CREEP FRACTURE OF INTERMETALLIC COMPOUND(Fe_(60)Ni_(40))_3(V_(98)Ti_2)

The creep fracture behavior of intermetallic compound(Fe_(60)Ni_(40))_3(V_(98)Ti_2)has been studied. The variation of dislocation substructure was observed with TEM in the process of steady-state creep.It is found that there exists a large amount of stacking faults,dislocation pairs and also high density dislocation networks.SEM analysis of section near fracture sur- face points out that the intergranular crack due to coalescence of small cavities is the main creep fracture mechanism of(Fe_(60)Ni_(40))_3(V_(98)Ti_2).

Structure of the Intermetallic Compound Ni_3Al Synthesized under Compression of the Powder Mixture of Pure Elements Part Ⅰ: Phase Composition and Microstructure of Main Phase

It was shown by TEM and X-ray analysis that there are four types of grains of the main Ni3Al phase in the structure of the intermetallic obtained by the self-propagation high temperature method (SHS). Every type of grains has its own domain and dislocation structure. There are mono- and polydomains with and without dislocations. The grains of the main phase of monoand polydomains without dislocations and polydomains with dislocations were formed by diffusion in the solid phase. In these conditions NiAl3 phase is located on the grain boundary of the main phase. The Ni2Al3 phase is located at the triple joints of the main phase.

Structure of the Intermetallic Compound Ni_3Al Synthesized under Compression of the Powder Mixture of Pure Elements Part Ⅱ: Influence of Alloying by Boron on the Phase Composition and the Microstructure of Grains of the Main Phase

The Ni_3B phase was formed when boron (0.5 at. pct B) was added to the intermetallic of sto- ichiometric and off-stoichiometric (Ni-24 at. pct Al) compounds. In the alloy of stoichiometric composition the particles of Ni_3B phase has the size around 0.1μm and is located on the grain boundary of the main phase. The decreasing of concentrations of Al in the ofF-stoichiometric alloy leads to increase in the degree of the long-range order parameter, increasing the concen- trations of boron in the solid solution and decreasing its localization on the grain boundary. Microalloying of boron leads to increasing in the fraction of grain monodomains with disloca- tions up to 0.7 in the alloy of the off-stoichiometric composition and up to 1 in the alloy of the stoichiometric composition. It was established the correlation between the degree of the concentration inhomogeneity, average density of the dislocations and the average long range-order parameter.

Bonding Characteristics of the Intermetallic Compound Al_3Ti+Cr

Based on our structural model and a tight-binding Hamiltonian the eIectronic structure has been calculated by use of a recursion method (RM) for two models of the tetragonal DO22 and the cubic Ll2 crystal structures in Al3Ti+Cr for contrast, from which bonding characteristics have been discussed. The results for the interaction energy (IE) show that Cr prefers to replacing Al site. Cr partly replacing Al can change the IE between the atoms and make the constriction of lattice constant c and the elongation of lattice constant a for the DO22 and thereby may induce the change of crystal structure from DO22 to L12. The results for bond order integral (BOI) and IE between the atoms also show that the strong (110) directional Cr-Ti bondings are existed.Thus, Al3Ti-base intermetallic compounds with addition of the Cr atom still remain brittle.

APPLICATION RESEARCH ON THE Ni _3 Al INTERMETALLIC COMPOUND IN CISRI

Research work and recent progress made toward the industrial applications of the Ni_3Al in CISRI are discussed in present paper. The development of a Ni_3Al base alloy named MX-246 hardened by carbides and fine dispersion of disordered γ is summaried. This alloy,with higher peak temperature of yield strength and higher strain hardening rate than alloyIC-218,has been successfully used as the material of rolling guider at elevated temperatures and in wear conditions. The Ni3Al base alloy of GH264 has been made into welding electrodes by horizontal continuous casting process, and recently successfully surfacing welded on hydraulic blades as cavitation erosion resistance material. The process of remelting Ni3Al base alloy in air was also developed. The processes of producing welding electrodes and remelting in air set the base of industrial applications of Ni3Al in welding, repairing and casting in mass production and into components of large size. Another application of the compound, manufacturing the jet engine rivets used at about 1300℃ , can be attributed to its excellent oxidation resistance and still keeping high strength up to the melting point.

Electronic Structure Effect on Model Cluster for L1_2 Structure of Al_3Ti Intermetallic Compound with an Addition of Alloying Elements Fe, Ni and Cu

