Fabrication of a multi-phase porous high-temperature Mo–Si–B alloy by in situ reaction synthesis

ABSTRACT

The pore formation process has been studied for a high-temperature porous Mo–Si–B alloy produced by in situ reaction synthesis from elemental starting powders. The expansions, phase transformations, microstructure and pore parameters were investigated systematically as a function of the sintering temperature. For sintering temperatures of 1200°C and above, a multiphase mixture of the oxidation-resistant intermetallic compounds Mo₃Si, Mo₅Si₃ and Mo₅SiB₂ was obtained. It was found that the porous alloys exhibit uniform skeletons with fine grains, high porosities and centred pore size distributions. Characterisation data obtained from samples sintered at temperatures from 1200 to 1600°C are used to deduce the processes which occur at each stage in the reaction synthesis. This helps to explain the formation mechanism for the pores and skeletons in this novel material.     

定向凝固NiAl-9Mo共晶合金的凝固组织特性

采用液态金属冷却法在恒定温度梯度GL=334 K/cm,大生长速率范围内（2~300μm/s）对Ni-45.5Al-9Mo （摩尔分数,%）共晶合金进行定向凝固制备。研究生长速率（v）对纤维间距（λ）、纤维直径（d）和纤维体积分数的影响。在实验中发现平界面和胞界面两类共晶生长界面。在平界面和胞界面组织中,生长速率（v）与纤维间距（λ）和纤维直径（d）的关系经回归分析分别为：λv1/2=5.90μm·μm1/2·s1/2和 dv1/2=2.18μm·μm1/2·s1/2。Mo纤维的体积分数可在一定的范围内随生长速率进行调整,这是由生长过程中界面前沿过冷度的增加及共晶组织中各组成相的生长特性引起的。     

Fe-Al金属间化合物材料的强化机理及其高温性能研究现状

对Fe-Al金属间化合物的高温力学性能和抗氧化性能的研究现状进行了回顾.归纳和描述了固溶强化、析出强化、有序强化、弥散强化等强化机理以及Fe-Al材料抗氧化的机理.并对Fe-Al材料研究的发展进行了展望.     

Aluminising of steel with a cathodic arc plasma based method

Steel samples have been aluminised by cathodic arc PVD using Al cathodes and AC bias. The effect of time and temperature on the growth behaviour of iron aluminide phases under the constant flux of Al vapour was investigated. For samples processed at 1000°C for 30?min a layered structure that consisted of FeAl, followed by dual phase regions of metastable Fe₃Al?+?FeAl and stable Fe₃Al?+?α-Fe was observed. Increase of processing time resulted in the formation of Fe₂Al₅. The increase of processing temperature to 1100°C extended the diffusion zone and increased the time for formation of Fe₂Al₅. After 90?min processing at 1000°C and 1100°C the presence of Fe₄Al₁₃ in the Fe₂Al₅ phase was determined. It has been observed that the metastable dual phase structures composed of Fe₃Al and FeAl can be transformed into stable Fe₃Al by heat treatment at 500°C.     

7A52铝合金搅拌摩擦焊焊缝第二相分析及微区电位测试

7A52铝合金搅拌摩擦焊焊缝第二相的种类、大小、分布和电位等都对材料的腐蚀行为有重要的影响.采用光学显微镜、扫描电镜、能谱分析仪、扫描开尔文探针力显微镜分析了焊缝中的第二相,并测试了其微区电位.结果表明,焊缝各区域第二相的组成主要为弥散分布的AlFeMnSi和Mg2Si,它们的尺寸约为几微米,电位都低于基体.Mg2Si...     

Powder metallurgy preparation of Al–Cu–Fe quasicrystals using mechanical alloying and Spark Plasma Sintering

This work is devoted to the preparation of ultrafine material based on Al–Cu–Fe quasicrystalline phase by powder metallurgy using mechanical alloying and Spark Plasma Sintering. The dependence of microstructure and phase composition of powders on the conditions of mechanical alloying was described. It was found that the Al₆₀Cu₃₀Fe₁₀ quasicrystalline phase forms directly already after 2 h of milling under optimized conditions. The stability of this quasicrystalline phase was studied at various temperatures of Spark Plasma Sintering compaction process.     

Mn和Ce对再生Al-Si合金富铁相的影响

研究了Mn、Ce对再生Al-Si合金富铁相的影响。分别采用光学显微镜(OM)、扫描电镜(SEM)和能谱仪(EDX)对试样组织进行形貌观察分析和生成相进行成分分析,利用差分扫描量热仪(DSC)研究相转变温度。结果表明,当Mn的含量为1%(质量分数)时,合金组织出现了初生α-Fe相,同时添加0.1%Ce(质量分数)时,能够有效促进初生α-Fe相形核与长大。     

Mg-Al-Si-Ca合金系金属间化合物的电子结构和力学性能的第一性原理计算

采用基于密度泛函理论的第一性原理赝势平面波方法,计算了Mg-Al-Si-Ca合金系金属间化合物Mg2Si,Mg2Ca,Al2Ca以及Si2Ca四相的形成焓,结合能,弹性常数及态密度。形成焓和结合能的计算结果表明:Al2Ca的合金化能力最强,Si2Ca相的结构最稳定;体模量(B)、剪切模量(G)、杨氏模量(E)和泊松比(ν)的计算结果表明:四相均为脆性相,且Mg2Si相的塑性最差,结合弹性模量和态密度分析,得出Mg2Ca的塑性最好;态密度和Mulliken布居分析表明:四相中均存在离子键和共价键,共价键由强到弱顺序为Si2Ca,Al2Ca,Mg2Si,Mg2Ca;而离子键强弱顺序按Mg2Si,Al2Ca,Si2Ca,Mg2Ca依次递减;而Si2Ca最稳定的原因是其共价键比其他三相更强。     

Effect of Fe-rich particles and solutes on the creep behaviour of 8xxx alloys

The creep behavior of 8xxx aluminum conductor alloys with different quantities of Fe-rich particles and solutes was investigated. Creep resistance was significantly improved with large amounts of Fe-rich particles and solutes. At 100 °C, a high Fe solute content (0.023 wt.%) had a stronger effect on creep resistance than FeAl₃ particles. However, as the temperature increased to 150 and 200 °C, the effect of a high amount of FeAl₃ particles (2.5 vol.%) was stronger. The threshold stress increased with increasing FeAl₃ particle and Fe solute contents, with the effect of each factor being independent, but it decreased with increasing temperature. The true stress exponents were calculated to be 3.1, 3.8, and 4.5 at 100, 150 and 200 °C, respectively.