封面图片说明

<正>封面图片出自论文"基于气体捕捉法的泡沫Ti-6Al-4V等温发泡规律研究"。为了确定等温发泡温度对泡沫Ti-6Al-4V孔洞状态的影响规律,进行了不同温度的等温发泡试验。这幅图片为经950℃/50 h等温发泡制备的泡沫Ti-6Al-4V(孔隙率为34.8%)孔洞状态扫描电子显微镜照     

气体捕捉法制备泡沫Ti-6Al-4V三明治结构与性能评价

基于气体捕捉法制备泡沫钛三明治结构工艺,对以钢包套+Ti-6Al-4V板+Ti-6Al-4V粉的封装工艺制备的泡沫Ti-6Al-4V三明治结构预制坯进行了900℃下不同变形量的轧制,并进行了950℃/10h的等温发泡。通过SEM对不同状态的三明治结构芯部孔洞状态进行观察和测量,探究了轧制变形量对泡沫Ti-6Al-4V三明治结构预制坯等温发泡行为的影响。结果表明:轧制主要是以沿轧制方向拉长孔洞和增加孔洞连通的方式影响泡沫Ti-6Al-4V三明治结构芯部,且轧制变形量越大越严重,但对孔洞内壁形态及孔洞在垂直于轧向平面内的形态未产生影响。当预制坯轧制变形量为80%时,经等温发泡成功制备了面板厚度为362μm,芯部孔隙率达到40%的泡沫Ti-6Al-4V三明治结构,其在高应变速率下抗压强度达到824.8 MPa,400℃下热导率仅为致密金属的52.8%。     

氢辅助气体捕捉法制备泡沫Ti-6Al-4V及其机理研究

对气体捕捉法制备泡沫Ti-6Al-4V过程中未发泡的坯料进行置氢处理,然后再进行等温发泡。运用阿基米德原理对发泡后坯料孔隙率进行测量。通过OM和SEM对坯料内部微观特征进行观察。研究氢对坯料等温发泡过程的影响规律及作用机制。结果表明:质量分数为0.15%的氢能将坯料最佳发泡温度降低60℃,即在890℃下孔隙率可达到32.88%(体积分数),孔径达到160μm,孔洞分布弥散的泡沫Ti-6Al-4V。主要机理:氢以降低坯料(α+β)/β相转变温度的方式,提高基体内塑性较好的β相比例,并能在一定程度上软化α相,降低坯料高温流变应力,进而降低最佳发泡温度。     

氢化钛预氧化处理和发泡温度对Al-7Si闭孔泡沫铝泡孔结构的影响

采用粉末冶金快速发泡法制备Al-7 Si闭孔泡沫铝,研究使用高导热发泡模具后制备工艺参数对泡沫铝膨胀率、孔隙率、泡孔个数与孔径的影响.结果表明:在450～550℃时对氢化钛预氧化处理1 h可细化颗粒尺寸,提高氢化钛开始分解温度和最大分解速率温度.过度预氧化处理会导致氢化钛释气量下降,获得的试样膨胀率较低.发泡温度的提高有助于提高泡沫铝膨胀率和泡孔个数,对孔隙率和平均孔径影响较小,但温度过高会使得试样顶部低圆度裂纹状泡孔分布范围增加.发泡模具的使用有助于约束膨胀方向,提高冷却过程中孔径均匀程度.粉末冶金快速发泡法可获得均匀泡孔结构泡沫铝.采用450℃预处理90 min的氢化钛作为发泡剂,发泡温度为720℃,发泡时间为160 s时可获得孔隙率为78.1％,孔径为(2.29±0.8)mm,并具有最优泡孔结构的泡沫铝材料.     