By use of self-consistent field Xα scattered-wave (SCF-Xα-SW) method, the electronic structure was calculated for four models of Ti4Al14X (X=Al, Fe, Ni and Cu) clusters. The Ti4Al14X cluster was developed based on L12 Al3Ti-base intermetallic compound. The results are presented using the density of states (DOS) and one-electron properties, such as relative binding tendency between the atom and the model cluster, and hybrid bonding tendency between the alloying element and the host atoms. By comparing the four models of Ti4Al14X cluster, the effect of the Fe, Ni or Cu atom on the physical properties of Al3Ti-based L12 intermetallic compounds is analyzed. The results indicate that the addition of the Fe, Ni or Cu atom intensifies the relative binding tendency between Ti atom and Ti4Al14X cluster. It was found that the Fermi level (EF) lies in a maximum in the DOS for Ti4Al14Al cluster; on the contrary, the EF comes near a minimum tn the DOS for Ti4Al14X (X=Fe, Ni and Cu) cluster. Thus the L12 crystal structure for binary Al3Ti alloy is unstable, and the addition of the Fe, Ni or Cu atom to Al3Ti is benefical to stabilize L12 crystal structure. The calculation also shows that the Fe, Ni or Cu atom strengthens the hybrid bonding tendency between the central atom and the host atoms for Ti4Al14X cluster and thereby may lead to the constriction of the lattice of Al3Ti-base intermetallic compounds.

热压烧结Fe_(3)Al金属间化合物滑动摩擦磨损性能研究

考察了25~500 ℃条件下热压烧结Fe_(3)Al与GCr15轴承钢配副时的干滑动摩擦磨损性能,利用扫描电子显微镜、X射线光电子能谱分析了Fe_(3)Al磨损面、磨屑的形貌和物质组成。结果表明:热压烧结Fe_(3)Al与GCr15轴承钢配副滑动磨损时摩擦因数在1~1.8,Fe_(3)Al的磨损机制以氧化磨损为主。室温条件下,Fe_(3)Al磨损率随着载荷的增加而增加,随着滑动速度的升高而降低。200~500 ℃条件下,Fe_(3)Al呈现出优异的磨损抗力,磨损率相比室温下降一个数量级。

XRD and TEM Analysis in the Interface of Diffusion Bonding for Fe_3Al/Q235 Dissimilar Materials

Phase structure characteristics near the interface of Fe3Al/Q235 diffusion bonding are investigated by means of X raydiffraction (XRD), transmission electronic microscope (TEM) and electron diffraction, etc. The test results indicatedthat obviously a diffusion transition zone forms near the interface of Fe3Al/Q235 under the condition of heatingtemperature 1050~1100℃, holding time 60 min and pressure 9.8 MPa, which indicated that the diffusion interfaceof Fe3Al/Q235 was combined well. The diffusion transition zone consisted of Fe3Al and a-Fe(Al) solid solution.Microhardness near the diffusion transition zone was HM 480~540. There was not brittle phase of high hardness inthe interface transition zone. This is favorable to enhance toughness of Fe3Al/Q235 diffusion joint.

ONE-CELL-STATE METHOD FOR DETERMINATION OF ELECTRONIC STRUCTURE OF INTERMETALLIC COMPOUNDS

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EFFECT OF ALLOYING ELEMENT ON MECHANICAL PROPERTIES OF Fe_3 AL AND FeAI ALLOYS

The effect of alloying element such as Mo,Si or B and its stoichoimetric composition on the tensile properties at room and elevated temperatures,and also on the microstructure of Fe_3Al and FeAl alloys has been investigated.Two Fe aluminides were found to be obviously strengthened by all of three elements,but seriously embrittled by Mo and Si.An improvemen over the plasicity of FeAl may be made by adding B,and the fracture surface is variedfrom intergranular to transgranular cleavage type.The room temperature plasticity of the Fe-rich Fe_3Al or Al-rich FeAl is much better than that of the stoichoimetric aluminides.An anoma- lous temperature dependence on the yield strength of Fe_3Al in range of 400 to 500℃ or of FeAl in range of 400 to 500℃ was found.Discussion has been carried out by the aspect of microstructure.

BEHAVIOR OF Mg AND ITS EFFECT ON MECHANICAL PROPERTIES OF CAST Fe_3Al ALLOYS

Proper addition of 0.002 wt-% Mg to cast Fe_3Al alloy may obviously improve the room and high temperature tensile properties.Auger spectra show that Mg segregates near grain boundaries as very thin layers.Observation under TEM reveals that a suitable amount of Mg enhances ability of cooperative internal deformation so that the dislocations will ease the con- tinuous slip deformation through grain boundaries.The fracture feature of Fe_3Al alloy is of transgranular cleavage at room temperature and cracks initiate at grain boundaries.

EFFECTS OF Cr AND Nb ON MICROSTRUCTURES AND MECHANICAL PROPERTIES OF Fe_3Al ALLOYS

The effects of Cr and Nb on tensile properties at room and elevated temperatures and also on the microstructure have been investigated.An improvement in ductiliy plasicity and the cleavage strength of Fe_3AI may result from adding Cr;the improvement is more pronounced at over 400℃.The formation of Fe_2Nb containing A1 precipitates in the Fe_3AI+Nb alloy provide significant strengthening effect.Additions of Cr and Nb in Fe_3AI can cause a signifi- cant improvement in the yield strength at 550℃.

