基于类等势场的粉末高温合金盘件等温锻造预成形设计

以体积成形工艺为例提出了一种新的预成形设计方法。通过静电场模拟选取适当的等势线作为预锻模型腔的基本形状，将选取的预成形形状通过频谱分析进行光顺处理，可以确定出六组预锻模型腔最终轮廓形状。利用有限元软件对粉末高温合金盘件两工步（预锻＋终锻）等温锻造过程进行模拟，进一步分析了相关场变量的分布，优选出预锻模型腔形状。分析表明，基于类等势场法的预成形设计和基于频谱分析的曲线曲面光顺处理方法适合体积成形工艺的预制坯设计。     

Ni-Cr-Al纳米晶合金在1000℃的高温氧化行为

研究了纳米晶Ni-Cr-Al合金的高温氧化行为，发现与 铸态合金不同，随成分不同纳米晶合金在1000℃氧化时，氧化物可分为四个区：A单一Al2O3区；B复杂氧化膜含一连续Al2O3内层区； C复杂氧化膜含内氧化物区；D Al2O3和NiAl2O4共生区.纳米晶化明显扩展了Al2O3生成区的成份范围.     

FRACTAL ANALYSES OF DIRECTIONAL SOLIDIFICATION BEHAVIOR OF A Ni-BASE SUPERALLOY

The morphology of solid/liquid interface of a directionally solidification process is describedby means of fractal analysis,and the relations among the fractal dimension of the solid/liq-uid interface,solidification rate,dendrite arm space and the phosphorus content of the test al-loys have been given.It was found that the increase of the solidification rate and the phos-phorus content of the test alloy will lead to a increase,following the regularity of exponentialfunction,in the fractal dimension of solid/liquid interface.Furthermore,by combining thefractal theory and the thermodynamic principle with the measured results,it has been provedthat the fractal dimension is not only a kind of simple geometrical parameter used in des-cribing irregular geometry,but also a state function depending the change of solidificationparameters and chemical compositions.     

Joining alumina to inconel 600 and UMCo-50 superalloys using an Sn10Ag4Ti active filler metal

Alumina ceramics were brazed to Inconel 600 and UMCo-50 superalloys at 900 °C for 10 min using an Sn10Ag4Ti active filler metal. The brazing filler showed good wettability on alumina and superalloys. The flexural strengths were 69 and 57 MPa for alumina/Inconel 600 and alumina/UMCo-50 joints, respectively. In both cases, the brazed specimens fractured along the Sn10Ag4Ti/superalloy interfaces after four-point bending tests. Electron probe microanalysis (EPMA) elemental mapping revealed that the Ni of Inconel 600 and the Co of UMCo-50 dissolved into Sn10Ag4Ti filler metal, which serves to reinforce the weak Sn10Ag4Ti matrix.     

高温运行对镍基异种金属接头力学性能的影响

对12Cr1MoV和0Cr17ni12Mo2两种管材的镍基异种金属接头进行焊后状态和高温运行后状态对比试验。结果表明，高温运行使异种钢接头σ-ε图中曲线移动，反映了高温运行后异种钢接头的屈服强度和塑性有所下降；高温运行使异种钢接头的各项力学性能指标σb,σ0.2,δ5,ψ均略有下降，该结果与接头组织变化及12Cr1MoV钢珠光体组织中碳化物球化倾向等不利因素有关；高温运行对异种钢接头断口部位及宏观断口形貌特征无大的影响；高温运行后异种钢接头拉伸试样仍断在母材处，表明镍基异种钢接头的抗拉强度是比较满意的。     

Studies on the hot corrosion of a nickel-base superalloy,Udimet 700

The hot corrosion of a nickel-base superalloy, Udimet 700, has been studied in the temperature range 900–950°C. The effect of the amount of Na ₂SO₄ on the corrosion kinetics was determined. Large weight gains and severe corrosion were associated with two different modes of degradation: (1) formation of large, interconnected sulfides beneath the external scale, and (2) formation of a Na₂MoO₄-MoO₃ melt. The corrosion due to formation of the Na₂MoO₄-MoO₃ melt occurred for all the salt-coating thicknesses, whereas, large sulfides were formed only for the heavier coatings of Na₂SO₄. The formation of Na₂MoO₄-MoO₃ melt required an induction period, and the length of the induction period was observed to be a function of the amount of Na₂SO₄ and of temperature.Work funded under NASA Grant NCC 3-43.     

The Influence of High Temperature Exposure on the Wear Performance of a Ni Based Alloy PTA Coating

Degradation phenomena like wear and corrosion, may have their effects accelerated as components operate at high temperature. The aim of this work is to make an indirect evaluation of the influence of high temperature exposure on wear behavior of Ni coatings. A Ni-Cr-Mo-W alloy, was deposited with Plasma Transferred Arc (PTA) process. An indirect approach based on the Ahrrenius relationship was used to evaluated long time exposures at high temperatures. To simulate longer exposures at lower temperatures, coatings were exposed to higher temperatures for the same time interval. So coatings were soaked in an air furnace at 650℃, 1000℃ and 1200℃. Metal/metal wear behavior was evaluated by pin-on-disc tests. Pins were removed from the coatings by eletrodischarge machining and rubbed against a VC31 quenched and tempered tool steel. Two sets of wear tests were run at 2m/s, for different loads (0.5, 1.0, 2.0 and 3.0Kg) and for different sliding distances (120, 720, 1080, 1440 and 1800m).Coatings characterization was done by scanning electronic microscopy and Vickers microhardness. Results showed as temperature is increased, coatings wear performance is altered,and this is associated with microstructural changes.     

喷焊工艺对钛基体镍基涂层显微组织和性能的影响

采用常规喷焊工艺和改进喷焊工艺,在Ti-6Al-4V合金表面上制备了镍基耐磨涂层,分析了涂层的形貌和合金元素的扩散,测试了涂层的显微硬度,定性地研究了基体和涂层的结合性能.结果表明:改进工艺所制备的涂层组织和性能均优于常规工艺的,涂层组织的均匀性大大提高,晶粒得到细化;基体和涂层为明显的冶金结合;涂层显微硬度的变化沿层深方向呈连续性和渐变性,其表层显微硬度高达HV933.2.采用合理的喷焊工艺能够在钛合金表面制备出性能优良的耐磨涂层.     

IC-6高温合金及其防护性涂层的摩擦特性

采用电弧离子镀技术在IC－高温合金上沉积NiCrAlY涂层。研究了NiCrAlY涂层及IC－6高温合金在室温和600℃空气中无润滑状态下，以K17高温合金为摩擦副的摩擦特性。采用带有能谱的扫描电镜（SEM／EDX）分析IC－6高温合金和NiCrAlY涂层磨损表面的形貌和成分。实验结果表明，室温条件下摩擦时，一些碎屑从K17合金上脱落下来，在IC－6合金及NiCrAlY涂层表面上形成磨粒，随着摩擦时间延长，磨损表面元素发生氧化。试样在环境温度在600℃摩擦时，NiCrAlY涂层的表面比较快的形成氧化膜，减少金属－金属间的直接接触。环境温度升高后，摩擦表面温度也随之升高，氧化物的粘滞性增强，600℃时，合金和涂层摩擦系数都有不同程度的减小。