Sintering behavior of W–30Cu composite powder prepared by electroless plating

Powder metallurgy technique was employed to prepare W–30 wt.% Cu composite through a chemical procedure. This includes powder pre-treatment followed by deposition of electroless Cu plating on the surface of the pre-treated W powder. The composite powder and W–30Cu composite were characterized by X-ray diffraction (XRD) and field emission scanning electron microscopy (FE-SEM). Cold compaction was carried out under pressures ranging from 200 MPa to 600 MPa while sintering at 850 °C, 1000 °C and 1200 °C. The relative density, hardness, compressive strength, and electrical conductivity of the sintered samples were investigated. The results show that the relative sintered density of the titled composites increased with the sintering temperature. However, in solid sintering, the relative density increased with pressure. At 1200 °C and 400 MPa, the liquid-sintered specimen exhibited optimum performance, with the relative density reaching as high as 95.04% and superior electrical conductivity of IACS 53.24%, which doubles the national average of 26.77%. The FE-SEM microstructure evaluation of the sintered compacts showed homogenous dispersion of Cu and W and a Cu network all over the structure.     

Cu@Ag包覆粉体的SPS烧结及其致密机理研究

采用化学镀法制备Cu@Ag包覆粉体,并利用放电等离子烧结技术(SPS)对其进行烧结,利用扫描电子显微镜、透射电子显微镜研究包覆粉体、烧结样品的微观结构,对烧结样品的物相、致密度及其致密化机理进行表征与分析。结果表明,化学镀法制备的Cu@Ag粉体表面存在高纯的包覆层。在较低的烧结温度下可以得到致密度高的Cu-Ag烧结块体,温度升高,Cu-Ag烧结块体的致密度逐渐升高,550℃时,致密度达到极大值96.76%。分析认为,得益于Cu@Ag粉体的包覆结构,在低温下,铜颗粒表面的纳米银的颈缩促进了烧结;在高温下,Cu、Ag间的固溶进一步促进了烧结。     

低W-W连接度65W-25Cu-10Ni合金的制备及准静态力学性能研究

利用W颗粒表面化学镀Ni结合SPS的方法,制备了低W-W连接度65W-25Cu-10Ni合金,并开展了准静态力学性能研究。结果表明,制得的Ni包W复合粉中Ni包覆层分布均匀且与W结合良好;以Ni包W复合粉和Cu粉为原料制备的65W-25Cu-10Ni合金组织均匀且致密。在准静态压缩加载条件下,与65W-35Cu合金相比,65W-25Cu-10Ni合金的强度及塑性均大幅度提高;在准静态拉伸加载条件下,与65W-35Cu合金相比,65W-25Cu-10Ni合金的强度较高,塑性没有明显提高。机理分析表明,与65W-35Cu合金相比,65W-25Cu-10Ni合金中W-W连接度较低、粘结相由Cu相转变为Cu0.81Ni0.19固溶体,且W与粘结相之间形成了冶金结合,以上三个因素共同导致65W-25Cu-10Ni合金强度的提高;此外,W-W连接度的降低以及W-粘结相界面结合强度的提高是65W-25Cu-10Ni合金在准静态压缩加载条件下塑性提高的原因。     

纳米相包覆AgC5电触头材料

采用化学镀技术，在高能球磨所得纳米石墨粉上包覆银，制得纳米晶银／石墨包覆粉体，经冷压、烧结、复压工序，制备了AgC5触头材料。采用此新工艺制备的触头材料与常规工艺制得的相比，在力学和物理性能等方面有了较大的提高。分断实验表明：将纳米技术应用到银／石墨触头材料的制备中，使材料的抗电弧磨损性能有了较大的改善。     

多壁碳纳米管增强银基复合材料的组织与性能

采用化学镀方法将银沉积在碳纳米管上,获得体积分数为8%的多壁碳纳米管/银(CNTs/Ag)复合粉末,通过高能球磨、压制烧结、热挤压粉末冶金手段制备了CNTs/Ag复合材料,并研究了复合材料的微观组织、导电率、抗拉强度及硬度。结果表明,化学沉积工艺能够显著改善CNTs和Ag之间的界面结合,进而提高CNTs/Ag复合材料的加工性能。与纯银比较,CNTs/Ag复合材料的抗拉强度增加了65%,硬度增加了近2倍,表明CNTs对银具有较好的强化作用。     

