添加W对机械合金化TiAl合金显微组织和性能的影响

采用机械合金化结合粉末冶金技术制备了Ti-44.7Al-xW(at%)合金材料.采用透射电镜、扫描电镜和金相显微镜研究不同W添加量对机械合金化TiAl基合金的显微组织和高温抗氧化性能的影响,并对合金的力学性能进行测试.研究表明,通过机械合金化在TiAl基合金系统中添加微量W元素会形成新的固溶体相,这种新成分相大大提高TiAl基合金的抗弯强度σb.当W添加量为1.0at%时,σb达到峰值;随后随着W含量的增加,抗弯强度降低.W元素的添加有效的制约了合金基体的内部氧化,使TiAl合金的高温抗氧化性能明显提高.     

机械合金化和微量添加剂对TiAl基合金显微组织及高温抗氧化性能的影响

研究了采用机械合金化方法制备TiAl基合金的工艺及其对显微组织的细化作用，概述了一系列添加剂对TiAl基合金高温抗氧化性能的影响。     

添加高铌对TiAl合金组织和高温性能的影响

由于γ-TiAl合金低密度和高温时的高比强度，因此很有希望在航空和汽车工业的高温领域得到应用。但该合金低的延展性和抗氧化能力限制了它的实际应用。研究发现，添加第3组元可以提高TiAl合金的工程性能。因此，人们相继开展了在含铝45mol％～49mol％的TiAl基合金中添加Cr，Mn，Ta，Nb，W，No，Si，B等第3组元的微合金化研究工作。高铌TiAl合金具有优良的高温强度和室温延展性，抗氧化性能及热加工性得到明显改善。因此对于高铌含量的TiAl合金研究得到快速发展。但是关于含铝量小于45mol％和含Nb量大于10mol％的TiAl合金研究很少。     

合金化对TiAl基合金性能的影响及机理

指出了ＴｉＡｌ基合金的主要缺点,即拉伸性能与蠕变抗力呈反比关系,１０００℃以上的高温强度相对较低、８００℃以上抗氧化性能不足;并提出了改善上述性能的途径,即合金化、热加工、热处理、涂层等,并重点分析了合金化的作用。     

机械合金化对TiAl基合金烧结组织的影响

对TiH2-47Al-0.2Si-10Nb和TiH2-47Al-0.2Si-12Nb成分的粉末机械合金化过程进行了研究,并将球磨30 h后的粉末进行放电等离子和真空烧结。借助X射线衍射仪、扫描电子显微镜和透射电子显微镜研究机械合金化对TiAl基合金烧结组织的影响。结果表明,高能机械球磨过程中形成了非晶相及TiAl金属间化合物,球磨30 h后粉末颗粒达到10 nm左右。采用放电等离子和真空烧结均获得了细小、均匀的TiAl和Ti3Al相组织,烧结组织晶粒在1μm左右。     

添加W对高铌TiAl合金组织和力学性能的影响

研究了添加W（0．2原子分数,％）对高铌TiAl合金组织和力学性能的影响。试验结果表明,W合金化能改变高铌TiAl合金的铸态组织,但不能改变热加工组织以及4种典型组织和温度对其力学性能的影响。W合金化能提高高铌TiAl合金的室温及高温强度、降低强度随温度下降的速率 、提高脆韧转变温度,但对室温塑性影响不大,有利于FAM组织在更高温度下使用。     

元素Si对TiAl合金抗氧化性能的影响

研究了元素Si对不同Nb含量TiAl合金抗氧化性能的影响．结果表明，合金中Nb含量越低，Si对合金抗氧化性能的提高作用越明显．主要表现为Si促使二元合金形成连续致密的Al2O3层及使不同Nb含量合金表层氧化物更加均匀细小．因而随Si含量的增加，TiAl合金的氧化增重速率系数降低，氧化速率下降．运用等温氧化增重实验、X射线衍射和扫描电镜等手段对Si的作用进行了分析讨论．     

机械合金化对W-20Cu复合材料的显微组织与性能的影响

采用机械合金化结合粉末冶金技术制备W-20Cu（vo1％）复合材料。利用扫描电镜和金相显微镜对不同球磨时间的W-20Cu复合材料显微组织进行表征，并对材料的各项物理性能进行测试。结果表明，随着球磨时间的延长，W-20Cu烧结体的组织越来越均匀，Cu相分布也越来越均匀。W-20Cu烧结体密度、收缩率、硬度、抗弯强度随球磨时间的延长而增大；球磨20h的W-20Cu复合粉烧结体热导率达到峰值（130．61Wm^-1K^-1），继续球磨，热导率减小。综合考虑所有研究结果，通过机械合金化所制备的W-Cu复合粉体可以获得具有优异综合物理性能的W-20Cu复合材料。     

Metastable Ti---Ni---Fe---Si alloys prepared by mechanical alloying

The phase formation and physical properties of mechanically alloyed Ti₅₆Ni₁₈Fe₁₀Si₁₆ have been investigated. The as-milled samples are amorphous and undergo a transition to the icosahedral quasi-crystalline phase on annealing at about 1025 K. Mechanical alloying in the presence of an additive of 1% quasi-crystalline phase yielded the same phase directly. Alloys have been studied by X-ray diffraction. Mössbauer spectroscopy and magnetic susceptibility methods. These results may be compared with those in the literature for amorphous and quasi-crystalline alloys of similar composition prepared by rapid solidification from the melt. In all cases the alloys produced by mechanical alloying show a greater concentration of open volume defects and in the icosahedral phase, a greater degree of disorder and largerphason strains. Hydrogen diffusion studies of these alloys have shown that the mean interatomic distance increases for short hydrogenation times, but that for longer hydrogenation times the hydrogen increases local atomic order which results in a reduction of mean interatomic distances.     

