鎳基超合金Hastelloy X銲件在950℃濕空氣環境之恆溫及循環氧化行為研究

The cyclic oxidation behavior of welded Hastelloy X superalloy at 950℃ in dry air

本研究主要探討Hastelloy X經銲接處理後之母材（SUB）、熱影響區（HAZ）及銲道（MZ）三種區域在950℃濕空氣下的恆溫及循環氧化行為。研究結果顯示，合金經恆溫及20次循環之氧化增重由快而慢之順序為MZ > SUB > HAZ。由微結構分析得知，氧化後三種區域皆生成兩層氧化層，其中內層主要生成Cr2O3，而外層主要生成MnCr2O4；在濕空氣之循環氧化產生氧化層間和母材間熱膨脹差異，進而產生熱應力並使部分氧化膜產生裂縫，是合金氧化速率增加的主因。

The isothermal and cyclic oxidation behaviors of three different zones of welded Hastelloy X, containing the substrate (SUB), the heat-affected zone (HAZ) and the melt zone (MZ) were studied at 950 in wet air. The results showed that the oxidation-resistant ability of the alloys after the isothermal and 20-cycle followed by the rank from fast to slow of MZ > SUB > HAZ. Duplex scales formed on all the alloys consisted of Cr2O3 in the inner layer, and MnCr2O4 in the outer layer. The cyclic exposure resulted in the thermal stress in between the scales and substrate, leading to the formation of cracks that is responsible for the fast oxidation rates.