热处理过程中FGH96合金的微观组织演变

通过热处理实验研究了热处理过程中FGH96合金的微观组织演化，量化了固溶温度和保温时间对晶粒尺寸、γ′相尺寸、面积分数及晶粒分布的影响，分析了γ′相和应变存储能对晶粒演变的影响。结果表明：在热处理过程中，含有大量应变存储能的变形晶粒发生静态再结晶，晶粒细化，而动态再结晶晶粒发生晶粒长大，当两者平衡时可获得均匀细小的晶粒组织。合金在1060℃保温120 min后，γ′相尺寸和晶粒尺寸分布较为均匀，平均晶粒尺寸为7.37μm。γ′相的面积分数随固溶温度和保温时间的增加而减小，一次γ′相在亚固溶保温过程中存在粗化和分裂现象，使得一次γ′相的面积分数和尺寸先增加后减小。γ′相的非均匀溶解会导致局部晶粒长大较快，形成混晶。     

FGH4102粉末高温合金等温热模拟压缩试验及动态再结晶组织研究

本文研究了新型第四代粉末高温合金FGH4102在等温热模拟压缩过程中的组织演变,对γ′相在动态再结晶过程中的作用进行了探讨。结果表明,热等静压态合金在1 060～1 120℃温度范围变形时,热加工性能较好。1 140℃变形后试样容易发生开裂,合金热加工性能较差。合金在γ+γ′两相区变形时均发生了不同程度的动态再结晶,再结晶晶粒尺寸远小于热等静压态的晶粒尺寸。变形过程中,尺寸较大的γ′相起到促进动态再结晶的作用。变形参数对动态再结晶的影响非常显著。低温高应变速率变形时,γ′相促进动态再结晶形核占主导地位,再结晶晶粒比较细小;高温低应变速率变形时,晶粒长大逐渐占据主导地位,再结晶晶粒尺寸较大。     

变形参数对GH4742合金动态再结晶及γ′相的影响

 为了研究不同变形参数对锻态GH4742合金动态再结晶及γ′相的影响,利用单道次等温压缩试验获得了变形温度为1 050～1 150 ℃、变形量为30%～70%、变形速率为0.1 s-1时的真应力-真应变曲线,分析了不同变形参数下真应力-真应变曲线以及峰值应力的变化规律,同时采用SEM、EBSD对不同变形参数下动态再结晶过程中的亚结构以及γ′相进行了精细表征,定量计算了基体内的几何位错密度以及发生动态再结晶的比例,并测试了不同变形参数下基体的硬度。重点探讨了不同变形参数下动态再结晶的形核机制,深入分析了动态再结晶过程中亚结构以及γ′相的演变规律。结果表明,变形温度为1 080 ℃时,基体中存在大量未溶的一次γ′相,小角度晶界比例超过35%,基体发生动态再结晶比例小于35%,主要形核方式为连续动态再结晶。变形温度为1 110 ℃,一次γ′相尺寸减小并发生回溶,小角度晶界比例小于8%,基体发生动态再结晶比例超过75%,主要形核方式为不连续动态再结晶。随着变形量增加,一次γ′相尺寸增大、数量密度降低,小角度晶界比例显著下降,动态再结晶比例明显提高。低温变形时基体硬度随着变形量增加而显著增加,而高温变形时硬度先增加后逐渐趋于不变。GH4742合金变形温度为1 110 ℃时,变形量50%时已完成动态再结晶,组织为等轴的动态再结晶晶粒,基体硬度较低,为357HV,在此变形参数下加工具有良好的热成型性能。     

固溶温度对GH2787合金组织性能的影响

研究了GH 2787合金在不同固溶温度处理后的组织性能.结果表明,在900、940和980℃固溶处理时,GH 2787合金的晶粒尺寸分别为20、30和40μm.当固溶温度低于γ'溶解温度时,GH 2787合金中的γ'相分布均匀,并有少量针状的η相出现.900℃固溶处理时,GH 2787合金硬度、屈服强度和拉伸强度最高.GH 2787合金的主要强化方式为γ'相沉淀强化和晶界强化.     

