Preparation and Microstructural Analysis of Ti2AlC/TiAl（Nb） Composite

By using the spark plasma sintering process, Ti2AlC/TiAlcomposite with the addition of Niobium （Nb） was prepared in-situ and the microstructure of Ti2AlC/TiAl （Nb） composite was investigated by means of transmission electron microscopy （TEM） and high-resolution electron microscopy （HREM）. The results indicate that new-formed Ti2AIC particles disperse with a high degree of uniformity and well combine with the matrix. In the area of phase interface the d-spaces of Ti2AlC （100） and TiAI （110） were measured as 0.2648 nm and 0.2991 nm,respectively. The atom arrangement beside the interface was only partly corresponding, existing in semicoherent state. On the contrary, in the area of grain interface the d-spaces of TiAl （100） and TiAl （110） were measured as 0.2462 nm and 0.2631 nm,respectively and the atom arrangement beside the interface was almost corresponding, existing in coherent state.     

中温烧结0.6Mg_4Nb_2O_9-0.4SrTiO_3复相陶瓷

采用传统固态反应方法制备0.6Mg4Nb2O9-0.4SrTiO3复合陶瓷。研究LiF掺杂对其烧结特性、相结构和微观形貌的的影响。通过X射线衍射(XRD)和扫面电镜(SEM)观察样品的相组成和显微结构。实验结果表明:1.5 wt%LiF添加,可将Mg4Nb2O9/SrTiO3陶瓷的致密化烧结温度从1300℃降至1100℃;XRD表明除主相Mg4Nb2O9、SrTiO3外,还有少量新相Sr(Ti1-xNbx)O3+δ生成。     

Dissolving of Nb and Ti carbonitride precipitates in microalloyed steels

The dissolving behaviour of Nb and Ti carbonitride precipitates in microalloyed steels during isothermal holding at 1300℃ was investigated by Transmission electron microscopy (TEM) and energy dispersion x-ray spectrum (EDX). It was found that all precipitates in Nb-Ti microalloyed steel are (Nb, Ti)(C, N). With holding time increasing, the atomic ratio of Nb/Ti in precipitates decrease gradually. These precipitates still existe even after holding for 48 h at 1300℃while Nb(C, N) precipitates dissolve away in Nb microalloyed steel only after 4 h at the same temperature. These results show that formation and thermostability of precipitates are considerably influenced by interaction between Nb and Ti.     

GRADIENT VARIATION OF COMPOSITION AND QUANTUM CHEMISTRY CALCULATION OF(Ti-Nb)C-Ni COMPOSITE

(Ti,Nb)C Ni composite is prepared.Theanalyses of SEM,EPMA and TEM/EDAX show that (Ti,Nb)C-Ni consists of three phases,which are called interior,transitional and Ni phases respectively.Several models arecalculated by self-consistent-field variational Xa(SCF-DV-Xa)me thod,one of the quantum chemistry calculatingmethods.The calculated results show that when Ni elementincreases,the bond orders(measures of strength of covalentbonding)of Ti-C and Ni-C in the models decrease corre-spondingly,which is to say that there is a gradient variation of the covalent bond in the transitional phase which is compat-ible with both the interior and Ni phases.It is beneficial for improving the mechanical properties of the materials.     

Nature of large （Ti, Nb）（C, N） particles precipitated during the solidification of Ti, Nb HSLA steel

To investigate the microsegregation phenomena and complex （Ti, Nb）（C, N） precipitation behavior during continuous casting, a unidirectional solidification unit was employed to simulate the solidification process. The samples of Ti, Nb-addition steels after unidirectional solidification were examined using field emission scanning electron microscope （FE-SEM） and electron probe X-ray microanalyzer （EPMA）. In such specimens, dendrite structure and mushy zone can be detected along the solidification direction. It shows that the addition of titanium, niobium to high-strength low-alloyed （HSLA） steel results in undesirable （Ti, Nb）（C, N） precipitation because of microsegregation. The effect of cooling rate on （Ti, Nb）（C, N） precipitation was investigated. The composition of large precipitates was determined using FE-SEM with EDS. Large （Ti, Nb）（C, N） precipitates could be divided into three kinds according to the composition and morphology. With the cooling rate increasing, Ti-rich （Ti, Nb）（C, N） precipitates are transformed to Nb-rich （Ti, Nb）（C, N） precipitates.     

