新型镍基高温合金1100℃氧化行为的研究

利用X射线衍射(XRD)、扫描电镜与能谱(SEM/EDS)、激光拉曼光谱(Raman)研究了新型镍基高温合金1 100℃氧化行为。结果表明,氧化增重基本遵循抛物线规律,约氧化100 h后氧化增重趋于稳定。在氧化初期,内层形成均匀连续的Al_2O_3氧化膜,中间层主要由NiAl_2O_4组成,外层氧化膜由NiFe_2O_4、Fe_2O_3、NiCr_2O_4和Cr_2O_3组成。随着氧化时间的延长,外层及中间层氧化膜逐渐变得疏松并脱落,而内层逐渐形成连续致密的Al_2O_3氧化膜。根据氧化膜的组成进一步分析了合金的氧化机制。该新型镍基高温合金具有优异的抗高温氧化性,可在1 100℃长期使用。     

Cr20Ni80电热合金在高温空气条件下氧化机制研究

通过高电阻电热合金快速寿命仪氧化装置研究了Cr20Ni80电热合金在空气中极限温度1200℃下的高温抗氧化性,并采用扫描电镜(SEM)和能谱分析(EDS)研究了氧化膜的表面形貌,氧化膜的厚度及成分,并通过热力学计算研究了氧化膜的形成过程。结果表明,在1200℃氧化60h形成了3层氧化膜。最外层为NiO和NiCr_2O_4,中间比较致密均匀的Cr_2O_3,最内层为疏松多孔的SiO_2,当氧化时间达到100h时,外层的氧化膜发生剥落。     

镍基铸造高温合金Mar-M247的高温氧化行为

研究了某工业重型燃气轮机叶片材料Mar-M247合金在800℃和900℃的恒温氧化行为。结果表明,Mar-M247合金在两个试验温度下的氧化动力学符合抛物线规律,并且均为完全抗氧化级,Mar-M247合金的氧化激活能约为268.4 kJ·mol~(-1),氧化过程主要是由Cr_2O_3的形成来控制。借助场发射扫描电镜和能谱对氧化层组成进行分析,结果表明,合金在800℃下氧化100 h后,氧化膜最外层为Cr_2O_3,中间层为TiO_2以及少量Ta_2O_5与HfO_2,内层为钉楔状的氧化物Al_2O_3;而900℃下氧化100 h后,氧化膜最外层是NiO和CoO,中间层为相对致密的Cr_2O_3和少量小块状不连续的TiO_2、Ta_2O_5与HfO_2,内层为尺寸较大的钉楔状氧化物Al_2O_3。内氧化区和贫化层区域随着氧化温度的升高而扩大。     

Si对Hastelloy N合金氧化行为的影响

利用不连续增重法,研究了不同Si含量的Hastelloy N合金850℃恒温氧化行为。结果表明,随Si含量的增加,氧化动力学曲线保持抛物线规律。氧化100 h后,氧化膜出现分层现象,最外层均为NiO、NiFe_2O_4等复合氧化物,中间层为Cr_2O_3、MoO_2等氧化物。由于在氧化层与基体界面处形成连续致密的SiO_2层,有效阻止Cr离子向外扩散进入氧化层,促进Hastelloy N合金中间层形成较为致密的Cr_2O_3氧化层,提高了合金的抗氧化性能。     

DZ125合金抗高温氧化性能研究

研究了DZ125合金在1 100℃时的氧化行为,分析了该合金表面氧化膜的生成和失效机制。结果表明,1 100℃氧化30h后DZ125合金表面氧化膜呈分层结构,其中外层为Cr_2O_3,中间层为NiO及NiCr_2O_4,内层为Al_2O_3。DZ125合金在1 100℃空气中的氧化动力学满足抛物线规律。在氧化过程中,聚集于晶界区域的Hf、Ta等高活性元素会优先发生氧化,为O的向内扩散提供通道,造成合金的选择性内氧化,并且随着氧化时间延长,氧化膜在应力的作用下开裂,最终导致膜层剥落失效。     

