含有闭孔的镍基合金涂层微观结构及性能

利用等离子喷涂和重熔技术制备多孔型镍基自熔性合金涂层,采用扫描电镜、显微硬度计、材料试验机、热膨胀仪等设备对涂层的微观组织、热膨胀系数和压缩过程中的力学性能进行分析。结果表明,涂层中存在封闭孔洞,大部分呈近似球形,直径在30~100μm;孔隙率由0.53%上升至30.6%时,涂层材料的弹性模量下降69.5%,弹性变形范围上升68.7%;在40~220℃的范围内,多孔涂层的平均线膨胀系数随着孔隙率的增加而下降。近球形闭孔的存在提升了原有材料的弹性变形范围,降低了热膨胀系数,使其可以实现低膨胀、高回弹的功能。     

多孔YSZ涂层的制备和可磨耗性

采用等离子喷涂方法在Ni718合金表面制备氧化钇稳定氧化锆（YSZ）涂层,通过在YSZ喷涂粉末中分别加入10%,30%和50%（质量分数,%）表面包覆TiO₂的聚苯酯材料,涂层平均孔隙率从原来的2.1%分别提高到12.3%,28.5%和29.7%,孔隙的平均直径从原来的4.2 μm分别变为14.4,18.5和25.4 μm.随着孔隙的增多,涂层的表面洛氏硬度下降,同时涂层在刮磨过程中的摩擦力和摩擦系数下降.当孔隙率由2.1%上升到30%左右时,涂层在刮磨过程中的磨耗质量上升3倍左右,相对应的转动销质量损失下降约50%.结果表明,孔隙率的提高使得涂层的可磨耗性上升.     

孔隙率对Mo／Cu复合材料热物理性能的影响

采用添加不同含量造孔剂并结合固相烧结方法制备出4种不同孔隙率的Mo/Cu合金试样,测试了其热膨胀系数和热导率λ.结果表明,孔隙率对Mo-Cu合金λ值影响很大.随孔隙率的增加,材料的热导率急剧下降:在一定孔隙率范围内,钼铜合金的平均热膨胀系数随孔隙率的增加而增加,当孔隙率超过一定范围后,其热膨胀系数开始出现下降趋势.对孔隙率影响Mo-Cu合金热物理性能的机制进行了分析和探讨,并对热导率的理论计算作了一定推导计算.     

折弯铝纤维多孔材料的制备与能量吸收

以φ0.15 mm的6061铝合金丝为原材料,通过弹簧机切割成折弯铝合金短纤维,利用特制圆柱形模具,采用真空热压烧结技术制备了孔隙率为60%、70%、80%的折弯铝纤维多孔材料。对折弯铝纤维多孔材料进行压缩性能测试。结果表明,压缩应力-应变曲线可分为3个阶段:初始非线性弹性变形阶段、伪平台阶段和致密化阶段。应力-应变曲线光滑,几乎未产生屈服现象。折弯铝纤维多孔材料的能量吸收值随应变的增加而增大,能量吸收效率先增大后下降;随着孔隙率的降低,多孔材料的能量吸收能力增大,能量吸收效率的峰值上升。     

Gd2 O3 -Yb2 O3 -Y2 O3 -ZrO2 热障涂层材料的热物理性能

目的通过多元稀土氧化物掺杂改性YSZ,提高传统热障涂层的性能。方法使用化学共沉淀法制备不同掺杂量的Gd2O3-Yb2O3-Y2O3-Zr O2(GYYZO)材料,并分别使用冷等静压-烧结和等离子喷涂工艺制备块材和涂层。通过测试块材的热导率和热膨胀系数,分析评价材料的热物理性能。对高温退火处理后的涂层进行X射线衍射分析,评价不同成分涂层的高温相稳定性。结果氧化锆基材料的热导率和热膨胀系数随总掺杂量升高而降低。氧化锆中稀土氧化物总掺杂量为5.5%~9.84%(摩尔分数)时,在1000℃下的热导率为1.25~1.56 W/(m·K),相对8YSZ材料下降了22%~37.5%;在200~1300℃的热膨胀系数为(10~11.1)×10-6/K,与传统8YSZ材料相当。在1400℃长时间退火处理后,低掺杂量GYYZO涂层中的单斜相含量明显低于8YSZ涂层。结论多元稀土氧化物掺杂改性氧化锆材料具有良好的高温相稳定性、低热导率和适当的热膨胀系数,可以作为高性能热障涂层的备选材料。     

