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.     

15Cr-25Ni-Fe基合金高温塑性变形行为的加工图

在Gleeble-1500热模拟机上对15Cr-25Ni-Fe基合金GH2674进行了热压缩实验，采用动态材料模型的加工图研究了其在950-1200℃和0．001-10S^-1条件下的热变形行为．结果表明：GH2674合金在热变形时呈现两个微观机制不同的动态再结晶峰区．再结晶Ⅰ区：功率耗散效率峰值为38％，峰值对应的温度和应变速率分别为1040℃与10s^-1；再结晶Ⅱ区：功率耗散效率峰值为40％，峰值对应的温度和应变速率分别为1075℃与0．04s^-1．在1075-1100℃温度区间内，可能是晶界相M382的溶解造成该合金的晶粒粗化，这在一定程度上会影响合金的热加工性能．在应变速率小于0．01s^-1、形变温度高于1050℃条件下，合金呈现晶粒急剧粗化现象，进而导致在热变形过程中楔形裂纹的产生；在应变速率高于0．1s^-1、形变温度低于1000℃条件下，合金有出现剪切变形带的趋势．根据上述加工图对GH2674合金的热变形工艺进行了初步设计．     

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.     

GH4169线性摩擦焊接头的焊合率与弯曲强度

论述了高温合金GH4169线性摩擦焊的试验过程。分析了弯曲强度、断裂挠度与焊合率之间的关系及接头的金相组织。结果表明,GH4169线性摩擦焊接头的弯曲强度与焊合率成正比线性关系,断口为韧性断口;断裂强度受摩擦时间的影响较大。     

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.     

初生M6C的形成及其对高钨铸造模具高温合金的影响

高钨铸造合金已用于铸造大型模具，由于大量初生M6C碳化物的形成使模具变脆，需探明初生M6C的形成条件．实验表明当含碳量超过0．15％时，合金中易析出初生M6C，而10％Co起有效的抑制作用．初生M6C是在1375℃时形成的，它对通过固-液范围的冷却速度十分敏感，快冷抑制它的形成．铸件中M6C的形成存在明显的尺寸效应，枝晶间距大于150μm时的较厚截面极易形成毫米量级的M6C，严重的损伤合金的高温强度．因此对大截面的模具合金，为防止初生M6C的析出，合金中最好保持0．04％—0．07％C和10％—15％Co．     

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。     

镍基高温合金真空感应熔炼脱氮的研究

研究了采用CaO坩埚真空感应熔炼镍基高温合金过程中的脱氮行为.试验表明在精炼过程中加Al对脱氮有促进作用;加Ti则对脱氮有明显不利影响;提高熔炼时的真空度是促进脱氮的有力措施.