一种多孔镍基合金在850~1000°C下的氧化行为和机理（英文）

以一种多孔Ni-Cr-Al-Fe合金为研究对象,分别利用金相显微镜、扫描电子显微镜(SEM)及能谱仪(EDS)、X射线衍射(XRD)、X射线光电子能谱仪(XPS)等分析手段,研究其在850~1000°C温度范围内的氧化行为及机理。研究表明,该多孔合金在950°C和1000°C时呈伪抛物线型的氧化动力学曲线特征,其表面形成由外层Cr_2O_3/NiCr_2O_4和内层α-Al_2O_3构成的复杂氧化物结构。γ相的存在能促进氧化初期NiO/Cr_2O_3/NiCr_2O_4复合氧化物的形成,而多孔合金中众多快速扩散的通道有利于其氧化膜的发展。随着氧化时间的延长和氧化温度的升高,多孔合金的开孔率和渗透率均有所减小,但可控制在一定的范围内。     

高温合金Inconel 740H在空气和水蒸气环境中的氧化行为

对Inconel740H高温合金在700、800、900℃分别进行空气和水蒸气环境下的高温氧化试验,采用热重法、X射线衍射、扫描电镜和能谱仪研究试样。结果表明:长时间空气氧化形成的氧化膜成分与长时间水蒸气的氧化膜类似,氧化物主要由Cr_2O_3、NiCr_2O_4、Al_2O_3与TiO_2组成。合金分别在800、900℃空气中及在800℃水蒸气中的氧化增重与氧化时间近似遵循抛物线规律。水蒸气环境下温度变化对氧化速率的影响要明显高于空气氧化。     

一种添加微量混合稀土镍基高温合金在950~1150℃下的氧化行为（英文）

开发了一种新型镍基高温合金(Ni48Cr28W5Co3Mn1Si1.6)并研究微量混合稀土对其氧化性能的影响。在950~1150℃下进行100 h的等温氧化试验,并对试样进行SEM和XRD分析。结果表明,添加和不添加混合稀土的试样,其氧化增重均满足抛物线规律。加入少量混合稀土对氧化增重影响很小,加入0.20%稀土的试样,其氧化速率常数降低5.9%~9.0%。常温氧化100 h后,氧化产物为MnCr_2O_4、Cr_2O_3和SiO_2。氧化层共3层,最外层为连续有保护性的Mn Cr_2O_4尖晶石层,中间层是致密的Cr_2O_3,最内层为不连续的SiO_2层。     

新型镍基高温合金GH4282的高温氧化行为

为研究新型镍基高温合金GH4282在800～1200℃空气中的高温氧化行为,采用静态增重法测定其氧化动力学曲线,并采用金相显微镜、X射线衍射仪、扫描电子显微镜和附带能谱以及电子探针分析仪对表面氧化膜组成、结构和形貌及其截面特征进行观察和分析。结果表明:GH4282合金的氧化动力学符合抛物线规律,氧化初期时氧化质量增加较快,随着氧化时间的延长,氧化质量增加逐渐变得缓慢;合金在800℃和900℃为完全抗氧化级;在1000～1200℃为抗氧化级。GH4282合金的氧化膜分为三层:外层是Cr_2O_3和TiO_2的混合层,并含有少量(Ni,Co)Cr_2O_4复合尖晶石相;中间层是TiO_2和Al_2O_3的混合层;内层是Al_2O_3氧化层。     

一种新型镍基合金在超临界多种离子共存环境下的腐蚀行为

研究一种新型镍基合金X-1#在550℃,23 MPa含PO_4~(3-),Cl~-和SO_4~(2-)超临界水中分别腐蚀72,159,248,429和537 h的腐蚀特性.结合SEM,EDS,XRD和XPS等分析测试方法研究了X-1#合金氧化膜和反应釜沉积物的形貌、物相组成和元素成分分布等.结果表明,X-1#合金在该环境下形成了均匀和完整的氧化膜,氧化膜由疏松外层和致密内层组成,外层主要包含NiO,Ni(OH)_2和磷酸盐,内层由NiCr_2O_4和Cr_2O_3组成.腐蚀初始阶段腐蚀速率较快,248 h后腐蚀速率明显下降,这是由于氧化膜内层稳定性好且连续致密分布,有利于X-1#合金抗高温氧化腐蚀.     

