新一代镍基变形高温合金GH4065A的组织控制与力学性能

由于GH4065A合金的强化相γ′相的体积分数为43.0%,显微组织演化规律不同于传统的变形高温合金与粉末高温合金。系统分析了GH4065A合金的锻态组织特点与演化机制,发现其显微组织是一种不完全的动态再结晶(DRX)组织,动态再结晶晶粒被大尺寸γ′相限制长大,同时这些γ′相因晶界短路扩散而粗化,而未动态再结晶(unDRX)晶粒内弥散分布的小尺寸γ′相阻碍位错运动,进而形成大量由位错胞壁构成的亚结构。基于合金的锻态组织特点,可以通过固溶处理,利用动态回复(DRV)机制基本消除残留的未动态再结晶组织。根据GH4065A合金γ′相的固溶温度,可将热处理制度分为亚固溶处理与过固溶处理2种,亚固溶处理后的晶粒度为8.0级,过固溶处理的晶粒度为4.0级。经亚固溶处理后,GH4065A合金涡轮盘锻件的力学性能达到了第2代粉末涡轮盘的水平。     

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.     

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The influence of Nb on tensile properties at room temperature and 650?? as well as the effects of Nb on stress rupture properties at 650??/690MPa of GH4169 alloy with standard heat treatment (STD) and direct aging heat treatment (DA) were investigated. Microstructure and thermodynamic calculation were also undertaken. The results show that as Nb content increases from 5??2% to 5??4% (mass percent), the mass fraction of strengthening phases in the alloy as DA increases, and the strength also improves obviously at room temperature and 650?? while the strength decreases when Nb content reaches 5??6%. At the same solution temperature, the increase of Nb content will promote the mass fraction of ?? phase in the alloy as STD, but the effect on the mass fraction of strengthening phases is not so apparent as the DA state, and the extent of strength promotion is small. The stress rupture life of the alloy as DA improves with the increasing of Nb content, and remains nearly unchanged after Nb content reaches 5??6%. Whereas when Nb content rises to 5??6%, the change of ?? phase??s amount and morphology in the alloy as STD may result in significant decrease of the stress rupture life.     

析出相对Monel K-500合金冲击韧性的影响

通过一系列实验研究了Monel K-500合金的冲击韧性。结果表明,合金经550~650℃时效后其冲击断口呈沿晶形貌;在750~850℃时效时,其冲击韧性与强度呈正相关关系。根据对合金在不同热处理状态的析出相形态及分布的研究,揭示了形成这些现象的原因。合金在550~650℃时效时,在晶内析出的γ’相呈球状均匀分布,而在部分晶界附近的γ’相呈条棒状或排成帘状垂直于晶界分布,由此导致时效态合金在断裂时,裂纹沿晶界扩展。在750~850℃时效会导致合金形成大量沿晶界网状分布的二次MC相,从而降低合金的冲击韧性。     

2205双相不锈钢连铸坯加热过程组织转变

对2205双相不锈钢连铸坯试样在1 220、1 240、1 260、1 280℃保温10、20、30和40 min进行加热处理,通过光学显微镜和铁素体仪试验分析2205双相不锈钢的组织和铁素体含量随保温时间和加热温度的变化情况.结果表明,2205双相不锈钢连铸坯试样在相同的保温时间下,随着加热温度的升高,铁素体含量逐渐增加,1 260℃时奥氏体晶粒明显变得粗大;在相同的加热温度下,随着保温时间的延长,铁素体的含量逐渐减少.     

第2代单晶高温合金DD6的燃气热腐蚀行为

在高温度梯度真空定向凝固炉中制备了第2代单晶高温合金DD6。研究了DD6单晶高温合金900℃燃气热腐蚀行为,采用扫描电镜、X射线衍射仪、能谱分析仪对腐蚀产物进行了分析。结果表明,DD6单晶高温合金具有优异的耐燃气热腐蚀性能,900℃试验100h的腐蚀动力学曲线基本遵循抛物线规律。腐蚀100h后合金表面生成了紧密排列的不规则的棱形NiO。腐蚀产物分为两层,外层为氧化物,内层为硫化物。由于Al含量降低,紧靠腐蚀产物的基体,γ′相的立方化程度降低。     

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。     

燃气轮机用GH4720Li合金组织与性能关联性

摘要：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：经亚固溶处理后,室温拉伸强度和屈服强度呈现出相似规律,并在1130℃附近出现峰值;经过固溶处理后,拉伸强度和屈服强度均明显降低。在亚固溶处理区间,随着固溶温度的增加,持久寿命逐渐增加;经过固溶处理后,合金的持久寿命明显提高,而持久塑性呈现出与持久寿命相反的趋势。结合燃气轮机的服役工况,燃气轮机用GH4720Li合金的合理固溶处理应为过固溶处理,可获得组织性能的较佳匹配。     

Multiphase microstructure and property of low carbon bainite/ferrite steel by quenching and carbon partitioning

The multiphase microstructure and properties of low carbon steel by IQ&PB process under different partitioning temperatures and time were studied by means of SEM, EPMA, XRD and tensile testing. Results show that the microstructures of experimental steel consist of ferrite, bainite and retained austenite. With the increase of the holding time in two- phase region, the C and Mn contents apparently increase in martensite which transformed from austenite, and C and Mn content are 1. 47 times and 1. 16 times than average value of the base. With the decrease of the quenching and partitioning temperature, the volume fraction of the bainite increases, the microstructure is refined, and the content of M/A islands increases. With the temperature and time increased, the volume fraction of retained austenite at room temperature increases, the tensile strength decreases, the total elongation increases, and work hardening behavior occurrs continuously. When the partitioning time is 30min and the partitioning temperature is 400??, the tensile strength of the steel is 1107MPa, the elongation is 24%, the product of strength and elongation reaches above 26568MPa??%.     

Effect of solid solution treatment on grain growth behavior of FB2 rotor steel

FB2 rotor steel, which had undergone different solid solution treatments, was examined carefully through OM, SEM, TEM. Meanwhile, the effect of solid solution treatment on the grain size was investigated in the above way. The results show that the growth rate of grain in test steel is slow when the solution temperature is below 1050??, and the grain will grow more quickly when the solution temperature is raised to over 1100??. The growth rate of grain gradually decreases if the solution time is prolonged and grain doesn??t grow apparently eight hours later. The relationship between FB2 rotor steel grain and the heating temperature as well as holding time is described clearly by using Sellars model. Raising the solution temperature can increase the intergranular activity and decrease the pinning effect of second phase particles on the grain boundary, which can make the grain grow up quickly. Although FB2 rotor steel experiences a long solution treatment process at 1100??, its grain doesn??t tend to grow up abnormally.