热轧对Ti50Ni50-xAlx(x=1,2,4)形状记忆合金微观组织、相变和力学性能的影响

形状记忆合金的相变和力学性能受机械加工过程影响明显.在850℃下将Ti50Ni50-xAIx(x=1,2,4)形状记忆合金轧制成为板材.采用扫描电镜、透射电镜和X射线衍射对合金的微观结构研究表明:合金由NiTi相和Ti2Ni相组成,Al元素在Ti2Ni相中的固溶度比在TiNi相中高.差示扫描量热分析和电阻-温度测试表明...     

Al含量对空心阴极等离子烧结Ti/Ni等原子比TiNiAl合金组织和力学性能的影响

 采用空心阴极等离子烧结工艺制备了Ti/Ni等原子比的Ti_50-x/2Ni_50-x/2Al_x(x=0,3,6,9)合金,研究了Al含量对合金微观组织以及力学性能的影响。结果表明:未添加铝的合金微观组织主要由NiTi基体、强化相Ti₂Ni、Ni₃Ti及孔隙组成;随着Al含量的提高,合金中Ti₂Ni(Al)数量不断增多,孔隙数量和孔径不断增加,Ni₃Ti(Al)数量不断减少,在Ti_45.5Ni_45.5Al₉中还生成了少量Ni₂TiAl相;合金的抗弯强度随Al含量的提高而增加,并在Al含量为6%时达到最大值296.3 MPa;合金的硬度随铝含量的提高而增加,Ti_45.5Ni_45.5Al₉的硬度值为295.6 HV。     

TiNiFeNb形状记忆合金的组织结构及相变特性

通过向TisoNiso合金中加入Fe和Nb元素,制备出一种四元Ti49Ni50-xFexNb1形状记忆合金.采用X射线衍射和背散射电子衍射的方法,测试和分析了合金的相结构及微观组织形态,采用电阻法系统研究了合金的相变特性.结果表明:Nb元素的加入并没有改变TiNiFe合金的B2结构,仅导致了广极少量的富Nb相在基体中析...     

轧制NiMnFeGa高温形状记忆合金的微观结构及拉伸力学性能

 采用包套热轧的方法，将Ni56Mn17Fe8Ga19和Ni56Mn15Fe10Ga19合金铸锭成功轧制为均匀板材，研究了其微观组织结构、相变特性和拉伸力学性能等。结果显示，轧制后合金的晶粒和γ相变得细碎，且沿着轧制方向伸长分布，其逆马氏体相变温度下降，相变滞后减小；轧制态合金的抗拉强度和延伸率分别超过500 MPa和2%，热处理后，强度降低而延伸率上升。     

新型Co基合金Co-9Al-(9-x) W-xMo-2Ta-0.02B的显微组织与高低温力学性能

以新型Co基合金Co-9Al-9W-2Ta-0.02B成分为基础,分别添加了原子分数为2％、4％、6％、9％的Mo元素替代W（分别称2Mo、4Mo、6Mo、9Mo合金,W+Mo的原子分数为9％,无Mo添加的称为0Mo合金）,研究了Mo元素对合金相组成、显微组织形貌、维氏硬度和高低温压缩强度的影响.结果表明铸态合金由Co...     

Effect of W addition on phase transformation and microstructure of powder metallurgic Ti-22Al-25Nb alloys during quenching and furnace cooling

Powder metallurgic Ti2 AlNb alloys with W addition are sintered at 900, 1000, 1070 °C,and 1150 °C(i.e., in the O + B2, a_2+ B2 + O, a_2+ B2, and single B2 phase regions, respectively)for 12 h, followed by water quenching and furnace cooling. Comparisons of phase and microstructure between quenched and furnace-cooled W-modified alloys are carried out to illustrate the phase transformation and microstructure evolution during the cooling process. Furthermore, a comparison is also made between W-modified and W-free alloys, to reveal the function of the W alloying.W addition accelerates the solutions of a_2 and O phases during the high-temperature holding, and a Widmannsta¨tten B2 + O structure, which contributes to the properties, is induced by furnace cooling from all the phase regions. The Widmannsta¨tten structure includes a B2 matrix, primary O, and secondary O precipitates. However, W alloying refines the Widmannsta¨tten structure only when the alloys are solution-treated and then cooled from the single B2 phase. Although the hardness of the W-modified alloys is lower than that of the W-free alloys sintered in the same phase region, an enhancement of hardness, 489 ± 18 HV, is obtained in the alloy solution-treated in the single B2 phase region for only 0.5 h.     

