具有梯度特性的齿科修复复合材料制备及表征

本工作的目的是研究原生牙齿的梯度力学性能,制备聚合物渗透陶瓷网络(PICN)复合材料,模拟天然牙的力学行为。采用纳米压痕法测定了牙釉质和牙本质的弹性模量和维氏硬度。结果表明,原生牙齿的力学性能具有梯度特性。树脂填充部分烧结硅铝酸钠、氧化铝和氧化锆的力学性能有很大差异。通过逐步改变陶瓷组分,实现了力学性能的梯度变化。一种是纳米玻璃相硅铝酸钠/微米α氧化铝层合复合材料。陶瓷坯体的烧结温度为700℃,保温时间分别为2、4和6 h。对复合材料的抗弯强度、断裂韧性、弹性模量和硬度进行了测试,结果表明:硅铝酸钠/微米α氧化铝复合材料的弹性模量和硬度呈现梯度特性。另一种是3Y-TZP/微米α氧化铝层合复合材料。坯体烧结温度分别为1150和1200℃,保温时间为2h。其弹性模量和硬度均呈现梯度特性。SEM观察表明,过渡区形成了相互咬合的网络结构。与普通均质材料不同,本研究制备的复合材料具有各向异性。因此,复合材料的力学性能更接近于原生牙齿。     

超高强钴基块体非晶合金的组成设计

块体非晶合金是一类具有高强度、高硬度和大弹性极限的无序金属材料,其优异的力学性能是目前先进金属材料领域研究热点之一,如何提高材料的强度是材料研究领域永恒的主题。系统地总结了已知具有超高强度的一类块体非晶合金材料——钴基块体非晶合金的成分、热学稳定性及力学性能;同时研究了不同非晶合金的断裂强度与其弹性常数、硬度和特征温度的关联。研究结果表明：在非晶合金体系中杨氏模量、维氏硬度、玻璃转变温度与断裂强度之间都存在较好的线性变化关系。基于以上结果,本课题组提出了超高强钴基块体非晶合金的组成设计方法,即选取具有强共价键特性的非金属元素和高模量、高熔点过渡金属元素与钴元素进行组合。     

Mechanical Response of Triply Periodic Minimal Surface Structures Manufactured by Selective Laser Melting with Composite Materials

It is of significance but remains a pivotal challenge to simultaneously enhance the strength and lightweight levels of porous structures. We provide an innovative strategy to improve the strength of porous structures with unchanged lightweight levels by applied composite materials. Selective laser melting (SLM) is convenient for integral forming of materials and structures. Hence, in this study, the research about the mechanical response of triply periodic minimal surfaces (TPMS) porous structures with 316L and composites fabricated by SLM was conducted. The compression test and finite element method (FEM) were used to characterize mechanical properties. The composite structures exhibit enhanced elastic modulus, yield strength, unvaried lightweight level and refined grain microstructure, which are difficult to realize for porous structures made by pure 316L materials. The elastic modulus, yield strength, plateau stress and energy absorption of composites were 3187.50, 67.73, 15.24 and 17.09 MJ/m³, respectively.     

Determination of Young's modulus and Poisson's ratio for coatings

Designing thin-film coatings to meet engineering needs requires the knowledge of accurate mechanical properties of the coatings. Young's modulus and Poisson's ratio are two basic mechanical properties of materials, which should be conveniently measured. This paper reports a direct and non-destructive method for the measurement of the Young's modulus and Poisson's ratio of a thin-film coating and its substrate based on the extended Hertz theory for the contact of coated bodies. The theory is used to analyze load-displacement data from a spherical indentation in the elastic range, in which the substrate effect is intrinsically modeled. The Young's modulus and Poisson's ratio are determined at the same time through minimizing the difference between the measured and specially defined modified Young's moduli. Two sets of validation experiments are also reported. This new method does not require any assumptions on pressure distribution and Poisson's ratio and can be easily incorporated into current indentation analysis systems.     

