锂硼合金的反应合成及相关现象研究

研究了Li-B合金的合成过程,对合金熔炼特性进行了分析,发现Li-B合金的第一步反应完成后,熔体对铁坩埚的润湿性大大增加,认为第二步反应主要依赖于熔体的Li-B化合物,XRD分析结果显示在第二步反应前有少量Li_7B_6生成,采用SEM对合金的显微组织进行了观察与分析。     

锂硼合金反应合成机制

提出了锂硼合金反应合成的物理模型,反应过程中有2次放热反应,第1次放热反应分成3个阶段:第1阶段为Li与B粒在界面(～330℃)的瞬时反应,此放热量与B粒的半径成反比;第2阶段为Li液通过附着在B粒表面LiB_3中的扩散而与内核B的反应,此过程可用固体反应中的金斯特林格模型来描述,其反应速率常数与B粒的半径平方成反比;第3阶段是在425℃以上将LiB_3溶解到Li液体中,但与此同时,第2次放热反应也在开始进行。第2次放热反应通过Li-B化合物的形核和长大来完成,它分成形核孕育和爆发反应2个阶段。有足够形核数目时,产生爆发性反应。温度越低,产生爆发性反应所需时间越长。运用该模型解释了合成实验中出现的现象。     

新型LiB化合物晶体结构和形貌的研究(Ⅰ)

对新型热电池阳极材料Li-B合金中的耐热骨架LiB化合物进行了晶体结构测定和形貌观察,获得了该化合物完整的X射线衍射谱线,经过XRD谱的衍射强度计算和电子密度函数分析,确定该化合物化学组成为LiB,属于六方晶系,空间群为No.194,晶格常数α=0.4022 nm,c=0.2796 nm;单中原子坐标B_1(0,0,0),B_2(0,0,1/2),Li_1(2/3,1/3,0),Li_2(1/3,2/3,1/2),理论密度d=1.50 g/cm~3,电子密度函数分析表明LiB化合物中Li原子的电子向B原子迁移,B原子之间有高密度电子云区,呈共价键特征,SEM观察结果表明,LiB化合物呈纤维状,合金经轧制后纤维沿轧向排列,X射线平板照相实验结果表明它具有丝织构特征,其衍射花样也与本结构模型计算结果一致。     

WC-Co合金的密度影响因素及变化范围

一、前言 密度是硬质合金的主要性能之一,它能够基本反映合金的成分。密度有三种,即真密度、似密度和有效密度。在烧结合金的表面和内部总会存在一些孔隙,在这些孔隙中与外表面相通的孔隙,叫作开孔或半开孔（一端相通）,不与外表面相通的孔隙叫作闭孔。合金质量除以不包括开孔和闭孔体积所得到的值称作真密度,真密度实际上就是合金的理论密。     

Ta-W合金的密度分析

通过Ｘ射线衍射实验的方法测定了较高Ｗ含量的Ｔａ－Ｗ二元合金的晶格常数。用纯Ｔａ与合金的晶格常数之比再乘以按重量百分比计算的密度，求出合金的理论密度，并与按重量百分比计算的密度和实验测定的密度对比。分析３种实验方法计算的密度存在差异的原因，溶质元素Ｗ添加引起晶体结构产生“缩距”现象。结果表明：（１）Ｔａ－Ｗ合金随Ｗ含量的增加，晶格常数明显缩小，合金的密度升高；（２）Ｔａ－Ｗ合金按重量百分比计算的密度与实测的密度存在较大差异，而按晶格常数计算的理论密度与实测密度基本一致；（３）对于推算二元系无限连续固溶体的密度，根据合金的晶格常数计算的理论密度较为准确。     

