Nanometer-scale solute segregation at heterophase interfaces and microstructural evolution of molybdenum nitride precipitates.

The interrelationship between coherency and solute segregation at metal/metal-nitride heterophase interfaces is studied on a subnanometer scale by both atom-probe field-ion and electron microscopies for molybdenum nitride precipitates in Fe-2 at% Mo-X, where X = 0.4 at% Sb or 0.5 at% Sn. Internal nitridation at 550 degrees C generates thin platelet-shaped molybdenum nitride precipitates, while nitridation at 600 degrees C produces, in addition to the small-scale structure with precipitates of the thin-platelet type, a much coarser structure of thick plates and spheroidal precipitates. The solute species Sn and Sb segregate at the heterophase interfaces of the coarse precipitates and Gibbsian interfacial excesses of up to 7 x 10(18) M(-2) are measured. The segregation is related to the presence of misfit dislocations at the interfaces of the coarse preciptitates, while the thin plates remain coherent with no detectable segregation.     

锗元素对Sn-3.5Ag合金/铜界面反应的影响

通过向Sn-3.5Ag共晶合金中添加质量分数为0.1%,0.3%的锗元素,研究了锗元素对Sn-3.5Ag合金/铜界面反应的影响。结果表明:对于Sn-3.5Ag合金/铜界面,没加入锗元素时界面反应初生相为扇贝状Cu6Sn5,在热老化过程中此化合物层不断长大,且在Cu6Sn5/铜界面处生成新的Cu3Sn化合物,同时在Cu3Sn/铜界面上出现柯肯达尔空洞;当钎料中添加锗后,界面初生相也为Cu6Sn5化合物,在热老化阶段,Cu6Sn5化合物层厚度增长非常缓慢,且无Cu3Sn化合物生成,整个老化过程中都无柯肯达尔空洞出现。     

TiAl/40Cr感应钎焊接头界面结构及力学性能分析

以Ag-Cu-Ti为钎料对TiAl与40Cr进行了感应钎焊试验。采用扫描电镜、电子探针和X射线能谱分析仪等分析测试手段对界面组织及生成相进行了分析;测试了接头的抗拉强度及界面生成相的显微硬度。结果表明,钎缝处出现了Ti Al3、Ag[s,s]、Ti(Cu,Al)2三种反应相,当钎焊温度为1 143~1 183 K时, 接头的界面结构为TiAl/ TiAl3 /TiAl3 + Ag[s,s]/ Ti(Cu,Al)2 + Ag[s,s] / Ag[s,s] + Ag-Cu共晶相/ 40Cr;当钎焊温度为1 223 K时,接头的界面结构为TiAl / Ti(Cu,Al)2+少量Ag[s,s]/ Ag[s,s] + Ag-Cu共晶相/ 40Cr。在试验所选的工艺参数范围内,最佳规范为连接温度为1 143 K,保温时间为5 min,此时接头的抗拉强度达到267 Mpa。     

等温时效对Sn3.0Ag2.8Cu/Cu焊点界面层组织的影响

对Sn3．0Ag2．8Cu／Cu焊点等温时效后其界面组织的变化进行了SEM、OM以及EDX分析研究，并与Sn37Pb／Cu焊点进行了比较。结果表明：在焊料与铜基板界面上存在Cu6Sn5和Cu3Sn两种金属间化合物，时效过程中Sn3．0Ag2．8Cu焊料与铜的生长速度较慢，金属间化合物的生长属于扩散控制。     

HREM of CoSi2/SiC heterophase interface: facts and artifacts in the interface distance profile measurements

When studying heterophase interfaces, one of the ultimate goals is to determine the local distortions and to extract a chemical profile. In this respect, HREM is a powerful tool. Nevertheless, the non-linearity of the image formation leads to artifacts both in the images and in the distance profiles extracted from the images. The present SiC/silicide interface study illustrates the misinterpretation, which might arise from measurements made on images recorded under limited experimental conditions.     

Linear least-squares fit evaluation of series of analytical spectra from planar defects: extension and possible implementations in scanning transmission electron microscopy

In a previous paper, a new technique was introduced to determine the chemistry of crystallographically well‐defined planar defects (such as straight interfaces, grain boundaries, twins, inversion or antiphase domain boundaries) in the presence of homogeneous solute segregation or selective doping. The technique is based on a linear least‐squares fit using series of analytical (electron energy‐loss or energy‐dispersive X‐ray) spectra acquired in a transmission electron microscope that is operated in nano‐probe mode with the planar defect centred edge‐on. First, additional notes on the use of proper k‐factors and determination of Gibbsian excess segregation are given in this note. Using simulated data sets, it is shown that the linear least‐squares fit improves both the accuracy and the robustness to noise beyond that obtainable by independently repeated measurements. It is then shown how the method originally developed for a stationary nano‐probe mode in transmission electron microscopy can be extended to a focused electron beam that scans a square region in scanning transmission electron microscopy. The necessary modifications to scan geometry and corresponding numerical evaluation are described, and three different practical implementations are proposed.     

