Production and Microstructure Control of High Strength Nb Base Superalloy by PM Processing

目前用于燃气轮机、航空发动机涡轮和航空发动机涡轮的技术在很大程度上依赖于镍基高温合金作为高温地区的建筑材料。这些合金的工作温度一般限制在1150摄氏度以下，尽管涂层和冷却系统的使用允许涡轮机进口温度高于镍本身的熔点(1453摄氏度)。虽然在发动机运行中使用较高的温度具有普遍的优势，而且对这类系统的研究仍在进行中，但可靠性、成本和排放控制的要求对实际进展施加了一些相当严格的限制。在传统的吸气式发动机中，理论上涡轮进口温度受绝热化学计量燃烧温度的限制，根据所用燃料的不同，该温度范围在1800到2100摄氏度之间。然而，在实践中，由于控制NOX排放的要求，即使是目前复杂的燃烧室设计也可能被限制在1650摄氏度左右的进口温度。这一极限设定了未冷却部件在高温区的使用温度目标。因此，本研究致力于通过粉末冶金(PM)工艺开发一种新的有潜力的Nb基高温合金。我们采用的粉末冶金工艺是机械合金化(MA)工艺和等离子体旋转电极工艺(FREP)。主要研究结果如下：(1)研究了碳添加对Nb-Al MA工艺的影响。Nb_2C分布在Nb固溶体和Nb_3Al金属间化合物中，起到了强化的作用。(2)研究了Si含量对Nb-Si MA工艺的影响。硅含量越大，非晶形成的倾向越大。Nb_5Si_3金属间化合物的形成有助于强化。(3)采用准等静压-自蔓延高温合成工艺制备Nb-Al预氧化电极。用该工艺成功地制备了Nb-Al预制粉。

The current technology for both gas turbines and aero engine turbines and aero engine turbines relies heavily on the nickel-base superalloys for construction materials in the high temperature regions. These alloys are generally limited to working temperatures below 1150C,although the use of coatings and cooling systems permits turbine inlet temperatures above the melting point of nickel itself (1453C). Although there is a general advantage in using higher temperatures in the engine operation, and the search for such systems is ongoing, the requirements of reliability, cost and emission control impose some quite severe limits on practical progress. In conventional air-breathing engines the turbine inlet temperature is theoretically limited by the adiabatic stoichiometric combustion temperature, in the range of 1800 to 2100C depending on the fuel used. In practice, however, even the present sophisticated combustor designs are likely to be limited to an inlet temperature of around 1650C because of the requirement to control NOX emissions. This limit then sets the goal for the use-temperature of un-cooled components in the high temperature region.Therefore, this study is focused to develop a new potential Nb based superalloy by Powder Metallurgy (PM) processing. The PM process we applied is Mechanical Alloying (MA) process and Plasma Rotating Electrode Process (FREP). The results are as follows.(1) Effect of carbon addition on Nb-Al MA processing is investigated. Nb_2C is distributed in Nb solid solution and Nb_3A1 intermetallic compound and contributed to the strengthening.(2) Effect of Si content on Nb-Si MA processing is investigated. Larger amount of Si lead to higher tendency of the amorphous formation. Nb_5Si_3 intermetallic compound is formed and contributed to the strengthening.(3) Pseudo HIP-SHS process is applied to produce Nb-Al PREP electrode. NB-Al PREP powder was successfully produced by this process.