不同表面粗糙度镍铬铝合金的高温氧化行为

采用热重法并结合X射线衍射、扫描电子显微镜、能谱仪等分析手段,研究在1000 ℃条件下Ni-10Cr-5Al (质量分数,%) 合金样品表面粗糙度对其氧化行为的影响。结果表明：经1000 ℃氧化215 h后,不同表面粗糙度的合金其氧化动力学均服从抛物线规律,并存在两个抛物线常数,氧化膜主要由Al₂O₃,NiCr₂O₄和NiAl₂O₄组成。随着表面粗糙度的增加,氧化增重越明显,同时氧化膜脱落越严重、氧化膜金属界面越起伏。其中,表面粗糙度对合金氧化的影响主要是在氧化前期阶段促进生成了尖晶石NiCr₂O₄和NiAl₂O₄氧化物。     

K438铸造高温合金表面热浸镀铝涂层的抗氧化性能

针对K438镍基高温合金在高温条件下抗氧化性能不足的问题,采用热浸镀铝技术在其表面制备了铝化物涂层。经1000 ℃、1 h真空扩散退火处理后,对高温合金的热浸镀铝涂层开展了1000 ℃、250次的高温循环氧化试验,并采用扫描电镜、能谱仪、X射线衍射仪等分析测试手段,对高温氧化后涂层截面组织进行了研究。结果表明,试验合金在1000 ℃、40次循环氧化后氧化增量曲线便开始下降,高温抗氧化性能较差,经1000 ℃、250次循环氧化后,形成了Al₂O₃、TiO₂、Cr₂O₃、NiO和尖晶石NiCr₂O₄、NiAl₂O₄等氧化产物。而热浸镀铝涂层经1000 ℃、40次循环氧化后,氧化增量变化较小,且经250次循环氧化后,氧化产物中未发现Cr₂O₃的存在,其高温抗氧化性能均较基体明显提高,其中热浸镀90 s的涂层高温抗氧化性能更好。     

一种可内生Al2O3扩散障的δ-Ni2Al3-Cr2O3/ Ni-Cr2O3涂层体系

通过对Ni-Cr₂O₃复合镀层620 ℃部分渗铝制备了δ-Ni₂Al₃-Cr₂O₃/Ni-Cr₂O₃涂层体系。Cr₂O₃颗粒在渗铝的过程中和Al反应生成更为稳定的Al₂O₃。1000 ℃恒温氧化20 h后发现,铝化物涂层和复合镀层内掺杂的Cr₂O₃颗粒完全转化为Al₂O₃,并在铝化物涂层/Ni镀层界面自发形成了一层Al₂O₃富集层,该富集层起扩散障作用,阻碍铝化物涂层因互扩散所致的退化。     

采用Au基钎料真空钎焊Al2O3陶瓷

首先选用AgCuTi活性钎料在880℃/10 min参数下对A1₂O₃陶瓷表面进行金属化处理,之后尽量去除金属化层中的AgCu共晶组织,然后选用两种Au基高温钎料在980℃/10 min参数下对金属化后的A1₂O₃进行了钎焊连接.结果表明,在Al₂O₃/Au-Ni/Al₂O₃接头中靠近Al₂O₃母材的界面处生成一层薄薄的扩散反应层,该反应层主要由TiO₂和Al₂O₃组成;在Al₂O₃/Au-Cu/Al₂O₃接头中同样存在扩散反应层,与前者不同的是,接头中检测到Ti-Au相的存在.分别对Au-Ni和Au-Cu两种钎料获得的Al₂O₃接头进行了抗剪强度测试,前者对应接头强度为95.5 MPa,后者对应接头强度达到102.3 MPa.     

Influence of Al2O3 or ZrO2 particulate addition on the microstructure aspects of AlNi and AlSi alloys

Different metal/ceramic composites (Al7Si0.3Mg, Al3Ni, Al6Ni, Al9Ni) reinforced with Al₂O₃ or ZrO₂ were prepared by vortex method. Metallographic investigations reveal that in all the composites -Al did not nucleate on the reinforcement particulates. The particulates were generally observed to be located in the last freezing regions regardless of matrix alloy, particulate type or size. The reason for that was the mismatch in the thermal diffusivity between the ceramic particulates and matrix alloys. SEM micrographs show that the presence of the particulates in the AlSi alloy tends to modify the silicon eutectic. In contrast, the addition of the particulates into AlNi alloys did not result in a significant modification of the NiAl₃ phase, but it displaced the eutectic point to lower Ni content.     