Solid state reaction in sandwich-type Al/Cu thin films

Al/Cu/Al and Cu/Al/Cu triple layers with approximately 10 nm single layer thickness deposited on tungsten substrates were analyzed in the early stages of reactive interdiffusion by means of atom probe tomography. The first reaction product is found after 5 min thermal treatment at 110 degrees C and identified by direct chemical analysis to be Al2Cu. Surprisingly, we found a significant asymmetry in the reaction rate of the new phase with the stacking sequence: the thickness of the product grown at the interfaces, at which Cu is deposited on top of the Al layer, is approximately 1.5-2 times thicker than the other one at the interfaces at which Al is deposited onto a Cu layer. On the other hand, at both interfaces the thickness of the product layer depends parabolically on time. No precursory interdiffusion and no distinct nucleation process of the product are observed.     

High-resolution Transmission Electron Microscopy Characterization of the Structure of Cu Precipitate in a Thermal-aged Multicomponent Steel

High-dispersed nanoscale Cu precipitates often contribute to extremely high strength due to precipitation hardening,and whereas usually lead to degraded toughness for especially ferritic steels.Hence,it is important to understand the formation behaviors of the Cu precipitates.High-resolution transmission electron microscopy(TEM) is utilized to investigate the structure of Cu precipitates thermally formed in a high-strength low-alloy(HSLA) steel.The Cu precipitates were generally formed from solid solution and at the crystallographic defects such as martensite lath boundaries and dislocations.The Cu precipitates in the same aging condition have various structure of BCC,9 R and FCC,and the structural evolution does not greatly correlate with the actual sizes.The presence of different structures in an individual Cu precipitate is observed,which reflects the structural transformation occurring locally to relax the strain energy.The multiply additions in the steel possibly make the Cu precipitation more complex compared to the binary or the ternary Fe-Cu alloys with Ni or Mn additions.This research gives constructive suggestions on alloying design of Cu-bearing alloy steels.     

Microstructure of a spray-formed Al/SiC composite

The microstructure of an Al–6Cu–2Mn–0·45 Mg–1(Ag, Ti, V, Zr, Cr) alloy, reinforced with 13 vol.% SiC particles, made by spray deposition has been investigated by transmission electron microscopy, high-resolution electron microscopy and electron diffraction X-ray spectroscopy. Particular attention was focused on the influence of the reinforcement on the precipitation sequence. Instead of the expected precipitation sequence due to the high Cu/Mg ratio, there is an additional σ precipitate which was previously observed in A1 alloys containing silicon. This precipitate becomes predominant at the T6 temper. The new precipitation sequence for this reinforced alloy is therefore The precipitation of σ phase is believed to be due to the presence of SiC particles, and seems to be correlated with the occurrence of large Mn-rich particles. Although expected, no S phase precipitation is found to occur in the matrix grains. At the matrix grain boundaries, small Al₂Cu (θ) and Al₂CuMg (S), as well as Mn-rich precipitates are found. At the SiC particle surfaces, preferentially orientated Ag-rich and Mg-rich intermetallic precipitates are found. They can coexist with amorphous patches containing oxygen enclosed in an irregularly shaped Al₂Cu (θ) phase remaining from large crystalline areas which did not go into solution.     

Preparation mechanism and grinding performance of single-layer self-lubrication brazed CBN abrasive wheels

In order to fabricate single-layer self-lubrication brazed cubic boron nitride (CBN) abrasive wheels, brazing experiments of graphite particles and AISI 1045 steel were carried out using Ag–Cu–Ti filler alloy. Optical microscope, scanning electron microscope, energy-dispersive spectroscopy, and X-ray diffraction were employed to characterize the microstructure and phase constitution of the brazing interface between graphite particles and Ag–Cu–Ti alloy. The formation mechanism was discussed. The results show that TiC resultants are formed via the diffusion behavior of Ti atoms and C atoms towards the joining interface. The chemical resultants of TiC have the granular shape at the early stage. Then, they grow across the joining interface between the graphite particle and Ag–Cu–Ti alloy. Finally, the continuous lamellar TiC compounds come into being around the graphite particle. Chemical joining of graphite particles and Ag–Cu–Ti filler alloy is accordingly realized. A comparative experiment displayed that the single-layer self-lubrication brazed CBN abrasive wheel has better performance than the conventional brazed counterpart.     

