Microstructure,texture evolution and mechanical properties of cold rolled Ti-32.5Nb-6.8Zr-2.7Sn biomedical beta titanium alloy

Ti-32.5 Nb-6.8 Zr-2.7 Sn(TNZS,wt%) alloy was produced by using vacuum arc melting method,followed by solution treatment and cold rolling with the area reductions of 50% and 90%.The effects of cold rolling on the microstructure,texture evolution and mechanical properties of the experimental alloy were investigated by optical microscopy,X-ray diffraction,transmission electron microscopy and universal material testing machine.The results showed that the grains of the alloy were elongated along rolling direction and stress-induced α' martensite was not detected in the deformed samples.The plastic deformation mechanisms of the alloy were related to {112} 111 type deformation twinning and dislocation slipping.Meanwhile,the transition from γ-fiber texture to α-fiber texture took place during cold rolling and a dominant {001} 110_(α-fiber) texture was obtained after 90% cold deformation.With the increase of cold deformation degree,the strength increased owing to the increase of microstrain,dislocation density and grain refinement,and the elastic modulus decreased owing to the increase of dislocation density as well as an enhanced intensity of {001} 110_(α-fiber)texture and a weakened intensity of {111} 112_(γ-fiber)texture.The 90% cold rolled alloy exhibited a great potential to become a new candidate for biomedical applications,since it possesses low elastic modulus(47.1 GPa),moderate strength(883 MPa) and high elastic admissible strain(1.87%),which are superior than those of Ti-6 Al-4 V alloy.     

Noise-induced transitions for random versions of Verhulst model

According to the Verhulst model the rate of increase/decrease of a biological population with size x(t) at time t is equal to the sum of $\rho x\left(t\right)$ and $-x{(t)}^2$, where $\rho \in \mathbb{R}$ is a constant. The constant ρ is positive and negative for favorable and hostile environments, respectively. The limitation of resources is quantified by the term $-x{(t)}^2$. We examine random versions of the Verhulst model obtained by replacing ρ with $(\rho +\mathrm{white}\mathrm{noise})$. Gaussian (GWN) and Poisson (PWN) white noise processes are considered. The state X(t) of the random Verhulst model satisfies stochastic differential equations driven by Gaussian and Poisson white noises. Our objective is to identify noise-induced transitions, that is, noise levels at which the stationary density of X(t) exhibits qualitative changes. It is shown that noise levels causing transitions under Poisson white noise approach those under Gaussian white noise as the frequency of Poisson jumps increases indefinitely while their size approaches zero.     

Experimental and computational investigations of LaNi5-xAlx (x = 0, 0.25, 0.5, 0.75 and 1.0) tritium-storage alloys

Although already scientists in recent years have reported some experimental and theoretical results of LaNi-Al series of tritium-storage alloys, several key aspects remain the subject of considerable debate. In an effort to interpret some of these unknowns, we have performed experimental and theoretical investigations for LaNi_(5-x)Al_x(x = 0, 0.25, 0.5, 0.75 and 1.0) tritium-storage alloys. Firstly, the XRD characterization indicates that the unit cell volumes of LaNi_(5-x)Al_x increase with Al content in alloys. Secondly, the PCisotherm measurement of LaNi_(5-x)Al_xalloys shows that their hydrogen absorption/desorption plateau pressures reduce with the increase of Al content while their plateau widths narrow simultaneously. The deuterium absorption/desorption plateaus have a similar trend to hydrogen's except for their plateaus being higher than hydrogen's. To explain the above experimental findings, a series of calculations based on density functional theory(DFT) and frozen phonon approach have been performed. The results manifest that:(1) the partial substitutions of Al for Ni reduce the hydrogen formation energies of LaNi_(5-x)Al_xH and the number of available interstitial sites, and therefore lead to the absorption/desorption plateau pressures being reduced and the plateau widths being narrowed down at the same experimental temperatures;(2) the covalent interaction between H and Ni is an important factor for estimating the stability of LaNi_(5-x)Al_x-H system;(3) since the calculated enthalpy change H is generally more accurate than the calculated entropy change S with respect to the corresponding experimental value for each LaNi_(5-x)Al_xH(or D), the curves of H vs. hydrogen storage capacity instead of Van't Hoff relation, can be used to predict the experimental plateau pressures of LaNi_(5-x)Al_x-H(D or T) at a given temperature;(4) the hydrogen isotope effect of LaNi_(5-x)Al_x-H(D or T) system can be quantitatively described as a linearity relation between ⊿ZPE + ⊿H~(vib) and 1/√mQ(Q = H, D, T). From the good agreement between the predicted and experimental ln(P_H/P_0) and ln(P_D/P_0), it is deduced that predicting ln(P_T/P_0) of LaNi_(5-x)Al_x T is feasible. The procedure of pre-computing and comparing curves of H vs. hydrogen storage capacity proposed in this paper provided an attractive tool to increase the efficiency of experimental alloying design of hydrogen(deuterium or tritium) storage materials.     

