【摘要】：在眾多NiAl基高溫合金材料中,NiAl-28Cr-6Mo共晶合金的綜合性能最佳,但其高溫強度不足和高溫組織熱穩(wěn)定性差等缺陷,仍制約著該合金的發(fā)展和應用。因此,本文采用真空感應熔煉制備出NiAl-28Cr-6Mo(at.%)母合金,并通過定向凝固制備出不同抽拉速率(2.5-160 μm/s)的該合金,研究其組織熱穩(wěn)定性的變化規(guī)律和失穩(wěn)機制,結論如下:在2.5-10μm/s的低速率下,合金的固液界面形貌為平界面,橫截面組織為平行相間的黑色NiAl相和灰白色Cr(Mo)相構成;在15-160μm/s的高速率下,合金固液界面形貌為胞界面或帶有二次枝的枝界面,橫截面組織為大小不一的共晶胞。通過對合金層片間距的測量,結果發(fā)現(xiàn)隨著抽拉速率的增大,合金組織中的層片間距逐漸減小,且抽拉速率同層片間距近似呈反比例關系。通過對不同層片間距的NiAl-28Cr-6Mo共晶合金進行1150℃的高溫熱處理,研究了層片間距對該合金的組織熱穩(wěn)定性的影響。結果發(fā)現(xiàn)該合金在抽拉速率為2.5 μm/s,層片間距為3.69 μm時,組織熱穩(wěn)定性較好;當抽拉速率增至160 μm/s時,層片間距為0.57μm,合金在高溫熱處理后組織完全失穩(wěn)。在淺腐蝕下組織失穩(wěn)主要呈現(xiàn)為層片夾斷和球化,經進一步的深腐蝕研究發(fā)現(xiàn),合金組織失穩(wěn)的真實情況是層片局部溶解和圓柱化。并得出該合金的組織失穩(wěn)機制為:終端遷移機制、粗化長大機制和圓柱化機制。通過對不同層片間距的NiAl-28Cr-6Mo共晶合金進行900-1100℃的高溫熱處理,研究了溫度對該合金組織熱穩(wěn)定性的影響。結果發(fā)現(xiàn)在平界面速率下(2.5-7.5μm/s),溫度對該合金組織熱穩(wěn)定性影響不大,組織中僅發(fā)生少量局部溶解,合金組織發(fā)生變化是由終端遷移機制控制的;在胞界面速率下(15-160μm/s),溫度對該合金組織熱穩(wěn)定性影響顯著,隨著熱處理溫度的升高,組織逐漸粗化,甚至圓柱化,導致胞界面速率下合金組織發(fā)生顯著變化是由于終端遷移機制、顆粒長大機制和圓柱化機制的共同作用。因此,通過本文的研究,得到影響定向凝固制備的NiAl-28Cr-6Mo層片共晶合金的組織熱穩(wěn)定的主要因素為層片間距和溫度。隨著抽拉速率的增大,層片間距的減小,該合金的組織熱穩(wěn)定降低;隨著熱處理溫度的增加,該合金的組織熱穩(wěn)定性顯著降低。
[Abstract]:The comprehensive properties of NiAl-28Cr-6Mo eutectic alloy are the best among many NiAl based superalloy materials, but the defects such as insufficient high temperature strength and poor thermal stability of high temperature structure still restrict the development and application of the alloy. In this paper, NiAl-28Cr-6Mo (at.%) master alloy was prepared by vacuum induction melting, and different drawing rates (2.5-160 渭 m / s) were prepared by directional solidification. The changes of thermal stability and the mechanism of instability of the alloy were studied. The conclusions are as follows: at the low rate of 2.5-10 渭 m / s, The morphology of the solid-liquid interface of the alloy is flat, the cross section of the alloy is composed of black NiAl phase and gray-white Cr (Mo) phase with parallel phase, and at a high rate of 15-160 渭 m / s, the morphology of the solid-liquid interface of the alloy is a cellular interface or a branch interface with secondary branches. The cross section structure is a eutectic cell of different size. By measuring the interlamellar spacing of the alloy, it is found that with the increase of the drawing rate, the lamellar spacing in the alloy structure decreases gradually, and the pulling rate is approximately inversely proportional to the lamellar spacing. The effect of interlaminar spacing on the microstructure thermal stability of NiAl-28Cr-6Mo eutectic alloy with different interlamellar spacing was investigated by high temperature heat treatment at 1150 鈩，

本文編號：2159457