Si对625合金激光熔覆层高温氧化特性的影响

利用循环氧化法,研究了不同Si含量（0%,1%,3%,质量分数）的625合金熔覆层在700、800、900 ℃下氧化144 h后的高温氧化行为。用XRD分析了氧化物相。通过SEM/EDS研究了氧化物表面和截面的形貌、元素组成和氧化膜的厚度。结果表明,不同温度下试样的氧化动力学都保持抛物线规律,随着温度的升高,氧化增重逐渐增加。通过观察,在900 ℃时,0% Si含量的625合金熔覆层出现了氧化膜大面积剥落的情况,3% Si含量的合金熔覆层氧化膜保持完整。在700 ℃时,随着Si含量增加,氧化膜表面的氧化颗粒尺寸减小且更加致密,同时促进了Cr₂O₃氧化物的生成。在700 ℃下,0 % Si含量的试样出现了大片的内氧化区域;1% Si含量的试样基体部分出现了2处条状的含Ni,Cr,Mo的氧化物相区;而3% Si含量的试样氧化后由于生成了富Si的内氧化层,这阻止了内氧化的发生。外层Cr₂O₃氧化膜和内层SiO₂的联合作用既阻止了O阴离子的渗入也抑制了Fe等金属离子的扩散,提高了合金熔覆层的抗氧化性。     

The Isothermal and Cyclic Oxidation Behavior of a Titanium Aluminide Alloy at Elevated Temperature

The isothermal and cyclic oxidation behavior of Ti-47Al-2Mn-2Nb with 0.8 vol.% TiB₂ particle-reinforced alloy was investigated in air between 700 and 1000 °C. In the study, the kinetics of isothermal and cyclic oxidation were performed by using a continuous thermogravimetric method which permits mass change measurement under oxidation conditions. The oxide scales and substrates were characterized by scanning electron microscopy with energy-dispersive x-ray analysis and x-ray diffraction. At 700 and 800 °C, the alloy showed an excellent oxidation resistance under isothermal and cyclic conditions. After exposure to air above 800 °C, the outer scale of the alloy was dominated by a fast-growing TiO₂ layer. Under the coarse-grained TiO₂ layer was the Al₂O₃-rich scale, which was fine-grained. At 900 and 1000 °C, the extent of oxidation increased clearly. The oxidation rate follows a parabolic law at 700 and 800 °C. However, the alloy, upon isothermal oxidation at 900 °C, can be divided into several stages. During the cyclic oxidation at 900 and 1000 °C, partial scale spallation takes place, leading to a stepwise mass change.     

High Temperature Oxidation Behavior of Alloy 617 and Haynes 230 in Impurity-Controlled Helium Environments

The high temperature oxidation behavior of alloy 617 and Haynes 230 have been investigated for VHTR intermediate heat exchanger applications. Oxidation tests were carried out for up to 500 h at 900 °C and 1000 °C in impure helium environments containing H₂, H₂O, CO, CO₂, and CH₄. The oxidation kinetics of the alloys followed a parabolic rate law in all cases. In the impure helium environments with very low oxygen, the external oxides of alloy 617 were composed of a Cr₂O₃ layer, TiO₂ ridges on the grain boundaries, and isolated MnCr₂O₄ grains on top of the Cr₂O₃ layer. On the other hand, those of Haynes 230 consisted of a Cr₂O₃ inner layer and a protective MnCr₂O₄ outer layer, which increased the oxidation resistance. The effect of small amounts of CH₄ and H₂ on the oxidation kinetics of the alloys was insignificant. Irregular oxide morphology, such as cellular Cr₂O₃ oxides for alloy 617 and MnCr₂O₄ platelets for Haynes 230, was formed in the impure helium environment at 900 °C. For Haynes 230, along with platelets, whiskers were frequently found at the tip of the MnCr₂O₄ oxide crystals.     

