微量纳米铜对铁基粉末冶金制品致密性的影响

为提高铁基粉末冶金制品的密度,试验采用高能球磨机在铁基粉末中添加少量不同含量的纳米铜粉体均匀混合,在相同压力750 MPa下压制块状试样,在920℃,保护性气氛下进行烧结,烧结时间6 h.对不同纳米铜含量烧结后的试样进行了密度、显微组织、硬度、TEM、XRD测试.结果表明:随纳米铜含量的提高,材料的密度明显提高.没有添加纳米铜试样烧结后的密度为6.6 g/cm3;添加3%纳米铜的试样烧结后的密度为7.3 g/cm3,显微组织中空隙率显著减少,同时提高了制品硬度.原因是纳米铜粉体在铁基颗粒界面上的作用,提高了材料的致密性.     

纳米粉体降低烧结件烧结温度与性能的研究

在传统铁基粉末冶金配方中添加质量分数为1%的纳米铜粉,研究纳米铜粉的加入对试样烧结温度和力学性能的影响。结果表明,添加1%粒度为13 nm的铜粉,可以将粉末冶金件的烧结温度降低到930℃。     

用喷雾转化法制备的纳米晶粉末烧结的WC—10Co硬质合金的力学性能

研究了纳米晶WC－10Co硬质合金的力学性能和显著结构。这种纳米晶WC－10Co硬质合金粉末是将含有偏钨酸铵（AMT）和硝酸钴的溶液喷雾干燥制得的纳米晶前驱体粉末再经过还原和碳化制备的。直径约100nm的WC粉末与Co炽结相混合均匀，并在1毫乇压力和1375℃下进行烧结。为了与纳米晶料WC－10Co的显微结构和力学性能相比较，将直径范围为0．57－4μm的工业用WC粉末与Co粉混合，并在与纳米晶粉末相同的条件下进行烧结，在纳米晶WC－10Co硬质合金中加入不同量的TaC、Cr3C2和VC作为晶粒长大抑制剂。为研究WC－10Co硬质合金中Co粘结相的显微结构，以WC－10Co硬质合金烧结温度下制备了Co-W-C合金。WC－10Co硬质合金随着WC粒度的减小而增加的硬度因而符合霍尔－佩奇型关系式。WC－10Co硬质合金的断裂韧性随着Co粘结相的HCP（密排六方相）／FCC（面心六方相）比的增大（由于HCP／FCC相引起的）而提高。     

纳米晶γ-NiFe粉的烧结行为

纳米晶材料作为新型结构材料和功能材料的应用 ,在颇大程度上取决于粉末固结成大块纳米晶固体的过程。在固结过程中形成的亚稳显微组织 ,对于所得材料的力学性能、磁性能或催化性能起着重大影响。研究了纳米晶γ 镍铁粉末的无压烧结行为 ,该镍铁粉末是由球磨后进行氢气还原制得的。研究用的试样具体的制备过程如下 :首先采用Ｆｅ2 Ｏ3粉 (纯度 99 99% ,粒径约为 30 μｍ)和ＮｉＯ粉 (纯度 99 99% ,粒径约 4 μｍ)按Ｎｉ Ｆｅ(50 %质量比 )的成分配成混合料 ,置于不锈钢磨碎机中以 350ｒ/ｍｉｎ的速度进行球磨混合 10ｈ ,同时作为研磨剂添加…     

氮含量对超细晶奥氏体不锈钢组织和性能的影响

通过机械合金化和放电等离子烧结技术制备超细晶奥氏体不锈钢,分析其组织与性能,研究了氮含量对该不锈钢组织和性能的影响。结果表明,随氮含量的增加,烧结试样中马氏体越来越少。氮具有稳定奥氏体的作用,当氮含量为1.2%时,试样基体转化为单一奥氏体相。制得试样晶粒均细小且均匀,尺寸都达到纳米级,氮含量为1.2%的试样,晶粒尺寸最小,只有100 nm。表明采用机械合金化方法结合等离子烧结技术成功制备了纳米级奥氏体不锈钢。氮的加入还能显著提高奥氏体不锈钢的硬度、耐磨性和抗拉强度。     

