NiAl／TiB2纳米复合材料的机械合金化合成

ＮｉＡｌ／ＴｉＢ２纳米复合材料可以通过室温球磨元素粉末而合成。其反应生成机理属于爆炸反应生成模式，并包含着两个独立的化学反应，即Ｎｉ＋Ａｌ→ＮｉＡｌ，Ｔｉ＋２Ｂ→ＴｉＢ２。巨大的生成热是反应进行的驱动力。     

MoSi2及MoSi2基材料的强韧化

MoSi2以其较高的熔点、适中的密度和优异的高温抗氧化性能而成为近年来倍受关注的金属间化合物,但其室温脆性和低的高温强度是限制其应用的主要原因. 从合金化和复合化等方面对MoSi2及MoSi2基高温结构材料的强韧化作了概述.     

NiAl及NiAl基合金的氧化

综述了近期NiAl及NiAl基合金的氧化研究成果.研究表明:在NiAl表面通常形成一层完整的Al2O3保护膜,而NiAl基合金中由于含有大量的合金化元素,使NiAl合金由单相转变为β相与其它贫铝相组成的多相结构,使得合金的氧化规律复杂化.在氧化过程中,Al2O3保护膜经历了由快速生长的不稳定相δ-Al2O3或θ-Al2O3向稳定相α-Al2O3的相变过程,不同的合金化元素对其转变速度有不同程度的影响.在氧化膜与合金之间形成的孔洞减弱了氧化膜的黏附性,加快了氧化膜的剥落速度.     

内生TiC颗粒增强NiAl基复合材料的初步研究

用ＨＰＥＳ工艺合成了２０ｖ．％ＴｉＣ颗粒增强的ＮｉＡｌ基复合材料，其维氏硬度、压缩屈服强度都比单相ＮｉＡｌ有大幅度提高。特别是室温和１０００℃以上，屈服强度比基体提高近二倍，室温塑性也优于单相ＮｉＡｌ。     

NiAl(Co)-TiC纳米复合材料的制备及力学性能

将Ni,Ai,Co,Ti,C各元素，按Ni50Al45C05 10%TiC和Ni50Al45Co5 20%TiC名义成分配比混合，在高能球磨机内进行机械合金化（MA），纳米晶粉末经过热压（HP）和热等静压（HIP）处理，制备出晶粒大小为80－250nm原位内生TiC颗粒，晶粒为100－350nm NiAl(Co)基体的块体复合材料，其室温屈服强度达1394－1660MPa,具有12％－13％压缩形变，NiAl(Co)-20%TiC纳米晶复合材料，在700℃压缩形变至30％时，表面光滑没有裂纹，在1100℃下，高温屈服强度为136MPa，是铸态纯NiAl的4倍。     

机械合金化法合成金属间化合物NiAl粉末

由于NiAl基金属间化合物的一些优异性能,长期以来作为高温结构的候选材料而得到了广泛的关注。本文中用机械合金化法合成了NiAl金属间化合物粉末,详细介绍了球磨工艺,对NiAl金属间化合物粉末的形貌和物相进行表征。结果表明,金属Ni和Al的粉末在球磨机内仅球磨5h就可以使大部分金属粉末转化为NiAl金属间化合物,随着球磨时间的延长,金属间化合物有细化的趋势。     

二硅化钼材料复合强韧化的研究进展

MoSi2因其优异的性能而被认为是最有前途的高温结构金属间化合物,但是低的室温韧性和高温强度限制了其作为高温结构材料的应用,第二相陶瓷复合化是一种有效的低温增韧和高温补强的方法.介绍了复合强韧化MoSi2所取得的成果,着重对氧化物、碳化物、氮化物和硼化物增强MoSi2材料进行了总结和评述,最后认为多元复合化是未来研究的方向.     

TiNb长纤维强韧化Ti-48Al-2Cr-2Nb基复合材料的研究

采用粉末冶金-热压成型工艺制备了连续纤维增强Ti-48Al-2Cr-2Nb基复合材料.其中1 250 ℃,20 MPa,2.5 h下制备的材料性能较好：σbb=700.2 MPa,K1c=19.2 MPa*m1/2.该复合材料的基体是由细小的片层组织和等轴组织构成的双态组织,界面由全片层组织构成,复合材料的界面结合状态良好.     

NiAl(Co)-TiC粉末的机械合金化原位制备纳米复合材料

用高能球磨机分别对四种成分的Ni50-Al50-x-Cox 10%(体积分数,下同)TiC (x=5,10,20)和Ni50-Al45-Co5 20%TiC粉末进行机械合金化,得到原位内生TiC弥散强化的NiAl(Co)纳米复合粉末.结果表明,球磨Ni50-Al45-Co5-10%TiC粉末过程中,爆炸反应机制生成NiAl(Co)和TiC化合物,其中NiAl(Co)化合物晶粒仅为10nm左右,TiC晶粒为35～50nm.但当TiC含量增加到20%时,其爆炸反应起始时间延后20min.同时随着Co含量增加,Ni50-Al40-Co10-10%TiC粉末的机械合金化的产物仍为NiAl(Co)和TiC,但NiAl(Co)化合物的生成机制转变为扩散反应机制.进一步增加Co含量(20%,原子分数)则导致了γ-Ni(Al,Co,Ti,C)过饱和固溶体的形成,反应机制仍为互扩散反应.     

