【作者】 赵忠刚；

【导师】 田素贵； 尚丽娟；

【作者基本信息】 沈阳工业大学 ， 材料学， 2009， 硕士

【摘要】 本文通过对等温锻造及热连轧GH4169合金进行不同条件的热处理、蠕变性能测试及组织形貌观察,研究了热处理制度对合金蠕变性能的影响;通过蠕变曲线的测定及变形合金的微观形貌观察,计算出不同工艺处理合金的蠕变激活能和应力指数,研究了不同状态合金在蠕变期间的变形与断裂机制。结果表明:与等温锻造合金相比,热连轧合金具有较小的晶粒尺寸;经直接时效后,热连轧GH4169合金在晶内析出大量弥散分布的细小γ″相;经长期时效后,有较多粒状、短棒状碳化物沿晶界不连续析出。在试验的温度和应力范围内,测定出等温锻造合金在蠕变期间的蠕变激活能为Q_a=519.3kJ/mol;与等温锻造合金相比,热连轧GH4169合金具有较高的蠕变抗力;计算出热连轧合金经直接时效和长期时效后的蠕变激活能分别为Q_a=559.2kJ/mol和Q_a=541.1kJ/mol。与其它制备工艺相比较,热连轧合金经直接时效处理后,具有较好的蠕变抗力,其在660℃、700MPa条件下的蠕变寿命达127小时。在蠕变期间,等温锻造态合金仅发生孪晶变形;热连轧态合金的变形机制是孪晶和孪晶内的位错滑移,并确定出孪晶面为{111}。其中,合金在热连轧期间形成的“预存”位错可激活蠕变位错在孪晶内发生单取向和多取向滑移,减缓因形变产生的应力集中,是提高热连轧合金蠕变抗力,延长蠕变寿命的主要原因。两种工艺制备合金经直接时效处理后,其蠕变期间的断裂方式均为沿晶解理断裂,且断口表面光滑,无明显析出物;蠕变后期,裂纹在与应力轴垂直的晶界处萌生,并沿晶界发生裂纹扩展是合金的蠕变断裂机制。而热连轧合金经过长期时效处理后,蠕变断裂后呈现非光滑断口表面,其中,沿晶界析出的碳化物晶界膜对合金的晶界强度影响较小,是使合金具有较长蠕变寿命的主要原因。更多还原

【Abstract】 In the paper,compared to the calcalation of creep activation energy and stress exponent,the influence of heat treatment regimes on the microstructure and creep properties of the forged and hot continuous rolling GH4169 alloy are investigated by means of heat treatment,creep properties measurment and microstructure observation,and the deformation mechanisms of the alloy during creep is discussed.Results show that,compared to the forged alloy,the finer grains is displayed in the hot continuous rolling alloy,and the finerγ″phase is dispersely precipitated within the grains after direct aged treatment(DA),but signficant amount carbides with short stick shape are discontinuously precipitated along the grain boundary.In the range of experimental temperatures and stresses,the activating energy of the forged alloy during creep is calculated as Q_a = 519.3kJ/mol.Compared to the forged alloy,the hot continuous rolling(HCR) alloy displays a better creep resistance,and the activation energies of DA-HCR and LTA-HCR alloys during creep are calculated to be Q_a = 559.2 kJ/mol and Q_a = 541.1 kJ/mol.Compared with other preparing technology,after direct aged treatment,the HCR alloy have a better creep resistance,and the creep lifetimes of the alloy is measured as 127 h in the applied stress of 700MPa at 660℃.During creep,the deformation feature of the forged alloy is twinning,the deformation mechanisms of the HCR alloy is the twinning and dislocations slipping within the twins,and the twinning plane activated during creep is determined as { 111 } plane.If the dislocations formed during hot rolling is defined as "pre-reserved ones,the ones may activate the creep dislocations occurring the single and double orientations slipping within the twinning to stave the stress concentrition, this is a main reason of enhancing the creep resistance and prolonging lifetimes of the alloy. After direct aged,the fracture modes of both forged and HCR alloys during creep are identified as the intergranular fracture,and appearring the smooth surface of the grain. During the later stage of creep,it is the fracture mechanism of the alloy during creep that the cracks are budded on the boundaries vertical to the applied stress axis,and expanded along the boundaries.But after crept up to fracture,the fracture of the long term aged HCR alloy displays a nonsmooth surface,thereinto,the carbides film formed on the boundaries has a few effect on the boundaries strength of the alloys,this is a main reason of prolonging the creep lifetimes of the alloy.更多还原