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燃气涡轮在海洋环境中遇到的主要问题是热部件材料的热腐蚀,尤其是第一级动叶和静叶的热腐蚀。在1969年决定采用LM-2500作为DD963级导弹驅逐舰的主推进发动机之前,在研制抗热腐蚀合金和涂层方面未取得什么进展。由GTS“卡拉汉”号安装LM-2500机的早期现场试验的结果表明其第一级动叶寿命还达不到2000小时。由于将动叶材料改为Ren’e80和将涂层改为CoCr-A1Y使得该机在几乎并接近全工况下运行时,其动叶寿命增加到7000小时。LM-2500终于在代表该舰DD循环的较低功率下运行。在低功率下,腐蚀速率明显地增加而不是如预料的那样降低了。这是美国海军第一次认识到当金属温度为1200—1400°F时会发生目前称之为低温(低功率)热腐蚀的腐蚀现象。在美海军海上系统司令部主持下由各实验室和工业实验室对低功率下叶片浸蚀的机理进行了深入的研究。同时已研制成一种叶片涂层,其寿命达9000小时,即比现有CoCrAlY涂层寿命长2倍,并将拟出LM-2500第一级和第二级材料涂层的细目表。然而,仍需要提高第一级翼面寿命以满足驱逐舰推进发动机翻修期要达到的目标。工业部门已着手于按计划研制一种涂层和两种合金。涂层研究计划的主要目的是鉴定新的涂料成分在按DD963型工况图运行时其抗热腐蚀能力为现有的用于LM2500第一级动叶片的CoCr-A1Y复层的4倍。合金研制计划的目的在于鉴定几种定向凝固合金,它们的抗热腐蚀性达LM-2500叶片合金的4倍。必须使这些合金的强度相当于或优于现有合金。定向凝固铸造合金与常规铸造组织相比,其强度、塑性和热疲劳性能都得到提高。一项研究中正在采用定向凝固柱状晶(多晶体)工艺使之能使用具有限界强度但耐蚀性好的常规铸造合金系。另一项计划是采用定向凝固单晶铸造工艺。单晶材料并不要求诸如C、Zr、B和Hf这些晶界强化元素,而Hf在满足抗热腐蚀性和强度的要求而改变合金成分方面有更大的灵活性。
The main problem gas turbines encounter in marine environments is the hot corrosion of hot component materials, especially the hot corrosion of the first stage bucket and vanes. Until the decision was made in 1969 to use the LM-2500 as the main propulsion engine for the DD963 guided missile destroyer, no progress was made in the development of hot corrosion resistant alloys and coatings. The results of an earlier field trial of installing the LM-2500 from the GTS Callaghan show that its first-stage buckets had less than 2,000 hours of life. With the blade material changed to Ren’e80 and the coating changed to CoCr-A1Y, the lifespan of the bucket was increased to 7,000 hours as the machine was operated in almost and nearly full-scale operation. The LM-2500 finally runs at a lower power on behalf of the ship’s DD cycle. At low power, the corrosion rate increases significantly rather than decreases as expected. This is the first time the Navy has realized that what is known as low-temperature (low-power) hot-corrosion corrosion occurs when the metal temperature is 1200-1400 ° F. In the United States Naval Marine Systems Command under the auspices of various laboratories and industrial laboratories under low-power blade erosion mechanism was studied in depth. At the same time, a leaf coating has been developed with a service life of 9,000 hours, which is 2 times longer than existing CoCrAlY coatings. A detailed list of the first and second material coatings of LM-2500 is to be developed. However, there is still a need to increase the life of the first stage airfoil to meet the target to be achieved by the destroyer in advancing the engine overhaul. The industry has started to develop a coating and two alloys as planned. The main purpose of the coating research program is to identify new coating compositions that have 4 times the hot corrosion resistance of the existing CoCr-A1Y cladding used on the LM2500 first-stage rotor blades when operated according to DD963. The purpose of the alloy development program is to identify several directional solidified alloys whose hot corrosion resistance is four times that of the LM-2500 blade alloy. The strength of these alloys must be equal to or better than that of existing alloys. Directional solidification cast alloy compared with the conventional casting structure, the strength, ductility and thermal fatigue properties are improved. One study is using a directional solidification columnar (polycrystalline) process that enables the use of conventional cast alloys with limited strength but good corrosion resistance. Another plan is the use of directional solidification single crystal casting process. Monocrystalline materials do not require grain boundary strengthening elements such as C, Zr, B, and Hf, and Hf offers greater flexibility in altering the composition of the alloy to meet the requirements of hot corrosion resistance and strength.