高温精炼处理对铸造镍基高温合金组织与性能的影响

研究了高温精炼处理对铸造镍基高温合金组织与性能的影响.普通铸造镍基合金枝晶组织粗大,晶界碳化物呈链状分布,晶内碳化物呈草体汉字状密集分布于枝晶间,是合金塑性低的主要原因.经高温精炼处理后,合金的枝晶组织细化,晶界及枝晶间的碳化物数量减少,γ γ共晶相数量增加,晶界碳化物呈不连续质点状分布,晶内碳化物的密集程度下降,拉伸塑性和蠕变(持久)寿命得以明显提高.经1 650℃,5 min高温熔体处理后,合金室温延伸率由3.5%提高到9.2%,700℃高温塑性由2.0%提高到8.0%,900℃高温塑性由2.8%提高到9.6%,蠕变寿命由34 h提高到52 h,蠕变塑性由4.3%提高到6.11%.推荐的最佳高温精炼处理制度为1 650℃保温4 h.分析了高温精炼处理对合金液态结构、凝固组织与性能的影响机理.     

NICKEL-BASED ALLOYS IN GE AIRCRAFT TURBINES：PAST,PRESENT ＆ FUTURE

1. Introduction Freedom to travel anywhere in the world, both quickly and inexpensively, defines our modern era. Despite year-to-year variation, the long term demand for travel by airplane continues to grow. Three ma- jor systems comprise the modern airplane: the aircraft structure that encompasses the fuselage, wings, and landing gear; the avionics that enable flight through crowded skies in nearly all weather conditions; and the propulsion system that powers the aircraft. Improvements in mat…     

K38G合金及其溅射微晶层的高温氧化

研究了K38G铸造镍基高温合金及其用平面磁控离广溅射工艺制备的微晶涂层在800-1000℃500小时内的抗高温氧化性。结果表明,微晶化极大改善合金的抗氧化能力,并改变合金表面生成的氧化物类型,由Cr_2O_3变为α-Al_2O_3。还讨论了铸态K38G合金及溅射微晶层的氧化机理。     

Oxidation Behavior of a Single-Crystal Ni-Base Superalloy in Air—II: At 1000, 1100, and 1150°C

The oxidation behavior of a single-crystal (SC) Ni-base superalloy was studied over the temperature range from 1000–1150°C and analysed by TGA, XRD, EDAX, and SEM. The results indicated that the SC Ni-base superalloy exhibited parabolic oxidation kinetics, which were controlled by the growth of the inner -Al₂O₃ layer. A mixed scale formed on the SC Ni-base superalloy after prolonged oxidation. The scale consisted of an outer layer of spinel, a sublayer of mainly -Al₂O₃ with small amount of spinel adjoined by a very thin and even discontinuous layer of CrTaO₄-rich oxide, and an inner -Al₂O₃ layer. The inner -Al₂O₃ layer provided good protection. No internal oxides or nitrides were observed below the inner -Al₂O₃ layer after 1000 hr at 1000°C, and after 200 hr at 1100 and 1150°C.     

预压缩单晶镍基合金的组织结构及在拉伸蠕变期间的粗化特征

对[001]取向单晶镍基合金进行压应力处理，获P-型筏状结构后，对其进行拉伸蠕变性能测试及SEM形貌观察，研究了P-型筏状结构的粗化特征及影响因素。结果表明：由于应力场的差别，样品不同位置筏状γ＇相粗化程度及特征不同，近断口处筏状γ＇相扭曲且粗化程度加剧，随离断口距离增加，γ＇相粗化程度减弱。有限元分析认为：外加载荷改变了水平和垂直γ基体通道中的错配应力分布，并使立方γ＇相不同界面晶格发生挤压或扩张应变，这可以促进元素的互扩散和γ＇相的定向生长，是形成P-型筏状组织的主要原因。在高温及拉应力作用下，P-型γ＇相端部沿垂直于应力轴方向优先生长和相互横向连接，并进一步形成折叠的层状组织。     

