Al对GH4169合金冲击性能的影响

研究了Al对GH4169合金晶界相的析出和冲击性能的影响.结果表明,提高Al含量可抑制晶界δ相的析出,促进晶界Laves相、M7C3相和σ相等有害相的析出;随着Al含量的提高,GH4169合金的室温冲击性能明显降低,冲击断口由穿晶型转变为沿晶型.提高Al含量所导致的Laves相等有害脆性相的析出降低了晶界强度,使晶界裂纹更容易萌生和扩展,降低了GH4169合金的冲击韧性.     

固溶处理对GH4169G合金蠕变的影响

研究了固溶处理温度对GH4169G合金晶粒组织、晶界析出和蠕变的影响。结果表明,随着固溶处理温度的提高(由980℃提高到1020℃)GH4169G合金的晶粒尺寸明显增大,晶界d相的尺寸和数量明显减少,晶内g″相的析出变化不大;合金的650℃/700 MPa稳态蠕变速率明显降低,表观蠕变激活能明显增大,蠕变断裂寿命显著延长。固溶处理温度对680℃/725 MPa的蠕变性能有相同的影响趋势,但其程度减弱。孪晶的形成是GH4169G合金的重要蠕变机制。提高固溶处理温度使晶界d相的析出减少,晶界滑动蠕变速率降低;同时使晶粒度增大,形成孪晶的阻力增大,晶粒蠕变速率降低。     

一种GH4169镍基合金的组织结构与蠕变性能

通过对一种等温锻造GH4169镍基合金进行直接时效处理,蠕变性能测试及组织形貌观察,研究了该合金的组织结构与蠕变行为。结果表明,GH4169合金的组织结构由γ基体,γ′相、γ″相和δ相组成,且各相之间保持共格界面。测定出合金在660℃/700MPa条件下的蠕变寿命为123h。合金在680℃/700MPa的蠕变寿命为39h,在实验温度和应力范围内,计算出直接时效合金的蠕变激活能为588.0kJ/mol。合金在蠕变期间的变形机制是位错滑移和孪晶变形,其中,沿晶界析出的粒状碳化物,可抑制晶界滑移,是使合金具有较好蠕变抗力的主要原因。随蠕变进行,开动的滑移系中位错运动至晶界受阻,并塞积于该区域引起应力集中,当应力集中值大于晶界的结合强度时,可促使其在与应力轴垂直的晶界处发生裂纹的萌生与扩展,直至断裂,是合金在蠕变期间的断裂机制。     

冷却方式对热连轧GH4169合金组织与蠕变行为的影响

通过对不同方式冷却的热连轧GH4169合金进行直接时效处理、蠕变性能测试和组织形貌观察,研究了冷却方式对热连轧GH4169合金的组织结构与蠕变行为的影响。结果表明:"水冷"HCR-GH4169合金经直接时效后,其组织由细小晶粒组成,大量细小γ′,γ″相在晶内弥散析出,可提高合金蠕变抗力,而"空冷"热连轧合金晶粒尺寸较大,且在基体中析出的γ′,γ″两相的数量明显减少;在实验条件下,"水冷"热连轧合金经直接时效后具有较好的蠕变抗力和较长的蠕变寿命;热连轧及直接时效合金在蠕变期间的变形机制是位错在基体中发生单、双取向滑移和孪晶变形,在蠕变后期,裂纹在晶界处萌生和扩展,并发生沿晶断裂是合金的蠕变断裂机制。     

固溶处理的热连轧GH4169合金的组织与蠕变特征

通过对热连轧GH4169合金进行固溶和时效处理、组织形貌观察和蠕变性能测试,研究了固溶和时效处理合金的组织结构和蠕变特征。结果表明,经固溶和时效处理合金由较大尺寸晶粒组成,并具有明显的孪晶特征,且细小γ′、γ″相在晶内弥散析出,可提高合金的蠕变抗力;在实验应力和温度范围内,测得该合金的蠕变激活能为537.8kJ/mol,且对施加应力和温度具有敏感性;在蠕变期间,热连轧GH4169合金的变形特征是位错的单双取向滑移和孪晶变形,随着蠕变进行,裂纹沿晶界萌生和扩展到发生沿晶断裂是该合金的蠕变断裂机制。     