Improvement of physical properties of Cu-infiltrated W compacts via electroless nickel plating of primary tungsten powder

In the present research, tungsten particles were coated using nickel/nickel-phosphorus electroless plating technique. The coated tungsten powders were pressed under constant pressure to achieve compact material of cylindrical shape with same porosity. Then, attained compacts were infiltrated/penetrated by liquid copper under the hydrogen atmosphere in order to obtain W-15 wt.% Cu composites. The coated/uncoated powders as well as its infiltrated compacts were characterized by optical microscopy (OM) as well as scanning electron microscopy (SEM), EDS and XRD methods. The microstructure, relative density and specific resistivity of composites were compared. The microstructural observations revealed that the infiltration behavior can be improved in the compacts prepared by both nickel and nickel-phosphorus coated tungsten powders, in comparison with uncoated ones. In addition, it was found that relative density may be raised from < 85% to > 95% by nickel electroless plating, that leads to decrease specific resistivity from 6 to 4 µΩ cm. Enhancement of electrical conductivity of infiltrated W-15 wt.% Cu compacts prepared by electroless nickel coated tungsten powders was related to its higher density.     

Investigation on the characteristics of micro- and nano-structured W-15 wt.%Cu composites prepared by powder metallurgy route

The properties of W-15 wt.%Cu composites were investigated by preparing two distinct composites of micrometer and nanoscale structures. Micrometer composite was produced by mixing elemental W and Cu powders and nanometer one was synthesized through a mechanochemical reaction between WO₃ and CuO powders. Subsequent compaction and sintering process was performed to ensure maximum possible densification at 1000-1200 °C temperatures. Finally, the behavior of produced samples including relative density, hardness, compressive strength, electrical conductivity, coefficient of thermal expansion (CTE) and room temperature corrosion resistance were examined. Among the composites, nano-structured sample sintered at 1200 °C exhibited better homogeneity, the highest relative density (94%) and mechanical properties. Furthermore, this composite showed superior electrical conductivity (31.58 IACS) and CTE (9.95384 × 10^- 6) in comparison with micrometer type. This appropriate properties may be mainly attributed to liquid phase sintering with particle rearrangement which induced by higher capillary forces of finer structures.     

Preparation and properties of W–Cu–Zn alloy with low W–W contiguity

The W–Cu–Zn alloy with a-brass matrix and low W–W contiguity was prepared by method of electroless copper plating combined with spark plasma sintering(SPS) method.The effects of process and parameters on the microstructure and mechanical properties of the alloy were investigated.The W–Cu–Zn alloy with a relative density of 96 % and a W–W contiguity of about 10 % was prepared by original fine tungsten particles combined with wet mixing method and SPS solid-state sintering method at 800 °C for 10 min.The microstructure analysis shows that Cu–Zn matrix consists of nano-sized a-brass grains,and the main composition is Cu_3Zn electride.The nano-sized Cu was coated on the surface of tungsten particles by electroless copper plating method,and the fairly low consolidation temperature and short solid-state sintering time result in the nano-sized matrix phase.The dynamic compressive strength of the W–Cu–Zn alloy achieves to1000 MPa,but the alloy shows poor ductility due to the formation of the hard and brittle Cu_3Zn electrides.The fine-grain strengthening and the solution strengthening of the Cu–Zn matrix phase are responsible for the high Vickers microhardness of about 300 MPa for W–Cu–Zn alloy.     

Solid state and liquid phase sintering of mechanically activated W–20 wt.% Cu powder mixture

W–20 wt.% Cu powder mixture was mechanically alloyed by high-energy ball milling for various times and the effect of mechanical alloying (MA) on the sintering response of the composite compacts was investigated. The densification, microstructure, hardness and electrical conductivity after solid phase sintering (SPS) and liquid phase sintering (LPS) were examined. It was shown that the microstructure of mechanically alloyed powder profoundly influence the sintering response, i.e. a meaningful relationship between the sintering kinetics and the milling time was observed. It is suggested that MA disintegrates the W–W particle networks and increases the contribution of solid phase sintering (SPS) of nanostructured Cu and W particles on the densification. Higher hardness and conductivity were achieved by prolonged MA and SPS, indicating a lower W–W contiguity of the milled powders compared with the conventionally prepared W–Cu composite. On the other hand, depression of the melting temperature of copper up to 145 °C was noticed by affording a prolonged MA. The lower melting temperature and finer distribution of the Cu particles in the W matrix enhanced the densification during LPS and improved the homogeneity and properties of the final product.     