Successful application of spatial difference technique to electron energy-loss spectroscopy studies of Mo/SrTiO3 interfaces

The electron energy‐loss near‐edge structure (ELNES) of Mo/SrTiO₃ interfaces has been studied using high spatial resolution electron energy‐loss spectroscopy (EELS) in a dedicated scanning transmission electron microscope. Thin films of Mo with a thickness of 50 nm were grown on (001)‐orientated SrTiO₃ surfaces by molecular beam epitaxy at 600 °C. High‐resolution transmission electron microscopy revealed that the interfaces were atomically abrupt with the (110)_Mo plane parallel to the substrate surface. Ti‐L_2,3 (～460 eV), O‐K (～530 eV), Sr‐L_2,3 (～1950 eV) and Mo‐L_2,3 (～2500 eV) absorption edges were acquired by using the Gatan Enfina parallel EELS system with a CCD detector. The interface‐specific components of the ELNES were extracted by employing the spatial difference method. The interfacial Ti‐L_2,3 edge shifted to lower energy values and the splitting due to crystal field became less pronounced compared to bulk SrTiO₃, which indicated that the Ti atoms at the interface were in a reduced oxidation state and that the symmetry of the TiO₆ octahedra was disturbed. No interfacial Sr‐L_2,3 edge was observed, which may demonstrate that Sr atoms do not participate in the interfacial bonding. An evident interface‐specific O‐K edge was found, which differs from that of the bulk in both position (0.8 ± 0.2 eV positive shift) and shape. In addition, a positive shift (0.9 ± 0.3 eV) occurred for the interfacial Mo‐L_2,3, revealing an oxidized state of Mo at the interface. Our results indicated that at the interface SrTiO₃ was terminated with TiO₂. The validity of the spatial difference technique is discussed and examined by introducing subchannel drift intentionally.     

Carbon-fibre reinforced magnesium alloys: nanostructure and chemistry of interlayers and their effect on mechanical properties

The micromechanical fracture behaviour of C/Mg–Al composites of varying interface reactivity was investigated by scanning electron microscope bending tests. Structure and chemistry of fibre/matrix interlayers were studied down to the atomic scale by imaging and spectroscopical transmission electron microscope techniques (high-resolution electron microscopy, energy dispersive X-ray spectroscopy, parallel-recording electron energy loss spectroscopy and energy-filtered transmission electron microscopy). The chemical reactions at the fibre/matrix interfaces of the C/Mg–Al composites were found to form plate-shaped carbidic precipitates, mainly Al₂MgC₂, which strongly influence the composite's mechanical properties by changing the fibre/matrix bonding strength.     

ZChSnSb11-6/20钢复合材料不同结合界面结合强度仿真与试验

针对巴氏合金与钢体组成的复合材料,建立了不同结合界面(不同的生产工艺条件)下工件结合强度理论计算模型。以微小单元作为模型构建的基础,利用COMSOL Multiphysics软件对其结合界面进行了有限元应力场仿真模拟,得到了不同生产工艺条件下界面应力分布情况。仿真结果表明：三种结合界面下提出的理论计算公式与模拟计算值之间的相对误差值在15%内。采用电弧喷涂技术制备了不同结合界面和不同表面粗糙度的ZChSnSb11-6/20钢复合材料,得到了不同结合界面许用结合强度。试验结果表明：对于同一表面粗糙度,其结合强度随结合界面接触面积的增大而增大,圆弧面（B型）和截球面（C型）两种结合界面的结合强度值较接近,差值在2MPa之内;光面（A型）结合界面的结合强度最小,约为B型、C型两种结合界面结合强度的60%。通过对比分析,对所构建模型进行了模型评价,得到了模型评价对照表。     

Interaction Of Grain Boundary Dislocations With Precipitates During High Temperature Creep

The interactions between grain boundary dislocations (GBDs) and intergranular TiC precipitates in an austenitic stainless steel (Alloy 800) have been investigated after creep at very low stresses at 800°C. The absence of Orowan looping suggests that the GBDs by-pass the precipitates by glide/climb in the particle/matrix interfaces. An approximate calculation shows that the stress for bowing of GBDs between TiC precipitates is consistent with a measured value of the threshold stress for diffusion creep. However, it is suggested that an additional factor may be present in the threshold stress due to attractive forces between the precipitates and the GBDs.     

Tribological Properties of TiN/Ag Nanocomposite Coatings

Morphology, structure, and tribological behavior of magnetron co-sputtered TiN/Ag nanocomposite coatings deposited at 150 °C with an Ag content in the range of 7–45 at.% were characterized. The coatings show a columnar structure with embedded Ag crystallites of 3–50 nm in diameter, where the columns are characterized by a layered structure with Ag-poor and Ag-rich layers. These layers originate from sample rotation during deposition, where the layer thickness increases with increasing Ag content. These Ag layers become continuous over a critical Ag content. At room temperature the friction coefficient is determined by the film structure, whereas friction and wear at high temperature depend on segregation of Ag to the surface.     