Effects of Sintering Technology on PMZN Piezoceramics Properties

Pb (Mn1/3Sb2/3) x(Zn1/3Nb2/3)y (Zr0.535Ti0.465)1-x-yO3(PMZN) piezoelectric ceramics were fabricated .The effects of sintering temperature and heat-treatment time on properties were discussed, the opti-mum preparation technology parameters were obtained. In this case, the ceramics have the highest electromechanical coupling coefficients and mechanical quality factor and the least dielectric loss. It is revealed that the PMZN piezo-ceramics material can be utilized for high-power ultrasound transducers.     

Microstructures and mechanical properties of a new titanium alloy for surgical implant application

A new titanium alloy Ti12.5Zr2.5Nb2.5Ta(TZNT) for surgical implant application was synthesized and fully annealed at 700℃for 45 min.The microstructure and the mechanical properties such as tensile properties and fatigue properties were investigated.The results show that TZNT mainly consists of a lot of lamellaα-phase clusters with different orientations distributed in the originalβ-phase grain boundaries and a small amount ofβphases between the lamella a phases.The alloy exhibits better ductility,lower m...     

Effect of Nb on the mechanical properties of Ti/Al2O3 composite

Ti/Al₂O₃ composite with improved mechanical properties was synthesized by the spark plasma sintering. The effect of Nb on the microstructure of the composite was analyzed by TEM, SEM and so on. The experimental results indicate that the bending strength, fracture toughness, micro-hardness and relative density of the composite are 897.29MPa, 17.38MPa·m^1/2, 17.13GPa and 99.24% respectively when adding 1.5vol Nb. The bending strength is improved by reason of forming dislocation ring and transfering fracture mode from integranular to mixture fracture of intergranular and transgranular. The crack propagating is mainly the deflection bridging. It indicates a reduction of crack driving force and an increase in crack growth resistance, which results in toughness enhanced. Funded by the National Natural Science Foundation of China (No. 50232020) and the Natural Science Foundation of Shandong Province (No. 2002F21)     

Effect of strong carbide forming elements in hardfacing weld metal

To achieve high carbon hard-facing weld metals with both high hardness and crack resistance, strong carbide forming elements Ti, Nb and V were alloyed into the weld metals, and their effect on the formation of carbides and the matrix microstructure were studied. Electron Probe Microanalysis (EPMA), Energy Dispersive Spectroscopy(EDS) and Transmission Electron Microscopy(TEM) were adopted to investigate the microstructure, then thermodynamics of the formation of carbides was calculated and their effect on the matrix was further discussed. It is revealed that Nb, Ti and V influence strongly the distribution and existing state of carbon, inducing precipitation of carbides accompanying with the depletion of carbon in matrix. But when only V are alloyed as carbide forming element, the carbides are scarce and distributed along grain boundaries, and the hard-facing alloy is too hard, while the using of only Nb or Ti could not reinforce the weld metals effectively. The hard-facing alloy reinforced with Nb, V and Ti can form dispersive fine carbides and low carbon martensite matrix.     

Interfacial microstructure and properties of Ti(C,N)/Ni bonded by transient liquid-phase diffusion

Effects of the main process parameters(temperature and time) on microstructure and properties of Ti(C, N)/Ni interface bonded by (Cu+Nb) interlayer in a vacuum diffusion bonding device were investigated. The interfacial microstructures consisted initially of Ni₃Nb metallic compound and eutectic of Ni₃Nb+CuNi_SS, and finally transformed to (Ti, Nb) (C, N)+Ni₃Nb near Ti (C, N) and NiCu_SS+Ni₃Nb near Ni when diffusion bonding temperature was 1 523–1 573 K. It was clear that Cu was a constituent in the transient liquid phase (TLP) into which Ni was dissolved by forming Cu-Ni transition liquid. Nb was dissolved in Cu-Ni transition liquid rapidly. Ti (C, N) conld be wetted by resultant Ni-Nb-Cu transient liquid phase which was followed by a little (Ti, Nb) (C, N) solid solution formed at interface. This increased the interface combining capability. Ultimately the interface shear strength was able to reach 140 MPa. The theoretle analysis and experimental results show that the growth of interfacial reaction layer Ni₃Nb accords with parabola law, and the activation energy of diffusion reaction is 115.0±0.5 kJ/mol, while the diffusion reaction speed constant is 12.53 mm/s^1/2. Funded by the National Natural Science Foundation of China (No. 50074017/E0408)     