硼粉粒度对Li-B合金结构及热稳定性的影响

分别以3种粒度的硼粉为原料,采用相同的成分配比和工艺参数熔炼制备Li-B合金铸锭。合金铸锭经挤出和轧制获得薄带。随后进行X射线衍射(XRD)测试、扫描电子显微镜(SEM)观察、化学成分分析和热稳定性测试。XRD结果显示,Li-B合金由Li_7B_6相和锂相组成,且Li_7B_6相与锂相的衍射峰强度比随硼粉粒度的增大而减小。SEM观察表明,随原料硼粉粒度的增大,Li-B合金的纤维组织变得粗大且不均匀。化学成分测试显示,Li-B合金中化合态硼含量随硼粉粒度的增大而减小。热稳定性测试表明,原料硼粉的粒度越大,Li-B合金的热稳定性越差。     

惰气熔融-红外吸收/热导法同时测定钒铝中间合金中氧氮

对惰气熔融-红外吸收/热导法同时测定钒铝中间合金中氧氮量的分析方法进行了研究。确定了最佳分析条件为：称取0.05～0.06 g样品于0.50 g镍囊中,将包裹好的样品投入高温型石墨坩埚中进行测定,分析功率为5.1 kW。方法采用钛标样确定氧的校正参数,氮的校正参数由钒铝中间合金内控样（氮的蒸馏-滴定法结果）确定。采用方法测定了AlV55、AlV65、AlV85样品中氧和氮,所得结果的相对标准偏差(n=8)均不大于3.9 %,氮的测定值与蒸馏 滴定法一致。在AlV85样品中加入碳化硅粉氧标样,氧的加标回收率为97%～105%;在AlV65样品中混入光谱纯Al₂O₃粉制备成新的样品,按方法测定该样品中氧的结果与理论计算值一致。     

Ta—W合金的密度分析

通过Ｘ射线衍射实验的方法测定了较高Ｗ含量的Ｔａ－Ｗ二元合金的晶格常数。用纯Ｔａ与合金的晶格常数之比再乘以按重量百分计计算的密度，求出合金的理论密度，并与按重量百分比计算的密度和实验测定的密度对比。分析３种实验方法计算的密度存在差异的原因，溶质元素Ｗ添加引起晶体结构产生“缩距”现象。结果表明：（１）Ｔａ－Ｗ合金随Ｗ含量的增加，晶格常数明显缩小，合金的密度升高；（２）Ｔａ－Ｗ合金按重量百分比计算计算的     

B/Zr摩尔比对Al-Zr-B合金的组织和晶粒细化效果的影响

以Al,K2ZrF6和KBF4为原料,采用熔体反应法制备不同B/Zr摩尔比Al-Zr-B合金。利用光学显微镜(OM)、扫描电子显微镜(SEM)、X射线衍射分析(XRD)等手段研究了B/Zr摩尔比对Al-Zr-B中间合金的组织和晶粒细化效果的影响。结果表明,随着B/Zr摩尔比的增加,Al-Zr-B中间合金的第二相组成发生改变。当B/Zr摩尔比为1时,第二相主要由粗大的块状ZrAl3相及少量团聚在晶界上的ZrB2粒子组成;当B/Zr摩尔比为2时,第二相为ZrB2粒子和少量块状ZrAl3相。当B/Zr摩尔比为3时,第二相全部为ZrB2粒子。对AZ91D合金的细化实验表明,随着B/Zr摩尔比的增加,晶粒细化效果越好,添加B/Zr摩尔比为3的Al-Zr-B中间合金具有明显的细化效果,合金由粗大的树枝晶转变成细小的等轴晶,固溶处理后的AZ91D合金平均晶粒尺寸由约328μm下降到约120μm;抗拉强度和延伸率达到213 MPa和4.95%,比未添加细化剂时分别提高了15.1%和30.3%。晶粒细化机制可归结为ZrB2粒子作为α-Mg的异质形核核心。     