放电等离子烧结温度对超细晶W-40Cu复合材料的影响

采用高能球磨法制备了W-40Cu超细晶复合粉体,继而进行了放电等离子烧结(SPS),获得了致密的超细晶W-40Cu块体复合材料,着重研究了烧结温度对复合材料组织和性能的影响.结果表明,随着烧结温度升高,材料的致密度、硬度和电导率也随之升高;在950℃烧结5 min的W-40Cu复合材料,W颗粒尺寸约300～500 nm,相对致密度达98％,显微硬度HV为287,电导率为17.9 MS/m.     

化学镀法制备Cu/Al2O3复合粉体及其烧结行为

为了解决颗粒增强铜基复合材料中颗粒与铜基体相容性的问题,采用化学镀法使得颗粒表面金属化,通过XRD、SEM、EDS等技术研究了Al2O3纳米粉化学镀铜的工艺,并对Cu/Al2O3复合粉体的烧结行为做了初步探讨.结果表明:Al2O3粉前处理工艺、镀液的各种成分都对粉体表面铜的含量有影响,通过改变装载量可有效控制粉体表面Cu含量.实验中确定了最佳的镀覆工艺,并得到了颗粒较为弥散的Cu/Al2O3复合粉体烧结体.     

钨粉化学镀铜对W／15Cu电子封装材料性能的影响

采用化学镀铜的方法在钨粉中加入诱导铜，经压型，熔渗后制成W／15Cu合金。用扫描电镜研究了材料的显微结构，并测出合金样品的密度、气密性、热膨胀系数等物理性能，通过与传统工艺制备的W／15Cu合金的显微组织以及物理性能方面做比较，讨论了钨粉化学镀铜对W／15Cu合金性能的影响。结果表明，钨粉化学镀铜对于提高钨生坯成形性能、改善钨铜复合材料的显微组织结构、提高材料物理性能方面都有很大作用。经过综合比较，镀铜含量以2％为宜。     

烧结工艺对纳米AgSnO2复合材料致密度的影响

对化学镀法制备的纳米AgSnO2粉末分别采用常压、热压和真空烧结的方法制成AgSnO2复合材料，研究了烧结方法及工艺对致密度的影响。结果表明，采用常压烧结，虽然成型压力、烧结温度和时间对致密度有一定的影响，但复压、复烧后，材料的致密度十分接近。热压能在短时间内获得96％以上的致密度，但复烧时膨胀严重，甚至出现鼓泡。真空烧结对去除吸附物有利，但仍会有少量残留并导致复烧时出现膨胀。在较低的压力下成型并采用分段保温烧结，不但能消除吸附物的影响，复烧后还可以得到94％的致密度。研究表明，纳米粉末表面大量的吸附物以及由此造成的封闭在压坯中的气体是阻碍烧结致密化的根本原因。     

Microstructure characterization and electrical conductivity of electroless nano Ni coated 8YSZ cermets

Using a common electroless bath, Ni-8YSZ (Ni-8 mol% yttria stabilized zirconia) composite nano powder have been synthesized without use of any expensive sensitizing agent. HRTEM micrographs indicated that the coating morphology of Ni nano particles on the 8YSZ showed a spotty, discontinuous distribution and the Ni nano particles appeared as a crystalline phase. The amount of Ni in the composite powders was varied from 36-51 wt.% by changing the substrate powder loading in the electroless bath. Bar type samples were prepared by uniaxial pressing and sintering at 1300 °C for 2 h with these coated powders. The cubic (c)-zirconia was found to partially dissociate into monoclinic (m)-zirconia on sintering with Ni content 41% or higher and also increases with the increase of Ni content. The microstructure of each Ni-YSZ cermet after reduction in a H₂ + Ar gas atmosphere showed dual scale porosity (micro and submicron porosity). The Ni-8YSZ cermet samples showed metallic electrical conduction behavior, proving the percolation capability of the synthesized nano composite.     