Behavior of precipitation in bainitic steel during relaxation processing of RPC technique

Thermal simulation test, TEM (Transmission Electron Microscope) and nanobeam EDS (Energy Dispersed x-ray Spectrum) techniques were used to investigate the precipitation behavior of Nb, Ti, Mo etc. in HSLA (High Strength Low Alloy) steel. The strain induced precipitation occurred during the isothermal relaxation stage after deformed in the non-recrystallization temperature region. After 30% predeformation at 850 and 900~C, there are two kinds of particles, (Ti,Nb)(C,N) and a few Nb(C,N), to precipitate during holding. The content of Nb in particles rises with the relaxation time increasing. During the final holding stage, some Nb and Ti atoms in the lattice sites of the precipitates would be replaced by Mo atoms, and the Mo content in the precipitates increases with the relaxation time. The results were compared with the refinement effect of microstructures caused by relaxationprecipitation controlling transformation (RPC) processing.     

Al,Nb含量对GH706合金长期时效组织及持久性能的影响

铝和铌含量的改变对GH706合金组织及持久性能影响的研究结果表明,将Al的质量分数升高至1.25%,而Nb的质量分数降低至2.0%,抑制了合金晶内强化相γ″-Ni3Nb相的析出,促进了γ′-Ni3Al相的析出,同时阻止了晶界η-Ni3（Ti,Nb）相形成.在650℃长期时效后,降Nb提Al后晶内γ″-Ni3Nb相长大及η相的析出受到抑制,合金组织具有更高的稳定性,合金持久寿命的降低幅度远低于原型合金.     

奥氏体不锈钢焊接热影响区开裂敏感性的测试与研究

应用热机械模拟系统Ｇｌｅｅｂｌｅ２０００Ｓｙｓｔｅｍ，通过焊接热影响区（ＨＡＺ）致脆开裂物理本质的模拟性试验———热拉力试验，对两种某核电站用高压热水管道材料———含铌和含钛奥氏体不锈钢的ＨＡＺ韧脆性变化行为进行了测试和研究．结果表明：ＨＡＺ致脆开裂敏感性随铌、钛含量的增加而提高，且含铌钢的ＺＤＲ（零韧性区域）远大于含钛钢．     

中温烧结Mg_4Nb_2O_9-CaTiO_3陶瓷相结构的研究

采用传统固态反应方法制备了(1-x)Mg4Nb2O9+xCaTiO3[(1-x)MN-xCT]复合陶瓷。探讨了烧结温度、组分x对Mg4Nb2O9/CaTiO3复合材料相结构的影响。通过XRD和EDS进行物相分析。实验结果表明:V2O5添加能够有效降低Mg4Nb2O9/CaTiO3陶瓷的烧结温度;(1-x)MN-xCT复相的形成主要取决于烧结温度和x的含量。1150℃烧结、0.5≤x≤0.7范围内,形成了Mg4Nb2O9/CaTiO3复相,无新相生成,但元素在不同相之间发生了扩散。     

SYNTHESIS AND CHARACTERIZATION OF A NEW NIOBATE: Sr6Ti7Nb9O42

A new niobate Sr_6Ti_7Nb_9O_(42) was synthesized for the first time by solid state reaction in SrO-TiO_2Nb_2O_5 ternary system. The new compound was characterized by EPMA, XRD, SEM and DTA. The X-ray owder diffraction data of Sr_6Ti_7Nb_9O_(42) were firstly reported in the paper. Sr_6Ti_7Nb_9O_(42) crystallizes the hexagonal system with unit cell parameters a=8.9991(4)(?), c=11.5118(9)(?), and space group P6_3/mcm(193), z=1. The calculated and measured densities are 4.783 g/cm~3 and 4.764 g/cm~3, respectively.     