电解铜粉的氧化机理及阻缓措施

本文通过模拟试验初步探讨了电解铜粉氧化的机理,寻找了生产、贮存过程中影响铜粉氧化的各种因素。确认电解铜粉在潮湿空气中所发生的氧化现象(指肉眼所见到的),主要是由铜粉颗粒表面发生电化学作用的结果,生成物疏松地沉积在铜粉颗粒表面上,对氧化过程继续进行几乎没有阻力。在电解铜粉颗粒表面上形成电化学的氧化过程必须具备两个条件:1.铜粉颗粒表面水膜的形成;2.铜粉颗粒表面上电化学的不均匀性。只有针对形成这两个必要条件的因素,采取限制措施,才能阻缓氧化速度,延长铜粉贮存时间。     

纳米Cu粉末的放电等离子烧结

利用放电等离子烧结装置考察了纳米铜粉坯体的升温过程,研究了烧结速度和烧结温度对烧结等效电阻、烧结体相对密度及晶粒尺寸的影响。结果表明：在烧结过程中存在着最佳的烧结速度,当烧结速度为150℃／min时,样品致密度达到峰值88％左右,晶粒的平均尺寸接近200nm,且烧结的等效电阻随升温速度的增加而降低;纳米Cu粉末在250℃时开始烧结成块,随烧结温度提高,烧结致密度不断提高,电阻降低;但是当升温速度过快,烧结温度过高时,出现反致密化现象。     

纳米晶镍块体的制备及烧结致密度研究

以高能球磨法和直流氢电弧等离子蒸发法两种不同工艺制备纳米晶镍粉体,并结合预压烧结工艺制备了纳米晶镍块体试样,研究了纳米晶镍块体结构、形貌的变化.运用TEM技术观察了两种粉体的形貌,并给出了选区电子衍射图;运用XRD、Archimedes法等分析手段对纳米晶镍块体的致密度及晶粒尺寸进行测定,并对两种试样进行了对比分析,表征结果显示,随着烧结温度的升高,纳米晶镍块体试样的晶体尺寸增大,晶格应变减小,同时致密度增加;高能球磨试样晶粒生长速率和致密度升高速率比等离子蒸发试样的快.     

Y2O3对SPS烧结纳米AlN粉末的影响

利用低温燃烧法合成出了平均粒度为100 nm的AlN粉末,将合成的粉末采用放电等离子(SPS)技术进行低温强化烧结,研究Y2O3对烧结过程以及烧结试样特性的影响.XRD进行物相分析,SEM观察断口形貌,排水法测烧结试样的密度,激光闪光法测烧结试样的热导率.实验表明采用低温燃烧法合成出的AlN粉末具有非常好的烧结性能,采用SPS烧结技术,40 MPa压力下,在1600℃保温4 min,就能得到非常致密的AlN陶瓷;Y2O3对纳米AlN粉末在SPS低温强化烧结过程仍有促进作用,使试样在更低的温度下烧结致密,并且晶粒更细小,从而热导率也较低;加入Y2O3的烧结试样晶界强度增加,断口中有较多的穿晶断裂形式,而不加入Y2O3的烧结试样主要以沿晶形式断裂.     

纳米银块体材料的制备及其结构表征

采用超高压冲击波将纳米银粉固结为具有纳米结构的致密块体材料。采用X射线衍射和透射电子显微镜研究了试样的显微结构。不同冲击波压力(2．98～6．65GPa)下压制的试样的晶粒尺寸在50～120nm之间。试样中除了纳米颗粒界面熔化并互相联接形成的纳米晶粒外，还出现{111}孪晶结构，而每一片孪晶又由许多小的纳米晶粒组成。孪晶和位错运动是纳米银在超高压冲压波作用下形变的两个重要特征。     

Solid-state properties of hot-pressed TiB2 ceramics

Due to the increasing industrial interest in TiB₂ the present work was accomplished to establish various solid-state properties of TiB₂ and to study the influence of sintering aids and different powder conditioning methods on the densification behaviour of TiB₂.

