Role of Al2O3 layer in oxidation resistance of Cu-Al dilute alloys pre-annealed in H2 atmospheres

Copper was alloyed with small amounts of Al (0.2, 0.5, 1.0 and 2.0 mass%) to improve the oxidation resistance. Copper (6 N) and the Cu-Al alloys were oxidized at 773-1173 K in 0.1 MPa oxygen atmosphere after hydrogen annealing at 873 K. Continuous very thin Al₂O₃ layers were formed on the surface of all Cu-Al dilute alloys during the hydrogen annealing. Oxidation resistance of Cu-Al alloys was improved especially for Cu-2.0Al at 773-973 K, while it decreases on increasing the oxidation temperature. Cu-Al alloys followed the parabolic rate law at 1173 K, but most of other cases do not at and below 1073 K. Oxidation resistance for Cu-Al alloys was found relevant to the maintenance of the thin Al₂O₃ layer at the Cu₂O/Cu-Al alloy interface.     

挤压铸造Al-Cu-Mn和Al-Zn-Mg-Cu合金耐腐蚀性能研究

采用酸性盐雾试验,对Al-4.5Cu-0.8Mn和Al-7.3Zn-2.9Mg-1.9Cu 2种挤压铸造合金的耐腐蚀性能进行了对比研究.结果表明,在盐雾腐蚀过程中,随着腐蚀时间的延长和压力的增大,两种合金的耐腐蚀性能都出现了一定程度的下降.前者的腐蚀是由分布于枝晶间和晶界处的T(Al12CuMn2)和θ(Al2Cu)相溶解引起的,后者的腐蚀是由合金中η相的优先溶解,以及沿晶界分布的S相边沿的(Al)基体溶解所致;前者的耐腐蚀性能明显优于后者.     

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.     

The oxidation of two ternary Fe-Cu-10 at.% Al alloys in 1 atm of pure O2 at 800-900 °C

The oxidation of two ternary Fe-Cu-Al alloys containing 10 at.% Al (Fe-65Cu-10Al and Fe-30Cu-10Al) has been studied at 800-900 °C under 1 atm O₂. Under all conditions both alloys show an initial faster stage during which Fe-65Cu-10Al corrodes more rapidly at 800 °C than at 900 °C, while Fe-30Cu-10Al follows nearly identical kinetics at both temperatures. As oxidation proceeds, a continuous alumina layer is eventually established on the surface of the two alloys, thus decreasing significantly their oxidation rates. Altogether, the Fe-rich alloy Fe-30Cu-10Al oxidizes slightly faster than the Cu-rich alloy Fe-65Cu-10Al at both temperatures. The possible reasons for the decrease in the critical Al content needed to form external alumina scales for the Cu-rich alloy in comparison with binary Cu-Al alloys are examined.     

Study on the Microstructure and Wettability of an Al-Cu-Si Braze Containing Small Amounts of Rare Earth Erbium

The effect of adding small amounts of rare earth Er on the microstructure of an Al-Cu-Si braze alloy has been investigated. Several Al-20Cu-7Si braze alloys containing various contents of Er were prepared, and their melting temperature, microstructure, hardness, and wettability in contact with 3003 aluminum alloy substrates were determined. The results indicate that the constituents of the microstructure of Al-20Cu-7Si-Er braze alloys are similar to those in the Al-20Cu-7Si alloy, and comprise of solid solutions of aluminum, silicon, and the intermetallic compound CuAl₂. When the Er content increases, the size of the Al phase decreases, and the needle-like Si phase is thickened, and transformed to a blocky shape. Moreover, small amounts of Er can improve the wettability and hardness of the Al-20Cu-7Si braze alloy; however, the melting temperature of the Al-20Cu-7Si alloy does not change.     

Al对Fe-20Cr-35Ni-0.6Nb合金显微组织和抗氧化性的影响

采用增量法研究了不同Al含量(0.5%、1.5%、2.5%,质量分数)的Fe-20Cr-35Ni-0.6Nb含Nb合金在1000 ℃空气条件下的抗氧化。采用SEM、EDS、TEM、拉曼光谱等手段研究了合金的显微组织和氧化膜特性。结果表明,3种含Nb合金组织为单相奥氏体,基体中存在少量弥散分布的NbC沉淀相,氧化前后沉淀相含量和晶粒大小保持不变。添加0.5%和1.5%的Al后,含Nb合金的表面形成多层结构的氧化膜,最外层和第三层为Cr₂O₃,次表层主要为NiCr₂O₄、NiFe₂O₄和Fe₂O₃,最内层为Al₂O₃内氧化层。基体中的NbC析出相和氧化膜中少量Nb的氧化物(Nb₂O₅)加剧了氧化膜的疏松。当Al含量增加到2.5%时,含Nb合金表面形成连续致密的Al₂O₃氧化膜,降低了Fe-20Cr-35Ni-0.6Nb合金的氧化速率,提高了抗氧化性。     

