Self-organized layered growth phenomena of diffusion couples with spinodal decomposition in binary alloys

In order to investigate the formation mechanisms of the layered growth phenomena in diffusion couples with spinodal decomposition,a phase field model combined with elastic strain field was employed.Microstructure evolutions of diffusion couple with spinodal decomposition in binary alloys were numerically simulated by considering concentration fluctuation and elastic anisotropy.The simulation results indicate that the number of the periodical layers decreases with the increase of initial concentration fluctuation,even with large elastic anisotropy.The growth of layered microstructures can be attributed to the directional diffusion enhanced by initially discontinuous chemical potential at the interface.

Phase equilibria in Ni-Ti-Ta ternary system

Phase diagrams of two isothermal sections of the Ni-Ti-Ta ternary system at 1000 and 1200℃in a full composition range were determined by X-ray diffraction and electron probe microanalysis.The experimental results indicated a ternary compoundτphase with low solid solubility and composition ranges of(16.3-22.4)at.%Ta,(15.9-24.1)at.%Ti and(58.5-60.0)at.%Ni at 1000℃.The two terminal solid solutions(bcc-(Ta)andβ-Ti)formed a continuous solid solution at 1000 and 1200℃.A certain amount of Ti can dissolve into Ni-Ta intermetallic compounds near the Ni-Ta side,with the highest value of 21.9 at.%observed in the Ni;Ta compound at 1000℃.

Phase equilibria in Co−Al−Re ternary system at 1100 and 1300℃

Isothermal sections of the Co−Al−Re ternary system at 1100 and 1300℃ were determined experimentally by electron probe microanalysis and X-ray diffraction.The results show that there are seven three-phase regions in the 1100℃ isothermal section and five three-phase regions in the 1300℃ isothermal section.The solid solubilities ofαCo,εRe and CoAl increase a little with temperature increasing from 1100 to 1300℃.The solubility of Co in compounds AlRe2,Al11Re4 and Al4Re is negligible,<1.5 at.%.And no ternary compounds are found.

Theoretical Exploration of Alloying Effects on Stabilities and Mechanical Properties ofγʹPhase in Novel Co–Al–Nb-Base Superalloys

The new developedγ/γʹCo–Al–Nb-base alloys show great potentials as high-temperature materials.However,finding appropriate compositions to improve performance of alloys still poses a great challenge to the development of Co–Al–Nb-base alloys.Motivated by the lack of alloying effects on fundamental properties of criticalγʹphase,we systematically performed a theoretical investigation on the effect of alloying elements TM(TM:Ti,V,Cr,Zr,Mo,Ta,W,Re,and Ru)on phase stabilities and mechanical properties of L1_(2)-typeγʹ(Co,Ni)_(3)(Al,Nb).By analyzing the stability ofγʹphase with respect to its competitive B2 and D0_(19) phases,the results shown that Ti,V,and Cr enhance the L1_(2) stability and widen the L1_(2)–D0_(19) energy barrier,in which V yields the maximum influence.The analysis of electronic structure indicated that the alternation of valence electrons at fermi level would be the atomic origin for doping TM inγʹphase.The calculated results of mechanical properties shown that V and Cr are expected to be optimal dopant for enhancing the strength and the ductility ofγʹphase.The addition of Ta is also beneficial for enhancing the strength at the slight expense of ductility ofγʹphase.By drawing the mechanical maps,the preferred composition range for the phases with desired properties is roughly demarcated in theory for the multi-addition of V/Cr and V/Ta inγʹphase.The findings would be useful for optimizing the performance of novelγ/γʹCo–Al–Nb-base superalloys.

Microstructure and properties of gradient nitrided layer on Ti6Al4V alloys

The vacuum electromagnetic induction nitriding technology was applied to prepare a gradient nitrided layer on the surface of a Ti6Al4V alloy,which possesses TiN andα-Ti(N)phases.Moreover,transmission electron microscopy was conducted to confirm the presence of numerous high-density stacking faults caused by TiN and Ti_(2)N phases distributed on the surface of the alloy,along with a large number of basal stacking faults inside.A highdensity stacking fault led to serious distortion of lattice fringes.Lattice and numerous edge dislocations caused by defects were observed in the subsurface layer.For the surface layer,the Vickers hardness reached HV_(0.25)1211.30and the residual compressive stress increased,while the nano-hardness increased to 14.07 from 5.31 GPa in the substrate.The micrometre scratch test results indicated that the plasticity and hardness of the nitrided layer changed in a gradient.The 50-μm effective hardened layer depth and surface compressive stress of the Ti6Al4V alloy were enhanced by the stacking faults.

Phase equilibria in Co-Ti-Re ternary system

The phase equilibria in the Co-Ti-Re ternary system at 800,1000,1100 and 12000C were studied combined with electron probe microanalyzer(EPMA),X-ray diffraction(XRD),scanning electron microscope(SEM)and transmission electron microscope(TEM).The new phaseτwith a large solubility was discovered at all four isothermal sections,and its structure still needs a further study.A large solubility of Re in the CoTi phase was observed.The solubility of Re in the Co_(3)Ti phase is6.1%at 800℃,8.7%at 1000℃and 7.7%at 1100℃.The present work could be significant for alloy design of Co-based alloys and thermodynamic analysis of the Co-TiRe ternary system.

Enhanced thermoelectric performance of n-type TiCoSb halfHeusler by Ta doping and Hf alloying

The p-type TiCoSb-based half-Heuslers are widely studied due to the good electrical transport properties after hole doping,while the pristine TiCoSb is intrinsically n-type.It is thus desired to obtain a comparable n-type counterpart through optimization of electron concentration.In this work,n-type Ti_(0.9-x)HfxTa_(0.1)CoSb half-Heuslers were fabricated by arc melting,ball milling,and spark plasma sintering.An optimized carrier concentration,together with a decreased lattice thermal conductivity,was obtained by Ta doping at the Ti site,leading to a peak figure of merit(ZT)of 0.7 at 973 K in Ti_(0.9)Ta_(0.1)-CoSb.By further alloying Hf at the Ti site,the lattice thermal conductivity was significantly reduced without deteriorating the power factor.As a result,a peak ZT of 0.9 at 973 K and an average ZT of 0.54 in the temperature range of 300-973 K were achieved in Ti_(0.6)Hf_(0.3)Ti_(0.1)CoSb.This work demonstrates that n-type TiCoSb-based halfHeuslers are promising thermoelectric materials.

Fibroblast growth factor 7 is a nociceptive modulator secreted via large dense-core vesicles

Fibroblast growth factor(FGF)7,a member of FGF family,is initially found to be secreted from mesenchymal cells to repair epithelial tissues.However,its functions in the nervous system are largely unknown.The present study showed that FGF7 was a neuromodulator localized in the large dense-core vesicles(LDCVs)in nociceptive neurons.FGF7 was mainly expressed in small-diameter neurons of the dorsal root ganglion and could be transported to the dorsal spinal cord.Interestingly,FGF7 was mostly stored in LDCVs that did not contain neuropeptide substance P.Electrophysiological recordings in the spinal cord slice showed that buffer-applied FGF7 increased the amplitude of excitatory post-synaptic current evoked by stimulating the sensory afferent fibers.Behavior tests showed that intrathecally applied FGF7 potentiated the formalin-induced acute nociceptive response.Moreover,both acute and inflammatory nociceptive responses were significantly reduced in Fgf7-deficient mice.These results suggest that FGF7 exerts an excitatory modulation of nociceptive afferent transmission.