多相多尺度铝基复合材料构型强韧化研究进展

总结了铝基复合材料制备方法及构型复合化设计思路,列举了近年来铝基复合材料通过构型复合化改进材料的强度与韧性匹配关系的最新研究成果,展望了具有先进构型的铝基复合材料走向工业化应用的途径。     

HfC颗粒增强NiAl基纳米复合材料的机械合金化与力学性能

球磨Ni,Al,Hf,C元素粉末反应合成NiAl-HfC复合材料,形成机制归结为机械碰撞诱发的双爆炸反应（Ni Al→NiAl △H;Hf C→HfC △H）。采用热压和热等静压工艺纳米粉末压制成较密实的块体材料,进而研究其微观组织与力学性能。结果表明反应球磨制备的NiAl-10FfC复合材料中强化相细小弥散;较大的颗粒（50－100nm）一般分布于晶界,恒应变速率压缩其室温至高温屈服强度均显著高于NiAl。且具备较好的高温塑性,材料的高温强度依赖于应变速率,变形受扩散机制控制。     

机械合金化制备NiAl-TiC复合材料的研究

利用机械合金化方法反应合成ＮｉＡｌ－ＴｉＣ复合材料,对合金化过程,反应机理,球磨时间对粉末颗粒度和晶粒度的影响以及粉末成分配比对反应孕育时间的影响进行了研究,并测试了热压致密后材料的压缩性能。     

Plasticity Enhancement Processes in NiAl and MoSi_2

This paper demonstrates that plasticity enhancement processes previously observed in bcc metalsand associated with the presence of surface films and precipitates or dispersoids are operative in or-dered intermetallic compounds.' Some specific results are given for NiAl-and MoSi_2-basedmaterials.The plasticity of NiAl and related B2 ordered alloys at room temperature during monotonicdeformation can be enhanced by application of surface films such as electroless nickel platings.Sig-nificant effects are also observed during cyclic deformation.The presence of ductile second phasessuch as fcc γ or the ordered phase γ' introduced by alloying also enhances the plasticity of NiAl.MoSi_2 exhibits similar effects of surface films and second phases,but primarily at elevated tempera-tures,T>900℃.In this paper,we illustrate the effects of ZrO_2 surface films deposited near roomtemperature and TiC particulate additions introduced by powder processing techniques.In all cases,the plasticity enhancement is associated with enhanced dislocation generation processes under theconditions of constrained deformation at the film-substrate or precipitate/dispersoid-matrix inter-face of the composite system.     

微量磷(P)对等原子比NiAl的微观组织与力学性能的影响

研究了微量P对挤压态等原子比NiAl的微观组织与高温力学性能的影响.结果表明:微量P的添加对NiAl的晶格常数有一定的影响,P偏聚于NiAl晶界处;并对其高温延伸率有重要影响.P偏聚于晶界阻碍了合金变形过程中的动态回复和再结晶,加剧了晶界处孔洞的形成,造成了NiAl-P合金与二元NiAl合金高温力学性能的显著差异,主要表现在:应力-应变曲线经历了较长的加工硬化阶段;最大延伸率明显下降;变形激活能升高,应变速率敏感指数下降.NiAl-P合金的高温变形机制为变形过程中位错的滑移与攀移共同作用.     

Reactive Milling and Mechanical Properties of NiAl Composite with HfC Dispersoids

A NiAl-based composite with HfB2 dispersed particles has been synthesized by mechanical alloying of Ni,Al,Hf and C powders.The formation mechanism of NiAl-HfC during milling can be attributed to two chemical reactions:Ni Al→NiAl ΔH;Hf C→HfC ΔH,induced by mechanical collision in a certain period of time,which results in an abrupt exothermic reaction.Hot pressing(HP) and hot isostatic pressing(HIP) have been used to make the NiAl-10HfC compacts near fully dense.Compressive testing from room temperature to 1000℃ indicated that the yield stress of NiAl-10HfC composite is 3-4 times higher than that of cast NiAl and correspond to the MA NiAl-10TiB2 composite.In the meantime,yield strength at high temperature is dependent on strain rate, and deformation is controlled by diffusion mechanism.     

Study on preparation and mechanical property of nanocrystalline NiAl intermetallic

Nanocrystalline NiAl materials were fabricated using mechanical alloying and hot-pressing sintering technique. The crystal structural and microstructure of milled powders during mechanical alloying, and the microstructure and mechanical properties of bulk NiAl intermetallic were characterized. The results show that B2 ordered nanocrystalline NiAl powders were successfully synthesized by solid-state diffusion via the gradual exothermic reaction mechanism during mechanical alloying. Scanning electron microscope image confirmed that the powder particles were flat and flake shape in the early stage of milling, but changed to a spherical shape with the crystallite size about 30 nm after the milling. After sintering, the crystal structure of nanocrystalline NiAl intermetallic was assigned to B2 order NiAl phase with the average crystallite size about 100 nm. The nanocrystalline NiAl intermetallic exhibited prominent room temperature compressive properties, such as the true ultimate compressive strength and the fracture strain were 2143 MPa and 32.2%, respectively. The appearances of vein-like patterns on the fracture surface of NiAl intermetallic materials indicated that the fracture mechanism could be characterized as ductile fracture. It can be concluded that higher sintering density and nanocrystalline of NiAl intermetallic were benefited for the improvement of mechanical properties.