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1.
高温合金铸锭凝固过程内部各区域散热条件不同,冷却速率存在明显差异。采用差示扫描量热分析(DSC)、高温共聚焦显微镜(HT-CLSM)原位观察和定向凝固(DS)的方法,研究了宽冷速范围下GH4738合金的凝固偏析和碳化物析出行为。结果表明, GH4738合金的凝固顺序为L→γ+L,L→γ+L+MC,L→γ+MC+η+(γ+γ′),其中MC型碳化物、η相和(γ+γ′)共晶相为合金凝固过程中的主要偏析产物;Ti、Mo元素是合金的主要枝晶间偏析元素;提高冷却速率能有效降低凝固前沿残余液相中的溶质富集程度;铸态组织中的的碳化物主要为富Ti的MC型碳化物(TiC、Ti(N)C)和以TiN或Al2O3为核心的MC型复合碳化物(Al2O3-TiC、TiN-TiC);随着冷却速率降低,碳化物平均尺寸增大,体积分数减小,形貌由小块状向长条状、汉字状和大块状演变。  相似文献   

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试样经酸溶解后,用同一母液对镍基高温合金中Fe、Mo进行联合测定。采用EDTA掩蔽干扰元素后直接进行铁量的测定,硫脲作还原剂测定钼量,两元素线性良好。该方法简便快速,已用于实际样品的测定,结果令人满意。  相似文献   

4.
研究一种镍基高温合金饼坯出现的宏观偏析"黑斑"区域相变行为及析出相的形成特点,并采用热力学相计算手段对合金黑斑区的相变规律和元素的热力学平衡分配进行计算。结果表明,合金中黑斑主要是富Ti的碳化物严重偏析造成。从黑斑的组织特点分析及热力学相计算可以得出,Ti在凝固过程中发生了强烈的枝晶间液态偏聚,同时C也有一定程度的偏聚,这些元素不同程度的液态偏聚行为是造成黑斑相富集的主要原因。  相似文献   

5.
肖桂华 《四川冶金》1997,19(4):37-39
本文较详细地分析了GH536合金的可焊性,介绍了GH536合金焊管的生产工艺流程以及在生产中采用一定的措施保证管坯成形良好;采用合理的焊接规范保证焊缝质量。焊管经过冷轧、冷拔加工后成品焊管的机械性能同母材比较基本一致,焊缝凸量完全消除,说明焊管经过冷轧、冷拔加工后。不仅规格多样化,而且焊管的使用性能进一步得到改善,这种焊管与无缝管生产相结合的方式是可行的。  相似文献   

6.
钴基高温合金DZ40M高温高周疲劳过程中碳化物的行为   总被引:2,自引:0,他引:2  
研究了DZ40M合金900℃高周疲劳过程中碳化物的行为,在900℃疲劳试验过程中,DZ40M合金中初生碳化物M7C3和MC发生溶解,同时,沉淀析出大量细小的二次碳化物M23C6,它与其他具有立方取向关系。M23C6相钉扎位错及亚晶界,强化合金基体,提高形变抗力。初生碳化物发生了断裂,降低了疲劳断裂抗力。DZ40M合金表面发生了严重的氧化,优先氧化的碳化物是疲劳裂纹源。  相似文献   

7.
镍基高温合金粉末中夹杂的研究   总被引:2,自引:0,他引:2  
研究了等离子旋转电极雾化FGH95镍基高温合金粉末中夹杂的性质(成分分类和形貌)及粉末处理过程去除非金属夹杂效果的影响,介绍了有效去除非金属夹杂的方法。  相似文献   

8.
研究了不同固溶冷速对一种难变形镍基高温合金组织及性能的影响,观察了合金的显微组织、冲击断口形貌、碳化物以及γ′相分布情况,并检测了其抗拉强度和持久寿命.结果表明:经过1 140℃固溶后,随着冷速的降低(风冷>空冷>控温慢冷),合金中析出的碳化物数量增多且尺寸增大,γ′相形貌发生变化且尺寸增大(170 nm→230 nm→680 nm),合金的抗拉强度和持久寿命显著降低(650℃+863 MPa, 169 h→91 h; 750℃+588 MPa, 130 h→94.3 h).在固溶后的冷却过程中冷速较慢,析出并长大的γ′相会与奥氏体基体的晶界有充分的时间发生交互作用.大角度的奥氏体晶界成为合金元素的快速扩展通道,使得晶界处γ′相的长大速度远大于晶内γ′相的长大速度,γ′相的形貌也从花瓣状长成条带状.综合分析,低冷速只能提升该合金的冲击吸收功和断后伸长率,而高冷速能大大提升合金的持久寿命.  相似文献   

