Zr-Cr合金的显微组织及腐蚀行为

以高纯锆为母材,在归一化条件下制备Zr-Cr二元合金,在400℃/10.3 MPa过热蒸汽中进行腐蚀试验。利用扫描电镜(SEM)、透射电镜(TEM)对合金及腐蚀生成氧化膜的显微组织进行研究。结果表明,Zr-Cr合金中只存在细小、呈条带状的密排六方结构Zr Cr2第二相,其数量和条带密度会随着合金中Cr含量的提高而增加,但颗粒尺寸没有明显变化。在高纯锆中添加Cr元素能够改善其在400℃/10.3 MPa过热蒸汽中的耐腐蚀性能。增加Cr含量能够降低Zr-Cr合金腐蚀后氧化膜的缺陷数量,提高氧化膜致密性,从而改善耐腐蚀性能。     

共渗制备NiCrAlY涂层及抗高温腐蚀研究

采用热扩散的方法在高温合金K417G基体上制备了NiCrAlY涂层,经测定,涂层以β–NiAl相为主,Cr以固溶态和AlCr(x)相同时存在。1000和1100℃恒温氧化试验表明,NiCrAlY涂层显著提高了合金的抗氧化性,氧化膜致密稳定的Al2O3为主,300h后氧化膜没有明显的剥落。对基体合金和涂层试样进行了900℃,NaCl/Na2SO4(25:75)融盐环境的热腐蚀试验。结果表明,NiCrAlY涂层氧化膜完整,涂层内硫化物含量低,有效提高了抗热腐蚀性能。     

碳对IN-738合金抗热腐蚀性能的影响

用坩埚熔盐腐蚀方法研究了不同碳含量的IN-738合金的热腐蚀行为。并用金相、X-线衍射分析、电子探针、扫描电镜等方法对试验后样品的腐蚀表面进行了观察研究。结果表明:碳能明显地改善IN-738合金的热腐蚀抗力,特别是在800℃附近这种效果最为突出。当合金中碳含量低于0.1％时,随着合金中碳量的增加,合金的热腐蚀失重明显地减少,碳含量在0.1～0.2％之间,其改善作用逐渐减弱,当碳含量超过0.2％时进一步增碳,就几乎不再起什么作用了。初步讨论了试验结果,认为碳能阻碍碱性融蚀并促进富铬的氧化膜形成,是其有益作用的主要原因。     

NiAl-31Cr-3Mo合金的低温热腐蚀性能

通过对NiAl-31Cr-3Mo合金在550℃、600℃、650℃和700℃四种温度下进行恒温热腐蚀试验,研究其低温热腐蚀行为,通过电子显微镜、SEM进行表面观察分析,探讨了NiAl-31Cr-3Mo合金的低温热腐蚀机理。结果表明:NiAl-31Cr-3Mo的热腐蚀存在孕育期,在孕育期间首先形成保护性Al2O3和Cr2O3氧化膜。在550~650℃之间,这种保护作用较为明显。最严重的低温热腐蚀发生在650~700℃之间,低温热腐蚀后合金表面为坑点状,发生点蚀,并且有贫铬、贫铝现象,这造成Mo含量升高,从而引发酸性腐蚀。     

镍基高温合金DD5、DD10和DSM11热腐蚀行为比较

镍基高温合金DD5、DD10和DSM11在涂覆10%NaCl+90%Na_2SO_4(质量分数)混合盐膜后进行(850℃,200 h)热腐蚀实验,并利用扫描电子显微镜(SEM)、能谱仪(EDS)和X射线衍射仪(XRD)等分析手段,对腐蚀200 h后的合金进行热腐蚀行为对比分析。结果表明:DD10和DSM11合金成分中含有较高含量的Cr和Ti,在表面易生成保护性Cr_2O_3和TiO_2氧化膜,氧化膜遇到熔盐中的O~(2-)会优先在表面发生溶解,保证内部Al_2O_3氧化膜的稳定生长,进一步抑制热腐蚀反应的进行,提高合金的抗热腐蚀性能。DD5合金中Cr和Al含量较少且相差不大,在合金表面形成Cr_2O_3和Al_2O_3混合型氧化物,导致内部元素的贫化,不易形成连续致密性氧化膜,基体会进一步遭受到腐蚀。     

