SiC-particulate aluminum composite foams produced by powder compacts: Foaming and compression behavior

The foaming behavior of SiC-particulate (8.6% by volume) aluminum composite powder compacts contained Titanium Hydride blowing agent was investigated by heating above the melting temperature (750°C) in a pre-heated furnace. Aluminum powder compacts were also prepared and foamed using similar compaction and foaming parameters in order to determine the effect of SiC-particulate addition on foaming and compression behavior. The linear expansions of the compacts at various furnace holding times were ex situ determined. Optical and scanning electron microscopy techniques were used to characterize prepared and deformed foams microstructures. The SiC-particulate addition was found to increase the linear expansion and reduce the extent of the liquid metal drainage and cell coarsening of the aluminum compacts. The composite foam samples also showed higher compressive stresses, but a more brittle behavior as compared with aluminum foams.     

Dynamic behavior of HIPed Ti–6Al–4V

The overall dynamic properties of hot isostatically pressed (HIPed) Ti–6Al–4V were throughout investigated. MIL-T-9047G was chosen as a standard material for property comparison due to its best combination of strength and ductility. The elastic constants of HIPed Ti–6Al–4V were measured by resonant ultrasound spectroscopy (RUS) method. Three types of Hopkinson bar tests (constitutive relations tests, strain-controlled specimen tests and hat-shaped specimen tests) were conducted on HIPed material as well as on the standard material to evaluate the high-strain-rate properties of HIPed Ti–6Al–4V. Thick wall cylinder explosion test was conducted to compare the post-critical behavior of baseline material (MIL-T-9047G) and Ti–6Al–4V HIPed material. The texture effect in high-strain-rate properties was checked as the main difference between HIPed (texture free) and standard material (grains elongated along the rod axial direction). The results show that the nonmilled HIPed Ti–6Al–4V has similar yield strength and strain-hardening curve in comparison with the standard material in forging direction but has a lower ductility, which is similar to the ductility of standard material normal to forging direction. The same conclusion also generated from the strain controlled specimen tests. The results that obtained in hat-shaped specimen tests show that HIPed material starts shear localization relatively earlier than standard material. This result is somewhat contradicted with the ballistic testing results that show better ballistic performance for HIPed materials in all three types of penetration tests (flat-ended, conical and long-rod) [see Refs. Nesterenko VF, Indrakanti SS, Goldsmith W, Gu Y. In: Staudhammer KP, Murr LE, Meyers MA, editors. Fundamental issues and applications of shock-wave and high-strain-rate phenomena. Amsterdam: Elsevier Science; 2001. p. 593–600; Nesterenko VF, Indrakanti SS, Brar S, Gu Y. Shock compression of condensed matter. AIP Conf Proc 2000; 505(1): 419–22; Nesterenko VF, Indrakanti SS, Brar S, Gu Y. Key Eng. Mater. 2000; 177-180: 243–8; Nesterenko VF, Goldsmith W, Indrakanti SS, Gu Y. Int J Impact Eng 2003; 28(2): 137–60; Gu Y, Indrakanti SS, Nesterenko VF. Shock compression of condensed matter. AIP Conf Proc 2002; 620(1): 1294–7]. The explanation for this contradiction might be the influences coming from the texture, and other microstructure features such as phase content, grain size distribution and fast shear localization propagation path at the grain boundary and the phase interface.     

Fabrication and characterization of nanostructured Ti6Al4V powder from machining scraps

In recent years researches on properties of nanocrystalline materials in comparison with coarse-grained materials has attracted a great deal of attention. The present investigation has been based on production of nanocrystalline Ti6Al4V powder by means of high energy mechanical milling. In this regard, Ti6Al4V powder was produced by ball milling of machining scraps of Ti6Al4V. The structural and morphological changes of powders were investigated by X-ray diffraction, scanning electron microscopy, and microhardness measurements. The results revealed that ball milling process reduced the size of the coherent-scattering region of Ti6Al4V to approximately 20 nm. Also a remarkable change in morphology and particle size was occurred during ball milling. Moreover, phase evolution during milling was taken into consideration. The as-milled Ti6Al4V powder exhibited higher microhardness comparing to the original samples.     

Sintering mechanisms of blended Ti6Al4V powder from diffusion path analysis

The sintering of master alloy-blended Ti6Al4V powder has been investigated to elucidate the mechanisms of sintering. Both blended powder compacts and diffusion couple samples were investigated using backscattered imaging and energy dispersive analysis to determine the phases present, and the diffusion path for sintering which has not been previously reported for this system. Transient liquid-phase sintering does not occur, and it is shown for the first time that the reason for the rapid sintering of this material in the temperature range of 1000–1150 °C is due to enhanced diffusion kinetics resulting from a combination of the concentration gradient and stress induced by a phase transformation in the ternary system. The results of this study have implications for the development of blended master alloy combinations in other powder metallurgy systems.     