热连轧GH4169合金的点阵常数与蠕变性能

通过对热连轧GH4169合金进行热处理、组织形貌观察、点阵常数测定及蠕变性能测试,研究热连轧GH4169合金的点阵常数与蠕变行为。结果表明:热连轧GH4169合金主要由γ基体、γ′和γ″相组成,经标准热处理后,合金中部分粒状γ′相重溶,且又在基体中析出扁平状γ″相;经X射线衍射分析表明,与热连轧合金相比,THR-ST-GH4169合金中γ基体、γ′和γ″相的点阵常数较小,但各相之间具有较大的晶格错配度,可有效阻碍位错运动,是合金具有较高蠕变抗力和较长蠕变寿命的重要因素之一;在蠕变期间,热连轧合金的主要变形机制为位错的双取向滑移,而在THR-ST-GH4169合金中,可形成形变孪晶和发生位错滑移。     

热等静压/热处理工艺对激光选区熔化成形GH4169合金微观组织与拉伸性能的影响

采用激光选区熔化(SLM)成形技术制备GH4169合金,利用金相显微镜(OM)、扫描电子显微镜(SEM)、电子背散射衍射(EBSD)和透射电镜(TEM)等分析热等静压/热处理工艺对SLM成形GH4169合金微观组织及拉伸性能的影响规律。结果表明:沉积态合金组织中,沿沉积方向的晶粒为柱状晶,晶粒内枝晶组织细小,枝晶间分布大量Laves相;经热等静压后,合金中的气孔及Laves相可被有效消除,沿沉积方向的晶粒转变为等轴晶;经980℃/1 h固溶处理后,合金中的晶界处析出大量短棒状δ相。热等静压/热处理后GH4169合金试样的室温及650℃拉伸性能均高于锻件标准要求的力学性能指标,且温度对断裂方式影响不大。     

热等静压/热处理工艺对激光选区熔化成形GH4169合金微观组织与拉伸性能的影响EI北大核心CSCD

采用激光选区熔化(SLM)成形技术制备GH4169合金,利用金相显微镜(OM)、扫描电子显微镜(SEM)、电子背散射衍射(EBSD)和透射电镜(TEM)等分析热等静压/热处理工艺对SLM成形GH4169合金微观组织及拉伸性能的影响规律.结果表明:沉积态合金组织中,沿沉积方向的晶粒为柱状晶,晶粒内枝晶组织细小,枝晶间分布大量Laves相;经热等静压后,合金中的气孔及Laves相可被有效消除,沿沉积方向的晶粒转变为等轴晶;经980℃/1 h固溶处理后,合金中的晶界处析出大量短棒状δ相.热等静压/热处理后G H4169合金试样的室温及650℃拉伸性能均高于锻件标准要求的力学性能指标,且温度对断裂方式影响不大.     

GH4169合金Delta工艺中的变形行为和微观组织演变

在950-1010℃用GH4169合金的Delta工艺进行应变速率为0.005-0.1 s-1的等温恒应变速率压缩实验,系统研究了δ相对合金热变形行为和微观组织演变的影响。结果表明:初始δ相含量分别为0、3.65%和8.14%的GH4169合金的真应力–真应变曲线均为具有单峰特征的曲线,其本构方程均满足双曲正弦函数,变形激活能分别为441.3、445.8和487.7 kJ/mol;3种合金在热变形过程中的主要软化机制均为动态再结晶;在相同变形条件下,随着δ相含量的增加,动态再结晶临界应变显著降低,再结晶晶粒尺寸减小,再结晶体积分数增大;其中固溶态合金的再结晶形核方式主要为基体γ相的晶界弓弯形核,而预析出δ相的合金中δ相与基体γ相的相界也是再结晶形核的有利位置。由此可见,δ相的存在能促进动态再结晶的发生。     

直接时效热连轧GH4169合金的力学性能与变形特征

通过对热连轧GH4169合金进行直接时效处理、组织形貌观察和力学性能测试,研究了直接时效热连轧合金的力学性能和变形特征.结果表明,直接时效热连轧GH4169合金组织由细小晶粒组成,具有明显的形变孪晶特征,且有细小#$和#%相在合金中弥散析出,可提高合金强度.在实验温度范围内,合金的抗拉和屈服强度随着温度的升高而逐渐下降;在拉伸过程中,直接时效热连轧GH4169合金的变形特征是孪晶变形和位错的双取向滑移;在拉伸后期,大量微孔沿晶界或晶内形成并聚合形成裂纹,致使合金发生韧性断裂.     

