EFFECT OF ELONGATED GRAIN STRUCTURE ON THEMECHANICAL PROPERTIES OF AN Fe_3Al-BASEDALLOY

The effect of hot-rolling processing on microstructure as well as the relationship between the elongated grain structure and tensile properties are investigated. The results indicate that the elongated grain structure influences the tensile properties and creep rupture life of Fe3Al alloy significantly. For the better strength and ductility at RT,a thinner elongated grain structure is desirable. When the elongated grain size is increased, the tensile properties will be decreased. On the other hand, the creeP rupture life at 600℃ is increased with the increase of elongated grain size.

The Kinetics of Hydrogen Diffusion in Ti_3Al-Based Alloy

The Proccss of gascous hydrogcn charging into a Ti_3Al- based alloy in the temperature range of 500-650℃isinvcstigatcd. The rcsnlls snoxvc that in rclatiollshil, between the average hydrogen concentration at constant tempreature and charging time reveals a parabolie rate law Applying the theory of lattice constant tcnlpcralurc and hrgillg tin rcvcals a parabolic riltc laiv. Applyillg tbcthcoly oftatticc dillbsio to allalyzc the hydrogcll diethesioll they andthat cncrgy of hydrogcn diffusion is 90.40 kJ/mol. and the equilibrium hydrogen content in the alloy depends on the temperature of the gaseous hydrogen charging process

双尺度Fe_(3)Si相调控对Cu-2.5Fe-0.2Si合金组织和性能的影响

通过在铜铁合金中添加微量Si元素,并利用组合形变热处理工艺对亚微米级Fe_(3)Si相和纳米级Fe_(3)Si相的析出行为进行调控。结果表明:处理后的Cu-2.5Fe-0.2Si合金中形成了大量细小的再结晶晶粒,其抗拉强度、电导率和伸长率分别为401MPa、69.25%IACS和12.50%。合金中纳米级Fe_(3)Si析出相与铜基体的位向关系为[011ˉ]Cu//[11ˉ1]Fe_(3)Si。双尺度Fe_(3)Si相对合金屈服强度的提高均有贡献。其中,纳米级析出相对屈服强度的贡献值更大,约为亚微米级第二相的6倍。相比于Cu-2.5Fe合金,Si的添加促进了合金基体中铁相的析出及细化,降低了动态再结晶温度,进而实现了合金强度、电导率和塑性的协同提高。

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.

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℃.

Phase Transformation and Deformation Mechanism of Ti_3Al-base Alloy

The phase transformation and deformation mechanism of the alloy based on composition Ti_3Al with addition of Nb,V,Mo have been studied by use of transmission electron microscopy (TEM).It has been shown that the orientation relationship of α_2 phase transformed from β phase is:(0001)α_2// (l10)β,[1210]α_2//[111]β.The present dislocation slip systems in α_2 phase are (1100)[0001] and (1100)<1120>.There also exist α_2 twins which have new twin relationship and the twin plane is (2021).

Microstructure and Properties of Ti_3Al-base Alloys

In the present paper, the relations between the microstructure and the properties of Ti-14Al-21Nb and Ti-14Al-20Nb-3.5V-2Mo alloys at different temperatures and different cooling rates of heat treatment were re-vealed by X-ray , optical microscope , HVTEM , auto-graphical-analyser and mechanical properties test at roomand high temperature. The experimental results show as follows: at 1040～1120℃ 14h WQ, the microstruc-ture of Ti-14Al-21Nb bar is primary phaseα_2+B2. With temperature increasing, the primary α_2 phase de-crease and the mechanical properties ultimate tensile strength (UTS), yield strength (YS) and elongation(EL) at room temperature increase. When it has reduced the α_2 phase by 50% (at 1080℃/4h WQ) , the me-chanical properties at room temperature are excellent , EL being 10. 5%. Following the α_2 phase reduces contin-uously , UTS, YS are going up, but EL is going down. After heated at two phases range and cooled down tothe room temperature with furnace, the microstructure of Ti-14Al-20Nb-3.5V-2Mo alloy is the equiaxed α_2+needle-like α_2+βphase. The mechanical properties at room temperature and 700℃ are fairly good.