Processing, microstructure, and properties of laser remelted Al2O3/Y3Al5O12（YAG） eutectic in situ composite

Laser remelting and rapid solidification were performed in preparing the high-performance Al2O3/Y3Al5O12（YAG） eutectic in situ composite. The microstructure characteristic and solidification behavior were studied using scanning electron microscopy（SEM）, energy dispersive spectroscopy（EDS）, X-ray diffractometry（XRD） and simultaneous thermal analysis（STA）. The hardness and fracture toughness were obtained using an indentation technique. The results show that the laser remelted Al2O3/YAG composite has a homogeneous eutectic microstructure without microcrack and pore. The component phases of Al2O3 and YAG are three-dimensionally and continuously reticular connected, and finely coupled without grain boundaries, colonies and amorphous phases between interfaces. The eutectic interspacing is greatly refined with increasing the scanning rate and average is only l μm. The synthetically thermal analysis indicates that the eutectic temperature of Al2O3-YAG is 1 824 ℃, well matching the phase diagram of Al2O3-Y2O3 system. The maximum hardness reaches 19.5 GPa and the room fracture toughness is 3.6 MPa.m^1/2.     

ZrSiO4 对低温陶瓷结合剂预熔玻璃料结构与性能的影响

在Al₂O₃-B₂O₃-SiO₂系低温陶瓷结合剂中添加不同含量的ZrSiO₄添加剂,用差示扫描热分析仪、X射线衍射仪、扫描电镜等研究ZrSiO₄含量对低温陶瓷结合剂结构与性能的影响。结果表明:ZrSiO₄含量增加,陶瓷结合剂耐火度无明显增加,其热膨胀系数在一定范围内降低;且当ZrSiO₄质量分数为4%时,陶瓷结合剂结构致密,微观状态均匀,陶瓷结合剂的综合性能最佳,其抗折强度为57.37 MPa,显微硬度为855.59 MPa。      

Three-point bending behavior of surface composite Al2O3/Ni on bronze substrate produced by vacuum infiltration casting

Al₂O₃/Ni surface infiltrated composite layer is a protective surface layer. It was fabricated on bronze substrate through vacuum infiltration casting technique using Ni-based powder and Al₂O₃ powder with different content as raw materials. With an appropriate choice of processing condition, a compact infiltrated layer is achievable as conformed through SEM observation. The infiltrated layer consists of surface composite layer and transition layer, and the thickness of transition layer decreases with increasing content of Al₂O₃. Metallurgical fusion formed at the interface between the surface infiltrated composite layer and substrate. Three-point bending tests were carried to investigate the mechanical and bonding properties of the surface infiltrated layer. It was found that load-holding circumstance appeared on the load–displacement curve of specimen with surface infiltrated layer comparing with that of the substrate. The peak load reduces with increasing content of Al₂O₃. The fracture extended to the substrate for specimen with Al₂O₃ content less than 20 (wt%). The fracture direction of specimen more than 30% with Al₂O₃ (wt%) is along with the interface of the surface composite and the substrate because of the thinner transition layer.     

表面活化Al2O3陶瓷与5005铝合金真空钎焊

采用Al-Si钎料对经过Ag-Cu-Ti粉末活性金属化处理的Al₂O₃陶瓷与5005铝合金进行了真空钎焊,研究了钎焊接头的典型界面组织,分析了钎焊温度对接头界面结构特征及力学性能的影响. 结果表明,接头典型界面结构为5005铝合金/α-Al+θ-Al₂Cu+ξ-Ag₂Al/ξ-Ag₂Al+θ-Al₂Cu+Al₃Ti/Ti₃Cu₃O/Al₂O₃陶瓷. 钎焊过程中,Al-Si钎料与活性元素Ti及铝合金母材发生冶金反应,实现对两侧母材的连接. 随着钎焊温度的升高,陶瓷侧Ti₃Cu₃O活化反应层的厚度逐渐变薄,溶解进钎缝中的Ag和Cu与Al反应加剧,生成ξ-Ag₂Al+θ-Al₂Cu金属间化合物的数量增多,铝合金的晶间渗入明显;随钎焊温度的升高,接头抗剪强度先增加后降低,当钎焊温度为610 ℃时,接头强度最高达到15 MPa.     