真空高温退火对锻态Ti-6Al-4V合金显微组织与超塑性性能的影响

退火处理是改善钛合金显微组织,提高力学性能及超塑成形性能的一种重要工艺。使用真空退火炉在850℃-950℃温度区间内对锻态Ti-6Al-4V合金的进行了高温退火处理,研究了退火态Ti-6Al-4V合金微观组织演变及其在温度为900℃,应变速率为0.01 s^-1时的超塑拉伸性能。结果表明,锻态Ti-6Al-4V合金的初生α晶粒尺寸随真空退火温度的升高而减小,β相比例随真空退火温度升高而增大。当真空退火温度为910℃时,Ti-6Al-4V合金的晶粒尺寸和α相与β相分布较为均匀,其超塑拉伸试验结果表明,该合金表现出最佳的超塑拉伸性能,其拉伸延伸率达到785%,峰值应力仅为26.8 MPa。     

泡沫铝累积叠轧制备方法及孔隙结构研究

以L2纯铝为基体金属,TiH2粉末为发泡剂,通过累积叠轧试验,探索泡沫铝制备的新方法。结果显示,叠轧道次对泡沫铝孔隙率与平均孔径影响显著,叠轧道次越多,孔隙率越高,平均孔径越小;TiH2含量与发泡温度是影响发泡驱动力的主要因素,试验温度范围内,发泡剂含量越大,温度越高,发泡驱动力越强,发泡后孔隙率越高,并且平均孔径也越大。叠轧6道次的L2纯铝,发泡剂含量0.5%(质量分数),在670℃条件下发泡5min,可以获得孔隙率61.4%,平均孔径1.6mm的泡沫铝。上述研究表明,累积叠轧焊是一种有效的泡沫铝制备方法,通过工艺参数的优化,可以获得孔隙均匀,高孔隙率的泡沫铝。     

泡沫钛蠕变发泡动力学研究

通过对基于气体捕捉法制备的泡沫钛发泡过程进行分析,推导出泡沫钛蠕变发泡动力学方程,影响泡沫钛孔隙率的主要因素是发泡温度和基体的蠕变抗力。通过实验获取了不同温度条件下,孔隙率与发泡时间的关系曲线,并建立了其动力学曲线;利用金相显微镜对泡沫钛基体的微观组织进行了分析。研究表明,虽然发泡速率与发泡温度成正比,与基体材料蠕变抗力成反比,但是随着温度的升高,发泡速率并没有一直增加,原因是基体材料的微观组织结构也在发生变化,导致其蠕变抗力随温度的升高先减小后增大,由此证明了上述动力学曲线的合理性。     

Ti及Ti-6Al-4V的水基凝胶注模成形研究

将凝胶注模工艺应用于金属Ti及Ti-6Al-4V合金粉末的坯体成形,研究了高固相含量的Ti粉和Ti-6Al-4V合金粉末的料浆的制备.结果表明,用凝胶注模工艺制备出了固相含量为54ψ%的钛合金粉末料浆和形状复杂的坯体;粉末的颗粒形状是影响料浆固相含量的重要因素,球形粉末配制成的浆料固相含量最高,近球形次之,片状最低;分散剂柠檬酸铵也可以显著提高浆料的固相含量.     

蛋白发泡法制备泡沫陶瓷固化工艺研究

选用蛋清蛋白作为发泡剂, 采用蛋白发泡法制备了高孔隙率的泡沫氮化硅陶瓷. 设计了三种不同固化工艺: 常压固化、恒压固化和高压固化, 固化气压依次升高, 研究了固化气压对泡沫陶瓷开孔率、孔隙形貌和孔径分布的影响. 其中, 恒压固化制品的平均孔径和开孔率最高, 分别为210 μm和78.6%, 且孔径分布比较均匀, 常压固化次之, 高压固化制品开孔率和平均孔径最低. 常压和恒压固化制品为椭球形孔洞, 有一定的排列取向, 而高压固化制品多为规则的球形孔. 随着固化气压的升高, 制品孔壁厚度增加, 高压固化制品的孔壁厚度最高, 其压缩强度接近50 MPa.     

外科植入用Ti-6Al-4V表面微球形粉末烧结过程中的微观结构变化

西班牙学者利用英国设菲尔德Thorton精密铸造公司提供的Ti-6Al-4V髋部植入骨干研究了表面微球形办末烧结过程中的微观结构变化.     

