镍基高温合金的平衡合金化

铝和过渡族元素在镍的面心立方晶格中的极限共同溶解度,取决于组元的平均原子量与其化合价电子浓度之间的线性关系。这一规律建立在平衡合金化规则的基础上,借助此规则,通过对失衡度及其符号的不太复杂的计算,便可预测有害于合金的化合物的形成及元素的偏析。采用平衡合金化规则评定相的稳定性,比现行相计算法有许多优点。平衡合金化规则不仅可广泛用于实际冶金学,而且可用于新合金化系统相的状态的研究。

Phase equilibria in Co-rich region of Co-Ti-Ta system

The phase equilibria in Co-rich region of Co-Ti-Ta system were studied.The microstructure and XRD analysis together with EDS determination show that L12 type Co3Ti phase and Laves_C36_Co3Ta phase get equilibrium with α-Co phase from 1 000 to 1 200 ℃.The Co3Ti phase possesses a solubility of Ta higher than 10%,and the addition of Ta stabilizes the Co3Ti phase.The isothermal sections of the Co-Ti-Ta system in the Co-rich region at 1 000,1 100 and 1 200 ℃ were constructed according to the result.

Vertical section phase diagrams of La−Fe−B ternary system

The vertical sections of the La−Fe−B system were investigated using electron probe microanalysis and differential thermal analysis.Based on the microstructures and phase compositions of the as-cast and equilibrium alloys,together with their heat flow−temperature curves,phase diagrams for three vertical sections were drawn:La_(x)Fe_(82)B_(y)(x+y=18),La_(x)Fe_(70)B_(y)(x+y=30)and La_(x)Fe_(53)B_(y)(x+y=47),where x and y represent mass fraction of La and B,respectively,%.Additionally,according to the phase diagrams,the compound La2Fe14B was identified as a stable phase at high temperatures.It was found to be stable between 926.2 and 792.6℃;at low temperatures,however,it decomposed into α-La,α-Fe and LaFe_(4)B_(4),according to the reaction La_(2)Fe_(14)B→α-Fe+α-La+LaFe_(4)B_(4).

Non-equilibrium alloy phase formation and transformation driven by ion beam mixing in the Fe-Hf-Nb multilayers

In the ion beam mixing experiments,eight Fe-Hf-Nb multilayered films,with overall compositions of Fe67Hf22Nb11,Fe67Hf11Nb22,Fe54Hf38Nb8,Fe54Hf30Nb16,Fe54Hf11Nb35,Fe25Hf67Nb8,Fe25Hf50Nb25 and Fe25Hf11Nb64,were irradiated by 200 keV xenon ions to doses ranging from 3×1014 Xe+/cm2 to 7×1015 Xe+/cm2.The results showed that unique amorphous phases were obtained at designed alloy compositions,falling in the favored glass-forming region deduced from three binary metal sub-systems.Interestingly,at some alloy compositions,the crystal-amorphous-crystal transformations were observed back and forth while varying the irradiation doses.In addition,at the alloy composition of Fe25Hf67Nb8,a metastable FCC phase was formed through an HCP-FCC structural phase transformation and it had a large lattice constant identified to be a=4.51 .Besides,the formation mechanism of non-equilibrium alloy phases was also discussed in terms of thermodynamics of solids and atomic collision theory.

α→β Transformation characteristics revealed by pulsed laser-induced non-equilibrium microstructures in duplex-phase Zr alloy

Microstructures of a duplex-phase Zr-2.5Nb alloy treated by pulsed laser were characterized by electron backscatter diffraction （EBSD） and electron channeling contrast （ECC） imaging techniques. Major attention has been paid to non-equilibrium hybrid microstructure consisting of both prior a and β phases, and a plates transformed from new β phases to probe α→β transformation characteristics in the alloy. The origin of the hybrid microstructure is attributed to the specific thermodynamic conditions induced by the pulsed laser treatment. ECC observation shows that newly formed [3 phases during laser heating prefer to nucleate and grow at the expense of edges of prior α grains rather than their interiors. EBSD analyses further reveal that orientations of the new β phases are not determined by the prior a grains according to the Burgers relationship but maintain those of the prior β phases in an epitaxial growth way.