Heat of Formation of N-Dimethylaminodiborane

The heat of reaction of N-dimethylaminodiborane with water has been determined according to the reaction: (CH3)2NB2H5(g)+6H2O(liq)=(CH3)2NH(g)+2H3BO3(c)+5H2(g),ΔH(25°C)=−374.99±2.71kj/mole=−89.62±0.65kcal/mole.A combination of this value with the heat of vaporization, and with the heats of formation of boric acid, dimethylamine, and water gives for liquid N-dimethylaminodiborane: ΔHf°(25 °C) = ?36.22 ± 0.75 kcal/mole.     

Heats of Hydrolysis and Formation of Potassium Borohydride

The heat of reaction of potassium borohydride with 0.060 molal HCl has been measured by solution calorimetry. The heat of solution of the hydrolysis products has also been measured and combined with certain literature values to calculate the process: KBH4(c)+HCl(g)+3H2O(liq)→KCl(c)+H3BO3(c)+4H2(g),ΔH°(25°C)=−354.06±1.84kj/mole(−84.62±0.44kcal/mole).A combination of this value with literature values for the heats of formation of HCl(g), H₂O(liq), KCl(c), and H₃BO₃(c) gives for KBH₄(c): ΔHf°(25°C) = ?228.86 ± 2.30 kj/mole(?54.70 ± 0.55 kcal/mole).Other data on the heats of formation of the alkali-metal borohydrides are discussed briefly.     

Exact explicit time integration of hyperbolic partial differential equations with mesh free radial basis functions

This study is a progress report that examines the numerical solution of inviscid hyperbolic partial differential equations (PDEs) without the need for upwind differencing and other numerical artifacts. The fixed frame PDEs are locally transformed by rotating and translating the coordinate system at each local discretization point. These transformations yield a simpler PDE system that is effectively linearized. It is assumed that in this transformed local frame within a time interval, $\mathrm{\Delta }t$, the dependent variables are products of the spatial dependent radial basis functions (RBFs), and the time dependent expansion coefficients, $\mathbf{\chi }(t)$. This linearization is exploited by transforming the PDEs into systems of linear ordinary differential equations (ODEs) in terms of the expansion coefficients. The affine space decomposition is used to obtain an ODE system of $N_i$ ODEs in $N_i$ unknowns that can be integrated exactly in time. Then the entire set of N expansion coefficients is found. Numerical results show that hyperbolic PDEs can be integrated in time without upwinding and the root mean square errors between the exact and numerical solutions are indeed very small.     

Heats of Hydrolysis and Formation of Dimethoxychloroborane

The heat of hydrolysis of dimethoxychloroborane has been measured; for the reaction, (CH3O)2BCl(liq)+3H2O(liq)=H3BO3(c)+2CH3OH(liq)+HCl(g)ΔH(25°C)=−26.6±0.8kj/mole=−6.4±0.2kcal/mole.From this, we have calculated the heat of formation of dimethoxychloroborane: for the liquid, ΔHf° (25 °C) = −782.1 ± 1.8 kj/mole (−186.9±0.4 kcal/mole), and for the gas, ΔHf° (25 °C) = −747.9 ±2.2 kj/mole (−178.8±0.5 kcal/mole).