A New Approach for Manufacturing a High Porosity Ti-6Al-4V Scaffolds for Biomedical Applications

Titanium and its alloys are currently considered as one of the most important metallic materials used in the biomedical applications, due to their excellent mechanical properties and superior biocompatibility. In the present study, a new effective method for fabricating high porosity titanium alloy scaffolds was developed. Porous Ti-6Al-4V scaffolds are successfully fabricated with porosities ranging from 30% to 70% using spaceholder and powder sintering technique. Based on its acceptable properties, spherical carbamide particles with different diameters （0.56, 0.8, and 1mm） were used as the space-holder material in the present investigation. The Ti-6Al-4V scaffolds porosity is characterized by using scanning electron microscopy. The results show that the scaffolds spherical-shaped pores are depending on the shape, size and distribution of the space-holder particles. This investigation shows that the present new manufacturing technique is promising to fabricate a controlled high porosity and high purity Ti-6Al-4V scaffolds for hard tissue replacement.     

加热条件对炭泡沫材料孔结构和性能的影响

以AR沥青为原料,利用高压釜在不同恒温条件下制备了炭泡沫,并测定了其孔结构、体积密度、显气孔率、压缩强度、常温热导率以及微晶参数.结果表明:相对于短恒温时间,长恒温时间制得的炭泡沫孔径大(412nm)、显气孔率高(83.82%)、体积密度小(0.34g/cm~3)、压缩强度高(4.92MPa),多孔连通结构更丰富.经过石墨化处理后,石墨泡沫呈现出较高的常温热导率(71.34W/(m·K))和较小的层片间距d_(002)(0.33556nm).石墨泡沫的常温比导热率能达到210(W·(m·K)~(-1)) /(g·cm~(-3)),是铜的5倍,铝的4倍.     

Fabrication of spherical Ti-6Al-4V powder by RF plasma spheroidization combined with mechanical alloying and spray granulation

Spherical Ti-6Al-4V powder was produced by RF plasma spheroidization combined with mechanical alloying and spray granulation. Particle size distribution, morphology, specific surface area, apparent density, flowability, element distribution and content of alloy powders after each stage during the process were investigated. Results show that the obtained spheroidized Ti-6Al-4V alloy powder has dense structure, good sphericity and high spheroidization ratio (98%), moderate particle size (37.8 μm) with narrow distribution. It also has excellent flowability (33.2 s· (50 g)^-1) and apparent density (2.53 g·cm^?3). In addition, elements distribution in the spherical Ti-6Al-4V alloy powder is uniform and most of elements content of it is within the standard of Ti-6Al-4V alloy.     

Hot Isostatic Pressing Modifications of Pore Size Distribution in Plasma Sprayed Coatings

Plasma sprayed coatings contain relatively large amount of pores. This is primarily due to the nature of deposition by the liquid droplets upon impact. This paper reports the modifications made in the pore size distribution of plasma sprayed yttria stabilized zirconia (YSZ) and Ti-6Al-4V/hydroxyapatite (HA) composite coatings following hot isostatic pressing (HIP). The pore size distribution was measured by a mercury intrusion porosimeter (MIP). The results indicated that the YSZ coatings which were HIPed for 1 hour and 3 hours in the temperature range 1000^° to 1200^°C and ∼185 MPa showed a small decrease in the average porosity (∼2.5%) for the 1 hour samples. However, the hardness increased ∼39%, and there was a corresponding increase in the coating density. This was due to reduction of the average pore size in the HIPed coatings. Thus, in the YSZ coatings, the pores responded to HIP by a general breakdown of large pores to smaller ones and effectively forming many 'new' interparticle contacts. Whilst the overall porosity was reduced marginally, the increase in physical property like hardness was significant because of the increase in interparticle and inter-lamellae contacts following HIP treatment. In the Ti-6A1-4V/HA composite coatings, the reduction of pores is most significant amongst the small pores. The porosity of the as sprayed 20 wt% HA composite was ∼19%. This value was reduced to 17% for the sample HIPed at 1,000%C for 1 hour. Although the reduction was relatively minor, the interesting aspect was the drastic reduction of small pores less than 0.3 μm. The average pore diameter was observed to increase from 0.1676 μm in the as sprayed coating to 0.787 μm in the sample HIPed at 1,000^°C, as a result of the elimination of the micro-pores. Physical properties such as microhardness, Young's modulus and density increased substantially. This is believed to be aided mainly by the plastic deformation of the ductile Ti-6A1-4V phase during HIP. Thus modification of the pore size distribution or even average pore size can elicit substantial improvement in the properties in two different material coating, albeit the difference in the manner the modification occur.     