Compression testing of a sintered Ti6Al4V powder compact for biomedical applications

In this study, the compression deformation behavior of a Ti6Al4V powder compact, prepared by the sintering of cold compacted atomized spherical particles (100–200 μm) and containing 36–38% porosity, was investigated at quasi-static (1.6×10⁻³–1.6×10⁻¹ s⁻¹) and high strain rates (300 and 900 s⁻¹) using, respectively, conventional mechanical testing and Split Hopkinson Pressure Bar techniques. Microscopic studies of as-received powder and sintered powder compact showed that sintering at high temperature (1200 °C) and subsequent slow rate of cooling in the furnace changed the microstructure of powder from the acicular alpha () to the Widmanstätten (+β) microstructure. In compression testing, at both quasi-static and high strain rates, the compact failed via shear bands formed along the diagonal axis, 45° to the loading direction. Increasing the strain rate was found to increase both the flow stress and compressive strength of the compact but it did not affect the critical strain for shear localization. Microscopic analyses of failed samples and deformed but not failed samples of the compact further showed that fracture occurred in a ductile (dimpled) mode consisting of void initiation and growth in phase and/or at the /β interface and macrocracking by void coalescence in the interparticle bond region.     

Ti–6Al–4V particle reinforced magnesium matrix composite by powder metallurgy

A novel Ti–6Al–4V particle (TCp) reinforced MB15 magnesium matrix composite, TCp/MB15, was fabricated using powder metallurgy route. Microstructural characterization revealed that a uniform distribution of TCp, good interfacial bond between TCp and the matrix, and a smaller grain-size compared to the unreinforced MB15 were achieved in the composite. Mechanical properties investigation showed the ultimate tensile strength, 0.2% yield strength and elastic modulus of MB15 were markedly increased by the addition of TCp, and the strengthening effect of TCp was better than that of SiC particles. The primary aim of this work was to compare the microstructural and mechanical properties of TCp/MB15 with those of MB15 alloy.     

微波烧结TiC/Ti6Al4V复合材料的高温氧化行为

采用微波烧结法制备TiC/Ti6Al4V复合材料,研究TiC/Ti6Al4V复合材料在550、650和750℃空气中的恒温氧化行为,并对氧化膜的表面、截面形貌及相组成进行了分析。结果表明:TiC/Ti6Al4V复合材料由TiC、ɑ-Ti+β-Ti三种物相组成。随着氧化温度的增加,TiC/Ti6Al4V复合材料的氧化规律由抛物线型转变为直线型,在650℃温度以下,复合材料的氧化产物主要由TiO_2组成,而750℃时氧化层主要有外层极薄的TiO_2、中间层Al_2O_3和TiO_2混合区及大部分内层TiO_2三部分组成。随着TiC含量增加,氧化激活能增大,氧化物粒径减小,TiC/Ti6Al4V复合材料的抗氧化性能也越好。     

置氢Ti6Al4V合金的微观组织演变规律

为研究置氢Ti6Al4V合金的高温加工改性机理,从微观组织的角度对合金进行了对比分析.利用OM、SEM、XRD等研究了置氢对Ti6Al4V合金变形前后微观组织演变的影响.研究结果表明:氢的加入不仅使置氢Ti6Al4V合金中β相比例明显增大,而且改变了α相与β相之间的电势差,在氢含量为0.3%~0.5%两相颜色将发生互换,氢含量增加到0.50%以上时,合金中将出现面心立方结构的δ氢化物;随氢含量的增加,合金超塑拉伸变形后的组织由α+β两相等轴晶粒变为粗大的β晶粒,造成α与β界面的协调能力下降,并改变了合金的变形机制.     

Damage evolution in Ti6Al4V–Al3Ti metal-intermetallic laminate composites

The crack propagation and damage evolution in metal (Ti6Al4V)-intermetallic (Al₃Ti) laminate composites were investigated. The composites (volume fractions of Ti6Al4V: 14%, 20% and 35%) were tested under different loading directions (perpendicular and parallel directions to laminate plane), to different strains (1%, 2%, 3%) and at different strain rates (0.0001 and 800–2000 s⁻¹). Crack densities and distributions were measured. The crack density increases with increasing strain, but decreases (at a constant strain) with increasing volume fraction of Ti6Al4V. Differences in crack propagation and damage evolution in MIL composites under quasi-static (10⁻⁴ s⁻¹) and dynamic (800–2000 s⁻¹) deformation were observed. The fracture stress does not exhibit significant strain-rate sensitivity; this is indicative of the dominance of microcracking processes in determining strength. Generally, the crack density after dynamic deformation is higher than that after quasi-static deformation. This is attributed to the decreased time for crack interaction in high-strain rate deformation. The effect of crack density, as quantified by a damage parameter, on elastic modulus and stress–strain relation were calculated and compared with experimental results.     

