Study on the microstructural evolution of different component alloys consisting of B2-NiSc intermetallics

Ni-50%Sc and Ni-51%Sc alloy were prepared with a vacuum arc smelting and water cooled copper mold suction-casting machine. The results showed that the two component alloys consisted of the primary phase B2-NiSc and lamellar (Ni2Sc+NiSc)eutectic due to the loss of Sc duringmelting. Two groups of alloys underwent (970 ℃, 72 h) homogenization heat treatment, and spherical or plate shape Ni2Sc particles were dispersed on the B2-NiSc matrix. With the increase of Sc content from50% to 51%, the amount of the second phase in the alloy decreases, the microstructure becomes uniform, and the grain gradually changes from long bar to a spherical particle. According to the Jackson boundary theory, the Jackson factor α of B2-NiSc =0.5 < 2, so the interface is rough, which explains that the growth pattern of the B2-NiSc phase is anon-faceted growth. It is consistent with the dendritic growth pattern of the B2-NiSc phase, which is observed from the experiment. After a longheat treatment, the number of vacancies decreases and the microstructure became uniform. The loss rate of Sc in rapidly quenched solidification was higher than that after the heat treatment

Therapeutic effect of teriparatide combined with lowfrequency pulsed electromagnetic field on hip fracture

Purpose: To evaluate the therapeutic effect of teriparatide in combination with low-frequency pulsed electromagnetic field in the management of hip fracture.Methods: Patients with hip fracture internal fixation and under conventional postoperative basic adjuvant therapy were compared with those patients who received teriparatide combined with low frequency pulsed electromagnetic field after operation. The content of Bone-Specific AlkalinePhosphatase (BALP), type I Procollagen Carboxy Terminal Propeptide (PICP), serum bone glaprotein (BGP), Ca2+, hip function and degree of bone scab formation were evaluated using Harris score and Fernadez-esteve scoring system. Kaplan-Meier survival curve was plotted to analyze differences in short-term prognosis of different postoperative adjuvant treatment measures.Results: Harris score of the hip joint and the effect of bone formation in the experimental group were higher than that of the control group. The blood levels of BGP, BALP, PICP and serum Ca2+ in the experimental group were higher than that of the control group (p &lt; 0.05). The plotted Kaplan-Meier survival curve indicates that the prognosis of the experimental group was better than that of control group (p &lt; 0.05).Conclusion: The adjuvant therapy of teriparatide combined with low-frequency pulsed electromagnetic field can improve the recovery function and enhance the prognosis of patients who underwent hip fracture surgery. Keywords: Teriparatide; Low frequency pulsed electromagnetic field, hip fractur

Microstructures and properties of AZ31 magnesium alloys formed by multi-channel porthole extrusion

This study investigated the effects of different extrusion temperatures and extrusion ratios on the microstructures and properties of AZ31 magnesium alloys formed by multi-channel porthole extrusion. The experimental results showed that equiaxed grains were formed during the dynamic recrystallization process and that alloy grains were refined by extrusion. Increased extrusion temperatures (from 340 ℃ to 420 ℃) resulted in larger alloy grains and decreased tensile strength of the alloy. Increased extrusion ratios (from 9 to 25) resulted in refined alloy grains and increased tensile strength of the alloy. Under conditions of low extrusion temperature and high extrusion ratio, the tensile strength and elongation of magnesium alloys were effectively improved. AZ31 magnesium alloys produced by multi-channel porthole extrusion at the extrusion temperature of 340℃ and the extrusion ratio of 25 possessed the finest average grain sizes (1.6 μm in the weld zone, 6.6 μm in the non-weld zone ) and the maximum tensile strength (290 MPa) and elongation (20.8 %)

Effect of cooling rate on microstructure of B2-NiSc intermetallics

Ni-50at%Sc alloy was prepared by centrifugal casting method. Volume fraction, the actual content of B2-NiSc and second phase Ni2Sc in alloy were analyzed with an Image-Pro Plus software. The cooling rates for the solidified thin plate with thickness of 2.65mm, 1.2mm, 0.75mm and 0.35 mm are 1164, 2570, 4112 and 8811 K·s- 1, respectively. It is found that d=0.5 mm was an critical dimension which corresponds to an abrupt change in the solidification rate. It is also found that (Ni2Sc+NiSc)eutectic was dispersed at grain boundary or between dendritic arms due to the loss of Sc element during melting. While d＞ 0.5mm (corresponding to the thin plate with thickness of 0.75mm, 1.20mm and 2.65 mm), the solidification structure consists of primary phase B2-NiSc and (Ni2Sc+NiSc)eutectic. While d ＜ 0.5mm (corresponding to the thin plate with thickness of 0.35 mm), the solidification structure is composed of fine globular B2-NiSc and relatively small amounts of (Ni2Sc+NiSc)eutectic. Based on the phase volumetric analyzing of the microstructure with an Image-Pro Plus software, the loss of Sc element during melting was about 3.01~3.10 at%. The eutectic NiSc in the lamellar eutectic structure together with the primary phase B2-NiSc form a larger single phase NiSc, while Ni2Sc with the form of particles is distributed on the grain boundaries after (970 ℃, 72 h) homogenization heat treatment

Stability of finite difference numerical simulations of acoustic logging-while-drilling with different perfectly matched layer schemes

In acoustic logging-while-drilling (ALWD) finite difference in time domain (FDTD) simulations, large drill collar occupies, most of the fluid-filled borehole and divides the borehole fluid into two thin fluid columns (radius ∼27 mm). Fine grids and large computational models are required to model the thin fluid region between the tool and the formation. As a result, small time step and more iterations are needed, which increases the cumulative numerical error. Furthermore, due to high impedance contrast between the drill collar and fluid in the borehole (the difference is >30 times), the stability and efficiency of the perfectly matched layer (PML) scheme is critical to simulate complicated wave modes accurately. In this paper, we compared four different PML implementations in a staggered grid finite difference in time domain (FDTD) in the ALWD simulation, including field-splitting PML (SPML), multiaxial PML(MPML), non-splitting PML (NPML), and complex frequency-shifted PML (CFS-PML). The comparison indicated that NPML and CFS-PML can absorb the guided wave reflection from the computational boundaries more efficiently than SPML and M-PML. For large simulation time, SPML, M-PML, and NPML are numerically unstable. However, the stability of M-PML can be improved further to some extent. Based on the analysis, we proposed that the CFS-PML method is used in FDTD to eliminate the numerical instability and to improve the efficiency of absorption in the PML layers for LWD modeling. The optimal values of CFS-PML parameters in the LWD simulation were investigated based on thousands of 3D simulations. For typical LWD cases, the best maximum value of the quadratic damping profile was obtained using one d[subscript 0]. The optimal parameter space for the maximum value of the linear frequency-shifted factor (α[subscript 0]) and the scaling factor (β[subscript 0]) depended on the thickness of the PML layer. For typical formations, if the PML thickness is 10 grid points, the global error can be reduced to <1% using the optimal PML parameters, and the error will decrease as the PML thickness increases.National Natural Science Foundation (China) (Grant 41174118)Postdoctoral Fellowship of China (Grant 2013M530106)China Scholarship Council (Grant 2010644006)Major State S&T Special Project (Grant 2008ZX05020-004