TiAl-Nb基合金高温抗氧化研究进展

TiAl-Nb基合金具有优异的综合性能,在先进飞行器及武器等耐高温部件中有巨大的应用潜力,但其高温抗氧化性能无法满足实际使用需求。综述了TiAl-Nb基合金高温抗氧化防护方面的研究进展,包括TiAl-Nb基合金的多元合金化、表面合金化、抗氧化涂层及其抗氧化机理,通过分析不同氧化防护措施的特性,展望了TiAl-Nb基合金高温抗氧化防护的发展趋势。国内外研究结果显示,通过多元合金化方法改善合金组织,并在氧化过程中促进形成保护性Al_2O_3而抑制形成TiO_2,是提高TiAl-Nb基合金高温抗氧化性能的有效手段。利用表面合金化对合金表面的显微组织和成分进行改善,氧化时促进抗氧化性能优良的Al_2O_3或SiO_2保护膜形成,显著提高了TiAl-Nb基合金的抗氧化性能。但高温下合金化层与基体之间的Al、Si、Ti等元素的互扩散会加剧合金化层的退化,进行表面多元合金化,特别是添加微量活性元素,对促进保护性氧化膜的形成及抑制互扩散有良好效果。通过制备表面抗氧化涂层,在氧化时生成保护性氧化膜,阻碍O的内扩散,能够起到良好的高温抗氧化作用,但需要解决涂层/基体合金的结合力较差和反应扩散等问题,制备复合涂层或扩散阻挡层是解决上述问题的有效途径。     

Regulative effect of Mg/Si ratio on microstructure evolution and mechanical properties of cast Al-Li-Mg-Si alloys

The effect of the Mg/Si ratio of Al-2.5Li-1Cu-0.8Mg-0.8Si,Al-2.5Li-1Cu-1.6Mg-0.8Si,and Al-2.5Li-1Cu-2.4Mg-0.8Si alloys on the microstructure evolution and mechanical properties was investigated.The results show that the primary phases and their morphologies in the as-cast alloys are found to vary with the Mg/Si ratio.The improvement of Mg/Si ratio of as-cast alloys promotes the formation of Mg₂Si primary phase at the expense of the AlLiSi primary phase.Moreover,a tiny amount of T_B-Al_7.5Cu₄Li phase transforms into S-Al₂CuMg phase with the increase of Mg content.In addition,the increase of Mg/Si ratio also causes the Cu-rich intergranular phase distributed along crystal boundary to Si-rich intergranular phase.After ageing treatment,the precipitation sequence as a function of Mg/Si ratio is as follows:δ/δ'+AlLiSi(Mg/Si is~1)→δ/δ'+β'-Mg₂Si+AlLiSi(Mg/Si is~2)→δ/δ'+β'-Mg₂Si(Mg/Si is~3).A good combination of strength and ductility can be obtained in Al-2.5Li-1Cu-2.4Mg-0.8Si alloy after solution and ageing.The rod-likeβ'-Mg₂Si precipitate has a positive influence on the comprehensive mechanical properties of the alloy.     

低压预处理对TiAl抗氧化性的影响

对５种ＴｉＡｌ基合金进行了１０＾－３Ｐａ／１０４０℃／９ｈ／ＦＣ（炉冷）表面预处理。随后进行的９００℃静止空气中１００ｈ断续氧化实验表明,ＴｉＡｌ的抗氧化性不但没有提高,反而明显下降。抗氧化性下降的主要原因在于低压预处理过程中合金元素（尤其是铝元素）的选择性蒸发导致ＴｉＡｌ表面活化并形成Ｔｉ３Ａｌ相,而Ｔｉ３Ａｌ的抗氧化性较差,从而使ＴｉＡｌ整体氧化增重增加。     

Al、Si及Y多元合金化对Cr-20Nb合金高温氧化行为的影响

针对软第二相Cr稍微降低Laves相NbCr2合金的1200℃抗氧化性,采用Al、Si及Y多元合金化来提高Cr-20Nb合金的高温抗氧化性能。结果表明,多元合金化的Cr-20Nb合金1100℃及1200℃抗氧化性均好于加入单一合金化的及纯Cr-20Nb合金,并随着Si合金元素含量增加,Cr-20Nb合金的氧化增重变小,抗氧化性变好;SEM结果表明,添加合金元素后,氧化膜与基体的粘附性得到了明显提高。     