Microstructure and Mechanical Properties of In-situ Synthesized Al2O3/TiAl Composites

Al2O3 particle-reinforced TiAl composites are successfully reaction-synthesized from the powder mixture of Ti, Al, TiO2, and Nb2O5, using the hot pressing reaction synthesis technique. The microstructure and mechanical properties of the as-sintered products are investigated. It is found that in the as-sintered products consisting of γ-TiAl, α2-Ti3Al, Al2O3, and NbAl3 phases, the fine Al2O3 particles tend to disperse on the grain boundaries. With the Nb2O5 content increasing, the grains are remarkably refined and the Al2O3 particles are dispersing more uniformly in the TiAl matrix, forming a partial lamellar structure containing α and lamellar phases. The hardness of the in-situ composites increases gradually, and the bending strength and the fracture toughness of the as-sintered products reach the maximum value of 398.5 MPa and 6.99 MPa·m^1/2, respectively, as the Nb2O5 content increases to 6 wt%.     

Mechanical Properties and Transformation Behavior of NiTiNb Shape Memory Alloys

NiTiNb shape memory alloys have attracted much attention in pipe coupling or sealing system because of their large transformation hysteresis upon a proper pre-deformation. In order to clarify the effects of adding Nb on the mechanical properties as well as the transformation behavior of NiTiNb shape memory alloys, Ni₄₇Ti₄₄Nb₉ and Ni_49.8Ti_45.2Nb₅ alloys with different microstructures but with similar martensitic transformation start temperature, are prepared. Comparative studies on the microstructures, mechanical properties and transformation characteristics are conducted by means of scanning electron microscopy (SEM), phase transformation measurements and mechanical property tests. It is found that Ni₄₇Ti₄₄Nb₉ and Ni_49.8Ti_45.2Nb₅ alloys possess similar transformation hysteresis in the as-annealed state. However, the presence of Nb and its status exerts important effects on the mechanical properties, especially the yield strength and the yield behavior of the alloys. Ni_49.8Ti_45.2Nb₅ alloy exhibits remarkable increase in the yield strength than the Ni₄₇Ti₄₄Nb₉ alloy. The transformation hysteresis of both alloys under pre-deformation is characterized and the relative mechanism is discussed.     

Nb对富钛TiNiAl金属间化合物强化机制的影响

 采用力学压缩试验、扫描电镜和X射线衍射方法研究了Nb元素对于Ti₅₀Ni₄₂Al₈合金的力学性能和微观组织结构的影响。结果表明，Nb能够显著提高合金从室温到700 ℃之间的强度。在600 ℃时，Ti₅₀Ni₄₀Al₈Nb₂合金的压缩屈服强度和比强度分别为1 237 MPa和216 MPa/(g·cm^-3)，超过Rene95高温合金。微观组织观察及成分分析表明，Nb元素在基体和强化相Ti₂Ni（Al）中固溶，促进强化相的弥散析出和细化，并导致高强富Nb相的析出，从而提高了合金的强度。     

Effects of Nb Content on Yield Strength of NiTiNb Alloys in Martensite State

Two near single-phase NiTiNb alloys—Ni₅₀Ti₄₈Nb₂ and Ni_49.5Ti_46.5Nb₄—are prepared and studied by means of scanning electron microscopy (SEM), energy dispersive spectroscopy (EDS), differential scanning calorimetry (DSC) and tensile tests in order to unearth the effects of Nb-atom solid solution in NiTi phase on the yield strength induced by self-accommodation of martensite variants. The results show that the yield strength of near single-phase NiTiNb alloys varies inversely with the amount of Nb-atoms solid-dissolved in NiTi phase. From the results out of the prior and current studies, it can be surmised that the effects of Nb content on the yield strength of NiTiNb alloys in martensite state depend on the coaction. Nb solid solution weakening mechanism and β-Nb phase composite strengthening mechanism. This inference might be a satisfactory explanation to the fact that the yield strength of (NiTi)_50–0.5xNb_x alloys in martensite state begins with decline and then rises when the Nb content increases.     

Microscopic Phase-field Simulation of Effects of Re-ageing Temperature on Precipitation of Ni-Al-Cr Alloys

This article, by means of the ternary microscopic phase-field model, investigates the effects of re-ageing temperature on the precipitation of Ni₇₅Al₁₀Cr₁₅ alloy with the help of atomic pictures, order parameters, particle density, averaged radii, and volume fractions. During pre-ageing at 873 K, DO₂₂ phases first appear through spinodal decomposition mechanism, and then L1₂ phases begin to form on the DO₂₂ phase-boundaries through non-classical nucleation mechanism. In either of them, ordering process is obviously faster than atom clustering. At the late stage of re-ageing at 923 K, the elastic strain energy seems to exert stronger effects on microstructure, and DO₂₂ and L1₂ phases exhibit directional alignment along <100> direction to a certain extent. When the temperature increases to 1 023 K, the influence of elastic strain energy begins to weaken, and the precipitated phases become randomly distributed in the matrix. The volume fraction of DO₂₂ phase decreases to zero, whereas that of L1₂ phase first increases and then decreases with the temperature rising from 923 K to 1 123 K. On the whole, the effects of elastic strain energy make the coarsening behavior of both phases deviate from the time-law predictions by LSW diffusion-controlled growth theory.     