论钢铁内部包晶反应时形成的热裂

对钢铁内部包晶反应期间固化时所形成的热裂进行了研究。利用MTS拉伸力试验机以及镜面反射炉进行了一系列现场固化试验。在固化过程中测量了样品温度和拉伸力的变化情况。经测量，样品固化时，在合金包晶温度周围，拉伸力会实然降低，与此同时，显微组织内部出现裂纹或二次填充裂纹。此外，作者在理论和试验的基础上，对包晶反应的类型进行了研究，以了解其在钢铁固化时对拉伸力变化的影响。理论分析证明，因包晶转变而出现的体积变化，是形成裂纹的原因之一。除此以外，当包晶反应在合金内部以无扩散（无分裂）方式出现，并且一次析出量很高的情况下，更有可能形成热裂。     

烧结合金致密化过程及其对性能的影响

配合发动机高质量气门座的研发，对Fe-Cr-Mo-Ni-Co-C粉末烧结合金致密化过程及其对产品性能的影响进行了实验研究。发现该合金的烧结样密度随生坯密度的提高而提高，当生坯密度较低时，其提高的幅度比较小，当心坯密度在6.5-6.7g/cm^3时，其提高的速度迅速增加，当生坯密度超过6.7g/cm^3，其提高速度减小；还发现该合金烧结密度的变化不仅影响试样孔隙数量的变化，而且影响孔隙形状的变化，因此该合金力学性能随密度的变化曲线并不是一条直线，而是一条分为不同阶段的曲线。还通过该合金的烧结密度对其物理性能的影响，导出了所研究合金于不同湿度时的热导率计算方程，进一步研究该合金的物理性能提供了理论依据。     

Combustion synthesis of LiGa and LiAl intermetallic alloys

LiAl and LiGa intermetallic alloys have been synthesized using the simultaneous combustion mode of combustion synthesis. LiAl intermetallic is potentially suitable as a temper alloy for producing aluminum-lithium alloys and as an anodic material for high-energy batteries. LiGa can be used as a reduction alloy to recover valuable reactive metals from molten salt effluent in actinide recovery technology. The effects of particle size, preignition heating rate, and theoretical green density on the ignition and combustion temperatures have been studied in an effort to more precisely control the synthesis reaction of these intermetallics. A lithium particle size of -20/xm was found to be suitable when the combustion synthesis reaction was conducted at a high heating rate (>1.0 cC/s) and a moderate green density (55 to 65 pct theoretical). Preignition diffusion is suggested as the cause for low exothermic heat release at high green densities. A combustion temperature above the melting point of the LiGa intermetallic compound can be achieved under optimized conditions. However, the exothermicity and, therefore, the adiabatic temperature is too low for either LiAl or LiGa to be produced by the propagating mode of combustion synthesis. Formerly graduate student with the Kroll Institute for Extractive Metallurgy     

PM processing and characterisation of Ti–7Fe low cost titanium alloys

Abstract

This work studies a set of low cost beta alloys with the composition Ti–7Fe, processed by conventional powder metallurgy (PM). The materials were prepared by conventional blending of elemental Ti hydride–dehydride powder with three different Fe powder additions: water atomised Fe, Fe carbonyl and master alloy Fe–25Ti. The optimal sintering behaviour and the best mechanical properties were attained with the use of Fe carbonyl powder, which reached a sintered density of up to 93% of the theoretical density, with UTS values of 800 MPa in the ‘as sintered’ condition. Coarse water atomised powder particles promoted reactive sintering, and coarse porosity was found due to the coalescence of Kirkendall porosity and by the pores generated during the exothermic reaction between Ti and Fe. The addition of Fe–25Ti produced brittle materials, as its low purity (91·5%) was found to be unsuitable for formulating Ti alloys.     

