness.
(2)
The microstructure obtained through water quenching has relatively higher plasticity and lower strengths than the microstructures obtained through air cooling and slow air cooling methods. Besides, the tensile properties for the microstructures obtained through air cooling and slow air cooling methods are almost the same.
(3)
Two major contributions to toughness are crack path tortuosity (extrinsic part) and material plastic deformation along the crack path (intrinsic part). Based on the existent models proposed by previous researchers, the respective contribution of the plasticity and crack path tortuosity to the fracture toughness of Ti-17 alloy are quantitatively evaluated. The results show that the intrinsic contributions for the three microstructures with different lamellar features don't show a big difference. However, their extrinsic contributions are dramatically different.
(4)
The microstructure which contains the longest and thickest α platelets gets the most rugged crack propagation path and moderate plasticity among the three microstructures, which results in the highest fracture toughness (95.9 View the MathML source). Moreover, due to the nature of the near-β Ti-17 alloy, the α platelets in this microstructure get very high aspect ratios, which results in its high strength. Thus for Ti-17 alloy studied in present work, the long and thick α platelets in microstructure can realize a good combination of fracture toughness and strength.
lamellar features on the fracture toughnessConclusions(1)Three microstructures with different lamellar features were prepared by controlling the cooling rates after β forging. The final microstructure characterized by short rod-like α platelets was obtained by Ti-17 alloy through water quenching, which are about 3–10 μm in length and 1–1.5 μm in thickness. The final microstructure characterized by thin needle-like α platelets were obtained by Ti-17 alloy through air cooling, which are about 10–20 μm in length and around 1 μm in thickness. The slow air cooling method can provide the Ti-17 forging the lowest cooling rates among the three cooling methods. Thus the longest and the thickest α platelets were obtained by Ti-17 alloy through slow air cooling, which are about 20–40 μm in length and around 1.5 μm in thickness.(2)The microstructure obtained through water quenching has relatively higher plasticity and lower strengths than the microstructures obtained through air cooling and slow air cooling methods. Besides, the tensile properties for the microstructures obtained through air cooling and slow air cooling methods are almost the same.(3)Two major contributions to toughness are crack path tortuosity (extrinsic part) and material plastic deformation along the crack path (intrinsic part). Based on the existent models proposed by previous researchers, the respective contribution of the plasticity and crack path tortuosity to the fracture toughness of Ti-17 alloy are quantitatively evaluated. The results show that the intrinsic contributions for the three microstructures with different lamellar features don't show a big difference. However, their extrinsic contributions are dramatically different.(4)The microstructure which contains the longest and thickest α platelets gets the most rugged crack propagation path and moderate plasticity among the three microstructures, which results in the highest fracture toughness (95.9 View the MathML source). Moreover, due to the nature of the near-β Ti-17 alloy, the α platelets in this microstructure get very high aspect ratios, which results in its high strength. Thus for Ti-17 alloy studied in present work, the long and thick α platelets in microstructure can realize a good combination of fracture toughness and strength.
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