Novel method for preparation of silver-tin oxide electrical contacts

A novel method of coating tin oxide particles with silver by an electroless plating process has been developed to produce silver-tin oxide electrical contact materials. A powder metallurgy process has been developed to consolidate the electroless plated silver- tin oxide composite powders. The effect of the various plating conditions on the morphology of the composite powder was studied using the transmission electron microscope (TEM) and the scanning electron microscope (SEM). An optical microscope and electron microprobe analysis (EMPA) were used to characterize the structure of the sintered silver-tin oxide compact. Ductility and hardness were measured to ensure that the mechanical properties are adequate, and electrical conductivity was also measured.     

Fabrication, microstructure and properties of SiCp/Cu heat sink materials

Cu-coated powder was fabricated by electroless plating process, and the composition and morphology of coated powder were studied.Moreover, Cu-30, 40, 50 vol.%SiCp heat sink materials were fabricated by hot pressing using coated and uncoated powder.And the microstructure and thermophysical properties of the heat sink materials were also studied.The results show that SiCp particles distribute uniformly in heat sink materials and the interface between SiCp particles and Cu matrix is clear and well bonded.On the condition of same volume fraction of SiCp, the thermal conductivity of the material using coated powder is larger than that of the material using uncoated powder.Under experiment conditions, the thermal conductivity and coefficient of thermal expansion of Cu-30 vol.%SiCp heat sink material is 236.2 W·m-1·K-1 and 9.9×10-6/K (30-200 ℃) respectively.It provides important reference data for future experiments.     

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。     

AI2O3/Cu复合材料制备工艺的优化

新型颗粒增强铜基复合电极材料Al2O3/Cu能较好地解决电阻点焊镀锌钢板时普通电极材料做电极寿命较短的问题。为了获得优化的Al2O3/Cu复合电极材料制备工艺,采用粉末冶金法制备Al2O3/Cu复合电极材料,通过改变制备过程中的工艺参数,以密度、显微维氏硬度、电导率、显微组织为检测内容,探讨压制力和烧结温度对Al2O3/Cu复合电极材料物理机械性能和显微组织的影响。结果表明,综合性能最优时的Al2O3/Cu复合电极材料制备工艺为:Cu-Al2O3混合粉末制坯压制力100 kN,烧结温度940℃。     

The effect of sintering temperature on some properties of Cu-SiC composite

Copper matrix composites reinforced with 1 wt.%, 2 wt.%, 3 wt.% and 5 wt.% SiC particles were fabricated by powder metallurgy method. Cu and Cu-SiC powder mixtures were compacted with a compressive force of 280 MPa and sintered in an open atmospheric furnace at 900-950 °C for 2 h. Within the furnace compacted samples were embedding into the graphite powder. The presence of Cu and SiC components in composites was verified by XRD analysis. Optical and SEM studies showed that Cu-SiC composites have a uniform microstructure in which silicon carbide particles are distributed uniformly in the copper matrix. The results of the study on mechanical and electrical conductivity properties of Cu-SiC composites indicated that with increasing SiC content (wt.%), hardness increased, but relative density and electrical conductivity decreased. The highest electrical conductivity of 98.8% IACS and relative density of 98.2% were obtained for the Cu-1 wt.%SiC composite sintered at 900 °C and this temperature was defined as the optimum sintering temperature.     

纳米晶W-Ni-Fe复合粉末及其烧结过程中的固溶特性

采用溶胶喷雾干燥-热还原法制备了50W-35Ni-15Fe(质量分数,%,下同)纳米晶复合粉末。利用X射线衍射及微区组织的能谱(EDAX)分析,揭示了纳米晶W-Ni-Fe复合粉末及其烧结过程中的固溶特性。研究发现:纳米晶50W-35Ni-15Fe复合粉末中,W在γ-(Ni,Fe)相中的固溶度达到了15%,Ni、Fe元素在W中的固溶度达到了2.4%,形成了超饱和固溶体;随着温度的升高,W的超饱和固溶体W(Ni,Fe)发生Ni、Fe元素的脱溶。而W在γ-(Ni,Fe)相中的固溶度随温度的升高而进一步增加,在1300℃以后基本维持在29%左右;稀土La的加入在低温阶段对W在γ-(Ni,Fe)相中的固溶度影响不大,在1200℃以上使固溶度有一定的降低。