Microstructure and corrosion properties of laser cladding MoNi based alloy coatings

Mo-based alloys are widely used for their excellent wear and corrosion resistance as well as high temperature resistance.Mo-NiCrBSi and Mo-Ni alloy coatings were prepared on 1020 water wall tube by laser cladding technology in the present study.The microstructure and phase compositions were analyzed by means of the scanning electron microscopy(SEM),energy-dispersive spectroscopy(EDS)and X-ray diffractometry(XRD).The corrosion properties of the coatings were evaluated by an electrochemical experiment at room temperature in 3.5 wt.%NaCl electrolyte.With increasing content of Mo,the structure homogeneity in Mo-Ni coatings deteriorated,the grain size increased,the average hardness and the corrosion resistance declined,due to the more content of harmful phases.Compared to the Mo-Ni coatings,the overall performance was better for the Mo-NiCrBSi,which had the higher hardness contributed by the element B and Si as well as the better corrosion resistance due to the addition of Cr.     

包渗法制备硅化物涂层的结构形貌及形成机理

采用包渗法在C-103铌合金基体上制备MoSi2涂层,通过X射线衍射、扫描电镜和能谱分析等手段研究涂层表面、截面形貌以及氧化后涂层结构变化,并分析硅化过程中涂层的形成机理。研究结果表明：包渗法制备硅化物涂层是通过反应扩散形成的,硅化过程服从抛物线规律;该涂层为复合结构：MoSi2相为主体层;以NbSi2相为主、并含少量Nb5Si3相的两相为过渡区;Nb5Si3相为扩散层。在高温氧化环境下,涂层表面生成致密的非晶氧化层,有效地阻止了氧向涂层内扩散。     

碳纳米管增强钛铝基复合材料的组织与性能

采用激光熔铸技术制备碳纳米管增强钛铝合金复合材料,对铸块的组织、结构及断口形貌进行分析。结果表明：铸块的基体主相为TiAl,Ti3Al合金,碳纳米管细化了基体组织晶粒,适量的碳纳米管提高了材料的硬度和韧性,w（CNTs）=1．5％时,复合材料显微硬度（738HV）与相同条件下基体合金硬度（647HV）相比提高了14％,材料断口为韧性断裂。     

Microstructure and properties of high emissivity coatings

A new coating on lining in industrial furnace for energy saving has been developed. Properties and microstructure of the coatings were revealed by emissivity instrument,X-ray diffraction (XRD),transmission electron microscope (TEM) and scanning electron microscope (SEM),respectively. The result indicates that the emissivity of coatings is higher than 0.90 and the thickness of coatings is about 200 μm. ZrO2,Cr2O3 and SiC in the coating benefit practical applications of coatings at high temperature with du-ra...     

Physical simulation of hot deformation of TiAI based alloy

In order to establish a model between the grain size and the process parameters, the hot deformation behaviors of Ti-49.5Al alloy was investigated by isothermal compressive tests at temperatures ranging from 800 to 1 100 ℃ with strain rates of 10^-3-10^-1 s^-1. Within this range, the deformation behavior obeys the power law relationship, which can be described using the kinetic rate equation. The stress exponent, n, has a value of about 5.0, and the apparent activation energy is about 320 J/mol, which fits well with the value estimated in previous investigations. The results show that, the dependence of flow stress on the recrystallized grain size can be expressed by the equation: σ = K1 drex^-0.56. The relationship between the deformed microstructure and the process control parameter can be expressed by the formula: lgdrex= -0.281 1gZ 3.908 1.     

镁锂合金表面磷酸盐转化膜研究

针对镁锂合金耐腐蚀性差的问题,采用无铬磷酸盐转化技术在室温条件下在镁锂合金表面形成磷酸盐转化膜,以改善镁锂合金的耐腐蚀性.利用极化曲线、析氢实验、SEM、EDS对磷酸盐转化膜的耐腐蚀性和结构进行研究.结果表明,室温成膜的最佳时间是9 min;磷酸盐转化膜使镁锂合金的腐蚀电位正移,腐蚀电流降低,并显著降低了镁锂合金的析氢速度,提高了镁锂合金的耐腐蚀能力;磷酸盐转化膜由花形团簇组成,主要成分为Mg、O、P以及少量的C、Mn、K、Na、Al.硬度与结合力分析表明,磷酸盐转化膜硬度明显高于镁锂合金,并与镁锂合金基体结合力良好,能够起到保护镁锂合金的作用.     

Effects of HIPing pressure on microstructures and properties of TiAl alloy

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Thermodynamics and kinetics of in-situ formation of TiAl3/7075 composites

The thermodynamics and kinetics of the reaction between Titanium powder and 7075 aluminum alloy were investigated to assess the possibility of preparing TiAl₃/7075 composites by in-situ synthesis method. Results show that Ti and Al melt can form TiAl₃ spontaneously, which is considered as a reinforced phase of the matrix. Measurements such as XRD, SEM, and EDX were performed to characterize the as-synthesized samples, and results confirmed the formation of TiAl₃ in aluminum matrix composites. The reactive kinetics was controlled by three main factors, which are the system temperature, particle size of Ti, and the thickness of external diffusion layer.     

