高温合金Inconel625切削用刀具材料抗氧化性能

通过化学热力学从理论上推导高温合金Incone1625切削用刀具材料在高温下可能发生的氧化反应,选用硬质合金(YG8)、涂层硬质合金和陶瓷3种刀具材料,利用高温加热炉对不同刀具材料进行抗氧化实验,并对高温氧化产物进行扫描电镜(SEM)和X射线衍射(XRD)分析。结果表明:在高温氧化试验中,YG8和涂层硬质合金的刀具材料中的WC和Co部分被氧化成WO_3、Co_3O_4,且随着温度的升高,氧化反应更加剧烈;而陶瓷刀具中只有TiC被氧化成了TiO_2,表现出较好的抗氧化性能;3种刀具材料的抗氧化性的顺序为:陶瓷刀具涂层硬质合金YG8。     

硬质合金高温氧化行为研究

选用牌号为YG8、YG6X和YG6三种硬质合金刀具材料,在700、800、900和1000℃下分别进行30、60、90、120和150min的抗氧化性能研究.结果表明:随时间的延长,刀具材料中的WC和Co被全部或部分氧化成WO<,3>和CO<,3>O<,4>;晶粒尺寸较小的刀具材料具有更好的抗氧化性能;在尺寸相差不大时,Co含量较高的刀具材料具有更好的抗氧化性能;三种刀具材料的高温抗氧化性能优劣顺序为:YG8>YG6X>YG6.     

镍基高温合金Al-Si涂层1000℃抗高温氧化性能和退化机制研究

为研究Si对简单NiAl涂层抗高温氧化性能的影响规律,改变料浆中Si/(Si+Al)比值(8wt.%、17wt.%和30wt.%),制备了三种不同Si含量的改性NiAl涂层。采用XRD、SEM、EPMA等表征方法分析了简单NiAl涂层和三种Si改性NiAl涂层氧化前后的相结构和显微组织。结果表明：四种铝化物涂层主要相均为δ-Ni₂Al₃和β-NiAl相。Si以CrSi₂、Cr₅Si₃和Ni₂Si硅化物的形式存在于涂层表层。在1000℃氧化500h后,简单NiAl涂层具有最大的氧化增重为1.93mg.cm_-2^,而Si/(Si+Al)比值为8wt.%的Si改性NiAl涂层具有最小的氧化增重。在NiAl涂层中掺杂Si可促进α-Al₂O₃膜的形成,通过形成硅化物减少难熔金属元素向涂层表面扩散,改善氧化膜表面质量,降低氧化速率。但是掺杂过量的Si会降低涂层表层Al含量,使涂层在氧化后期出现β相不足的问题,无法维持表面Al的选择性氧化。因此,当料浆中Si/(Si+Al)为8 wt.%,涂层表面Si含量为9.6 at.%时,涂层具有最高的抗高温氧化性能。     

Ti6Al4V合金激光熔覆NiMoSi复合涂层的高温抗氧化性能

为提高Ti6Al4V合金的高温抗氧化性能,以Ni-48%Mo-32%Si混合粉末为原料,采用激光熔覆技术在Ti6Al4V合金表面制备复合涂层,分析涂层物相、组织结构、高温抗氧化性能及抗磨损性能,并讨论相关机理。结果表明：复合涂层中无裂纹,与基体实现了良好的冶金结合;硬质相Ti₅Si₃、MoSi₂和Mo₅Si₃均匀分布于基体α-Ti、NiTi中。经恒温800 ℃氧化100 h后,复合涂层的氧化膜主要由TiO₂、SiO₂和NiO组成,结构连续致密,表现出较好的高温抗氧化性能。而Ti6Al4V合金氧化膜主要为疏松TiO₂,表面氧化严重;氧化后,复合涂层和基体的单位面积增重分别为1.31和23.38 mg/cm²;复合涂层和基体的摩擦因数分为0.44和0.52、磨损率分别为16.2×10^-5和22.6×10^-5mm³/Nm,复合涂层的摩擦学性能亦有明显提高。     