Reactive sintering in Fe-Co system

Abstract

Low porosity powder metallurgy compacts have been manufactured from treated elemental iron and cobalt powders sintered at 1150°C under an H_2(g) atmosphere. Their microstructures consist of an interconnected mixed oxide network which encapsulates both the iron and cobalt phases. The production technique employed is an innovative process termed reacto-thermitic sintering (RTS), which leads to near full density and near net shape parts utilising conventional uniaxial compaction and mesh belt furnace practices. The RTS technique relies on microscale exothermic reaction between small quantities of added elemental Al and oxides present on the surface of the bulk powder, together with the bulk powder itself. This results in the production of a transient liquid phase which freezes rapidly and consolidates the compact without slumping. In order to generate an interconnected mixed oxide network, experiments were designed such that the Al powder reacts with the cobalt and the surface of the iron powder which is artificially doped with Fe and Cr oxides.

Differential thermal analysis (DTA) and energy balance calculations revealed that the Al and the oxide coating reaction does not proceed directly. Instead the main contribution to the exothermic process is the reaction between Al and Co/Fe. The system does not exhibit true RTS behaviour and the interconnected network of mixed Al, Cr, and Fe oxides is created by subsequent reaction of Co-Al and Fe-Al intermetallics with the artificial Fe-Cr oxide coating on the Fe. The microstructure obtained exhibits negligible porosity with the metallic particles on the whole fully encapsulated by the oxide.     

Chemical composition of regions alloyed by DIGM or DIR

The zinc concentrations of zinc-rich regions formed in a pure copper specimen by diffusion induced grain boundary migration (DIGM) and diffusion induced recrystallization (DIR) with a zincification technique are observed to be typically lower than that of the CuZn zinc source alloy. This phenomenon in the Cu(Zn) system has been analyzed on the basis of a new model to evaluate the chemical driving force of the reactions. The activity of zinc in the zincification atmosphere is assumed to be constant during the reaction. A contribution of the zinc atoms, which diffuse from the atmosphere into the specimen, to the Gibbs energy change of the reaction is considered in the model. The molar Gibbs energy of the copper-rich solid solution phase has been described using a subregular solution model. The experimental results have been accounted for rather well in DIR but not in DIGM. On the other hand, a rather satisfactory agreement between calculation and experiment for DIGM has been obtained through consideration of the effect of an elastic stress on the Gibbs energy of the alloyed phase.     

SHS—离心法制备铁—铬—镍合金的耐蚀性能

利用ＳＨＳ－离心法制备铁－铬－镍合金内衬复合钢管，系统研究内衬层的耐蚀性能，结果表明，含碳量较低的ＳＨＦ耐蚀合金在硫酸中的耐蚀性优于１Ｃｒ１８Ｎｉ９不锈钢，具有优异的抗点蚀和抗均匀腐蚀性能，但抗晶间腐蚀性能较差，也不耐盐酸腐蚀。     

Direct consolidation of γ-TiAl-Mn-Mo from elemental powder mixtures and control of porosity through a basic study of powder reactions

A gamma titanium aluminide was made by elemental powder metallurgy. For consolidation of the alloy from powder blending, either hot extrusion or hot forging was used. A good combination of tensile yield strength and ductility was obtained by hot extrusion that produced a grain size of 50 μm. Consolidation by forging, however, resulted in a porous microstructure. On the basis of an investigation of the cause of the porosity by an Al/Ti diffusion couple experiment and by characterization of the temperature peaks due to an exothermic reaction among elemental powder particles, it was concluded that a transient phase such as TiAl₃ was the culprit. Being the source of Al diffusion, the transient phase leaves behind Kirkendall voids when it forms prior to the major exothermic reaction among elemental powder particles. From this study, two processing techniques to circumvent the porosity were proposed and verified: a fast heating to the consolidation temperature or sufficient soaking above the reaction temperature prior to consolidation. A sound, fully lamellar, β-phase controlled microstructure was obtained by these methods.     

热电池电极材料的研究进展

综述了热电池电极材料的应用及研究现状，着重介绍了新型阴、阳极材料的特性，特别是Li-B合金的合成机理、性能及结构特点，在此基础上展望了未来热电池的发展方向。