Microstructure and properties of sputtered thermal barrier coatings

A 3 kW radio frequency (RF) magnetron-sputtering unit was used to produce zirconia ceramic coatings on hollow turbine blades and vanes, which had been deposited a NiCrAlY bond coat layer by cathodic arc deposition. The NiCrAlY coating surface was shot-peened, and the residual stress in the bond coat layer and the effects of heat treatment on the residual stress are presented. After shot peening porosities and microgaps disappear in the NiCrAlY bond coat, the whole depth profile is residual compressive stress. Coarseness tests show that the roughness value (Rz) decreases from 16.4 to 3.3 μm. The microstructure and phase composition of the coatings were investigated using electron probe microanalysis (EPMA) and X-ray diffraction (XRD). The results show that tho/NiCrAlY bond coat is composed of γ and Cr phases, and the Al2O3 scales are formed near the interface between the ZrO2 ceramic layer and the NiCrAlY bond coat. No degradation occurred to RF sputtered ceramic coatings after oxidating at 1150℃ for 100 h, heating at 1150℃ for 5 min and then air-cooling for 500 thermal cycles.     

碳纤维和尼龙纤维对TiAl合金型壳退让性的影响

为了改善TiAl合金精密铸造用氧化锆陶瓷型壳的退让性,利用电子万能试验机和扫描电子显微镜对添加不同含量碳纤维和尼龙纤维后的型壳退让性进行了测试.结果表明,添加少量碳纤维可以提高型壳湿强度并降低型壳室温和高温干强度,但当所添加碳纤维的质量分数达到10%后,会同时提高型壳的三种强度.当尼龙纤维的质量分数处于10%以内时,型壳三种强度均会降低.当碳纤维的质量分数达到5%时,型壳的湿强度和室温干强度可分别提高51. 9%和20. 7%,高温干强度降低8. 5%,同时改善了型壳的退让性并降低了铸件的裂纹倾向.     

Microstructure and superelasticity of porous NiTi alloy

The microstructure, porosity, phase composition and superelasticity (SE) in porous NiTi alloys produced by elemental powder sintering are examined by SEM, image analysis and XRD. It is found that it is feasible to produce porous NiTi alloy by elemental powder sintering, and the porosity of sintered porous NiTi alloy is in the range of 36.0 %-41.5 %. The pores are interconnected and the microstructure is sponge-like. Meanwhile, porous NiTi alloy has good SE. XRD patterns show that there is no pure Ni in alloy sintered at 1223 K-9 h. Compared with the biomedical criteria for choice of implanting materials, porous NiTi alloy is satisfying to a great degree.     

Microstructural evolution of TiAl base alloy during three-stepped thermo-mechanical treatment

ＴｉＡｌｂａｓｅａｌｌｏｙｓｈａｖｅｂｅｉｎｇｃｏｎｓｉｄｅｒｅｄａｓｐｒｏｍｉｓｉｎｇｈｉｇｈｔｅｍｐｅｒａｔｕｒｅｓｔｒｕｃｔｕｒａｌｍａｔｅｒｉａｌｓ.Ｂｅｉｎｇｓｔｕｄｉｅｄｆｏｒｎｅａｒｌｙ 2 0ｙｅａｒｓ,ｔｈｅｆｕｎｄａｍｅｎｔａｌｏｆＴｉＡｌｂａｓｅａｌｌｏｙｓｈａｖｅｂｅｅｎｕｎｄｅｒｓｔｏｏｄ(ｍｏｒｅｃｌｅａｒｌｙ) ,ａｎｄｔｈｅｉｒｍｅｃｈａｎｉｃａｌｐｒｏｐｅｒｔｉｅｓ ,ｅｓｐｅ ｃｉａｌｌｙｔｈｅｒｏｏｍｔｅｍｐｅｒａｔｕｒｅｄｕｃｔｉｌｉｔｙ ,ｈａｖｅｂｅｅｎｇｒｅａｔｌ…     

AZ31B合金的铸轧组织

利用金相及扫描电镜对AZ31B合金热模拟和铸轧样组织结构进行研究。研究结果表明：在不同应变量下,热模拟样品的晶粒粒度均随应变速率的增加而减小,而当其他条件相同时,变形量越大晶粒粒度越小,冷却强度降低,合金呈典型铸态组织;利用铸轧技术生产的AZ31B合金,当应变速率一定时,随着初始铸轧温度的降低,铸轧态板材的树枝晶粒度逐渐减小;而在初始铸轧温度一定时,随着应变速率的增大,铸轧态合金板材的树枝晶粒度也逐渐减小;而随着应变速率的提高,树枝晶沿轧向呈流线状排列的趋势增强;在AZ31B合金铸轧过程中,轧制力不能太大,否则容易引起热裂。     