9.
一种镍基单晶高温合金的显微偏析行为   总被引:5,自引:0,他引:5  
研究了一种新型镍基单晶高温合金DD98铸态组织的显微偏析行为.实验结果表明,当合金以枝晶凝固时,组织中存在显微偏析.其中元素Mo、Cr、Ti、Ta、Al在枝晶间富集,Ti、Mo、Ta、Cr的偏析较为严重,Al的偏析程度相对小一些,Ni、Co、W为枝晶干偏析元素,其中W的偏析最为严重;共晶中富集Al、Ta、Ti、Ni,贫Co、W、Cr、Mo.凝固速率对枝晶偏析有显著的影响.随着抽拉速率的增加,元素Al、Mo、Co、Ti的偏析程度增加,而Ta的偏析程度降低,其它元素的偏析程度变化不大.  相似文献   

10.
介绍了粉末筛分设备及其主要工艺参数 ,并围绕筛分处理的生产效率及粉末质量的影响因素展开了讨论  相似文献   

11.
A M23C6 carbide phase has been observed to precipitate at relatively low temperatures (732 to 760 °C) in a nickel base superalloy.* Transmission Electron Microscopy shows the low temperature carbide to reside at the grain boundaries in a continuous morphology. The continuous carbide has a typical width of 25 to 40 nm with aspect ratios on the order of 30:1. The structure of the carbide is face-centered cubic with a lattice parameter (α0) of approximately 1.063 nm, which is typical of the M23C6 carbides that form at higher temperatures. STEM analysis indicates the carbide to have a typical M23C6 chemistry, enriched in chromium with lesser amounts of molybdenum, cobalt, and nickel. The formation of the continuous carbide occurs readily around 760 °C; however, at temperatures 55 °C lower the precipitation kinetics are significantly reduced. The extent of the low temperature carbide reaction is observed to be dependent upon the duration of the low temperature exposure and the degree of prior M23C6 stabilization at an intermediate temperature. Alloy modifications, involving hafnium additions and lower carbon levels, were studied with the aim of reducing the extent of this carbide reaction. Despite these chemistry modifications, the low temperature carbide was still observed to form to an appreciable extent. The presence of the continuous carbide is also observed to reduce the stress-rupture life of the alloy.  相似文献   

12.
A nickel base superalloy (Nimonic 80A) has been rapidly solidified at cooling rates of between 105 to 106 K.S-1 by pendant drop melt extraction and by chill block melt spinning in an evacuated chamber backfilled with helium or argon. The internal structure is described in terms of process variables pertaining to rotating chill block quenching techniques. Both transmission electron microscopy and atom-probe field-ion microscopy have been employed to give structural and constitutional data on quenched and aged specimens. The as-quenched structure is homogeneous apart from fluctuations in titanium concentration which upon aging undergoes a spinodal phase decomposition to form disordered Ni3(Ti,Al,Cr) precipitates in the matrix, which after prolonged aging produces ordered γ (Ni3(Ti,Al)). inin6 particles form readily on grain boundaries and also appear in conjunction with ordered γ, via a discontinuous reaction, after short aging times.  相似文献   

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14.
A Nickel base solid solution strengthened alloy has been made with a nominal chemical composition of 15Cr-15Mo (balance Ni) through vacuum melting route and was characterized in hot worked and heat-treated conditions. Processing parameters have been optimized to get the desired microstructure and mechanical properties. The alloy has shown very good mechanical properties at elevated temperatures as well as at cryogenic temperatures. Role of solution treatment temperature and correspondingly role of grain size on mechanical properties at different temperatures has also been evaluated and reported. Heat treatment cycle for application of alloy upto 700°C has been optimized. Properties of the alloy have been compared with similar class of alloys.  相似文献   

15.
通过蠕变曲线测定和组织形貌观察,研究了FGH95合金的蠕变特征与变形机制.结果表明:经高温固溶及"盐浴"冷却后,FGH95合金的组织结构由细小γ'相及粒状碳化物弥散分布于γ基体所组成,由于沿晶界不连续析出的粒状(Ti,Nb)C相可提高合金的晶界强度,并抑制晶界滑移,故使其在650℃、1 034MPa条件下有较小的应变速率和较长的蠕变寿命.合金在蠕变期间的变形机制是位错切割γ或γ'相,其中,当(1/2)<110>位错切入γ相,或<110>超位错切入γ'相后,可分解形成(1/6)<112>肖克莱不全位错或(1/3)<112>超肖克莱不全位错+层错的位错组态;蠕变后期,合金的变形特征是晶内发生单取向和双取向滑移,随蠕变进行位错在晶界处塞积,其引起的应力集中致使裂纹在晶界处萌生及扩展是合金的蠕变断裂机制.  相似文献   

