Abstract
本研究開發出一項新的數學近似方法可用於分析氫在金屬片中之滲透速率，且進一步求出氫之擴散係數及表面濃度。此項結果ｉ（ｔ） -6Dt/L2───── ＝１－ｅ 並與McBreen 所得之ｉ（∞） 2ｉ（ｔ） １ －Ｌ －π•Ｄt╱Ｌ2──── ＝ ──── •ｅｘｐ〔─────〕及 １－２ｅｉ（∞） ｔ1/2 ４Ｄｔ結果互相此較。利用電化學方法充氫於高鉻肥粒型不鏽鋼表面，藉以研究其氫脆機構。此種題主要發生在陰保護系統中，由於氫氣的產生，遂造成此類合金的嚴重脆。化試樣之拉伸斷裂面顥示非常清楚的類似劈裂(quasi-cleavage)，其氫脆的程度則隨充氫之電壓、電流、及充氫時間之增加而愈加嚴重。觀其機械性質則有顥著硬化之果。基於這些發現，一改良後的斷裂形成能量公式(crack formation energy )W=2.γ.a+k.ρm.Vp 可用來解釋廣泛之金屬氫脆。試片預先充氫480 小時，再經過不同時間自然時效後，做拉伸驗，並以掃瞄式電子顥鏡觀察斷裂面，發現該條件下存在芋一臨界濃度值能使延性的微孔聚合(micro-void-coalesence) 型轉變成脆性的穿晶斷裂(transgranular cracking) 型。此臨界值可經由數學模式的分析，擴散係數及表面濃度的量測，以及掃瞄式電子顥微鏡的觀察求得該臨界值。高鉻肥粒型不鏽鋼在高溫1050℃空氣中加熱，其表面形成的氧化膜係由Fe，Cr，Mn之混之合氧化物組成，對氫脆(或氫的滲入)具有防止的效果。經由滲透速率實驗的量測，及幾種可能模式的數學分析與討論，則可分辨出此阻止氫脆的效果係由於氧化物表面氫濃度降低所致，抑或係由於氧化物之氫擴散係數低所造成，在肥粒型不鏽鋼中則屬後者。///////A new mathematical model for the determination of the permeation rate ofhydrogen through metal membrane is described and a simpler pertimentdiffusion equation is derived. Comparisions between this result and theMcBreen's are made. Some extra effects (such as trapping effect andsurface effect) that exist in real cases, are reviewed.The introduction of hydrogen to the ferritic stainless steel (Sea-cure) byelectrochemical charging has been employed to study the mechanism ofembrittlement in a ferritic stainless steel. Charging of electron as aresult of cathodic protection is particularly detrimental to this alloy.Cases of severe embrittlement are frequently observed and the fracturemode is unequivocally of quasi-cleavage. The degree of embrittlement wasfound to increase with the charging voltage, current, and time. Themechanisms of such embrittlement are discussed on the basis of thesefindings. As a consequence, a generalized equation for crack formationenergy (w=2.γ.a+k.ρm.Vp) is established to demonstrate the hydrogenembrittlement of metals.The slow strain rate technique (ε＝２＊１０-5Ｓ-1) has been employedto elucidate the tensile behavior of this alloy responding to the effectof aging after cathodically charged of hydrogen. There exists thecritical concentration of hydrogen which changes the fracture mode fromductile microvoid coalescence (M.V.C.) to brittle transgranular cracking,was determined through a mathematical modeling, with the diffusivity andsurface concentration of hydrogen obtained through permeation measurementswith sensitive electrochemical Devanathan cell.The introduction of hydrogen to the high chromium stainless steel(Sea-cure) by electrochemical charging has also been employed to study thestress-strain curve of these tenssile specimens. It was found that athermally grown oxide film at 1050℃ can effectively prevent Sea-cure fromhydrogen embrittlement (HE). Through permeation measurements, it is clearthat a low hydrogen diffusion coefficient of the oxide film retardhydrogen entry.