新型Co-Al-W合金高温氧化行为研究

研究了γ′-Co3(Al,W)相沉淀强化的新型钴基高温合金,Co-Al-W抗高温氧化性能。利用SEM、EPMA、XRD等方法研究了新型Co-Al-W合金在800℃和900℃空气中静态氧化增重动力学和抗高温氧化机理,并与镍基高温合金Manaurite900相比较。研究发现,在800℃氧化时,9.8W合金抗氧化能力最强,但在900℃时,9.8W和7.5W合金的增重最大,Manaurite900和10.7W的抗氧化能力最好。合金在2种温度下氧化后,表面氧化膜主要由三层构成,即Co氧化物Co3O4组成的氧化膜最外层,Co、Al、W复杂氧化物组成的中间过渡层及Al和Co氧化物组成的氧化膜最内层。     

Oxidation characteristics of Ti3Al-Nb alloys and improvement in the oxidation resistance by pack aluminizing

The oxidation behavior of three T_i3-Al-Nb alloys: Ti-25Al-11Nb, Ti-24Al-20Nb, and Ti-22Al-20Nb was investigated in the temperature range of 700–900°C in air. The uncoated alloy Ti-25Al-11Nb showed the lowest weight gain with nearly parabolic oxidation rate; while the other two alloys had much higher weight gain, accompanied by excessive oxide scale spalling. The scale analysis, using XRD, SEMIEDAX, and AES revealed that the scale was a mixture of TiO₂, Al₂O₃, and Nb₂O₅ with the outer layer rich in TiO₂. The effect of variation in Al and Nb content on the oxidation behavior is discussed. A decrease in Al content of the alloy adversely affects the oxidation resistance; and it seems that a Nb content as high as 20 at.% is also not beneficial. Hence these alloys, especially Ti-24Al-20Nb and Ti-22Al-20Nb, should not be used in the as-received condition above 750°C. An attempt was made to improve the oxidation resistance of these alloys by pack aluminizing which led to the formation of an Al rich TiAl₃ surface layer doped with Nb. The coating process was gaseous-diffusion controlled with a parabolic Al deposition rate. The weight gains for the aluminized alloy specimens oxidized at 900°C in air were much lower than that of the uncoated specimens. The weight gains were further decreased in the case of Si-modified aluminized specimens. The scale analysis revealed an alumina-rich scale with some amount of titania doped with Nb. The improvement in the oxidation resistance of the pack-aluminized alloys at 900°C is attributable to the formation of the alumina-rich oxide scale. The addition of Si to the aluminizing pack seems to promote further the growth of an alumina-rich scale by lowering the oxygen partial pressure in the system.     

液相渗Si提高TiAl基合金的高温抗氧化性

使用液相Al—Si合金对TiAl基合金进行表面渗Si处理，可明显增强TiAl基合金的高温抗氧化性．经1273K，100h的恒温氧化后，不同的表面涂层使合金在40—100h之间的氧化速率降低了2个数量级，恒温氧化100h后的最终氧化皮脱落量也减少3个数量级．液相渗Si使TiAl基合金表面高温抗氧化性能得到大幅度改善，其根本原因是Si与TiAl中的元素Ti结合，降低了Ti的活度，相对增强了涂层中元素Al的活度，而且涂层中Al的绝对含量也得到明显提高，这些均抑制了高温氧化过程中TiO2的生成，涂层最外层形成了致密的Al2O3氧化膜．     

含钪Al-9.0Zn-2.5Mg-1.2Cu-0.15Zr合金铸态组织与力学性能

采用铸锭冶金法制备了Al-9.0Zn-2.5Mg-1.2Cu-0.15Zr、Al-9.0Zn-2.5Mg-1.2Cu-0.12Sc-0.15Zr和Al-9.0Zn-2.5Mg-1.2Cu-0.20Sc-0.15Zr三种合金,采用金相显微镜、扫描电子显微镜和透射电子显微镜,研究了三种合金铸态及不同热处理状态下的显微组织,测试了不同热处理状态下合金的力学性能。结果表明,Sc含量增加可以提高Al-Zn-Mg-Cu-Zr合金的抗拉强度和伸长率,Al-9.0Zn-2.5Mg-1.2Cu-0.15Zr-0.20Sc经固溶和T6处理后,抗拉强度达到774.6 MPa,伸长率为8.3%。其作用机理主要为Sc含量增加,使合金中Al(3 Sc,Zr)引起的细晶强化、亚结构强化和弥散强化更进一步加强。     