16.
A discontinuous precipitation reaction has been investigated in a high-refractory content nickel-base alloy. The reaction transforms the two-phase γ-γ′ parent microstructure into a three-phase cellular structure with a γ′ matrix containing Re-rich P-phase and agglomerated γ lamellae. The reaction has been studied in polycrystalline material and in bicrystals with varying degrees of boundary misorientation at temperatures in the range of T/T m =0.78 to 0.85. The early stages of the reaction are characterized by heterogeneous nucleation of P-phase precipitates and migration of the grain boundary. At low-angle, near-tilt boundaries misoriented by less than 10 deg, nucleation of P-phase particles was observed, but the cellular reaction did not occur, due to limited boundary mobility and diffusivity. The high degree of supersaturation of Re and W in the initial γ-γ′ alloy appears to be the primary driving force for the reaction. Small amounts of creep deformation did not significantly influence the extent of the transformation. The diffusivity of Re associated with the moving boundary was calculated to be 5×10−8 cm2 s−1 at 1093 °C, which is approximately four orders of magnitude greater than the bulk lattice diffusivity of tungsten.  相似文献   

17.
The effect of Al addition on a new Co-Ni-Cr base superalloy containing Nb are discussed. The main strengthening phase was found to be γ′ which grows by Lifshitz-Wagner theory of diffusion controlled growth. On prolonged aging, γ′ loses its coherency with the matrix but maintains its ordered FCC structure. Carbon, present as an impurity element, gave rise to NbC phase which precipitates at the grain boundary as well as within the grains. Occasionally sigma phase was also observed in the overaged specimens. An attempt has also been made to analyze the structure of the precipitates on the electronic consideration of Engel-Brewer theory.  相似文献   

18.
A directionally solidified cobalt-base alloy, DZ40M, was solidified with a columnar grained austenitic matrix with a 〈001〉 preferential orientation and primary carbides of chromium-rich M7C3 and MC at grain boundaries and interdendritically. Secondary carbides in DZ40M alloy are chromium-rich M23C6 and tungsten-rich M6C. The M23C6 carbide has a cube-cube orientation relationship with the austenitic matrix. Initial precipitation of secondary carbide, M23C6, occurred on dislocations in the austenitic matrix of the as-cast DZ40M alloy during cooling. Aging treatment (100 to 1000 hours at 850°C) produced a profusive precipitation of the M23C6 carbide mainly around the primary carbides. In the interior of grains, M23C6 precipitated preferentially on dislocations and stacking faults. Subsequently, M23C6 grew into laths near the primary carbides and coalesced into chains. The precipitation behavior of M23C6 can be explained by the following reaction: 23M+6C→M23C6. The primary carbides are a carbon reservoir for the precipitation of M23C6. The M6C carbide was found only on the surface of the primary M7C3 carbide adjacent to tungsten-rich MC in the aged condition. The precipitation of the tungsten-rich M6C is atributed to the tungsten segregation, which resulted from decomposition of the tungsten-rich MC and good lattice match between M6C and M7C3. The inhomogeneity of secondary precipitation is due to the uneven distribution of alloying elements.  相似文献   

19.
Exposure in air in the temperature range 900 to 1100 °C produces a major loss in stress rupture life and ductility of IN738. The sensitivity to this environmental damage increases with decreasing test temperature in the range 1000 to 700 °C. Oxygen is identified as the source of the damage for air exposure and indirect evidence supports grain boundary penetration of the gas to considerable depth. It is argued that oxygen segregation can lead to grain boundary immobilization and unstable intergranular fracture at intermediate temperatures. It is shown that compositional modifications, particularly boron and hafnium additions, may reduce the oxygen damage susceptibility, and that a cobalt base coating effectively eliminates the susceptibility. The relevance of these observations in understanding the effect of test environment on creep-rupture and fatigue crack propagation is considered.  相似文献   

20.
Yiwa Luo  Jing Guo 《钢铁冶炼》2013,40(7):698-704
The influence of cooling rate during austenitising process on the transformation characteristics and precipitation behaviour of carbides in AISI M42 high-speed steel was investigated through thermodynamic calculation, dilatometry, microstructural analysis, and steel inclusion analysis system. Results show that under low cooling rate (<1?K?s?1), the carbides in the steel are coarse, growing along the grain boundaries, and forming a network distribution. Under high cooling rate (≥1?K?s?1), the morphology of carbides turns into block shape, and martensitic microstructure has been achieved. The volume fraction of the carbides decreases with the increase of cooling rate, meanwhile, the size distribution of the carbides is meliorated. However, when the cooling rate further increases from 5 to 20?K?s?1, the precipitated carbides becomes non-uniform with the increasing cooling rate. Consequently, an appropriate cooling rate of heat treatment can be selected to optimise the distribution of carbides.  相似文献   

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