雾化气体对热喷涂NiCr涂层弹性模量的影响

准确评价热喷涂涂层的弹性模量对于确保工业构件的服役安全性与耐久性是十分重要的,但是利用传统技术很难进行评价。尽管纳米压痕技术可以表征涂层局部的弹性模量,但是无法反映出孔隙、裂纹等缺陷对涂层弹性模量的影响。而脉冲激励技术（IET）是一种用于评价块体材料弹性模量的简单、准确方法。本文结合相对法,利用IET可对热喷涂涂层的弹性模量进行评价。首先构建了涂层、基体、涂层/基体复合体系的弹性模量间的解析关系,然后通过测量制备涂层前后试样的弹性模量,即可获得涂层的弹性模量。以Q235钢基体/NiCr涂层为研究对象,研究了雾化气体对NiCr涂层弹性模量的影响。结果表明以空气作为雾化气体制得的NiCr涂层（NiCr-Air）的弹性模量高于以N2作为雾化气体制得的NiCr涂层（NiCr-N2）的弹性模量,其原因在于NiCr-Air中形成了Ni(Cr2O4)氧化物增强NiCr合金的层状复合材料,且这种层状复合结构有利于提高NiCr涂层的弹性模量。     

The Microstructure and Mechanical Properties of SiC Reinforced Magnesium Based Composites by Rheocasting Process

In the present study, rheocasting process was adopted to synthesise AZ91D composites reinforced with silicon carbide (SiC) particulates. Particle-matrix interfacial reaction, distribution of particles, hardness and mechanical properties of as cast and T4 heat-treated alloy-composites were reported. The rheocast composite materials reveal uniform distribution of SiC particulates. The composite materials show an increase in hardness and elastic modulus compared to unreinforced rheocast alloy. Τhe ultimate tensile strength and ductility of composite materials were lower than those of the unreinforced alloy. 15 μm particles-composite shows significantly higher elastic modulus than the 150 μm SiC particles-composite.     

Determination of elastic moduli for a spherical specimen by resonant ultrasound spectroscopy

Resonant ultrasound spectroscopy (RUS) is based on the principle that mechanical resonant response of solids depends on its elastic moduli, shape and density. Elastic moduli or the other properties can be identified from resonant frequencies as inverse problem. In this study, the method to determine elastic moduli of a spherical specimen without information of resonant mode was described. We confirmed that resonant frequencies have to be measured under condition of free surface, and adequate number of resonant frequencies used in calculation needs enough number to include the sensitive mode to Poisson's ratio. By this method, we determined elastic moduli of BK-7 glass. The calculated frequencies from the elastic moduli determined by this technique had good agreement with the measured, the absolute accuracies for the Δf was less than 0.4%.     

冷热循环对挤压铸造AlNp/Al复合材料室温力学性能的影响

研究了3种不同温差冷热循环处理对AlN颗粒增强铝基复合材料室温力学性能的影响。结果表明冷热循环处理能明显改善复合材料的室温力学性能。其中大幅循环处理改善材料抗拉强度的效果最好，平均值较压铸态时提高54％；中幅循环处理工艺在改善复合材料屈服强度和弹性极限方面效果最佳，平均值分别提高了75％和79％；而小幅循环处理则从整体上提高了材料室温力学性能的稳定性。试验还发现中小幅温差循环处理使材料的弹性模量较压铸态的明显提高，平均值提高27％～44％；而大幅循环的弹性模量值仅与压铸态的相近。     

薄壁内外齿杯形件多轮行星旋压成形

针对内外齿结构杯形件现行工艺中存在的材料利用率低、力学性能低等问题,提出了一种新型的成形工艺方法。利用有限元与试验相结合的方法,对这种新型成形工艺的机理进行研究,分析了内外齿杯形件的旋压成形特点,研究了内齿、外齿以及侧壁区域的残余应力、等效应变分布规律,预测了缺陷最易出现的区域,利用有限元仿真确定工艺参数,并进行了工艺试验。结果表明:在成形的起始位置处,坯料的外齿区域因受拉而最容易产生断裂缺陷,内齿区域的外侧金属受三向拉应力而发生变形,是产生裂纹缺陷的另一个主要位置;内、外齿旋压件的变形在圆周方向上呈现周期性。     

Substrate stiffness determination in curved layered composites using bending methods

Bending tests are conveniently used to determine mechanically the elastic modulus of materials. However, in the case of asymmetrical, coated specimens that exhibit warping due to mismatch in thermal or isothermal expansion of the individual layers, non-linear deformation behaviour is present and the stiffness evaluation becomes difficult with this method. A bending test procedure is outlined which uses a flat composite specimen obtained by joining two spherically curved layered specimen along their coating surfaces. The elastic behaviour of the joint specimen essentially reflects the stiffness of the substrate since the thin coatings and the thin adhesive layer are located close to the neutral specimen axis of the bending test. The method is illustrated using warped anode-substrate/electrolyte sheets of solid oxide fuel cells. The results of ring-on-ring tests with anode substrate or electrolyte under tension and with the joint specimen are presented and discussed.     