氧化铝增强镍基合金涂层的组织与耐冲蚀磨损性能研究

采用等离子喷涂(APS)方法制备了用Ni包Al作为过渡层材料,球磨法混合G112和不同含量的Al2O3粉末作为面层材料的金属-陶瓷涂层。用扫描电镜(SEM)、X射线衍射仪(XRD)对涂层显微组织和相结构进行了分析,用图像分析系统测试了涂层孔隙率,并对涂层在冲蚀磨损试验机上以30°、60°和90°冲蚀角进行了冲蚀磨损试验。结果表明,随Al2O3含量增加涂层的耐冲蚀磨损性能先上升后下降,18%wt.AlO时耐冲蚀性能最好,其升降规律与冲蚀角度无关而与孔隙率密切相关。     

烧结保温时间对堇青石多孔陶瓷性能的影响

采用常压烧结工艺在1450℃制备了孔隙率为40%左右的堇青石多孔陶瓷.结果发现随着烧结保温时间的延长气孔隙率基本保持不变,堇青石多孔陶瓷的晶粒逐渐长大;同时弹性模量与抗压强度均有下降的趋势,且变化趋势基本一致.烧结保温时间从2h延长到14h,对应材料的弹性模量和抗压强度分别从2.93GPa,89MPa降到2.70GPa和70MPa.随保温时间的延长,热膨胀系数随之下降;烧结保温14h材料的平均热膨胀系数(RT～1000℃)降到1.7×10-6/℃.     

参数对超音速等离子喷涂高炉风口Cr_2O_3-TiO_2涂层性能的影响

为了研制一种致密、结合强度高的高炉风口用Cr_2O_3-TiO_2复合涂层,研究了工艺参数对超音速等离子喷涂Cr_2O_3-TiO_2涂层结合强度和孔隙率的影响。确定了涂层致密度和结合强度最佳时的工艺参数。利用图形分析软件和涂层的截面显微组织照片计算涂层的孔隙率,通过拉伸实验测定涂层的结合强度。结果表明,随着喷涂参数(喷涂距离、喷涂功率、送粉率)的增大,涂层的结合强度先上升后下降,而涂层的孔隙率呈相反趋势。喷涂距离是影响涂层的孔隙率和结合强度的最主要因素,喷涂功率稍次之,送粉率的影响力最小。参数范围在喷涂功率64～66 kW、喷涂距离98～105mm、送粉率33～36 g/min时,涂层结合强度最高,孔隙率最低。     

Al基金属玻璃涂层孔隙特性的精确表征及对其腐蚀行为的影响规律

选用Al86Ni6Y4.5Co2La1.5铝基非晶粉体材料,采用自研的低温超音速喷涂系统,在ZM5表面制备了具备良好耐蚀性能的铝基金属玻璃涂层,分析了涂层的孔隙类型及成因,优选出X射线三维成像法测定了涂层孔隙率,表征了涂层孔隙几何特征,阐明了孔隙对涂层腐蚀行为的影响规律。结果表明,涂层主要包含宏观型、层间型、微球型和微细型四类常规孔隙缺陷;涂层孔隙率基本小于1%且沿厚度方向上变化不大,孔隙呈近球形,尺寸均小于10μm,尤以5μm左右居多;不同孔隙率的涂层均呈现出较宽的自钝化区间,自腐蚀电位较为接近,腐蚀电流密度与孔隙率正相关,大尺寸、贯穿型、边界处的个别特殊孔隙是导致涂层腐蚀失效的根本原因。     

热喷涂Fe基非晶涂层耐腐蚀性与孔隙率研究进展

热喷涂Fe基非晶合金涂层的综合性能优异,特别是在耐磨、耐腐蚀方面具有传统晶体材料无可比拟的优势,因而广泛应用于材料表面的防护领域。然而热喷涂涂层为典型的层状结构,涂层内部会存在一定量的孔隙,致使涂层耐腐蚀性能下降。首先介绍了热喷涂Fe基非晶涂层的腐蚀机理及其影响因素,总结了热喷涂涂层孔隙产生的机制、分类和影响因素。接着重点介绍了孔隙与热喷涂Fe基非晶涂层耐腐蚀性之间关系的研究进展。最后,通过对热喷涂涂层的形成过程与孔隙形成机理进行分析,粒子铺展变形能力差是显著影响涂层形成时粒子相互嵌套叠加和变形能力的主要原因。所以,Fe基非晶涂层可以从改变喷涂粉末成分和粒度、第二项粒子加入及喷涂工艺参数优化等措施,来改善粒子铺展变形能力,提高致密度。采用激光快速表面重熔技术对涂层微表层进行快速重熔处理,同样可以达到降低涂层孔隙率、提高涂层耐腐蚀性的目的。     

