Influence of shot peening parameters on high‐cycle fatigue strength of steel produced by powder metallurgy process

In this study, the effect of shot peening parameters on fatigue strength of steel manufactured by powder metallurgy (PM) was investigated. Steel material obtained from Höganas ASC 100.29 in chemical composition of Fe–0.5% C–2% Cu was produced by using a single action press PM process. To determine the effect of shot peening parameters on fatigue performance, fatigue tests were performed on 20 unpeened and 80 shot‐peened samples, which were machined from sintered steel. Furthermore, shot‐peened samples were peened at different peening intensities, 100% and 200% saturation and full coverage conditions. Fatigue performance of steel, produced by PM process, was improved by surface peening process. For the studied PM steel, the best fatigue performance was obtained with the samples that were shot peened at 20 Almen intensity and 100% saturation. Fatigue strength and limit of the samples, however, were reduced after a certain cold work level. Higher intensity and saturation levels of peening process thus deteriorated the beneficial effect on fatigue strength and limit.     

Influence of carbon nanotubes and dispersions of SiC on the physical and mechanical properties of pure copper and copper‐nickel alloy

This paper investigates the physical and mechanical properties of copper‐nickel alloy (at 50 wt.%–50 wt.%) and pure copper, mixed with various types of reinforcement materials such as carbon nanotubes (0.5 wt.%–2 wt.%) as nanoparticles, silicon carbide (1 wt.%–4 wt.%) as microparticles. The acquired composite specimens characteristics were estimated such as microstructure, density, electrical and thermal conductivity, hardness, and compression stress properties to determine the suitable reinforcement percentage that has the best physical and mechanical properties with different main matrix material whether copper‐nickel mechanical alloying or pure copper powder. The micron‐sized silicon carbide and nanosized carbon nanotubes were added to improve the mechanical and physical properties of the composite. The electrical and thermal conductivity of pure copper alloy enhanced compared with the copper‐nickel alloy matrix material. The hardness and compression yield stress of both pure copper and copper‐nickel composites have enhancement values and for copper‐nickel base composites hardness and compression yield stress have enhanced with the most positive enhancement values to examined an optimum percentage of reinforcing material.     

Effect of enhanced interfacial reaction on the microstructure,phase transformation and mechanical property of Ni–Mn–Ga particles/Mg composites

This study investigated the microstructure, phase transformation and mechanical property of Ni–Mn–Ga particles/Mg composites with a strong interfacial reaction between the particles and the matrix. The strong interfacial reaction was related to the large surface area and energy per unit volume of the flaky shape Ni–Mn–Ga particles that favors the reaction between the particles and matrix. The martensitic transformation behavior was largely weakened due to the interfacial reactions and thus the reduced volume fraction of Ni–Mn–Ga particles. The composites exhibited a much improved compressive strength and ductility in comparison with that of the Ni–Mn–Ga alloy. The compressive plasticity of the composites was decreased when the Ni–Mn–Ga particle content exceeded 40 wt%. In comparison with the Mg-composites with large size Ni–Mn–Ga particles, the composites with small size particles would have a much stronger interfacial reactions, which was detrimental to the phase transformation and mechanical ductility of the composites. The investigation results in this article could provide a reference for the design and preparation of the particles reinforced metal matrix functional composites.     

Phase transformation in Ti–48Al–6Nb porous alloys and its influence on pore properties

Ti–48Al–6Nb porous alloys were synthesized by the powder metallurgy (PM) method, and the associated phase transformation and pore parameter were investigated in order to reveal the pore-formation mechanism. The present results indicate that the Nb–Al and Ti–Al phase transformations contribute to the pore-formation. It was found that the five-step phase transformations for the Ti–48Al–6Nb porous alloys occur as follows: (1) Ti + Al → TiAl₃ at 600–700 °C; (2) Nb + Al → NbAl₃ at 700–900 °C; (3) TiAl₃ + Ti → TiAl at 900–1100 °C; (4) TiAl + Ti → Ti₃Al/TiAl at 1100–1350 °C; (5) NbAl₃ + Nb → Nb₂Al and the Ti₃Al turns to the major phase at 1350 °C. These phase transformations made the pore-diameter increasing continuously from 1.71 μm to 12.10 μm and also made the pore volume distributing widely. At the second step of 700–900 °C, the Nb–Al phase transformation leads to 5% more volume expansion compared to the Ti–Al based porous alloys. Meanwhile, the porosity and total pore area initially increase and then decrease at this step, but they increase intensely at the final step, which is needed as a catalytic carrier.     

