鎳基超合金 IN 738LC 之PAW修補銲接研究

Abstract

本文是對鎳基超合金IN 738LC的銲接性研究，主要是探討電漿氣體電弧銲接（Plasma Arc Welding, PAW）的外送粉製程，應用於渦輪引擎組件（land-base turbine components）的修補使用。經由此方法修補的試片再利用高溫拉伸試驗、高溫衝擊試驗及彎曲試驗測試其機械性質。此外配合微硬度量測、金相及SEM觀察其微觀組織及破斷面的破斷型態。 本研究應用田口式分析方法（Taguchi Methods），探討冷卻速率、銲接電流、銲接速度、電漿氣體流量、保護氣體流量及粉末流量等六個參數，對銲接品質影響程度的大小。藉以組合出適當的銲接參數，並加以測試其機械性質。 實驗結果顯示，大的銲接電流容易產生銲接裂縫（包括銲接熱裂縫及效應變裂縫）。經修補後的試片，其高溫衝擊強度可達母材強度之94%左右；而其抗彎曲強度並不遜於母材。

This research describes an investigation on the weldability of Ni-base superalloy IN-738LC. The objective of this investigation was to study the effect of plasma arc welding, PAW, with the IN-73LC powder a the filler metal on the repairing land-base turbine components. High temperature tensile test, high temperature impact test and bending test were conducted to determine its mechanical strength. Microhardness, metallography, and SEM examination were also used to study its microstructure and the type of failure surface. The effects on the qualities of weldments with cooling rate, welding current, travelling speed, flow rate of plasma gas, flow rate of shielding gas, and flow rate of powder with were analyzed with Taguchi Methods. And then the adequate combinations of welding parameters were selected to investigate its mechanical strength. From the experimental results, large welding current causes welding cracks easily (both hot cracks and strain-age cracks). The result also shows that the repaired specimens can reach 94% high temperature impact strength of IN-738LC parent metal with proper welding parameters. The bending strength of repaired specimen is also better than IN-738LC parent metal.