Friction characteristic of micro-arc oxidative Al2O3 coatings sliding against Si3N4 balls in various environments

The alumina ceramic coatings were prepared on 2024Al alloy by micro-arc oxidation (MAO) technique. The phase structure of the MAO Al₂O₃ coating was determined using X-ray diffraction. The thickness and micro-hardness of the MAO Al₂O₃ coatings was measured using eddy current thickness equipment and micro-hardness tester. The friction property of MAO Al₂O₃ coatings sliding against Si₃N₄ ceramic balls were investigated in air, water and oil by a ball-on-disk tribo-meter, and the worn surfaces of the MAO Al₂O₃ coatings were observed using scanning electron microscope (SEM). The results showed that the MAO Al₂O₃ coatings mainly contained -Al₂O₃ and γ-Al₂O₃ phase. The micro-hardness of the polished MAO coatings was HV1740 ± 87. With an increase in normal load and sliding speed, the friction coefficient in air increased from 0.74 to 0.87, while decreased from 0.72 to 0.57 in water and 0.24 to 0.11 in oil. This indicates that the fluid lubrication could improve the friction behavior of the MAO Al₂O₃ coatings. The worn surfaces' observation indicated that the wear mechanism of the MAO Al₂O₃ coatings changed from abrasive wear in air to mix wear in water, and became microploughing wear in oil.     

Development of moderate temperature CVD Al2O3 coatings

Chemically vapor deposited Al₂O₃ coatings, due to their high hardness and chemical inertness, are currently the state of art in the cutting tool industry. The conventional high deposition temperature of about 1050 °C for Al₂O₃ coatings, based on the water–gas shift process, has to a great extend restricted the development of several hybrid coatings, such as TiC/TiN/TiCN/Al₂O₃. To overcome this limitation, alternate systems to deposit Al₂O₃ at moderate temperatures have been investigated. Systems using NO–H₂, H₂O₂, NO₂–H₂ and HCOOH were identified and thermodynamic calculations were performed to evaluate them as potential sources of oxygen donors to form Al₂O₃ in the moderate temperature range of 700–950 °C. Preliminary results have clearly demonstrated that it is possible to grow moderate temperature alumina (using such alternate sources) on the TiC/TiN coated cemented carbide substrates.     

High temperature oxidation of an oxide-dispersion strengthened NiAl

The oxidation behavior of an oxide-dispersion strengthened (ODS) NiAl has been studied between 900 and 1100°C in air. The dispersoids of mostly Al₂O₃ in fine-grained β-NiAl were incorporated by mechanical alloying (MA) in an argon atmosphere and hot pressing. It was found that excessive amounts of dispersoids and voids within the matrix had serious negative effects on the oxidation resistance of β-NiAl, by allowing for a more rapid formation of oxide scales and by providing fast diffusion paths for oxygen. Below the thin surface oxide scales consisted of -Al₂O₃, NiAl₂O₄ and Ni₂O₃, an internal oxidation zone was formed deep into the matrix. No metastable transient aluminas were formed during oxidation. The oxide ridge structure began to evolve after oxidation at 1100°C at the oxide–gas interface.     

Isothermal oxidation of air plasma spray NiCrAlY bond coatings

The isothermal oxidation behaviors of plasma-sprayed NiCrAlY bond coatings (Ni22Cr10Al1Y and Ni31Cr11Al 0.6Y) have been evaluated. Two unique microstructures, oxide stringers and improperly flattened zones, can be observed in the air plasma spray (APS) bond coatings. The structures and chemical compositions of the oxide stringers were examined by transmission electron microscopy (TEM) and energy dispersive spectroscopy (EDS). Improperly flattened zones had a high density of open pores. These features affected the oxidation behaviors in both the transient and the steady-state stages. In the transient oxidation stage, NiO, Cr₂O₃ and -Al₂O₃ were observed on the surface simultaneously. The oxide stringers and improperly flattened zones had an especially high density of NiO and Cr₂O₃, which implied that these regions had inherently lower contents of Al. During steady-state oxidation, a continuous -Al₂O₃ layer reduced the diffusion rate of oxygen and, thus, the rate of isothermal oxidation became low. As the oxidation time was increased, depletions of Al, the formation of NiAl₂O₄ layers and the formation of Cr₂O₃ subsequently occurred. Hemispherical protrusions were also detected on the surface after cooling to room temperature.     