煤基炭泡沫孔结构调控

以肥煤镜质组富集物为前驱体, 采用高压渗氮法制备煤基炭泡沫, 研究了发泡温度、发泡压力和发泡时间对炭泡沫孔结构的影响。利用SEM观察炭泡沫的孔胞形貌, 同时利用Nano Measurer分析软件统计SEM照片孔胞直径分布和孔喉直径分布以及平均孔径。结果表明: 微孔塑料成核理论可以定性解释炭泡沫的孔结构变化趋势。发泡温度的升高导致成核密度增加, 同时导致气体在胶质体的溶解度降低, 不利于孔胞长大。发泡压力的增大导致炭泡沫的孔胞密度增加, 临界成核半径降低, 同时加剧了热聚合反应, 导致胶质体的粘度增大, 不利于孔胞长大。发泡时间的延长会使热聚合更加充分, 影响胶质体粘度, 进而影响孔结构。     

Microstructure evolution during solid-state foaming of titanium

Solid-state foaming of commercially pure titanium was achieved by high-temperature expansion of high-pressure argon bubbles trapped in titanium by a powder-metallurgy technique. The foaming step was performed at constant temperature, where creep of the titanium matrix controls pore expansion, or during thermal cycling around the β allotropic temperature, which induces transformation superplasticity of the matrix. Superplastic foaming led to significantly faster pore growth and higher terminal porosity than isothermal creep foaming. During thermal cycling, the porosity remains nearly fully closed to the surface of the specimen up to the point where the maximum porosity (44%) is obtained, despite the presence of some internal pore coalescence. With continued thermal cycling, pores coalesce further by fracture of thin interpore walls and pores finally open to the surface, but without a significant increase in the amount of total porosity. The remnants of these walls result in a jagged pore morphology. Under isothermal conditions, pores remain small, equiaxed and unconnected with no pore surface roughness. However, after long annealing times, they exhibit faceting due to surface diffusion.     

Fatigue behavior of Ti-6Al-4V cellular structures fabricated by additive manufacturing technique

Porous titanium and its alloys have been considered as promising replacement for dense implants, as they possess low elastic modulus comparable to that of compact human bones and are capable of providing space for in-growth of bony tissues to achieve a better fixation. Recently, the additive manufacturing (AM) method has been successfully applied to the fabrication of Ti-6Al-4V cellular meshes and foams. Comparing to traditional fabrication methods, the AM method offers advantages of accurate control of complex cell shapes and internal pore architectures, thus attracting extensive attention. Considering the long-term safety in the human body, the metallic cellular structures should possess high fatigue strength. In this paper, the recent progress on the fatigue properties of Ti-6Al-4V cellular structures fabricated by the AM technique is reviewed. The various design factors including cell shapes, surface properties, post treatments and graded porosity distribution affecting the fatigue properties of additive manufactured Ti-6Al-4V cellular structures were introduced and future development trends were also discussed.     

粉料形貌对多孔Al2O3支撑体的影响

采用球形和非球形Al2O3粉料，探讨扩出成型中粉料颗粒形貌对多孔支撑体的性能的影响，用压汞仪，扫描电子显微镜（SEM）等于手段分析了1450和1500℃下4h烧成的试样，结果表明，规则球表Al2O3粉料可以按球形密堆积的形成支撑体，使气孔率变小，不利于制备高气孔率的支撑体，并且球表Al2O3粉料颗粒自身的多孔性使制得的试样出现孔径的双峰分布，要在较高烧成温度下可以消除，但该双峰分布结构对透气度没有影响，球形颗粒间的接触面积减少，不利不烧结和支撑体强度，但是，球形粉料形成的孔的形状规则，易于使支撑体整体均匀化。