落管中Ni-Pb偏晶型合金的快速凝固组织特征及形成机制

Ni基偏晶合金是一种优良的自润滑耐磨材料,其组织形成规律对力学性能的影响十分关键.在自由落体条件下,对不同成分二元Ni-Pb偏晶型合金的快速凝固进行了实验研究.随着液滴直径的减小,Ni-20%Pb亚偏晶合金中α-Ni枝晶生长经历"粗大枝晶→等轴晶→蠕虫状枝晶"的转变.Ni-31.4%Pb偏晶合金的凝固组织以偏晶胞为主,...     

铣削加工透波性Si3N4陶瓷表面质量研究

为了探索透波性Si3N4陶瓷铣削中加工表面创成机理及加工工艺参数对其影响规律,对加工表面形貌和边缘破损特征,以及加工参数与切削力、表面粗糙度、边缘破损的映射关系等开展了试验研究。首先对加工表面形貌进行了分析,由于存在陶瓷粉末去除和破碎性颗粒去除两种形式,造成加工表面形貌结构一种体现为变化平缓,而另一种包含微裂纹、层状结构体等,且存在凹坑、沟槽等缺陷。其次研究了边缘破损形式及产生机理,当刀具运动到出口棱边处,刀尖应力集中处将产生微裂纹,并向工件侧面扩展,从而在加工表面和加工侧面诱导形成边缘破损。最后基于均匀设计试验,分析了工艺条件对加工性能的影响。结果表明:随着切削深度从0. 2增加到0. 5 mm和切削宽度从1增加到4 mm时,x轴切削力呈耦合增长,y轴切削力呈二次方增长;当切削深度和切削宽度分别为0. 2 mm和1 mm、进给速度为500 mm/min时,加工表面粗糙度值最小;转速为2 000 r/min、切削深度和切削宽度最小时,边缘破损幅值最小。此结果可为提高透波性Si3N4陶瓷铣削加工质量提供技术支撑。     

气氮调温器Y型喷嘴实验及数值研究

基于FLUENT软件离散相模型及气体助力雾化模型,采用欧拉-拉格朗日方法研究通过Y型喷嘴雾化液氮的雾化特性.由于液氮液滴的蒸发相变,与水相比喷雾锥角更清晰且明显减小,约为10°,喷雾距离缩短.分析喷嘴气液工作压力对液氮雾化索太尔平均直径（SMD）、液滴体积分数和数量分数的影响.结果表明：SMD沿喷射方向变化幅度极小;SMD主要受气相速度及气液比影响,气压低时气相速度影响较大,气压高时气液比影响较大;由于相变作用,液氮雾化粒径分布更为集中.数值研究Y型喷嘴用于不同流量需求的气氮调温器的调温效果,出口温度低于98K,进出口温差达到12K,且整个出口温差在±1K以内,能够实现精确控温要求.     

Satellite Measurements of Middle Atmospheric Impacts by Solar Proton Events in Solar Cycle 23

Solar cycle 23 was extremely active with seven of the largest twelve solar proton events (SPEs) in the past forty years recorded. These events caused significant polar middle atmospheric changes that were observed by a number of satellites. The highly energetic protons produced ionizations, excitations, dissociations, and dissociative ionizations of the background constituents in the polar cap regions (>60 degrees geomagnetic latitude), which led to the production of HO_x (H, OH, HO₂) and NO_y (N, NO, NO₂, NO₃, N₂O₅, HNO₃, HO₂NO₂, BrONO₂, ClONO₂). The HO_x increases led to short-lived ozone decreases in the polar mesosphere and upper stratosphere due to the short lifetimes of the HO_x constituents. Polar middle mesospheric ozone decreases greater than 50 % were observed and computed to last for hours to days due to the enhanced HO_x. The NO_y increases led to long-lived polar stratospheric ozone changes because of the long lifetime of the NO_y family in this region. Upper stratospheric ozone decreases of >10 % were computed to last for several months past the solar events in the winter polar regions because of the enhanced NO_y.     