SUPERPLASTICITY IN LARGE-GRAINED Fe_3Al ALLOYS

The superplasticity behavior of Fe-28Al, Fe-28Al-2Ti, Fe-28Al-4Ti (all composition reported in this paper are in atomic percent) alloys has been investigated by tensile testing.optical microscopy and transmission electron mocroscopy.Tensile test were performed at 700 to 900℃ under a strain rate range of about 10-5/s to 10-2/s. Maximum strain rate sensitivity index m was found to be 0.5 and the largest elongation reached 620%. The flow activation energy was measured to be 263kJ/mol for Fe-28Al and 191kJ/ mol for Fe-28Al-2Ti, which are much lower than the creep activation energy generally observed in Fe3Al alloys. After deformation grain size became much finer from about 100 μm to 20-30μm.As combined with TEM observations, we suggested that a continuous recrystallization process took place and superplasticity may arise from this process.

NANOCRYSTALLINE STRUCTURE AND INITIAL PERMEABILITY OF ANNEALED Fe_(73.5)Cu_(1)W_(3)Si_(13.5)B_(9) Alloy

The nanocrystalline structure of annealed Fe73.5 Cu1 W3Si13.5B9 alloy has been investigated by using the XRD and the TEM methods. The relation between the initial permeability and the microstructure of the annealed alloy has been discussed. The crystalline phase in annealed Fe73.5 Cu1 W3Si13.5B9 alloy is the α-Fe(Si) phase with DO3 superstructure. The volume fraction, Si content and degree of order of the αFe(Si) phase increase with increasing annealing temperature. In the temperature range of 490-570℃, the α-Fe(Si) phase has a size of 13 nm, and its grain number increases as the annealing temperature is increased. The DO3 ordered region in the α-Fe(Si) grain is spherical approximately, and its size increases as the annealing temperature increases. The size of the DO3 ordered region is 12.8 nm at the temperature of 570℃,which is close to that of the α-Fe(Si) grain. There is obvious change in the structure of the residual amorphous phase during annealing, and the nearest atomic distance and the short-range order of residual amorphous phase reach maximum and minimum at 530℃, respectively. The initial permeability of annealed Fe73.5 Cu1 W3Si13.5 B9 alloy is not only dependent on the size, volume fraction and Si content of the α-Fe(Si) phase but also related to the structure state of the residual amorphous phase.

Effects of laser shock processing,solid solution and aging,and cryogenic treatments on microstructure and thermal fatigue performance of ZCuAl_(10)Fe_(3)Mn_(2)alloy

The materials used in variable temperature conditions are required to have excellent thermal fatigue performance.The effects of laser shock processing(LSP),solid solution and aging treatment(T6),and cryogenic treatment(CT)on both microstructure and thermal fatigue performance of ZCuAl_(10)Fe_(3)Mn_(2) alloys were studied.Microstructure and crack morphology were then examined by scanning electron microscopy(SEM)and energy-dispersive X-ray spectroscopy(EDS).The result showed that,after being subjected to the combination treatment of T6+CT+LSP,the optimal mechanical properties and thermal fatigue performance were obtained for the ZCuAl_(10)Fe_(3)Mn_(2) alloy with the tensile strength,hardness,and elongation of 720 MPa,300.16 HB,and 16%,respectively,and the thermal fatigue life could reach 7,100 cycles when the crack length was 0.1 mm.Moreover,the ZCuAl_(10)Fe_(3)Mn_(2) after combination treatment shows high resistance to oxidation,good adhesion between the matrix and grain boundaries,and dramatically reduced growth rate of crack.During thermal fatigue testing,under the combined action of thermal and alternating stresses,the microstructure around the sample notch oxidized and became loose and porous,which then converted to micro-cracks.Fatigue crack expanded along the grain boundary in the early stage.In the later stage,under the cyclic stress accumulation,the oxidized microstructure separated from the matrix,and the fatigue crack expanded in both intergranular and transgranular ways.The main crack was thick,and the path was meandering.