Upward modulus trend in NiAl and NiFeAl single crystals

Dynamic Young modulus, torsion modulus and elastic energy dissipation were measured in Ni_56.2Fe_0.3Al_43.1Ta_0.3Mo_0.1 (NiAl crystal) and Ni_56.6Fe_12.3Al_30.2Hf_0.6(Al₂O₃)_0.3 (NiFeAl crystal). The elastic constant C′=(C₁₁−C₁₂)/2 has in both alloys a positive temperature derivative: (dC′/dT)>0 from 150 K up to 1300 K. The elastic energy dissipation exhibits a Debye-like peak whose activation energy is 2.36±0.05 eV in NiAl and 1.98±0.09 eV in NiFeAl. The peak is described as a Zener’s pair reorientation.     

Influence of high-energy impact actions on the elastic and anelastic properties of martensitic Cu–Al–Ni crystals

The influence of high-energy impact shock-wave loading on the microplasticity and macroscopic performance of the Cu–Al–Ni crystals in the β₁′ martensitic phase has been studied. Elastic and anelastic properties of quenched and aged polyvariant single crystals before and after impact shock-wave loading were measured in the temperature range 80–300 K, at a frequency of about 100 kHz in the strain amplitude-independent and amplitude-dependent ranges by means of the composite oscillator technique, and in the MHz frequency range using the pulse–echo technique. High-velocity impact loading of the specimens was realised by plane shock-waves with stress pulses with a duration of 2·10⁻⁶ s and stress amplitudes up to 5 GPa. A pronounced influence of impact shock-wave loading on the elastic and anelastic properties of the β₁′ martensite has been observed. A strongly marked softening of the material and an enhancement of damping properties are revealed up to the highest stress pulse amplitudes. This behaviour differs fundamentally from the one observed in ‘ordinary’ fcc metals. Changes of the defect structure induced by shock-wave loading, which may be responsible for the observed phenomena, have been discussed.     

Dislocation contribution to modulus defect in nanocrystalline pure metals

The characteristic properties of dislocations in nanocrystalline pure metals are discussed in detail. It is considered that nanocrystalline metals prepared by inert gas condensation and compaction method or gas deposition method would contain dislocation densities equivalent to almost one dislocation in each grain, in general. Modulus defect expected from these dislocations is estimated to be roughly 1%. Further, a sensitivity of dislocation pinning effect to a number of point defects introduced in the specimen, is shown to be smaller by a factor of more than 10⁻⁶ in nanocrystalline metals, than in coarse-grained metals. These figures seem to be in reasonable agreement with recent results of low-temperature irradiation experiments.     

Elastic and anelastic properties of Marval 18 steel

Marval 18 is a precipitation hardened steel with particularly high hardness and low creep, presently used for constructing parts of the interferometers for the detection of gravitational waves in the experiments VIRGO and LIGO. The elastic moduli have been measured in samples subjected to the same treatments as the parts of the interferometer VIRGO. In addition, the anelastic spectra of samples subjected to different thermal treatments have been measured between 50 and 350 K. It is found that, in the absence of plastic deformation, the elastic energy loss coefficient under flexural vibrations around 1 kHz can vary by more than one order of magnitude depending on the thermal treatments, and is dominated by the thermoelastic effect. The main reason for such strong variations is supposed to be the dependence of the thermal conductivity on the average sizes and distances between the precipitate particles.     

Monoclinic phases and stress-relief conditions in (1 − x)Pb(Mg1/3Nb2/3)TiO3–xPbTiO3 solid solutions

A comparative study on heterophase states in perovskite-type solid solutions of (1 − x)Pb(Mg_1/3Nb_2/3)TiO₃–xPbTiO₃ is carried out for compositions near the morphotropic phase boundary. The conditions for mechanical stress relief at elastic matching of phases are analysed at x = const in a wide temperature range. The heterophase states concerned with the presence of the intermediate monoclinic phase are interpreted using the domain state–interface diagrams calculated for x = 0.28, 0.32 and 0.34. It is shown that optimum volume fraction parameters of the domains in the monoclinic phase of the B type are varied in relatively wide ranges and promote complete stress relief with cubic–monoclinic phase coexistence. Two scenarios of stress relief at x = 0.32 are considered in connection with different heterophase states (either tetragonal–monoclinic of the B type or tetragonal–monoclinic of the C type) in a wide temperature range. Possibilities of elastic matching of two polydomain phases (tetragonal–monoclinic of the B type) with almost equal relative widths of the domains in these phases are shown for x = 0.34. The active role of domains of the monoclinic phases in stress relief and forming the planar unstrained interfaces is discussed.     