Dynamic recrystallization behavior of GH4169G alloy during hot compressive deformation

The microstructure evolutions and nucleation mechanisms of GH4169 G alloy were studied by optical microscope, electron backscatter diffraction (EBSD) and transmission electron microscope (TEM). The hot compression tests were performed different imposed reductions in the range of true strain from 0.12 to 1.2 at the temperatures of 930 ℃-1050 ℃ with strain rates of 0.01 s⁻¹-1 s⁻¹. It is found that cumulative and local misorientation increase firstly and then decrease when the strain is increased due to the progress of dynamic recrystallization (DRX). The low angle boundaries (LAGBs) rapidly develop to high angle boundaries (HAGBs) at relatively high deformation temperature or the low strain rate. There are three DRX mechanisms observed for GH4169 G alloy during hot deformation. Discontinuous dynamic recrystallization (DDRX) as the dominant mechanism for GH4169 G alloy is characterized by typical necklace structures and bulged-original boundaries. Besides, different deformation bands with dislocation cells formed in deformed matrix at low temperature and large strain, which indicates that continuous dynamic recrystallization (CDRX) contributed to the DRX process. The twin boundaries lost their coherent characteristics and provide sites for nucleation, which also accelerates the nucleation of DRX.     

一种4.5%Re镍基单晶合金在980℃蠕变期间的变形与损伤机制

通过蠕变性能测试和组织形貌观察,研究了一种Re含量为4.5%Re(质量分数,下同)的镍基单晶合金的高温蠕变行为、变形和损伤机制。结果表明,4.5%Re合金在980℃/300MPa的蠕变寿命为169h。蠕变初期,合金中立方γ′相转变为垂直于应力轴的N型筏状结构。稳态蠕变期间,合金的变形机制为位错在基体中滑移和攀移越过筏状γ′相。蠕变后期,合金的变形机制为位错在基体中滑移和剪切进入筏状γ′相。由于γ基体通道较窄,位错在基体通道中滑移所需的阻力较大。剪切进入γ′相的110超位错可由{111}面交滑移至{100}面,形成K-W锁,从而抑制位错的滑移和交滑移,这是合金具有较好蠕变抗力的主要原因。主/次滑移位错的交替开动,可致使筏状γ′相扭曲,并促使裂纹在筏状γ/γ′两相界面萌生;裂纹沿垂直于应力轴方向扩展,直至断裂,这是合金的蠕变断裂机制。     

Microstructure evolution and deformation features of AZ31 Mg-alloy during creep

By means of the measurement of the creep curve and the observation of SEM and transmission electron microscope (TEM), an investigation has been made into the microstructure evolution and deformation features of AZ31 Mg-alloy during high temperature creep. Results show that the deformation features of the alloy in the primary stage of creep are that significant amount of dislocation slips are activated on basal and non-basal planes, then these ones are concentrated into the dislocation cells or walls as creep goes on. At the same time, twinning occurs as an additional deformation mechanism in the role of the compatibility stress. During steady state creep, the dislocation cells are transformed into the subgrains, then, the protrusion and coalition of the sub-boundaries results in the occurrence of dynamic recovery (DRV). After the dynamic recrystallization (DRX), the multiple slips in the grain interiors are considered to be the main deformed mechanism in the later stage of the steady state creep. An obvious feature of creep entering the tertiary stage is that the cracks appear on the locations of the triple junction. As creep continues, the cracks are viscous expanded along the grain boundaries; this is taken for being the fracture mechanism of the alloy crept to failure. The multiple slips in the grain interiors and the cracks expanded viscous along the grain boundary occur in whole of specimens, that, together with the twins and dynamic recrystallization, is responsible for the rapid increase of the strain rate in the later stage during creep.     