High-Temperature Corrosion Resistance of Al–Re and Re Coatings

The oxidation behavior in air at 1473 K, and sulfidation behavior in a H2S–H2 gas mixture with a sulfur partial pressure of 10^–2 Pa at 973 K of Al–Re coated CMSX-4 were studied. Investigation on the sulfidation behavior of the Re-coated CMSX-4 was carried out in a H2S–H2 gas mixture with a sulfur partial pressure of 10^–2 Pa at 973 K. The experimental results show that a Re-rich alloy layer was formed between an -Al₂O₃ layer and the inner concentration zone of Ta and Ti for the CMSX-4 single crystal alloy with an Al–Re coating after oxidation. The Re-rich alloy layer containing Cr, W, Ni, Co, and Mo effectively inhibited the outward diffusion of alloying elements and the inward diffusion of Al. The Al/Re-coated CMSX-4 single crystal alloy had excellent sulfidation resistance; the Re-rich alloy layer, containing W, Ti, Ta, and Mo, which formed during the sulfidation process and located between the alumina scale and the CMSX-4 base alloy, plays a role in inhibiting the outward diffusion of alloying elements. The sulfidation resistance of CMSX-4 single-crystal alloy is greatly improved by a Re coating on the CMSX-4 alloy surface; this is attributed to a Re–Cr–W alloy layer that retarded the outward diffusion of cations and the oxide layer containing Ta, Ti, and Al, which inhibited the inward penetration of sulfur.     

Evaluation of the superplastic formability of SP-inconel 718 superalloy

The superplastic formability of SP- lnconel 718 superalloy was evaluated using the argon blowing method. Relationships among superplastic forming parameters (forming temperature, argon pressure, and forming time) and specific dome height (dome height/workpiece diameter) were investigated, as were changes in material properties after superplastic forming. Experimental results showed the optimum forming temperature range for SP- lnconel 718 to be between 975 and 995 °C. During the superplastic forming process, 5- phase precipitates formed at grain boundaries and limited the grain growth, which is considered beneficial for superplastic deformation. On the other hand, increasing the forming deformation also increased the formation of cavities, which can be attributed to the existence of niobium- rich inclusions. This degraded the superplasticity of the superalloy. Electrochemical tests showed that the corrosion resistance of SP- lnconel 718 after superplastic forming worsened because of the existence of both S- phase precipitates and niobium- rich inclusions.     

凝固速率对定向凝固合金DZ22枝晶臂间距和枝晶偏析的影响

采用新研制的超高梯度定向凝固装置，研究了不同凝固速率下定向凝固高温合金ＤＺ２２枝晶臂间距和枝晶偏析。结果表明，冷运速率增大，枝晶臂间距显著细化，枝晶偏析被强烈抑制。当冷运速率为５２．４Ｋ．ｓ＾－１时，一次、二次枝晶臂间距λ１和λ２分别为２８．８和８．４μｍ，Ｎｂ，Ｔｉ，Ａｌ，Ｃｒ，Ｃｏ，Ｗ等元素的偏析比均趋近于１。     

Creep-induced local lattice parameter changes in a monocrystalline nickel-base superalloy

The γ-γ lattice mismatch of specimens of the monocrystalline nickel-base superalloy SRR 99 has been measured by a high-resolution X-ray diffraction technique for the undeformed state and after high-tem-perature creep deformation. During creep deformation beyond the minimum creep rate (total strain =0.5%), the lattice mismatches, measured in and perpendicular to the [001] stress axis, respectively, un-dergo changes in opposite directions. This reflects the buildup of a complex deformation-induced triaxial state of internal stress in the phases y and γ. The overall resolved shear stresses that act in γ and y due to the combined action of the external and internal stresses are estimated, and the conditions under which cutting of the γ phase by dislocations should occur are discussed.