Diffusion coefficients for modeling the heat treatment of Ti-6Al-4V

Values of the diffusivity of aluminum and vanadium that can be used for engineering-oriented calculations of the diffusional growth of primary alpha during the heat treatment of Ti-6Al-4V were established using diffusion couples consisting of various Ti-Al-V alloys. After taking compositional influences into account using thermodynamic correction factors, the pertinent diffusivities in the ternary alloy were found to be approximately 80 pct of those previously estimated from tracer or impurity (binary) diffusion experiments. This work was conducted as part of the in-house research of the Metals Processing Group of the Air Force Research Laboratory’s Materials and Manufacturing Directorate.     

Deformation and recrystallization behavior during hot working of a coarse-grain,nickel-base superalloy ingot material

The deformation and dynamic recrystallization behavior of Waspaloy-ingot material with coarse, columnar grains was established using isothermal uniaxial and double-cone compression tests. Testing was conducted along different test directions relative to the columnar-grain microstructure at supersolvus temperatures (1066 °C and 1177 °C) and strain rates (0.005 and 0.1 s⁻¹), which bracket typical ingot-breakdown conditions for the material. The flow behavior of axial samples (i.e., those compressed parallel to the columnar-grain direction) showed an initial strain-hardening transient followed by steady-state flow. In contrast, the stress-strain curves of samples upset transverse to the columnar grains exhibited a peak stress at low strains, whose magnitude was greater than the steady-state flow stress of the axial samples, followed by flow softening. The two distinct flow behaviors were explained on the basis of the solidification texture associated with the starting ingot structure, differences in the kinetics of dynamic recrystallization revealed in the double-cone tests, and the evolution of deformation and recrystallization textures during hot working. Dynamic recrystallization kinetics were measurably faster for the transverse samples as well as specimens oriented at ∼45 deg to the forging direction, an effect partially rationalized based on the initial texture and its effect on the input rate of deformation work driving recrystallization. Despite these differences, the overall strains required for dynamic recrystallization were comparable to those measured previously for fine-grain (wrought) Waspaloy. However, the Avrami exponents (∼2 to 3) were somewhat higher than those for wrought material (∼1 to 2), an effect attributable to the particle-stimulated nucleation in the ingot material.     

Parathyroid hormone-related protein expression in vascular smooth muscle of spontaneously hypertensive rats: evidence for lack of response to angiotensin II

OBJECTIVE: We studied the expression of parathyroid hormone (PTH)-related protein in vascular smooth muscle cells of spontaneously hypertensive rats (SHR) using Wistar-Kyoto (WKY) and Sprague-Dawley rats as normotensive controls. METHODS: Aortae from 4- and 18-week-old SHR versus age-matched WKY and Sprague-Dawley rats were excised to obtain total RNA or smooth muscle cells. The cells were subcultured in Dulbecco's Modified Eagle's Medium containing 10% fetal calf serum, then serum-deprived for 72 h and stimulated with 0.1 micromol/I angiotensin II. PTH-related protein, c-myc and angiotensin II type qa receptor (AT1aR) messenger (m)RNA levels were measured by Northern blot, using total RNA extracted by phenol/chloroform. The effects of PTH-related protein(1-34)NH2 intravenous injections on arterial blood pressure and the heart rate were studied in anesthetized SHR and WKY rats. RESULTS: The Northern blots showed a significantly higher abundance of PTH-related protein mRNA in aortae of SHR versus WKY rats in the prehypertensive state but no significant difference in adult animals. In cultured aortic smooth muscle cells, angiotensin II induced a four- to sixfold increase in PTH-related protein mRNA levels in smooth muscle cells from normotensive animals, but failed to elicit a significant response in smooth muscle cells derived from SHR in either the prehypertensive or the hypertensive state. This lack of response to angiotensin II in SHR smooth muscle cells was not due to decreased expression or responsiveness of the AT1aR, since SHR smooth muscle cells had more AT1aR mRNA than Sprague-Dawley smooth muscle cells, and angiotensin II-induced activation of c-myc was faster and greater in smooth muscle cells derived from 4- or 18-week-old SHR than in Sprague-Dawley smooth muscle cells. In contrast, PTH-related protein(1-34)NH2 induced a long-lasting dose-dependent hypotensive and tachycardic response in both SHR and WKY rats, indicating that SHR retained responsiveness to the vasodilator. CONCLUSIONS: PTH-related protein gene expression in response to angiotensin II is impaired in SHR arteries. A deficiency in this potent local vasodilator may contribute to the development and/or maintenance of arterial hypertension in this model.     