铝合金高频感应热丝TIG焊接方法

提出了高频感应热丝TIG焊接新方法,焊丝加热温度和深度可控,加热速度快,能适应高速送丝要求.高频感应加热消除了常规热丝TIG焊旁路电流磁场引起的电弧偏吹现象.另外,由于该方法不需利用焊丝本身的电阻产热,所以适用于铝合金等低电阻率金属焊丝.根据感应线圈的电感和工作频率要求,设计制造了适用于Φ1.6 mm铝合金焊丝的高频感应加热线圈和套筒.利用热电偶测量了不同送丝速度下的焊丝温度.结果表明,当送丝速度高达6～10 m/min时,焊丝的温度完全能够满足热丝焊的要求.6～10 m/min的送丝速度较常规TIG焊接提高了3倍以上,大大提高了焊接效率.     

乳状液膜法分离钨钼的研究——酸性体系

研究了以三烷基氧化膦（ＴＲＰＯ）为载体、ＮａＯＨ为反萃试剂的液膜体系在酸性介质中进行的钨钼分离．其特点是利用钨、钼与Ｈ２Ｏ２生成的过氧化合物的迁移性能的显著差异来分离钨钼．考察了影响钨钼分离的诸因素．经二级间歇液膜处理，Ｍｏ／ＷＯ３（重量比）从０．５％降到０．００１％以下，达到要求（最高级钨酸产品要求钼含量不大于０．００８％）．本文提供了一种适用于从盐酸分解钨酸钙精矿制取钨酸时分离钨钼的新方法．     

钙钛矿/钨青铜两相复合BSTN陶瓷的形成与性能研究

设计了特殊配方0.7BaO.0.3SrO·(1-y)TiO₂·yNb₂O₅, 通过过量组成控制,制备了钙钛矿相和钨青铜相共存的复相陶瓷.用XRD和阻抗仪测试了相结构及介电常数.结果表明,在形成以钙钛矿为主相的体系中,Nb₂O₅过量6mol％以上时开始形成钨青铜相;在形成以钨青铜为主相的体系中,BaO和SrO过量11mol％以上时开始形成钙钛矿相.两相含量相当的体系中,钙钛矿相几乎不固溶Nb₂O₅,而钨青铜相固溶一定量TiO₂.复相陶瓷的介电性能具有BST和SBN两相的特点.BSTN复相体系中钨青铜相的铁电/顺电转变温度随固溶TiO₂量增加而降低,随钙钛矿相增加而升高,其最低转变温度约在200℃,比纯SBN相下降90℃.     

A robust approach to model densification and crack formation in powder compaction processes

This paper deals with the question of how to efficiently integrate a constitutive model that describes the densification of powders and the potential formation of cracks in Powder Metallurgy (P/M) cold compaction processes. The analyzed model is a large strain, elastoplastic model of the Drucker–Prager/Cap type, refined to cover also the prediction of crack formation, and featuring non‐conventional elements such as a density‐dependent Von Mises yield surface; a parabolic plastic potential function for the Drucker–Prager envelope; and a softening law whose softening modulus is dependent on the level of densification. The employed integration procedure is a non‐conventional hybrid or IMPLicit–EXplicit (IMPL‐EX) scheme, whose essence is to solve explicitly for some variables and implicitly for others, with the peculiarity of the ‘explicit’ variables being but extrapolated values of the same quantities computed, at previous time steps, by means of a fully implicit scheme. The return‐mapping equations stemming from this implicit scheme are solved using an unconditionally convergent, fractional step method‐based iterative procedure. The performance of the IMPL‐EX integration algorithm is critically assessed in two different situations: the densification of a cylindrical specimen, and the fracture process in a diametral compression test. Results obtained show conclusively that the proposed hybrid integration strategy offers an efficient solution to the trade‐off between robustness and computational time requirements. Copyright © 2011 John Wiley & Sons, Ltd.