NiTiAl Intermetallic Alloys Strengthened by Mo Replacement

 NiTiAl based alloys have attracted attention as potential high temperature structural materials. Alloying is an effective way to improve their mechanical properties. The microstructures and mechanical properties of Ni₅₀Ti_44-xAl₆Mo_x (x = 0, 0.5, 1, 1.5, 3) alloys have been investigated by X-ray diffraction (XRD), scanning electron microscope (SEM), transmission electron mi-croscope (TEM) and compressive tests. It is found that Ni₅₀Ti_44-xAl₆Mo_x alloy is composed of NiTi (B2) and Ti₂Ni (FCC) phases when Mo content is no more than 1 at%. The effect of Mo solid solution hardening at room temperature has been indi-cated by the rise of yield strength and the fall of plasticity with increasing Mo content. For Ni₅₀Ti_42.5Al₆Mo_1.5 and Ni₅₀Ti₄₁Al₆Mo₃ alloys, a Mo solid solution appears and increases the yield strength by precipitation strengthening. The maxi-mum yield strength at 600 °C and elevated temperatures is presented in Ni₅₀Ti₄₃Al₆Mo₁ alloy not in alloys with a higher Mo content, which is possibly due to the softness of Mo-Ti-Ni solid solution phase.     

Microstructural evolution and hardness of as-cast Be-Al-Sc-Zr alloy processed by laser surface remelting

As-cast beryllium-aluminum (Be-Al) alloy exhibits a coarse microstructure with pore defects due to a large solidification interval, greatly limiting its mechanical properties. In this research, the relationship between laser surface remelting process and microstructure and hardness of as-cast Be-Al-Sc-Zr alloy was established. The experimental results demonstrated that a pore-free refined microstructure of remelted layer was obtained by controlling the parameter of effective laser energy input. The microstructure of as-cast Be-Al-Sc-Zr alloy consisted of equiaxed grains with Al phase forming a continuous frame wrapping Be phase, which was significantly refined in the remelted zone (from 25 μm to 2 μm). The Vickers hardness in the remelted zone (approximately 210 HV) was approximately 3 times that of as-cast Be-Al-Sc-Zr alloy. Analysis of the Vickers hardness and the Be phase size showed a good agreement with a Hall-Petch equation. In addition, transmission electron microscopy (TEM), auger electron spectroscopy (AES) and X-ray diffraction (XRD) analysis evidenced that Sc and Zr elements formed a single blocky phase Be₁₃(Sc_x,Zr_1-x), which was also greatly refined from 8 μm to 1.5 μm in the remelted zone. The results obtained in this study indicate that the laser surface remelting allowed refining the microstructure and further strengthening the Vickers hardness of Be-Al-Sc-Zr alloy.     

Yield anisotropy and tension/compression asymmetry of a Ni3Al based intermetallic alloy

In order to investigate the yielding behavior of the newly developed Ni 3 Al-based intermetallic alloy IC10, yield stresses have been measured in tension and compression with different orientations. The specimens were cut from a sheet with different angles inclined from the solidification direction. The inclined angles were taken to be 0 , 22.5 , 45 , 67.5 and 90 . All experiments were conducted at room temperature except for orientation 0 , whose deformation temperatures ranged from 298 to 1273 K. Experimental results show that the yield strength of alloy IC10 has the anomalous behavior which has been observed for other Ll 2 -long-range ordered intermetallic alloys, but it is less pronounced. The abnormalities show the following characteristics: (i) the yield strength increases as the temperature is raised below the peak temperature, (ii) yield strength anisotropy, (iii) tension/compression asymmetry. Compared to Ni 3 Al single crystals, the polycrystalline exhibits some different yielding behaviors which may be due to the high volume fraction of c phase.     

掺Mg对Bi Pb Sr Ca Cu O体系中110K超导相生成的影响

用固相反应法合成了名义组分为Bi_xPb_ySr₂Ca_1.7Mg_0.3Cu_zO_w的块状超导体。根据直流电阻和交流磁化率测量的结果,给出了在7个不同温度下烧结的6个组分化合物的超导临界温度。在833℃到843.3℃范围内,110K相对80K相的体积比随着烧结温度的提高而增加。分析了断口形貌。对110K相的生成有影响的Pb和Bi在样品中的剩余量受烧结温度和时间的控制。Bi Pb Sr Ca Mg CuO体系之所以能在较低烧结温度下形成超导相是由于掺Mg造成了部分熔点的降低。     

A组分变化对AB5型储氢合金组织结构及电化学性能的影响

通过实验验证的方法选取AB5型合金三种成分La1-xAx(Ni,Co,Sn)5,采用SEM、EDXA、XRD以及P-C-T曲线和电化学性能测定装置,综合研究了三样品中A组分变化时对合金组织结构及电化学性能的影响.结果表明,合金三样品均为CaCu5型六方结构.用Nd和Ce部分取代La后,合金吸氢后体胀率降低.P-C-T曲线测定结果表明用Ce部分取代La的3号样品的动力学性能及大电流放电性能较好.合金的充放电循环稳定性是AB5-3﹥AB5-2﹥AB5-1,但容量以纯La 合金的较高.