The powders were hot-pressed in graphite dies with various loads up to 45 MPa and the vertex temperature of 1800 °C was held for 1 h. For the pure, non-activated powders theoretical densities between 97.4% and 99.5% were obtained at a pressure of 45 MPa. Hot-pressed activated powders at this pressure led to densities of up to 99.9%. The addition of 0.5 wt.% of various sintering aids also increased the densities. It is shown that pre-alloying TiB₂ with CrB₂ is to favour over mixing the powders. If TiB₂ and the sintering aid were mixed the best result was obtained with Cr₂N. Ceramics with high Young’s moduli and hardnesses were obtained. The Poisson’s ratios of two samples were 0.08 and 0.09, respectively, which are the lowest known values for a ceramic hard material. The heat conductivity of pure TiB₂ is approximately 1/4 of that of copper and the electrical resistivity is only 6 times higher than that of copper.     

粉末冶金法制备金刚石/铜复合材料热导率研究

为研制更高热导率的产品,采用粉末冶金法将金刚石与高纯度铜粉热压在一起,制备新型金刚石/铜复合材料。通过正交分析法,研究了金刚石/铜复合材料热导率的影响因素。结果表明:用粉末冶金法制备的金刚石/铜复合材料,其热导率最高为245.89 W/（m·K）。对金刚石/铜复合材料热导率影响最大的因素是金刚石与铜粉的体积比,并且随着体积比的增大,金刚石/铜复合材料热导率逐渐下降。金刚石/铜复合材料的致密度以及界面结合程度是影响金刚石/铜复合材料热导率大小的重要因素,致密度高、界面结合好的复合材料热导率高,反之则低。      

Preparation of electrolytic copper powders with high current efficiency enhanced by super gravity field and its mechanism

Super gravity field was employed to enhance electrolytic reaction for the preparation of copper powders. The morphology, microstructure and size of copper powders were characterized by scanning electron microscopy, X-ray diffractometry and laser particle analysis. The results indicated that current efficiencies of electrolytic copper powders under super gravity field increased by more than 20% compared with that under normal gravity condition. Cell voltage under super gravity field was also much lower. The size of copper powders decreased with the increase of gravity coefficient (G). The increase of current efficiency can be contributed to the disturbance of electrode/electrolyte interface and enhanced mass transfer of Cu2+ in super gravity field. Meanwhile, the huge gravity acceleration would promote the detachment of copper powders from electrode surface during electrolytic process, which can prevent the growth of copper powders.     

复合稀土氧化物掺杂W-20Cu复合材料的制备及组织性能研究

以偏钨酸铵和硝酸铜为原料,采用EDTA-柠檬酸法制备了含有0~0.8wt.%稀土氧化物( Ce_0.8Sm_0.2O_1.9, SDC)的W-20Cu复合粉体,所制备的复合粉体经压制成型、1250°C烧结2h后获得SDC/W-20Cu复合材料烧结体。对所制备复合粉体进行物相、形貌的表征;研究稀土氧化物的添加对SDC/W-20Cu烧结体的密度、组织结构和物理力学性能的影响。实验结果表明：所制备的W-Cu复合粉体平均粒度为100~200nm;同时,SDC的添加对烧结体的密度和电导率会有轻微的影响,但能够抑制晶粒的长大并明显改善烧结体的力学性能。经1250°C烧结后,SDC/W-20Cu烧结体的相对密度均高于97%;当SDC的添加量为0.6%时,具有最大的抗弯强度和显微硬度,分别是1128MPa和258HV;此外,在室温和600°C的测试条件下,其最大的抗拉强度可以达到580MPa和258MPa。     

溶胶-凝胶法应用于Cu粉抗氧化工艺研究

应用钛酸丁酯水解形成二氧化钛溶胶对铜粉表面进行包覆处理，样品的耐腐蚀性通过在5％硫酸溶液中浸泡，然后测定溶液在760nm处的透光率来表征，据此研究了不同加水量、加酸量以及溶胶用量对包覆处理效果的影响。结果表明，钛酸丁酯与水的摩尔比为1：2，H^＋浓度为0．32mol／L，溶胶用量在4％～6％范围内，包覆样品浸泡4h后溶液的透光率为80％以上，而原始样品为15％。应用SEM、EDS、XPS以及XRD对包覆样品进行表征。XPS结果表明，样品表面主要有C、Ti、Sn、O、Cu等元素，其中Ti、Sn元素分别为四价和二价。对空气中放置60天后的包覆样品以及原始粉体的X射线衍射（XRD）检测表明，原始粉体表面有Cu2O存在，而包覆处理Cu粉的图谱中仅出现Cu的特征峰。     