高铌γ-TiAl合金表面微弧氧化陶瓷涂层的耐蚀性及高温氧化行为

利用微弧氧化技术（MAO）在硅酸钠和氢氧化钾溶液中对高铌γ-TiAl合金表面原位生长陶瓷涂层以提高γ-TiAl合金的抗高温氧化性能。采用扫描电子显微镜（SEM）、X射线衍射仪（XRD）、X射线光电子能谱（XPS）、电化学工作站和箱式电阻炉高温氧化测试分析涂层的表面及截面形貌、相组成、元素化学结合状态、耐蚀性和高温氧化行为。XRD和XPS结果表明,陶瓷涂层主要由Al₂TiO₅、SiO₂和Nb₂O₅组成。涂层与基体界面结合良好,厚度约2.15 μm。高铌γ-TiAl合金经微弧氧化处理后,在3.5%NaCl溶液中的腐蚀电流降低近1个数量级。微弧氧化处理试样在800~900 ℃中的氧化增重仅为基体的8.9%~37.5%。微弧氧化陶瓷涂层将基体的氧化激活能从247.79 kJ/mol增加到涂层试样的574.41 kJ/mol。     

La元素对MoSi2涂层的宽温域氧化行为影响

采用包渗法在稀土 La₂O₃ 掺杂钼合金基体上制备 MoSi₂ 涂层,并就 La 元素对 MoSi₂ 涂层宽温域氧化行为的影响机制进行了系统研究。 结果表明:钼镧合金基 MoSi2 涂层组织结构较为致密,主要物相为 MoSi₂ 相。 不同温度下 La 元素对 MoSi₂ 涂层的抗氧化性能的影响不同,1600 ℃高温静态氧化条件下,La 元素的存在促进了涂层与基体的化学反应,加剧了 MoSi₂ 抗氧化主体层的消耗速度,使得 MoSi₂ 涂层的高温抗氧化性能有所下降;800 ℃ 中温静态氧化条件下, La 元素对 MoSi₂ 涂层抗氧化性能影响不明显;500 ℃低温静态氧化条件下,La 元素的加入加速了涂层中 Si 元素的扩散, 使得涂层表面能较快形成一层致密的氧化层,“Pest”效应得到抑制,从而显著提升涂层的低温抗氧化性能。     

CoCrNiAlY涂层制备工艺对组织形态及高温氧化行为的影响

为了研究CoCrNiAlY涂层微观组织结构对高温氧化行为和剥落行为的影响规律,采用激光熔覆技术和等离子喷涂工艺在718高温合金表面制备CoCrNiAlY涂层,观察其微观组织形态。利用XRD和SEM对1150 ℃高温氧化试验样品进行氧化层物相分析和形貌观察。结果表明,激光熔覆制备的CoCrNiAlY涂层中形成了胞状亚结构的等轴晶凝固组织,相对于等离子喷涂制备的CoCrNiAlY涂层结构更致密,具有更优异的抗高温氧化性能。在高温氧化过程中,等离子喷涂CoCrNiAlY涂层生成了以Cr₂O₃结构为主的复合氧化膜。激光熔覆CoCrNiAlY涂层生成Al₂O₃结构的单一氧化膜,而且熔覆层中原位形成的Y₂O₃钉扎作用能有效提高氧化膜的抗剥落性。文中系统分析讨论了两种不同工艺制备的组织形态对高温氧化膜形成机制的影响,激光熔覆涂层在高温下主要是以界面扩散方式形成致密的Al₂O₃膜,等离子喷涂涂层在高温下以界面反应的方式快速形成Cr₂O₃复合氧化膜。     

N含量对Cr-N涂层结构和抗高温水蒸汽氧化性能的影响

为提高锆( Zr)合金的抗高温水蒸气性能,采用磁控溅射技术,通过改变沉积过程中的 N₂ 流量,在 Zr 合金表面制备不同 Cr/ N 比的涂层,研究不同 N 含量对涂层结构和抗高温水蒸汽氧化性能的影响。 利用扫描电镜、 能谱仪、X 射线衍射仪对涂层氧化前后的表面与截面形貌、化学组成、相结构进行观察和分析,利用纳米压痕仪测量涂层的力学性能,通过高温水蒸汽氧化试验评估涂层的抗氧化性能。 结果表明,随 N 含量的增加,涂层的生长结构分别为“疏松柱状” 、“致密非柱状” 、“致密柱状” 。 其中,“ 致密非柱状” 结构的涂层具有最高的硬度,是“ 疏松柱状”涂层的 2 倍。 同时,该涂层在氧化过程中生成的 Cr₂O₃ 氧化层均匀致密,可以有效防护 Zr 合金基底 6 h 不被氧化。     