Micro mechanical properties of n-Al2O3/Ni composite coating by nanoindentation

A new type of nano test system was introduced, the test principle and the indentation data analysis method were described. It was used to test the micro mechanical properties, such as hardness, elastic modulus and indentation creep property of n-Al2O3/Ni composite coating on steel prepared by brush plating, and the variety of mechanical properties with coating thickness was researched. The results show that the mechanical properties are basically identical within the whole coating, the hardness and modulus decrease in the defect fields, especially within the dendritic crystals, whereas the mechanical properties are not influenced greatly at the interspaces among dendritic crystals. The average hardness and elastic modulus of n-Al2O3/Ni coating are 6.34 GPa and 154 GPa respectively, and the hardness is 2.4 times higher than that of steel and the indentation creep curve of n-Al2O3/Ni coating is similar to that of the uniaxial compression creep, and the creep rate of steady-state is about 0. 104 nm/s. These results will supply useful data for process improvement, new type material development and application expansion.     

特种模型材料弹性模量的测量

层状复合方法适用于测定高阻尼材料的弹性模量。特种模型材料由环氧树脂、增韧剂、固化剂和金属粉构成。用层状复合方法测定了特种模型材料的弹性模量，得到的数据分散性小。特种模型材料的弹性模量随着金属粉的增加而增加。     

细晶富铝Al/Fe复合材料动态力学性能及本构关系

利用分离式霍普金森杆对通过热压烧结法制备得到的细晶富铝Al/Fe复合材料进行了动态力学性能测试,得到了应变率为100~2300 s-1范围内材料的应力-应变曲线,并与准静态条件下(0.01 s-1)的力学性能作了对比。结果表明:随着应变率增加,材料强度提高,塑性下降,应变率为2300 s-1时的屈服强度与弹性模量分别为准静态时的7.8和2.3倍。对材料断口形貌进行了分析,断裂方式由脆性解理断裂、沿晶断裂和韧窝断裂共同组成。根据试验所得数据,构建了改进型一维弹脆性损伤本构模型,得到了试样断裂失效前的动态本构方程及式中参数的率相关特性。改进后的本构模型与实验数据吻合良好。     

自修复金属搪瓷高温防护涂层

搪瓷涂层作为一种惰性涂层,能与大多数金属零部件相容并提供优异的腐蚀防护效果。但搪瓷的高温软化及本征脆性限制了其在高温以及热冲击等苛刻环境下的服役。总结了国内外解决搪瓷涂层烧结温度与服役温度相矛盾、涂层热循环时易剥落等问题的最新进展:首先介绍了通过复合陶瓷颗粒以及对搪瓷/陶瓷界面反应的调控,实现提高涂层使用温度的同时不改变其熔炼和烧结温度的方法体系;接着分析了影响搪瓷涂层抗热震剥落性能的因素(包括搪瓷釉热膨胀系数、涂层/基体界面结合、搪瓷釉力学性能等)。基于搪瓷的硅氧网络基本结构,从热物理性能以及力学性能角度改性等方案仅能在有限范围内提高其抗热震剥落能力的现实,最后提出了发展自修复金属搪瓷高温防护涂层,从根本上解决搪瓷开裂与剥落的问题。     

Accuracy of Young’s Modulus of Thermal Barrier Coating Layer Determined by Bending Resonance of a Multilayered Specimen

The Young’s modulus of individual layer in thermal barrier coating (TBC) system is an important mechanical property because it allows determining the parameters of materials mechanics in the TBC system. In this study, we investigated the accuracy of the evaluation method for the Young’s modulus of a TBC layer according to the first bending resonance of a multilayered specimen comprising a substrate, bond coating, and TBC. First, we derived a closed-form solution for the Young’s modulus of the TBC layer using the equation of motion for the bending vibration of a composite beam. The solution for the three-layered model provided the Young’s modulus of the TBC layer according to the measured resonance frequency and the known values for the dimensions, mass, and Young’s moduli of all the other layers. Next, we analyzed the sensitivity of these input errors to the evaluated Young’s modulus and revealed the important inputs for accurate evaluation. Finally, we experimentally confirmed that the Young’s modulus of the TBC layer was obtained accurately by the developed method.     

