Fabrication of Ti-6Al-4V Scaffolds by Direct Metal Deposition

Direct metal deposition (DMD) is a rapid laser-aided deposition method that can be used to manufacture near-net-shape components from their computer aided design (CAD) files. The method can be used to produce fully dense or porous metallic parts. The Ti-6Al-4V alloy is widely used as an implantable material mainly in the application of orthopedic prostheses because of its high strength, low elastic modulus, excellent corrosion resistance, and good biocompatibility. In the present study, Ti-6Al-4V scaffold has been fabricated by DMD technology for patient specific bone tissue engineering. Good geometry control and surface finish have been achieved. The structure and properties of the scaffolds were investigated by X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), and tension test. The microstructures of laser-deposited Ti-6Al-4V scaffolds are fine Widmanstätten in nature. The tensile and yield strengths of the as-deposited Ti-6Al-4V were 1163 ± 22 and 1105 ± 19 MPa, respectively, which are quite higher than the ASTM limits (896 and 827 MPa) for Ti-6Al-4V implants. However, the ductility of the as-deposited sample was very low (～4 pct), which is well below the ASTM limit (10 pct). After an additional heat treatment (sample annealed at 950 °C followed by furnace cooling), both strength (UTS ～ 1045 ± 16, and YS ～ 959 ± 12 MPa) and ductility (～10.5 ± 1 pct) become higher than ASTM limits for medical implants.     

Viscoelastic flow between two infinite parallel porous plates,one plate oscillating and the other plate in uniform motion

The problem of viscoelastic incompressible flow between two infinite parallel porous plates, one oscillating and the other in uniform motion, was studied and an iteration method was used to solve the fluid dynamical equations. The solution obtained is valid for small values of the elastic parameter S. The effects of the flow parameters S and σ (the Reynolds number) on the velocity distribution and on the shearing stress at the plates are presented graphically.     

Dispersion of contaminant in oscillatory flows

Summary An extension of the Aris-Barton method of moments is presented for the study of statustucal behaviour of dispersion of contaminant molecules in oscillatory flows inside uniform conduits. The main idea is to replace the constant pressure gradient which causes the flow simply by the time-dependent one, and then investigate the effects of the amplitude and frequency of the pressure pulsations on the dispersion process. The technique incorporates the case of the time-independent flow also, and gives an exact analysis of the central moments of the distribution of the cloud of contaminant, which are valid for all times after the injection. The general theory is applied to oscillatory laminar flows in tubes, and between parallel plates.With 5 Figures     

Compact multiple-valued multiplexers using negative differentialresistance devices

Quantum electronic devices with negative differential resistance (NDR) characteristics have been used to design compact multiplexers. These multiplexers may be used either as analog multiplexers where the signal on a single select line selects one out of four analog inputs, or as four-valued logic multiplexers where the select line and the input lines represent one of four quantized signal values and the output line corresponds to the selected input. Any four-valued logic function can be implemented using only four-valued multiplexers (also known as T-gates), and this T-gate uses just 13 devices (transistors) as compared to 44 devices in CMOS. The design of the T-gate was done using a combination of resonant tunneling diodes (RTD's) and heterojunction bipolar transistors (HBT's) with the folded I-V characteristic (NDR characteristic) of the RTD's providing the compact logic implementation and the HBT's providing the gain and isolation. The application of the same design principles to the design of T-gates using other NDR devices such as resonant tunneling hot electron transistors (RHET's) and resonant tunneling bipolar transistors (RTBT's) is also demonstrated     

Microstructure of laser clad Ni- Cr- Al- Hf alloy on a γ′ strengthened ni- base superalloy

Alloys and coatings for alloys for improved high temperature service life under aggressive atmo-spheres are of great contemporary interest. There is a general consensus that the addition of rare earths such as Hf will provide many beneficial effects for such alloys. The laser cladding technique was used to produce Ni-Cr-AI-Hf alloys with extended solid solution of Hf. A 10 kW CO₂ laser with mixed powder feed was used for laser cladding. Optical, scanning electron (SEM) and scanning transmission electron (STEM) microscopy were employed to characterize the microstructure of alloys produced during laser cladding processes. Microstructural studies revealed grain refinement, considerable in-crease in solubility of Hf in the matrix, Hf-rich precipitates, and new metastable phases. The size and morphology of γ′ (Ni₃Al) phase were discussed in relation to its microchemistry and the laser processing conditions. This paper will report the microstructural development in this laser clad Ni-Cr-AI-Hf alloy. Formerly Visiting Assistant Professor, Department of Mechanical and Industrial Engineering, University of Illinois at Urbana-Champaign.     

Spinodal decomposition of a Co-Ti-Nb alloy

The microstructural evolution on aging a Co-3 wt pct Ti-2 wt pct Nb alloy has been followed by transmission electron microscopy and diffraction to show that the solid solution decomposed by the spinodal mode. The strengthening observed has been correlated with the differences in lattice parameters of the coexisting phases. The several stages of coarsening have been documented to yield information about their kinetics and morphological changes. Formerly Visiting Assistant Professor, Department of Mechanical and Industrial Engineering, University of Illinois at Urbana-Champaign, 1206 West Green Street, Urbana, IL 61801, is with .     

Laser-clad Ni70Al20Cr7Hf3 alloys with extended solid solution of Hf: Part II. Oxidation behavior

Ni-Al-Cr-Hf coatings with an extended solid solution of Hf were fabricated by laser cladding a premixed powder with a Ni-Al-Cr-Hf ratio of 70∶20∶7∶3 onto a substrate of RENé 80. Isothermal oxidation tests in slowly flowing air reveal that the claddings have a lower weight-gain rate than the substrate itselt. Microchemistry and microstructures of the oxidized samples were examined using scanning electron microscopy (SEM) and Auger electron spectroscopy (AES). The improvement in oxidation resistance is believed to be at least partially due to the formation of large numbers of hafnium-rich oxide spikes penetrating the unoxidized sample.     

Chemical Investigations on Celastrus paniculatus Seed Oil I

Fatty acid compositions of four lipid fractions of Celastrus paniculatus seed namely normal triglycerides (20.2%), polar triglycerides (44.4%), polar nonglyceridic ester (23.5%), and nonpolar nonglyceridic ester (11.9%), have been determined by gas liquid chromatography. Percentage contents of major component acids in these fractions are: palmitic, 25.1, 42.0, 12.7, 58.2; stearic, 6.7, 4.5, 15.8; oleic, 46.1, 24.8, 4.7, 14.2; linoleic, 15.4, 14.7, 10.0; and linolenic, 3.0, 13.1, 43.0, respectively. The major molecular species constituting the normal triglycerides are: palmitooleopalmitin, 6.8%; palmitooleostearin, 5.6%; palmitodiolein, 14.7; palmitooleolinolein, 7.0%; stearodiolein, 6.1%; triolein, 8.0% and dioleolinolein 7.6%. Lipolysis of the polar triglyceride indicated as high as 59.6% of saturated acids linked to the 2-position of glycerol.