A comparative study of the impurity segregation from commercially pure Ti, Ti6Al4V and Ti3Al8V6Cr4Zr4Mo

The surface composition of commercially pure Ti, Ti6Al4V and Ti3Al8V6Cr4Zr4Mo during annealing at different constant temperatures was experimentally investigated. Auger electron spectroscopy was used to monitor the APPHs of the specified elements present on the surfaces. The surfaces of Ti and its alloys were contaminated by oxygen and carbon, and the contamination is attributed to the continual uptake of the background gases, even in the UHV chamber. It was found that mainly C and S segregated at 400 °C, and Cl at higher temperatures (500–630 °C) for commercially pure Ti. However, S was the main segregating species for all three samples. The segregation of Al was measured for the Ti6Al4V and Ti3Al8V6Cr4Zr4Mo samples at higher temperatures. The linear least-square fit method was employed to determine the contribution of pure Ti and TiC from the measured APPH's. The AES fitting confirmed the formation of TiC on the surface at temperatures 400–500 °C.     

Ti、Ti6Al4V和Ti6Al7Nb对成骨细胞生物活性影响的研究

研究Ti、Ti6Al4V和Ti6Al7Nb 3种钛金属表面经喷砂酸蚀处理后的表面形貌、亲水性及对成骨细胞生物活性的影响。在Ti、Ti6Al4V和Ti6Al7Nb 3种钛金属表面进行Al2O3喷砂和盐酸、硫酸混合物酸蚀的表面改性处理(SLA),通过扫描电子显微镜(scanning electron microscope,SEM)观察样品的表面形貌,通过接触角测量仪在显微镜下测量接触角的大小;将SD大鼠成骨细胞以1×104cells/m L密度接种于Ti、Ti6Al4V和Ti6Al7Nb表面后通过MTT活性实验观察成骨细胞在样品表面的增殖,通过SEM观察细胞在样品表面生长的形态,通过碱性磷酸酶(AKP)活性实验,检测成骨细胞的分化能力。Ti、Ti6Al4V和Ti6Al7Nb在经过喷砂酸蚀处理后,表面均呈现出微米级多孔形貌,3种样品均为亲水性表面;细胞在SLA处理后的Ti、Ti6Al4V和Ti6Al7Nb表面增殖良好,细胞伸展显著;其中在Ti6Al7Nb表面细胞的增殖、黏附、分化能力最强。大颗粒喷砂酸蚀技术的表面处理方法能够促进Ti、Ti6Al4V和Ti6Al7Nb的生物活性;经SLA处理的Ti6Al7Nb比Ti和Ti6Al4V表现出更好的生物学活性,成骨细胞在其表面呈现出更好的增殖、黏附及分化能力。     

Ti6Al4V等离子体浸没式离子注入

采用新型等离子体浸没式离子注入技术,对Ti6Al4V合金进行氮离子注入.对注入层的成分、组织和性能的分析表明,注入层中氮浓度的分布具有类高斯分布特征,在注入层中有TiN和非晶态相形成.注入层的显微硬度和摩擦性能得到了明显的改善.     

Experimental and numerical evaluation of forming limit diagram for Ti6Al4V titanium and Al6061-T6 aluminum alloys sheets

The forming limit diagram (FLD) is a useful concept for characterizing the formability of sheet metal. In this work, the formability, fracture mode and strain distribution during forming of Ti6Al4V titanium alloy and Al6061-T6 aluminum alloy sheets has been investigated experimentally using a special process of hydroforming deep drawing assisted by floating disc. The selected sheet material has been photo-girded for strain measurements. The effects of process parameters on FLD have been evaluated and simulated using ABAQUS/Standard. Hill-swift and NADDRG theoretical forming limit diagram models are used to specify fracture initiation in the finite element model (FEM) and it is shown that the Hill-swift model gives a better prediction. The simulated results are in good agreement with the experiment.     

Self-lubricating CrAlVN coatings for turning of Ti6Al4V: oxidation and wear behavior

The titanium alloy Ti6Al4V enables significant performance increases in various branches of industry. Nevertheless, it is difficult to machine, because of its material properties. Due to the low thermal conductivity of titanium, the heat generated while turning Ti6Al4V mainly flows into the tool leading to high temperature loads. In addition, the comparatively low Young's modulus and high yield strength contributes to high mechanical stresses during machining. Temperature active, self-lubricating physical vapor deposition hard coatings appear to be suitable for reducing friction and tool wear during turning of Ti6Al4V compared to the most commonly used uncoated carbide tools. The ability of the coating to form lubricating oxide phases at high temperatures is crucial for this purpose. This paper investigates the oxidation and diffusion behavior of vanadium doped chromium aluminium nitride (CrAlN) coatings after heat treatment at ϑ = 600 °C, ϑ = 700 °C und ϑ = 800 °C in atmosphere as well as the resulting coating properties. The wear behavior of certain coating variants while turning of Ti6Al4V is analyzed.     