机械合金化制备Cu-0.5Wt%Nb合金组织与性能的研究

采用机械合金化法制备了Cu-0.5wt％Nb纳米弥散强化铜合金。通过金相、透射电镜观察了该合金粉末态、冷轧态及不同温度退火后合金的组织结构变化。通过测量该合金不同状态的硬度及相对电导率,实验结果表明,其冷轧态硬度较高(可达160kg/mm2),随退火温度升高硬度呈缓慢下降趋势;900℃退火后,硬度仍可达91kg/mm2,表明此合金抗高温软化性能较好.此外该合金相对电导率最高可达89% IACS,这进一步说明利用机械合金化法制备的Cu-0.5wt%Nb合金具有优越的综合性能.     

On the general outline of physical properties of amorphous-nanocrystalline Fe-Cr-Mn-N alloy powders prepared by mechanical alloying under nitrogen

This paper reviews last findings about physical properties of Fe-Cr-Mn-N powders synthesized by mechanical alloying under nitrogen. Their thermal, magnetic, indentation, and grain growth behaviors and nitrogen distribution in their amorphous-nanocrystalline structure are regarded as a function of milling time. Particularly, the role of nitrogen in the aforementioned phenomena is reviewed in detail.     

Oxidation resistance of TiAl alloy treated by plasma Nb-C alloying

In this paper, the duplex treatment of plasma surface niobizing and carburization (Nb-C alloyed or duplex treated) has been performed on TiAl substrates. Cyclic-oxidation tests for untreated and duplex treated TiAl were carried out in static air at 900 °C for 103 h. The mass gain due to oxidation was measured using an electrobalance. The chemical compositions of the Nb-C alloyed layer as well as its microstructure were examined by glow discharge spectrum (GDS) and the optical microscopy (OM). The electronic diffraction spectrum (EDS) and scanning electronic microscopy (SEM) were used to analyze and observe the oxide layers. The phase structures of the oxide scale were identified by X-ray diffraction (XRD). The results show that the oxidation rate of the duplex treated TiAl specimens decreased significantly, compared with the untreated TiAl. The roles of duplex treatment for improving the oxidation resistance are discussed.     

Effect of CNT addition approach on the microstructure and properties of NiAl-CNT nanocomposites produced by mechanical alloying and spark plasma sintering

An approach was offered to synthesize NiAl-CNT intermetallic matrix nanocomposite by mechanical alloying (MA) to ensure the effective distribution of carbon nanotubes (CNTs) within the matrix. For this purpose 0.5 and 1 wt% of CNTs were added to the powder mixture before the completion of reaction between Ni and Al. The resultant powders were compared to the powders obtained from MA of ex situ synthesized NiAl intermetallic compound with CNTs. Bulk samples were fabricated by spark plasma sintering (SPS) that retained the integrity of CNTs in the matrix. Structural evolutions were investigated by X-ray diffractometery (XRD). Field emission scanning electron microscopy (FESEM) micrographs showed that the offered MA approach caused the CNTs to uniformly embed in the in situ synthesized NiAl matrix. Meanwhile better distribution of CNTs resulted in higher density of SPSed bulk nanocomposite as well as higher hardness up to 5.6 GPa compared to 5.41 of NiAl intermetallic obtained from the same MA time. Fracture toughness showed more than 6.4% increase with bridging and pull out of CNTs and deflection of cracks as toughening mechanisms.     

微量Nd的添加对Mg-Al-Zn合金微观组织和高温力学性能的影响

分析研究了微量Nd的添加对Mg-Al-Zn合金显微组织和高温力学性能的影响.结果表明:Nd的加入,显著细化了合金的铸态组织,同时出现了新相Al3Nd化合物.当Nd添加量为1.0%时,可使铸态Mg-8.5Al-0.5Zn合金在150℃高温下的抗拉强度达到最大值为160MPa,和未加入Nd的合金相比提高了13.2%.     

Fabrication of Ti-Cu-Ni-Al amorphous alloys by mechanical alloying and mechanical milling

Ti-based amorphous alloy powders were synthesized by the mechanical alloying (MA) of pure elements and the mechanical milling (MM) of intermetallic compounds. The amorphous alloy powders were examined by X-ray diffraction (XRD), differential scanning calorimetry (DSC), and scanning electron microscopy (SEM). Scanning electron micrographs revealed that the vein morphology of these alloy powders shows deformation during the milling. The energy-dispersive X-ray spectral maps confirm that each constituent is uniformly dispersed, including Fe and Cr. The XRD and DSC results showed that the milling time required for amorphization for the MA of pure elements was longer than that of the MM for intermetallic compounds. The activation energy and crystallization temperature of the MA powder are different from those of the MM powder.