Oxidation Resistance of a Cr0.50Al0.50N Coating Prepared by Magnetron Sputtering on Alloy K38G

A Cr_0.50Al_0.50N coating has been prepared by a reactive-magnetron-sputtering method on alloy K38G. The coating possesses mainly the B1 type with a small amount of B4-type crystal structure phase. Isothermal oxidation tests were performed at 900–1,100 °C for 20 h by thermogravimetric analysis (TGA) in air. The results reveal that the coated samples have much lower mass gain than that of the bare alloy. The parabolic rate constants of the coated samples decrease by 2 orders of magnitude compared with the bare alloy at 1,000 and 1,100 °C. During the oxidation of the coated samples below 1,000 °C, the main oxide is Cr₂O₃, but above 1,000 °C, the scale changes to α-Al₂O₃. The observed oxidation behaviors demonstrate that the Cr_0.50Al_0.50N coating can provide good protection against corrosion over a wide temperature range.     

Roles of Nb on the oxidation characteristics and oxide scale evolution of Fe-25Cr-35Ni-2.5Al-XNb alloys at 1000°C and 1100°C

The oxidation characteristics of Fe-25Cr-35Ni-2.5Al-_XNb (0, 0.6, and 1.2 wt%) alumina-forming austenitic alloys at 1000°C and 1100°C in air were investigated. Results show that Nb has an important effect on the high-temperature oxidation resistance. A bilayer oxide scale with a Cr₂O₃-rich outer layer and Al₂O₃-rich internal layer forms on the surface of the Nb-free alloy and exhibits a poor oxidation resistance at 1000°C and 1100°C. With Nb addition, both the 0.6Nb-addition and 1.2Nb-addition alloys exhibit better oxidation resistance at 1000°C. Because of the third element effect, Nb addition reduces the critical Al content and forms a single external protective Al₂O₃ scale, which greatly improves the oxidation resistance. After oxidation at 1100°C, niobium oxides (mainly Nb₂O₅) are formed on the surface of the 1.2Nb-addition alloy and destroy the integrity of the Al₂O₃ scale, which causes the formation of Cr-rich oxide nodules and eventually develops to be a loose bilayer oxide scale with NiCr₂O₄, Cr₂O₃, and Fe₂O₃ outer layers and Al₂O₃ inner layer.     

High-Temperature Corrosion Behaviour of Aluminized-Coated and Uncoated Alloy 718 Under Cyclic Oxidation and Corrosion in NaCl Vapour at 750 °C

To evaluate the suitability of HR3C and 22Cr–25Ni–2.5Al AFA steels as the heat-resistant alloys, the oxidation behavior of them was investigated in air at 700, 800, 900 and 1000 °C. The evolution of oxide layer on the surface and subsurface was investigated using a combination of compositional/elemental (SEM, EDS) and structural (XRD, GDOES) techniques. A dense and continuous Cr₂O₃ healing layer on the HR3C was formed at the temperature of 700 or 800 °C, but the Cr₂O₃ oxide film on HR3C was unstable and partly converted into a less protective MnCr₂O₄ with the increase in temperature to 900 or 1000 °C. The composition and structure of oxide film of 22Cr–25Ni–2.5Al AFA steels are significantly different to the HR3C alloys. The outer layer oxides transformed from Cr₂O₃ to Al-containing oxides, leading to a better oxidation resistance at 700 or 800 °C compared to HR3C. Further, the oxide films consist of internal Al₂O₃ and AlN underneath the outer loose layer after 22Cr–25Ni–2.5Al AFA oxidized at 900 or 1000 °C. It can be proved that the internal oxidation and nitrogen would make 22Cr–25Ni–2.5Al AFA steels have worse oxidation resistance than HR3C alloys at 900 or 1000 °C.     