Damage evolution in compacted graphite iron during thermomechanical fatigue testing

Thermomechanical fatigue properties of a compacted graphite iron in an out of phase configuration are investigated for different maximum temperatures and mechanical strain ranges. Furthermore, the stress–strain hysteresis loops are analysed, and, in particular, the unloading modulus, i.e. the elastic modulus measured during specimen unloading, is obtained from each cycle. This material parameter has earlier been explicitly related to the amount of microcracking in cast irons. The results show that the unloading modulus linearly declines with the numbers of cycles in all tests performed. In addition, the rate of change of the unloading modulus is closely related to the number of cycles to failure. Accordingly, it is concluded that microcracks are independently propagated by fatigue until a point of rapid crack linking resulting in ultimate failure. This is supported by microstructural analyses consisting of optical microscope images taken at different stages throughout the life of a specimen.     

Effects of line and passivation geometry on curvature evolution during processing and thermal cycling in copper interconnect lines

A simple theoretical analysis for curvature evolution in unpassivated and passivated copper interconnect lines on a silicon substrate is proposed. A layer consisting of copper and oxide lines is modeled as a homogenized composite that has different elastic moduli and thermal expansion coefficients in two different directions, i.e. along and across the lines, due to the anisotropic line geometry. These effective thermoelastic properties of the composite layer are approximated in terms of volume fractions and thermoelastic properties of each line using standard composite theory. This analogy facilitates the calculation of curvature changes in Damascene-processed copper lines subjected to chemical–mechanical polishing and/or thermal cycling. The effects of line height, width and spacing on curvature evolution along and across the lines are readily extracted from the analysis. In addition, this theory is easily extended to passivated copper lines irrespective of passivation materials by superimposing the curvature change resulting from an additional layer. Finite element analysis has been used to assess the validity of the theoretical predictions; such comparisons show that the simple theory provides a reasonable match with numerical simulations of curvature evolution during the Damascene process in copper interconnects for a wide range of line and passivation geometry of practical interest.     

Multi-scaled polymer-based composite materials synthesized by mechanical alloying

Multi-scaled composite materials are of great importance, because they exhibit higher mechanical properties than those attained using conventional fillers or polymer blends. In this work, multi-scaled composite materials based on ultra-high-molecular weight polyethylene (UHMWPE), quasicrystals, polyimide and bronze are investigated for use in the moving parts of machines, gears, bearings, and sliding elements. The main object is to investigate the process of fabricating such composite materials, and to check if these materials are reproducible and reliable to an industrial extent. The specimens were prepared using a high-energy planetary mill. When milled with bronze, the quasicrystalline phase was dissolved into an intermetallic solid solution; milling with polymers showed to conserve the quasicrystalline phase, whereas the crystallization of UHMWPE was achieved during the milling process. Tribological study of consolidated samples showed an increase in the wear resistance for the bronze-containing composite materials. In comparison with pure UHMWPE, the polyimide-based specimen exhibited higher strength and hardness. This work has demonstrated the possibility of producing composite materials with acceptable and reliable properties using the mechanical alloying technology.     

Processing and mechanical properties of porous 316L stainless steel for biomedical applications

Highly porous 316L stainless steel parts were produced by using a powder metallurgy process, which includes the selective laser sintering（SLS） and traditional sintering. Porous 316L stainless steel suitable for medical applications was successfully fabricated in the porosity range of 40%-50% （volume fraction） by controlling the SLS parameters and sintering behaviour. The porosity of the sintered compacts was investigated as a function of the SLS parameters and the furnace cycle. Compressive stress and elastic modulus of the 316L stainless steel material were determined. The compressive strength was found to be ranging from 21 to 32 MPa and corresponding elastic modulus ranging from 26 to 43 GPa. The present parts are promising for biomedical applications since the optimal porosity of implant materials for ingrowths of new-bone tissues is in the range of 20%-59% （volume fraction） and mechanical properties are matching with human bone.     

Mechanical properties of an iron oxide formed by corrosion in reinforced concrete structures

The paper deals with elastic properties of iron oxides formed in reinforced concrete structures. Due to the difficulty to perform mechanical tests on the real oxides presented in the form of (multiple) laminated stratums, the elastic modulus of iron oxides remains unknown. Young’s moduli of porous compact “synthetic oxides” in powder form, obtained in laboratory conditions, were measured from both acoustic measurements and oedometric tests. The elastic modulus of the compact polycrystalline iron oxide is deduced with respect to two models, a micromechanical one and a Hertz’ theory. The full method is validated on a well-known material, the alumina.