ZrB2-玻璃陶瓷复合材料氧化分析

对ZrB₂-玻璃陶瓷复合材料氧化行为进行热力学分析,对氧化形成的氧化层进行物相分析和显微结构分析。结果表明：在1000°C-1400°C的反应温度范围内,ZrB₂氧化生成ZrO₂,B₂O₃玻璃相,氧化产物ZrO₂与SiO₂反应生成ZrSiO₄,当温度低于1177°C(1450K)时,氧化层主要包括ZrO₂,B₂O₃玻璃相,ZrSiO₄。当氧化温度超过1177°C(1450K)时,B₂O₃玻璃相蒸发,此时SiO₂玻璃相具有良好的流动性,氧化层主要包括ZrO₂,SiO₂玻璃相,ZrSiO₄。氧化过程中的反应产物B₂O₃玻璃相,ZrSiO₄和流动性良好的SiO₂玻璃相,均对氧气向基体的扩散均起到了良好的阻碍作用。     

磁控溅射Cr/CrN和Cr/CrN/CrAlN涂层的抗高温氧化性能

为了提高航空紧固件涂层的高温工况防护能力,采用磁控溅射技术在钛合金表面分别制备 Cr/ CrN 交替涂层和 Cr/ CrN / CrAlN 涂层,研究氧化时间和氧化温度对涂层高温氧化性能影响。 利用 SEM、EDS 和 XRD 进行微观形貌和物相成分分析,采用热重法分析氧化增重量( w) 和氧化速率常数( k) ,使用显微硬度计测试涂层高温氧化后硬度。 结果表明:随着氧化时间和氧化温度的增加,涂层硬度均降低,但 Cr/ CrN / CrAlN 涂层下降趋势更缓; 两种涂层的 w 和 k 均上升,其中 Cr/ CrN / CrAlN 涂层 w 和 k 增幅均低于 Cr/ CrN 交替涂层,950 ℃ 氧化 96 h 后 Cr/ CrN / CrAlN 涂层和 Cr/ CrN 交替涂层的 w 值分别为 40 mg / cm ² 和 135. 7 mg / cm ² ,其对应的 k 分别为 0. 1996 和 0. 4092,说明 Cr/ CrN / CrAlN 涂层抗高温氧化性更好。 Cr/ CrN / CrAlN 涂层活化能 E_a 值比 Cr/ CrN 交替涂层高 48. 5%,Cr/ CrN / CrAlN 涂层在高温下产生 Cr₂O₃ 和 Al ₂O₃ 的混合氧化物,结构更致密,Cr/ CrN / CrAlN 涂层抗高温氧化性能高于 Cr/ CrN 交替涂层。     

Oxidation of niobium particles embedded in a sintered ceramic matrix

The toughness of ceramic materials can be improved through the inclusion of metallic particles in the ceramic matrix. The plastic deformation of the particles limits the rupture of the ceramic matrix. Al₂O₃‐Nb composites show the ability of niobium to form a strong bond with Al₂O₃, but the poor resistance to oxidation of niobium hinders the use of niobium for high temperature applications. The study of the oxidation mechanism was done using thermogravimetric analysis under an oxygen atmosphere in order to obtain the oxidation reaction rate constants of the Al₂O₃‐Nb composite. At the beginning the oxidation kinetics are linear, probably due to a great availability of oxygen. Later on, the oxidation mechanism showed to be parabolic, indicating that the process depends on the oxygen diffusion through the ceramic matrix.     

Comparison of the wear behaviors of advanced and conventional cemented tungsten carbides

In this study, the wear behaviors of an advanced WC-15%Al₂O₃ composite (WA15) were compared with a commercially available WC-8%Co cemented carbide (YG8). In order to evaluate and compare their anti-wear performance, the ball-on-flat dry sliding wear tests were conducted under different loads using a reciprocating tribometer. The cross sectional profiles of the wear scar on both materials were drawn using a surface profilometer. The volume loss and the wear rates were calculated depend on the cross sectional area (CSA) of the wear scar. The load-dependent wear results suggested that the anti-wear performance of WA15 was superior to YG8. The examination of worn surfaces from field emission scanning electron microscopy showed that the wear mechanisms of surface damage were mainly brittle fracture and plastic deformation.     