The effect of small additions of Zr, Cr, Mg, Al, and Si on the oxidation of 6∶4 brass

The oxidation behavior of 60%Cu-40%Zn brass having small amounts of Zr, Cr, Mg, Al, and Si was studied between 873 and 1043 K in air. The alloying element of Mg was harmful, while other alloying elements were beneficial to oxidation resistance. Particularly, the simultaneous addition of Al and Si decreased the oxidation rate drastically. During oxidation, Zr formed ZrO₂ Cr formed CuCr₂O₄, Mg formed MgO, Al formed Al₂CuO₄, and Si formed amorphous SiO₂. These oxides were incorporated in the oxide scale composed predominantly of ZnO. The oxide scales formed on all the tested alloys were prone to cracking, wrinkling, and spallation.     

High-Temperature Oxidation Behavior of Ti-22Al-27(Nb, Zr) Alloys

研究了Ti2Al Nb基合金Ti-22Al-(27-x)Nb-x Zr(x=0,1,6,at%)在650~800℃的氧化行为。采用XRD和SEM等测试技术对此温度区间形成的氧化层特征进行了分析。结果表明,相比Ti-22Al-27Nb,含锆合金具有较好的抗氧化性能。Ti-22Al-(27-x)Nb-x Zr合金在650℃氧化100 h,主要氧化产物为Ti O2,而在800℃氧化100 h,Ti O2,Al2O3和Al Nb O4为主要产物,但是在Ti-22Al-21Nb-6Zr合金中还有Zr O2生成。Ti-22Al-26Nb-1Zr合金具有优异抗氧化性能,归因于氧化产物细化形成了致密的氧化层,而Ti-22Al-21Nb-6Zr合金,虽然在800℃也形成了较多Al2O3,但是氧化层中的Zr O2为氧的快速扩散提供通道,进而导致该合金氧化增重明显。     

影响Ti合金热稳定性的因素

综述了合金元素、环境气氛、相变、涂层等因素对Ti合金热稳定性的影响.     

预处理对压铸镁合金微弧氧化膜的影响

微弧氧化前,用打磨和喷砂两种方法对基材进行预处理,获得两种氧化膜试样,对比了这两种试样的形貌、化学组成及耐腐蚀性能,分析了预处理方法对微弧氧化电压值的影响。结果表明:打磨后微弧氧化的电压值高于喷砂后微弧氧化;微弧氧化膜的耐蚀性能较基体大幅度提高,打磨试样的耐蚀性能较喷砂试样提高了40%左右;喷砂试样的氧化膜表面整体保留了喷砂后粗糙不平的形貌,而打磨试样的氧化膜较喷砂试样平整,微孔尺寸均匀且较喷砂试样的尺寸小;氧化膜表面的化学成分主要有O,Mg,Si,Al等,预处理对氧化膜化学成分及含量的影响不显著。     

石墨含量对镍基高温合金在900 ℃氧化行为的影响

采用粉末冶金方法制各不同石墨含量(0%、3%、6%)的镍基高温合金,研究合金材料在900℃和100 h下的恒温氧化行为,用扫描电镜和X射线衍射对其氧化表面形貌和成分进行观察和分析.结果表明:石墨含量较低(0%,3%)时,镍基合金氧化动力学符合抛物线规律,表面氧化膜无剥落;石墨含量为0%的合金氧化膜由Cr2O3和NiCr2O4组成,石墨含量为3%的合金氧化膜由Cr2O3组成,当石墨含量增加到6%时,大量石墨的氧化分解导致合金初始氧化严重,石墨分解后的孔洞加速氧化反应过程.根据氧化膜的组成分析了合金的氧化机制.     

Si3N4陶瓷材料的高温氧化理论及其抗氧化研究现状

从热力学、动力学和整体控速过程探讨了氮化硅陶瓷材料高温氧化理论和氧化性质,在空气中的热化过程, 因为PO2>Psio, 是纯化氧化过程,氧化产物为SiO2和N2.氧扩散是控制氧化速度的主导因素.氧在Al2O3中的高温扩散系数为10-15~10-14量级,而在SiO2中扩散系数为10-8量级,因此人们探索各种方法在Si3N4陶瓷表面改性以提高其抗氧化性能,其中, 制备金属氧化物的效果显著.在试验沉积Al2O3薄膜的基础上,讨论了Al2O3薄膜对氮化硅陶瓷抗氧化性能的作用,并且展望了精密氮化硅陶瓷表面形成具有良好结合力的金属氧化物-氧化硅混合结构表层的表面改性技术.