Strength and residual stresses of functionally graded Al2O3/ZrO2 discs prepared by electrophoretic deposition

Biaxial strength testing of functionally graded Al₂O₃/ZrO₂ discs revealed that the strength of such discs, prepared by electrophoretic deposition, was almost doubled from 288 MPa for pure Al₂O₃ to 513 MPa for the graded discs; this was due to the compressive surface residual thermal stresses in the Al₂O₃ surface layer caused by the graded compositional profile. The surface compressive stress measured by means of X-ray diffraction was compared with the analytically calculated stress distribution in the graded component.     

NiCrAlY/Al-Al2O3/Ti2AlNb高温抗氧化和力学性能研究

采用电弧离子镀技水在NiCrAlY涂层与O相Ti₂AlNb合金之间沉积不同Al:Al₂O₃比例的Al-Al₂O₃薄膜作为扩散阻挡层.研究了900℃下恒温氧化500 h后NiCrAlY/Al-Al₂O₃/Ti₂AlNb体系中Al-Al₂O₃层阻挡合金元素互扩散的行为,以及对涂层氧化动力学曲线的影响.结果表明,没有添加扩散阻挡层的NiCrAlY/Ti₂AlNb体系,涂层和基体之间的元素互扩散十分严重,涂层丧失抗氧化能力;而添加扩散阻挡层的材料体系,涂层和基体之间的元素互扩散受到抑制,涂层的长期抗高温氧化性能得到提高.对于3Al-Al₂O₃,1Al-Al₂O₃和0Al-Al₂O₃ 3种扩散阻挡层,综合比较材料体系的抗氧化性能、阻挡层阻挡涂层和基体元素互扩散能力、以及涂层和基体之间结合力,当1Al-Al₂O₃薄膜作为扩散阻挡层时,材料性能最优异.同时,本文利用扩散阻挡系数简洁定量地表示出不同Al:Al₂O₃比例阻挡层的阻挡扩散能力.     

保护渣对铝钛系夹杂物溶解的吸收规律

以CaO-SiO₂-Al₂O₃-Na₂O-CaF₂-MgO为基础渣系,采用旋转动力学方法研究了不同碱度、BaO质量分数(0~15%)、B₂O₃质量分数(0~15%)对连铸保护渣吸收Al₂O₃或TiO₂速率的影响以及吸收前后矿相变化。结果表明,保护渣吸收TiO₂的速率要远大于吸收Al₂O₃的速率;添加BaO或B₂O₃后均能提高保护渣吸收Al₂O₃和TiO₂的能力;保护渣主要物相为钙镁黄长石(2CaO·MgO·2SiO₂)、钙铝黄长石(2CaO·Al₂O₃·2SiO₂)、枪晶石(3CaO·2SiO₂·CaF₂)及玻璃相(Na₂O·Al₂O₃·SiO₂);添加BaO后,钙镁黄长石转变为重硅酸钡钙镁(2CaO·MgO·2SiO₂·BaO),并抑制黄长石和枪晶石晶体长大;当添加B₂O₃的质量分数不低于10%,保护渣形成的物相为玻璃相。试验条件下,不同碱度的保护渣和添加B₂O₃的保护渣中TiO₂仍以TiO₂形式存在,而在添加BaO的保护渣中,TiO₂形成钙钛矿。     

Thermodynamic properties and phase diagrams of the binary systems B2O3–Ga2O3, B2O3–Al2O3 and B2O3–In2O3

We calculated the binary phase diagrams B₂O₃–Ga₂O₃, B₂O₃–In₂O₃ and B₂O₃–Al₂O₃, and the Gibbs energy of formation of the binary compounds, using experimental liquidus data. The B₂O₃–Ga₂O₃ system is of industrial importance, because liquid B₂O₃, in which Ga₂O₃ is not very soluble, is used to protect GaAs during growth of single crystals of GaAs. During recovery of noble metals B₂O₃ is added to slags containing Al₂O₃ to lower the melting point and the viscosity. The B₂O₃–In₂O₃ system is of much less importance to industry. In all three systems we have a liquid miscibility gap, and also solid binary compounds, none of which melt congruently. The miscibility gaps are not surprising, because even in the B₂O₃–Bi₂O₃ system where four congruently melting compounds are present, a liquid miscibility gap exists close to B₂O₃.     