Cr含量对Fe_(3)Al合金电子结构及力学性能影响的第一性原理

采用基于密度泛函理论的第一性原理方法研究了Cr含量对DO_(3)-Fe_(3)Al合金电子结构及力学性能的影响.通过计算掺杂前后体系的形成热和结合能明确Cr在超晶胞模型中的占位;通过计算各体系的弹性模量、布居、态密度及差分电荷密度揭示了Cr对Fe_(3)Al合金力学性能影响的微观机制.结果表明:含量为3.125 at.%时,Cr优先占据FeΙ位,含量为6.25 at.%时,Cr倾向于占据FeΙ和Al位;Cr的掺杂提高了体系的稳定性,改善了合金的脆性,且增韧效果随着Cr含量的增加而增加;Cr掺杂改变了原子之间的电子分布,随着Cr含量的增加,Fe-Al之间p-d杂化电子数减少、共价键性减弱,同时原子之间电荷转移量增加,Fe-Fe键的增强以及Fe-Cr、Al-Cr反键的存在增强了体系的金属性,加之(100)面上共价键的减弱以及(010)面原子间键合强度的增加等因素都提高了Fe3Al合金的韧性.

Laser powder bed fusion of a Ni3Al-based intermetallic alloy with tailored microstructure and superior mechanical performance

Ni3Al-based alloys are excellent candidates for the structural materials used for turbine engines due to their excellent high-temperature properties.This study aims at laser powder bed fusion and post-hot isostatic pressing(HIP)treatment of Ni3Al-based IC^(-2)21 M alloy with a highγ0 volume fraction.The as-built samples exhibits unavoidable solidification cracking and ductility dip cracking,and the laser parameter optimization can reduce the crack density to 1.34 mm/mm^(2).Transmission electron microscope(TEM)analysis reveals ultra-fine nanoscaleγ0 phases in the as-built samples due to the high cooling rate during rapid solidification.After HIP treatment,a fully dense structure without cracking defects is achieved,which exhibits an equiaxed structure with grain size~120-180μm and irregularly shapedγ0 precipitates~1-3μm with a prominently high fraction of 86%.The room-temperature tensile test of as-built samples shows a high ultimate tensile strength(σUTS)of 1039.7 MPa and low fracture elongation of 6.4%.After HIP treatment,a significant improvement in ductility(15.7%)and a slight loss of strength(σUTS of 831.7 MPa)are obtained by eliminating the crack defects.Both the as-built and HIP samples exhibit retained highσUTS values of 589.8 MPa and 786.2 MPa,respectively,at 900C.The HIP samples exhibita slight decrease in ductility to~12.9%,indicating excellent high-temperature mechanical performance.Moreover,the abnormal increase in strength and decrease in ductility suggest the critical role of a highγ0 fraction in cracking formation.The intrinsic heat treatment during repeating thermal cycles can induce brittleness and trigger cracking initiation in the heat-affected zone with notable deteriorating ductility.The results indicate that the combination of LPBF and HIP can effectively reduce the crack density and enhance the mechanical properties of Ni_(3)Al-based alloy,making it a promising material for high-temperature applications.

Effect of post-weld heat treatment on microstructure and properties of Ti-23Al-17Nb alloy laser beam welding joints

The mechanical properties of Ti-23Al-17Nb (mole fraction,%) laser beam welding alloy joint at room temperature are comparable to that of the base materials.However,the strength and ductility of the as-welded joint deteriorate seriously after high temperature circulation.The effect of post-welded heat treatment on the microstructure and mechanical properties of the joint was investigated.The heat treatment was taken at 980 ℃ for 1.5 h,then furnace cooling and air cooling were performed separately.The results indicate that proper post-welded heat treatment improves the ductility of the joint at high temperature.