Influence of oxygen on the tool wear in machining

High temperatures generated in machining are known to facilitate oxidation wear. A controlled atmosphere chamber was developed to investigate the effects of oxygen on tool wear and high speed machining tests were conducted on air and in argon. Cemented carbide, cermet and cubic boron nitride tooling was used on alloyed steel, hardened tool steel and superalloy Alloy 718. Machining in argon resulted in higher flank wear, higher cutting forces, and larger tool–chip contact length on the rake face. However, in hard machining, argon atmosphere reduced rake cratering. Transmission electron microscopy of tools worn on air showed formation of nanocrystalline Al₂O₃ film on the rake when machining aluminium containing Alloy 718, while no oxide films was detectable in the other cases.     

低碳钢搅拌摩擦焊用摩擦头的失效研究

选用YG8硬质合金作为摩擦头材料进行低碳钢的搅拌摩擦焊试验。采用游标卡尺测量工具、X射线衍射仪和能谱仪等分析摩擦头在焊接过程中的主要失效形式。结果表明,YG8硬质合金摩擦头在低碳钢的搅拌摩擦焊过程中的主要失效形式为机械磨损、氧化剥落、搅拌针脆性断裂和轴肩变形失效等。引起失效的主要原因是摩擦头长时间的高温高压摩擦,导致粘结相Co分布不均匀或部分扩散流失,严重破坏了硬质合金的骨架模型;失效后摩擦头组织中出现了游离碳和硬脆相Co6W6C,减弱粘结相Co对基体相碳化钨的固溶强化作用,最终导致摩擦头的硬度、强度和耐磨性等下降。     

Mechanical properties of thermal barrier coatings after isothermal oxidation.: Depth sensing indentation analysis

Thermal barrier coatings (TBC) are extensively used to protect metallic components in applications where the operating conditions include aggressive environment at high temperatures. Isothermal oxidation degrades the performance of these coatings, so this work analyses the mechanical properties (Young's modulus, E, and hardness, H) of TBC and its evolution after thermal exposure in air. ZrO₂(Y₂O₃) top coat and NiCrAlY bond coating were air plasma sprayed onto an Inconel 600 Ni base alloy. The TBC were isothermally oxidized in air at 950 °C and 1050 °C for 72, 144 and 336 h. Depth sensing indentation tests were carried out on the ceramic coating to evaluate E and H in the as-sprayed materials and after isothermal oxidation. An approach based on multiple tests at different loads was used to determine size independent apparent E an H. These mechanical properties, measured perpendicular to the surface, clearly decreased after isothermal oxidation as a consequence of microcracking within the ceramic coating.     

Oxidation behavior of porous Ti3SiC2 prepared by reactive synthesis

High-purity porous Ti₃SiC₂ with a porosity of 54.3% was prepared by reactive synthesis and its oxidation behavior was evaluated under air in the temperature range from 400 to 1000 °C. Thermogravimetric analysis and differential scanning calorimetry (TG-DSC), scanning electron microscope (SEM), X-ray diffractometometry (XRD), energy dispersive spectrometer (EDS), Raman spectrum, BET surface area analysis, and pore-parameter testing were applied to the studies of the oxidation kinetics, phase composition, micro morphology, and porous structure parameters of porous Ti₃SiC₂ before and after oxidation. The results showed that the formation of TiO₂ oxidized products with different modifications was the primary factor influencing the oxidation resistance and structural stability of porous Ti₃SiC₂. Cracks were observed in the samples oxidized in the full temperature range of 400-1000 °C because of the growth stress and thermal stress. At 400-600 °C, anomalous oxidation with higher kinetics and the aberrant decrement in pore size and permeability were attributed to the occurrence of severe cracking caused by the formation of anatase TiO₂. At raised temperatures over 600 °C, the cracking phenomena were alleviated by the formation of rutile TiO₂, but the outward growth of the oxide scales detrimentally decreased the connectivity of porous Ti₃SiC₂.     

