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The feasibility of applying the fluidized bed furnace to the solution and aging treatments of aluminum alloys was assessed by examining concerns such as the efficiency of heat treatments and delay of quenching, together with its merits such as the shortening of heat treatment and the possibility of high temperature heat treatments. It was concluded that this method realizes high efficiency of heat treatments, which is comparable to that attainable with the combination of a salt bath and oil bath. By suppressing the delay time within 20 to 30sec. after the removal of works from the fluidized bed furnace, no degradation in mechanical properties occurs. The allowable delay time is dependent on the work size. The solution treatment time can be shortened to 60min. or below. Good mechanical properties were obtained even with a short solution treatment time of 15min. depending on the size and thickness of the work. This also enables suppression of pore growth at the same time. In addition, high temperature heat treatment at around ternary eutectic temperatures was realized by precise temperature control, thereby realizing superior mechanical properties and shorter heat treatment time.

H-2ロケットは1994年2月に1号機、8月に2号機そして1995年3月には3号機が打ち上げられ、宇宙輸送手段としての機能は確立されている。このロケットの第1段主エンジンのLE-7には数多くのインコネル-718材溶接継手が使用され製作が行われている。LE-7はエンジン始動時から停止時にわたり厳しい熱応力にさらされ、開発過程で経験した不具合の多くはこの溶接継手部で発生した。このため、不具合の改善およびLE-7の信頼性を向上するための重要課題として、溶接継手に関する特性の向上が挙げられ、また、エンジン設計の見直しが検討された。この様な背景の下、これまでに1228Kと1338Kの温度で溶体化処理されたGTA(ガスタングステンアーク溶接)溶接継手の引張特性を調べた。今回は、組織検査、硬さ検査を通して、1228Kと1338Kの温度範囲内での溶体化処理条件(温度と時間)の影響を調べた。その結果、母材の結晶粒の粗大化は、溶体化処理温度、時間の狭い範囲で急速に起こり、それは時間よりも温度に敏感であること、および溶接部に析出したNi3Nbの溶解は、母材の結晶粒の成長と同時に進行することが明らかになった。また、代表的な溶体化処理条件を選択し、その条件で溶体化処理を施した溶接継手の引張特性を調べた。その結果と前回までに報告した結果とを比較検討した結果、Ni3Nbの連続性を減少させることにより、引張強度の低下を招くことなく溶接継手の延性の向上が可能であることが明らかになった。, The H-2 rockets have been successfully launched three times since its first success in February 1994, and Japan has established its own means of space transportation. The main engine of the H-2 rocket, LE-7, uses many welded Inconel-718 joints. The hot section materials of the LE-7 engine has suffered from severe thermal shock during the start and cutoff sequence, and these welded joints were the cause of many of the accidents during development. Hence, the welded joints were redesigned to increase the reliability of the LE-7 engine. Against this background, the tensile properties of the GTA (Gas Tungsten Arc welding) welded joint with solution treated at 1,228 K and 1,338 K were studied in a previous report. This report shows the effects of solution treatment condition (time and temperature) ranging from 1,228 K to 1,338 K on the microstructure, hardness and tensile properties. The solution treatment condition study shows that the grain growth of the parent metal occurs rapidly in a very narrow window of time and temperature and that these phenomena are more sensitive to temperature than to time. This study also shows that the dissolution of the Ni3Nb phase and the grain growth of the parent metal occur simultaneously. The tensile property test for different solution treatment conditions shows that the appropriate condition increases the ductility without loss of tensile strength by partially dissolving the continuous Ni3Nb phase to a discrete one., 資料番号: AA0000444000, レポート番号: NAL TR-1285