Al-La合金组织形貌的试验研究

采用真空熔炼方法,用石墨铸型,在常规铸造条件下分别制备了Al-20%La、Al-30%La、Al-35%La和Al-40%La合金试样.通过组织形貌观察和相组成测定,发现Al-35%La合金组织形貌的特殊性,其先结晶相Al11La3枝晶沿主干方向成分不连续,枝晶主干由a-Al和Al11La3两相交替排列构成.通过线扫描分析表明,枝晶主干上化学成分呈周期性变化,因此,称其为周期性双相枝晶组织.     

Al-35La定向凝固组织的力学性能及形成机理

采用定向凝固技术,研究了Al-35La合金的组织形貌特征、力学性能及其形成条件。结果表明,定向凝固Al-35La合金试样中的枝晶沿主干方向成分是不连续的,表现为周期性双相枝晶组织。对其力学性能进行测试发现,各定向凝固试样压缩性能较好,硬度值较高。分析了Al-35La合金周期性双相枝晶的形成条件。讨论了一定强度的对流在枝晶形核与长大过程中起到的促进溶质交换、带走结晶潜热的作用。由此认为,一定强度的对流促进了Al-35La合金液中两相的交替形核和生长,最终在合金中形成周期性双相枝晶组织。     

Al-35%La合金定向凝固组织的形成机理及力学性能

研究了Al-35%La合金定向凝固组织的形貌特征、形成条件及其力学性能。结果表明:在定向凝固Al-35%La合金试样中,枝晶是成分沿其主干方向呈周期变化的双相组织。各定向凝固试样的力学性能测试发现:压缩性能较好,硬度值较高。分析了Al-35%La合金周期性双相枝晶的形成条件,说明一定强度的对流在枝晶形核与长大中起到促进溶质交换,带走结晶潜热的作用。由此认为,一定强度的对流促进了Al-35%La合金液中两相的交替形核和生长,最终在合金中形成周期性双相枝晶组织。     

Na盐和La变质对Al-10Si合金组织与硬度的影响

研究了Na盐、La和Na盐+La复合变质对Al-10Si合金组织与硬度的影响,分析了Na盐、La的变质机制。研究发现,Al-10Si合金经Na盐+La复合变质后,宏观组织中晶粒细小呈等轴状,退火后晶粒粗化不明显;显微组织中共晶Si分枝、细化,趋于纤维状,初生α枝晶趋于熔断且呈等轴状,共晶组织与初生α相间的界面趋于清晰且平整;退火对经Na盐+La复合变质的Al-10Si合金的组织形态影响较小;变质处理提高了Al-10Si合金的硬度。研究认为Na盐变质机制在于触发共晶Si孪晶并不断封锁孪晶凹槽;La变质机制在于其在固液界面前沿的富集改变了共晶Si的生长特征。     

型砂及壁厚对锶变质A356铸造合金组织和性能的影响

采用硅砂、宝珠砂和铬铁矿砂3种不同砂型作为造型材料浇注多阶梯铸件试样,对比研究不同冷却条件对Al-10Sr中间合金变质A356（Al-7Si-0.3Mg）铸造合金力学性能和显微组织的影响。结果表明：在3种造型材料中,铬铁矿砂浇注试样具有最好的组织和力学性能。随着冷却速度的增加,枝晶间距显著变小,力学性能有所改善,其中伸长率对冷却速度比抗拉强度更敏感。这种性能的提高主要是由于枝晶间距更加细密和基体中自由Sr原子数的提高造成的。根据实际的试验数据,模拟建立不同砂型条件下枝晶间距和力学性能之间的回归分析模型,该模型可用于预测Sr变质A356合金铸件的抗拉强度和伸长率。     