硫酸钙沉积导致铁基和镍基合金的热腐蚀

作者在几种铁基和镍基高温合金的试样上涂硫酸钙盐膜在1000℃及1150℃加热研究了硫酸钙对这些合金热腐蚀的影响。测定了这些合金的高温腐蚀动力学曲线。对腐蚀产物进行了 X 射线衍射、电子衍射、电子探针分析及金相检查。实验结果证明:由硫酸钙沉积导致的热腐蚀与合金成份有密切的关系。温度愈高,盐膜愈厚,腐蚀也愈严重。含钼又有足够铝含量以生成 Al_2O_3氧化皮的合金,由于 Al_2O_3被 MoO_3酸性熔融,与 CaSO_4反应可能生成液态的 CaMoO_4,会发生严重的腐蚀。合金的铬含量增高会提高抗 CaSO_4沉积腐蚀的能力,抗蚀性原来不好的合金渗铬后抗蚀性亦显著提高。     

Zr-Nb-Cu合金在500℃/10.3MPa过热蒸汽中的腐蚀行为

将添加不同Cu、Nb含量的Zr-Nb-Cu合金在500℃/10.3MPa过热蒸汽条件下腐蚀,用TEM和SEM研究合金腐蚀后生成氧化膜的显微组织。结果表明:添加Nb或Cu元素总含量较低时,Zr-Nb-Cu合金在500℃/10.3MPa过热蒸汽中会出现较严重的不均匀腐蚀。Zr-0.2Nb-0.2Cu和Zr-0.2Nb-1.0Cu合金表现出较好的耐腐蚀性能;Zr-0.2Nb-Cu合金中的Cu含量达到0.2%(质量分数)后,能够完全抑制不均匀腐蚀现象的发生,但在实验条件下继续提高Cu含量对其耐腐蚀性能的影响作用不大。锆合金腐蚀生成氧化膜中的微结构,特别是微孔洞、微裂纹等缺陷的形成与合金元素及第二相的氧化过程密切相关。Nb元素的存在会延缓Zr_2Cu相的氧化及其氧化物的扩散迁移,抑制氧化膜中裂纹的产生,延缓氧化膜中柱状晶向等轴晶形态的转变,从而提高含Cu锆合金的耐腐蚀性能。     

真空电弧镀Al-Si-Y涂层的热腐蚀行为研究

采用真空电弧镀技术在镍基高温合金基材上制备Al-Si-Y涂层.通过涂盐试验对涂层的热腐蚀性能进行了测试,利用场发射电子显微镜和X射线能谱仪对显微组织进行了观察和成分检测,研究了高温合金基材及Al-Si-Y涂层在900℃条件下不同NaCl Na2SO4含量熔盐中的热腐蚀行为.结果表明,Al-Si-Y涂层能有效提高合金抗热腐蚀性能,对NaCl的加入量不敏感,这与涂层在热腐蚀过程中生成了连续致密的Al2O3氧化膜有关.     

含碲钴基高温合金熔盐腐蚀行为探讨

非真空环境下烧结不同Te含量的钴基合金粉末,研究其在静态800±5℃75%Na2SO4+25%NaCl下的高温熔盐腐蚀行为,采用OM、SED和 XRD衍射仪分析了合金金相组织、腐蚀产物形貌和物相组成。结果表明：随着钴基合金中含Te质量分数的增加,合金的高温熔盐腐蚀速率逐渐降低;当Te含量为1.6wt%左右时,合金基体表面形成均匀、致密的Cr2O3氧化保护膜及弥散在基体中的新相（CoTeO3、Fe2TeO5）抑制Co原子向晶界扩散,延缓合金基体元素溶解,平均腐蚀速率由不含Te的4.0483mg/(cm2*h)降低至0.216mg/(cm2*h) ,提高合金热腐蚀性能。     

钎料合金BCo46的抗热腐蚀性能

采用涂盐方法研究了新型钴基钎料BCo46的抗热腐蚀性能,并与BNi-2和基材合金DZ468进行了对比.评估了完全热处理后的采用BCo46钎焊DZ468合金接头的抗热腐蚀性能.研究表明,BCo46合金的热腐蚀抗力优于DZ468和BNi-2合金,热腐蚀过程中3种合金都发生了氧化膜溶解和硫化物析出,合金的腐蚀进程可以用硫化-酸碱熔融的热腐蚀模型解释;钎焊接头中形成的硼化物会显著降低合金的热腐蚀抗力,完全热处理后的钎焊接头组织均匀,接头抗热腐蚀性能与DZ468合金相当.     