一种含4.5%Re/3.0%Ru的单晶镍基合金的高温蠕变行为

通过对含4.5%Re/3.0%Ru单晶镍基合金进行高温蠕变性能测试,并采用扫描电镜(SEM)、透射电镜(TEM)对不同蠕变期间的试样进行组织形貌观察,研究了该合金的高温蠕变行为。结果表明,本实验所选用的单晶合金在高温蠕变期间具有良好的蠕变抗力,在1040℃/160MPa的蠕变寿命达到725h。高温蠕变初期,合金中γ′相沿垂直于应力轴方向转变成筏状结构,其稳态蠕变期间的变形机制是位错在基体中滑移和攀移越过筏状γ′相。高温蠕变后期,合金的变形机制是位错在基体中滑移和剪切筏状γ′相。位错的交替滑移使筏形γ′相扭曲,并在γ/γ′两相界面发生裂纹的萌生与扩展直至断裂,是合金在高温蠕变后期的断裂机制。     

Deformed microstructure evolution in AM60B Mg alloy under hypervelocity impact at a velocity of 5 km s

Deformed microstructure in AM60B Mg alloy under hypervelocity impact at a velocity of 5 km s⁻¹ were investigated through optical microscope, scanning electron microscope and transmission electron microscope. The results show that four deformed zones around the crater can be classified based on the different deformed microstructure, including ultrafine grain zone, ultrafine grain and deformation twin zone, high and low density deformation twin zones. The dislocation slipping, deformation twins and ultrafine grains are the dominant components in the four deformed zones, and the evolution of deformed microstructure is speculated based on the deformed microstructure observed in four zones. Slipping and twinning play a critical role for the formation of the dynamic recrystallized grains, and twinning-induced rotational dynamic recrystallization mechanism is thought to be the main mechanism for the formation of ultrafine grains. The microhardness and dynamic compressive strength in different deformed zones were measured, and the high microhardness and yield strength in ultrafine grain zone should be attributed to the strain hardening and grain refining.     

热挤压AZ31镁合金的组织结构与蠕变行为

通过对热挤压态AZ31镁合金进行组织形貌观察、内摩擦应力测定及蠕变性能测试,研究了热挤压AZ31合金的组织结构和蠕变行为.结果表明:热挤压AZ31镁合金的组织具有带状结构特征,并沿轧制方向分布,且有β-Mg17Al12相在合金中弥散析出.蠕变期间,位错运动的内摩擦力有较强的温度敏感性,随温度增加,内应力值明显降低,致使合金具有较高的蠕变速率.合金在蠕变期间,大量位错的形成与运动是蠕变初期的变形机制;蠕变稳态阶段,高密度位错逐渐束集形成位错胞,进一步发生蠕变期间的动态再结晶.随裂纹在晶界处萌生使蠕变进入第三阶段,而裂纹沿晶界韧性撕裂扩展是合金的蠕变断裂机制.     

铸态Mg-6Al-1.5Ca合金高温蠕变行为研究

采用光学显微镜（OM）、能谱分析（EDS）及X射线衍射（XRD）研究了铸态Mg-6Al-1.5Ca合金显微组织,并测试了合金的高温蠕变性能。结果表明：该合金由呈枝晶形貌的α-Mg基体和沿晶界分布的Al2Ca共晶相组成;通过幂律蠕变方程得出在150-200℃/50-90MPa下合金蠕变变形机制为扩散控制的高温位错攀移和晶界滑移机制;蠕变断裂行为可以用Monkman-Gran经验公式来描述,175℃蠕变断裂特征为脆性穿晶断裂。     

预变形程度和变形温度对CoCrFeMnNi高熵合金的变形机制及后续再结晶行为的影响

使用电子背向散射衍射技术研究了预变形程度和变形温度对CoCrFeMnNi高熵合金的变形机制和后续再结晶行为的影响。结果表明,在低应变量条件下,变形温度对CoCrFeMnNi高熵合金的形变微观组织没有显著的影响,形变机制均以位错滑移为主导;在室温下变形,随着应变量的增大位错滑移和孪生变形共同主导变形。在低温退火条件下预变形程度对再结晶行为也没有显著的影响,难以发生再结晶。但是在高温退火条件下,变形程度的提高使再结晶晶粒显著细化和∑3晶界的比例大幅度提高。