Measurement of the elastic modulus of dental pieces

Understanding the mechanical properties of human teeth is important to clinical tooth preparation and to the development of restorative materials. Particularly, the elastic modulus of materials used in restoration of dental parts subjected to endodontic treatment must be compatible with the original tooth. The major difficulty to measure mechanical properties of biological materials is, in general, the geometry of the specimen. Actually, even when there are different methodologies to determine the elastic modulus, samples with flat and parallel faces of uniform section are usually required. Dental parts not only do not fulfil this condition, but also constitute a composite material formed essentially by enamel and dentin with quite different elastic moduli. In this work the elastic moduli of canine and pre-molar teeth, measured by using piezoelectric excitation at high frequency, are presented. The measuring procedure considers the tooth as a composite, that is, gives a mean value according to the complex distribution of enamel and dentin in the different cross-sections of the specimen. Results are compared with Young’s modulus of enamel and dentin obtained by indentation techniques.     

Internal friction and elastic properties of the high pressure-induced phases of solid C60

Solid C₆₀ is a new promising material made from giant high-symmetric carbon clusters. Though C₆₀ molecules are extremely stable at ambient conditions, heat treatment under high pressures induces transformations to other phases, in which some weak van der Waal-type bonding between C₆₀ molecules is replaced with covalent sp³ bonds. Many new C₆₀ high pressure phases (HP) demonstrate a set of unique physical properties including mechanical and elastic ones. This paper is an analytic review of the experimental measurements of the elastic and dissipative properties of solid C₆₀ (from C₆₀ single crystal to C₆₀ ultrahard phase).     

Snoek relaxation in a copper-precipitated alloy steel

We studied the effect of thermal embrittlement of a steel containing 1.29 at% copper on the Snoek relaxation. The hardness increased with isothermal aging at 723 K and decreased after showing a maximum. Hardness change is governed by bcc–copper clusters precipitated from the ferrite iron crystal. Using a forced-vibration torsion-pendulum method, we studied the internal-friction spectrum and recovery of the maximum relaxation strength after quenching from 723 K. We observed a broad nonsymmetrical spectrum which apparently consists of three Debye peaks. With higher hardness, the recovery rate increased. We interpreted our results in terms of Nowick’s theory of interstitial/substitutional-solute interactions. For recovery, we used the Cottrell–Bilby–Harper t^2/3 model.     

Ab initio lattice dynamics of Ni2MnX (X = Sn, Sb) magnetic shape memory alloys

In this study, we present the results of first principles calculations of elastic constants and phonon properties of nickel-manganese based magnetic shape memory compounds Ni₂MnSn and Ni₂MnSb in stoichiometric composition. The plane wave basis sets and pseudopotential method within spin-polarized generalized gradient approximation (σ-GGA) scheme of the density functional theory is applied. In investigation of the phonon dispersion spectra, linear response technique of the Density Functional Perturbation Theory is used. Phonon softening is observed in dispersion spectra at the transverse acoustic mode (TA₂) in [ζ ζ 0] direction as an indication of the structural instability of these systems to shear deformation. The vibrational instability of Ni₂MnSb system is larger than that of Ni₂MnSn yielding negative phonon frequencies. This vibrational anomaly is also verified by the low shear modulus and large elastic anisotropy ratio. The minority spin Fermi surfaces of both systems exhibit strong nesting features.     

Changes in the thermoelectric power of a Ni base superalloy induced by elastic and plastic strain

Induced changes in the thermoelectric power (TEP) of the Inconel 718 by elastic and plastic strain have been previously reported by López Cuéllar et al. [1]. Now, in this work, the TEP of a nickel-based superalloy Waspaloy with different heat treatments has been followed during stressing tests. In all cases plastic deformation has been attained. TEP measurement variations of ∼160 nV/°C have been attained for a certain heat treatment that produces the desirable γ′ phase, and low changes of TEP are observed for the treatment that does not produce γ′. Like for the Inconel 718, results indicate that TEP of the Wasploy is clearly affected by the elastic and plastic strain induced during tests. The previously proposed model to describe the change in TEP induced by the strain in specimens of Inconel 718 [1], is validated with the Waspaloy superalloy in this work. Thus, these results confirm that the TEP technique is a powerful tool to detect non-desirable states and levels of strain in alloys containing γ′ phase like the Waspaloy and Inconel superalloys.