DD3高温合金与Ti3AlC2陶瓷的真空钎焊

通过对比试验优选出了合适钎料,并进行了后续钎焊试验.在钎焊温度800~900℃,保温时间为10 min的条件下,采用Ag-Cu-Ti钎料实现了DD3镍基高温合金与Ti₃AlC₂陶瓷的真空钎焊连接.利用扫描电镜、能谱仪、XRD等对接头的界面结构进行了分析.结果表明,接头的典型界面结构为DD3/AlNi/Al₃(Ni,Cu)₅+Al(Ni,Cu)+Ag_ss/(Al,Ti)₃(Ni,Cu)₅/Al₄Cu₉+AlNi₂Ti+Ag_ss/TiAg/Ti₃AlC₂.接头的力学性能测试表明,在钎焊温度为850℃,保温时间为10 min的条件下,接头的最高抗剪强度可达135.9 MPa,断裂发生在靠近钎缝的Ti₃AlC₂陶瓷侧.降低和提高钎焊温度对接头界面组织影响不大,但接头强度有一定程度下降.     

Properties of copper matrix reinforced with various size and amount of Al2O3 particles

Copper matrix was reinforced with Al₂O₃ particles of different size and amount by internal oxidation and mechanical alloying accomplished using high-energy ball milling in air. The inert gas-atomised prealloyed copper powder containing 1 wt.% Al as well as a mixture of electrolytic copper powder and 3 wt.% commercial Al₂O₃ powder served as starting materials. Milling of Cu-1 wt.% Al prealloyed powder promoted formation of fine dispersed particles (1.9 wt.% Al₂O₃, approximately 100 nm in size) by internal oxidation. During milling of Cu-3 wt.% Al₂O₃ powder mixture the uniform distribution of commercial Al₂O₃ particles has been obtained. Following milling, powders were treated in hydrogen at 400 °C for 1 h in order to eliminate copper oxides formed at the surface during milling. Compaction was executed by hot-pressing. Compacts processed from 5 to 20 h-milled powders were additionally subjected to high-temperature exposure at 800 °C in order to examine their thermal stability and electrical conductivity. Compacts of Cu-1 wt.% Al prealloyed powders with finer Al₂O₃ particles and smaller grain size exhibited higher microhardness than compacts of Cu-3 wt.% Al₂O₃ powder mixture. This indicates that nano-sized Al₂O₃ particles act as a stronger reinforcing parameter of the copper matrix than micro-sized commercial Al₂O₃ particles. Improved thermal stability of Cu-1 wt.% Al compacts compared to Cu-3 wt.% Al₂O₃ compacts implies that nano-sized Al₂O₃ particles act more efficiently as barriers obstructing grain growth than micro-sized particles. Contrary, the lower electrical conductivity of Cu-1 wt.% Al compacts is the result of higher electron scatter caused by nano-sized Al₂O₃ particles.     

The oxidation of nanocrystalline Ni3Al fabricated by mechanical alloying and spark plasma sintering

Nanocrystalline Ni₃Al was fabricated through mechanical alloying of elemental powders and spark plasma sintering. The nanocrystalline Ni₃Al has a nearly full density after being sintered at 1223 K for 10 min under a pressure of 65 MPa. Isothermal and cyclic oxidations of nanocrystalline Ni₃Al were tested at 1173–1373 K with intervals of 100 K. The results indicate that nanocrystalline Ni₃Al exhibits excellent isothermal and cyclical oxidation resistance. The oxide scales consist primarily of dense and continuous -Al₂O₃. The grain refinement is beneficial for improving the oxidation resistance of Ni₃Al by providing more nucleation centers for the Al₂O₃ formation, promoting the selective formation of Al₂O₃ and improving the adhesion of oxide scales to the matrix.