La和Er对Al-13Si-5Cu-2Ni-1Mg合金组织和性能的影响

研究了La和Er对铸造Al-13Si-5Cu-2Ni-1Mg合金组织和力学性能的影响。结果表明,La对共晶Si有较强的变质作用,在合金中生成块状、长针状富La相;Er可以明显减小二次枝晶间距,在合金中可生成块状、短棒状富Er相。合金中复合添加0.2%的La和0.2%的Er时,二次枝晶间距、初生Si、共晶Si和金属间化合物的尺寸同时减小,La、Er相互作用可以抑制富稀土相的生长,使合金中引入尺寸细小且弥散分布的富稀土相,此时合金力学性能最佳,25和350℃时抗拉强度分别为274MPa和91MPa。     

冷速对Al-4.29Cu-1.09Mg合金凝固组织的影响

选取Al-4.29Cu-1.09Mg合金,采用石墨型、砂型、保温材料等3种铸型进行了凝固试验,采用扫描电镜、能谱分析等手段研究了不同冷速铸锭的凝固相组成与形貌、硬度、二次枝晶间距等。结果表明,随着冷却速率的提高,合金凝固组织的二次枝晶臂间距明显减小,硬度增大。在二次枝晶臂尺度范围内,砂型铸锭中Cu和Mg元素出现了明显的微观偏析,枝晶臂边缘成分明显高于枝晶臂中心,并发现Cu元素的偏析程度要大于Mg。     

Al-Cu合金凝固组织演变的模拟与预测

采用相场法对铸造Al-4.2Cu合金的凝固组织中的枝晶生长速率和枝晶尖端半径进行了计算机模拟,并与Ivantsov理论计算得到的Peclet数值进行了对比分析。结果表明,Al-4.2Cu合金凝固过程中枝晶尖端生长速率基本分布在0.04 m/s附近,Al-4.2Cu合金凝固过程中枝晶尖端半径则主要分布在1.0×10-7m;本文的相场法计算模拟得到的非等温和等温凝固结果和Ivantsov理论计算得到的值基本吻合,相对而言,非等温凝固的模拟结果相对要比等温凝固模拟结果更接近Ivantsov理论值。     

In含量对Cu-Cr-In三元合金组织的影响

采用组合金属铸型制备了不同In含量的Cu-Cr-In三元合金试样。对试样进行了显微组织观察、电子探针分析和X射线衍射分析，研究了In含量对合金组织的影响。结果表明，当In含量增加时，合金晶粒组织中枝晶倾向增加。对于合金枝晶组织，当In含量增加时，使二次枝晶的间距增加。对于基体Cu固溶体晶体，In在基体晶体中形成置换原子，当In的含量增加时，基体晶体的晶格常数变大。合金的相组成为Cu固溶体相即基体相、Cu9In4相和Cr固溶体相。     

稀土对Al-3.0wt.%Mg合金微观组织结构的影响和作用机理

通过光学显微镜(OM)、扫描电子显微镜(SEM)和能谱分析仪(EDS)观察分析了不同混合稀土(37.3wt.%La,61.5wt.%Ce)含量的Al-3.0wt.%Mg合金微观组织结构和第二相三维形态,并研究了稀土元素对该合金微观组织影响和作用机理。结果表明:适量的稀土能够细化Al-3.0wt.%Mg合金的晶粒、枝晶和骨骼状富铁第二相,具有优秀的除杂作用,并显著提高合金的性能;过量的稀土会使合金晶粒和枝晶变得粗大,并在晶界处形成大量粗大的骨骼状Al4Ce/Al4La相。     

Interface reaction during titanium alloys investment casting by residue gas in ceramic mold

The chemical reaction between mold material and titanium melt during investment casting was studied intensively. However, the influence of residue gas in ceramic mold on interface reaction remains unclear. In this investigation, the effect of residue gas in Y_2O_3-silica sol shell mold on interface reaction during Ti-6Al-4V alloy investment casting was investigated. Two groups of shell molds were prepared by adding different kinds of pore formers, i.e., spherical starch particles or nylon fibers,respectively. Ti-6Al-4V alloy was cast under vacuum by gravity casting through cold crucible induction melting(CCIM) method. Porosity of different shell molds was measured based on Archimedean method. Scanning electron microscopy(SEM) and energy-dispersive X-ray spectroscopy(EDS) were employed to characterize the micromorphology and composition of the reaction area,respectively. White light interferometer(WLI) was used to obtain the surface topography of the shell mold. The results show that the direct chemical reaction is very weak for all specimens. The release of residue gas in closed pores is the key factor influencing surface defects. However, open pores make nearly no difference on the interface reaction.     