四种镍基高温合金的热腐蚀行为

采用涂盐热腐蚀试验方法研究了M-38等四种镍基合金(二种铸造:M-38和K_3;二种板材:GH-30和GH-128)在900℃下的热腐蚀。用重量变化和渗透深度评价合金的热腐蚀抗力;用金相、X射线衍射、扫描电镜(配EDS分析)和电子探针分析鉴别腐蚀层结构和产物。结果说明:M-38和GH-30合金热腐蚀过程可分三个阶段—孕育期、扩展期和加速期;GH-128和K_3合金分二个阶段—孕育期和加速期。含有较高铝和钨的GH-128和K_3合金的热腐蚀受到酸性熔融控制,而M-38和GH-30合金受“沿晶界硫化—氧化—开裂—剥落过程”控制。晶粒细、成份均匀的热轧/板材渗透轻微;反之,晶粒粗、成份呈枝晶偏析的铸造合金渗透严重,必须采用失重和渗透深度来评价热腐蚀抗力。     

Use of plasma spray technology for deposition of high temperature oxidation/corrosion resistant coatings – a review

High temperature oxidation is one of the main failure modes of the hot‐section components in gas turbines, boilers, waste incinerations, diesel engines, coal gasification plants, chemical plants and other energy generation systems. In such applications the use of Fe‐, Ni‐ and Co‐based alloys, especially of superalloys is well known. The superior mechanical strength and good corrosion resistance of the superalloys at high temperature make them favorites for such applications. However, the presence of combustion gases constitutes an extreme environment and hot corrosion is inevitable when superalloys are used at high temperatures for long durations of time. Therefore these alloys need to be protected against this type of oxidation. Several countermeasures have been suggested in the literature to combat the same. One such countermeasure against hot corrosion and oxidation constitutes the deposition of protective coatings on these alloys. Among the various techniques used for deposition of coatings, plasma spraying is a versatile technology that has been successful as a reliable cost‐effective solution for many industrial problems. It allows the spraying of a wide range of high performance materials from superalloys and refractory intermetallic compounds to ceramics with continuously increasing commercial applications. Furthermore it does not cause deterioration of the substrate alloys, and relatively thick coatings can be formed with high deposition rates. In this paper the technique of plasma spraying has been detailed and the role of plasma sprayed coatings to arrest high temperature oxidation has been discussed with the help of a comprehensive literature survey. The main focus of this investigation is the studies related to plasma sprayed NiCrAlY, Ni‐Cr, Nickel aluminide and Co‐based coatings.     

热腐蚀环境中高温合金的蠕变与断裂

研究了分别为轧制、普通铸造、定向凝固及单晶的6种高温合金在热腐蚀条件下的蠕变断裂性能.其中涉及到试验温度、晶粒尺寸、晶界状态等对性能的影响.探讨了蠕变应变与热腐蚀交互作用下,合金中所产生的灾害性侵蚀及断裂过程.     

Effect of a chromium-containing fuel additive on hot corrosion

Four cast superalloys (one cobalt-base and three nickel-base) were tested at 900°C for 100 h in Mach 0.3 combustion gases. 5 ppm of synthetic sea salt were added to the gases in the combustion chamber. Several types of thermal cycle and washing procedures were employed. Similar tests were made with the addition of 300 ppm of a chromium-containing fuel additive. In both sets of tests the extent of hot corrosion was evaluated by specific weight change and metal recession. In general, the chromium additive in the fuel reduced the extent of hot (salt) corrosion but did not eliminate it. The percentage reduction of hot corrosion attack was similar for all four alloys. As great a reduction of hot corrosion was achieved by reducing the number of thermal cycles during the test from 100 to 5 of 6. The effect of washing the alloys every ten cycles as opposed to the end of the test was erratic; some alloys were attacked slightly more, others somewhat less. A NiCrAlY coating was found to be more effective in reducing hot corrosion than either the fuel additive or the washing schedule.     

