基於長程規律(Long range ordered)結構的Fe-Al介金屬對銲接輸入熱非常敏感。本研究目的在探討不同合金成分之鐵鋁介金屬銲件，在環境濕氣下誘發之脆化(Moisture-induced environmental embrittlement)現象及原因。其銲接性、銲件機械性能及銲道微觀組織之變化一併討論。本研究以真空感應電弧熔煉(VIM)法煉製7種不同成份介金屬Fe-Al錠，經線切割、均質熱處理及熱軋延製程，完成所需之1.58mm薄板。用TIG銲接法完成之銲件分別在相對濕度RH98%及WD40防？油下，以定變形之四點彎曲試驗來探討鐵鋁介金屬銲件受濕度環境引裂(Moisture-induced environmental embrittlement)的敏感性及其機制。 Fe-Al based intermetallic alloys have been well-known for their excellent high-temperature corrosion resistance as well as relative low materials cost, conservation of strategic elements and better strength-to-weight ratio among the conventional materials used. In addition, it is one of few known alloys which possess resistance to both of oxidation and carburization. Despite these property advantages, limited ductility at ambient temperatures and a sharp drop in strength above 600℃ have been major deterrents to their acceptance for structural applications. The poor ductility has been indicated as primary due to the hydrogen embrittlement induced by the presence of the moisture in air. The renewed interest in the Fe-Al system has been concentrated on overcoming environment effects through control of composition and microstructure. The long range ordered structure of Fe-Al based alloys is very sensitive to the welding heat input. The object of this project is to investigate the effect of the different alloying additions, and microstructures on the weldability, mechanical properties and microstructure of the weldment, especially focusing on the influence of moisture-induced environmental embrittlement. Although the special alloying additions plus thermo-mechanical treatments of Fe-Al based intermetallic alloys have improve their corrosion resistance, room temperature ductility and strength and even high temperature strength, the weldability of the Fe-Al based alloys still unknown, seven kinds of round Fe-Al ingots(Fe-18Al, Fe-18Al-5Cr, Fe-28Al, Fe-28Al-5Cr, Fe-28Al-2Cr, Fe-28Al-2Ti, Fe-28Al-1Nb) have been made by vacuum induction melting plus vacuum arc refining process. Thin plates of seven alloys with a thickness of 1.58mm were made through electrical-discharge wire cutting, homogenization and hot-rolling processes. Welding heat input of 87.5 J/mm by TIG process was used to evaluate the weldability, including welding cold cracks, microstructural variations of the weldment in seven Fe-Al based intermetallic alloys. Good welds among seven alloys were exposed to 98% relative humidity under 4 point bent-beam apparatus to investigate their sensitivity of moisture induced environmental embrittlement.
Fe-Al based alloys