Intermetallic Phase Evolution of Cold-Sprayed Ni-Ti Composite Coatings: Influence of As-Sprayed Chemical Composition

Owing to low-temperature deposition conditions and high deposition rate, cold spray offers unique advantages in manufacturing a wide variety of metallic and composite coatings including metal matrix composites produced from physically blended powders. One of the challenges of producing composite coatings using cold spray is the deviation of coatings composition from the blended feedstock powder composition. This is of utmost importance as it affects the composition and phase evolution of intermetallic forming coatings during post spray heat treatment. In this work, cold spray of composite Ni-Ti coatings and formation of intermetallics from post spray heat treatment were investigated as a first step to examine the potential of producing equiatomic bulk Ni-Ti by cold spray. Three different physically blended Ni and Ti powders mixtures were sprayed on titanium substrates to address the coating composition variation from the blended feedstock powder and study its influence on phase evolution during post spray heat treatment. High-density and well-dispersed composite coatings were achieved for each case. EDS analysis revealed as-sprayed coatings with 10.5, 35.9 and 56.9 at.% Ni (and with balanced Ti ratios) from the three powder mixtures. Annealing treatments were conducted at 400, 500 and 900 °C for 1 and 2 h and comparative studies of the intermetallic compound formations were carried out. Microstructural investigation showed that all three equilibrium intermetallics phases of binary Ni-Ti phase diagram (Ni3Ti, Ti2Ni and NiTi) formed in the two Ni-rich composite coatings with NiTi phase being maximum in the coating with the closest composition to equiatomic ratio while only Ti2Ni phase formed in the Ti-rich coating after annealing. Thermal etching analysis of coatings showed that NiTi phase forms with a gradient microstructure from Ti splats boundary toward the center of splats, which is attributed to the grain refinement of CS samples at splat boundary and intermetallic nucleation mechanism.

Ranolazine: Electrophysiologic Effect, Efficacy, and Safety in Patients with Cardiac Arrhythmias

Ranolazine is currently approved as an antianginal agent in patients with chronic angina (class IIA). Ranolazine exhibits antiarrhythmic effects that are related to its multichannel blocking effect, predominantly inhibition of late sodium (late INa) current and the rapid potassium rectifier current (IKr), as well as ICa, late ICa, and INa-Ca. It also suppresses the early and delayed after depolarizations. Ranolazine is effective in the suppression of atrial and ventricular arrhythmias (off-label use) without significant proarrhythmic effect. Currently, ongoing trials are evaluating the efficacy and safety of ranolazine in patients with cardiac arrhythmias; preliminary results suggest that ranolazine, when used alone or in combination with dronedarone, is safe and effective in reducing atrial fibrillation. Ranolazine is not currently approved by the US Food and Drug Administration as an antiarrhythmic agent.

Deformation Microstructure of Cold Gas Sprayed Coatings

Cold Gas Spraying is a new coating technique, in which the formation of dense, tightly bonded coatings occurs only due to the kinetic energy of high velocity particles of the spray powder. These particles are still in the solid state as they impinge on the substrate. Adiabatic heating after impingement can cause local shear instabilities and jet formation. The local microstructure is strongly dependant on local stress state and temperature rise. A variety of different microstructures is observed by TEM. The results are compared with modelling of the spray process.

Competitive Phase Selection in Fe-Ni Alloy Droplets

In the solidification of Fe-Ni droplets (≤ 30 at.% Ni), the selection of different microstructures is dominated by the competition between the bcc and ccp phases. In drop-tube experiments ccp is the primary phase in some dilute (up to 7at% Ni) alloys although the bcc phase is favoured by a lower free energy and by a lower interfacial energy with the liquid. Competitive dendrite growth is a possible explanation for the formation of primary ccp. Comprehensive thermodynamic (CALPHAD) and kinetic modelling is undertaken to understand the growth competition. The origin of the observed primary phases is discussed.

Solidification of Intermetallic Compounds

Kinetic modelling, incorporating variation in the degree of chemical order, is developed for the solidification of intermetallic compounds, and qualitative comparisons are made with experiment. It is found that a disordered phase can be obtained other than by the process of disorder trapping, and that partitioning can increase or invert with increasing solidification velocity. Solid-state ordering and its effects on final microstructure are also considered.

Long-term renal function and cardiovascular disease risk in obese kidney donors

BACKGROUND AND OBJECTIVES

Increasing demand for live-donor kidneys has encouraged the use of obese donors despite the absence of long-term outcome data and evidence that obesity can adversely affect renal function. We wished to determine whether obesity increased the risk for renal dysfunction and other medical comorbidities in donors several years after donation.

DESIGN, SETTING, PARTICIPANTS, & MEASUREMENTS

Ninety-eight patients who donated a kidney 5 to 40 years previously were stratified according to body mass index (BMI) at donation and evaluated for renal dysfunction and risk factors for cardiovascular disease. Patients who were from the 2005 through 2006 National Health and Nutrition Examination Survey database; did not have renal disease; and were matched for age, gender, race, and BMI served as two-kidney control subjects.

RESULTS

Renal function in obese (BMI > or =30) and nonobese (BMI <30) donors was similar, and both donor groups had reduced renal function compared with BMI-matched two-kidney control subjects. Obesity was associated with more hypertension and dyslipidemias in both donors and two-kidney control subjects; however, there were no significant differences between the two groups within each BMI category.

CONCLUSIONS

These results indicate that obese donors are not at higher risk for long-term reduced renal function compared with nonobese donors and that the increased incidence of hypertension and other cardiovascular disease risk factors in obese donors is due to their obesity and is not further exacerbated by nephrectomy. These findings support the current practice of using otherwise healthy overweight and obese donors but emphasize the need for more intensive preoperative education and postoperative health care maintenance in this donor group.