EFFECT OF Ce AND Cr ON ROOM TEMPERATURE MECHANICAL PROPERTIES OF Fe_3Al

Small amount addition of Ce to FeAl results in a significant increase of room temperaturestrength of the alloy,and the combined addition of Ce and Cr improves both strength andductility.The fracture mode of FeAl containing Ce is a mixed one of approximately 70%transgranular cleavage and 30% intergranular failure.In the deformed specimens of binaryFeAl the dislocations observed are mainly single dislocations with =(1/4)a~’〈111〉.However,a number of superlattice dislocations can be observed in the deformed specimens ofthe alloys with Cr addition.

Stress distribution at diffusion-bonded interface of Fe_3Al with Cr18-Ni8 steel

Fe3Al and Crl8-Ni8 steel were bonded in vacuum and an interface was formed between Fe3Al and Crl8-Ni8 steel. Stress distribution at the diffusion-bonded interface was researched by numerical simulation and finite element method （FEM）. The results indicated that the peak stress appeared at the interface near Cr18-Ni8 steel side. This is the key factor to induce crack at this position. With the enhancement of heating temperature, the peak stress at the bonded interface increases. When the temperature is 1 100 22, the peak stress is up to 65.9 MPa, which is bigger than that at 1 000 22 by 9. 4%. In addition, the peak stress becomes bigger with the increase of the thickness of base metal from 1 mm to 8 ram. While the thickness is more than 8 ram, the peak stress varies slightly with the change of the thickness.

Kinetics of Oxidation Resistance of the Ti_3Al-base Intermetallic Alloys

1.IntroductionThe research of the TD1 and TD2 al-loys based on intermetallic compound TiAl,which possesses high temperature capabilityfrom 650 to 700℃ was conducted.However,the limitation used at high temperature isimposed by oxidation and degradation ofcreep strength,and relatively little know-

Effect of Fe_(2)O_(3)nanoparticle on the interface microstructure and properties of Al/Cu plasma arc fusion-brazing joints

The lap joint of T2 copper plate and 1060 pure aluminum plate was made by using the plasma arc welding method with adding Fe_(2)O_(3)nanoparticles in different proportions.The research analysis found that the thickness of the IMC(intermetallic compound)and eutect-ic region decreased after the addition of nanoparticles due to its inhibitory effect.When the proportion of Fe_(2)O_(3)nanoparticles is 3%,the in-terface intermetallic compound layer is the thinnest.However,after this ratio is continuously increased,the inhibition effect is weakened by the agglomeration of nanoparticles,and the thickness begins to increase significantly.The mechanical and electrical properties of the joint are mainly affected by the thickness of the IMC layer.Excessive nanoparticles are agglomerated into large particles with high resistivity.Therefore,the tensile strength and relative electrical conductivity of the joint are first increasing and then decreasing with the increase of nanoparticle ratio.When the proportion of nanoparticles is 3%,the tensile strength and electrical conductivity are maximum.

AB INITIO CALCULATION OF THE ELASTIC AND OPTICAL PROPERTIES OF Al3Sc COMPOUND

The ab initio method has been performed to explore the elastic and optical properties of Al3Sc compound, based on a plane wave pseudopotential method. It can be seen that the calculated equilibrium lattice parameter and elastic constants are in reasonable agreement with the previous experimental data. The elastic constants satisfy the requirement for mechanical stability in the cubic structure of the Al3Sc compound. The optical property calculations show that a strong absorptive peak exists from O-15eV and a relative small absorptive peak exists around 30eV. The form is caused by the optical transitions between high s, p, and d bands, and the latter results from the optical transitions from high s, p, and d bands to the low 2p band.

Ti_3Al基金属间化合物的研究进展

对Ti3 Al基金属间化合物的研究情况及其合金组织、力学性能、影响因素作了概述 ,并重点介绍了其熔炼技术和铸造特性。最后 ,展望Ti3

Effect of extrusion process on microstructure and mechanical properties of Ni_3Al-B-Cr alloy during self-propagation high-temperature synthesis

The well-densified Ni3Al-0.5B-5Cr alloy was fabricated by self-propagation high-temperature synthesis and extrusion technique. Microstructure examination shows that the synthesized alloy has fine microstructure and contains Ni3Al, Al2O3, Ni3B and Cr3Ni2 phases. Moreover, the self-propagation high-temperature synthesis and extrusion lead to great deformation and recrystallization in the alloy, which helps to refine the microstructure and weaken the misorientation. In addition, the subsequent extrusion procedure redistributes the Al2O3 particles and eliminates the γ-Ni phase. Compared with the alloy synthesized without extrusion, the Ni3Al-0.5B-5Cr alloy fabricated by self-propagation high-temperature synthesis and extrusion has better room temperature mechanical properties, which should be ascribed to the microstructure evolution.

TiC与TiC-WC的添加对FeAl/Al_2O_3复合材料力学性能的影响

在FeAl/Al2 O3复合材料基体中分别加入TiC或TiC WC固溶体可显著提高其抗弯强度。当添加 2 0 %TiC和 2 0 %TiC WC固溶体时 ,复合材料的抗弯强度分别达到 10 2 8.4 6MPa和 132 8.72MPa ,但其断裂韧性分别降低约 4 0 %和 30 %。当TiC WC固溶体加入量为 5 %时 ,可同时提高复合材料的抗弯强度和断裂韧性。