Electron crystallography applied to the structure determination of Nb(Cu,Al,X)2 Laves phases

The presence of primary precipitates of the Laves phases considerably improves the mechanical properties and the resistance to thermal degradation of the high‐temperature shape memory Cu–Al–Nb alloys. The structure analysis of the Laves phases was carried out on particles contained in the ternary and quaternary alloys as well on synthesized compounds related to the composition of the Nb(Cu,Al,X)₂ phase, where X = Ni, Co, Cr, Ti and Zr. The precise structure determination of the Laves phases was carried out by the electron crystallography method using the crisp software.     

C/Al-40%Cu复合材料的原位热解-热压法制备及微观结构

以聚乙烯醇缩丁醛为碳源,采用原位热解-热压法制备C/Al-40%Cu(体积分数)复合材料,研究了该复合材料的物相组成、微观结构以及界面反应特性。结果表明:复合材料主要由铝相、铜相、原位生成的碳材料以及少量残留的高分子材料组成,碳材料连续存在于铝、铜相颗粒之间,有效抑制了Al2Cu和Al4Cu9等金属间化合物的生成;复合材料的实测密度接近于理论密度,组织中未见明显孔洞,致密程度较高;复合材料界面结合良好,铝相和铜相、铝相和碳材料层之间均发生了元素互扩散,形成了厚度分别为2.0~3.5μm和1.0~1.5μm的扩散层,铜相和碳材料层之间以机械结合方式连接。     

SiCf–SiBC composites: microstructural investigations of the as-received material and creep tested composites under an oxidative environment

SiC_f–SiBC composites fabricated by Snecma Propulsion Solide (St Médard en Jalles, France) were investigated by SEM and HRTEM in the as‐received state and after creep tests performed in air, in a temperature range 1423–1573 K, under 170 and 200 MPa. These composites are reinforced by Hi‐Nicalon fibres (Nippon Carbon). A pyrocarbon interphase was first deposited on the fibres. The matrix was then deposited on the fibrous preform by several chemical vapour infiltrations (CVI). As a result the matrix is multilayered and based on the Si–B–C ternary system. This matrix is self‐sealing: this is due to the presence of boron inducing the formation of a sealant glass if the material is heated in an oxidative environment. This glass will protect fibres and fibre/matrix interphases against oxidation. Hi‐Nicalon fibres as well as the different matrix layers were studied by HRTEM and EDX. Some investigations were carried out on the creep‐tested specimens in order to characterize modifications observed in the different constituents of the composites, particularly at the interfaces between the matrix layers and at the fibre/matrix interface. It was shown that several matrix layers crystallized during the creep tests. Moreover, a thin silica layer was observed at the pyrocarbon/matrix interfaces. Differences between the behaviour of the same type of material creep tested under neutral atmosphere are discussed.     

Models and observations of fcc/bcc interfaces

Whereas models of the structure and periodicity of CSL or near CSL high angle grain boundaries are relatively well developed and have been to some extent verified by experiment, the nature of more general (e.g. fcc/bcc) interfaces is very imperfectly understood. One of the major differences between homo- and heterophase boundaries is the occurrence, in the latter case, of reproducible orientation relationships due to the crystallographic requirements of phase transformation (e.g. a glissile interface for martensitic growth, low energy interfaces for classical nucleation). A review is given of the relationships commonly observed to obtain between fcc and bcc crystals (as well as ordered phases based upon these structures). Within a given relationship, it is possible to use models of the available interfaces to predict their dislocation content; the success of the various approaches is considered. It is shown that the dislocation arrays identified on fcc/bcc boundaries are consistent with the occurrence of a primary structural relaxation, but that the latter does not appear to be complete. Possible reasons for this are discussed, together with the extent to which secondary structural models may be applicable. Attempts to rationalize the observed orientation relationships and morphologies are discussed, and it is pointed out that these all rely on searches for situations of minimum primary misfit, but that the way in which the latter is quantified determines the results of the analyses. Nevertheless, the implication is that the primary misfit does appear to determine the actual behaviour, though no structural or mechanistic conclusions can safely be drawn from this observation.     

铝(铝合金)与不锈钢的过渡层钎焊工艺及机理分析

研究了铝(铝合金)与不锈钢的镍／铜过渡层钎焊的工艺方法以及焊缝的组织与力学性能，并对各连接界面进行了机理分析。对焊缝的XRD、SEM和TEM等分析发现焊缝与母材之间没有生成铝与铁脆性的金属间化合物。结果表明，镍／铜电刷镀层能有效地阻挡铝、铁等原子扩散，焊缝与镀铜界面上虽然生成了少量的AlCu2，但没有降低焊缝的抗剪强度。