Fabrication of High-purity Ternary Carbide Ti3AlC2 by Spark Plasma Sintering （SPS） Technique

The effect of silicon on synthesis of Ti3AlC2 by spark plasma sintering （SPS） from TiC/Ti/Al powders was investigated. X-ray diffraction （XRD） and scanning electron microscope （SEM） were used for phase identification and microstructure evaluation. The results show that addition of silicon can considerably accelerate the synthesis reaction of Ti3AlC2 and fully dense, essentially single-phase （purity 〉98%） polycrystalline Ti3AlC2 could be successfully obtained by sintering 2TiC/lTi/lAl/0.2Si powders at 1 200- 1 250 ℃ under a pressure of 30 MPa. SEM photographs show that the obtained Ti3AlC2 samples from mixtures powders are in plane-shape with a size of about 2-5 μm and 10-25 μm in the thickness dimension and elongated dimension, respectively.     

Composition Optimization of Nb-Ti Microalloyed High Strength Steel

Four Nb-Ti microalloyed steels were refined and rolled to study the composition optimization of Nb-Ti microalloyed steels. The effects of Nb and Ti on the microstructures, precipitates and properties of Nb-Ti microalloyed steel were investigated. The results showed that an increase in Ti content resulted in the appearance of many fine precipitates leading to a strong precipitation strengthening effect. Hence, the yield strength increased. Besides, the increased strength by the combined increase of Nb and Ti was similar to that observed for the increase in Ti content alone. This increase in strength was attributed widely to the increase in the Ti content alone rather than Nb. Moreover, the increase in Nb content beyond 0.036 wt% exerted no significant effect on the strength of Ti-Nb microalloyed steels, in which more Ti could be added to further improve the strength of steels.     

高锰钢中硬质点对形变强化的影响

高锰钢中加入Nb或Ti且吹N_2后形成大量的含Nb或Ti的硬相,促进了高锰钢形变强化,吹N_2和Nb或Ti合金化促进了A形变强化,提高了锰钢的耐磨性。     

Spark Plasma Sintering Preperties of Ultrafine Ti （ C, N）-based Cermet

Ultrafine Ti( C, N)-based cermet was sintered by SPS from 1050℃ to 1450℃ and its sintering properties, such as porosity, mechanical properties and phase transformation , were investigated by optical microscopy ( OM ), scanning electron microscopy (SEM), X-ray diffraction ( XRD ), and differential scanning calorimeter (OSC). It is found that the spark plasma sintering properties of Ti ( C, N )-based cermet differ from those of conventional vacuum sintering. The liquid phase appearance is at least lower by 150℃ than that in vacuum sintering. The porosity decreases sharply belove 1200℃ and reaches minimum at 1200℃ , and afterwards it almost keeps invariable and no longer increases. SPS remarkably accelerates the phase transformation of Ti ( C, N )-based cermet and it has a powerful ability to remorse oxides in Ti( C, N)-based cermets. Above 1350℃, denitrification occurred. Fresh graphite phase formed above 1 430℃ . Both the porosity and graphite are responsible for the poor TRS.     

Fabrication and Microstructure Evolution of Niobium-Niobium Silicide Composites by Spark Plasma Sintering

By using Nb and Si elemental powders as raw materials,dense Nb/Nb 5 Si 3 composites were successfully fabricated by a spark plasma sintering(SPS)technology.The microstructure of the fabricated composites was analyzed by OM,SEM,XRD and EPMA;the microstructure evolution of the composites was also investigated by a quenching test.The experimental results show that the prepared composites consist of Nb and Nb 5 Si 3 phases;Nb particle uniformly distributes in the in-situ synthesized Nb5 Si3 matrix.During the SPS process,an interfacial reaction occurs between Nb and Si particles to synthesize Nb 5 Si 3 until reactant silicon has been completely depleted.