Research on optimal laser texture parameters about antifriction characteristics of cemented carbide surface

Cemented carbide (YG8) is commonly applied to workplaces where friction and wear are severe. Therefore, improving the surface friction performance is of great significance. Surface micro-texture technology is exactly a feasible method. However, due to high wear resistance and hardness of YG8, it is difficult to process surface texture with accurate feature size by traditional methods. In this paper, four types of groove-shaped textures were etched on the surface of YG8 discs by high peak power UV nanosecond laser. The error of texture width could be controlled within ±5 μm. Friction and wear tests were performed using a standard ball-on-disc configuration to investigate the influence of the texture parameters (width and area ratio of grooved textures) on the friction-reducing and wear-resistance properties under constant load and relative sliding speed. Antifriction mechanism of textures was analyzed and a theoretical model of texture under dry friction condition was presented. As shown in the experimental results, the optimal texture parameters have a good gain effect on friction-reducing and wear-resistance of cemented carbide surface under dry friction and solid lubrication. Friction coefficient was reduced from 0.301 to 0.275 and 0.138, respectively. The theoretical model has good agreement with the experimental data and could provide theoretical support for predicting the optimal parameters of texture.     

Improvement of thermally grown oxide layer in thermal barrier coating systems with nano alumina as third layer

A thermally grown oxide (TGO) layer is formed at the interface of bond coat/top coat. The TGO growth during thermal exposure in air plays an important role in the spallation of the ceramic layer from the bond coat. High temperature oxidation resistance of four types of atmospheric plasma sprayed TBCs was investigated. These coatings were oxidized at 1000 °C for 24, 48 and 120 h in a normal electric furnace under air atmosphere. Microstructural characterization showed that the growth of the TGO layer in nano NiCrAlY/YSZ/nano Al₂O₃ coating is much lower than in other coatings. Moreover, EDS and XRD analyses revealed the formation of Ni(Cr,Al)₂O₄ mixed oxides (as spinel) and NiO onto the Al₂O₃ (TGO) layer. The formation of detrimental mixed oxides (spinels) on the Al₂O₃(TGO) layer of nano NiCrAlY/YSZ/nano Al₂O₃ coating is much lower compared to that of other coatings after 120 h of high temperature oxidation at 1000 °C.     

Investigation of wear and corrosion resistance of nanocomposite coating formed on AZ31B Mg alloy by plasma electrolytic oxidation

Ceramic-WC coatings were prepared on AZ31 B Mg alloy by plasma electrolytic oxidation (PEO) from a phosphate based bath containing suspended tungsten carbide nanoparticles at various process times. Scanning electron microscope results indicated that increase of coating time and incorporation of tungsten carbide into the ceramic coating during the PEO process led to a decrease in the number and diameter of coating pores. Phase analysis showed that the nanocomposite coating was composed of MgO, Mg₃(PO₄)₂ and WC. Tribological properties and corrosion behaviour of uncoated AZ31 B Mg alloy and ceramic coatings were evaluated using a pin-on-disc tribometer and potentiodynamic polarisation technique in 3.5% NaCl solution, respectively. The wear and electrochemical tests showed that wear and corrosion resistance of ceramic-WC nanocomposite coatings were better than ceramic only ones. In addition, wear and corrosion behaviour of coatings improved with increasing the coating time.     

Crack healing and strength recovery of Al2O3/TiC/TiB2 ceramic tool materials

Because ceramic tool materials are sensitive to defects such as microcracks, this paper develops ceramic tool materials with crack healing function to solve this problem. In this paper, Al₂O₃/TiC/TiB₂ ceramic tool materials were prepared by vacuum hot pressing sintering technology. Cracks of different lengths are prefabricated on the surface of the material through Vickers hardness tester. The crack healing of the material was studied by high temperature air heat treatment. According to the recovery of material strength after heat treatment and the change of microstructure, the crack healing effect of the material was judged. The effects of different heat treatment temperature, heat treatment time and crack length on the healing behavior of ceramic materials were mainly studied. Research shows that the surface crack of the material is completely filled and healed by oxidation products. The flexural strength of the specimen with pre-cracked surface is only 24.50% of that of the smooth specimen. After heat treatment at 700 °C for 60 min, the strength of the cracked specimen returns to 91.35% of that of the smooth specimen. The maximum effective crack length for crack healing of this ceramic material is 500 μm. Through micro-morphology and elemental analysis, it is found that the main mechanism of surface crack healing is the filling and healing of cracks by liquid phase oxidation products of titanium diboride, namely boron trioxide and titanium dioxide, thus restoring the flexural strength of the material.