Crystallization of amorphous Zr_(70)Cu_(30-x)Ni_x alloys

X-ray diffraction (XRD) and differential scanning calorimetry (DSC) wereemployed to investigate the influence of Ni content on the crystallization of amorphousZr_(70)Cu_(30-x)Ni_x (atom fraction in percent) alloys. Experimental results show that with the Nicontent increasing the activation energies for crystallization of amorphous Zr_(70)Cu_(30-x)Ni_xalloys increase correspondingly, indicating that the thermal stability is greatly improved. All theDSC traces of amorphous Zr_(70)Cu_(30-x)Ni_x alloys exhibit two exothermic peaks, suggesting thatthe crystallization process proceeds via a double-stage mode. The first exothermic peak at lowertemperature mainly corresponds to the precipitation and growth of Zr_2Cu particles, while the secondone corresponds to the precipitation of nano-scale Zr_2Ni phase and crystallization of residualamorphous phase. The mechanism on the crystallization of amorphous Zr_(70)Cu_(30-x)Ni_x alloys wasdiscussed.

DISACCOMMODATION OF INITIAL SUSCEPTIBILITY IN AMORPHOUS Fe_(90-x)Ni_xZr_(10) ALLOYS

The disaccommodation(DA)measurements of initial susceptibility were performed in amorphous Fe_(90-x)Ni_xZr_(10)(x=10,20,30)alloys.The DA was measured for two different amorphous states:as-quenched and pretreated at 537 K for 45 min.For all the as- quenched samples,in the isochronal spectra of DA a well defined relaxation peak around 350 K is accompanied by a samll but distinct peak near the Curie temperature of Fe_(90)Zr_(10) phase(T_c=230 K).The reversibility and annealing effect on DA are analyzed within the framework of two-level model.The fits of the theory to the experimental data of reversible relaxation processes gave a spectrum,of activation energies and pre- exponential factor.

Phase Relationship in Nd_2(Fe_(1-x)Ni_x)_(14) B and Pr_2(Co_(1-y)Ni_y)_(14)B Pseudo-ternary Compounds

The melting behavior,solid state phase transformation and structure of pseudo-ternary compounds Nd_2(Fe_(1-x)Ni_x)_(14)B and Pr_2(Co_(1-y)Ni_y)_(14)B were studied using differential thermal analysis,optical microscopy X-ray diffraction,and electron probe micro-analysis techniques.At high temperature,eutectoid decomposition R_2(Ni,M)_(17)→R(Ni,M)_5+x-Ni(M) takes place in these two pseudo-ternary compounds,in the composition range x=0.6～1.0 and y=0.3～1.0,respectively.When x(or y)≤0.2,both Nd_2(Fe_(1-x)Ni_x)_(14)B and Pr_2(Co_(1-y)Ni_y)_(14)B are single phase tetragonal.The phase constitutents of these two systems at room tempera- ture are similar in the composition range 0.6≤x(or y)≤1.0.

STRUCTURAL AND MAGNETIC PROPERTIES OF RTiFe_(11),RTiCo_(11) AND RTi(Fe_(1-x)Ni_x)_(11) COMPOUNDS(R=Nd,Sm,Gd,Tb,Dy,Ho,Er AND Y)

The crystallographic structure and intrinsic magnetic properties have been investigated in the RTiFe_(11), RTiCo_(11) and RTi(Fe_(1-X)Ni_X)_(11) compounds,where R represents Nd,Sm,Gd,Tb,Dy,Ho,Er and Y.Neutron diffraction and Mossbauer spectra analyses have been used to study the nuclear and magnetic structure of these compounds.the Fe,Co,Ni and Ti atoms are found to exhibit strong site preference with f and j sites fa- voring Fe,Co and Ni atoms and the i site Ti atoms.Two different types of magnetic behavior were observed in the RTiFe_(11) and RTiCo_(11) compounds.In the former,the interatomic distance and the number of nearest neighbor atoms play essential roles.In particular,anomalous thermal expansion behavior is presented in RTiFe_(11).In the latter,the magnetic properties are essentially determined by the modification of the cobalt electronic configuration brought about by the transfer of rare earth conduction electrons to the transition 3d band.The saturation magnetization,Curie temperature and magnetocrystalline anisotropy data of RTiFe_(11), RTiCo_(11)and YTi(Fe_(1-X)Ni_X)_(11)are presented.A tempt to improve the intrinsic magnetic properties in RTiFe_(11)has been made,and the results are reported.On the basis of the crystalline field theory by using a single-ion model,the anisotropy constants and their temperature dependence of the R ions have been calcu- lated,which helps explain the spin reorientation observed in RTiFe_(11).

Magnetism and superconductivity in Eu(Fe_(1-x)Ni_x)As_2(x= 0,0.04)

We report Eu-local-spin magnetism and Ni-doping-induced superconductivity(SC)in a 112-type ferroarsenide system Eu(Fe_(1-x)Ni_x)As_2.The non-doped EuFeAs_2exhibits two primary magnetic transitions at ~100 and ~40 K,probably associated with a spin-density-wave(SDW)transition and an antiferromagnetic ordering in the Fe and Eu sublattices,respectively.Two additional successive transitions possibly related to Eu-spin modulations appear at 15.5 and 6.5 K.For the Ni-doped sample with x=0.04,the SDW transition disappears,and SC emerges at T_c=17.5 K.The Eu-spin ordering remains at around 40 K,followed by the possible reentrant magnetic modulations with enhanced spin canting.Consequently,SC coexists with a weak spontaneous magnetization below 6.2 K in Eu(Fe_(0.96)Ni_(0.04))As_2,which provides a complementary playground for the study of the interplay between SC and magnetism.

Ni对快速凝固Cu75Cr25合金相变及其凝固组织的影响

采用合金化的方法得到快速凝固Cu75-xCr25Nix(X=0.5,1和3) 合金的凝固组织。利用带有能谱(EDS)的扫描电子显微镜(SEM)分析了富Cr相的形态、成分以及形成机制。结果显示,合金元素Ni扩大了Cu、Cr之间的固溶度; Cu75Cr25合金快速凝固过程中的液相分解得到抑制。Cu75-xCr25Nix 合金富Cr液相分解组织的数量、尺寸、形貌较Cu75Cr25 合金富Cr液相分解组织均有较大的变化。在Cu75-xCr25Nix 组织中发现,除富Cr液相分解组织之间有聚集现象以外,还存在富Cr液相分解组织与富Cr枝晶间的聚集。