Microwave absorption properties regulation and bandwidth formula of oriented Y_(2)Fe_(17)N_(3-δ)@SiO_(2)/PU composite synthesized by reduction-diffusion method

As concepts closely related to microwave absorption properties,impedance matching and phase matching were rarely combined with material parameters to regulate properties and explore related mechanisms.In this work,reduction–diffusion method was innovatively applied to synthesize rare earth alloy Y_(2)Fe_(17).In order to regulate the electromagnetic parameters of absorbers,the Y_(2)Fe_(17)N_(3-δ)particles were coated with silica(Y_(2)Fe_(17)N_(3-δ)@SiO_(2))and absorbers with different volume fractions were prepared.The relationship between impedance matching,matching thickness,and the strongest reflection loss peak(RLmin)was presented obviously.Compared to the microwave absorption properties of Y_(2)Fe_(17)N_(3-δ)/PU absorber,Y_(2)Fe_(17)N_(3-δ)@SiO_(2)/PU absorbers are more conducive to the realization of microwave absorption material standards which are thin thickness,light weight,strong absorbing intensity,and broad bandwidth.Based on microwave frequency bands,the microwave absorption properties of the absorbers were analyzed and the related parameters were listed.As an important parameter related to perfect matching,reflection factor(√ε_(r)/μ_(r))was discussed combined with microwave amplitude attenuation.According to the origin and mathematical model of bandwidth,the formula of EAB(RL<-10 dB)was derived and simplified.The calculated bandwidths agreed well with experimental results.

非晶合金Fe_(3)Ni_(3)的轨道杂化及成键性质研究

为探究团簇Fe_(3)Ni_(3)优化构型内的轨道杂化及成键情况,在密度泛函理论中的B3LYP/Lanl2dz水平下,利用Gaussian软件对构型进行全参数优化计算后,得到9种稳定的优化构型,发现三重态构型均较单重态构型稳定。进一步分析各优化构型的态密度发现,团簇Fe_(3)Ni_(3)各优化构型内部主要存在4s-4s、4p-4p、4p-3d与3d-3d 4种轨道杂化方式,其中4s-4s轨道杂化贡献最弱,3d-3d轨道杂化的贡献最强。从键长、键级与键级贡献比3个角度探究成键性质发现,Fe—Fe键与Fe—Ni键的存在对构型稳定性均具有促进作用,其中三重态中Fe—Ni键起主要贡献作用,而单重态中Fe—Fe键贡献作用最大,说明自旋多重度对构型内成键具有选择性,进而影响其稳定性。

EFFECT OF HYDROGENATION ON THE MICROSTRRUCTURE OFTi-24Al-14Nb-3V-0.5Mo ALLOY

The ebct of hydrogenation-dehydrogenation on the microstructure of forping Ti-24Al14Nb-3V-0.5MO alloy was investigated by TEM and X-ray ddection. The resultsshowed that the microstructure consists of O and B2 phases as received materials, and tmoprmation of B2 phase to O phase can be eNctively promoted 6y hydrogenation. The lamellate γ hydride was found in O phase with more hydmpen content, and this γ hydride could be decomposed by dehydmpenation treatment. The sole fine Ophase could be obtained 6y hydmpenation-dehydmpenation treatment, and two possible mechanisms for the microstructure improvetnent have been discussed on the basis of experimental results.

Effect of near isothermal forging on the microstructure of Ti_3Al/TC11 welding interface

The as-forged Ti3Al-based alloy and TC11 titanium alloy were welded by electron beams in vacuum, and then they were processed using near isothermal forging and gradient heat treatment. The experimental results show that the near isothermal forging processing parameters have little effect on the phase constitution of the weld. The weld consists of Ti2AlNb, MoNb, Nb3Al, and TiAl3 phases as well as the two main phases of α and α2. However, the near isothermal forging processing parameters have significant effect on the shape, size, and volume fraction of α and α2 phases of the welding interface. The sizes of the α and α2 phases increase as the strain rate decreases. Because the distortion energy of the lattice and the volume fraction of the grains occurring in dynamic recrystallization increase with an increase in deformation, the sizes of the α and α2 phases of the welding interface decrease.