梯度组织FGH96合金残留枝晶区的组织特征研究

采用梯度热处理工艺制备了具有梯度组织结构的FGH96合金亚尺寸盘坯, 对盘坯存在的残留枝晶区组织进行了研究。结果表明, 残留枝晶区实质上是一种γ′相未完全再结晶的组织区, 其呈区域性不均匀的分布于盘芯部位。残留枝晶区的形成与粉末颗粒冷凝组织的遗传性及未充分变形再结晶密切相关, 通过采用合适的热加工和固溶热处理工艺可以消除这种组织不均匀性。     

FGH96合金固相扩散连接界面组织与失效机制

对原始状态分别为锻态、固溶态和半时效态的FGH96合金固相扩散连接界面显微组织进行表征,并对连接界面的拉伸性能进行测试,对失效行为进行研究。结果表明,锻态、固溶态和半时效态试样经固相扩散连接后界面均实现了良好的冶金结合,连接界面无孔洞和缝隙等缺陷。锻态试样界面扩散更为充分,组织过渡更为平缓;固溶态和半时效态试样界面存在明显的连接影响区。锻态试样经固相扩散连接和标准热处理后,二次γ?相细小、均匀且呈典型椭球状;固溶态和半时效态试样因固相扩散连接热循环的作用导致γ?相发生长大和分化。二次γ?相尺寸及形貌的不同决定了界面区域性能水平的差异。电子背散射衍射测试结果表明,连接界面处大晶粒的择优取向为{100},距离固相扩散连接界面越近,晶粒的择优取向越明显。拉伸试验结果表明,锻态试样经固相扩散连接和标准热处理后,连接界面处的强度达到基体强度的99%以上。拉伸裂纹主要萌生于连接界面大晶粒及γ?相粗化聚集区域,体现为穿晶的韧窝型断裂。     

含5%铬镍基单晶高温合金相分析

近年来单晶技术的发展解决了镍基高温合金晶界强化问题,使镍基高温合金具有优良的综合性能。合金的高温性能除取决于合金成份和工艺外,还必需进行适宜的热处理。对于新型单晶合金应选择合适的固溶温度,尽可能使铸态粗化γ′,相固溶而使显微组织均匀化,以便时效时能保证析出大量均匀弥散的γ′,相(二次γ′),这种弥散γ′相能提供在一定γ′体积百分数下的最佳蠕变抗力。为了研究不同固溶温度对NASAIR—100合金的组织和性能的影     

燃气轮机用GH4720Li合金组织与性能关联性

基于光学显微镜、场发射电镜组织分析及系列力学性能测试,研究了固溶处理对燃气轮机用GH4720Li合金组织特征的影响,分析了组织特征与力学性能的关联性.结果表明:随着固溶温度的升高和固溶时间的增加,合金一次γ'相回溶,平均晶粒尺寸增加,当固溶温度高于1160℃,晶粒尺寸增大明显.GH4720Li合金的力学性能变化规律如下...     

FGH95合金等温锻造工艺研究

对FGH95合金细晶制备和超塑性等温变形工艺进行了研究。结果表明，双冷速缓冷处理可以有效细化FGH95合金晶粒，改变γ′相的尺寸和分布，并且通过粗化的γ′相对再结晶晶粒的钉扎作用，使FGH95合金细晶组织保持很高的热稳定性；具有细晶组织的GH95合金进行高、低应变速率组合的等温压缩变形时，在低应变速率条件下，可实现超塑性变形。双冷速缓冷处理 超塑性等温锻造工艺具有较强的适应性，可推广至大尺寸粉末高温合金盘件的等温成形，采用该技术研制的等温锻造FGH95合金盘件具有良好的综合力学性能。     

变形量、热处理制度对GH536焊管焊缝区铸态组织、晶粒度及力学性能的影响

研究了用无填料自动氩弧焊工艺生产GH536合金焊管时,借助冷加工变形和固溶再结晶处理实现无缝化的问题.通过研究冷加工变形量和热处理制度对GH536合金焊管焊缝区铸态组织、晶粒度及力学性能的影响得知当冷加工总变形量达到77%,并进行1100～1150℃×15 min固溶再结晶处理时,可以完全消除GH536合金焊管焊缝区的铸态组织,使基体和焊缝都具有均匀一致的10.0级左右的细晶组织,确保其力学性能达到并超过技术条件所规定的要求.     

Plastic Flow and Microstructure Evolution during Thermomechanical Processing of a PM Nickel-Base Superalloy

Plastic flow and microstructure evolution during sub- and supersolvus forging and subsequent supersolvus heat treatment of the powder-metallurgy superalloy LSHR (low-solvus, high-refractory) were investigated to develop an understanding of methods that can be used to obtain a moderately coarse gamma grain size under well-controlled conditions. To this end, isothermal, hot compression tests were conducted over broad ranges of temperature [(1144 K to 1450 K) 871 °C to 1177 °C] and constant true strain rate (0.0005 to 10 s^?1). At low temperatures, deformation was generally characterized by flow softening and dynamic recrystallization that led to a decrease in grain size. At high subsolvus temperatures and low strain rates, steady-state flow or flow hardening was observed. These latter behaviors were ascribed to superplastic deformation and microstructure evolution characterized by a constant grain size or concomitant dynamic grain growth, respectively. During supersolvus heat treatment following subsolvus deformation, increases in grain size whose magnitude was a function of the prior deformation conditions were noted. A transition in flow behavior from superplastic to nonsuperplastic and the development during forging at a high subsolvus temperature of a wide (possibly bi- or multimodal) gamma-grain-size distribution having some large grains led to a substantially coarser grain size during supersolvus annealing in comparison to that produced under all other forging conditions.     