Characteristics of wire-electro discharge machined Ti6Al4V surface

Titanium and titanium alloys (e.g., Ti6Al4V) are increasingly used in aerospace and automotive industries, and also used as medical implant material in wide variety of applications. Wire-electro discharge machining (WEDM) is an important non-traditional machining process, widely used for machining a variety of difficult-to-machine materials including titanium alloys with intricate shapes. The process is essentially a thermal process and the nature of surface produced is studied in this paper. It is observed that more uniform surface characteristics are obtained with coated wire electrode. Among the parameters such as time between two pulses, pulse duration, injection pressure, wire speed and wire tension that have more influence on the surface characteristics, the time between two pulses is the most sensitive parameter.     

Selective electrochemical machining of the steel molds in hot isostatic pressing of Ti6Al4V powder

Anodic dissolution is proven to be an effective method to remove stainless steel molds from Ti6Al4V compacts obtained from powder by hot isostatic pressing. Two different working solutions were studied: 2?M NaCl and 2?M NaCl?+?0.05?M Na₂EDTA. While both were capable of removing the steel mold, the latter was also capable of removing the diffusional layer made by the intermetallic phases generated between titanium and steel during the compaction process.     

凝胶注模成形Ti6Al4V钛合金的组织和性能研究

目的 为了实现低成本、低能耗、高效率制备大尺寸复杂形状钛合金的问题,以凝胶注模技术为成形手段,制备近净成形Ti6Al4V合金,并研究其组织及性能.方法 通过溶液包覆法,在Ti6Al4V钛合金球形粉末表面包覆石蜡(PW),分析有机包覆层在凝胶注模过程中的作用机制及流变行为的影响,测定包覆前后不同粉末进行凝胶注模烧结后的组...     

Improved thrombogenicity on oxygen etched Ti6Al4V surfaces

Thrombus formation on blood contacting biomaterials continues to be a key factor in initiating a critical mode of failure in implantable devices, requiring immediate attention. In the interest of evaluating a solution for one of the most widely used biomaterials, titanium and its alloys, this study focuses on the use of a novel surface oxidation treatment to improve the blood compatibility. This study examines the possibility of using oblique angle ion etching to produce a high quality oxide layer that enhances blood compatibility on medical grade titanium alloy Ti6Al4V. An X-ray photoelectron spectroscopy (XPS) analysis of these oxygen-rich surfaces confirmed the presence of TiO₂ peaks and also indicated increased surface oxidation as well as a reduction in surface defects. After 2 h of contact with whole human plasma, the oxygen etched substrates demonstrated a reduction in both platelet adhesion and activation as compared to bare titanium substrates. The whole blood clotting behavior was evaluated for up to 45 min, showing a significant decrease in clot formation on oxygen etched substrates. Finally, a bicinchoninic acid (BCA) total protein assay and XPS were used to evaluate the degree of key blood serum protein (fibrinogen, albumin, immunoglobulin G) adsorption on the substrates. The results showed similar protein levels for both the oxygen etched and control substrates. These results indicate that oblique angle oxygen etching may be a promising method to increase the thrombogenicity of Ti6Al4V.     

Microstructures and mechanical properties of electron beam-rapid manufactured Ti–6Al–4V biomedical prototypes compared to wrought Ti–6Al–4V

This study represents an exploratory characterization and comparison of electron-beam melted (EBM) or rapid manufacturing (RM) of Ti–6Al–4V components (from nominal 30 μm diameter powder) with wrought products. Acicular α and associated β microstructures observed by optical metallography and electron microscopy (SEM and TEM) are compared along with corresponding tensile test and hardness data; including the initial powder particles where the Vickers microindentation hardness averaged 5.0 GPa in comparison with the fully dense, EB manufactured product with an average microindentation hardness ranging from 3.6 to 3.9 GPa. This compared with wrought products where the Vickers microindentation hardness averaged 4.0 GPa. Values of UTS for the EBM samples averaged 1.18 GPa for elongations ranging from 16 to 25%. Biomaterials/biomedical applications of EBM prototypes in direct prosthesis or implant manufacturing from CT or MRI data are discussed in the context of this work, especially prospects for tailoring physical properties through EB control to achieve customized and optimized implant and prosthetic products direct from CT-scans.