Microstructure Evolution of Primary γ′ Phase in Ni3Al-Based Superalloy

In this work,water cooling,air cooling(AC)and furnace cooling(FC)were applied to investigate the effect of cooling rate on microstructure evolution of primaryγ′in a newly designed Ni3Al-based alloy.The results showed that nucleation rate of primaryγ′increased with increasing cooling rate.In addition,higher cooling rate shortened growth period of primaryγ′,which made its morphology close to the initial precipitatedγ′.For AC and FC specimens,due to the lower cooling rate,primaryγ′possessed longer growth period and its morphology was mainly due to the evolution of lattice misfit betweenγand primaryγ′.Meanwhile,growth of primaryγ′depended on lattice misfit distribution between its corner and edge area.Moreover,primaryγ′morphologies of sphere,cube and concave cube with tip corners were illustrated by considering interaction between elemental diffusion and elastic strain energy.

Microstructure and mechanical properties of directionally solidified Al-rich Ni_(3)Al-based alloy under static magnetic field

The influence of a longitudinal static magnetic field on microstructures and mechanical properties of Ni_(3)Al-based alloy during directional solidification at the growth speed of 25μm/s and 100μm/s has been experimentally investigated.Results reflected that the utilization of a 0.5 T magnetic field refines the Ni Al dendrites at both speeds of growth.When applying a high magnetic field,the columnar-to-equiaxed transition(CET)occurred at growth speed of 25μm/s and dendrite networks formed at growth speed of 100μm/s.Tensile property results indicated that the refinement of dendrites enhanced both plasticity and ultimate tensile strength of Ni-Al alloy.The change of microstructures and mechanical properties should be attributed to the combined action of the thermoelectric magnetic convection(TEMC)in mushy zone together with the thermoelectric magnetic force(TEMF)acting on the solid.When applying a low magnetic field(0.5 T),the TEMF is too small to fragment the dendrites,and the refined dendrites is mainly due to the TEMC in the interdendritic regions.At a lower growth speed,the TEMF is supposed to strong enough to fragment the dendrites and induce the occurrence of CET under 2 or 4 T.When the growth speed increased to 100μm/s,no obvious CET was observed,but a vertical secondary convection is induced by the circulation in the parallel plane,which promotes the growth of secondary and tertiary branches,leading to the formation of abnormally developed high order dendrites.The hierarchical dendritic structure was suggested to provide a channel for rapid crack propagation and thus degraded the mechanical properties.

Fe_(34)Cr_(30)Mo_(15)Ni_(15)Nb_(3)Al_(3)高熵合金在500℃下氧含量为10^(-6)%的液态铅铋合金中腐蚀行为研究

制备了Fe_(34)Cr_(30)Mo_(15)Ni_(15)Nb_(3)Al_(3)高熵合金,铸态组织包含FCC相、Laves相和B2-NiAl相。随后将高熵合金置于500℃、氧浓度为10-6%(质量分数)的液态铅铋合金中进行1000~2000 h的静态腐蚀实验。结果表明:高熵合金未发生明显的元素溶解、铅铋渗透和相变。静态腐蚀1000~2000 h后,Laves相区域表面只生成了Fe-Cr尖晶石。但腐蚀1000 h后,FCC/B2-NiAl相区域表面除了内层生成了Fe-Cr尖晶石,外层还生成了贫Cr的FeCr尖晶石;随着腐蚀时间增加到1500 h,FCC/B2-NiAl相区域外层贫Cr的Fe-Cr尖晶石发生脱落;腐蚀2000 h后,Fe3O4开始生成,覆盖FCC/B2-NiAl相区域外表面。高熵合金表面的氧化层均较薄,厚度不超过3μm,表现出较好的耐腐蚀性。高熵合金具有良好耐腐蚀的原因是由于Laves相分布均匀,抑制了金属元素的向外扩散。