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Influence of solution treatment temperature on microstructure and high- temperature tensile properties of Ni3Al- based alloy sheet was investigated. The results show that volume fraction of ?? phase reduces and volume fraction of ?á?+?? region increases with increasing heat treatment temperature up to 1280??. When the temperature reaches to 1310??, volume fraction of ?á?+?? region keeps at the same level but that of ?? phase increases. Due to precipitation of ?? phase along grain boundary with the temperature raising, grains begin to grow up until the temperature reaches 1280??. The grain sizes are different for different directions at the solution treatment temperature below 1280??. Crack initiates at the interface of ?? and ?á? envelope during 1000?? tensile test. The increase of volume fraction of ?á?+?? region can increase the strength of the alloy. The alloy has excellent comprehensive mechanical properties after heating at 1280?? for 16min and AC.     

一种含铁Ni_3Al基合金的热变形行为

采用Gleeble-1500D热模拟试验机对一种含铁Ni3Al基合金进行了高温压缩试验,试验温度为1 050~1 150℃,应变速率为0.1~1.0s-1,工程应变量为50%。获得了不同变形条件下的真应力-真应变曲线,并分析了合金微观组织的变化。结果表明:合金的流变应力随着变形程度的增加先达到峰值应力,之后逐渐降低,趋于稳态流变。提高变形温度及减小应变速率能有效促进动态再结晶过程。在变形温度1 100℃以上,工程应变为50%时,能够获得完全再结晶的锻态组织。基体中的γ′相粒子对合金动态再结晶有抑制作用,β相的存在促进了相界处动态再结晶形核但抑制了完全动态再结晶晶粒的长大。高温下β相的软化效应和γ′相的回溶转变都有效提高了Ni3Al基合金热加工性能。     

热处理对FGH95合金组织和性能的影响研究

通过热处理工艺试验设计,研究了不同热处理条件下FGH95合金的组织和性能。与亚固溶线温度热处理后细晶试样比较,过固溶线温度热处理的试样获得了晶粒度8级的相对粗晶组织,强度仅比细晶试样的降低不超过5%,而蠕变性能显著提高,700℃/690MPa条件下,0.2%残余应变的蠕变寿命提高了3～4倍;另外,通过优化γ’相的尺寸与分布,可进一步提高合金的力学性能。     

固溶温度对GH4202合金组织及拉伸性能的影响

为充分挖掘沉淀强化型镍基高温合金GH4202管材性能,以满足我国航天新型发动机的要求,研究了固溶处理温度对合金组织及拉伸性能的影响规律.结果表明,在1 050~1 075℃范围固溶处理后合金晶粒度无明显变化,当固溶温度升至1 100℃时,合金局部出现异常晶粒长大,当固溶温度达到1 150℃时,合金晶粒均匀长大.随固溶温度升高,合金晶界硼、碳化物数量明显减少,由链状向孤立的颗粒状转变.随固溶温度升高,GH4202合金室温及高温拉伸强度均呈降低趋势,尤其以屈服强度降低幅度最为显著.合金的室温面缩率随固溶温度升高而降低,且降低幅度较大,但室温断裂延伸率变化并不显著;700℃下合金的断面收缩率与断裂延伸率随固溶温度的变化均表现为先升高后降低的趋势.GH4202合金最佳固溶处理工艺为1 110℃保温30 min后水冷,此时合金晶粒度为5.0级、晶界碳化物呈细小链状,晶内沉淀强化γ'相弥散析出,可保证合金具有优异的室温及高温力学性能.     