Hot corrosion of four superalloys: HA-188, S-57, IN-617, and TD-NiCrAl

Four superalloys were subjected to cyclic oxidation and hot corrosion attack in a Mach 0.3 burner rig. Two of the alloys, HA-188 and S-57, were cobalt-base and the other two, IN-617 and TD-NiCrAl, were nickel-base. The alloys were exposed to maximum temperatures of 900 and 1000°C. For hot corrosion tests the burner rig flame was doped with various concentrations of sea salt and one concentration of sodium sulfate. Samples were evaluated based on maximum depth of attack. These data were subjected to a regression analysis for the development of model equations relating corrosion to temperature and for determining how significantly changes in salt concentration and composition affected the corrosion. The ranking of the alloys with respect to their corrosion resistance was found to vary with temperature, sea salt concentration, and salt composition. Some of the variation was attributed to changes in the mode of attack from straight oxidation to hot corrosion. Under those test conditions where the mode of attack was readily discernible S-57 was found to be the most hot corrosion-resistant alloy and TD-NiCrAl was the least resistant. This order was reversed when the attack was straight oxidation, TD-NiCrAl being the most resistant alloy and S-57 the least.     

Ni-Cr-Al合金中Cr、Al含量对热加工性的影响

Ni-Cr-Al系高温合金作为一种常用的新型航空发动机密封材料,通过调整Cr、Al含量可以提高耐高温及热腐蚀性能,但同时也会影响合金的热加工性。通过热模拟压缩试验,分析了Cr,Al含量分别在15%~25%,4%~5%（质量分数,下同）范围调整时,对合金高温变形特性的影响规律。结果表明,Cr、Al含量的提高会不同程度缩小合金的安全热加工区域。通过热力学平衡相计算和组织观察发现,成分变化影响热加工性的主要原因是晶界胞状碳化物的形态及析出量变化。综合考虑热变形试验、组织观察结果以及耐高温腐蚀的因素,20%Cr和4%Al是比较合适的成分选择。     

Effect of Co on oxidation and hot corrosion behavior of two nickel-based superalloys under Na2SO4–NaCl at 900 °C

Nickel-based superalloys with and without Co by partial replacement of W were prepared using double vacuum melting. A comparison of the oxidation in air and hot corrosion behaviors under molten 75wt.%Na₂SO₄+ 25wt.%NaCl at 900 °C were systematically investigated. The results showed that partial replacement of W with Co promoted the formation of chromia scale and consequently decreased the oxidation rate. Besides, the addition of Co also retarded the internal oxidation/nitridation of Al and consequently promoted the growth of Al₂O₃ scale, which further decreased the scaling rate and improved the adhesion of scale. Moreover, the addition of Co also further improved the hot corrosion resistance under molten Na₂SO₄–NaCl salts.     

Effect of Alloying Chemistry on Fireside Corrosion Behavior of Ni–Fe-Based Superalloy for Ultra-supercritical Boiler Applications

The fireside corrosion behavior of a group of nickel–iron-based superalloys was studied in the presence of a mixture of synthetic alkali sulfates and oxides, and a sulfur dioxide/sulfur trioxide-containing mixed gas. The formation and growth kinetics of corrosion scale was sensitive to alloy composition. The chromium content was key to corrosion, levels that approached 25 wt% improved the oxide film integrity, and chromium was consumed continuously during hot exposure. A higher aluminum content reduced the oxide film integrity by slagging of combustion products. Silicon content has a small effect on alloy corrosion resistance, but a sample alloy without silicon corroded catastrophically. Tungsten and molybdenum accelerated oxide film spallation. Corrosion products on the sample surfaces consisted mainly of a protective chromium oxide film. Internal aluminum- and titanium-rich oxide particles with different content existed in the sample alloys. The synergistic effect of anti-corrosion elements against fireside corrosion was discussed.     

铌对镍基铸造高温合金抗热腐蚀性能的影响

采用坩埚法和单管法评定了几种不同含铌量的商用镍基铸造高温合金的抗热腐蚀性能。结果指出:对于含铬量较低、形成Al_2O_3氧化膜的合金,加铌会损害其抗腐蚀性能;对于含铬量中等、形成Cr_2O_3氧化膜的合金,加入一定量的铌是有益的。如果铌的加入量过大,由于块状η相的出现,反而会使合金的抗热腐蚀性能降低。 通过对腐蚀层的分析,发现铌能改变合金表面氧化层的组成,从而影响了合金的抗热腐蚀性能。