离心力及铸件模数对Ti-6Al-4V合金组织与力学性能的影响

该论文主要研究在石墨型中不同立式离心力场下离心力及铸件模数对Ti-6Al-4V合金组织及性能的影响。实验过程中铸型的旋转速度主要考虑了三种情况：0, 110及 210 rpm。结果表明：晶粒尺寸及片层厚度随铸件模数的减小和离心力的增加而减小,拉伸强度随铸件模数减小和离心力增加而明显增加,但铸件延伸率呈现相反的变化趋势。文中给出了重力系数、铸件模数与Ti-6Al-4V合金组织和力学性能之间的定量关系。作为与重力场下石墨型中Ti-6Al-4V合金铸件对比分析,研究了金属型中Ti-6Al-4V合金阶梯铸件组织的变化情况,研究发现：两种铸型中浇铸的合金铸件晶粒尺寸、片层厚度随冷却速度的变化趋势基本一致,结合两组实验数据,给出了重力场下Ti-6Al-4V合金铸件组织随冷却速度变化的定量关系。     

Precision casting of Ti-15V-3Cr-3AI-3Sn alloy setting

In this research, Ti-15V-3Cr-3Al-3Sn alloy ingots were prepared using ceramic mold and centrifugal casting. The Ti-15V-3Cr-3Al-3Sn setting casting, for aeronautic engine, with 1.5 mm in thickness was manufactured.The alloy melting process, precision casting process, and problems in casting application were discussed. Effects of Hot Isostatic Pressing and heat treatment on the mechanical properties and microstructure of the Ti-15V-3Cr-3Al-3Sn alloy were studied.     

Precision casting of Ti-15V-3Cr-3Al-3Sn alloy setting

In this research, Ti-15V-3Cr-3Al-3Sn alloy ingots were prepared using ceramic mold and centrifugal casting. The Ti-15V-3Cr-3Al-3Sn setting casting, for aeronautic engine, with 1.5 mm in thickness was manufactured. The alloy melting process, precision casting process, and problems in casting application were discussed. Effects of Hot Isostatic Pressing and heat treatment on the mechanical properties and microstructure of the Ti-15V-3Cr-3Al- 3Sn alloy were studied.     

热处理对吸铸TiAl基合金铸件组织的影响

利用金属型底浇式真空吸铸技术和添加合金元素获得TiAl基合金薄板,观察并研究薄板热处理前后的组织。结果表明,在金属型强制冷却和添加合金元素的共同作用下,利用金属型底浇式真空吸铸技术获得的TiAl基合金薄板件铸态组织细小、致密。其中Ti-47Al-5Nb-0.5Si和Ti-47Al-2W-0.5Si合金的铸态平均晶粒多在20μm左右,但是,铸态组织的片层组织不均匀,且在组织内部存在较大的偏析。将试样加热到1300℃,保温5 h,随炉冷却热处理后,TiAl基合金薄板的铸态组织有所长大,但是片层更加平整稳定,偏析也明显得到改善。     

Effect of mold temperature and casting dimension on microstructure and tensile properties of counter-gravity casting Ti-6Al-4V alloys

The cast Ti-6Al-4V alloy bars with different section sizes were fabricated by investment casting at counter-gravity condition with the mold temperatures of 300 °C and 650 °C, respectively. The microstructure of the alloy was observed by means of OM and SEM, and the effect of mold temperature and casting dimension on tensile properties was studied. Results show that equiaxed grains are obtained regardless of the casting dimension. β grain size tends to increase with an increase in mold temperature. Hot isostatic pressing of the alloy was carried out for tensile properties' comparison. Room temperature tensile test results show that Ti-6Al-4V alloy produced via counter-gravity casting has good balance of strength and ductility after hot isostatic pressing(HIP). The alloy shows higher ductility due to the elimination of porosity. In both cast and HIP status, the tensile strength is inclined to decrease with an increase in mold temperature, while the ductility is prone to slightly increase. Both the strength and ductility tend to decrease with an increase in the casting dimension.     

