1991 Fiscal Year Final Research Report Summary
Fatigue Fracture Mechanisms of Titanium Alloy at Cryogenic Temperature
| Project/Area Number |
02650057
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| Research Category |
Grant-in-Aid for General Scientific Research (C)
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| Allocation Type | Single-year Grants |
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| Research Field |
機械材料工学
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| Research Institution | Iwate University |
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Principal Investigator |
KATAGIRI Kazumune Iwate Univ., Faculty Eng., Professor, 工学部, 教授 (90029893)
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| Co-Investigator(Kenkyū-buntansha) |
TSUJI Masahiro Osaka Univ., Faculty Eng., Assistant, 工学部, 助手 (10132630)
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| Project Period (FY) |
1990 – 1991
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| Keywords | Titanium Alloy / Fatigue Mechanisms / Cryogenic Temperature / Fatigue Crack / Crack Closure / Fracture Surface |
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| Research Abstract |
The fatigue crack initiation and growth mechanisms of Ti-6Al-4V alloy at 77K were investigated. Measurement relevant to the crack growth as well as observations on the specimen surface, longitudinal section as well as fracture surface through optical microscope, SEM and high voltage TEM revealed the following results. 1)Crack was initiated in the surface alpha-grain at 77K. No subsurface crack initiation was observed in the 10^5 cycles life time stressing. 2)The fatigue crack growth rate at 77K is lower by factors of 1/2-1/4 as compared with that at 293K. The difference in the growth rate is larger at low growth rate region. The crack closure revel at 77K is higher than that at 300K through all the growth rates measured. The crack growth rate at 77K and 293K coincided to each other as a paramer of effective DELTAK. 3)Marked bifurcation of crack was observed at low growth rate in 77K fatigue. 4)The fracture surface in the low growth rate was consisted of facets of fine alpha-grain and it changed into plateaus as the growth rate increased. The fracture surface at 77K was rather flat as compared with that at 293K. Other than striations, as another difference in the fracture surface, facets elongated in the growth direction like "flute" observed in corrosion cracking was observed at 77K in the high growth rate region. 5)Arrays of dislocation in the prismatic slip plane in alpha-grain were observed in region remote from a crack tip which is growing at low rate.
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Research Products
(8 results)