Quantitative measurements of FPGA utility in special and general purpose processors

We present experimental results on FPGA use in special and general purpose processors, using as case studies a computational accelerator for gene sequence analysis, an integer implementation of the DLX microprocessor and a real-time signal processor for rocket telemetry. All these devices have been successfully prototyped, and are now completely functional. We present detailed analysis of our experience with FPGAs in these machines, describing savings in chip count, power consumption, area, and cost. For all quantitites except cost, measured savings were typically an order of magnitude improvement over discrete IC implementations. References     

Dynamic-coarsening behavior of an α/β titanium alloy

The dynamic-coarsening behavior of Ti-6Al-4V with an equiaxed α microstructure was established via isothermal hot-compression testing of cylindrical samples cut from an ultra-fine-grain-size (UFG) billet. Compression experiments were conducted at 900 and 955 °C, strain rates between 10⁻⁴ and 1 s⁻¹, and imposed true strains between 0 and 1.4. Following deformation, quantitative metallography revealed marked coarsening of the primary α particles at low strain rates (10⁻⁴ and 10⁻³ s⁻¹). The dynamic-coarsening rate followed rⁿ vs time kinetics, in which n was between 2 and 3, or behavior between those of bulk-diffusion and interface-reaction controlled. An examination of the temperature and strain-rate dependence of theoretical coarsening rates, however, strongly suggested that bulk diffusion (with n=3) was more important. The dynamic-coarsening behavior was also interpreted in the context of the observed plastic-flow behavior. At low strain rates, high values of the strain-rate sensitivity (m>0.5) and the overall shape of log stress-log strain rate plots indicated that the majority of the imposed strain was accommodated by grain-boundary sliding (gbs) and only a small amount via dislocation glide/climb processes. In addition, an analysis of the flow hardening that accompanied dynamic coarsening indicated that the flow stress varied approximately linearly with the α particle size, thus providing support for models based on gbs accommodation by dislocation activity in grain-mantle regions.     

Armstrong databases for functional and inclusion dependencies

An Armstrong database is a database that obeys precisely a given set of sentences (and their logical consequences) and no other sentences of a given type. It is shown that if the sentences of interest are inclusion dependencies and standard functional dependencies (functional dependencies for which the left-hand side is nonempty), then there is always an Armstrong database for each set of sentences. (An example of an inclusion dependency is the sentence that says that every $\text{MANAGER}$ is an $\text{EMPLOYEE}$.) If, however, the sentences of interest are inclusion dependencies and unrestricted functional dependencies, then there need not exist an Armstrong database. This result holds even if we allow only ‘full’ inclusion dependencies. Thus, a fairly sharp line is drawn, in a case of interest, as to when an Armstrong database must exist. These results hold whether we restrict our attention to finite databases (databases with a finite number of tuples), or whether we allow unrestricted databases.     

Calculating the FHT in hardware

A parallel, pipelined architecture for calculating the fast Hartley transform (FHT) is discussed. Hardware implementation of the FHT introduces two challenges: retrograde indexing and data scaling. A novel addressing scheme that permits the fast computation of FHT butterflies is proposed, and a hardware implementation of conditional block floating point scaling that reduces error due to data growth with little extra cost is described. Simulations reveal a processor capable of transforming a 1 K-point sequence in 170 μs using a 15.4 MHz clock