镍基单晶高温合金DD5的组织演变和冷热疲劳的研究
发布时间：2018-07-26 15:19
【摘要】：随着国内航空发动机产业的不断发展,镍基单晶高温合金处在高速发展阶段,现阶段的单晶制备工艺也已经相当成熟。因此,对单晶合金在热处理以及服役过程中进行组织和性能研究更有实际应用价值,这对提高合金性能,了解合金的高温稳定性和寿命预测有重要意义。此外,随着气膜冷却技术在国内单晶叶片上应用,国内涡轮发动机的承温能力得到进一步上升,而对气膜孔周围在热疲劳循环下裂纹萌生扩展机制缺少研究和探索。本文主要研究国内自主研发第二代镍基单晶高温合金DD5合金的热处理过程中组织改善、性能提升,在高温服役过程中组织演变,以及合金冷热疲劳循环下圆孔周围裂纹萌生扩展情况。本文通过JMatPro和DSC曲线对DD5单晶高温合金固溶处理的温度范围进行确定,并分别对合金进行固溶处理工艺和时效处理工艺后研究发现:均匀化处理和高温固溶处理均能显著改善合金组织中的枝晶偏析现象;固溶处理后的冷却方式影响γ’组织形态,水冷则是析出100nm以下尺寸的γ’组织;炉冷后组织显得异常粗大,尺寸超出600nm;空冷后的γ’颗粒均匀且有序排列。固溶处理空冷后合金的显微硬度是465左右,比铸态组织的硬度要高出120;而固溶处理水冷样品的显微硬度则最高。热处理中的时效处理对合金中γ’的尺寸形貌进一步的调整,研究过程中发现一次时效(高温时效)的温度过低时,会出现圆形的γ’颗粒,呈现出不规则排列;当温度上升时,则γ’颗粒逐渐呈立方态有序排列,从而获得有序排列的立方γ’相;当温度继续上升,标准的立方态的γ’相颗粒边角钝化。本文获得DD5单晶高温合金的最佳热处理工艺为:1270℃,2h+1280℃,2h+1290℃,2h+1300℃,2h+1310℃,2h+1320℃,6h AC+1080℃/4h AC+780℃/24h AC。DD5单晶高温合金在长期时效实验中的研究表明:时效时间越长,γ’相越大,最终出现形筏现象;长期时效的温度越高,γ’相的粗化越明显。长期时效过程中,一般合金的显微硬度会随着时间的延长而下降。γ’相长期时效前后尺寸的立方差和时间成正比,1050℃的粗化系数要高于900℃γ’相粗化系数,说明1050℃长期时效过程中γ’相粗化速度要高于900℃。在冷热疲劳的实验中发现:DD5合金第二取向为[110]和[100]的裂纹扩展方向都是与枝晶生长方向成45°;但是第二取向[110]样品在裂纹扩展程度上要比第二取向[100]样品明显要多。单晶高温合金的内部缺陷组织,孔周围的氧化层都对裂纹扩展有巨大的影响。
[Abstract]:With the continuous development of domestic aero-engine industry, nickel base single crystal superalloy is in a high speed development stage, the preparation process of single crystal has been quite mature. Therefore, it is more valuable to study the microstructure and properties of single crystal alloys during heat treatment and service, which is of great significance to improve the properties of the alloys and to understand the high temperature stability and life prediction of the alloys. In addition, with the application of film cooling technology to domestic single crystal blades, the temperature bearing capacity of domestic turbine engines has been further increased, but the mechanism of crack initiation and propagation around the gas film holes under thermal fatigue cycle has not been studied and explored. In this paper, the microstructure and properties of the second generation Ni-base single crystal superalloy DD5 are studied during heat treatment, and the microstructure evolves during the service at high temperature. And the crack initiation and propagation around the circular hole under the cold and thermal fatigue cycle of the alloy. In this paper, the temperature range of solution treatment for DD5 single crystal superalloy is determined by JMatPro and DSC curves. The results of solution treatment and aging treatment showed that both homogenization treatment and high temperature solution treatment could improve the dendritic segregation in the alloy structure, and the cooling mode after solution treatment could affect the morphology of 纬 'structure. The water cooling is 纬 'structure with the size below 100nm precipitated, the structure of the furnace is very large after cooling, and the size exceeds 600 nm. The 纬' particles after air cooling are arranged in a uniform and orderly manner. The microhardness of the air-cooled alloy after solid solution treatment is about 465, which is 120 higher than that of the as-cast structure, while the microhardness of the water-cooled sample treated by solid solution treatment is the highest. Aging treatment in heat treatment further adjusts the size and morphology of 纬'in the alloy. It is found that when the temperature of primary aging (high temperature aging) is too low, round 纬 'particles will appear, showing irregular arrangement. When the temperature increases, the 纬 'particles are arranged in cubic order gradually, thus the ordered cubic 纬' phase is obtained, and when the temperature continues to rise, the edge angle of the standard cubic 纬 'phase particle is passivated. In this paper, the optimum heat treatment process of DD5 single crystal superalloy is obtained as follows: 1: 1270 鈩，
本文编号：2146429
[Abstract]:With the continuous development of domestic aero-engine industry, nickel base single crystal superalloy is in a high speed development stage, the preparation process of single crystal has been quite mature. Therefore, it is more valuable to study the microstructure and properties of single crystal alloys during heat treatment and service, which is of great significance to improve the properties of the alloys and to understand the high temperature stability and life prediction of the alloys. In addition, with the application of film cooling technology to domestic single crystal blades, the temperature bearing capacity of domestic turbine engines has been further increased, but the mechanism of crack initiation and propagation around the gas film holes under thermal fatigue cycle has not been studied and explored. In this paper, the microstructure and properties of the second generation Ni-base single crystal superalloy DD5 are studied during heat treatment, and the microstructure evolves during the service at high temperature. And the crack initiation and propagation around the circular hole under the cold and thermal fatigue cycle of the alloy. In this paper, the temperature range of solution treatment for DD5 single crystal superalloy is determined by JMatPro and DSC curves. The results of solution treatment and aging treatment showed that both homogenization treatment and high temperature solution treatment could improve the dendritic segregation in the alloy structure, and the cooling mode after solution treatment could affect the morphology of 纬 'structure. The water cooling is 纬 'structure with the size below 100nm precipitated, the structure of the furnace is very large after cooling, and the size exceeds 600 nm. The 纬' particles after air cooling are arranged in a uniform and orderly manner. The microhardness of the air-cooled alloy after solid solution treatment is about 465, which is 120 higher than that of the as-cast structure, while the microhardness of the water-cooled sample treated by solid solution treatment is the highest. Aging treatment in heat treatment further adjusts the size and morphology of 纬'in the alloy. It is found that when the temperature of primary aging (high temperature aging) is too low, round 纬 'particles will appear, showing irregular arrangement. When the temperature increases, the 纬 'particles are arranged in cubic order gradually, thus the ordered cubic 纬' phase is obtained, and when the temperature continues to rise, the edge angle of the standard cubic 纬 'phase particle is passivated. In this paper, the optimum heat treatment process of DD5 single crystal superalloy is obtained as follows: 1: 1270 鈩，
本文编号：2146429
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