A new route for preparing Mo-10wt.%Cu composite compacts

In this work, high pure Mo-10 wt% Cu composite powders with a ultrafine particle size are prepared by a two-step reduction process (first carbothermal reduction and then hydrogen reduction). Ammonium heptamolybdate and copper nitrate trihydrate powders are used as molybdenum and copper source, respectively. The mixtures of raw materials are calcined at 400 °C firstly to form the composite oxides which are then reacted with insufficient carbon black at 1050 °C for 2 h. The as-prepared powders are further reduced by hydrogen at 750 °C for 2 h to obtain the ultrafine Mo-10 wt% Cu composite powders. The experimental results show that the residual carbon of the Mo-10 wt% Cu powders can be decreased to 0.015 wt%, and the composite powders have an average particle size of 200 nm. The sintering behavior of ultrafine MoCu powders and the properties (vickers hardness and thermal conductivity) of samples after sintering are investigated. High sintering temperature is beneficial to increase the density of the compact. At 1200 °C, the relative density of the MoCu compacts is 98.8%. The vickers hardness and thermal conductivity of the Mo-10 wt% Cu composites sintered at 1200 °C for 3 h are 233 HV and 130 (W/m·k), respectively.     

Tailoring powder processing and thermal treatment to optimize the densification of W–CuO powder mixtures

W–CuO powder mixtures were prepared by attritor mixing/milling of commercial powders. The reduction steps during heating under He/H₂ gas flow were identified by thermogravimetric analysis (TGA). W–Cu powder mixtures with three different O-content were prepared by adjusting the reduction conditions in a furnace. The effect of O-content on the sintering of powder compacts was then especially investigated. Two sintering steps were identified by dilatometry during liquid phase sintering under He/H₂ atmosphere. The first step was associated to rearrangement after copper melting. The second step was related to the presence of W-oxides at the particle surface: shrinkage was enhanced and the second step was shifted to lower temperatures by using initial powders with low oxygen content, by decreasing the heating rate or by introducing a holding time at 1050 °C. This behaviour was related to a gradual reduction of W-oxides from the edge to the bulk of the samples. Microstructural observations were performed at different stages to confirm the analysis. Powder processing and thermal cycle were optimized to obtain materials with 96–97% relative density.     

CNTs/SiC/Cu复合材料制备及性能

以碳纳米管(CNTs)、碳化硅(SiC)粉体、锌(Zn)粉和CuSO_4·5H_2O为主要原料,用化学镀的方法制备CNTs /Cu复合粉体,再采用非均相沉淀法制备CNTs/SiC/Cu复合粉体.在750 ℃、100 MPa的制度下进行真空热压烧结后制得CNTs/SiC/Cu复合材料,其中Cu的含量(体积分数,下同)为70%,CNTs的含量(体积分数, 下同)分别为0,3%,5%,8%,12%.利用XRD、SEM分析样品的物相组成和显微结构;利用阿基米德排水法、显微硬度计、三点弯曲法测试了复合材料的密度、显微硬度和抗弯强度.结果表明,随着碳纳米管含量的增加,CNTs/SiC/Cu复合材料的密度、显微硬度和抗弯强度等性能发生相应变化,其中,抗弯强度呈现逐渐升高趋势.与未添加碳纳米管的30SiC/70Cu复合材料相比,添加12%CNTs的12CNTs/18SiC/70Cu 样品,抗弯强度提高了21.45 MPa.     

The comparison of W/Cu and W/ZrC composites fabricated through hot-press

In this study the W/Cu and W/ZrC composites have been fabricated by hot-press and then their mechanical properties were compared in addition to their ablation resistance. To produce W-20vol.%Cu composite at first stage the elemental W and Cu powders were ball milled for 3 h in rotation speed of 200 rpm, in which 2% nickel was added in order to reduce the density. The mixed powders were hot-pressed for 1 h at 1400 °C and compact pressure of 30 MPa. Additionally W/40vol.%ZrC composite has been fabricated by hot-pressing of mixed W and ZrC powders in 30 MPa and 2200 °C for 1 h. Since these materials are used at elevated temperature applications, where ablation is the main source of material failure, after producing the composites their ablation resistance was evaluated in a real condition. The results show that not only W–ZrC composite is better than W–Cu composite in mechanical properties, but also in ablation resistance.     

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.