Oxidation of orthorhombic titanium aluminide Tl-22AL-25NB in air between 650 and 1000 °C

The oxidation behavior of orthorhombic titanium aluminide alloy Ti-22Al-25Nb was studied in air between 650 and 1000 °C by isothermal thermogravimetry and postoxidation scanning electron microscopy (SEM), energy dispersive spectroscopy (EDS), and x-ray diffraction. Microhardness measurements were performed after exposure to gage hardening due to nitrogen and oxygen ingress. The parabolic rate constant of Ti-22Al-25Nb was of the same order as conventional titanium alloys and Ti₃Al-based titanium aluminides at and below 750 °C. Between 800 and 1000 °C, the oxidation resistance of Ti-22Al-25Nb was as good as that of γ-TiAl based aluminides; however, the growth rate changed from parabolic to linear after several tens of hours at 900 and 1000 °C. The mixed oxide scale consisted of TiO₂, AlNbO₄, and Al₂O₃, with TiO₂ being the dominant oxide phase. Underneath the oxide scale, a nitride-containing layer formed in the temperature range investigated, and at 1000 °C, internal oxidation was observed below this layer. In all cases, oxygen diffused deeply into the subsurface zone and caused severe embrittlement. Microhardness measurements revealed that Ti-22Al-25Nb was hardened in a zone as far as 300 μm below the oxide scale when exposed to air at 900 °C for 500 h. The peak hardness depended on exposure time and reached five times the average hardness of the bulk material under the above conditions.     

Oxidation behaviour of Super 304H stainless steel in supercritical water

Oxidation of Super 304H steel in supercritical water at 600°C and 25?MPa was investigated, for the oxidation time of up to 1000?h. The oxidation kinetics approximately followed a parabolic law. The composition and microstructure of the oxide were investigated using the SEM equipped with EDS, EBSD and XRD. The phase compositions of the oxide evolve with increasing time. Cr₂O₃ was present at the initial stage and not detected while Fe₂O₃ appeared at longer time. EBSD indicated that continuous Cr₂O₃ formed at the interface of oxide and matrix for HR3C at 600°C for 40?h but only scattered Cr₂O₃ can be observed for 200?h. After the formation of a thin Fe–Cr–Ni oxide film on the Super 304H steel surface, the Fe-rich outer nodular oxide begins to grow and forms a continuous layer after 1000?h. The growth process of Super304H steel in supercritical water was discussed.     

High-Temperature Oxidation Behavior of Sputtered IN 738 Nanocrystalline Coating

A sputtered nanocrystalline coating of IN 738 alloy was obtained by means of magnetron sputtering. The isothermal oxidation behavior at 800, 900, and 1000°C and the cyclic oxidation behavior at 950°C of the coating were studied in comparison with IN 738 cast alloy. The results indicated that a double external oxide scale was formed on the nanocrystalline coating at 900, 950, and 1000°C without internal oxide and nitride. The scale consisted in an outer mixture of Cr₂O₃, TiO₂, and NiCr₂O₄ and an inner, continuous Al₂O₃ layer, which offered good adhesive and protectiveness. However, at 800°C a continuous Al₂O₃ scale could not be formed during oxidation of nanocrystalline coating and aluminum was still oxidized internally.     

AlCoCrFeNiTi_(0.5)高熵合金的高温氧化行为

采用水冷铜坩埚真空感应悬浮熔炼法制备AlCoCrFeNiTi_(0.5)多主元高熵合金,研究合金在800、900、1000和1100℃下的高温氧化行为,采用XRD,SEM及EDS对氧化膜的成分及形貌进行了分析,探索了合金的氧化机制。结果表明,合金的氧化动力学曲线在800和900℃时近似遵循六次方抛物线规律,在1000和1100℃时近似遵循四次方抛物线规律。合金具有优异的抗氧化性,在800、900和1100℃下为抗氧化级别,而在1000℃下为完全抗氧化级别。合金的氧化主要发生在枝晶间和共晶区,呈岛状团聚堆叠生长,1100℃氧化时该区域的氧化物发生明显剥落,氧化产物主要是TiO_2、Fe_2TiO_5和FeCr_2O_4等;而枝晶相的氧化产物较单一,1000℃及以下温度氧化时为弥散分布的Al_2O_3颗粒,1100℃氧化时为致密的Al_2O_3氧化层。高温氧化后,合金基体相结构稳定,未出现软化现象。