Origin of Significant Grain Refinement in Co-Cr-Mo Alloys Without Severe Plastic Deformation

We have previously reported that ultrafine-grained (UFG) microstructures can be obtained in a Co-29Cr-6Mo (wt pct) alloy by utilizing dynamic recrystallization (DRX) that occurs during conventional hot deformation (Yamanaka et al.: Metall. Mater. Trans. A, 2009, vol. 40A, pp. 1980?94). The present study investigates the novel DRX mechanism of this alloy in detail. The microstructure evolution during hot deformation under relatively high Zener?CHollomon (Z) parameter conditions for which ultrafine grains can develop was systematically investigated by electron backscatter diffraction (EBSD) and transmission electron microscopy. This alloy exhibited a different flow stress behavior and microstructural development from conventional DRX mechanisms. The deformation microstructure contained a large number of stacking faults, which implies that planar dislocation slip is the primary deformation mechanism in the hot deformation of the Co-29Cr-6Mo alloy due to its abnormally low stacking fault energy (SFE) at elevated temperatures. Inhomogeneities in local strain distributions induced by planar slip will enhance grain subdivision by geometrically necessary (GN) dislocation boundaries. Deformation twinning may also contribute to grain refinement. The DRX mechanism operating in the Co-29Cr-6Mo alloy is discussed by considering the relationships between anomalous dislocation structures, flow stress behavior, texture development, and nucleation behavior.     

Research on novel cast and wrought superalloy FGH4096 for aircraft turbine disk applications

The ingot metallurgy of electro- slag remelting continuous directional solidification(ESR- CDS) followed by multiple forging and isothermal forging, a novel cast and wrought(C&W) routes for preparation of FGH4096 turbine disk, was developed to solve the difficulties of microstructure controlling, the macro- segregation, poor processing of ingot with high alloying element used for the turbine disk of advanced aircraft engine. From aspects of ingot microstructure characteristics, hot working plasticity, microstructure controlling, mechanical properties and strengthening mechanisms, the preparing processes of C & W superalloy FGH96 turbine disk were studied. The formation of bulk ?? phase, borides phase and carbonitride strips can be avoided by the directionally solidified ingot, which resulted in excellent hot working plasticity. Multiple forging was applied to achieve the homogeneity of microstructure. The grains are fine in different parts of the billet, and the deformation dead zone can be eliminated. The mean grain size for alloy billet is close to ASTM 9-10. Because of the fine grains and the homogeneity of microstructure, the ultra- inspection capability for disk forging can be significantly improved. With the increase of solution temperature, the yield strength decreases. Under sub- solvus temperatures, the creep resistance decreases with the increase of solution cooling rate. The micro- twining shearing is the main creep deformation mechanism for the samples from disk rim.     

高温合金GH4065A的恒温静态氧化行为

研究了新型镍基高温合金GH4065A在650～750℃的静态氧化行为,基于对氧化动力学与氧化产物的分析,探讨了合金的氧化机制.结果表明:采用平均氧化增重速率指标评定GH4065A合金在650～750℃温度范围内均为完全抗氧化级别,试验条件下合金的抗氧化能力与典型涡轮盘材料FGH96、GH4720Li合金相当;合金的氧化产物主要为内层富铝的氧化物颗粒、外侧富铬的氧化物膜及表面金红石型TiO2颗粒,TiO2颗粒在氧化温度超过700℃后开始生成;合金的氧化动力学遵循抛物线型规律,受钛离子与铬离子穿过氧化膜的扩散过程共同控制.     

等温锻造工艺对GH4720Li合金盘锻件组织的影响

采用物理模拟得到了GH4720Li合金的热变形特征,同时利用数值模拟研究了不同锻造工艺对GH4720Li盘锻件温度场、应力场、设备载荷等参数的影响规律,并通过实际锻造Ф150mm的GH4720Li合金盘锻件进行了验证。结果表明,GH4720Li合金变形组织对温度、应变等参数非常敏感,采用普通锻造会造成温度应力分布不均,...     

固溶冷却介质对优质GH738合金组织及力学性能的影响

研究了不同固溶冷却介质(油、空、棉)及之后的时效处理对优质GH738 (HQGH738)合金组织及力学性能的影响.分别利用光学金相显微镜(OM)和场发射扫描电镜(FESEM)对热处理各阶段合金的晶粒组织及γ'相分布情况进行观察,同时检测热处理各阶段拉伸强度.结果表明:冷却介质对HQGH738合金晶粒尺寸无影响,而主要影响一次及二次γ'相的回溶及析出行为,进而影响合金的性能.固溶阶段,随冷速的提高(油淬＞空冷＞棉冷),合金中二次γ'相减少,尺寸越小,固溶后合金抗拉强度降低.经过稳定化处理后,3种冷却方式下合金强度顺序不变,但差值减小.再经过双时效后,三者抗拉强度相当.冷速越快,一次γ'相粗化越慢,从而在双时效过程中析出更多的细小二次γ'相,最终合金的屈服强度随冷速的增加而增强.