AlFeCuCrCoMo_x系高熵合金的组织性能

为了研究AlFeCuCrCoMo_x系高熵合金的组织性能,利用等离子弧堆焊方法制备了AlFeCuCrCoMo_x系高熵合金,并测试了其硬度、耐磨性与热膨胀性能.结果表明,高熵合金组织为枝晶和枝晶间组织.当Mo含量较低时,高熵合金主要组织为单一BCC结构.随着Mo含量的增加,其组织逐渐转变为BCC+FCC结构.当Mo含量为1. 5 mol时,高熵合金重新转变成简单BCC结构.随着Mo含量的增加,高熵合金的硬度和磨损量总体上呈现先升高后降低的趋势.当Mo含量为1. 5 mol时,高熵合金的硬度和磨损量达到最大.     

粘结TbDyFe合金的组织及磁致伸缩性能

粘结TbDyFe合金是由TbDyFe粉末与粘结剂混合后压制成型并固化而成的。TbDyFe合金的原始组织是由RFe2基体相和富稀土析出相以及RFe3相组成。均匀化热处理后，富稀土相和RFe3相减少。粘结TbDyFe合金的磁致伸缩性能与TbDyFe粉末颗粒尺寸的大小，粘结剂的粘度系数，粉末与粘结剂的配比，预应力的大小以及颗粒调整有很大关系。试验结果表明，TbDyFe粉末颗粒尺寸的大小和颗粒调整对粘结TbDyFe合金的磁致伸缩性能影响较大。在一定尺寸范围内，粘结TbDyFe合金的磁致伸缩性能随TbDyFe粉末颗粒尺寸的增大而提高；在压型过程中由于外加磁场作用使颗粒调整，即使得磁畴取向，从而提高了磁致伸缩性能。     

FeTiNbMoW高熵合金的组织和性能

为了研究一种能够吸收γ射线的含W合金的性能,按照等摩尔比设计了一种FeTiNbMoW五组元高熵合金.利用X射线衍射仪、扫描电子显微镜、能谱仪、显微硬度计、密度仪和万能力学试验机对合金的晶体结构、微观组织、成分、硬度、密度和压缩性能进行了分析.结果表明,FeTiNbMoW高熵合金组织由简单BCC固溶体基体和分布其上的少量金属间化合物组成.BCC结构的实际晶格常数为0.315 5 nm,组织形貌为典型枝晶组织.枝晶硬度和枝晶间硬度分别为830.05和793.04 HV.合金的实测密度为10.7 g/cm3,略高于其理论值10.21 g/cm3.室温下合金的抗压强度和对应塑性应变分别为604 MPa和3.19%.合金呈粉末性断裂,其断裂机制为解理断裂.     

激光熔覆Fe基非晶／纳米晶复合涂层的组织与性能

对以激光熔覆方式在45钢基体上制备的FeNiSiBVRE非晶涂层进行激光晶化,制备非晶／纳米晶复合涂层.利用X射线衍射仪、透射电镜、扫描电镜和磨损试验机研究非晶／纳米晶复合涂层的组织与性能.研究结果表明,涂层存在着分层结构,组成相有晶化相、非晶相和纳米晶相;涂层底部和顶部的显微组织由大量的稀土树枝晶、板条状硼化物和粒状碳化物组成,涂层中部的显微组织是由大量的纳米晶相镶嵌在非晶基体上构成.与没有进行激光晶化的非晶涂层相比,涂层的耐磨损性能下降.其磨损机制以粘着磨损和剥层磨损为主.     

等离子喷涂梯度涂层的显微组织结构和性能

针对低散热发动机主要部件铝活塞顶部制备热障涂层的需要，用等离子喷涂法在铝基体上制备出梯度涂层，对其性能与显微组织结构进行了研究．抗热震实验结果表明，梯度涂层具有较高的结合强度．金相显微观测结果表明，梯度热障层结构致密，由基体至涂层表面。形成5种无宏观结合界面的成分呈梯度变化的组织结构．     

Analysis of diffusion bond interface of TiAl base alloy with Ti, TC4 alloy and 40Cr steel

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Ni基合金表面激光熔覆Co基合金的组织与性能

用同步送粉法，在Ni基合金表面上制取了Hoegan aes Co基合金（HMSP 2537）的激光熔覆层。利用金相显微镜，扫描电镜，X射线衍射仪，显微硬度计对熔覆层的组织，相结构，硬度进行了分析和测试。结果显示，熔覆层的不同区域组织及性能不均匀；激光输入功率增大，枝晶间距增大，硬度降低。