報告書番号

T97012

タイトル（和文）

ガスタービン動翼材Ｉｎｃｏｎｅｌ７３８ＬＣの高温強度評価法の開発第３報：クリープ疲労損傷機構に基づく寿命評価法の提案

タイトル（英文）

DEVELOPMENT OF HIGH TEMPERATURE STRENGTH EVALUATION METHOD FOR INCONEL 738LC -3RD REPORT: PROPOSAL OF CREEP-FATIGUELIFE EVALUATION METHOD BASED ON FAILURE MECHANISMS-

概要 （図表や脚注は「報告書全文」に掲載しております）

ニッケル基超合金Ｉｎｃｏｎｅｌ７３８ＬＣのクリープ疲労特性および損傷メカニズムを把握するために，疲労・クリープ疲労試験および試験中の損傷過程の連続観察を実施した。圧縮ひずみ保持のある試験で粒界すべり損傷，引張ひずみ保持のある試験では粒界すべりに加えて粒界クリープ損傷が観察され，共にクリープ疲労寿命を低下させる要因と考えられた。粒界すべり損傷ｄｓｌおよび粒界クリープ損傷ｄｃｒを疲労損傷を加速する損傷パラメータとし，非線形累積損傷則の考え方にのっとった新しい寿命評価法を提案した。本評価法により，ひずみ保持波形に関わらず，ほとんどのクリープ疲労試験結果が良好に整理された。

概要 （英文）

IN ORDER TO INVESTIGATE CREEP-FATIGUE LIFE PROPERTY AND CLARIFY THE CREEP-FATIGUE DAMAGE MECHANISMS AND REASONS OF THE LIFE REDUCTION, STRAIN CONTROLLED CREEP-FATIGUE TESTS AND IN SITU SCANNING ELECTRON MICROSCOPE (SEM) OBSERVATION DURING THE CREEP-FATIGUE TESTS WERE CARRIED OUT. IN THE TENSILE STRAIN HOLD TEST, MULTI-SITE GRAIN BOUNDARY CRACKING ON THE SURFACE OF THE SPECIMEN WAS OBSERVED AND ITWAS SUGGESTED THAT CREEP-FATIGUE LIFE WAS SHORTENED BY TENSILE CREEP DAMAGE DURING HOLD PERIOD. IN THE COMPRESSIVE STRAIN HOLD TEST, GRAIN BOUNDARY SLIDING DAMAGE OCCURRED AT MOST OF THE GRAIN BOUNDARIES ON THE SURFACE OF THE SPECIMEN AND FATIGUE LIFE REDUCTION AND CHANGE OF FAILUREAPPEARANCE SEEMED TO BE RELATED TO THIS DAMAGE. ON THE BASIS OF THESE DAMAGE MECHANISMS, A NEW CREEP-FATIGUE LIFE PREDICTION MODEL WAS PROPOSED INTRODUCING TWO DAMAGE PARAMETERS (I.E., DSL RELATED TO THE GRAIN BOUNDARY SLIDING DAMAGE, AND DCR RELATED TO THE TENSILE CREEP EFFECT). INTHIS MODEL, THE DAMAGE UNDER THE CREEP-FATIGUE CONDITIONS WAS ASSUMED TO BE ACCUMULATED NONLINEARLY BY THE EFFECT OF THESE DAMAGES. BY USING THE NEW MLODEL, CREEP-FATIGUE LIFE CAN BE PREDICTED WELL REGARDLESS OF THE STRAIN HOLD POSITIONS COMPARED TO EXISTING LIFE PREDICTION MODELS.

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