粉末冶金Nb-35Ti-6Al-5Cr-8V合金组织演变及其力学行为

采用粉末冶金法对不同球磨时间的Nb-35Ti-6Al-5Cr-8V合金机械合金化粉末塑变行为,热压烧结材料的微观组织结构和力学行为进行了研究。研究结果表明：塑性良好的Nb-35Ti-6Al-5Cr-8V粉末随着球磨时间增加首先变形为大尺寸的片状、后经持续的加工硬化破碎成絮状;热压烧结能够制备微观组织可控晶粒细化的Nb-35Ti-6Al-5Cr-8V合金,合金由单一的Nbss相构成,Ti、Al、Cr、V元素固溶引起Nb晶格尺寸减小0.0685 ?;随着球磨时间增加合金晶粒明显细化进而显著提高了合金的维氏硬度和室温压缩强度,其变化符合材料硬度和强度的Hall-Petch规律。粉末冶金制备Nb-35Ti-6Al-5Cr-8V合金的各项力学性能明显优于熔铸法制备合金。     

铸造Al-Mg-Mn合金的显微组织及力学性能

研究了Mg含量、冷却速度、固溶处理对Al-6.8Mg-0.3Mn、Al-3.8Mg-0.3Mn两种合金力学性能的影响。结果表明,随着Mg含量提高,晶界相增多。当Mg含量提高到6.8%时,晶界出现网状组织;随着Mg含量升高,合金强度提高,塑性下降;通过砂型铸造空冷、金属型铸造空冷、金属型铸造淬火来实现不同的冷却速度,发现金属型淬火试样的金相组织中,在晶界附近没有析出网絮状或颗粒状第二相,而强度和伸长率要高于其他两种工艺。两种合金经过430℃×60h固溶处理后,合金的综合力学性能得到大幅度提高。Al-6.8Mg-0.3Mn金属型铸造空冷试样固溶后抗拉强度由280MPa提高到335MPa,伸长率由10.4%提高到20%。     

压铸条件下过共晶铝硅合金P变质的必要性

在铝合金压铸生产过程中,Al-P中间合金变质处理和压力铸造工艺都能够使过共晶铝硅合金中的初晶硅晶粒细化.探讨Al-P中间合金变质处理,分别在压铸工艺条件下和普通金属型条件下,对过共晶Al-15Si合金组织的不同影响.试验表明,压铸条件下未经Al-P变质的和经Al-P变质的Al-15Si合金与金属型条件下未经Al-P变质的Al-15Si相比,初晶Si尺寸分别减小50%和75%左右;在相同的压铸工艺条件下,Al-P变质后Al-15Si合金初晶Si尺寸,比未经过Al-P变质的Al-15Si合金初晶Si尺寸减小40%左右.论证了在Al-Si系过共晶铝合金压铸件生产过程中,Al-P中间合金进行变质处理的必要性.     

Titanium castings using laser-scanned data and selective laser-sintered zirconia molds

Titanium casting molds, made of stabilized and unstabilized zirconium oxide, were created using a combination of selective laser sintering (SLS) and colloidal infiltration. The mold material system was chosen for its thermal shock resistance and low reactivity with molten titanium. The starting material, stabilized zirconia powder mixed with a copolymer binder, was laser sintered into the desired green shape. The binder was removed during pyrolysis and replaced by unstabilized zirconia. As infiltrant weight gain increased, the density, flexural strength, and surface roughness improved to levels adequate for titanium casting trials. A half-scale casting mold for the ball of a human femur bone was produced from laser-scanned data and cast with Ti-6Al-4V alloy. The castings exhibited an as-cast surface roughness (R _a ) of 8 μm and a typical microstructure. This work demonstrates a feasible method of producing complex titanium castings for one-of-a-kind and custom components without the necessity of part-specific tooling or wax patterns.